P-51 too slow.

[Heckpupper]

 

 

Nothing too fancy here, just comparing test speeds in-game with available documentation.

 

In-game numbers:

 

P-51 D-15, 150oct, 10 000ft, standard atmospheric conditions (Kuban Autumn).

3000 RPM, full throttle (70"Hg) - 355-360MPH IAS (409 - 414 MPH TAS) 

 

P-51 D-15, 100 oct, 10 000ft,  standard atmospheric conditions (Kuban Autumn)

3000 RPM, full throttle (67"Hg) - 350 MPH IAS (405 MPH TAS) 

 

 

Compare it with the charts presented here:

(providing several tests of various configurations  for cross reference)

 

 

P-51D at 3000 RPM and 67"Hg at 10 000ft - 418 TAS (13 MPH faster than in-game)

 

 

 

 

 

P-51B, 3000 RPM, (originally 75"Hg, matches with 67"Hg at 10 000ft) - 420 MPH TAS, 17 MPH FASTER THAN IN-GAME

 

 

 

 

Lastly, calculated performance for the P-51D at 67" - also states approx. 420 MPH TAS, SO ABOUT 17 MPH FASTER THAN IN GAME

 

I do realize that these errors might be due to the methods of calculating airspeed (not sure how the pitot tube errors are modeled in-game), but 10+ mph is quite of a staggering difference so I'd love if someone could clear this up. I haven't tested other altitudes yet because I can't be bothered, but I might when I have more time.

 

edit: just tested FTH at 7700ft at 75"Hg, ended up with 364 MPH IAS and 404 MPH TAS which leaves us with the same result of aproximately X-teen MPH missing in action. 

 

Thanks. 

Edited November 12, 2020 by ACG_Onebad

[unreasonable]

FYI - pitot errors are not included in the game at all. So what you see as "IAS" in game is either CAS or EAS  (I am not sure which).

From P-51-D-5 manual:

 

 

Edited November 12, 2020 by unreasonable

[Heckpupper]

Yeah alright that's exactly what I though which futher strengthens my point.

Additionally, the top speed of 382 MPH at sea level at 75"Hg is also at the low end of all tests performed with that engine power with some tests stating 390 MPH and even more. 

[HandyNasty]

2 hours ago, ACG_Onebad said:

Additionally, the top speed of 382 MPH at sea level at 75"Hg is also at the low end of all tests performed with that engine power with some tests stating 390 MPH and even more. 

At SL Kuban Autumn, set rpm to 86% (2750 rpm) and close oil rad manually with 150 octane : you'll get 629kph which is 391mph.

[Mitthrawnuruodo]

@ACG_Onebad What weights (fuel and weapon loads) and radiator shutter settings did you use for these tests?

Edited November 12, 2020 by Mitthrawnuruodo

[-=PHX=-SuperEtendard]

I tested the P-51 and compared it to the 44-15342 test, at the same weight of 4427 Kg (9760 pounds) that the real test and with wing racks as indicated in the report. With radiators in automatic.


The speed at high altitudes and top speed look good, the speeds in the first supercharger gear a bit too slow though, around 20 km/h at most altitudes, and this shrinks down to 13 km/h too slow at sea level.

Edited November 13, 2020 by -=PHX=-SuperEtendard

[Heckpupper]

5 hours ago, =FSB=HandyNasty said:

At SL Kuban Autumn, set rpm to 86% (2750 rpm) and close oil rad manually with 150 octane : you'll get 629kph which is 391mph.

 

Okay, but that still doesn't mean my point is invalid - you should be reaching that sort of speed with the oil radiator controlled automatically and 3000 RPM as per source material. There is no documentation that states that reducing RPM increases top speed. 

2 hours ago, Mitthrawnuruodo said:

@ACG_Onebad What weights (fuel and weapon loads) and radiator shutter settings did you use for these tests?

 

Wing tanks full or so, standard 6 ,.50 armament. Radiators all controlled automatically. 

There's a stability report for the P-51B also saying that putting the 85 gal tank in the fuselage and additional weight '... has no measurable effect on the maximum speed of the airplane', and if tweaking the rads or weight can give you all the missing MPH the problem is more serious than just tweaking the top speeds since it would imply that the AoA is significantly impacted by weight where it shouldn't be.

[the_emperor]

If you translate IAS to TAS you have to use Equivalent Airspeed. That was recently discoverd when looking at the speeds of the 109 G6:

 

https://aerotoolbox.com/airspeed-conversions/

 

If you use calibrate Air speed for translation the planes will seem much slower espeacially with inceasing altitude.

 

Cheers

[HandyNasty]

11 hours ago, ACG_Onebad said:

Okay, but that still doesn't mean my point is invalid - you should be reaching that sort of speed with the oil radiator controlled automatically and 3000 RPM as per source material. There is no documentation that states that reducing RPM increases top speed

I didn't say it in my original post, but I actually do agree with you on those points.

[6FG_Moonbeam]

Hello gentlemen !

Here is my contribution for this topic. Well, in this message, it's not about top speed but more on the acceleration of the plane itself.
In the following video, a TF-51 Mustang pilot describes the differences between the real one, the DCS Mustang module and the Mustang in IL-2 Great Battles.

He chose 3 sequences : taxiing, take-off and landing.

 

I let you see the sequences

 

 

 

[Na-zdorovie]

i know this is a little bit older thread, but didnt think its worth a new one.

i found the same in the above video, the "stang we have is quite a bit under powered in normal flight, just wondering if there is anything on the horizon for a bit of an update?

the DCS module is deff nearer, and although im a long time DCS flyer, im actually drawn more towards IL2 planes and content, hence i have most il2 stuff now,

even considering re buying some to get off steam

[DJBscout]

On 11/12/2020 at 1:50 PM, =FSB=HandyNasty said:

At SL Kuban Autumn, set rpm to 86% (2750 rpm) and close oil rad manually with 150 octane : you'll get 629kph which is 391mph.

 

The IRL tests were done at 100%, as lower RPM would result in detonation. We shouldn't need to do weird shenanigans. Hell, that should (potentially) cause engine damage. The aircraft should hit the specs at the conditions it did in IRL tests.

 

EDIT: oop, this is old and that bit was already addressed. My bad.

Edited June 15, 2021 by DJBscout

[6./ZG26_Klaus_Mann]

P-51Bs were faster than the Ds though. The Bubble Canopy and thicker Wings to turn the .50 cals right side up so they wouldn't jam und G-Load reduced Top Speed.

 

P-51B Tests thus aren't relevant.

[BCI-Nazgul]

IL-2 51 is underpowered.  I wish I could say I'm surprised.

[6./ZG26_Klaus_Mann]

14 hours ago, BCI-Nazgul said:

IL-2 51 is underpowered.  I wish I could say I'm surprised.

It was historically. It's a ton heavier than a Spit, with the same Power. It's saving grace is its low drag.

Edited June 18, 2021 by 6./ZG26_Klaus_Mann

[BCI-Nazgul]

7 hours ago, 6./ZG26_Klaus_Mann said:

It was historically. It's a ton heavier than a Spit, with the same Power. It's saving grace is its low drag.

OK, the guy that flies a REAL one just showed us it has too low thrust on a REAL video and you dispute what I said?  I'm not saying it should be just like a Spitfire.

 

Also noteworthy, a fully loaded P-47 will also roll off at very low power.  Setting the parking brake is a required step in the start up process.

Edited June 18, 2021 by BCI-Nazgul

[LColony_Kong]

On 6/17/2021 at 4:15 PM, 6./ZG26_Klaus_Mann said:

P-51Bs were faster than the Ds though. The Bubble Canopy and thicker Wings to turn the .50 cals right side up so they wouldn't jam und G-Load reduced Top Speed.

 

P-51B Tests thus aren't relevant.

No they weren't. P51Ds were every bit as fast as the B. Both planes hit 440mph. And the flight tests of the D show it was about 10mph faster on the deck.

[354thFG_Drewm3i-VR]

Obviously we want the il2 p51 to perform like real life, but Its honestly amazing that we've gotten to the point where it's so close that we can point out the few things that are off in il2 and dcs.

[Angry_Kitten]

Methinks the sheenanigans will be interesting when the normandy mustang is open for public gripes. 

 

Though dive speed may not be a good indicator as no one knows how cautious the testing pilot in real life was when doing the speed dive test... 

 

did he throttle down a bit,   or did he just leave it full throttle and hope st francis was looking out for him..

[CountZero]

with this engine timers and crap guns, no one will be flying normandys mustang, it will be in hangars like normandys 47 LOL

RAF rules west front !

[von_Tom]

On 6/18/2021 at 4:59 PM, BCI-Nazgul said:

OK, the guy that flies a REAL one just showed us it has too low thrust on a REAL video...

 

I'm curious - what is the difference between a TF51 and a combat effective P51, in terms of armour, guns, all up weight, fuel load and so on?  As far as I know the TF version doesn't have armour, guns, other equipment and the aft fuel tank so I'm wondering what difference that would make.

 

von Tom

[Dakpilot]

43 minutes ago, CountZero said:

with this engine timers and crap guns, no one will be flying normandys mustang, it will be in hangars like normandys 47 LOL

RAF rules west front !

 

What is wrong with P-51 engine limits? 

 

Cheers, Dakpilot 

[Cpt_Siddy]

2 hours ago, Dakpilot said:

 

What is wrong with P-51 engine limits? 

 

Cheers, Dakpilot 

 

It is not the timers, it is why the timers existed. According to Greg, the timers were for inter cooler temp. He is quit astute person and i put much weight on his word. 

 

Edited July 13, 2021 by Cpt_Siddy

[LColony_Kong]

17 hours ago, Cpt_Siddy said:

t is not the timers, it is why the timers existed. According to Greg, the timers were for inter cooler temp. He is quit astute person and i put much weight on his word.

Greg doesn't know what he is talking about. He presents no evidence of that claim whatsoever. He guesses because he knows after-coolers are going to get pretty hot, and he straight up admits his "1min until its good to go again" is a guess. There is no documented evidence whatsoever that the after-coolers overheat after 5min. 5min is a semi-arbitrary limit that is imposed so that pilots don't wear out the engine and cause the TBO to be dramatically shortened. This is explicitly stated in other manuals, including some later P-51 manuals. He understands this so little that he just glosses right over the explanation he directly quotes, which is that the engine has to be checked after 5 hours of operation at said setting.

 

The limit setting on most American planes is 5 min. What a coincidence that every airplane, despite completely different inter coolers or engines, different fuels, and other factors....end up being 5 minutes. Incidentally, the 150 octane mustangs running 75inches of boost at 1920bhp also are limited to 5min.

 

 

Edited July 14, 2021 by LColony_Red_Comet

[Cpt_Siddy]

57 minutes ago, LColony_Red_Comet said:

Greg doesn't know what he is talking about. He presents no evidence of that claim whatsoever. He guesses because he knows after-coolers are going to get pretty hot, and he straight up admits his "1min until its good to go again" is a guess. There is no documented evidence whatsoever that the after-coolers overheat after 5min. 5min is a semi-arbitrary limit that is imposed so that pilots don't wear out the engine and cause the TBO to be dramatically shortened. This is explicitly stated in other manuals, including some later P-51 manuals. He understands this so little that he just glosses right over the explanation he directly quotes, which is that the engine has to be checked after 5 hours of operation at said setting.

 

 

Yeah, like i said, he got chops to show for what he talk, and you just said "he don't know what he is talking about". 

 

See the problem here? Someone without a hint for what the actual reason there was to limit 5 mins other than "don't cause too much trouble to your mechanic because overhaul" is just dismissing what other person, who gave some rather compelling reasons, said out of hand. Charge air cooling is one of the reasons some ww2 engines were limited to lower settings, the reason Greg gave here is not unreasonable limit setter for engine timer. Because, lets be frank, 5 hours continues operation before overhauls is not 5 minute limit. The 5 minute continuous limit is what we are debating here. Why it existed, what governed it, etc...

 

If i got a 109 on my tail, i care very very little of what my mechanic may think when i open the throttle and run the engine at war emergency a bit longer. Only thing that is on my mind is "how much i can reasonably get away with abusing my engine and still get home". In real world, most of this was a mixture of factors like how new the engine was, when was it last overhauled and what are the conditions outside that aid or hamper my engine. Not an arbitrary "manual says 5 minutes or the mandatory self destruct mechanism will be triggered".

 

Greg also said that WEP did nothing for P-51 below 5000 ft. Is this because the engine could develop max permitted manifold pressures without going full open? Or is this something else?  

Edited July 14, 2021 by Cpt_Siddy

[357th_KW]

From the P-51D pilots operating instructions: “Use of the War Emergency Rating will decrease the engine’s normal service life and time between overhauls, and therefore should be held for use only when emergency conditions are exist.”

 

From the post war F-51D manual: “It is often asked what the consequences will be if the 5-minute limit at Takeoff Power is exceeded.  Another frequent inquiry is how long a period must be allowed after the specified time limit has elapsed until Takeoff Power can again be used.  Those questions are difficult to answer, since the time limit specified does not mean that engine damage will occur if the limit is exceeded.  Instead, the limit means that the total operating time at high power should be kept at a reasonable minimum in the interest of prolonging engine life.   ….  How the time at high power is accumulated is of secondary importance; I.e. it is no worse from the standpoint of engine wear to operate at takeoff power for one hour straight than it is to operate in twelve 5 minute stretches, provided engine temperatures and pressures are within limits.  In fact, the former procedure may even be preferable, as it eliminates temperature cycles which promote engine wear.”

 

There’s a P-47 manual out there which I don’t feel like digging up at the moment that says the same stuff, along with “Don’t let the time limits prevent you from using maximum power if you need it in combat”.  Try to save the engines but pilots and airframes are obviously more important than maintaining the maintenance schedule.

At least some pilots were aware of this (or just ignored the limits).

 

As a further example, the USAAF did 7.5 hour war emergency runs on their engines to test suitability of 150 octane fuel.

Rolls Royce performed destructive testing on their Merlin 66 (V-1650-7 equivalent) and Merlin 100 (V-1650-9) engines to find their endurance limits by running them at WEP.  The basic unimproved Merlin 66 started breaking things after around 27 hours of constant WEP.  The various issues were worked through so that the later 100 series engines could run for 100 hours at those power settings.

 

Greg is a guy that makes YouTube videos, not a primary source, and I’d take everything he says with a grain of salt.  A quick look at any actual P-51 performance test shows that going from 61” to 67” was worth about 150hp and 10-15 mph.  The current system in IL-2 where the engine blows up after exceeding the time limit is simply incorrect.

 

 

Edited July 14, 2021 by VBF-12_KW

[41Sqn_Skipper]

Also, the time limits don't overrule temperature limits, i.e. you are not allowed to ignore the oil temperature limits during the 5 min WEP use and may need to throttle back earlier to stay within the allowed temperature limits.

 

 

[Cpt_Siddy]

3 hours ago, VBF-12_KW said:

 

 

Greg is a guy that makes YouTube videos, not a primary source, and I’d take everything he says with a grain of salt.  A quick look at any actual P-51 performance test shows that going from 61” to 67” was worth about 150hp and 10-15 mph.  The current system in IL-2 where the engine blows up after exceeding the time limit is simply incorrect.

 

 

 

Greg is prolific user of primary sources and has actual qualification to talk about this stuff. Do i trust him more than i trust most people here? Yes, because he is a first principles thinker. The problem with timers is that they simulate nothing. It is just a clock countdown for a self destruction of engine. In reality, it was a guideline because something or other might overheat because cooling systems or lubrication eventually cant keep up. 

[41Sqn_Skipper]

@VBF-12_KW in the context of the F-51 manual, is "takeoff power" the same as WEP? 

 

In RAF doctrine takeoff power uses less boost and shorter duration than emergency power.

[357th_KW]

Takeoff is listed as 61"/3000 RPM in that manual, so the same as Combat (which is listed as a 15 minute limit).  Here's a fun question.  On the morning of January 1st, 1945 should pilots of the 352nd Fighter Group have stuck with the 5 minute limit for takeoff?  Or the 15 minute limit for combat? 

 

Again from the F-51D manual: "It is established in these runs that the engines will withstand sustained high power without damage.  Nevertheless, it is still the aim of the manufacturer and to the best interest of the pilot to keep within reasonable values the amount of high-power time accumulated in the field.  The most satisfactory method for accomplishing this is to establish time limits that will keep pilots constantly aware of the desire to hold high-power periods to the shortest period that the flight plan will allow, so that the total accumulated time and resulting wear can be kept to a minimum."

[LColony_Kong]

On 7/14/2021 at 3:35 AM, Cpt_Siddy said:

See the problem here? Someone without a hint for what the actual reason there was to limit 5 mins other than "don't cause too much trouble to your mechanic because overhaul" is just dismissing what other person, who gave some rather compelling reasons, said out of hand. Charge air cooling is one of the reasons some ww2 engines were limited to lower settings, the reason Greg gave here is not unreasonable limit setter for engine timer. Because, lets be frank, 5 hours continues operation before overhauls is not 5 minute limit. The 5 minute continuous limit is what we are debating here. Why it existed, what governed it, etc...

No you fundamentally do not understand the issue, or where Greg got his idea from. Greg got his idea that 5 minutes is for inter-cooler temp from pure speculation. He states this in the video.  There is no evidence anywhere in any documentation that the 5 minute limit is because the intercooler will overheat at that time. Not only do we know the  ACTUAL reason, as given in manuals and other sources, but the arbitrary time simply doesnt make sense. For example, if the inter-cooler was going to gradually overheat, the time limit would change depending the temperature, air speed, and what power setting was being run before WEP was initiated.

 

The cooling systems of these aircraft did not allow the inter cooler temperature to EVER reach a temperature that would result in detonation. In the few cases where a plane was poorly designed and cooling issues occurred at normal operating power settings, such as the Yaks, we know about it because it was considered to be unusual and undesirable.

 

From NAVWEPS 00-80T-80, which you should know that Greg quotes all the time. But he clearly has forgotten or does know know about this part.

 

 

 

 

[ZachariasX]

Maybe it is also time to point out that our engines in the game are almost undestructible, if it wasn‘t for the timer. The post above makes it also clear that most settings besides the ones recommended by the manual will kill the engine very quickly and they can do so short of full power output.

 

Common behavior in the throttle in MP matches kills engines much, much faster than the timer and again it can do so at much lower ratings.

 

It‘s just, if we got rid of the timer, then planes like the P-40 get a tremendous advantage as you can obscenely overboost them, but you cannot do that with more automated or regulated systems. Supposed 70 inches in humid aequatorial conditions or in the african desert are not 70 inches during russian winter.

 

If we had engines with the load tolerances of real engines, I think the 109 and the 190 again got an advantage, as you could keep on flying as you are used to in MP without fear of blowing the engine. In planes without automatation, you‘d be careful working your throttle like that. Now, German planes have just an (arbitary) advantage of a different sort.

[Cpt_Siddy]

12 hours ago, ZachariasX said:

 

 

Common behavior in the throttle in MP matches kills engines much, much faster than the timer and again it can do so at much lower ratings.

 

 

Yeah, this is what ill rather prefer to the timers, imo. 

There is myriad of things that can go wrong in engine, ill rather have them go wrong than some timer that will kill hard, but optimally, ran engine. 

 

12 hours ago, ZachariasX said:

Supposed 70 inches in humid aequatorial conditions or in the african desert are not 70 inches during russian winter.

 

 

Hot 70"inches develops less power than cold 70", just by the function of gas law (ignore the humidity to simplify the example), yes. This also translates to auto ignition point of the air fuel mixture. To get less denser air to the same pressure, you can compress the gas and warm the gas.. or  in the case of most ICE, both. The thing is, that in less dense tropical air, the heating will be playing bigger role. You are having less dense initial air at the same 70", meaning the gas is hotter. So assuming adiabatic conditions at the end of compression stroke, the air fuel mixture will be at higher temperature than colder 70" air.

This will have less oxygen available to generate energy AND run the risk of pre ignition aka Knock.

In this day and age of computers, i find it hard to think it cannot be modeled in such a refined product as IL-2.

Edited July 18, 2021 by Cpt_Siddy