General Forums => Aircraft and Vehicles => Topic started by: DaveBB on October 01, 2016, 10:02:41 AM
Title: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 01, 2016, 10:02:41 AM
I came across an article that said escort fighters could only stay with bombers for 20-40 minutes due to the higher speed and zig-zagging pattern the fighters had to fly. The article implied this was P-51s escorting B-24s and B-17s. It went on to say that multiple fighter squadrons had to be used to escort the bombers on different parts of the missions.
Few questions: (1) Is this true? (2) Why didn't the escort fighters simply slow down to a cruise speed and conserve fuel?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: MiloMorai on October 01, 2016, 10:16:25 AM
There was 3 escort groups. One escorted the first stage, a second did the middle stage (bombing stage) and a third group did the egress stage. The line was approximately the Dutch/German border but on the German side of the border.
Spitfires and P-47s did the initial and egress stages, P-51s the more dangerous middle stage.
You want the escorts flying at the bomber's 180mph? Takes time to accelerate and the bogeys would be on the bombers before the fighters could get up to speed.
Suggest reading The Mighty Eighth by Roger Freeman.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 01, 2016, 10:27:33 AM
Do you know how many times escort groups missed the rondevouz with bombers? Lots. Then the German fighters had a field day.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: MiloMorai on October 01, 2016, 10:43:00 AM
How many is lots?
Here is a list of the 8th AF's heaviest losses, http://www.taphilo.com/history/8thaf/8aflosses.shtml
Which were because of fighters not showing up.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Serenity on October 01, 2016, 10:51:06 AM
Do you know how many times escort groups missed the rondevouz with bombers? Lots. Then the German fighters had a field day.
Acceleration takes time. And more gas. It's much safer to keep a constant fuel burn by maintaining a constant speed. How much of the flight will be spent at the slow cruise? How much time with fighters? Where do we draw the bingo line? How do you expect the pilot to make the calculation on when to go home with a varying fuel rate and in the middle of a fight? By keeping your speed up, you keep your burn rate stable, and you can calculate your range and bingo back home, not on the fly. Not to mention, this isn't Aces High. You can't see the fighters coming from 6k out. You may not see them until they're on top of you. Then how much good are you going half of their speed?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 01, 2016, 11:00:11 AM
The fighters' best cruise speed is higher then the bombers'. Going slower means burning more fuel per mile, i.e. reduced range. The P-51 could fly to Berlin and back, but not at the speed of the bombers, so they had to use a relay system. It's as simple as that.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Chalenge on October 01, 2016, 11:48:52 AM
Rendezvous was usually briefed for a particular location. Navigators did the best they could, but relative winds and obscuring clouds could have them miles off course. Even several hundred bombers can be impossible to see if you are not looking in the right location. Defending fighters could bounce the escorts before they get to rendezvous, also. Even just 300 bombers, and the stream could be as much as 1,000 bombers (I think Schweinfurt was a total of 1,070 sorties).
Still, it seems like the Cliff notes version of how it really was.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Oldman731 on October 01, 2016, 05:34:28 PM
Suggest reading The Mighty Eighth by Roger Freeman.
This almost should be required reading for all AH peoples. Don't confuse it with "Mighty Eighth" books by other authors.
- oldman
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: bozon on October 02, 2016, 03:21:43 AM
RAF mustangs said that escorting mosquitoes to Norway was so much better than escorting heavies or even Beaufighters, because the mossies cruise speed was about the same as the mustangs. Not to mention that cruising fast and straight make the sortie much shorter - including the 1 hour of loiter time over the fjords.
Photorecon mossies had to slow down for their mustang escorts, at least while the latter still had their DT on.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: save on October 02, 2016, 05:17:05 PM
But the Mossies did never have to encounter more than a maximum of one JG without the Sturmgruppen that where attached to the Reichverteidigung (home defense). The Sturmgruppen could have a field day when escorts where fighting the 109s of the High JG's 109s.
Also the German radars together with the shadow following ju8s where very precise in directing unescorted bombers in the bomber stream.
If they could find the Sturmgruppen before they attacked, it was nothing less of a carnage, as many as 25 pilots dead ( some of them shot in their parachutes).
After the first successes with the Sturmgruppen with their 120 * 30mm, US threaten the Sturmgruppens of imminent death. Some Sturmgruppen had 300% casualties during their active time, but many bombers paid the price. 2-3 30mm was enough for a bomber (less for the very vulnerable B24s), and they where almost totally resistant to .50 fire from front or sides. (source : Defense over Germany) Probably the best book of the subject.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 06, 2016, 08:42:11 PM
Acceleration takes time. And more gas. It's much safer to keep a constant fuel burn by maintaining a constant speed. How much of the flight will be spent at the slow cruise? How much time with fighters? Where do we draw the bingo line? How do you expect the pilot to make the calculation on when to go home with a varying fuel rate and in the middle of a fight? By keeping your speed up, you keep your burn rate stable, and you can calculate your range and bingo back home, not on the fly. Not to mention, this isn't Aces High. You can't see the fighters coming from 6k out. You may not see them until they're on top of you. Then how much good are you going half of their speed?
Depends on which side of the power curve you are on. Flying at max endurance with a lower fuel flow will save far more gas regardless of any acceleration penalty.
Acceleration is measured in seconds not hours.
The gas saved over three hours by pulling back the fuel flow is not going to be erased in the time it would take to accelerate. Obviously fuel burn wasn't the consideration unless slowing down would burn more gas during the cruise phase than weaving at a higher speed.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Randall172 on October 08, 2016, 09:54:37 AM
Depends on which side of the power curve you are on. Flying at max endurance with a lower fuel flow will save far more gas regardless of any acceleration penalty.
Acceleration is measured in seconds not hours.
The gas saved over three hours by pulling back the fuel flow is not going to be erased in the time it would take to accelerate. Obviously fuel burn wasn't the consideration unless slowing down would burn more gas during the cruise phase than weaving at a higher speed.
they are going for (fuel)/distance not (fuel)/time. They want to get to the rendezvous point with as much fuel as possible, slowing down would mean that they would be flying longer, while speeding up would mean they would be wasting fuel to drag.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 08, 2016, 10:40:58 AM
they are going for (fuel)/distance not (fuel)/time. They want to get to the rendezvous point with as much fuel as possible, slowing down would mean that they would be flying longer, while speeding up would mean they would be wasting fuel to drag.
Without performance charts you cannot say that definitively.
There is also no requirement for a single method only. There are times when endurance (time) is more important than range.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 08, 2016, 10:41:34 AM
How did the P-51s that escorted B-29s to Japan do it? Were there multiple fighter squadrons or was it a single squadron that escorted them the entire way?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 08, 2016, 11:44:47 AM
How did the P-51s that escorted B-29s to Japan do it? Were there multiple fighter squadrons or was it a single squadron that escorted them the entire way?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 08, 2016, 12:31:17 PM
A funny story I remember from the above site. The Mustang drivers figured out that if you tucked in tight behind the #3 engine the P-51 would stay in place hands off. Sometimes the B-29 guys would get uncomfortable and jockey the throttle tossing the Pony out of the bubble. Lol.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: MiloMorai on October 08, 2016, 02:44:24 PM
I came across an article that said escort fighters could only stay with bombers for 20-40 minutes due to the higher speed and zig-zagging pattern the fighters had to fly. The article implied this was P-51s escorting B-24s and B-17s. It went on to say that multiple fighter squadrons had to be used to escort the bombers on different parts of the missions.
Few questions: (1) Is this true? (2) Why didn't the escort fighters simply slow down to a cruise speed and conserve fuel?
This series of points isn't directed to you but to the many questions raised.
For a really long mission, carrying 108 gallon externals, the P-51B/D FREQUENTLY escort 2 1/2 + hours from Rendezvous to Break escort for . As an example the 355th FG flew escort to the lead boxes of 1st BD to Zwickau on May 12, 1944 for 8th FC, F.O. 337. The escort R/V was made at 1200 hrs S. Bonn, escorted to target at 1350, then broke escort (relieved by 20th FG P-38s) over Eisenach at 1405.. total mission duration was 1026 to 1558.
Another example - 8th FC F.O. 456 to Munich area on July 19, 1944. Mission from 0644 hrs to 1245. R/V at 0837 with BE at 1200 near Antwerp. In between there was a fight around Munich at 0930.
The optimal cruise speed for maximum range (not duration) was ~ 260mph TAS with 110 gallon externals at 25000 feet. After tanks dropped optimal cruise increased to 295/300mph TAS at 25000 feet. Right at 4-5 miles/gallon for squadron/flight leaders.
8th AF Doctrine from February 1944 forward was a three relay system with P-47s performing the short range legs (Penetration/Withdrawal) and P-38 performing intermediate Penetration sometimes as well as intermediate Target support, with P-51B/D doing Target support but also long Penetration, Target and Withdrawal as given above.
Even after the P-38J's received 55 gallon LE tanks they basically were limited to a Gardelegen, Magdeburg, Augsburg, Freidrichshafen combat radius.
Essing above and/or to either side was SOP in two flight sections- covering each other. Sweeps out in front or flanking 50 miles along bomber stream were variations of a theme - both for Penetration and Target escort as independent Group tasked to 'Hunt'.
From personal observation (from Logbook), in 72 missions my father flew fifteen 6+ hour missions, six 7+ hour missions and one 7:55 hour mission - the latter while leading the last Shuttle FRANTIC VII mission from Steeple Morden to Piryatin, Ukraine after meeting the B-17s near Stettin, Poland.
As to 'slowing down' to bomber speed (~210 mph TAS for B-17 at 25000 feet), the range was dramatically decreased as miles per gallon at the less than optimal RPM and Boost reduced to the 3+ mpg range for the duration of that actual escort leg. The second reason as addressed before is that the time to accelerate from say 200 mph to 400 mph for combat took some time and exposed the fighters to attack. "Tiny specks' become Big very rapidly when closing at 250+ Mph from the rear.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Rich46yo on October 13, 2016, 03:10:43 PM
Interesting. I knew we had developed navigation aids by the end of the war but never knew it was called "Uncle Dog". Nor did I ever know we used it in a B29 mother plane.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 13, 2016, 06:29:00 PM
I'm not buying it.
The fuel flow at 210 mph will be a fraction of that used for 300 mph. This will vary with weight but I do not see a Mustang being on the backside of the power curve at 210 mph. No way.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 13, 2016, 07:47:09 PM
Ok, the math of why the P-51 cruised most efficiently at 260mph is explained on pages 57/58. Below 260mph, induced drag increases. Above 260mph, parasitic drag increases.
Ok, the math of why the P-51 cruised most efficiently at 260mph is explained on pages 57/58. Below 260mph, induced drag increases. Above 260mph, parasitic drag increases.
Strangely enough, a pilot on F-16.net said the best cruise speed for the F-16 was right at 200mph. But that's comparing pistons to turbines.
Then 260 it is but not 300.
Induced drag will vary with weight also.
I think it depends on the goal. Max range will give you better mpg, but weaving over the stream means you are working at cross purposes. I can see how max endurance at the expense of range would be a benefit depending on the mission.
I don't hop the Atlantic in my bird at max endurance, but if there is a storm over the field the latter becomes vital.
I can see how 225 will save gas over 260... Wish I had those charts. :salute
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Serenity on October 14, 2016, 12:19:52 PM
The fuel flow at 210 mph will be a fraction of that used for 300 mph. This will vary with weight but I do not see a Mustang being on the backside of the power curve at 210 mph. No way.
I'm not sure if that remark was directed to me. That said, look to the flight envelope at which CL/CD is maximum to plan a flight test to adjust key variables RPM and Manifold Pressure settings which a.) minimize #fuel/distance traveled . The exercises for determining loiter is focused on minimum fuel flow and is found at (CL)^^3/2 divided by CD.
Rich and Randall are on the right track. Essentially look to the region in which Induced Drag= Parasite Drag for the Gross weight and altitude and speed for that region of the Drag vs Velocity Plot.
For an 8th AF escort profile only one scenario really calls for best Loiter settings - namely when fighters got to R/V place and bombers were late.
Summary - the key interest for determining Combat Radius - all things equal (GW, External stores, internal ammo and fuel load), in the Flight test program, is looking at fuel flow vs airspeed as a function of RPM and MP. At this point (in time) the Power Required = Power Available for those setting to maintain altitude.
The outcome is Gallons (or weight) per mile traveled until you find the settings that give you the 'minimum' #/mi ratio.
That said, as GW changes with time based on internal fuel (and changes as step function when external load dropped), the Breguet equation for Range = (prop eff)/(BHP) times CL/CD times the Integral of dW/W from starting gross weigh to final gross weight - where dW is the change in weight as a function of fuel consumption along the course.
With that equation the design team is looking to get the largest possible prop efficiency, the lowest possible pounds of fuel per mile, at lowest Required BHP possible for L=W, the highest Wo to W1 fuel fraction and flight at highest L/D.
I'm having brain farts re: posting images but go to the P-51D Flight Test Reports in Mike Williams site spitfireperformance.com for the development of P-51 Range and Endurance data for the Operating manual.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: FLS on October 14, 2016, 01:52:41 PM
The fuel flow at 210 mph will be a fraction of that used for 300 mph. This will vary with weight but I do not see a Mustang being on the backside of the power curve at 210 mph. No way.
210 TAS at 25,000 ft is about 140 IAS.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Dobs on October 14, 2016, 02:33:37 PM
The fuel flow at 210 mph will be a fraction of that used for 300 mph. This will vary with weight but I do not see a Mustang being on the backside of the power curve at 210 mph. No way.
DaveBB said "Ok, the math of why the P-51 cruised most efficiently at 260mph is explained on pages 57/58. Below 260mph, induced drag increases. Above 260mph, parasitic drag increases."
The only comment worth making is that all the optimal cruise settings were Different for different GW, different external stores, and different altitudes. At lower altitude, for same gross weight and external stores conditions the entire Induced Drag/Parasite Drag plot shifts to the left so that the bottom of the drag curve is at a lower airspeed.
In the attached report at 25K for take off weight of 9600+ pounds racks only the optimal cruise speed is 303mph with 29"MP/2050 RPM and 52 gal/hr fule flow.
Add another 1400 pounds for two 110 gallon externals shows optimal cruise at 281mph TAS with 32"MP/2250 RPM and 57 gph ---------------> higher total drag, more power required for level flight, higher AoA for greater Induced Drag (than clean Mustang).
In this example the inbound cruise is 281mph, make RV, Ess around the bombers, drop tanks and automatically increase speed to 303mph straight line when you reduce throttle to 29" and decrease RPM to 2050.
With the Mustang as the center of discussion, the first fact you have to nail a.) the Gross Weight, and b.) the external stores condition.
At 25000 feet the chart I point you to below is Appendix B is: http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf
The values tabulated are those for the P-51D Manual for Range as a function of GW, external stores (or racks only), Max Continuous Power, Military Power and WEP at different altitudes.
The summary report is: http://www.wwiiaircraftperformance.org/mustang/p51d-15342.html
The important point for Vraciu is that for the aircraft to sustain level flight, there is very little leeway in the Drag bucket at 25,000 feet (and you know this) to lower speed and fuel flow because you also don't have much to play with to maintain Power Available = Power Required for level flight at the lower airspeed.
So the Max Loiter fuel consumption is lower than best cruise setting as expected but the angle of attack and Induced drag increases exponentially as the velocity decreases.
To your point, so what? - reduced fuel flow for greater loiter time is good as the bomber stream is zipping along at 2/3 the TAS of the Mustang? Why not drop even further on MP and RPM?
Well three reasons - First, to Fighter pilots in ETO with LW having altitude advantage nearly always, means that occasionally to throttle up ASAP is far better starting at 300 TAS than 220mph. The second reason is that Merlins are grumpy around 1600 RPM and MP below 30". The last reason is that the range at optimal cruise and higher airspeed gave the escort a lot of leeway.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 18, 2016, 05:59:47 PM
Techniques used in the ETO were different than the Pacific.
Oversquaring was a big one that increased efficiency. There were others.
ETO Mustangs were not flown as efficiently as they could have been IMO.
The penalty in range for endurance is sometimes worth the price. It depends on the situation and variables involved.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 18, 2016, 09:07:24 PM
Also note at 5,000' with drop tanks there is a 34+ percent increase in fuel efficiency (thus range AND endurance) flying at a TAS of 187 mph vs 298 mph -- 5.29 MPG vs 3.48 MPG. (Indicated speeds will be fairly close to TAS at this low of an altitude.)
The fuel flow at 210 mph will be a fraction of that used for 300 mph. This will vary with weight but I do not see a Mustang being on the backside of the power curve at 210 mph. No way.
By interpolation 210 MPH TAS will yield close to 5 MPG or an increase of more than 30 percent over 300 MPH TAS.
Now, these numbers will change with altitude but will be generally similar. At 25,000' 280 MPH TAS is more efficient than 300, etc. etc. I will make a terrible guess and say shave 80 or 90 MPH off TAS to get IAS at 25,000 (it has been a long day so my mental math may be wrong).
Going faster is, generally speaking, only helpful in terms of range when you are on the backside of the power curve--or close to it. Then we start accounting for headwind vs. tailwind, temperature, weight, configuration/loadout, and so on which will cause the most efficient speed to change.
All things equal, there is not a single point on the cruise chart where the slowest LISTED speed is less efficient than the higher one(s).
(I am presuming a typo at 321 and 331 MPH at 25,000' with drop tanks where fuel mileage bucks the trend mysteriously.)
----
Bomb racks-only fuel flow doubles between 300 MPH TAS and 400 MPH TAS at 25,000' (~210 IAS vs. ~310) -- 52 GPH vs. 100 GPH.
With drop tanks the fuel flow nearly doubles from 281 MPH TAS to 357 MPH TAS (~200 IAS vs. 270 IAS) -- 57 GPH vs. 100 GPH. Range AND endurance suffer dramatically as a result.
----
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: FLOOB on October 19, 2016, 12:05:02 AM
"You don't pay escorts to stay, you pay them to leave."
I note that DragonDog's dad is Burt Marshall. I recently finished Bud Fortier's book I which he wrote of Marshall extensively and highly. Very cool.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 19, 2016, 04:35:04 AM
Ponies are special. Their laminar-flow wings are less efficient than more conventional profiles outside of the drag bucket. To go anywhere far a pony needs to stay in the drag bucket.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 19, 2016, 04:35:55 AM
(http://www.dreesecode.com/primer/p5_f003.jpg)
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 19, 2016, 08:39:11 AM
Also note at 5,000' with drop tanks there is a 34+ percent increase in fuel efficiency (thus range AND endurance) flying at a TAS of 187 mph vs 298 mph -- 5.29 MPG vs 3.48 MPG. (Indicated speeds will be fairly close to TAS at this low of an altitude.)
Which makes my exact point.
I'm sorry. I must have missed the memo about the Post question? If the question was, as I understood it, was "Escorts could only stay with the bombers for20-40 minutes"?
I confess that I thought the question was ETO/8th AF bombers, not torpedo bombers.
By interpolation 210 MPH TAS will yield close to 5 MPG or an increase of more than 30 percent over 300 MPH TAS.
Now, these numbers will change with altitude but will be generally similar. At 25,000' 280 MPH TAS is more efficient than 300, etc. etc. I will make a terrible guess and say shave 80 or 90 MPH off TAS to get IAS at 25,000 (it has been a long day so my mental math may be wrong).
I'm pretty sure I mentioned that the variables were altitude, GW, airspeed and drag conditions (racks, tanks, bombs, etc) that move the CD=CL point from optimal 'clean'.
Mr GScholz just posted a CD vs CL plot that explains the key factor for discussion of flight test planning. He posted the 2415 vs 66-415 with same T/C for rough wing drag efficiency snapshot. Although it says nothing about RN and the Drag (total Parasite Drag= wing+Fuse+empennage+cowl+exhaust stacks, external stores, etc). It says a great deal about the CL range for most efficient cruise conditions. The 2315 has a pretty well defined bottom CL for which the CD is a minimum, not so the 66-415 (on NACA.NAA 45-100).
On a P-51 (or any other fighter) this plot is essential for Performance calcs and usually start at RN=~2x10^^6 and slopes DOWNWARD as a function of true airspeed until it flattens out near 20-30x10^^6. Reynolds Number is a function of density, Mean Aero Chord of the wing, Velocity in fps and inversely proportional to absolute viscosity.
The reason I bring all this crap to the discussion is that CL is absolutely critical to the discussion. At the CL range of 0.25 to 0.5 Drag is at its lowest for the Wing. CL has to be examined at L=W for level flight and solved for Velocity for that range and then calculate Induced Drag for the velocity range above - then plot CDtotal = CDparasite+CDinduced
With this in hand the test pilot can test plan changes in velocity for a specific altitude and unaccelerated flight for the drag parameters stated above. He will have a real good idea for the velocity envelope for test.
Next he (They) need to calculate Powere Required for level flight and start tweaking MP and RPM to find maximum efficiency of the engine-prop system consistent with safety factors for engine performance and life.
What you see in the flight tests shown on spitfireperformnce.com generates the tables that you will see in the future Pilot's Manual in the table for Range/speed per MP/RPM settings as a function of total fuel on takeoff, internal fuel, for Gross Weight and altitude comparisons.
The ones plotted are the foundation for developing Combat Radius with mission segment variables (warm up/taxi, takeoff/climb to cruise altitude, Cruise to RV, Drop externals and Fight, Return at optimal cruise speed to letdown - and have 30 minutes of fuel reserve.
The combat radius calc have to take into account the drag conditions inbound with external tanks/ordnance for inbound leg to Combat profile, the jump in fuel consumption for WEP and MP which taps your internal fuel reserve and gives you a new Gross Weight/less Drag and different MP/RPM for new maximum range which has to be managed to be carried home with internal fuel remaining.
Going faster is, generally speaking, only helpful in terms of range when you are on the backside of the power curve--or close to it. Then we start accounting for headwind vs. tailwind, temperature, weight, configuration/loadout, and so on which will cause the most efficient speed to change.
To quibble the point, going at the recommended speed. Speed/MP/RPM vs altitude is the first step to pick 'close to best case for range' before headwinds/tailwinds/etc have to be taken into account.
Respectfully, diverting from that setting range to lower airspeed/RPM/MP to minimize fuel consumption per hour only extends the time before you have to crash land out of fuel - but you won't travel as far as the other gent that flies to maximize miles/gallon
All things equal, there is not a single point on the cruise chart where the slowest LISTED speed is less efficient than the higher one(s).
(I am presuming a typo at 321 and 331 MPH at 25,000' with drop tanks where fuel mileage bucks the trend mysteriously.)
----
Bomb racks-only fuel flow doubles between 300 MPH TAS and 400 MPH TAS at 25,000' (~210 IAS vs. ~310) -- 52 GPH vs. 100 GPH.
With drop tanks the fuel flow nearly doubles from 281 MPH TAS to 357 MPH TAS (~200 IAS vs. 270 IAS) -- 57 GPH vs. 100 GPH. Range AND endurance suffer dramatically as a result.
----
Respectfully, if the data is presented in toto, there are many points in which less airspeed at the recommended MP/RPM settings - all of them. Go back to picking the optimal CL as a function of airspeed and gross weight. Lower airspeed for that airplane from the recommended 'bottom' of the drag bucket drives the required angle of attack higher to sustain level flight ----------> Higher Induced Drag value from optimum ------> higher total Drag from optimum.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 19, 2016, 08:57:19 AM
Ponies are special. Their laminar-flow wings are less efficient than more conventional profiles outside of the drag bucket. To go anywhere far a pony needs to stay in the drag bucket.
The Mustang wing was not a true laminar flow wing. It was a noble attempt but could not be manufactured with the tolerances needed to achieve much, if any, laminar flow.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 19, 2016, 08:59:35 AM
Again, I am not saying lower speed is always better. It's not. I have stated that REPEATEDLY.
But my original point remains valid and is backed up by the numbers.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 19, 2016, 10:30:38 AM
I am not trying to cause indigestion in this debate.
Vraciu - what is your specific point that you felt you have made in fuel consumption versus miles per gallon optimization? And thank you for your comments re: Bud Fortier.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 19, 2016, 01:02:18 PM
This is worth taking about. First is it a 2D section lift and drag plot from wind tunnel result at a specific Reynolds number - with no induced Drag so the entire Drag component is Parasite Drag. The introduction of a finite wing reduces the Max L/D as Induced Drag is introduced. For a very large AR the comparison is close.
You can note that the range of 66-415 superior CL/CD ratio (over 2315) is much broader than the 0.25 to 0.5 CL range. All things equal this a/c will exhibit far better Drag reduction across most of the performance envelope until in the lower speed range where CL has to increase due to angle of attack increase to maintain level flight.
Vraciu's comment that laminar flow was not achieved is true in a practical sense, although the Mustang surface prep on flush rivet construction, filling, sanding, priming and painting did delay boundary layer separation. That said slower velocity gradient of the 'laminar' flow airfoil delayed pressure gradient induced separation ---- and a fundamental reason why a 'fat wing' NACA/NAA 45-100 Low Drag wing had delayed shock wave formation over conventional airfoils (like the 2315).
That said the actual real life low drag result was achieved - just not to expected theoretical laminar flow objectives. As a contrast - The CDparasite of the P-51 at RN=9x10^^6 =~ .017 while the F4U and F6F comparable parasite Drag values, all derived from full scale wind tunnel testing, is ~ 0.26 and 0.27 respectively. That is mostly wing and both the F4U and F6F had, IIRC 23015 section airfoils (Ditto P-38 and FW 190 and F8F). The Total Drag comparisons between the latter five fighters varied primarily due to Induced Drag via AR.
To toodle back to our discussion, looking at the respective Total Drag vs Velocity plots for each fighter yields a plot of CDparasite which increases from CDzero lift (low) and a CDinduced which starts high and decreases non-linearly from low speed to high. When you look at each plot, where the two curves cross is CDminimum.
THAT is the Golden strike zone for fine tuning speed vs engine settings to get maximum mileage per pound of fuel - for That altitude, That GW, That External Drag condition and it changes every minute as fuel is consumed, lowering GW and reducing AoA required for level flight.. and so on.
Why does the F4U, et al - Never- get the same range attainable, per pound of fuel carried, nor cruise at the same relative high speed for that Golden Strike zone, you ask? They all start with 50% more parasite drag - which shifts the plot to the left (Lower airspeed at the CD=CL bottom of the plot) - AND only the Allison had essentially the same (or better) fuel consumption for same MP/RPM- all the rest had gas guzzling powerful radials.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 19, 2016, 07:40:51 PM
More than one race plane has had around 100 pounds of bondo removed from the plane when they decide it's cracking and could come off.
They are changing the profile of the wings.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 19, 2016, 08:11:26 PM
The Mustang is fast because it is slick. The attempt at laminar flow drove the design to be streamlined. The big brute radials had more power than the Mustang which really is in need of more horses in that Merlin.
Mustang empty weight is nearly 1500# less than the Corsair and has a higher fuel fraction. I don't know if a Corsair gets its range (1050 miles) with drop tanks or not, but the Pony does (1650 miles).
The Corsair is extremely fast and slick in its own right.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 19, 2016, 08:29:26 PM
Vraciu - all the F4F, F6F and P-38 were able to outmuscle terrible drag with HP. So, what? has nothing to do with CL=CD to pick optimal cruise speed.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 19, 2016, 09:13:31 PM
Vraciu - all the F4F, F6F and P-38 were able to outmuscle terrible drag with HP. So, what? has nothing to do with CL=CD to pick optimal cruise speed.
You're claiming the Mustang had long range because of its wing. That's simply not the case. Fuel fraction and a slick slick fuselage with an efficient cooling system did it.
It was also more advanced in design and tech than any of those you mention.
The F6F and F4F were very very slow relatively speaking. The 38 actually had more range than the Mustang, to boot. The Mustang "laminar flow" wing is an overrated legend. A wive's tale.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 20, 2016, 05:07:30 PM
The radial engines themselves were 20 inches wider than the merlin but I'm not sure if they counted the stacks or not.
Also the air cooled engines needed a little bit of space between the engines and the cowling.
The frontal area of a pilot in the sitting position is very close to the frontal area of the mustang until you figure in the doghouse.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 20, 2016, 05:15:58 PM
At 400mph at 25,000 feet, the P-51's prop produced 1000 pounds of thrust. Meanwhile, it's radiator produced 375 pounds of thrust. Meredith Effect. While most aircraft had to dedicate approximately 10% of engine power to cooling, the P-51 only needed to dedicate 1-2%.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 20, 2016, 05:27:33 PM
You're claiming the Mustang had long range because of its wing. That's simply not the case. Fuel fraction and a slick slick fuselage with an efficient cooling system did it.
Certainly a combination of low drag and fuel fraction. That said the first P-51B had less fuel fraction than a.) P-47C/D, F4U-1, P-38F thru H but had more range than all Before the addition of the 85 gal tank, and b.) a wing which drag was less than 70% of the other candidates.
It was also more advanced in design and tech than any of those you mention.
The F6F and F4F were very very slow relatively speaking. The 38 actually had more range than the Mustang, to boot. The Mustang "laminar flow" wing is an overrated legend. A wive's tale.
Laminar Flow - No. Low Drag - Yes.
As to P-38 having more range - only by performing un-natural acts such as shutting down one engine and transferring fuel - which was suicide in a high threat environment. The important fact is that AAF mission planners considering the cruise speeds for the mission to achieve a long range escort or a medium range bomb/CAS mission went by the book for Combat Radius as determined by AAF Flight test performance.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 20, 2016, 05:30:16 PM
As to P-38 having more range - only by performing un-natural acts such as shutting down one engine and transferring fuel - which was suicide in a high threat environment. The important fact is that AAF mission planners considering the cruise speeds for the mission to achieve a long range escort or a medium range bomb/CAS mission went by the book for Combat Radius as determined by AAF Flight test performance.
Uhhhh, no.
The 38 always had more range than a Mustang, particularly with payload. The techniques used in the Pacific stretched this even further.
And no, they (mission planners) did not use max combat radius on every mission. We've already shown that.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 21, 2016, 06:46:56 AM
At 400mph at 25,000 feet, the P-51's prop produced 1000 pounds of thrust. Meanwhile, it's radiator produced 375 pounds of thrust. Meredith Effect. While most aircraft had to dedicate approximately 10% of engine power to cooling, the P-51 only needed to dedicate 1-2%.
Junkers effect! :old:
All liquid cooled fighters used Junkers' "jet cooler" effect to reduce cooling drag, including the P-51. It is a myth that the Pony was unique in this regard. It was a well known effect long before WWII. Junkers patented it in 1915.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 21, 2016, 08:50:39 AM
The 38 always had more range than a Mustang, particularly with payload. The techniques used in the Pacific stretched this even further.
And no, they (mission planners) did not use max combat radius on every mission. We've already shown that.
I agree that 'mission planners' did not always use Combat Radius to plan the mission, particularly for PTO common mission profiles. Kenney, via Gunn, directed a lot of programs and techniques to stretch range including dissimilar capacity tanks (much larger than ETO/MTO) that were made in Australia.
What you may be missing in the context is that range planning was at far lower altitudes for bomber escort as well as Fighter Sweeps.
That said, the planners in the ETO/MTO did have a specific Mission profile for bomber escort. It was plan for climb, cruise, RV and escort B-17s and B-24s in the 20-28K altitude envelope.
The P-38J with LE tanks was relegated to mid long range (max Berlin and very few that long after early March) target escort because the P-51B could (and did) go to Stettin/Posnan Poland or Brux/Prague CZ. During Big Week the 15th AF P-38s couldn't make Munich, but with P-51B/D they went to Berlin.
As an aside, the fourth ranking MTO Mustang Group - the 332nd - outscored every one of the P-38 FGs (1st, 14th and 82nd) from July 1 forward. This record despite having so many good fighter pilots and experience, compared to 332nd experience, because they didn't have the range to do deep target escort.
You might ask - "Where were all the great P-38 FG's when the missions to escort B-29s to Japan from CBI and PTO where the Mission Profile was the same as ETO - with one exception, the B-29 at altitude could cruise as fast as P-51D optimal cruise speed at that altitude."
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 21, 2016, 09:33:35 AM
The 38 always had more range than a Mustang, particularly with payload. The techniques used in the Pacific stretched this even further.
I would draw your attention to the Combat Radius Profiles, as well as ferry ranges reproduced in one set of reference - in Dean's "America's One Hundred Thousand". Page 600
For Ferry Range plots look to Graph 41 and 42 for P-51, 51A, 51B/D, and Graph 17 for P-38G, P-38H and 38J/L.
And no, they (mission planners) did not use max combat radius on every mission. We've already shown that.
If you look at them you should see that a.) the P-51 (20mm cannon drag) had 180 gallons of internal fuel - no external and its competition for range was P-38E/F/G with 300 gallons of internal fuel.
The Ferry ranges for 1941-mid 1943 were 850 mi for P-38 with 300 at combat load out at 15,800 pounds (full ammo/full internal fuel) 1100 mi for P-51 with 180 gallons at load out at 8700 pounds (full ammo/full internal load)
The Combat radius with external tanks (1550 w/2x75 P-51A, 1400 w/2x150 for P-38H)
The Combat Radius for internal fuel only for P-38J/L with 2x55 gal LE tanks versus P51D with 85 gallon fuse tank
275 mi for P-38J/L at 17,500# at 25K Graph 17, pg 143 375 mi for P-51D at 10,100# at 25K Graph 42, pg 327
Pappy Gun was extremely resourceful, as well as Lindbergh, in figuring out ways of extending range but his methods would Not have worked in the ETO/MTO
As to Meridith Effect to P-51B/D/F. for drag calcs in NAA Performance Analysis the effect of cooling drag was assumed to Net=0 but the calculated drag for cooling system/cowl was far less that 100 pounds at RN>9x10^^6 (say >270 mph). In climb the full cooling drag parameters were applied in the drag build up to determine Power Required.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 21, 2016, 03:23:00 PM
All liquid cooled fighters used Junkers' "jet cooler" effect to reduce cooling drag, including the P-51. It is a myth that the Pony was unique in this regard. It was a well known effect long before WWII. Junkers patented it in 1915.
The P-51 was only mass produced piston aircraft to use the Meredith Effect to a useful potential. Even the rear doors of the radiator scoop open and close to the optimal level, like that of an afterburning jet engine.
While other aircraft like the 109 series were using engine power to get rid of heat, the P-51 was turning it into 40% additional thrust.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 21, 2016, 03:46:38 PM
Myth. Here's the P-51's radiator: Fixed inlet (but with a variable air bleed vent), expansion chamber, radiator, compression chamber and variable outlet. A very typical jet cooler design.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 21, 2016, 03:49:23 PM
Here's the 109's jet cooler: Variable inlet, expansion chamber, radiator, compression chamber and variable outlet. The P-51's radiator is narrow and tall, the 109's is wide and short (and divided into two units). Other than that they are practically identical.
The P-51 was only mass produced piston aircraft to use the Meredith Effect to a useful potential. Even the rear doors of the radiator scoop open and close to the optimal level, like that of an afterburning jet engine.
While other aircraft like the 109 series were using engine power to get rid of heat, the P-51 was turning it into 40% additional thrust.
Dave -as much as I love the NAA design team and the performance of the Mustang, the major contributors to Thrust was a.) Engine Prop combo (say 1200 pounds at WEP at 20,000 feet), b.) Exhaust Gas (say 140 pounds), c.) Merideth Jet effect - perhaps 20-60 pounds to overcome the cooling drag and spot a few pounds of delta thrust.
That is in full rage, heat generating, ram air effect in level flight. When climbing at 160mpg with cooling drag at peak, the ram effect is much, much less.
Grab a copy of NAA Report 8449, dated 12-1-44 for the Performance Calculations for Model P-51D-5-NA Airplane (N.A.A. Model NA-109) and amble to the Drag Discussion starting on Page 19. On page 21 begins the discussion of parasite drag changes due to angle of attack changes and dives into the cooling drag assumptions for high speed level flight vs climb.
Don't take my word for it, but check out NAA Ed Horkey's analysis as Chief Aerodynamicist. The Co-signatory authority is Louis Waite Chief of Tech Section (i.e. Wind Tunnel and flight measurements among other responsibilities).
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 21, 2016, 04:08:58 PM
Here's the 109's jet cooler: Variable inlet, expansion chamber, radiator, compression chamber and variable outlet. The P-51's radiator is narrow and tall, the 109's is wide and short (and divided into two units). Other than that they are practically identical.
The P-51 specifically kept it's radiator scoop out of the boundary layer. That's why it is offset from the fuselage so much.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 21, 2016, 04:12:04 PM
Pony has an external boundary layer splitter. The 109 has an internal boundary layer channel that avoids the radiator. Different approaches to achieve the same thing.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 21, 2016, 09:59:03 PM
I'm not sure you guys are getting it on the mustang scoop/doghouse.
Sure, it makes thrust but it does not make enough thrust to overcome the drag it creates by being there.
This has nothing to do with the topic, though.
I quote from the NA-8449 pg 21 Paragraph C. Cooling Drag - High Speed
"For this condition the energy recovery from the cooling air is sufficient to overcome any flow losses. Calculations show that for most cases a small amount of thrust is derived, however, for this analysis any thrust from the cooling air is neglected. High speed cooling drag is then considered zero"
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 22, 2016, 12:24:56 PM
The careful usage of "cooling drag" needs to be added to "radiator drag".
The usage of "all of the cooling drag" is just a single source being repeated over and over.
Try a few other sources that aren't copies of the atwood article.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 22, 2016, 01:36:00 PM
The careful usage of "cooling drag" needs to be added to "radiator drag".
The usage of "all of the cooling drag" is just a single source being repeated over and over.
Try a few other sources that aren't copies of the atwood article.
You are a funny guy, Icepac. :rofl I suspect you meant that as a calculated insult and wonder why you thought it necessary?
It is quoted Verbatim from the text of the Drag Analysis of The North American Aviation Report NA-8449 Performance Calculations for Model P-51D-5-NA (N.A.A. Model NA-109) dated 12-1-44.
Prepared for E.D. Horkey and L.L. Waite by Aerodynamics Section Performance Group.
Further down on page 21 is the discussion regarding climb and Drag of Items Exposed to the Slipstream which included increments in parasite drag due to angle of attack - including specifically "Net Internal flow losses plus additional profile drag, Delta Cd = 0.0064" plus Carburetor Duct (form)= 0.0004 plus Radiator Duct = 0.0019"
If you wish mentoring in Aerodynamics, PM me and I'll help you understand.
For what it is worth IMO Lee Atwood's oft repeated comments re: Meridith Effect thrust indicates that he never read the report for either the P-51D or NAA Report-8264-A for the P-51H. See page 40 of the NAA Report 8264-A which, quoted Verbatim for the DEFINITION of Cooling Drag (same as P-51D report but I only referred to comments under High Speed):
"The basic drag includes the external drag of the radiator duct for flush exit flap condition, but does not include internal losses or dr drag due to change in scoop exit flap position"
etc, etc. All the Cooling Drag, the Drag due to Carbuetor Air Momentum Loss, and the Drag of Items exposed to the slipstream are included in the Determination of Power Available
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 22, 2016, 04:06:22 PM
I can't find the chart that shows the % of engine power needed for cooling. Like I posted in my earlier statements, the Mustang only needed 1-2% engine power for cooling, while other aircraft (the 109 included), needed around 10% for cooling.
Also, from everything I've read, the semi-laminar flow wing was a bust. True laminar flow could never be achieved. Even something as small as a piece of masking tape could disrupt laminar flow. A different wing would have aided the Mustang.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 22, 2016, 04:43:24 PM
I can't find the chart that shows the % of engine power needed for cooling. Like I posted in my earlier statements, the Mustang only needed 1-2% engine power for cooling, while other aircraft (the 109 included), needed around 10% for cooling.
You won't find a 'chart'. At least not for the Mustang. You could make estimates of Power Available and Power Required based on the Drag data, then make calculations regarding total Cooling Drag as a function of Power Required. Reminder - Cooling Drag is at its peak in low speed, high angle of attack flight profiles - like climb.
Also, from everything I've read, the semi-laminar flow wing was a bust. True laminar flow could never be achieved. Even something as small as a piece of masking tape could disrupt laminar flow. A different wing would have aided the Mustang.
Well, for the time - it was a home run. Disrupting flow from laminar to turbulent is common for All airfoils - but an airfoil which has a high velocity gradient from zero Chord point to 25% versus ~40-50% Chord was huge relative to Mach Divergence.
Today, there are Super Critical wings of Composite build up that have BL separation aft of 50%.
Sure, boundary layer separation was delayed a little but while not Laminar to expectations w/Boundaty layer separation at 40-50% Chord, the reduction in Drag over the common fighter wing section NACA 23015 was DRAMATIC.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 22, 2016, 06:45:57 PM
It's been a while, but it's still on the forums: This is where I got my 1-2% and 10% rules, and why other aircraft trying to use the Meredith effect were not successful.
Commentary by Lee Atwood.
What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)? The answer depends on whom you ask. The editors at Air & Space/Smithsonian asked the late Lee Atwood, vice president at North American Aviation when the fighter was born, and the question started an interesting correspondence. Atwood's explanation of what gave the Mustang the edge over the Spitfire and Curtiss P-40 was the design of its cooling system, especially the radiator duct's variable exit. In an address to the Yorkshire Air Museum in June 1998, Atwood described the effect of the design on the Mustang's performance. An excerpt from his speech follows, along with drawings he made to illustrate his point to the editors.
In 1940 we had a young, energetic, and first-class engineering department with competence in aerodynamics, structures, materials, and thermal technologies as developed up to that time, and the factory had a nucleus of expert machine shop, tooling, and production personnel. We gave the Mustang design credit to Edgar Schmued who led the design room effort and brought the components together under the direction of Raymond Rice, who succeeded me as a chief engineer, and the technical specialists.
All these and many others contributed significantly to the project, including Colonel, now General (Retired), Mark E. Bradley who directed the installation of the 85-gallon fuselage tank. He then demonstrated that the longitudinal instability created by this weight behind the pilot could be managed by the combat pilots, and the effective endurance could be increased by some two hours.
In considering the speed performance of the Mustang, which is really its primary advantage and distinction, it is necessary to adjust one's thinking and point of reference to a rather early period in the science of aerodynamics. In the 1930s, there was no jet propulsion, and by any measure of comparison, the technical resources, personnel employed, test equipment and financial expenditures were really insignificant when compared to the aerospace establishment of today. Of course, the basics were there--which involved derivations of Newton's laws and Bernoulli's hydraulic principles--and aero sciences had been basically defined by Prandl, von Karman, and many other mathematical and scientific authorities, but applications to actual aircraft were relatively crude and empirical. Wind tunnel models were the primary proving element in design, and there were still many elements of such testing that had to be estimated or extrapolated with opinion and hope.
In these circumstances it is not very surprising that, among these early practitioners of aeronautical engineering, there were discontinuities of information and differences of opinion on various fine points in the application of general aerodynamic science, as then known, to actual airplane design. This was most apparent in one of the critical aspects of airplane design during the period of reciprocating engines and propeller-driven airplanes. The liquid-cooled designs favored in England and Germany--and also used in the United States and other countries--were generally considered of lower drag because of their in-line cylinder configuration. Air-cooled engines were generally of radial design, with all cylinders facing the cooling air stream, and the diameter was considerably larger.
The well-known radiator became the automobile standard early on, and everyone in the pre-war era had various experiences with these installations and their belt-driven fans. The common experience usually involved adequate cooling at cruising speeds, with frequent over-heating on mountain grades or slow traffic, and the fans were not always adequate to control the temperature. Generally, most people had an occasional bad experience with an overheated engine.
Airplane radiators had a lot of the same troubles, and while separate cooling fans were not seriously considered, ground cooling from propeller circulation alone was frequently inadequate. Basically, the radiators were designed to cool the engines at full power in a climb--which was usually something like half the maximum possible level flight speed with the same power--so at high speed, the cooling capacity was much more than needed.
Now it is clear that we were then quite sure that, as in an automobile, there was no reasonable dynamic use for the warm air discharged from a radiator, and a low and medium speeds, up to say 200 miles per hour, that was quite true. The temperature rise was small, and the expansion was correspondingly modest, and heat energy recovery was insignificant.
However, as engine power increased and better aerodynamic shapes were developed in monoplane designs, we were all slow to realize that, with a normally ducted radiator at high speed, we had at our disposal a really remarkable air pump.
This air pump, like all pumps, had three elements--a compressor stage, a metering or valving stage (radiator core), and a discharge function through an air outlet. This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed. To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible.
This intuitively easy to follow and was also logical from a general streamlined design point of view--which all designers tried to follow as a matter of course. The potential magnitude of this effect was more difficult to appreciate, however, and since little or no data were available, these possibilities were overlooked in most cases.
In the case of the Mustang, the air duct pumping system at full speed at 25,000 feet was processing some 500 cubic feet of air per second, and discharge speed of the outlet was between 500 and 600 feet per second relative to the airplane. This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag. To offer some approximate numbers, the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller.
This air discharge had what can actually be called a regenerative effect. Maximum aircraft speed is the point where the line of power available, created in the engine and delivered by the propeller, crosses the line of power required to propel the plane through the air. Since the propelling force of the pressurized air from the radiator discharge increases as the square of the speed, we have the favorable situation where the faster you fly the more help you are getting from this regenerative air pumping system.
Since this high speed phenomenon could not be effectively measured by regular wind tunnel model test, it was viewed as ephemeral or even imaginary by many in the engineering practice. Actually, it is quite real and has a close relationship with jet propulsion.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 22, 2016, 06:47:49 PM
Lee Atwood on the P-51, pt 2
Regarding the Mustang, I have always referred to the work of F. W. Meredith of the RAE, whose report (RAE No. 1683) of August 1935, greatly influenced me as chief engineer for North American Aviation to offer the British Purchasing Commission the ducted radiator design configuration in 1940. That report showed how the momentum loss in the cooling radiator could be largely restored when excess cooling air was being forced through the radiator at high speed. As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above. This was possible, in Meredith's words, because the outlet was "adjusted to suit the speed,o and back pressure was available accordingly.
Here again, while Meredith's analysis was coherent and mathematically instructive, he failed to convey the practical aspects through an example or two, although he did offer a chart showing drag reduction for various discharge area ratios and conditions. The point I am making was that his work was generally in unfamiliar mathematical terms and was poorly understood. In fact, in two cases I know about, it was described in terms of mild ridicule. In any case, some if not most of the designs of wartime aircraft, including the Spitfire, failed to get the full advantage of this available air pump.
It should be pointed out here that the controversy and misunderstanding of the Meredith Effect on the performance of the Mustang developed largely because it was essentially impossible to get a reasonable measure of the effect from wind tunnel models at the time. The mass flow and momentum could not be accurately measured on a scale model, and no large tunnels were fast enough--200 to 400 miles per hour--to get meaningful results.
It has been reported that Messerschmitt made extensive efforts to determine the reason for the low drag of the Mustang, but his wind tunnel measurements did not disclose the restoration of momentum to the radiator cooling air, and most probably could not have done so with the wind tunnel equipment available at the time.
At this point I would like to interpolate what is , to me, a most fascinating element in Meredith's 1935 report. As you may have noted, I have made no reference to the thermal element in the momentum recovery of the radiator cooling air and at the temperatures involved, the air expansion was relatively small and could be neglected. Real jet propulsion, however, involves fuel burning, and the velocity of the gases and heated air is greatly augmented by this high temperature.
In his report, undoubtedly independent of Whittle's jet engine work, Meredith suggests piping the engine exhaust heat and gases to discharge behind the radiator to heat the discharged air just as burning fuel would do. This would have increased the volume and velocity of the discharged air at the same back pressure and increased the favorable thrust force.
Of course, the thrust of the short stack exhausts had been recognized by Sir Stanley Hooker of Rolls-Royce in his book, NOT MUCH OF AN ENGINEER, and others, but Meredith's suggestion might have produced a much more powerful effect, but it involved complications and practical difficulties. As far as I can determine, it was never tried on any airplane.
This brings me to the Spitfire comparison, although that is probably a poor choice of words. That airplane was in a class by itself and at the top level of defense against the Luftwaffe in 1940, and was undoubtedly the most important defensive weapon in history. It was some 1,000 pounds lighter than the Mustang and was at the peak of interceptor efficiency and was essentially in classic conformity with the objectives of the RAF fighter command. It overmatched its opposition and was there when most needed.
In the cold illumination of hindsight, however, and probably for reasons I have outlined above, it missed the opportunity to restore much of the air flow momentum to the radiator cooling air and, with it, a possible speed increment of more than 20 miles per hour. The late Jeffrey Quill, Supermarine test pilot, describes the incorporation of the Meredith Effect in the Spitfire in his book, SPITFIRE, A TEST PILOT'S STORY, and that the radiators were enclosed in ducts under the wings. Here I would like to quote from an article "The Mustang Margin" I wrote for the AIR POWER HISTORY JOURNAL which involves some background and detail on the subject. It will, of course, be glad to try to answer any questions you may have at the end of my presentation.
"The most notable and probably the first application of the Meredith Effect was incorporated in the Supermarine Spitfire, one of the world's most successful airplanes. Over 20,000 were built in various models, but the Mark IX, with the Merlin -61 engine, was typical of the later wartime production, and a sketch of this model with detail of the radiator installation is shown. Two aspects of this design are significant. First, the radiator outlet has two positions--that is, fully open and partly closed--and cannot be progressively 'adjusted to suit the speed.' Second the inlet upper wall is a continuation of the lower surface of the wing and expands the duct cross section by rapidly curving upward.
"The first, the non-adjustable exit, of course, is a deviation from Meredith's dictum and precludes the progressive build-up of pressure behind the radiator with increasing speed. However, the second can only be judged in hindsight, from an airplane design point of view. The inlet seemed to be configured properly to recover the ram air pressure, and the first Mustang design had a similar entry opening. It was later apparent that the thin boundary layer of air flowing along the lower surface of the wing was progressively thickening ahead of the duct opening, and that the flow would break away at a point on the upward curve of the duct wall. While the resulting turbulent unsteady flow apparently did not create a serious vibration, it certainly reduced the efficiency of the radiator and prevented a more complete closure of the exit opening, which is necessary to develop the jet thrust. Very interestingly, the R.A.E. Subcommittee on Aerodynamics in 1936--in commenting on the Meredith and Capon reports--rather accurately predicted this problem: 'Experiments upon air-cooled engines in the 24-foot tunnel have shown that it is necessary to pay particular attention to the design of the entrance to cowlings and the cooling ducts in order to avoid loss of energy by the formation of eddies.' (Somewhat easier said than done at that time.)
"In the case of the Mustang, the duct volume was larger and flow instability more violent, creating an unacceptable vibration and rumble. Resourceful engineers at North American, working with wind tunnel models, overcame the problem by lowering the intake upper lip below the wing surface boundary layer, thus beginning a new upper duct surface. In this design, the flow expanded gradually as the duct velocity decreased, and the pressure at the radiator face was reasonably uniform. This permitted the appropriate closure of the exit with a temperature-controlled power actuator, and a minimum pressure drop across the radiator consistent with efficient radiator function and cooling demand.
"As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes. While the comparable power used for cooling by the Spitfire is not available to me, the measurements made by Rolls-Royce show a total power required for the same speed (400 mph) as 200 horsepower more for the Spitfire than for the Mustang.
"Records show the P-51D's speed was 437 mph and the Spitfire Mk IX speed was 405 mph. While the Spitfire had exposed tail wheel and other small differences from the Mustang, most of the speed difference was in the cooling drag. The Mark VIII with retracted tail wheel is rated at 414 mph at a somewhat higher altitude. Advanced models of both airplanes with higher performance were produced late in the war, but were not available in significant numbers before V-E Day, May 8, 1945.
"It seems that most other contemporary airplanes attempting to take advantage of the Meredith Effect failed for one reason or another to combine an efficient duct system with a properly designed and regulated exit-closing mechanism and did not develop the energy recovery inherent in the Meredith method. They generally used 10 percent or more of their power available at high speed to overcome cooling drag. A notable exception was the DeHavilland Mosquito multi-purpose plane with the same Rolls-Royce engines and which used a wing leading edge radiator mounting with a short and direct inlet duct. The controllable exit opening had a minimum area little more than half that of the Spitfire, and while it was a larger two-engine airplane, it had a speed of 425 mph.
"Since jet engines do not require cooling systems of the type described here, the subject has become moot and of little current importance. There was a time, however, when this rather insignificant subject made a critical difference."
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 22, 2016, 06:51:24 PM
"What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)?"
I literally just read the first sentence then stopped right there. If that's the level of accuracy or the integrity of Mr. Atwood, then I don't need to read the rest. Being proud of your creation is one thing, but that's just disingenuous.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 22, 2016, 06:59:17 PM
That's the journalist writing. Atwood doesn't start talking for a few more sentences.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 22, 2016, 07:23:04 PM
The first aircraft to use a jet cooler was the Junkers J1 in 1915. (It was also the world's first practical all-metal aircraft.) The radiator with its variable inlet and outlet flaps is visible under the fuselage in the picture. In a speech the 1930s Willy Messerschmitt praised Junkers' jet cooler as the most important single contribution to high speed flight as it cut down the otherwise prohibitive cooling drag.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 22, 2016, 08:12:04 PM
If you read the article, you see that the shape of the radiator housing plays a huge part. The air must compress. It must be out of the boundary layer. It must have an adjustable rear ramp. It's not as simple as sticking a radiator in a tube and hoping it works.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 23, 2016, 08:25:09 AM
Yes of course it does Dave. I suspect Atwood chose to compare the P-51 and Spitfire because the Spit has a rather marginally effective jet cooler. On equal horsepower the P-51 is faster than the Merlin Spits. However, let's compare against the 109. The 109 was also faster than the Spit on equal horsepower. Even on significantly less horsepower. The 109 was as fast or even faster than the P-51 on equal horsepower. The 109K is often thought of as a late-war "monster," but it only has about 1,750 hp. Almost exactly the same hp as the D-Pony and Spit XVI. Back in 1941-42 the 109G-2 made about 410 mph on 1,430 hp. And before you start arguing about the weight difference... Weight has very little effect on top speed. Top speed is limited by parasitic drag (including cooling drag), not induced drag. If you don't believe me, try upping a Pony at 100% fuel and read off the top speed. Then try with 25%. That's a weight difference of more than 1,100 lbs. The difference in speed is not measurable.
Willy Messerschmitt knew a thing or two about making things go fast in the air. After all he did design the Me 109R/Me 209 that set the world speed record for piston engine planes of 469 mph in 1939. A record that stood for 30 years until Darryl Greenamyer's modified F8F broke it in 1969. The Me 209 achieved that amazing speed on 1,775 hp.
So yes, The P-51 had an effective jet cooler, but it wasn't unique in this regard. Nor was it a magical "afterburning jet engine". If you still believe the jet cooler on the P-51 is so awesome that it cancels out cooling drag or even produce net thrust, why is it Reno racers keep removing it in favor of evaporative cooling systems. They must be pretty dumb...
Well, for the time - it was a home run. Disrupting flow from laminar to turbulent is common for All airfoils - but an airfoil which has a high velocity gradient from zero Chord point to 25% versus ~40-50% Chord was huge relative to Mach Divergence.
Today, there are Super Critical wings of Composite build up that have BL separation aft of 50%.
Sure, boundary layer separation was delayed a little but while not Laminar to expectations w/Boundaty layer separation at 40-50% Chord, the reduction in Drag over the common fighter wing section NACA 23015 was DRAMATIC.
Not really.
But it drove the rest of the design's drag reduction which was significant.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 23, 2016, 10:50:27 AM
You are a funny guy, Icepac. :rofl I suspect you meant that as a calculated insult and wonder why you thought it necessary?
It is quoted Verbatim from the text of the Drag Analysis of The North American Aviation Report NA-8449 Performance Calculations for Model P-51D-5-NA (N.A.A. Model NA-109) dated 12-1-44.
Prepared for E.D. Horkey and L.L. Waite by Aerodynamics Section Performance Group.
Further down on page 21 is the discussion regarding climb and Drag of Items Exposed to the Slipstream which included increments in parasite drag due to angle of attack - including specifically "Net Internal flow losses plus additional profile drag, Delta Cd = 0.0064" plus Carburetor Duct (form)= 0.0004 plus Radiator Duct = 0.0019"
If you wish mentoring in Aerodynamics, PM me and I'll help you understand.
For what it is worth IMO Lee Atwood's oft repeated comments re: Meridith Effect thrust indicates that he never read the report for either the P-51D or NAA Report-8264-A for the P-51H. See page 40 of the NAA Report 8264-A which, quoted Verbatim for the DEFINITION of Cooling Drag (same as P-51D report but I only referred to comments under High Speed):
"The basic drag includes the external drag of the radiator duct for flush exit flap condition, but does not include internal losses or dr drag due to change in scoop exit flap position"
etc, etc. All the Cooling Drag, the Drag due to Carbuetor Air Momentum Loss, and the Drag of Items exposed to the slipstream are included in the Determination of Power Available
sure dude.....I'll be sure to get your opinion next month when i'm doing aerodynamic testing at kennedy space center and need a true expert's opinion over the engineers that will be present.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 23, 2016, 10:58:54 AM
sure dude.....I'll be sure to get your opinion next month when i'm doing aerodynamic testing at kennedy space center and need a true expert's opinion over the engineers that will be present.
:rofl
Well I may not be an engineer, but I did stay at a Holiday Inn Express last night.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 24, 2016, 09:32:18 AM
sure dude.....I'll be sure to get your opinion next month when i'm doing aerodynamic testing at kennedy space center and need a true expert's opinion over the engineers that will be present.
Ah yes - you are correct that I am no longer in the biz relative to hypersonic bodies. That said, I do have a BS/MS in Aero, practiced as an Aero and Airframe Structures engineer at both Lockheed and Bell, as a contractor at Vought and TI - on real aircraft, both recip and jet.
If you want to debate drag analysis methods and performance - step into the discussion and be polite.
You have a talent for snide remarks. Didn't you get some form of role model 'pass through' from your father and mother?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 24, 2016, 09:41:40 AM
As you are a self appointed expert that has the experience and academic and industry expertise to toss around well honed sneers at my experience and observations in this post, may we have a summary of your airframe design experience?
Perhaps taking a spec for bids, sketches of layouts that seem to fit, research weight fractions, etc for a Conceptual Design discussion - or maybe later in the Detailed Analysis phase?
If you actually have such experience why would you question mine and instead yank out the snide 'Lee Atwood' comment in your very first reply to my posts?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Oldman731 on October 24, 2016, 09:57:14 AM
It's been a while, but it's still on the forums: This is where I got my 1-2% and 10% rules, and why other aircraft trying to use the Meredith effect were not successful.
Thanks for posting this, very interesting stuff.
- oldman
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: BuckShot on October 24, 2016, 06:18:32 PM
20 to 40 minutes?
I always thought escorts were by the hour.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: ACE on October 25, 2016, 09:34:22 AM
As you are a self appointed expert that has the experience and academic and industry expertise to toss around well honed sneers at my experience and observations in this post, may we have a summary of your airframe design experience?
Perhaps taking a spec for bids, sketches of layouts that seem to fit, research weight fractions, etc for a Conceptual Design discussion - or maybe later in the Detailed Analysis phase?
If you actually have such experience why would you question mine and instead yank out the snide 'Lee Atwood' comment in your very first reply to my posts?
Atwood did not quantify beyond simply stating "all the cooling drag" when other sources put it at 90% or less.
He also made no distinction between "cooling drag" and "radiator drag"......or whether he was referencing the drag of the ducting...........or whether he addressed the addition to the frontal area of the airplane.
It is his article that is parroted over and over across the entire internet whenever meredith effect is mentioned and I don't believe the article shows enough data points to be worthy of said parroting.
And while we're at it.............no, the racing P51s are not adding "boundary layer bumps" but rather reshaping the profile of the wing.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on October 25, 2016, 08:43:59 PM
Atwood did not quantify beyond simply stating "all the cooling drag" when other sources put it at 90% or less.
He also made no distinction between "cooling drag" and "radiator drag"......or whether he was referencing the drag of the ducting...........or whether he addressed the addition to the frontal area of the airplane.
It is his article that is parroted over and over across the entire internet whenever meredith effect is mentioned and I don't believe the article shows enough data points to be worthy of said parroting.
And while we're at it.............no, the racing P51s are not adding "boundary layer bumps" but rather reshaping the profile of the wing.
Two points and then a question.
First I disagree Atwood's comments and remarked that he must not know what his team wrote in the P-51D-5-NA Performance Calculations per NA-8449 in the Drag Discussion from page 19 through 26. You don't either because you missed the point that I quoted directly from the report and so noted them by reference and quotes.
Second point - I knew Bruce Boland and maintained contact with him over the years until he left us. If you recognize the name, you should stop and pause and ask yourself "Do I REALLY know what I am talking about" relative to the experiment of introducing a BL trip up front on the airfoil for improvement in the .67-.77M range? I won't say whether the practice is continuing. As far as I know it was used on only one racing Mustang, but could have been more.
Question, repeated. What are Your academic and industry experience credentials - which you clearly think are far superior to mine that you feel comfortable making snide remarks about my background or 'belief' systems relative to Aerodynamics?
You cleverly avoided answering the question, you haven't demonstrated any real technical expertise to analyze Drag parameter to build performance estimates, and you casually threw off a vague comment about aero background. Blowhard or just a nasty cynic?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 29, 2016, 07:43:13 AM
I did not. Just finished recurrent and two long drives. Haven't had time for anything serious as yet.
Vraciu - To help narrow your focus, I would direct your attention to both the P-51D and P-38J Pilot Handbooks and go to the 10-15 page Flight Operations Charts for both.
Both Are documented from exhaustive flight tests for all the standard load outs, altitudes in 5K increments, Max Continuous Power (MP/RPM) settings and working down to best MP/RPM for maximum Combat range, also citing cruise speed in both Kts and Mph TAS.
These Flight Operations Charts are the source for all the published AAF tables, and particularly collected by Dean in his excellent "America's One Hundred Thousand".
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 29, 2016, 07:48:05 AM
Icepac - My question to you to give me a brief summary of your Aerospace Engineering academic credentials and industrial experience has resulted in resounding silence.
The sound of Crickets in the background is deafening by contrast.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on October 29, 2016, 06:29:23 PM
How about this.........
"you win the bragging rights".
My credentials don't need to exceed yours for you and I to realize that we are in partial agreement on some points and that I am not "wrong enough" for you to lodge a tick in the "w column".
As far as "missing points you made"............I simply didn't read them.
Maybe we could continue this at the AAFO forums where the guys who reprofiled the wings of strega, voodoo, dago red, and were involved with scoopless mustangs communicate on the internet.
You can post your stuff and we'll see how it is recieved.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on October 30, 2016, 07:12:30 AM
Peace brother - send me a link. I probably know some of them and I have a solid understanding of the changes stimulated by Pete Law, Bruce Boland and Lednicer.
As you know, reprofiling the wings are an important modification to squeeze the last iota of wing parasite drag, but the changes to thrust lines, mods to the lower cowl (both external and internal), canopy and other changes also helped.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 30, 2016, 08:47:02 AM
What is the evaporative radiator that they installed in the wings of the racing Mustang?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 30, 2016, 06:02:11 PM
The water/alcohol mix is used to cool the oil. http://www.airspacemag.com/flight-today/how-reno-racers-keep-their-cool-16828199/?no-ist=&page=1
Cool, and I've also learned Rare Bear wasn't the F8F Darryl Greenamyer flew either. His plane is in the Smithsonian now.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: DaveBB on October 31, 2016, 04:55:38 PM
So, the evaporative cooling system would be totally impractical for combat. Back to the P-51's awesome jet air-pump radiator that no other WW2 plane came close to replicating. Sure, the 109 had some junky little radiators in its wings, but how much thrust did they produce? The P-51 was not a high horsepower plane compared German aircraft or even US radial engine planes. It only produced 1470hp at max power.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on October 31, 2016, 05:54:05 PM
Lol What a troll. The P-51D's Packard V-1650 Merlin produced 1725 hp on WEP, almost identical to a 109K-4's DB 605DB.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: MiloMorai on October 31, 2016, 06:35:56 PM
Site your source. I keep seeing 1470-1490hp for the P-51's Merlin.
You can't have been looking very hard. Even the simplest wiki search: "Powerplant: 1 × Packard V-1650-7 liquid-cooled V-12, with a 2 stage intercooled supercharger, 1,490 hp (1,111 kW) at 3,000 rpm; 1,720 hp (1,282 kW) at WEP"
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on November 01, 2016, 09:23:16 AM
The 109 was a.) a lot smaller in wetted area, b.) much draggier but total D in pounds was compensated for by the smaller wetted area to offset the 50+% greater CDparasite.
The last round of 109G-10 and K series were about as fast as the P-51D, even with 72" MP and accelerated slightly better intitially from medium speed envelope.
As near as I have been able to find, there is zero NAA 'official' thrust number for the Meridith effect. I spent some energy trying to calculate pressure drag of the radiator, exit velocity of the pass through air through the radiator with coils at 200 degrees F, estimating the mass flow rate of ambient air (at both SL, STP and 25000 feet), and exit velocity out the butt (closed) - assuming no mass flow rate loss and some other factors to 'assume' heat transfer rate into the 'system'.
I could never get more than ~30-40 pounds of thrust. BTW, that is about 30% of Max Exhaust Thrust (axis component) at 67". Then the other side of the equation is to apply the Drag of the Radiator duct, the stagnation Pressure against the radiator to figure out the Net. At 2x10^^ the Cdp for the radiator duct is .0019 (below 100mph). You have to go the CD vs RN to pick the correct CD (reduced) for RN for the velocity you are basing your calcs on.
Lee Atwood's claims of '300' or whatever else he stated was way overstated. You will note that Ed Horkey and Edgar Schmued never backed up Atwood's claims.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on November 01, 2016, 09:27:15 AM
Military Power for Mustang with 1650-7 is at 3000RPM/61"MP, Max Continuous Power is at 2700RP/47"MP - Ditto for later series 1650-3 and as the 1650-9
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 01, 2016, 09:34:00 AM
We have the best possible 109K in the game, and it is significantly faster than the P-51D on almost the same power. With 100/150 grade fuel the Pony should edge out the 109 though. Pitty we don't have that as perk-fuel or something. Souped up Spits and Ponies would be awesome, even if we could only fly them once in a while.
109 of course could only run at WEP as long as it had a supply of MW50 for anti-detonation and cooling. Mustang had no such limitations and even went to 80" of manifold pressure for extreme situations.
https://en.wikipedia.org/wiki/MW_50
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 01, 2016, 04:35:38 PM
109G-14, G-10 and K-4 had enough MW50 for more than 30 minutes of use. 109 pilots were instructed to limit WEP use to 10 minute intervals with 5 minute cool down. P-51 pilots were instructed to not use WEP for more than 5 minutes. However, these limitations were often exceeded in emergencies.
Do you concede any of the arguments in this thread, or will you just keep on trolling?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 01, 2016, 08:44:55 PM
109G-14, G-10 and K-4 had enough MW50 for more than 30 minutes of use. 109 pilots were instructed to limit WEP use to 10 minute intervals with 5 minute cool down. P-51 pilots were instructed to not use WEP for more than 5 minutes. However, these limitations were often exceeded in emergencies.
Do you concede any of the arguments in this thread, or will you just keep on trolling?
What data have you provided? Also what arguments are you speaking of? At the very least, provide some data to show the thrust that the 109 produces with its radiators. You suddenly jumped the conversation to "Evaporative cooling racing Mustangs" when I asked about that.
Dumping water and alcohol into the engine for 30 minutes? That must be a big reservoir tank. Please provide data on that too.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: FLOOB on November 01, 2016, 11:31:29 PM
Can't you two see that you love each other?
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on November 02, 2016, 04:58:58 AM
The 109 was a.) a lot smaller in wetted area, b.) much draggier but total D in pounds was compensated for by the smaller wetted area to offset the 50+% greater CDparasite.
The last round of 109G-10 and K series were about as fast as the P-51D, even with 72" MP and accelerated slightly better intitially from medium speed envelope.
As near as I have been able to find, there is zero NAA 'official' thrust number for the Meridith effect. I spent some energy trying to calculate pressure drag of the radiator, exit velocity of the pass through air through the radiator with coils at 200 degrees F, estimating the mass flow rate of ambient air (at both SL, STP and 25000 feet), and exit velocity out the butt (closed) - assuming no mass flow rate loss and some other factors to 'assume' heat transfer rate into the 'system'.
I could never get more than ~30-40 pounds of net thrust. BTW, that is about 30% of Max Exhaust Thrust (axis component) at 67" EDIT about 3% of Max Exhaust Thrust. Then the other side of the equation is to apply the Drag of the Radiator duct, the stagnation Pressure against the radiator to figure out the Net. At 2x10^^ the Cdp for the radiator duct is .0019 (below 100mph). You have to go the CD vs RN to pick the correct CD (reduced) for RN for the velocity you are basing your calcs on.
Lee Atwood's claims of '300' or whatever else he stated was way overstated. You will note that Ed Horkey and Edgar Schmued never backed up Atwood's claims.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: save on November 02, 2016, 05:05:09 AM
"The amount of MW booster fuel being carried (75 liters) is sufficient for 26 minutes of flight while using the Sondernotleistung. Therefore Sondernotleistung can be used for two 10 minute periods, or in any other subdivision; in no case should one fly with Sondernotleistung for over 10 minutes. For further servicing instructions, see L. Dv. T. 2109 K-4/Fl.
Between two uses of the Sondernotleistung the engine must be run at a lower power output for ca. 5 minutes."
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on November 02, 2016, 06:08:19 AM
It is an interesting article and parallels the model I used to get my 30-40 pounds of Net Thrust.
What the article leaves conveniently untouched are the Major assumptions and calculations of the pressure drag of the impinging airflow on the radiator as well as the drag of internal flow losses.
The Model must have a.) Mass flow - Inlet, b.) Physical dimensions of inlet, c.) Drag due to internal flow between inlet and radiator, d.) Radiator (both heat transfer to the passing fluid and pressure drag of flow impinging on coils), e.) Drag due to higher energy flow in Plenum, f.) physical dimensions of exit shutter for the flight conditions modeled.
He treats the model as a venturi tube model - and then calculates the Net thrust based on the delta between input flow properties versus exit velocity. This is a.) a Thermodynamic System, and b.) it is 'attached' to the airframe and, as such, a major component of drag in low to medium speeds.
Another observation that should be noted is that he is basing all of his mass flow calcs on 430 mph at Sea Level.. good for Reno, but about 60mph above top speed at 72" MP for a P-51B/D.
This is why NAA engineers separates the Cooling Drag discussions between High Speed and Climb and why they state in the Performance Calculations Report NA-8449. pg 21 of 62.
Cooling Drag "The basic drag includes the external drag of the radiator dust for the flush exit flap position, but does not include the internal losses or drag due to change in scoop exit flap position. These added drags are given as follows:
Calculations show that for most cases a small amount of thrust is derived, however, for this work any thrust from the cooling air is neglected. High speed Cooling Drag is then considered equal to zero".
[/NOTE: I commented that the best I could extract from My assumptions was 30-40 pounds of Net Thrust. Joesupercool derives 270 pounds. Ya think NAA engineers would ignore 270 pounds of 'found' thrust in a Performance Estimate, an amount far in excess of exhaust thrust?
BTW - to get 430mph at SL in a P-51D would take more than 2400 Hp ~ 1775 pounds of Thrust plus another ~ 200 pounds of exhaust thrust.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on November 02, 2016, 07:32:14 AM
109 of course could only run at WEP as long as it had a supply of MW50 for anti-detonation and cooling. Mustang had no such limitations and even went to 80" of manifold pressure for extreme situations.
https://en.wikipedia.org/wiki/MW_50
The P-51H with 50 gallons of coolant could run 80" at WEP with 150 octane and 90" with WI with the new 1650-9. Impossible with 1650-7 or -3 in combat conditions.
That said, when the CC notices the wire 'gate' is broken at 61", there is a discussion. The specs state 5 minutes at WEP. Not 5 minutes, 'rest', 5 minutes more...
5 minutes at WEP. Period. Some P-51s came home, some P-51s landed in Germany well short of home after running at WEP too long - the 'book' sez 5 minutes.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 02, 2016, 12:18:04 PM
But even ten percent is significant I would argue.
Nah, the Buchon is just a license produced 109G with a Merlin engine. 109G fuselage. 109G wings. I'll bet that last 109G-6 started life as a Buchon too, as with most rebuilt 109Gs.
I agree that 10% isn't insignificant, but I wouldn't call it "a lot". If we were to compare with Jugs or Lightnings however... It seems to me that people tend to overestimate the size of the P-51 and underestimate the size of the 109. People also typically overestimate the size of the Fw 190A, often comparing it to the Jug. In reality the early 190As were shorter than the 109G, albeit with a slightly wider wingspan (each wing less than a foot longer).
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 02, 2016, 12:22:08 PM
5 minutes at WEP. Period. Some P-51s came home, some P-51s landed in Germany well short of home after running at WEP too long - the 'book' sez 5 minutes.
Well, you know what they say about limits on combat aircraft. The aircraft limits are only there in case there is another flight planned for that particular airplane. If subsequent flights do not appear likely, there are no limits. ;)
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 02, 2016, 01:57:48 PM
Nah, the Buchon is just a license produced 109G with a Merlin engine. 109G fuselage. 109G wings. I'll bet that last 109G-6 started life as a Buchon too, as with most rebuilt 109Gs.
I agree that 10% isn't insignificant, but I wouldn't call it "a lot". If we were to compare with Jugs or Lightnings however... It seems to me that people tend to overestimate the size of the P-51 and underestimate the size of the 109. People also typically overestimate the size of the Fw 190A, often comparing it to the Jug. In reality the early 190As were shorter than the 109G, albeit with a slightly wider wingspan (each wing less than a foot longer).
The Buchon with the Merlin has a way bigger nose not to mention protrusions for the valve covers.
All else I agree is the same.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 02, 2016, 05:57:42 PM
I can't say I agree that it's got a "way bigger nose". The different engine and propeller makes the nose look different. With the long chin scoop and upright V-12 the Buchon nose is taller, but I think the DB engine 109G is actually slightly longer. Difficult to say.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 02, 2016, 08:20:22 PM
I spent a lot of time around Buchons. They're definitely fatter-nosed. The DB engine is a lot smaller.
Also the Buchon's Merlin protrudes in odd places. When you see them in the flesh the difference is stark.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Devil 505 on November 02, 2016, 09:29:04 PM
You don't even need to see one in person to tell that the difference is huge. Hell, when I was a kid watching HBO's "Tuskegee Airmen" I thought the Buchon was a P-40 painted like a 109.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 02, 2016, 10:50:47 PM
I've been lucky enough to have seen both up close. The Buchon's nose is not "way bigger". Very different yes, but not bigger. The Merlin and DB 605 are almost identical in size. The DB is just an inverted-V and the 109's fuselage is designed around it, not the Merlin. That's why the Merlin fit is so bad. The 109's fuselage is wide at the bottom and narrow on top to accommodate an inverted-V engine. Exactly the opposite of the Spitfire. Both aircraft are designed around their engines. The Merlin 60-series is 3.7 inches longer than the DB 605. The difference in height and width is one inch or less.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: shift8 on November 03, 2016, 06:51:35 AM
Just want to point out something for the previous WEP discussion. This is not a response to any specific point of view, just something I didnt see mentioned specifically, it it was and I missed it, my bad.
The WEP limits on 109s, Spits, P-51s, P-40s etc etc etc. Are in no way thermal limits by any stretch of the imagination. The five minute time limit or 10 minute time limit is a semi-arbitrary number intended to guarantee a certain length of engine life at a operational level. We are talking multi mission engine life, not omg you ran the engine at WEP for 5 min 1 second BOOM.
There are an overwhelming number of accounts and tests, aside from general knowledge of engines, that back this up. Pilots routinely ran WEP for periods greater than 15-20min with no adverse effects during that specific mission. Some of the engine tests run by the AAF were for period of over 7 hours, just to make sure it wasnt going to ruin the engine. I am sure there are German tests of a similar nature. It certainly wore the engine out faster, but it almost never caused failure during combat. There is a reason for example, that the 5min WEP time on the P-51B of 67inches is still 5min at 75 or 72 inches. Same goes really with almost any WEP setting. You will notice they keep the arbitrary time limits despite upping power significantly.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Dawger on November 03, 2016, 07:33:01 AM
Just want to point out something for the previous WEP discussion. This is not a response to any specific point of view, just something I didnt see mentioned specifically, it it was and I missed it, my bad.
The WEP limits on 109s, Spits, P-51s, P-40s etc etc etc. Are in no way thermal limits by any stretch of the imagination. The five minute time limit or 10 minute time limit is a semi-arbitrary number intended to guarantee a certain length of engine life at a operational level. We are talking multi mission engine life, not omg you ran the engine at WEP for 5 min 1 second BOOM.
There are an overwhelming number of accounts and tests, aside from general knowledge of engines, that back this up. Pilots routinely ran WEP for periods greater than 15-20min with no adverse effects during that specific mission. Some of the engine tests run by the AAF were for period of over 7 hours, just to make sure it wasnt going to ruin the engine. I am sure there are German tests of a similar nature. It certainly wore the engine out faster, but it almost never caused failure during combat. There is a reason for example, that the 5min WEP time on the P-51B of 67inches is still 5min at 75 or 72 inches. Same goes really with almost any WEP setting. You will notice they keep the arbitrary time limits despite upping power significantly.
You are absolutely correct. The book time limits were aimed at prolonging service life if the engine.
To paraphrase " If you probably arent going to use the engine again, there are no limits"
A better modeling would be to allow unlimited WEP ( except on thise aircraft with injected fluid ) but inflict damage to the engine if certain temperature limits were exceeded. Allow the player to heat the engine up to the limit and then if he pulls the power back and cools it down he can use the WEP some more. But if he exceeds the critical temperature, then detonation occurs, inflicting damage to the engine and power loss or failure of the engine.
This sort of modeling may be beyond the realism limits HTC desires from a gameplay standpoint since the player can unwittingly blow up his own engines.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 08:24:31 AM
Allow the player to heat the engine up to the limit and then if he pulls the power back and cools it down he can use the WEP some more.
That's exactly how it works in AH, except for not blowing up, just WEP shutting itself off. All planes have unlimited WEP, but with different cool down intervals. In the DB 605 powered rides the WEP cycle is typically 10/5 meaning you get max 10 minutes of WEP before you have to cool down, but it only takes 5 minutes to "recharge" the WEP completely. If you run on MIL power or less for one minute you get to use WEP for another two minutes. If you run out of WEP in a critical moment just keep hitting the WEP button and you will get WEP back for a couple of seconds at a time. The Merlins in this game have 5/10 or 5/15 cycles if I remember correctly.
As Shift8 points out WEP really has nothing to do with engine heat. Unless your in a long steep climb there is very little chance you're going to overheat the engine at any power setting. At high speed the radiator/cowl flaps are almost closed on most planes even at max power.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Krusty on November 03, 2016, 08:26:37 AM
Just want to point out something for the previous WEP discussion. This is not a response to any specific point of view, just something I didnt see mentioned specifically, it it was and I missed it, my bad.
The WEP limits on 109s, Spits, P-51s, P-40s etc etc etc. Are in no way thermal limits by any stretch of the imagination. The five minute time limit or 10 minute time limit is a semi-arbitrary number intended to guarantee a certain length of engine life at a operational level. We are talking multi mission engine life, not omg you ran the engine at WEP for 5 min 1 second BOOM.
There are an overwhelming number of accounts and tests, aside from general knowledge of engines, that back this up. Pilots routinely ran WEP for periods greater than 15-20min with no adverse effects during that specific mission. Some of the engine tests run by the AAF were for period of over 7 hours, just to make sure it wasnt going to ruin the engine. I am sure there are German tests of a similar nature. It certainly wore the engine out faster, but it almost never caused failure during combat. There is a reason for example, that the 5min WEP time on the P-51B of 67inches is still 5min at 75 or 72 inches. Same goes really with almost any WEP setting. You will notice they keep the arbitrary time limits despite upping power significantly.
That's not true. The limits are thermal in nature because running the engine that way can over-stress seals, bearings, joints, moving parts not designed to move 200 rpm faster than they should, and so forth. There is a component of prolonging service life, yes. However, saying it's not thermal is just dishonest. You could say "It's not the absolute melting point of the engine" and have an argument, but there was a lot of variation from engine to engine. The standards and operating limits were there as a baseline. They were only guaranteed to behave in predictable manners up to those specifications. You COULD run an engine at higher RPM for twice as long as you should, but you COULD also cause something to fail and never make it back. Also, there is a very inter-connected relationship between the various systems on a plane. It's not just more power. The power has to be properly translated to a gearbox. That gearbox can only work within certain inputs/outputs at certain gearings. That output will go to a prop shaft and that prop shaft will have an oil-based governor on it limiting RPMs. Those RPMs can only work so well with a prop designed for efficiency within a certain range.
Just last night I was reading a comment about engine tests in WW2 where the end result was deemed (to paraphrase) "Running at these settings will produce no more power or performance but will significantly shorten the life of the engine."
Remember: Engines are complex machines. You can run them improperly. Running them WRONG doesn't make them uber or super, it just means you're being reckless and/or ignorant. Many WW2 pilots never went into WEP their entire career, even through multiple combats. Many just firewalled the throttle to the max allowed (non-wep) setting for the duration of combat and only afterwards did they think about throttling back.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 03, 2016, 08:35:55 AM
Unlimited WEP is gone now. HiTech coded it out.
The DB nose is sleeker and has better aerodynamics than the Merlin on the 109/1112. It is significant. You can see it in your picture, GS.
The Merlin cowling is a big fat block that protrudes below the bottom of the wing. It also is a straight line at a right angle from the windscreen.
The DB tapers toward the nose from the windscreen and meets the lower edge of the wing without protruding. It is also longer as you stated.
The net result is a far sleeker, more aerodynamic nose on the DB 109, particularly F-K.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Dawger on November 03, 2016, 09:23:46 AM
That's exactly how it works in AH, except for not blowing up, just WEP shutting itself off. All planes have unlimited WEP, but with different cool down intervals. In the DB 605 powered rides the WEP cycle is typically 10/5 meaning you get max 10 minutes of WEP before you have to cool down, but it only takes 5 minutes to "recharge" the WEP completely. If you run on MIL power or less for one minute you get to use WEP for another two minutes. If you run out of WEP in a critical moment just keep hitting the WEP button and you will get WEP back for a couple of seconds at a time. The Merlins in this game have 5/10 or 5/15 cycles if I remember correctly.
As Shift8 points out WEP really has nothing to do with engine heat. Unless your in a long steep climb there is very little chance you're going to overheat the engine at any power setting. At high speed the radiator/cowl flaps are almost closed on most planes even at max power.
There is a time limit to WEP in Aces High so you are incorrect in that respect.
Higher power levels increase the likelihood of detonation by "hot spots" in the induction system and cylinder.
The areas that produce the hot spots that cause detonation are not directly influenced by the normal cooling system. The heat from these areas must dissipate into the surrounding structure which is cooled directly by the liquid or air cooling. The cooling system, by the rules of physics, can only reduce overall temperature of the engine components through thermal transfer. It cannot directly address small hot spots created deep in the induction system and cylinder where they are likely to cause detonation to occur.
This is why Anti Detonation Injection fluids(generally water alcohol blends) were used on many aircraft. The fluid directly cooled the induction system and cylinder, allowing operation at higher boost levels because it help delay the formation of hot spots.
You can create detonation and engine damage on an ice cold engine by cramming the throttle forward with the mixture leaned. Rich mixture is required at high power settings because the excess fuel serves the same function as Anti Detonation Injection fluid, cooling of the induction system to reduce hot spots.
The reason for time and temperature limits when running at power levels above normal rated power is because the temperature of the engine is rising. The cooling system cannot keep the engine at its "cruise" temperature and as the overall engine temperature rises, the greater the likelihood of a hot spot in the engine causing detonation. This is because there is a decrease in the rate of thermal transfer from the combustion chamber to the cooling system.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: shift8 on November 03, 2016, 10:03:46 AM
That's not true. The limits are thermal in nature because running the engine that way can over-stress seals, bearings, joints, moving parts not designed to move 200 rpm faster than they should, and so forth. There is a component of prolonging service life, yes. However, saying it's not thermal is just dishonest. You could say "It's not the absolute melting point of the engine" and have an argument, but there was a lot of variation from engine to engine. The standards and operating limits were there as a baseline. They were only guaranteed to behave in predictable manners up to those specifications. You COULD run an engine at higher RPM for twice as long as you should, but you COULD also cause something to fail and never make it back. Also, there is a very inter-connected relationship between the various systems on a plane. It's not just more power. The power has to be properly translated to a gearbox. That gearbox can only work within certain inputs/outputs at certain gearings. That output will go to a prop shaft and that prop shaft will have an oil-based governor on it limiting RPMs. Those RPMs can only work so well with a prop designed for efficiency within a certain range.
Just last night I was reading a comment about engine tests in WW2 where the end result was deemed (to paraphrase) "Running at these settings will produce no more power or performance but will significantly shorten the life of the engine."
Remember: Engines are complex machines. You can run them improperly. Running them WRONG doesn't make them uber or super, it just means you're being reckless and/or ignorant. Many WW2 pilots never went into WEP their entire career, even through multiple combats. Many just firewalled the throttle to the max allowed (non-wep) setting for the duration of combat and only afterwards did they think about throttling back.
No this is not how it works.
WEP ratings are not over the limits of the engine. If they were over the specific thermal or mechanical limits, the engine would outright fail. ALL power ratings, and in fact ALL engineering rating in general, are designed to guarantee certain ranges. For example, the 9G limit on the F-15 is not even close to the actual hard limit. Running WEP for longer than 5min will reduce the life of the engine over the long haul. It does not (usually) causes imminent failure.
The 5min rating for the Mustangs WEP, or a 109s 10 min of MW50 is not a magical structural or thermal limit. It is a number chosen because the designers/operators want the plane to last a certain number of missions or flight hours. We are talking 2-5 missions etc. IE: unless the engine is poorly maintained or already at its limits, the engine is not likely to fail simply from running we WEP for too long. The engine is not a time bomb that is headed for doom when the WEP is thrown on. Yes, it is running harder. Yes that causes more stress on the engine. And yes that stress wears out parts. But NOT during a single mission. All the ratings are relative short of violating the literal real limits of the engine.
Like I said before, you need only look at the available data. There are tons of pilots reports, and official tests regarding this. There is a reason that engine with no fuel or coolant change consistently had their WEP rating upped but the time periods remained the same. The only thing that matters is if the users think the loss in long term engine life is worth the power rating. Even simpler evidence is in most aircraft's general performance testing. Time to Climb, and Max climb rate charts were performed at WEP. It take most planes well over 5min or even 30min to finish such a test at max power.
I dont mind the AH WEP model too much because attempts to made decent thermodynamic systems in other sims have failed laughably. Its not easy to model. Its one of those things that if you try usually results in less realistic result than a simplified system like in AH. Although since AH has been brought up, I would be of the opinion that WEP should be indefinite for at least the first sortie in a plane. If you rearm, then maybe some penalty should exist after several reuppings of the same plane. Then again, you could always argue the engine got replaced as needed.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 10:40:26 AM
Just did a test. Upped a Spit8 flew around shooting drones for 5 minutes until the WEP ran out. After waiting about three seconds I got one second of WEP back, just as I should with the 5/15 WEP cycle. I waited longer then engaged WEP again and got several seconds worth. Then I did a slow half-loop and waited some more, and got WEP back for longer. It works just like it used to. In the video I never manually turn WEP off:
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 10:49:11 AM
The DB nose is sleeker and has better aerodynamics than the Merlin on the 109/1112. It is significant. You can see it in your picture, GS.
This is true. More bumps is the last thing a 109G needs. However, despite that the Buchon is the better performer of those two 109s in the picture. The Merlin's extra 170 hp made up for the less than ideal engine fitting.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 03, 2016, 12:33:22 PM
Just did a test. Upped a Spit8 flew around shooting drones for 5 minutes until the WEP ran out. After waiting about three seconds I got one second of WEP back, just as I should with the 5/15 WEP cycle. I waited longer then engaged WEP again and got several seconds worth. Then I did a slow half-loop and waited some more, and got WEP back for longer. It works just like it used to. In the video I never manually turn WEP off:
Try it in a Mustang. Eventually you get no more WEP.
HiTech posted elsewhere that unlimited WEP in AH2 was a bug that he fixed in 3. At some point you lose it for good and must replane to get it back.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 03, 2016, 12:34:23 PM
This is true. More bumps is the last thing a 109G needs. However, despite that the Buchon is the better performer of those two 109s in the picture. The Merlin's extra 170 hp made up for the less than ideal engine fitting.
Guess so. Although the K probably destroys the Buchon.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 06:35:20 PM
Try it in a Mustang. Eventually you get no more WEP.
HiTech posted elsewhere that unlimited WEP in AH2 was a bug that he fixed in 3. At some point you lose it for good and must replane to get it back.
OK so I just did. Upped a D-Pony. Flew it on WEP for five minutes until it shut down. Cruised on MIL for ten minutes to let it cool down. Watched the temp needle go back down to normal. Turned WEP back on for another full five minutes. Vraciu, I want those 20 minutes of my life back! :furious
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: icepac on November 03, 2016, 07:33:51 PM
Certain planes depended on "consumables" for thier "wep".
I believe those are the ones that hitech coded for a total wep time limit.
This goes back to warbirds.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Dawger on November 03, 2016, 07:40:15 PM
OK so I just did. Upped a D-Pony. Flew it on WEP for five minutes until it shut down. Cruised on MIL for ten minutes to let it cool down. Watched the temp needle go back down to normal. Turned WEP back on for another full five minutes. Vraciu, I want those 20 minutes of my life back! :furious
I would bet you don't get a third five minutes
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 07:45:18 PM
Nice try :D
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: GScholz on November 03, 2016, 08:09:08 PM
Ran out of fuel before I ran out of WEP in the 109K-4, so that's business as usual. :aok
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 04, 2016, 08:41:19 AM
OK so I just did. Upped a D-Pony. Flew it on WEP for five minutes until it shut down. Cruised on MIL for ten minutes to let it cool down. Watched the temp needle go back down to normal. Turned WEP back on for another full five minutes. Vraciu, I want those 20 minutes of my life back! :furious
You gotta keep going. Eventually it quits for good. I fly Mustangs pretty much exclusively. They have a total time limit now for WEP.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 04, 2016, 08:42:01 AM
Correct. It has a definite limit. Eventually it doesn't come back no matter what.
This is correct! If you want to test do it offline and set fuel burn to .1,not 1 but .1 and you will have plenty of flight time to test the WEP limitations.
The AH wiki has the wep times and recharge rates but it doesnt list the total limitation,since HTC hasnt released that yet I cant say definitively what the total limits are but there is indeed a point where you can no longer recharge the wep cycle in the plane you are flying,that said with a 2 fuel burn rate most planes will run out of fuel before the wep limits because there just isnt enough flight time. There are a few exception like the 51 that can fly forever,well not really, on full fuel and DT`s.
:salute
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Devil 505 on November 04, 2016, 03:38:31 PM
The real question is what effect rearming has on recharging WEP/ resetting charge times.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: Vraciu on November 04, 2016, 03:55:38 PM
Here is a list of the 8th AF's heaviest losses, http://www.taphilo.com/history/8thaf/8aflosses.shtml
Which were because of fighters not showing up.
Haven't been around for some time - and that link doesn't work now.
That said, the great losses had three root causes. 1) Either fighters or bombers missed r/v times and location. Examples 4th FG missed R/V by minutes for the 2nd BD task force heading to Bernberg on 7 July,1944 and 355th/4th FG missed R/V by minutes for 2nd BD headed for Stettin on 20 June 1944 . 2.) The bombers were far off course and missed R/V. Examples 1st/3rd BD 29 April 1944; 1st BD on 12 May, 1944; 445th BG on 27 Sept, 1944. 3.) Numerically Overwhelming and persistent LW attacks against insufficient fighter escort - Berlin 6 March 1944, Munich area 24 April 1944.
Title: Re: Escorts could only stay with bombers for 20-40 minutes?
Post by: drgondog on January 15, 2023, 01:39:57 PM
We have the best possible 109K in the game, and it is significantly faster than the P-51D on almost the same power. With 100/150 grade fuel the Pony should edge out the 109 though. Pitty we don't have that as perk-fuel or something. Souped up Spits and Ponies would be awesome, even if we could only fly them once in a while.
For unknown reasons I can't explain I revisited this thread
Your data on the P-51D doesn't reflect the later Flight Tests for your speed vs altitude and Hp ratings. Two significant points on the May 1945 test results below. First, the top speed of 442mph at 67"/3000RPM at 26,000ft with 1410Hp - is With external racks. The improved racks for D/H achieved about 50% reduction in drag penalty overP-51A/B racks. For purposes of this comparison you should find Flight testing of the K with Schlob 503 rack inclusion for your 109K speeds.
I exchanged a lot of emails with Dr. Millei (Kurfurst) to try to get best individual comparisons between P-51B and various ther fighters, normalized to full (internal) gross weights, including 109G-6 (including DB606A/S. I included those in my book (co-authored with Lowell Ford) P-51B:North America's Bastard Stepchild that Saved 8th AF" (agree to a little hyperbole).
Didn't find a 'racked' 109K at full combat load that exceeded 440mph. Your source? From your source, what were the conditions at takeoff and FTH?
Further comment - you rebutted 'much larger' comment of Mustang compared to 109 (all) as in 90% range but that isn't representative of 'size' relative to area, volume or drag.
While the Linear span of a 109 is about 90% of the 51, the AREA of 172x2= 344sf to P-51 235x2= 470sf, a 70% factor with similar effects for all wetted area. It is much smaller - and yet according to Hoerner, chaper 14-9 the CDw=.0095 for the109, to P-51 CDw=0.0040.
You might also note that MILITARY Power at 29K results in 439mph in the P-51D-15-NA with the 1650-7 developing 1288hp.
Haven't been around for some time - and that link doesn't work now.
That said, the great losses had three root causes. 1) Either fighters or bombers missed r/v times and location. Examples 4th FG missed R/V by minutes for the 2nd BD task force heading to Bernberg on 7 July,1944 and 355th/4th FG missed R/V by minutes for 2nd BD headed for Stettin on 20 June 1944 . 2.) The bombers were far off course and missed R/V. Examples 1st/3rd BD 29 April 1944; 1st BD on 12 May, 1944; 445th BG on 27 Sept, 1944. 3.) Numerically Overwhelming and persistent LW attacks against insufficient fighter escort - Berlin 6 March 1944, Munich area 24 April 1944.