Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: joeblogs on July 13, 2005, 08:27:27 PM
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I know a million threads have been devoted to this, and there are a lot of reasons.
But I am just reading Graham White's new book R2800 and I heard a new facet - RAM air at low to medium altitudes.
Here he discusses how the supercharger on the Hellcat worked:
"The main stage was driven at all times and had a single speed. The auxilarry stage could operate in three modes: neutral, i.e. the blower impeller was not driven; low speed; and high speed. For low altitudes, those under 12,000 feet, the engine was aspirated through the single speed main stage. ... Therefore, at all altitudes below 12,000 feet the R2800-10 operated soley on the main stage. Rather surprisingly, ram air was not supplied to the main stage blower, only to the auxillary stage. This anomally explains why a Corsair handily outperforms a Hellcat at lower altitudes. The Corsair's main stage was fed ram air and thus gained a significant amount of power. At higher altitude, with the auxillary stage engaged, there was little to choose between the Hellcat and an F4u-1." (p. 503)
-blogs
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I know also that the F6F was a deceptively big plane. It looks stubby taken by itself and maybe it's resemblance to the F4F plays into that too.
Another item of note - the gull wings of the Hog, specifically where they attached at 90 degrees to the tangent of the fuselage, allowed for a nice little decrease in drag. Some kind of airflow thing. The gull wings were originally put on the Hog to allow for shorter landing gear struts yet still have the huge prop clear. I don't know if the drag thing was a happy discovery or something that was anticipated as a secondary benefit.
One thing I've always wondered about is why the vertical stabilizer is slid forward on the fuselage several feet. what's that all about, strength?
Magoo
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I've wondered that too. About the stabilizer. looks ugly.
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there was little to choose between the Hellcat and an F4u-1
I'm not real familiar with Navy aircraft, but from what I know, the Hellcat came out much later than the F4U. Add that to the fact they are comparing the Hellcat to the F4u-1 and the comparison seems a little 'stacked' in the Hellcat's favor.
It is akin to comparing the FW190A5 to the 109E when the 190 was introduced in combat.
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the Hellcat came out much later than the F4U.
Not so this all depends on what F6F and what F4U you are compairing.
The F6F-3 first entered combat in August 1943 and the F4U enterd operational service in February 1943. The F6F-5 entered service April 1944 but was actually about 10mph slower than the F6F-3.
Take this as you will Got the dates from a book here so if there are any arguements, argue with the author not me :)
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Originally posted by Flayed1
Not so this all depends on what F6F and what F4U you are compairing.
The F6F-3 first entered combat in August 1943 and the F4U enterd operational service in February 1943. The F6F-5 entered service April 1944 but was actually about 10mph slower than the F6F-3.
Take this as you will Got the dates from a book here so if there are any arguements, argue with the author not me :)
No need to argue, talk to one of the Grumman test pilots. According to him and supporting data from various agencies, the F6F-5 was a genuine 400+ mph fighter (typically 406-412 mph depending upon the test) and about 10-12 mph FASTER than the F6F-3.
My regards,
Widewing
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This may all be true.
White is pointing out a performance disadvantage for the F6f at altitudes below 12k.
Both planes hit their maximum true airspeed at much higher altitude, where both are pushing RAM air through the supercharger.
-Blogs
Originally posted by Widewing
No need to argue, talk to one of the Grumman test pilots. According to him and supporting data from various agencies, the F6F-5 was a genuine 400+ mph fighter (typically 406-412 mph depending upon the test) and about 10-12 mph FASTER than the F6F-3.
My regards,
Widewing
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My understanding of the F4U vs F6F speed difference was from design considerations. The F4U was designed in the late thirties with specifications requiring speed, more speed, and above all ... speed. The F6F was optimized to kill the japanese zero (which was a slow plane) and its design was an extension of the F4F Northrop Grumman design. The F4U was designed and optimized (even before WW2) to have minimum drag for the engine configuration used. I have read many reports on the XF4U-1 from the NACA Langley wind tunnels on drag reduction. The F6F was also tested, but not as thoroughly (due to the urgency of the war). Also, as noted before due to the landing gear strength concerns, the F4U wing root makes a 90 deg angle with the airframe which minimizes drag.
The F4U was raced successfully after WW2, but I don't think the F6F was ever raced. If so, I never read about it. While the F6F was a great design, and held a higer kill/death ratio than the F4U, the F4U was designed to make it a faster plane. Along with the wing root drag reduction, the F6F was designed as a lower wing loaded plane with about the same weight as the F4U. That requires the F6F to have more wing surface than the F4U which generates more drag. The F6F could turn better than the F4U because of the lower wing loading, but that lower wing loading also made it slower. That's oK if you are still faster than your opponent, which in this case was the zero.
Regards,
Malta
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Not to quibble, but the F6F was designed from scratch, taking into consideration everything pilots wanted, needed, and were most likely to use to kill the enemy. They externally made it resemble the F4F, as it was a direct descendent. However it's not an extension of the F4F design. It was totally new.
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the f6f is *as* big as a p-47... and the f4u is surprisingly smaller than one would imagine.
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Originally posted by Shane
the f6f is *as* big as a p-47... and the f4u is surprisingly smaller than one would imagine.
Have u ever "seen" a 47, F4u, and a Hellcat together?
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My impression of the F4U size was that similar to the Spitfire 7. Of course that is not having them side by side, but rather after looking at the Spitfire 7 in the Smithsonian Institue and the F4U(D) in the Hampton Air and Space Center. As a note, the 109G was a smaller aircraft than the Spit 7. The P&W R2800 engine is not that big either, per the Smithsonian. What I did find impressively huge was a F4E Phantom II in the Hampton Air and Space. That's a big aircraft!
I have never seen a P47 or F6F (any model). Although I did assemble a model of the F6F as a kid. :) I have been in the full scale wind tunnel at Langely AFB where most of the (US) WW2 aircraft were tested by the NACA. It's a continuous flow fan driven tunnel currently operated by Old Dominon University.
Regards,
Malta
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Originally posted by Bodhi
Have u ever "seen" a 47, F4u, and a Hellcat together?
yes. reading, pa... 2001 i think, not sure if the cat was there, but jug and hog were.
as well as scale models.
just like the 109, while small, the FW is also surprisingly smallish.
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Originally posted by Bodhi
Have u ever "seen" a 47, F4u, and a Hellcat together?
Using my "Giant Book of Aircraft of Doom" from all-knowing Jane...
F4U-5N had a wingspan of 41 ft and was 33 ft 6 in long.
F6F-5 had a wingspan of 42 ft 10 in and was 33 ft 6 5/8 in long.
P-47D had a 40 ft 9 1/4 in wingspan and was 36 ft 1 1/4 in long.
It only listed the data for one of the models in each series, but I'm guessing they didn't change much.
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Seen the f6f in flight, right over my head and low and loud, its a big bulky bird and damn cool sounding. seen the f4u but it was higher but seems to me it was smaller than the f6f or maybe its because the f6f is so fat looking.
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(http://img303.imageshack.us/img303/9835/f4uside7dd.jpg) (http://www.imageshack.us)
(http://img303.imageshack.us/img303/6688/f6fpushedcv2ow.jpg) (http://www.imageshack.us)
Here's a person to plane comparison. F6 is quite a bit bigger than the F4U.
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Originally posted by OOZ662
F4U-5N had a wingspan of 41 ft and was 33 ft 6 in long.
F6F-5 had a wingspan of 42 ft 10 in and was 33 ft 6 5/8 in long.
Either I'm not comparing the right thing to you guys or you're just ignoring me...:rolleyes:
The F4U is only 5/8 of an inch shorter than the F6F, but the F6F has a longer wingspan by 1 ft 10 in.
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Originally posted by Swarmed
(http://img303.imageshack.us/img303/6688/f6fpushedcv2ow.jpg) (http://www.imageshack.us)
Note that this F6F has been pranged. A big dent in the upper cowling, a dent in the top side of the belly tank and a bent propeller blade.... I'll bet it was hit by another aircraft, possibly being towed or pushed on the flight deck.
My regards,
Widewing
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Looks to me it got caught in the arrestor wires or in the crash barrier as evidenced by the cables on the deck and the one hung up in the prop.
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I've wondered that too. About the stabilizer. looks ugly.
I can tell all your taste is in your mouth :D. Nothing ugly about teh HOG!
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Originally posted by Swarmed
(http://img303.imageshack.us/img303/9835/f4uside7dd.jpg) (http://www.imageshack.us)
(http://img303.imageshack.us/img303/6688/f6fpushedcv2ow.jpg) (http://www.imageshack.us)
Here's a person to plane comparison. F6 is quite a bit bigger than the F4U.
It is NOT "quite a bit bigger."
The sizes are comparable, within a foot in wing length, inches of overall length. The weights are also comparable.
So HOW is it quite a bit bigger????
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all i claimed was the f6f was as big as a jug and that the f4u is smaller than expected... :aok
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Originally posted by Bodhi
It is NOT "quite a bit bigger."
The sizes are comparable, within a foot in wing length, inches of overall length. The weights are also comparable.
So HOW is it quite a bit bigger????
Bodi you've made quite the logical error here....
"bigger" is not limited to wingspan. You must take into account mass, fuselage area, etc. The corsair's wings may reach to the same dimensions as the F6F, but the fuselage, engine, body, and everything, are all MUCH smaller, part for part, than the F6F's. The F6F is bulky, wide, deep, and has a lot more "displacement" (let's use that term) than the f4u1
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Originally posted by Krusty
Bodi you've made quite the logical error here....
"bigger" is not limited to wingspan. You must take into account mass, fuselage area, etc. The corsair's wings may reach to the same dimensions as the F6F, but the fuselage, engine, body, and everything, are all MUCH smaller, part for part, than the F6F's. The F6F is bulky, wide, deep, and has a lot more "displacement" (let's use that term) than the f4u1
Currently we are working on an F4u. I am well aware of it's size, and am able to look at numerous Hellcat carcasses any time I please. I am also well aware that the F6F aircraft has a larger diameter fuselage, and the wings are thicker midspan. They are relatively the same at the root. The Corsair actually has larger wings if you strech them out from the gull.
At the end of the day, side by side, the Hellcat is bigger than the F4u, but not by such a margin that it is a major size difference.
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I started the post to add a piece of new (I think) info about how these planes are different. It doesn't pertain to top speed, but rather to speeds below 12k, well below the critical alt for max speed of either...
I think we know all this other stuff already. Anyone can look up the physical measurements of these planes...
-blogs
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ok, but if you really want to argue size, look at a frame by frame comparison of the Hellcat to Corsair.
Then tell me the F4u is that much smaller....
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As for size comparisons I love the OFMC birds flying in formation. It shows the small medium and large viariety of warbird types all in formation.
(http://www.sky-flash.com/airshows/zeltweg2000/37.jpg)
(http://www.flybyaviation.com/F4U-1A%20and%20F6F-5%20%20%20-%20%20Akron,%20OH%206-22-2003.jpg)
(http://mywebpages.comcast.net/markw4/HellcatAndCorsair.jpg)
The Cd0 of the F4U was lower than the F6F by a fair margin due mostly to the frontal area being smaller, the cockpit being moved further aft and the slightly smaller wing area. It is said that "The F6F is the box the F4U came in".
However the big difference at low altitude was the RAM air capability of the F4U. In fact the later flight manuals of the F4U and F6F despite having the same engine rate the F4U-1 R2800-8W with 2300HP at sea level while the F6F R2800-10W remains at 2250HP rating no doubt due to RAM air.
Also the later F4U-1's were cleared for 2800RPM on takeoff.
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Shane says the Hog is smaller than expected....heh, well all I know is the first time I saw one up close I was very suprised at how big it looked. Airshow at ElToro, Pappy was gonna be there, and a F4U was parked at one of the squadrons, in blacksheep markings of course. It seemed HUGE. We rolled in there on the guard detail, changing out the guards.
I gotta mention the dolt we were relieving at that post had been up walking around on its wings. He very nearly got a beatin over it.
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Hi Joe,
>Rather surprisingly, ram air was not supplied to the main stage blower, only to the auxillary stage.
Have you ever seen a diagram of the supercharger intake arrangement? I'm not quite certain on how the description translates into a system.
>This anomally explains why a Corsair handily outperforms a Hellcat at lower altitudes. The Corsair's main stage was fed ram air and thus gained a significant amount of power.
Well, I don't believe this is a correct intepretation. Below full throttle height, you actually lose power to ram effect because the throttle has to be closed further to avoid overboosting, deteriorating volumentric efficiency.
Ram effect is beneficial above full throttle height only.
The reason for the Corsair's superior speed is its smaller frontal area (there's little to chose between the wings), made possible by embedding the air intakes into the wing root. As mentioned above, the gull-wing arrangement helps to reduce fuselage-wing interference drag, too.
Regards,
Henning (HoHun)
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Originally posted by F4UDOA
As for size comparisons I love the OFMC birds flying in formation. It shows the small medium and large viariety of warbird types all in formation....
Relative size in perspective can be deceptive.
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Hi HoHun
Ram effect is beneficial above full throttle height only.
Have been rolling this statement over in my head. And debating the accuracy.
I agree ram air is more benificial above critical alt. Just wondering if the higher inlet pressure do to ram air (I.E. inlet to Super charger) has the effect of lowering torque requirements of the super charger and hence more brake horse power?
HiTech
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Hi Hitech,
>Just wondering if the higher inlet pressure do to ram air (I.E. inlet to Super charger) has the effect of lowering torque requirements of the super charger and hence more brake horse power?
I have to admit that I'm not fully comfortable either with any of the explanations I have read for the drop of power with incrased supercharger intake pressure below full throttle height.
I tend to believe it's all accounted for in the volumetric efficiency value, but that's more of a black box approach.
However, looking at the power over altitude engine curves, it's clear that mechanically-driven superchargers of the centrifugal type lose power with increasing intake pressure below full throttle height.
The ram effect yields a slightly different temperature/pressure combination than just decreasing altitude, but the overall effect should be very close.
How the force/torque balance changes for the individual components of the system, I'm not certain.
The relation I postulated is not entirely universal, either, as the Jumo 213 (for example) contradicts it by the use of the spin throttle and the constant charge mass control (instead of the usual constant boost control).
Regards,
Henning (HoHun)
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Hi HoHun,
The ram effect yields a slightly different temperature/pressure combination than just decreasing altitude, but the overall effect should be very close.
This is very close to how we model it.
I have pretty much concluded that the loss in power is do to increase in temp. more than the pressure effiency gained by the charger.
HiTech
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HoHun
Originally posted by HoHun
Hi Joe,
Have you ever seen a diagram of the supercharger intake arrangement? I'm not quite certain on how the description translates into a system.
The diagrams are in White's new book called R2800.
Originally posted by HoHun
>This anomally explains why a Corsair handily outperforms a Hellcat at lower altitudes. The Corsair's main stage was fed ram air and thus gained a significant amount of power.
Well, I don't believe this is a correct intepretation. Below full throttle height, you actually lose power to ram effect because the throttle has to be closed further to avoid overboosting, deteriorating volumentric efficiency.
At 12k, you are at full throttle height for the first stage of the supercharger. remember the 2nd stage is not engaged. If the pilot engages the second stage, he MUST throttle back or he will overboost the engine.
Originally posted by HoHun
The reason for the Corsair's superior speed is its smaller frontal area (there's little to chose between the wings), made possible by embedding the air intakes into the wing root. As mentioned above, the gull-wing arrangement helps to reduce fuselage-wing interference drag, too..
We are all familiar with the other arguments that explain the disparity in Vmax between these two planes. White's explanation suggests the disparity should be greater at lower altitudes. That should be pretty easy to check, but I am afraid I can't do it right now.
-Blogs
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F4uDOA
Greetings -
I agree with most of your points, but I'm a bit confused about your horsepower numbers.
The r2800-8W & r2800-10W are B series engines. Even with 100/125 PN gas, these are rated for no more than 2100 HP with ADI. Now the r2800-18W is a C series which will reach 2,300 HP with ADI.
So it sounds like you are comparing the output of a C series engine on very late model Corsairs to the F6f, which never had such an engine.
-Blogs
Originally posted by F4UDOA
...However the big difference at low altitude was the RAM air capability of the F4U. In fact the later flight manuals of the F4U and F6F despite having the same engine rate the F4U-1 R2800-8W with 2300HP at sea level while the F6F R2800-10W remains at 2250HP rating no doubt due to RAM air.
Also the later F4U-1's were cleared for 2800RPM on takeoff.
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Hitech:
You know how to reach him or Kimball McCutcheon. Why not ask them while you can?
-Blogs
Originally posted by hitech
Hi HoHun,
This is very close to how we model it.
I have pretty much concluded that the loss in power is do to increase in temp. more than the pressure effiency gained by the charger.
HiTech
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I added a note to your thread on turbosupercharging on the P47.
White documents the evolution of engine changes within and across the plane model numbers. So it is possible to trace when the GE turbos change and what impact there is on performance.
-Blogs
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I thought it was slower because the pitot tube location reported speed differently, and they are really close in speed.
Might just be nonsense I read here.
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I'm not sure about the larger frontal area being the F6F's problem.
Large frontal area does not automatically mean more drag. Radials have suprisingly low drag compared with the pointed nosed liquid cooled inlines. What liquid cooling saves in a streamlined shape it looses to the need to stick a radiator into the wind. The P51's low drag is said to be due to a good design of the radiator.
This cooling drag is extremely dependent on the specific design on the intake the tunnels and the exit. I'm not an expert but I belive this drag is not a simple function of airspeed since higher speed -> higher engine output -> more air mixing needed for heat transport -> more drag depending on design.
Cowl flaps and radiator doors can be adjusted for the cooling needed and they affect the drag.
Bozon
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Originally posted by joeblogs
F4uDOA
Greetings -
I agree with most of your points, but I'm a bit confused about your horsepower numbers.
The r2800-8W & r2800-10W are B series engines. Even with 100/125 PN gas, these are rated for no more than 2100 HP with ADI. Now the r2800-18W is a C series which will reach 2,300 HP with ADI.
So it sounds like you are comparing the output of a C series engine on very late model Corsairs to the F6f, which never had such an engine.
-Blogs
The -8W and -10W are generally credited with anywhere from 2130 to 2250 hp WEP @ 56-60 in Hg and 2700 rpm in neutral blower. The -18W running at the same map but 2800 rpm would do about 2375 hp, increase map to 65 in Hg would put power about 2450-2550 hp. Which matches the figures I have for -18W map fairly well.
Welcome to the wonderful world of trying to figure out exactly how much power the R-2800 was capable of, I have at least 3 different official figures for the -8/8W. They are all 2250 hp, but at anywhere from 57 in Hg to 60 in Hg.
As near as I can tell, all B-series R-2800 were 2000 hp @ 52 in Hg SL & 2700 rpm core engines. From there they varied according to whether they had a 2nd gear for the integral blower or what aux blower setup they had. IE the 2-speed aux blower setup in the -8/-10 or the exhaust driven supercharger in the P-47.
My guess is that the -8 was initially 52 in Hg 2000 hp mil, then was first allowed 56 in Hg for about 2150 hp. Then bumped to 58 in Hg and about 2230 hp, finally to 60 in Hg and approx 2250-2300 hp. While the -10W was cleared for 60 in Hg and about 2250-2300 hp initially. The lack of compression heating of the charge for the -10W could explain why it was allowed higher map than the -8W at first.
Besides which, the 360 mph at SL range for the F4U-1 is much more believable at 2250-2300 hp than it is at 2100 hp.
I need to pick up White's new book, but I take all his stuff with some reservations. I have found too many minor errors and inconsistencies in his other WWII Allied Piston Aircraft Engines book to trust him fully. I would really like to see a Whitney-esque treatment of the R-2800 like his opus on the V-1710.
Greg Shaw
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White´s second book is much better than his first one but not on par with Whitney´s effort. One of White´s problems is his use of sources. E.g. his descriptions of individual aircraft type development is often taken from very dubious sources like Squadron/Signal in actions. Another problem is that he gives the power rating, but the tables don´t have any boost info.
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JoeB/GWShaw,
I haven't been on the boards in a while so this conversation is refreshing.
Here is my source. It is the 15 October 1945 POH for the F4U-1D. It is revised with updates until 1 December 1952 and it is very thorough with a full performance diagrams. It shows the R2800B block producing 2300HP at sealevel at 57.5"MAP, 2100HP at 58.5"MAP at 14500FT and 1925HP at 19,000FT all at WEP.
Both lower ratings are at 2700RPM and the High blower is at 2550RPM.
Also there is a column for with RAM and NO RAM that shows no difference for HP rating only in critical altitude.
I would show you the scan but my PC has been down for months and all my scans are trapped in a lifeless hunk of junk. If I can retrieve the doc I will post it ASAP.
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I was looking at my copy of the AN 01-45HB-1 Pilots Handbook for the F4U-4, revised 15 December 1944 and noticed on the last page, which has a engine calibration curve, there is a statement that says "no allowance has been made for ram". So, what exactly is ram? Is that air taken in by the chin scoop on the F4U-4?
Regards,
Malta
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Originally posted by stantond
I was looking at my copy of the AN 01-45HB-1 Pilots Handbook for the F4U-4, revised 15 December 1944 and noticed on the last page, which has a engine calibration curve, there is a statement that says "no allowance has been made for ram". So, what exactly is ram? Is that air taken in by the chin scoop on the F4U-4?
Regards,
Malta
Yes, ram is the pressure increase created by the forward movement of the aircraft. The faster you go.... the faster you go. It is the reason maximum climb performance is typically a bit above the rated altitude of the engine, and max speed performance is even more above engines rated altitude.
Greg Shaw
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Thanks Greg, that's what I though.
But, where is the ram air taken in for the F4U-1 models? They have no chin scoop like the -4. I don't think the oil coolers in the wing roots would work very well for carburettor air. Would part of the engine cooling air be used? If that is the case I see no reason why the F6F or P47 could not have done the same.
Regards,
Malta
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Originally posted by stantond
Thanks Greg, that's what I though.
But, where is the ram air taken in for the F4U-1 models? They have no chin scoop like the -4. I don't think the oil coolers in the wing roots would work very well for carburettor air. Would part of the engine cooling air be used? If that is the case I see no reason why the F6F or P47 could not have done the same.
Regards,
Malta
There are splitters in the wing inlets; oil cooling, carb air and intercoolers. The F4U-4 and -5 moved the carb inlets to the chin and cheeks IIRC. I have diagrams of them all, but in storage somewhere until november or so.
Greg Shaw
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This is the second time I've seen you take swipes at engine experts based on little more than a hand waive (the first was Wilkinson).
White's new book is based on heaps of P&W internal reports. His data on engine models in the earleir books were generally drwan from primary, not secondary materials.
Now if you want to talk about his description of planes, that's another thing. But when it comes to engines, this guy is one of the best.
Originally posted by pasoleati
White´s second book is much better than his first one but not on par with Whitney´s effort. One of White´s problems is his use of sources. E.g. his descriptions of individual aircraft type development is often taken from very dubious sources like Squadron/Signal in actions. Another problem is that he gives the power rating, but the tables don´t have any boost info.
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F4u
What was the PN number on the fuel for the rating?
-Blogs
Originally posted by F4UDOA
JoeB/GWShaw,
I haven't been on the boards in a while so this conversation is refreshing.
Here is my source. It is the 15 October 1945 POH for the F4U-1D. It is revised with updates until 1 December 1952 and it is very thorough with a full performance diagrams. It shows the R2800B block producing 2300HP at sealevel at 57.5"MAP, 2100HP at 58.5"MAP at 14500FT and 1925HP at 19,000FT all at WEP.
Both lower ratings are at 2700RPM and the High blower is at 2550RPM.
Also there is a column for with RAM and NO RAM that shows no difference for HP rating only in critical altitude.
I would show you the scan but my PC has been down for months and all my scans are trapped in a lifeless hunk of junk. If I can retrieve the doc I will post it ASAP.
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JoeB,
100/130
I promise I will post this when I can.
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Originally posted by joeblogs
This is the second time I've seen you take swipes at engine experts based on little more than a hand waive (the first was Wilkinson).
White's new book is based on heaps of P&W internal reports. His data on engine models in the earleir books were generally drwan from primary, not secondary materials.
Now if you want to talk about his description of planes, that's another thing. But when it comes to engines, this guy is one of the best.
Wilkinson is pure unadulterated ****, nothing more.
As for White, do check the section giving basic info on each engine model and tell me if you can find e.g. the well known R-2800-57 WER of 2800 hp. It is mentioned in another part of the book, but no WER data is found in the model data section.
True, White privileged access to P&W archives. He told of this long before the book was published.
Whitney´s major problem is that his knowledge of non-American engines (except the Merlin) is not on par with the knowledge on US engines. This makes many of his comparisons quite dubious.
And he also tends to look everything through Bushian lenses. Trust me, I know this.
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Hi Joe,
>We are all familiar with the other arguments that explain the disparity in Vmax between these two planes. White's explanation suggests the disparity should be greater at lower altitudes. That should be pretty easy to check, but I am afraid I can't do it right now.
Well, I guess I'm in direct opposition ot White then :-) In my opinion, the disparity should be decreased at lower altitudes because the F6F has the benefit of not being hindered by ram.
There's an engine power chart for the BMW801D showing both rammed and static power that illustrates just that point.
The external air intakes for the Fw 190A that were designed to reap the benefit of ram effect also worked in the way I described: They improved high-altitude performance while deteriorating low-altitude performance.
Regards,
Henning (HoHun)
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Hi Joe,
>I added a note to your thread on turbosupercharging on the P47.
Ah, thanks, I'll have to check that one out! :-)
Regards,
Henning (HoHun)
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Hm... Depending on MAP, the engine stage of the R-2800s used in the F4U and F6F had very low FTH. If we assume high MAP, the difference between the FTH of the engine stage and the optimal height to activate lower gear of the auxilary stage is several hunred meters. At this altitude range the plane which utilize RAM has an advantage. The first FTH is a bit higher and the optimal altitude to activate the auxilary stage is higher as well.
Anyway, the speed curves in the F4UDOA's pdfs seem to support this, there is a difference between the activate height of the auxilary stage of the F4U and F6F (roughly a bit less than 1000m). Infact, some curves seem to indicate that the sea level is "above" the first FTH for both planes ie the F4U has an advantage from sealevel until it reaches the optimal height to activate the auxilary stage.
gripen
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Originally posted by pasoleati
Wilkinson is pure unadulterated ****, nothing more.
As for White, do check the section giving basic info on each engine model and tell me if you can find e.g. the well known R-2800-57 WER of 2800 hp. It is mentioned in another part of the book, but no WER data is found in the model data section.
True, White privileged access to P&W archives. He told of this long before the book was published.
Whitney´s major problem is that his knowledge of non-American engines (except the Merlin) is not on par with the knowledge on US engines. This makes many of his comparisons quite dubious.
And he also tends to look everything through Bushian lenses. Trust me, I know this.
One correction: That major problem paragraph refers to White, not Whitney. And the Bushian eyes refers also to White.
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Well, while everyone has a right to have an opinion about White, it's quite clear that White is right in this case; the F4U had an advantage over the F6F at low altitude due to use of RAM air for engine stage charger (at high MAP). It also seems that there were also differences when using the auxilary stage; the F6F has a bit higher FTH than the F4U despite it's claimed to be a bit slower (according to this (http://mywebpages.comcast.net/markw4/MSWF4UDATA.pdf)) ie it uses the RAM air more efficient.
gripen
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See what I mean?
Wilkinson can be criticized because he only had access to the data in real time, and that meant poorer data for some countries. But that's not your tack.
White knows his US & UK engines and he really doesn't write about anything else.
Why don't you get his book and look up the -57 himself.
-Blogs
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That would make sense when you have to throttle back to avoid over boosting. These things sound consistent to me.
If you had a continuously variable speed supercharger (as in the 109) you would not have that trade off.
-Blogs
Originally posted by HoHun
Hi Joe,
>We are all familiar with the other arguments that explain the disparity in Vmax between these two planes. White's explanation suggests the disparity should be greater at lower altitudes. That should be pretty easy to check, but I am afraid I can't do it right now.
Well, I guess I'm in direct opposition ot White then :-) In my opinion, the disparity should be decreased at lower altitudes because the F6F has the benefit of not being hindered by ram.
There's an engine power chart for the BMW801D showing both rammed and static power that illustrates just that point.
The external air intakes for the Fw 190A that were designed to reap the benefit of ram effect also worked in the way I described: They improved high-altitude performance while deteriorating low-altitude performance.
Regards,
Henning (HoHun)
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hmm,
sometime ago, ( over 8 years or so), there was a report I read where Grumman and Vought did some after war experiments on the F6f-3/-5 and the F4U-1/-1D
at different alts both planes flew side by side full throttle and was with in a couple of KIAS/TAS of each other. no big significant differences from each other. In the report the main factor in why one plane ( the F4U) showed higher speeds etc was because of the location of the pitot tube.........when the pitot tube was located in nearly the same place on each aircraft, the speeds were near identical, but when placed in there orginal locations the F4U always showed superior speed over the Hellcat......
might be something, someone would want to research........maybe someone recalls this from long ago......( best I recall I found this article/report in the historical Grumman data back around 96/97 when I was a Hellcat F6f-3 fanatic )
If I find the photo copy of the report I will send to someone to post here.....but this is all from my memory so don't hold your breathe :)
TC
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Originally posted by joeblogs
That would make sense when you have to throttle back to avoid over boosting. These things sound consistent to me.
If you had a continuously variable speed supercharger (as in the 109) you would not have that trade off.
-Blogs
In fact the DB 605 blower drive isn´t completely infinite. In the 605A at TO&WER setting the boost control thottle restricts the boost to 1.42 ata up to about 2100 m altitude. The drive has two oil pumps (two gear pumps in one casing), one of which supplies the clutch and another supplies all of its flow to cool the clutch up to that altitude. From 2100m to 5700 m (at WER) the latter pump feeds increasingly the clutch until at 5700 m both pumps supply all oil to the clutch.
Source: Finnish edition of the DB 605A-C manual.
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Originally posted by joeblogs
See what I mean?
Wilkinson can be criticized because he only had access to the data in real time, and that meant poorer data for some countries. But that's not your tack.
White knows his US & UK engines and he really doesn't write about anything else.
Why don't you get his book and look up the -57 himself.
-Blogs
Maybe, but the Jane´s AWA of the same period has much more reliable data and e.g. the sections on the Jumo 211J and DB 605A are in perfect agreement with the respective engine manuals while Wilkinson is pure speculation.
And I do have White´s latter book.
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It depends entirely on the editions you are looking at. Wilkinson's coverage of Axis engines AFTER the war is pretty good. During the war it was sketchy.
-Blogs
Originally posted by pasoleati
Maybe, but the Jane´s AWA of the same period has much more reliable data and e.g. the sections on the Jumo 211J and DB 605A are in perfect agreement with the respective engine manuals while Wilkinson is pure speculation. ...
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I have never seen any references giving the F6F-5 a 400mph top speed, for an operational example. 380 mph I have seen, with 20,000 ft being reached in 7 min.
Would be nice if references were given when making claims like that.
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Originally posted by Squire
I have never seen any references giving the F6F-5 a 400mph top speed, for an operational example. 380 mph I have seen, with 20,000 ft being reached in 7 min.
Would be nice if references were given when making claims like that.
That's not a claim, it's actually a fact. However, I will provide a reference you can verify.
In December of 1944, the Royal Navy issued a document to be distributed to all Hellcat squadrons either in or headed to the Pacific. This document, titled Naval Air Tactical Note 106, included test results of the F6F-5 conducted by the Naval Air Intelligence Center at NAS Patuxent, Maryland.
Within the document, the maximum speed of the F6F-5 was reported as 409 mph @ 21,600 feet.
The original TAIC document is currently in the National Archives.
A copy of the Royal Navy document was published by Historian Barrett Tillman in his book, "Hellcat: The F6F in World War II".
Retired Grumman test pilot Corwin Meyer described in detail why the F6F was rated below its actual maximum speed in Flight Journal magazine. It boiled down to incorrect positioning of the airspeed pitot tube. Due to this, an error of about 5 up to about 20 mph (depending upon actual airspeed) was seen on the airspeed indicator. Aircraft instrumented with independent test equipment showed this discrepancy. Grumman asked the Navy to allow them to change the location. However, the Navy did not wish to delay manufacturing (the modification wasn't a simple one) over an unimportant issue that added nothing to performance. Request denied.
Besides, the F8F-1 was entering production and was expected to completely replace the F6F-5. Indeed, the Navy didn't bother to issue a contract for the R-2800 C series powered F6F-6 because the F8F was deemed superior as a fleet defense fighter. Various sources quote speeds between 417 and 425 mph for the XF6F-6. However, Meyer has stated that when corrected for pitot tube error, actual max speed of the XF6F-6 was 435 mph @ 25,400 feet.
Head to head testing of the F4U-1A and F6F-5 showed virtually indentical max speeds at altitude. Down low, the F4U was faster as described in this thread.
My regards,
Widewing
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Maybe the F6F needs some tweaking.
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I think Widewing needs to take his argument up with the Navy: Naval historical archives (http://www.history.navy.mil/branches/hist-ac/f6f-5.pdf)
I will leave it to each person to decide if this is really the 'word' on historical peformance data, but it is documented. And seeing how the Navy approved the document, there is probably some level of its validity. I have to note that the F4U-4 climb rates present in this archive are ignored by the AH staff, for what that's worth.
Regards,
Malta
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Originally posted by stantond
I think Widewing needs to take his argument up with the Navy: Naval historical archives (http://www.history.navy.mil/branches/hist-ac/f6f-5.pdf)
Regards,
Malta
Been there, read that. Standard stuff, NOT signed on to by TAIC. The aircraft were not instrumented independently, but use the standard F6F static pitot system, so their data is flawed.
We have TAIC documents, there are Grumman documents available at CAM, and we have the testing performed by Vought (yes Vought was given a Hellcat to test, just like Grumman received an F4U). All agree that the F6F-5 was just about as fast as the F4U-1A at altitude. We have the writings of Bob Hall and Corwin Meyer, both of whom have addressed this issue. Any aviation historian who has researched the F6F will state, categorically mind you, that the F6F-5 was a genuine 400 mph+ fighter.
My regards,
Widewing
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in one airshow, I've seen a P47, F6f-5, and an F4U-1D all together in a line.
The Hellcat's wing area is huge, and it has a surprisingly bulky body. Funny thing is, it "tapers" at the end. It looks like a big bellybutton tadpole. The wings were made big to give it better lift, I suppose.
The F4 is tall as hell, but is relatively far more streamlined then the other two. Note that I saw it on the ground- that bent wing coupled with probably the biggest gear I ever saw on a WW2 fighter makes it stand out. Like Uncle Sam in his dress blues on stilts.
But nothing comes to the sheer girth and bigness that is the P-47 Thunderbolt. That plane is just mammoth. From the first mooment you see her up close, she looks like a bomber, she's so big. No fancy streamlined lines, no sex appeal whatsoever. Brutal and lethal function is all that comes to mind when looking at her.