Is the P-40 too slow?

[YankeeDoodle]

 I've been doing some research on the American aircraft used during world war 2 ever since the announcement of Bodenplatte to see what other aircraft can possibly be used from our current plane set and I keep seeing the P-40s top level speed listed as 360 MPH. However in game I've only been able to get the P-40 to 320 MPH. I don't think it is due to engine time limits either because the speed stabilized at about 320 MPH for about 30 seconds before engine failure at emergency power.  

[Mad_Mikhael]

 I've been doing some research on the American aircraft used during world war 2 ever since the announcement of Bodenplatte to see what other aircraft can possibly be used from our current plane set and I keep seeing the P-40s top level speed listed as 360 MPH. However in game I've only been able to get the P-40 to 320 MPH. I don't think it is due to engine time limits either because the speed stabilized at about 320 MPH for about 30 seconds before engine failure at emergency power.  

The question is, which one? 

 

P-40 Variants

Edited December 1, 2017 by =L/R=Mad_Mikhael

[YankeeDoodle]

The E variant. P-40E_Operation_Instructions.jpg (1400×1060)

Edited December 1, 2017 by YankeeDoodle

[Finkeren]

The specifications in the game states the maximum TAS at 5000m as 601 km/h, which is quite a bit faster than 360 mph, so if anything our P-40 is too fast.

[19//Moach]

It's not slow in a normal sense... It's actually not bad as far as top speed goes.

 

It's climb rate is dismal however, and the engine limits are much too severe, unrealistically fragile from the interpretation of it's historically debunked recommended tolerances as physical thresholds for clock-mandated Doom™

 

Engine-wise, yes, it is rather handicapped against its historical namesake. 

 

Aerodynamically, however, I see nothing plainly amiss.  The new FMs did a fantastic job in restoring that much of its glory

Edited December 1, 2017 by 19//Moach

[Finkeren]

Just ran a quick speed test:

 

Autumn map (which should mean normal SI testing standards)

 

Alt: 5000m above SL

 

Standard loadout, 100% fuel.

 

Throttle 100%, RPM 100%, mixture auto rich, cowl flaps closed (at that altitude the engine can only go into combat mode and doesn't overheat, even with flaps fully closed)

 

Within a few minutes I reached 447km/h IAS which is around 590km/h TAS at 5K which again equals slightly above 366mph.

 

So the top speed of the P-40E is fine. If anything it is slightly too fast.

[Finkeren]

 I've been doing some research on the American aircraft used during world war 2 ever since the announcement of Bodenplatte to see what other aircraft can possibly be used from our current plane set and I keep seeing the P-40s top level speed listed as 360 MPH. However in game I've only been able to get the P-40 to 320 MPH. I don't think it is due to engine time limits either because the speed stabilized at about 320 MPH for about 30 seconds before engine failure at emergency power.  

 

I think I might have found the cause of the issue. You are trying to reach the designated top speed at too low an altitude. If you can go into emergency mode on the manifold pressure, you are at too low an altitude to actually reach the 360mph top speed.

[19//Moach]

 

... (at that altitude the engine can only go into combat mode and doesn't overheat, even with flaps fully closed) ....

 

 

 

Yes, there is something blatantly wrong with that engine's heat model.   It suffers from an absurd degree of overcooling under all conditions, including such as "idle on the ground", where multiple sources clearly state it would overheat with rads fully open.  Yet it overcools fully closed instead.

 

This is true of all planes in the game, however.  Such that there is indeed cause for a revision of engine heat models in general.   The P40, as with flight models prior to .012, stands as the "most wrong" of the bunch, illustrating the problem more visibly than in any of the others.

 

 

While slightly off the original topic, this does contribute to the plane's larger than normal cruising speed, as radiators are commonly closed shut in normal flying conditions due to the overcooling issue.   This somewhat offsets some of the disadvantages of the "glass engine" issue.   But two wrongs do not make one right.  Definitely not in this case.  

 

Engine model revision is long overdue.

Edited December 1, 2017 by 19//Moach

[YankeeDoodle]

  Face palm, you know Fink it never occurred to me that they were listing the True Airspeed it all makes sense now thanks.

[Guest deleted@50488]

Although not really on topic, I confess the P-40E is my goto VVS fighter at MP...

 

I still pick the Spitfire, but  prefer the P-40 :-)

[ACG_Smokejumper]

Although not really on topic, I confess the P-40E is my goto VVS fighter at MP...

 

I still pick the Spitfire, but  prefer the P-40 :-)

 

It's a joy to fly. I agree with you. Love it.

[Barnacles]

Yes, there is something blatantly wrong with that engine's heat model. It suffers from an absurd degree of overcooling under all conditions, including such as "idle on the ground", where multiple sources clearly state it would overheat with rads fully open. Yet it overcools fully closed instead.

 

This is true of all planes in the game, however. Such that there is indeed cause for a revision of engine heat models in general. The P40, as with flight models prior to .012, stands as the "most wrong" of the bunch, illustrating the problem more visibly than in any of the others.

 

 

While slightly off the original topic, this does contribute to the plane's larger than normal cruising speed, as radiators are commonly closed shut in normal flying conditions due to the overcooling issue. This somewhat offsets some of the disadvantages of the "glass engine" issue. But two wrongs do not make one right. Definitely not in this case.

 

Engine model revision is long overdue.

Agree with the ground heat issue but I see nothing wrong at flight speed. Generally on a non winter map you need 20 to 10% on the flaps else it overheats at max continuous power

[ACG_Smokejumper]

Hey Moach, above 175mph IAS you can fully close the P40 cowl flaps. No more overcooling.

[Dave]

The specifications in the game states the maximum TAS at 5000m as 601 km/h, which is quite a bit faster than 360 mph, so if anything our P-40 is too fast.

 

That 360mph is CIAS not TAS.

[Dave]

Standard sea-level barometric pressure and temperature (the zero reference used for the flight manual) is 101.325kPa @ 15℃.

Flight manual says CIAS of 359mph at 15000' at 3000RPM and 43.9"MP.

This produces a TAS of 478mph at 15000'.

 

Moscow average temperatures have been gradually increasing over the period I can find records so the figures given should possibly be considered maxima for WW2:

Summer: 26℃@1012.3hPa

Autumn: 5℃@1017.8hPa

Winter: -12℃@1019.2hPa

 

Note that average surface pressure in Moscow fluctuates widely between 1010 and 1030hPa reflecting the passage of weather systems affecting performance on any given day.

 

If the ASI reads 360mph the temp@pressure given above yield TAS at 15000' of:

Summer: 487mph

Autumn: 468mph

Winter: 455mph

The point of this is to demonstrate that relying upon numbers taken from different contexts can be very misleading.

You end up comparing apples and oranges because in the conditions given the ASI would not read 360mph. Engine and airframe performance depend on ambient conditions so to check the model against a flight manual you need to set the mission's ambient airfield conditions to standard sea level pressure and temperature and then zero your altimeter to the airfield elevation, climb to 15000' and fly straight and level at 3000RPM and 43.9"MP for 5 minutes. Recording the ASI reading and TAS.

Only then will you have comparable and meaningful data.

[-=PHX=-SuperEtendard]

The Kuban Autumn map has standard conditions, temperature at sea level is 15°C and when setting the altimeter to standard atmosphere, sea level is 0 altitude.


There at 15000 feet the P-40 does 455 km/h or 283 mph IAS with full throttle at 3000 rpm, which is 42.5 ", 30% neutral radiator cowling and auto rich mixture


With a temperature of around -13°C at that altitude the TAS is ~ 575 km/h or 358 mph

Edited January 5, 2018 by -=PHX=-SuperEtendard

[JtD]

Flight manual says CIAS of 359mph at 15000' at 3000RPM and 43.9"MP. This produces a TAS of 478mph at 15000'.

360mph is TAS. No P-40 ever managed 480mph in level flight, speeds like these were reserved for jets.

[Dave]

360mph is TAS. No P-40 ever managed 480mph in level flight, speeds like these were reserved for jets.

Yeah I'll have to concede this one. Didn't even sanity check the result. Calculation was based on the assumption that all speeds in a flight manual are Indicated which has been my experience.

[D3VNT]

The biggest issue with the P-40 is how manifold pressure is modeled. 

 

The P-40E had a longer duration of boost power, and was able to maintain -much- higher manifold pressure than the game allows it to, to the tune of over 10"Mg. Russian pilots purportedly flew it consistently at 60"Mg continuous, and just replaced engines more often than other fighters - and the game models only factory-new aircraft. 

 

I'll go hunt down sources and figures, but the pre-war manual had very low restrictions compared to what it could actually handle. 

[Jade_Monkey]

From what i heard the P39 uses the same engine. It will be interesting how it's modeled.

 

I wouldn't be surprised if a new P40 engine revision comes out once the P39 is out in the next patch.

[[CPT]Crunch]

The CSP is suspect, it doesn't behave as one would expect.  Adjusting full forward prop control from 2100 RPM's in a climb should change conditions rapidly with the prop and RPM's, it does nothing.  Meanwhile a rapid push into a dive drives RPM's right through the roof way before airspeed is built up without adjusting it.  What kind of CSP does that, it's air, not rubber on a highway.

[Max_Damage]

I think its better stick to strict manual values for all planes. including 109 and p40. if you didnt IRL then you suffered a variety of consequences which may look and feel diffirently to what we have in game but they still were very real. In short you had a lot worse engines IRL which produced less power if you abused them.

Edited January 10, 2018 by Max_Damage

[Dave]

I discussed the current behaviour of the P40 CSU we have with the chief mechanic of our local warbird maintenance team. He has maintained P40's, spits, hurricanes, mustangs and others for the last 20 years and was previously a black hand at BoBMF.

He agreed that the behaviour of our CSU is too laggy and that the RPM overruns we have are exaggerated.

Edited January 10, 2018 by Dave

[JtD]

Nice info.

[=TBAS=Sshadow14]

LMAO Faster in summer ?

ah lol what

[Dave]

TAS can be faster in summer for the same IAS. The error was that it wasn't the same IAS.

[ACG_Smokejumper]

I got to 300mph indicated on the gauge on the deck yesterday. Is that good?

 

Seriously I have no idea of deck top speed but I thought that was pretty good. 483Kmh, perhaps a tad under.

[Ehret]

I got to 300mph indicated on the gauge on the deck yesterday. Is that good?

 

Seriously I have no idea of deck top speed but I thought that was pretty good. 483Kmh, perhaps a tad under.

 

This isn't too great for continuous speed - even LaGG can fly faster for longer time. That isn't the issue, thought: the problem lies in a relatively short (5m) combat, and a very brief (under 1m) emergency power time. Allison V1710 engines didn't behave like they do in BoX now - they could run for much longer on those elevated power settings without blowing up. Of course, they would wear down much quicker after such use, rendering the plane slower, eventually making her useless for combat.

 

For amusement purposes, fly a quick mission with custom option "unbreakable" set and see how fast (at sea level @ full throttle and 100% pitch) BoX's P40 could be, if not for that pesky time limiter...

[-=PHX=-SuperEtendard]

Around 580 km/h at sea level... Which makes me wonder which is really the max power setting the Allison has... 1470 HP would be a bit too low for such high speed? The manifold pressure indicator goes up to 50" so I don't really know if the max is 56" like it is said in the specifications tab. IIRC in another thread it was said that the max power at sea level would be around 1700 HP at like 60".

 

Would like to see one of Holtzauge's simulations about it.

[Panthera]

The P-40N managed 314 mph (505 km/h) TAS at SL with 57" MP (1470 hp), so I think it's pretty safe to assume that the P-40E should never be capable of 360 mph (580 km/h) at SL. 

 

For comparisons sake the 109G averaged 525-530 km/h at SL @ 1.3ata (1,290 hp), whilst it would need 1750 hp to reach 580 km/h at SL.

[Ehret]

The P-40N managed 314 mph (505 km/h) TAS at SL with 57" MP (1470 hp), so I think it's pretty safe to assume that the P-40E should never be capable of 360 mph (580 km/h) at SL. 

 

For comparisons sake the 109G averaged 525-530 km/h at SL @ 1.3ata (1,290 hp), whilst it would need 1750 hp to reach 580 km/h at SL.

 

Done a few checks and I think this is what is exactly happening with P40: 100% throttle is 70" MP, not 56" as I thought. After 10" on MP gauge (@ 30% throttle), to gain extra 5" you have to open throttle by 5%, too. At 50" MP throttle is around 80% - extrapolating to 100% MP should rise to... 70" MP. Max emergency power as stated in specification (at 56" MP) is approx 85% throttle then.

 

Looks like things are alright after all. We just have an option to over-boost the over-boost, blowing up the engine shortly, as it probably should.

[-=PHX=-SuperEtendard]

Done a few checks and I think this is what is exactly happening with P40: 100% throttle is 70" MP, not 56" as I thought. After 10" on MP gauge (@ 30% throttle), to gain extra 5" you have to open throttle by 5%, too. At 50" MP throttle is around 80% - extrapolating to 100% MP should rise to... 70" MP. Max emergency power as stated in specification (at 56" MP) is approx 85% throttle then.

 

Looks like things are alright after all. We just have an option to over-boost the over-boost, blowing up the engine shortly, as it probably should.

That's really good information! thanks for pointing it out. I did some tests at 85% which would be 55"-56" and the engine got damaged at around 1 minute mark:

 

1:01

1:00

1:03

0:50

0:57

 

The P-40N managed 314 mph (505 km/h) TAS at SL with 57" MP (1470 hp), so I think it's pretty safe to assume that the P-40E should never be capable of 360 mph (580 km/h) at SL. 

 

For comparisons sake the 109G averaged 525-530 km/h at SL @ 1.3ata (1,290 hp), whilst it would need 1750 hp to reach 580 km/h at SL.

 

I think the P-40 might be too fast at these very high power settings, the 109 is a good comparison, but i'm doubtful about the 505 km/h sea level speed at 57" for the P-40N. I have seen that graph, and they list a top speed at altitude of around 566 km/h, at 57", slower than P-40E, which is kinda suspicious. Maybe there was something special about the test conditions or the plane itself?

 

A US test of a P-40N at altitude reports a similar top speed at altitude, but it's at around 44.5", 1100 HP.

 

There is also another report at 57" for the P-40N (a P-40K modified to have similar drag and weight conditions to a standard P-40N), they list 608 km/h at 10550 feet (1480 HP) and around 553 km/h at 2960 feet (1415 HP). Since below critical altitude the P-40's speed curve is a straight line, you could extrapolate these results and would give around 530 km/h at sea level at 57".

 

Our P-40E does 534 km/h at 85% thorttle which would be 56" according to Ehret (1470 HP according to ingame specs).

Edited January 15, 2018 by -=PHX=-SuperEtendard

[Venturi]

The structural strength of he engine was 1500hp / 3000rpm / 60” MP.

 

The 100/130oct instantaneous fuel detonation point, given the V1710-39’s CR, was estimated about 65” MP.

 

The engine was later officially rated by Allison at 56” MP / 3000rpm for 5 min. Hazen’s letter sets out higher “unofficial limits” even than these, that he felt were an acceptable compromise between engine longevity and engine performance.

[Venturi]

Obviously, the reason why the MP regulator was required by the USAAF before clearing the engine for the 56” MP rating, was because it provided the engine a better ability to automatically and quickly modulate throttle input to prevent going beyond the detonation point, than manual pilot modulation of the throttles.

 

When in for instance, an aerobatic maneuver like a loop - which might cause momentary RPM drop and subsequent MP increase for a given throttle setting (unlike how the game models it) - the manually-controlled MP which is set at 56” in level flight, might go higher as airspeed is bled quickly (before the prop governor raises engine RPM again) and when at a high setting such as 56”, it might cross the instaneous detonation threshold.

 

It was *THIS* concern for instantaneously crossing the detonation point while under maneuvers which was the reason for the MP regulator being a requirement for the uprating. Not the structural strength of the engine or fuel limitations.

[Panthera]

That's really good information! thanks for pointing it out. I did some tests at 85% which would be 55"-56" and the engine got damaged at around 1 minute mark:

 

1:01

1:00

1:03

0:50

0:57

 

 

I think the P-40 might be too fast at these very high power settings, the 109 is a good comparison, but i'm doubtful about the 505 km/h sea level speed at 57" for the P-40N. I have seen that graph, and they list a top speed at altitude of around 566 km/h, at 57", slower than P-40E, which is kinda suspicious. Maybe there was something special about the test conditions or the plane itself?

 

A US test of a P-40N at altitude reports a similar top speed at altitude, but it's at around 44.5", 1100 HP.

 

There is also another report at 57" for the P-40N (a P-40K modified to have similar drag and weight conditions to a standard P-40N), they list 608 km/h at 10550 feet (1480 HP) and around 553 km/h at 2960 feet (1415 HP). Since below critical altitude the P-40's speed curve is a straight line, you could extrapolate these results and would give around 530 km/h at sea level at 57".

 

Our P-40E does 534 km/h at 85% thorttle which would be 56" according to Ehret (1470 HP according to ingame specs).

 

Apparently they had issues with the carburettor, but similar tests were carried out here where top speed was 378 mph at FTH and 323 mph at 2,960 ft @ 57" MP:

http://www.wwiiaircraftperformance.org/P-40/P-40N_42-9987_FS-M-19-1535-A.pdf

 

Thus I believe we can be fairly certain that 314 mph is the expected top SL speed of the P-40E/N at 57" MP.

[JtD]

The structural strength of he engine was 1500hp / 3000rpm / 60” MP.

Design limit of RPM as a standalone were in excess of 4000rpm. A truly excellent engine in that regard.

[Venturi]

I am looking forward to the pair of contra rotating, super-turbocharged Allisons in the P-38.

[Sgt_Joch]

The issue of how much boost the Allison could take is still a mystery and you have a lot of contradictory data. 

 

P-38s were running with 70" of boost in 1944-45, but they were running with 150 octane fuel and had powerful intercoolers to cool the engine. The 1942 P40E had neither.

 

You have the infamous (or famous) Born letter of august 1943 which states:

 

 

  36.       In view of the British operation and the fact that we have an approved war emergency rating on the 1710-39 engine of 56”, it is suggested that immediate steps be taken to remove the automatic boost controls from our P-51 airplanes in this theatre and that the instrument dials be marked with the proper lights. The British have operated at full throttle at sea level (72” Hg) for as much as 20 min. at a time without hurting the engines. According to them, the Allison is averaging 1500 hours between bearing failures as compared to 500 to 600 hours for the Merlin. The Allison, they have found, will drag them home even with the bearing ruined.

 

 

http://www.wwiiaircraftperformance.org/mustang/e-geh-16.html

 

this is one of the letter everyone relies on to state that the 1942 P40E should be running at 70" boost in 1942, i.e. the same pressure that was only officially approved in the P-51/P-47/P-38 in 1944 once 150 octane fuel was available.

 

Yet when the British carried out a series of flight tests in late 42-early 43 specifically to find out what was the maximum boost that could be used on the F.3.R model, i.e. the same engine used in the 1942 P40E, they stated the maximum boost was 56":

 

 

...The level speed measurements with the F.21.R engine installed were first made using a boost limitation of 51" Hg. Measurements were made subsequently using full throttle down to ground level to determine the maximum boost and airspeeds obtainable. With the supercharger gear changed to that of the F.3.R, level speeds were measured using various boost pressures up to a maximum of 56" Hg.

 

http://www.wwiiaircraftperformance.org/mustang/ap222.html

 

The matter gets further complicated when you review the equally infamous december 42 letter from the manufacturer of the engine (the Hazen letter). It contains a quote that pilots in Australia are claiming to be running the engine at 70" boost' but the letter goes on to say that this is only physically possible in a dive or if the engine is running at 3200 RPM, both of which would appear to be impossible for "prolonged period". The letter also states that the maximum boost that can be used on the F.3.R with a 8.8 blower gear ratio (i.e the P40E engine) is 60" since this is the  "structural limit" of the engine.

 

http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

 

so all in all, I find all these claims that Allisons were being regularly run at 70" in 1942 to be very dubious. I read the Hazen letter as being a very polite blow-off, i.e. the engineer is using very polite language to say the pilots are probably exaggerating when they say they can run at 66-70 inches.

Edited January 15, 2018 by Sgt_Joch

[-=PHX=-SuperEtendard]

Apparently they had issues with the carburettor, but similar tests were carried out here where top speed was 378 mph at FTH and 323 mph at 2,960 ft @ 57" MP:

http://www.wwiiaircraftperformance.org/P-40/P-40N_42-9987_FS-M-19-1535-A.pdf

 

Thus I believe we can be fairly certain that 314 mph is the expected top SL speed of the P-40E/N at 57" MP.

That's the report I was talking about earlier, at 2960 feet it's 344 mph (553.6 km/h) at 57", the 323 mph value is with a lower manifold pressure which isn't specified, note it says 1125 HP in comparison to the 1415 HP of the 57" setting at the same altitude

Edited January 15, 2018 by -=PHX=-SuperEtendard

[Venturi]

so all in all, I find all these claims that Allisons were being regularly run at 70" in 1942 to be very dubious. I read the Hazen letter as being a very polite blow-off, i.e. the engineer is using very polite language to say the pilots are probably exaggerating when they say they can run at 66-70 inches.

 

He is saying it is possible, but not advised. By running up the RPM beyond 3000, you can provide higher supercharger impeller speeds, which generates higher boost pressures. You can do the same by ram effect in a dive.

 

so all in all, I find all these claims that Allisons were being regularly run at 70" in 1942 to be very dubious. I read the Hazen letter as being a very polite blow-off, i.e. the engineer is using very polite language to say the pilots are probably exaggerating when they say they can run at 66-70 inches.

 

Detonation point of the fuel in regards to manifold pressure, varies depending on the temperature density of the atmosphere. 65" at 10C ambient is not the same as 65" at 25C ambient. The actual O2 content of a given volume of air differs, because the air temperature differs (PV=nRT .... n = moles of gas... higher T, lower n for a given pressure...). O2 content is the oxidizer in the stoichiometric ratio of air to fuel...

 

66" manifold pressure was certainly possible in the P40E at high speeds, low altitude, and especially with over-rev of the engine.