Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on September 10, 2003, 11:19:02 PM
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I have been doing some research to explain my earlier post so I could show you what I mean.
Here is an example of what makes sense to me.
JoeBlogs did this chart in a prior post when I provided the manual data for the F4U and F6F.
(http://mywebpages.comcast.net/markw4/r2800.jpg)
It shows very basic info. What I look at is the SFC based on fuel consumption and HP.
SFC = Fuellbs/HP/HR
The R2800
Burns 42GPH at min cruise for a best SFC of .44
Burns 290GPH at mil power .870 which is
290GPH*6(pounds per gallon)=1740lbs/2000=.87
In AH the F4U-1D has 237gallons of internal fuel. and burns 290GPH. That gives the F4U-1D an endurance of 49 minutes at mil power. In the MA at 2.0 multiplier the endurance should be 24.5 minutes. It is 28 minutes so it is 3.5 minutes high.
Easy Cheesy right;)
The SFC is always best at minimun cruise and increases with power output.
Ok
The P-38 (one engine)
Burns 33GPH at min cruise 425HP =SFC .46
burns 167 per hour at mil power at 1425HP
167*6=1002LBS/1425HP=SFC.70
Better than the R2800 at mil power but slightly lower at min cruise. Results well within reason.
The P-38L had 410 gallons of internal fuel buring 167GPH*2 = 334GPH. 73 minutes of endurance at mil power. In the MA at 2.0 36.5 minutes of flight time.
In the MA the P-38L has exactly 37minutes of flight time. Well done.
(http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif)
Great.
Here is what does not make sense and I believe to be impossible.
The La-7
I don't have min cruise data.
Mil power 1650 HP 122gallons of internal fuel.
In AH it has 28 minutes of flight time at 2.0 fuel burn so that means 56 minutes IRL to burn 122gallons of fuel. In one hour that would be 130 gallons.
130*6=780lbs/1650HPmil power=.47SFC
This is what the P-38L Allison and R2800 SFC are at Min Cruise. I do not believe the La-5/7 engine (Ash-82) could do this or that any engine is as efficient at mil power as it is at max cruise. And this is with 87octane fuel!
Also I have German document on the La-5 with the same engine and fuel capacity that states that endurance at normal power was 30 minutes. At mil power that would be less than the MA without the fuel multiplier.
Here are some other anomolies IMHO
The BF109G-10 Puts out more HP than the La-7 and only has 106gallons of fuel!! How is that possible when this A/C couldn't hardly fly across the channel and back at cruise?I don't know what the mil power HP is but this doesn't sound right.
The Spit IX
Every reference I look at shows a max interal fuel capacity of 85 gallons imperial which is 102 gallons internal. But in AH it has 136 gallons. Why?
Also it has a Merlin 61 I believe that put out approx 1400+HP. How can this A/C have a duration of 35minutes which would indicate a real life endurance of greater than an hour at mil power. That would indicate less than 136 gallons per hour at mil power. And that is assuming its not really 102 gallons. This really sounds odd too.
The P-51D
At 150GPH as you have stated.
150*6=900lbs / 1490HP= .60SFC very low compared to the Allison which puts out less HP.
Here are the endurance numbers I am using.
(http://mywebpages.comcast.net/markw4/fuelma.bmp)
FYI I have an entire German AFDU type doc on the La5
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Remember altitude decreaces fuelburn. The 109G10 has a 25 min fuel duration on mil power in the MA at sea-level. the 109G10 never saw action over Britton, that was the 109E ;). The 109E had 30 minutes of combat time over England during the BoB, and that's without any provisions for DT. Altitude is the key to increase your range, I use this a lot in the MA flying 109s. The 109F uses a quarter tank just to get to 20k, howerer at 20k I can cruise for what seems as an hour or more on the remaining 75% on mil power. With a DT I can cross the map flying that high.
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Gsholz,
I don't care about range. I know how to do it but that is not my point. I am only talking about duration at mil power.
Do you know what the G10's mil power HP rating was?
Also I know it was the 109E over Briton. My point is that the E did not have nearly the HP of the G10. The more HP you create the more fuel you burn. The Merlin and Allison engines did not produce the HP the G10's engine did and they burned at least 150GPH. I don't see how the 109 could burn any less. And the 109 has a tiny little gas tank.
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109-e4
(http://bellsouthpwp.net/w/o/wotans/bf109e-perf-chart3.jpg)
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Originally posted by F4UDOA
I do not believe the La-5/7 engine (Ash-82) could do this or that any engine is as efficient at mil power as it is at max cruise. And this is with 87octane fuel!
Also I have German document on the La-5 with the same engine and fuel capacity that states that endurance at normal power was 30 minutes. At mil power that would be less than the MA without the fuel multiplier.
FYI I have an entire German AFDU type doc on the La5
Can I have a copy of your German La5 stuff please.........
btw re octane the Ash82FNV figures I have state the design fuel was 90 Octane which I would believe to be the octane used in Russian tests.
I believe the LW however had two standards of Octane (early109's used lower octane fuel and the 190's used a higher grade)
I agree with the generalisation that mil power endurance for the la5/7 would be about 28 to 30 mins. I do not know what you refer to as normal power is.
It seems to me that AH fuel presents many opportunities for revision.....
a)actual burn rates mil power (AH full throttle no WEP)
b)actual burn rates at various (engine)rpm and levels of boost/WEP.
c)fuel availability at different field fuel attrition levels.
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Originally posted by F4UDOA
Do you know what the G10's mil power HP rating was?
I believe it was 1475hp mil power and 2000hp with MW50 boost, 0.45 lb/hp/hr at sea level at mil power. Although I might be mistaken.
EDIT: All the 109's had a 400 liter /88 Imp. gallon tank.
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Gscholz,
The E4 according to Batz document burned 114 gallons (433litres) per hour to create 1175HP. You can see by that chart the more HP you create the more fuel you burn. In order to create 1475HP you will be burning in the 150+GPH range.
The best SFC of any WW2 fighter was .40. The P&W R2800 was very good at .44. But this is at min cruise. No WW2 fighter could run full Mil power and maintain SFC. It's like your car milage staying the same regardless if your cruising on the highway or drag racing full speed.
What I believe HTC did was apply the SFC of min cuise to A/C in which the specific fuel consumption was not available. So the SFC never changes regardless of power setting.
The 109E produced 1175HP at max power and burned 114GPH it would have 56minutes of flight time IRL and 28 minutes in the MA. Which means that the 109E is 3 minutes short in duration in the MA according to the MA chart I posted. However the 109G10 would create 300 more HP reducing flight time at mil power dramatically.
The SFC for the 109E at max power would be
114*6=684lbs/1175HP=.58
That is good but remember that number gets worse with more HP created.
Tilt,
The wording in the translated German document I believe is rated power which is typically max continious or Normal rated power.
I will zip and post it.
BTW the performance of the German La-5 is much lower than what we have in AH however they considered the handling excellent.
Also can anyone tell me why the fuel tank is so big on the Spitfire??
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Gents,
If there is one point I am despritely trying to make is the fuel burn and HP are a direct ratio.
The more HP you create the more you burn. And most WW2 engines were almost equal in burn rate.
Take a look at the E4 fuel burn to create 1,100HP and compare it to the P&W and Allison Engines I posted creating the same HP.
All Sea level.
109E4
1100HP= 84GPH
F4U/F6F/P-47
R2800
1070HP= 83GPH
P-38L
Allison V-1710
1100HP= 113GPH!!
They all are almost the same with the inline allison being highest.
So how does an Aircraft with a 100 gallons fuel tank fly in the MA for 28minutes at a 2.0 multiplier while buring enough fuel to create 1600+HP??
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About that e4 info,
I am not sure how accurate it is because here the power settings that seem to be agreed upon most
DB601A-1
SL@1100PS@2400rpm@1.40ata (1' minute) takeoff
SL@990PS@2400rpm@1.30ata (5' minutes) climb
SL@910PS@2300rpm@1.23ata (30' minutes) combat
SL@810PS@2200rpm@1.15ata cruise
4.5km@1020PS@2400rpm@1.30ata (5' minutes) climb
5.0km@960PS@2400rpm@1.23ata (30' minutes) combat
5.7km@890PS@2400rpm@1.15ata cruise
DB601N
SL@1175PS@2600rpm@1.35ata (5 minutes) climb
SL@1020PS@2400rpm@1.25ata (30 minutes) combat
SL@910PS@2300rpm@1.15ata cruise
5.5km@1190PS@2600rpm@1.35ata (5 minutes) climb
5.4km@1060PS@2400rpm@1.25ata (30 minutes) combat
6.1km@970PS@2300rpm@1.15ata cruise
As you can see there slight variations(I know the image shows hp and the data above is ps).
Maybe some one with better info can confirm.
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This may be useful for comparison.
One PS is approx 98.6% of a HP
To convert from BHP to PS multiply by 1.01387
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Hi F4UDOA,
>The E4 according to Batz document burned 114 gallons (433litres) per hour to create 1175HP. You can see by that chart the more HP you create the more fuel you burn. In order to create 1475HP you will be burning in the 150+GPH range.
Well, you're using the very wasteful 1 min power setting for comparison. The 5 min power setting was more economical, and in fact the DB605 didn't burn 150 GPH at 1475 PS but just 480 L/h (127 GPH).
By the way, the equivalent to "MIL" power is "Kampfleistung" ('Combat Power'). The DB605A was rated at 1310 PS Kampfleistung, burning 400 L/h (106 GPH).
(Data from "D. (Luft) T.3605 A-B, 0 u. 1 Motoren-Karte")
Regards,
Henning (HoHun)
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Originally posted by F4UDOA
Also I know it was the 109E over Briton. My point is that the E did not have nearly the HP of the G10. The more HP you create the more fuel you burn. The Merlin and Allison engines did not produce the HP the G10's engine did and they burned at least 150GPH. I don't see how the 109 could burn any less. And the 109 has a tiny little gas tank.
Sorry, but it doesn`t works this simply... Unlike you would expect, the fuel consumption of DB60x engines actually decreased proportionally to the power they developed with later engines.
Why? Because German engineers increased compression ratio as well, not just boost. More fuel effiencient. Also, more volume, better effiency again.
The increase in fuel effiency with the development of Daimler Benz engines can be seen from their compression ratio increase:
CR values:
DB 601A : 6.7 : 1
DB 601N : 8.2 : 1 (100 octane)
DB 601E : 7 : 1
DB 605A : 7.5 : 1
DB 605D: 8.5 : 1
Comparing them the Merlins is not a very good idea... Merlins operated at low CR values (all of them at 6 : 1), were low displacement engines, meaning worse fuel effiency. I can`t say for Allisons, I don`t know them for detail.
As for G-10 details, I am still waiting for more data on the DB 605D engine fuel consumption, I only have parts of details. However I will attempt to give it for Kampfleistung (30min limit for 1370PS for DB605DC), for which I have data, consumption is given as 225 gram/PS/h.
This would give 430 lit/hour consumption for 1370 PS power. In other words, 400 liter internal tankage was enough for 1 hour 4 minutes.
According to German docs, at this power G-10 could do 653 kph+ at 9km altitude.
So range about 650 km, endurance 1 hour at Kampfleistung/Military rating.
This is of course NOT economic cruise !! That would give around 1 h 30min endurance, and ~750 km range, taking into account takeoff, climb etc., but no combat. (=ferry range).
Assuming Sondernotleistung spec. consumption was somewhat higher (235 gr/PS/h assumed), this would mean (.235 x 2000)/.7205 = 650 lit/hour consumption of fuel. 400 liter int. tank enough for 37 minutes at WEP.
In addition, 180 lit/hour MW50 liquied is consumed, which would run out after about 30 mins.
So at WEP settings for G-10, Range = 425 km, Endurance = 37 min.
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Ie, specific consumption for DB 605 A-1 to see how efficient it was, in Imperial units, at rated altitude:
Min. (economic) cruise :
WEP, 1355 PS at 18 700ft = .517 lbs / HP / h
Military*, 1250 PS at 19k ft = .484 lbs / HP / h
Max. cruise, 1080 PS at 18k ft = .473 lbs / HP / h
Eco/Min cruise, 890 PS at 18.7k ft = .454 lbs / HP / h
*Military rating : 30 min
So don`t be surprised if you experience that 109s - as opposed to urban myths - have rather long endurance compared to their small tankage. They had probably the most fuel efficent aero engines of WW2 installed !
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Eh ... compression ratio does not have anything to do with fuel mixture. Increased CR increases power output (and actually limits boost unless fuel grade is increased as well).
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Hi Isegrim,
>Assuming Sondernotleistung spec. consumption was somewhat higher (235 gr/PS/h assumed), this would mean (.235 x 2000)/.7205 = 650 lit/hour consumption of fuel. 400 liter int. tank enough for 37 minutes at WEP.
Actually, specific gasoline consumption at "Sondernotleistung" decreased compared to combat power. Only the specific total liquid consumption (gasoline + water-methanol) increased.
I don't have any figures for the DB605, but for the Jumo 213, specific fuel consumption went down from 268 g/PS/h at "dry" war emergency power to just 221 g/PS/h at special ("wet") war emergency power.
This is an 18% decrease, which was countered with a 22% increase in total liquid consumption due to the injection of MW50.
By the way, the fuel injection used by German engines did contribute to their relatively good fuel efficiency, too. For comparison: The Jumo 211G was 8% more efficient than the Jumo 210Da of identical bore, stroke, rpm and power. That's a major advance.
When comparing mechanically supercharged engines like the Merlin or the DB605 to turbo-supercharged engines like the Allison or the R-2800, it's important to consider that in addition to the shaft power, the former also delivered considerable exhaust thrust - unlike the latter. That makes them a bit more efficient than the bare SFC figure suggests - the higher the speed, the greater the gain.
(The German conclusion was that turbo-supercharged engines were better suited for bombers and mechanically supercharged engines were better for fighters. That didn't stop them from experimenting with turbo fighters, though, but they couldn't get them operational.)
With regard to the most fuel-efficient WW2 aero engine, I'd suspect that the Jumo 205 Diesel would be the winner with an SFC of 0.35 lbs/HP/h :-) It wasn't a fighter engine, though.
Regards,
Henning (HoHun)
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I have found some German PDF docs that show the SFC of the DB605 at 5.1 at a mil power of 1475HP.
This is 127GPH and a duration of exactly 50minutes meaning 25 minutes in the MA.
Chalk one up for HTC, they hit that nail on the head.
If compression in the secret to greater efficiency then explain this.
I just found the ASH-82FN compression is at 6.9 to 1.
This is not very high, how would you explain the duration of that engine??
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FYI compression ratios on Ash82 FNV
1st stage boost 7.14:1
2nd stage boost 10:1
I can see how higher compression ratio's would increase engine efficiency re conversion of fuel Kcal/hour into Kw's or HP.
Mechanical losses would be much the same at the same rpm and so efficiency would be increased even after the additional boster losses are subtracted.
Having said all this.......IMO it would be the application of a minor modifier when compared to the descrepencies F4UDOA describes.....
A direct corellation between HP and fuel consumption would be more accurate generally than we have now IMO. Having achieved this it would then seem time to add modifiers re differing engine efficiencies.
All this is to nought if the corresponding (lower) consumptions at lower levels of rpm and boost can not be modelled in some way to allow the player to reach target albeit some what slower but with the same ratio of endurance and range enjoyed (or suffered) by those ac his ride represents.
Equally should be considered is the attritional fuel model............
Fuel attrition did not limit short range AC (to shorter ranges) over long range AC as our % attrition model does now.
It limited range ...ie the number of gallons or litres available per mission.
If 100% = 600 litres then the 300litre capacity AC should still be granted a full tank at 50% attrition.
Whilst variable consumption with engine settings and the % attrition model remain as they are then I would argue that correcting actual consumption models would produce as many errors as they cure.
Having said that this does not reflect upon some glaring range issues with some AC (mossie and Ju88 come to mind)
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F4u1doa is right on about fuel consumption at cruise and max HP settings. Good engines could cruise with an SFC (in U.S. units) on the order of 0.41-0.45. That's aviation gas only, not diesel. Those numbers are based on my analysis of data on several hundred high output engines produced by all major combatants before and during WWII.
At military settings, SFC rises to 0.8 or much higher depending on the engine and altitude (power consumed by the supercharger). Using WEP will lower fuel consumption as water is used to cool the charge, so the fuel mixture can be leaned out.
Rich fuel mixtures in these engines is almost twice that of the lean (cruise) mixtures which explains the near doubling of SFC.
In earlier posts I reported the best SFC of the ASH82FN was in the low 0.4x range, about the same as its western contemporaries. There is no way then, using the same technology, this engine would have an SFC much below 0.8 at altitude and at military power. Yet the endurance of the La-7 at military power in Aces High implies an SFC of an engine operating on a cruise setting.
It is true that higher compression is typically associated with better fuel economy. But this only changes SFC by about ten percent and in some engines even less.
An engine can have a better SFC at a lower compression ratio if either (1) it breathes better, giving a more even fuel mixture, or (2) it is cooled better. So it is not immediately obvious to me that a Merlin would be all that less fuel efficient than a DB601.
In my data the fuel economy of the Merlin varies considerably by its model number. In addition, the Merlin was generally run on higher octane fuels, which is often associated with better fuel economy because the mixture can be leaned out more than when using a lower octane fuel. An offsetting variable is the use of fuel injection in german engines versus a carburetor on most other engines.
-Blogs
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Tilt:
You are comparing the blower ratios on the supercharger, which is not the compression ratio that Isegrim refers to.
The reason why compression ratio can influence fuel economy is that the engine generates higher pressure over the entire cycle of compression and decompression, which translates into more power generated per stroke. So long as the fuel does not detonate due to the higher heat, you get more fuel economy.
Given my experiments with the FW190 in Aces, it does appear that cruise settings are reasonably well modeled for at least some planes. The trick is to regulate both RPM and manifold pressure. Why this does not seem to be properly modeled in all the planes is beyond me.
Originally posted by Tilt
FYI compression ratios on Ash82 FNV
1st stage boost 7.14:1
2nd stage boost 10:1
....
Having said all this.......IMO it would be the application of a minor modifier when compared to the descrepencies F4UDOA describes.....
A direct corellation between HP and fuel consumption would be more accurate generally than we have now IMO. Having achieved this it would then seem time to add modifiers re differing engine efficiencies.
All this is to nought if the corresponding (lower) consumptions at lower levels of rpm and boost can not be modelled in some way to allow the player to reach target albeit some what slower but with the same ratio of endurance and range enjoyed (or suffered) by those ac his ride represents.
...
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Hi F4UDOA,
>I have found some German PDF docs that show the SFC of the DB605 at 5.1 at a mil power of 1475HP.
I'm not sure that this is equivalent to MIL power - it really depends on the definition.
Usually, WEP is a 5 min rating while MIL is 15 - 30 min. In German terms, the former would be "Notleistung" while the latter would be "Steig- und Kampfleistung" (and last 30 min).
Methanol-water injection would be "Sondernotleistung" for which there doesn't seem to have a direct equivalent in American WW2 terminology (though the technology was employed). In post-war American technical slang, it would be "wet" WEP.
So if you're using MIL-equivalent power for a DB605 capable of 1500+ HP, it should be in the region of 1300 HP at a fuel consumption of around 106 GPH.
Regards,
Henning (HoHun)
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Originally posted by joeblogs
Using WEP will lower fuel consumption as water is used to cool the charge, so the fuel mixture can be leaned out.
This is AC dependent isn't it?.......not all AC injected water.
You can help me understand something re supercharging........
The Ash82FNV had "two stages of boost" Stage 1 used below 4500metres Stage 2 used above 4500.
I always took this to be either a two speed supercharger or indeed the ability to super charge the super charger.
A look at the engine in Kbely showed just one super charger and since then I have assumed it could run at two speeds.
Or at least two speeds obtained as a result of gearing from the main crank.
Its clear that manifold pressure (at a given stage of boost) is a direct correlation of engine rpm and that manifold pressure relates also (in this engines case) to power.
So as engine rpm changes so does boost and (real) compression ratio with a compound effect upon manifold pressure.
To me this explains the significant increase in power from 1650hp to 1800hp when the Ash 82 FNV merely increases revs from 2400 to 2500 (Man pres. from 1000mm to 1200mm) when at its first stage of boost at sea level. (btw at 2600 rpm power was rated 2000hp).
At the 2nd stage of boost the effective compression ratio is raised significantly and it seems that this then gave a less than linear relation ship of Power to engine rpm. Its clear that the 1st stage was backing off its linear power/alt curve at 3500 metres but the 2nd stage did not kick in until nearly 4500 metres.
At 4500metres (2nd stage) we see again manifold pressures of 1000mm so power was in effect still only 1650hp and fuel consumption still that of a reduced compression ratio at lower altitude.
This leads me to three conclusions
a) that fuel consumptions at less than mil power could vary widely between AC with differing boost systems and differing fuel mixture control systems.
b) that fuel consumptions at more than mil power could vary widely between AC with differing WEP systems.
c)that use of compression ratio as a guide to engine efficiency is misleading if not qualified with its boost component at various altitudes.
I must admit to some lack of confidence in my logic and so would welcome any correction.
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HoHun,
What I think is the mil power setting shows the use of fuel only and reflects with a PS rating of 1475 at 480 ltrs per hour or 127 gph. The next level above that uses both C-3 fuel (560ltrs hour) as well as MW50 (150ltrs hour) at a PS rating of 1800.
JoeB,
Where you been man?? I have found a German doc that says the La-5 with the ASH-82FN had a rated power duration of 40 minutes. I think that is pretty much the deal closer as far as I am concerned. That mean Mil power could not have lasted longer than 30 minutes.
I need to post that DOC asap.
BTW, Tilt, I know I said 30min. I just reread it. Sorry.
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Originally posted by joeblogs
Tilt:
You are comparing the blower ratios on the supercharger, which is not the compression ratio that Isegrim refers to.
My appologies
if ******* is compression then its 7.0 (+/-0.1) :1
edit
I type the correct cyrillic in the text and this BB changes it to gobble di gook...........I have changed it to stars.
Please refer to line 7 on this doc
http://www.tilt.clara.net/pics/page122.gif
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http://www.kolumbus.fi/staga/wwiiol/scans/db601_enginechart.gif
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Great post tilt
>>This is AC dependent isn't it?.......not all AC injected water.
Blogs: Yes, but the general principal of all these systems was either to (1) reduce the temperature of the mixture going into the engine; or (2) increase the mass of air going into the engine when the plane was at higher than critical altitude for the supercharger. The Germans did (2) a lot because they tended to rely more on single stage superchargers. Effects in terms of induced horsepower, fuel economy, and duration depended on the installation...
>>You can help me understand something re supercharging........
The Ash82FNV had "two stages of boost" Stage 1 used below 4500metres Stage 2 used above 4500.
I always took this to be either a two speed supercharger or indeed the ability to super charge the super charger.
A look at the engine in Kbely showed just one super charger and since then I have assumed it could run at two speeds.
Or at least two speeds obtained as a result of gearing from the main crank.
Blogs: Sounds like a single stage two speed supercharger. The way to tell is that a two stage supercharger (without a variable clutch) will have two critical altitudes - one for the first stage and the other for the second stage. For US and British planes, you will see charts of the climb rate with two or more notches in them.
>>Its clear that manifold pressure (at a given stage of boost) is a direct correlation of engine rpm and that manifold pressure relates also (in this engines case) to power.
Blogs: The compression ratio that isegrim referred to is a constant in WWII era engines. It's simply the difference in the volume of a cylinder with the piston at the bottom dead center versus when it is at top dead center.
Holding everything Else constant, increasing engine RPM has a tendency to Lower manifold pressure. Think of an engine as a giant air pump. As RPM increases, the engine is pushing more air out of the exhaust and sucking more air into the intake manifold, where pressure is measured on these engines. The only way to maintain the manifold pressure then is to push the throttle forward a bit. I can't remember if this is modeled in Aces.
In your example, you get a 10 percent increase in horsepower by raising rpm by 4 percent and manifold pressure by 20 percent. So the engine is pushing an additional 150/4 times its displacement (I can't remember exactly how big this engine is but it's around 2600 cu in) in heated air (divide by 4 as there is one intake stroke in 4 cycle engines) plus the previous 1650/4 of cycles now have contain 20 percent more hot air.
>>At the 2nd stage of boost the effective compression ratio is raised significantly and it seems that this then gave a less than linear relation ship of Power to engine rpm. Its clear that the 1st stage was backing off its linear power/alt curve at 3500 metres but the 2nd stage did not kick in until nearly 4500 metres.
At 4500metres (2nd stage) we see again manifold pressures of 1000mm so power was in effect still only 1650hp and fuel consumption still that of a reduced compression ratio at lower altitude.
Blogs: What you are observing is two things. First running the supercharger at a higher speed requires even more power from the engine (a deduction from horsepower). Second you may be observing lower manifold pressure if your data has the plane above the critical altitude for the supercharger. With a two stage supercharger, you can go even higher, but you have to deduct additional horsepower to run the second blower and the larger blower is typically less efficient too.
>>a) that fuel consumptions at less than mil power could vary widely between AC with differing boost systems and differing fuel mixture control systems.
Blogs: Yes definitely. Engines varied in fuel economy and even across planes using the same engine as induction systems also vary in their efficiency. Different carburetors or fuel injection systems matter. Boosting systems matter because they consume different amounts of power and differences in gear ratios mean that different planes have sweet spots at different altitudes.
>>b) that fuel consumptions at more than mil power could vary widely between AC with differing WEP systems.
Blogs: Certainly true. I am trying to locate as much info as I can on fuel consumption of German engines at high power settings. Some of the information in this thread helps me.
>> c)that use of compression ratio as a guide to engine efficiency is misleading if not qualified with its boost component at various altitudes.
Blogs: I'd put it another way, compression ratio just doesn't matter enough to argue about relative to other variables. Maximum boost, for example, is typically a far more important indicator.
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Just back from a long work trip... Your post induced me to pull out some of my notes...
-Blogs
Originally posted by F4UDOA
HoHun,
What I think is the mil power setting shows the use of fuel only and reflects with a PS rating of 1475 at 480 ltrs per hour or 127 gph. The next level above that uses both C-3 fuel (560ltrs hour) as well as MW50 (150ltrs hour) at a PS rating of 1800.
JoeB,
Where you been man?? I have found a German doc that says the La-5 with the ASH-82FN had a rated power duration of 40 minutes. I think that is pretty much the deal closer as far as I am concerned. That mean Mil power could not have lasted longer than 30 minutes.
I need to post that DOC asap.
BTW, Tilt, I know I said 30min. I just reread it. Sorry.
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Originally posted by joeblogs
Holding everything Else constant, increasing engine RPM has a tendency to Lower manifold pressure. Think of an engine as a giant air pump. As RPM increases, the engine is pushing more air out of the exhaust and sucking more air into the intake manifold, where pressure is measured on these engines. The only way to maintain the manifold pressure then is to push the throttle forward a bit. I can't remember if this is modeled in Aces.
ASh82FNV engine speed was controlled by an R7 govenor. I assume this works by effecting the throttle in some way to limit the system at maximum speeds? I also always assumed that the supercharger (which I can now confirm was a two speed centrifugal unit) was geared directly of the engine so its max pressure (at each stage)was subject to engine rpm.
In your example, you get a 10 percent increase in horsepower by raising rpm by 4 percent and manifold pressure by 20 percent. So the engine is pushing an additional 150/4 times its displacement (I can't remember exactly how big this engine is but it's around 2600 cu in) in heated air (divide by 4 as there is one intake stroke in 4 cycle engines) plus the previous 1650/4 of cycles now have contain 20 percent more hot air.
1650 > 1800 is 9% increase (1800 is 109% of 1650)
I was under the impression that manifold pressure had gone up as a function of the gearing between engine and supercharger............ie as the engine goes faster the supercharger goes faster........... the massive increase of 20% manifold for 4% rpm suggests that the relation ship is not linear.
This is born out by the fact that a further increase to 2600 rpm (3.85%) brings about a further increase in Hp to 2000hp (not used in flight) which is 11% increase.
I assume that the near exponential curve is a function of the centrifugal type supercharger . Its efficiency is highly speed dependent?
I note the following manifold presures taken at 1000m alt.
rpm2400 man 1040
rpm2200 man 875
rpm2000 man 745
rpm1800 man 665
rpm1600 man 610
rpm1500 man 580
When you look at level flight endurance for this range of settings you note that 365 litres of fuel would last 1hour 45 minutes at the lower setting but only 35 mins at the higher
swept volume is 41.2 litre
You seem to imply that manifold pressure can be raised independently of engine rpm........ I assume this would be the case where supercharger speed was independantly variable of engine speed. There is a boost control lever in the Lavochkin......but again I always assumed that the two cables coming from it enabled either one super charger speed stage selection or another.
Having said all that i lost the precise point of your maths......
are you saying
Given the airpump had increased capacity by 10% and only 4% of that was due to increased rpm (ie at constant pressure the volume /hour had only gone upto 104%) then the remaining 6% was a function of increased manifold pressure?
This shows that a 20% increase in manifold pressure and therefore a 20% increase in weight of air/fuel only returns a 6% increase in power. In fact 6/104 is 5.8%. I assume this is a function of the mixture running leaner plus some air flow efficiency factors.
FYI the la7 did not have pilot mixture adjustment.........it was synchronised off the the throttle.........this was a first.........in the La5 the pilot had to set throttle and mixture separately.
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Tilt: ASh82FNV engine speed was controlled by an R7 govenor. I assume this works by effecting the throttle in some way to limit the system at maximum speeds? I also always assumed that the supercharger (which I can now confirm was a two speed centrifugal unit) was geared directly of the engine so its max pressure (at each stage)was subject to engine rpm.
...You seem to imply that manifold pressure can be raised independently of engine rpm........ I assume this would be the case where supercharger speed was independantly variable of engine speed. There is a boost control lever in the Lavochkin......but again I always assumed that the two cables coming from it enabled either one super charger speed stage selection or another....
Blogs: I'm not sure. Is that the propeller governor?
Typically RPM and manifold pressure (throttle) are controlled independently. I can't remember if that was true of the nifty german units on the BMW 801 etc.
The way this works is that the throttle controls a choke in the carburetor, or a metering valve in the fuel injection unit. That choke limits the amount of air that can pass through the induction system at any point in time. Thus, holding RPM constant, pushing the throttle forward opens the choke and allows more air to enter a cylinder on every fourth stroke.
Conversley, holding the throttle constant but raising engine RPM increases the number of strokes per minute but does not change the amount of air sucked into the cyclinders on every fourth stroke. The combination of more RPM and more throttle increases both the number of strokes per minute and the amount of air drawn into the cylinders on every fourth stroke.
Gear driven superchargers are essentially synchronized with the demands of the engine. When RPM is higher, so more air is pumped through the engine every minute, the supercharger runs comensurately faster. Manifold pressure should stay roughly constant, but it can drop off a bit if the induction system is not well designed. This is a second order effect and is not worth emphasizing.
Tilt: I was under the impression that manifold pressure had gone up as a function of the gearing between engine and supercharger............ie as the engine goes faster the supercharger goes faster........... the massive increase of 20% manifold for 4% rpm suggests that the relation ship is not linear.
This is born out by the fact that a further increase to 2600 rpm (3.85%) brings about a further increase in Hp to 2000hp (not used in flight) which is 11% increase.
I assume that the near exponential curve is a function of the centrifugal type supercharger . Its efficiency is highly speed dependent?
I note the following manifold presures taken at 1000m alt.
rpm2400 man 1040
rpm2200 man 875
rpm2000 man 745
rpm1800 man 665
rpm1600 man 610
rpm1500 man 580
When you look at level flight endurance for this range of settings you note that 365 litres of fuel would last 1hour 45 minutes at the lower setting but only 35 mins at the higher
Blogs: I don't have the test report in front of me but I think the complication is that we observe different combinations of RPM and throttle. So lots of variables are changing. You are correct that as engine rpm rises so does the rotation of the supercharger. The ratios you mentioned earlier are constants. So if the supercharger gear ratio is 6.7:1, andy increase in engine RPM is multiplied by 6.7 at the supercharger. But in a well designed system you are increasing the airflow proportionally so the resulting increase in horsepower should be a linear function of RPM. It might actually be a little less than proportional if there are friction losses, and the supercharger becomes less efficient when airflow approaches the speed of sound.
I think what is suggesting the geometric increase you observe is the combination of more RPM and more manifold pressure. In that case you get the combination effect I described in earlier in this post.
I'm working on some charts that show how airflow, horsepower and fuel consumption increase at different engine settings and I'll post those soon. Airflow and horsepower increase proportionately, as does fuel consumption with one exception--that point on the power curve where the pilot must shift from a lean fuel mixture to a rich mixture (to cool the charge).
Tilt: Having said all that i lost the precise point of your maths......
are you saying
Given the airpump had increased capacity by 10% and only 4% of that was due to increased rpm (ie at constant pressure the volume /hour had only gone upto 104%) then the remaining 6% was a function of increased manifold pressure?
This shows that a 20% increase in manifold pressure and therefore a 20% increase in weight of air/fuel only returns a 6% increase in power. In fact 6/104 is 5.8%. I assume this is a function of the mixture running leaner plus some air flow efficiency factors.
Blogs: Well output went up by 10 percent. I am not sure of the relative contribution of the increase in RPM vs. the increase in manifold pressure, but it should be easy to work out: compare the change in the number of strokes times the airmass contained in each stroke (the RPM effect) to the change in the airmass drawn times the initial engine RPM (the throttle effect).
Fuel air mixture shouldn't change dramatically except for the jump from lean to rich mixture at about 50 percent of rated horsepower in most engines and again when WEP is engaged.
Tilt: FYI the la7 did not have pilot mixture adjustment.........it was synchronised off the the throttle.........this was a first.........in the La5 the pilot had to set throttle and mixture separately. [/B][/QUOTE]
Blogs: Sounds like some of the german units. I think those worked the following way. If the measured manifold pressure reaches a certain level, the quadrant automatically enriches the mixture before detonation sets in. When the throttle is pulled back and manifold pressure drops, the reverse is done. This works because the temperature of the charge is an increasing function of manifold pressure.
-Blogs
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Originally posted by F4UDOA
I have found some German PDF docs that show the SFC of the DB605 at 5.1 at a mil power of 1475HP.
This is 127GPH and a duration of exactly 50minutes meaning 25 minutes in the MA.
That means that the R2800-8 consumed more than twice the amount of fuel at mil power while producing less than 200 hp more. I know German engineering was superb, but this sound incredible. You sure about this?
EDIT: Confused the alts. Still at 290 gph producing 2000 hp is horribly inefficient compared to your numbers on the DB605.
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Hi Tilt,
>You seem to imply that manifold pressure can be raised independently of engine rpm........ I assume this would be the case where supercharger speed was independantly variable of engine speed.
Manifold pressure can be raised independly of engine rpm even with a fixed gear ratio as long as you're below the full throttle altitude for the respective rpm/manifold pressure combination.
Below this altitude, the supercharger produces more pressure than desired so that the engine has to be throttled back. Advancing the throttle then will give you greater manifold pressure even though you don't spin the supercharger any faster than before.
Above this altitude, the throttle is completely opened anyway, and manifold pressure and supercharger speed aren't independend any more.
Regards,
Henning (HoHun)
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Very good discussion ! Congrats, Gentlemen ! :)
I`d like to ask a question on supercharger charactertics... it can be seen on all fixed-gear superchargers, that engine power output is less below critical altitude. Taking the 1st (fixed) speed of the DB 605A-1 for example, one can see that the engine power output is 1475 PS at SL, and steadily increasing to 1550 PS at around 2100m. Yet the boost pressure, RPM is constant.
This is because of "the extra work the SC has to do", as I have read....
Now, what is this extra work?
I have been thinking on this and the only explanation I could arrive at is that the SC, being fixed to a ratio towards the engine RPM, is trying to run at constant speed, compressing air in the process. Now, when it operates at lower altitudes, whereas it`s compressive capability has surplus, it overcompresses the air too much... since compressing already dense air is harder than thin air, it needs more power to keep supercharger RPM constant. It needs more torque. So it drains more power from engine.
Now, my question is, is my theory correct, or there is/are other reason(s)?
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Originally posted by joeblogs
There is a boost control lever in the Lavochkin......but again I always assumed that the two cables coming from it enabled either one super charger speed stage selection or another....
Blogs: I'm not sure. Is that the propeller governor?
Thank you and ho hun for pointing out that throttle setting can adjust manifold pressure....... obviously I missed that flow rate via throttle is a function of pressure differential across the variable choke point.
Re La boost control its a big lever with two apparant positions attached to a wheel which push/pulls a boden cable...........actually the La9 now flying should be the same control system.
There was an additional "airscrew control" but the prop was a constant speed unit....... I assume this would be used to set engine speed as using the prop as variable ratio gear box.
To summarise
I can set manifold pressure as a function of rpm, stage of boost and throttle.
I can set rpm as a function of prop speed
the r7 govenor is a mystery .. could it be used to limit over rev?
would control via throttle or by prop pitch? how is this normally done on other aero engines?
The link between throttle and fuel mixture was directly copied from an FW190
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I don't believe the high output numbers on the fuel consumption of the DB605. But I need to look at the document before I can say anything.
-Blogs
Originally posted by GScholz
That means that the R2800-8 consumed more than twice the amount of fuel at mil power while producing less than 200 hp more. I know German engineering was superb, but this sound incredible. You sure about this?
EDIT: Confused the alts. Still at 290 gph producing 2000 hp is horribly inefficient compared to your numbers on the DB605.
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My guess is that if the supercharger is engaged, but the throttle is not fully advanced, you are paying a penalty for diverting power to the supercharger and not getting the most out of it. In the absence of the supercharger, that power would go to the propeller.
This also appears in the German engines where the supercharger is connected to the engine with a continuously variable clutch. At medium altittudes the supercharger is spinning, but not all that fast. The result is diverted power and not much increase in manifold pressure.
If you didn't hold back the throttle at low altitudes, you would get too much compressed air. In other words manifold pressure would be so high you would either produce detonation or simply blow somthing off the induction system.
On the U.S. engines, you can take off with the supercharger disengaged, so there is no penalty. At a higher altitude you would engage it at the lower of two gear ratios, immediatley pulling back on the throttle to avoid excessive manifold pressure. This would be repeated again above the critical altitude of the supercharger in the low blower ratio. In a two stage engine, there would be one more of these steps at a quite high altitude.
In the example you use, the one difference across the altitudes is that the throttle is further advanced at higher altitudes, so that the supercharger is adding more pressure than it does at a lower throttle setting at a lower altitude.
-Blogs
Originally posted by VO101_Isegrim
Very good discussion ! Congrats, Gentlemen ! :)
I`d like to ask a question on supercharger charactertics... it can be seen on all fixed-gear superchargers, that engine power output is less below critical altitude. Taking the 1st (fixed) speed of the DB 605A-1 for example, one can see that the engine power output is 1475 PS at SL, and steadily increasing to 1550 PS at around 2100m. Yet the boost pressure, RPM is constant.
This is because of "the extra work the SC has to do", as I have read....
Now, what is this extra work?
I have been thinking on this and the only explanation I could arrive at is that the SC, being fixed to a ratio towards the engine RPM, is trying to run at constant speed, compressing air in the process. Now, when it operates at lower altitudes, whereas it`s compressive capability has surplus, it overcompresses the air too much... since compressing already dense air is harder than thin air, it needs more power to keep supercharger RPM constant. It needs more torque. So it drains more power from engine.
Now, my question is, is my theory correct, or there is/are other reason(s)?
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The airscrew control should tell the constant speed unit how fast the propeller, and therefore the engine should turn (it's not 1:1 as there is typically a reduction gear somewhere in between).
I'm not sure what the boost control does, but I've seen similar switches on some British inlines. It may be an easy way to change manifold pressure when you are engaging different gears on the supercharger, but I am not sure on that. This is especially important for engines running at very high manifold pressures at low altitudes.
I suspect the R7 is an overspeed control for dives.
A good source for information on actually running one of these high output engines is Bent McKinley's Aircraft Powerplants. Also a number of people have posted links to a series of excellent articles written for a pilot's magazine. If I can find the links, I'll post them here.
-blogs
Originally posted by Tilt
Thank you and ho hun for pointing out that throttle setting can adjust manifold pressure....... obviously I missed that flow rate via throttle is a function of pressure differential across the variable choke point.
Re La boost control its a big lever with two apparant positions attached to a wheel which push/pulls a boden cable...........actually the La9 now flying should be the same control system.
There was an additional "airscrew control" but the prop was a constant speed unit....... I assume this would be used to set engine speed as using the prop as variable ratio gear box.
To summarise
I can set manifold pressure as a function of rpm, stage of boost and throttle.
I can set rpm as a function of prop speed
the r7 govenor is a mystery .. could it be used to limit over rev?
would control via throttle or by prop pitch? how is this normally done on other aero engines?
The link between throttle and fuel mixture was directly copied from an FW190
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the column is Pelican's Perch from Avweb:
http://www.avweb.com/news/columns/182146-1.html
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always good how people use there own charts as reference...
get at least 1 more reference on that (preferably in book form) then whine
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The first chart F4u1doa posted is based on data from a specific engine chart for the corsair fighter. I made that chart from a scan of the original US Navy document. He's also just found some new data on the ASH-82 FN engine.
Tilt is citing a Russian flight test report for La-7 using that engine.
Batz posted a chart for the 109e4. Isegrim is posting engineering data for the DB605 engine.
All of this information is from primary sources, although translations are sometimes a problem.
My data is collected from a few hundred engine specifications published in the 1940s and a number of engineering books published during that period.
So what's the problem?
-blogs
Originally posted by vorticon
always good how people use there own charts as reference...
get at least 1 more reference on that (preferably in book form) then whine
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Hi Isegrim,
>it overcompresses the air too much... since compressing already dense air is harder than thin air, it needs more power to keep supercharger RPM constant. It needs more torque. So it drains more power from engine.
>Now, my question is, is my theory correct, or there is/are other reason(s)?
That's how I understand it, too.
I think Tilt's comment shows where the surplus power vanishes to:
"flow rate via throttle is a function of pressure differential across the variable choke point"
Here's the title of an engine book I found very enlightening even though it doesn't mention aviation at all:
"Motorcycle Turbocharging, Supercharging & Nitrous Oxide" by Joe Haile.
Except for computerized fuel injection, pretty much all of the technology he describes was employed on WW2 fighters, too :-)
The great thing about the book is that (on merely 200 pages) it has in-depth explanations that are easy to read, with a good measure of drawings and photographs (and motorcycle examples of course).
The author is not an engineer, but a journalist - which may explain the great readability ;-)
Regards,
Henning (HoHun)
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Hi Tilt,
>ASh82FNV engine speed was controlled by an R7 govenor. I assume this works by effecting the throttle in some way to limit the system at maximum speeds?
Could it be that the R7 unit actually controls the throttle (and perhaps mixture etc.) to make sure any throttle lever position corresponds to a constant boost?
Without any automated system, the pilot would have to keep an eye on the boost indicator continuously and manually change the throttle setting constantly to adapt it to changing altitude, outside air temperature, ram pressure etc.
Regards,
Henning (HoHun)
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Any idea what PS means?
Am I right that most continental calculations of specific fuel consumption are in grams/ps/hour?
-Blogs
Originally posted by 214thCavalier
This may be useful for comparison.
One PS is approx 98.6% of a HP
To convert from BHP to PS multiply by 1.01387
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PS is metric HP. I guess different averaging in the calculations result in the slight power difference.
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Hi Joe,
>Any idea what PS means?
Pferdestärke = horse power.
>Am I right that most continental calculations of specific fuel consumption are in grams/ps/hour?
Yes.
Regards,
Henning (HoHun)
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Vorticon,
Are you serious? That chart in the beggining is right out of the F4U and F6F manuals. JoeB just added the SFC calculations to make it easy.
If you thing any of this is wrong please point it out old boy.
Gsholz,
I have a German doc that says that is the right consumption. I find it hard to believe myself.
What I really don't get it how the consumption doesn't worse with increased power. It just seems to stay the same.
Of course the La-5/7 is the greatest mystery so far.
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Anybody know how much MW50 the 109G10 carried?
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JoeBlogs,
Just taking a quick look at the NIK2.
1990HP WEP
190 gallons internal
44 minutes in the MA * 2= 88minutes IRL
I don't have a Mil power reference for this but even if mil power is 1500HP and I think it would be higher the SFC would be .51
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MW50 on the 109K-4 was limited to a total of 26min (flowrate 180 l/hr, contents 75l) with a max of 10min per use and resting period of 5min between use.
I assume the g10 would be the same.
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I'm trying to see if I can work out implied fuel mixtures for these engines using just RPM and manifold pressure. Will let you know.
I may have some numbers on the engine in the N1k2
-Blogs
Originally posted by F4UDOA
JoeBlogs,
Just taking a quick look at the NIK2.
1990HP WEP
190 gallons internal
44 minutes in the MA * 2= 88minutes IRL
I don't have a Mil power reference for this but even if mil power is 1500HP and I think it would be higher the SFC would be .51
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Originally posted by F4UDOA
Anybody know how much MW50 the 109G10 carried?
The MW tank in late 109Gs and the K series was of 115 liter capacity, but for CG reasons - MW was heavier than the avgas that could be also carried in tank on K4 - usually 70(or 75liter)
According to German GLC documentation, G-10, G-14 carried 63 was carried, whereas K series carried 85 liter in the tank.
kg MW, whereas K-4 carried 77kg MW. That`s roughly 75 and 85 liters.
MW consumption varied, being 150 lit/hour on G-14 with DB605AM, and 180 lit/hour on K-4 with DB 605D. I believe that`s why tankage varied, to give enough MW for about 30 min use.
MW was practically enough for the whole duration flight, as it was only injected at 110% (Sondernotleistung) power. During 30 min use of Sondernotleistung, about 300 liter fuel out of 400 int. tankage was used up, so by time MW run out it was time to head for home.
MW50 and max. power could be used for 10 minutes , after which apprx. 5 minutes were required on lower power to allow the engine to cool down. Then MW could be used for another max. 10 minutes. Of course many variations were possible.