P-40 turn rate/Flight model check

[Venturi]

I think the defining point for the initiated here, is that I can induce a near unrecoverable spin from simply using rudder in a straight line at 200mph. That is baloney.

 

Additionally it cannot fly or maneuver at low speeds with the 109e, by all accounts it was more capable at low speed dogfighting than the 109F. Again, baloney.

Edited December 24, 2016 by Venturi

[Stig]

The problem with people like you, Stig from Denmark, is that you demand "evidence" and then discount it when it is presented. You are not interested in doing the work to understand, because your mind is already made up. 

 

 

 

I can't say whether the FM of the game's P-40 is correct or not, nor have I commented on that. I am just curious as to what is  the  'historical representation' of the  P-40 that you want?

The history I see being presented for the most part is very subjective and largely based on what happened from the Allied side. You can easily get the impression that the P-40 was at least equal to the 109 if you just look at the claims; however, when you try to match those claims with actual 109 losses, then the P-40 doesn't look quite as effective anymore.  

[6./ZG26_Klaus_Mann]

I think the defining point for the initiated here, is that I can induce a near unrecoverable spin from simply using rudder in a straight line at 200mph. That is baloney.

 

Additionally it cannot fly or maneuver at low speeds with the 109e, by all accounts it was more capable at low speed dogfighting than the 109F. Again, baloney.

I can't. I actually made a Video showing that you can't. It will not Spin the way you describe. 

 

The Problem I see is that it seems to produce too little lift on the transition from low to high angles of attack, so that instead of turning at medium AoA and therefore medium drag, you turn at waaay too high AoA, high drag and get too little turn.

 

The Stall/Spin is absolutely fine.

[Venturi]

I can't. I actually made a Video showing that you can't. It will not Spin the way you describe. 

 

The Problem I see is that it seems to produce too little lift on the transition from low to high angles of attack, so that instead of turning at medium AoA and therefore medium drag, you turn at waaay too high AoA, high drag and get too little turn.

 

The Stall/Spin is absolutely fine.

 

 

Oh, like these?

 

 

Edited December 24, 2016 by Venturi

[Dakpilot]

I think the defining point for the initiated here, is that I can induce a near unrecoverable spin from simply using rudder in a straight line at 200mph. That is baloney.

 

Additionally it cannot fly or maneuver at low speeds with the 109e, by all accounts it was more capable at low speed dogfighting than the 109F. Again, baloney.

 

The FM update of over effective rudders should be a help in this area, to try and advocate for change before this overall patch is introduced seems a wrong use of effort.

 

It also has the largest rudder, which exacerbates the issue, I would also guess that this large over effective rudder will have unnecessary corresponding drag which also does not help overall, but the aircraft was known for instability , the tail extension on later F etc. models was needed, and pilots appreciated its change in handling  

 

 

The P-40E weighed more than the Me-109G6! it is no lightweight, about 700 kg heavier than an E7 with similar power, no slats, and a not much lower wing loading, mid between Hurricane and 109E,

 

What is there in it's specs that suggest it should be able to 'fly' with an E7, or an F4 for that matter?

 

Cheers Dakpilot

[6./ZG26_Klaus_Mann]

Oh, like these?

 

 

These are not Spins, these are Flick Rolls like this: 

 

As well as unintentional Flick Rolls (not Spins) 

 

These are Spins: 

 

You are Flick-Rolling  the Aircraft. 

Edited December 24, 2016 by 6./ZG26_Klaus_Mann

[Venturi]

At which part of the envelope are you referring to Dakpilot, 

 

Diving, it will be better (2880kg empty for P40E, 2050kg empty for Bf109E7)

Climbing, it will be worse (0.40hp/kg for P40E, 0.57hp/kg for Bf109E7)

Low speed turning should better, but need CLmax - wing loading approx equal (131kg/m2 for P40E, 128kg/m2 for Bf109E7, empty weights)

Power, it is the same (1150hp for Allison, 1158 for Db601N) - but Allison should be able to be pushed harder than Db601N

 

Again, the 109E7 is leagues ahead of the P40 in this game, it is not even a contest. 

The P40E should be able to maneuver just fine with the 109E, which at this moment, is one of the most maneuverable planes in this game...

Edited December 24, 2016 by Venturi

[Venturi]

Well your first video is a snap roll, not a flick roll as you state. That requires crossed controls, IE, left aileron with right rudder, full back elevator. I am not doing anything other than rudder input at level cruising speed in my videos. IE, no aileron OR elevator input.

 

Your second video includes aileron input into the rudder, with full back elevator, inducing a flick role. There is no aileron input or elevator input in my videos.

 

Your third video shows excessive rudder input at edge of stall, but what happens is identical to what occurs at level cruising speed of 220mph in my video, with only 60-70% rudder input.

 

Your fourth video is again, on the edge of a stall with full rudder, regardless it too shows what happens in my video...

 

a spin.

 

 

Edited December 24, 2016 by Venturi

[ACG_KaiLae]

IMO spin behavior is not important to check until after we confirm the wings are simulated correctly. Neither is the rudder behavior in a dive.

 

There's a lot to go over, in time.

[Venturi]

No doubt, there is.

[6./ZG26_Klaus_Mann]

You get into a spin after 1 or 2 FULL ROTATIONS. A Cessna Effing 172 Will Spin all day if you do that. It proves absolutely nothing at all. And what really do you expect in an Aircraft with a Full Fuel Tank in the rear? Try the Same thing with 330 liters and you will have absolutely no Spin. 

It's the fuel load that makes all the Difference. 

 

Anyways, let's fight the Battle of Lift/AoA first. 

 

 

PS: This Film puts the Stall Speed Clean at 92 and Dirty at 82 mph. Also: Stalling results in a Spin of 1000ft per turn according to them. 

 

Many of the Pages I read about the stability of the P-40 also say that it lacked a Supercharger, so I wouldn't trust those too much.

Of course I can only infer, but I know enough about Aircraft to know that the Fuel Tanks and Fuel Amount as well as wether Armor was fitted etc. would have made a huge difference in behaviour, more than in most other fighters. 

Unfortunately the Manuals don't specify Spin behaviour by fuel, instead they flatout forbid it. They warn of improper Coordination leading to Spins, constant Trim Changes and everything leads me to believe that the ingame Aircraft represents pretty much all that's said. 

"Stability" is vague, to some it can mean that it simply cruises with very little Control Input, to others it can mean Manouvering. So the same word has two meanings. 

 

I can reasonably infer the Negative Effect on Characteristics by looking at both the Mustang and Spitfire, both of which exhibited worse flying characteristics when the Tank behind the Pilot was full. Same applies for the P-39 which exhibited worse flying characteristics when the 37mm Ammunition was expended shifting the weight bias rearwards. 

Why would this not apply for the enormous barrel behind the Pilot's Seat?

 

You seem to have very accurate Expectations from very vague wording, but I think your Epistemology seems faulty and controlled by your opinions and intentions. 

Edited December 25, 2016 by 6./ZG26_Klaus_Mann

[Venturi]

And I think you have a national bias

[Farky]

 

 

... but the aircraft was known for instability , the tail extension on later F etc. models was needed, and pilots appreciated its change in handling  

 

 

No, it wasn't known for instability, please stop saying that or show some evidence. Tail extension was needed for other reasons than "instability" and I already tell you this at least twice.

[6./ZG26_Klaus_Mann]

And I think you have a national bias

I'll take it as a compliment being called biased by all sides. I read what I can, I form an opinion, I fly the ingame Aircraft and see if it matches. 

 

And I'm not entirely happy with a lot of the engine modelling, in all honesty I rather would have liked a 1943 P-40E for BoS and a 1941 P-40C for BoM. That would have given the Devs more Leeway with those. 

I also think that adjusting Lift Coefficient will help you with your spinning Problem as well. 

 

Stability is such a vague term and in many ways the P-40 is stable.

 

It is amazingly good at flying straight when trimmed, without need for adjustments, almost like an Airliner. It is a bit like a Bf110 in that way. No other ingame fighter can compare and I never need Autolevel. 

That is one Checkmark for Stability. 

 

You can pull it from 600 to 250kph, stick  to the belly and it will keep straight and true. So in a continouos turn it is Stable. 

 

It will exit Spins just by centering the controls, so Spin behaviour is Stable. An unstable Aircraft would Flatspin, a thing the P-40 never does. 

 

In sharp, low Speed Manouvering the stability around the Vertical Axis is the only point at which it doesn't seem overly stable. It get's better the less fuel you carry though. 

 

However, the one thing that clashes with the stability claims for me is the constant mention of Trim Adjustments and warnings of Stall/Spin Characteristics and requiring good Coordination, It has nothing to do with National Bias, just that there seems to be a dissonance. 

Edited December 25, 2016 by 6./ZG26_Klaus_Mann

[Dakpilot]

Ok slip of the tongue, I should have said stability issues in certain areas rather than Instability, and 'stability issues' is a bit of a catch all as well.

 

see my pilot anecdotes from earlier, long tail Kittyhawk III much better handling-short tail 'edgy'

 

The subjects of P-40 issues is easily found, this from a guy researching a book on P-40

 

"The P-40 had stability issues in in high speed dives and low speeds at landing. At high speed dives the tail forces were often too great for the pilot to control the aircraft, some times resulting in shredding of the rudder fabric, sometimes removing the aft fuselage, and usually putting the pilot in a tough spot. The solutions were to limit the dive speed, extend the tail (which would have delayed production), and add the tail fillet until such time as the tail could be lengthened. (Sorry - there are tons of reports on on this stuff, but I haven't had time to study them all yet.)

When landing, the traditional approach was to aim for a three-point landing. While this had worked for the P-36, the results weren't so good on the P-40 with its lengthened nose. So many aircraft were damaged ground looping in landing accidents that the Army quickly used up all its spare wings and had to steal Tomahawk wings from the British-bound production line. (The resulting mating of Tomahawk wings and P-40 fuselages was designated P-40G.) There were three solutions: increase the size of the wing fillet (compare the first P-40 photos with the shots from late 1940 to see the difference); lengthen the tail wheel (I still have trouble seeing the difference in photos, but all tail wheel struts were eventually lengthened), and land on the main wheels only until the aircraft slowed enough for the tail to drop. (which lessened, but didn't eliminate, ground looping). "

 

And there is much more

 

"The most visible difference between the P-40F and the preceding versions was its rear fuselage, which was lengthened by 25.72 inches (starting with P-40F-5 variant) in order to improve lateral stability. Curtiss delivered over 1,300 P-40Fs between August 1942 and January 1943. The British, who received only 150 aircraft (of the early, short-tailed P-40F-1 variant), called it Kittyhawk Mk II."

 

"The later versions of the F had a lengthened fuselage in an attempt to compensate for longitudinal stability problems. This solution was only marginally effective."

 

"There was another significant change from the P-40F-5-CU and P-40K-10-CU blocks onwards when the fuselage was lengthened to cure some stability issues."

 

Why did the P-40K (Kittyhawk III) also get an extended tail fin as well as fuselage extension said to be for helping continued directional stability issues?

 

"The P-40K was a development of the P-40E easily recognized by its extended vertical tail fin, an unsuccessful attempt to cure the P-40’s lateral instability issues."

 

 

There is so much info out there even from books directly quoting designer Don Berlin being very unhappy with Curtiss and the 'stop gap' solutions to issues being made, himself wanting to make more fundamental changes, which were refused by Curtiss due to the need to halt production which would make them default on army contracts.

 

The later models were quite simply much better than earlier D/E versions, which whatever way you want to look at had 'issues" unscientifically mention by many pilots, there is loads more info out there but I am not going to copy from books, they are available there to read

 

I have never flown a P-40 of any model, and so can only get my info from what is available, but on reading a lot I have made a considered opinion

 

Which of course could be wrong

 

Cheers Dakpilot

[Dakpilot]

At which part of the envelope are you referring to Dakpilot, 

 

Diving, it will be better (2880kg empty for P40E, 2050kg empty for Bf109E7)

Climbing, it will be worse (0.40hp/kg for P40E, 0.57hp/kg for Bf109E7)

Low speed turning should better, but need CLmax - wing loading approx equal (131kg/m2 for P40E, 128kg/m2 for Bf109E7, empty weights)

Power, it is the same (1150hp for Allison, 1158 for Db601N) - but Allison should be able to be pushed harder than Db601N

 

Again, the 109E7 is leagues ahead of the P40 in this game, it is not even a contest. 

The P40E should be able to maneuver just fine with the 109E, which at this moment, is one of the most maneuverable planes in this game...

 

 

Just consider this for one minute (after Christmas dinner)

 

If you strapped on 830 KG (your figures, for difference P-40E/109E7) to the E7, would it perform better or worse?, and remain one of the most maneuverable planes in the game

 

Cheers Dakpilot

[Farky]

Did you read this NACA report Dakpilot? I am sure that I posted this in response to you already.

 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092648.pdf

[Venturi]

End of pg 5 for the TLDR ^

Just consider this for one minute (after Christmas dinner)

 

If you strapped on 830 KG (your figures, for difference P-40E/109E7) to the E7, would it perform better or worse?, and remain one of the most maneuverable planes in the game

 

Cheers Dakpilot

Yes, if I strapped 830 kg.... and added wing area, with a different airfoil and wing rootlets to boot.

 

You do realize that matters, yes? Slats induce a quite large amount of drag when open, you also realize that?

[6./ZG26_Klaus_Mann]

End of pg 5 for the TLDR ^

 

Yes, if I strapped 830 kg.... and added wing area, with a different airfoil and wing rootlets to boot.

 

You do realize that matters, yes? Slats induce a quite large amount of drag when open, you also realize that?

The 109E also has a DB601A-1 ingame, with the 2600rpm increase of November 1940, so 990 PS at 1.3ata. With full Revs it may actually get above 1100, maybe 1200, but that's an extreme setting you wouldn't use in offensive combat. 

The Comparison should favour the P-40 a bit more, not massively, but it's not as clear cut as he put it. 

 

The P-40 despite total P/W disadvantage has the exact same Speed Range of 460 Cont and 475 at 5 Minute Setting. The P-40 will go 575 at full throttle, the Emil about 505. 

So concerning either Propeller Efficiency or Aerodynamics the P-40 seems to have the Nose well ahead, and since the VDM Props were literally Rainbows excreted by an  Alpha Unicorn, it has to be Aerodynamics. 

Edited December 25, 2016 by 6./ZG26_Klaus_Mann

[Venturi]

The 109E also has a DB601A-1 ingame, with the 2600rpm increase of November 1940, so 990 PS at 1.3ata. With full Revs it may actually get above 1100, maybe 1200, but that's an extreme setting you wouldn't use in offensive combat. 

The Comparison should favour the P-40 a bit more, not massively, but it's not as clear cut as he put it. 

 

The P-40 despite total P/W disadvantage has the exact same Speed Range of 460 Cont and 475 at 5 Minute Setting. The P-40 will go 575 at full throttle, the Emil about 505. 

So concerning either Propeller Efficiency or Aerodynamics the P-40 seems to have the Nose well ahead, and since the VDM Props were literally Rainbows excreted by an  Alpha Unicorn, it has to be Aerodynamics. 

 

Would be interesting to see how the props are modeled, indeed... 

 

There is no doubt that the planes should be similar in top speeds at their best respective altitudes... at least at official power ratings.

 

Obviously if you add in 340hp from pushing the Allison to 56", it will make a difference. I am not sure if it should get the P40 to 575kph at sea level, which is 357mph (I assume your figures are TAS at sea level). 

 

Revised, using the power output of 1085hp for the Db601A-1 (by the way, 2600 rpm was only approved over FTH when supercharger pressure dropped off - increasing RPMs only helped power at altitude by spinning SC faster to increast boost back towards best pressures, so 2400rpm is still the correct revs for maximum power... per official docs...), the stats are now:

 

Diving, it will be better (2880kg empty for P40E, 2050kg empty for Bf109E7)
Climbing, it will be worse (0.40hp/kg for P40E, 0.53hp/kg for Bf109E7 .... but using 1490hp @ 56" - a real 5min WEP rating for the Allison - then you get 0.52hp/kg for the P40E...)
Low speed, turning should better but need CLmax - wing loading approx equal (131kg/m2 for P40E, 128kg/m2 for Bf109E7, empty weights)
Power, P40E has more (1150hp for Allison, 1085hp for Db601A) - and Allison should be able to be pushed harder than Db601A...

Edited December 25, 2016 by Venturi

[ACG_KaiLae]

I'll have some data tomorrow, and then we can have some facts to go from.

[6./ZG26_Klaus_Mann]

I'll have some data tomorrow, and then we can have some facts to go from.

I'll be back home from X-Mas in a couple O'Days. 

[BlitzPig_EL]

I have just placed a call to the curator of the Glenn H. Curtiss Museum in Hammondsport NY, in an effort to find more data.

 

Left a message, and I sure hope I get a call back.  I'm off this week and have time to dig in to some things.

[Crump]

 

 

I have just placed a call to the curator of the Glenn H. Curtiss Museum in Hammondsport NY, in an effort to find more data.

 

I hope he has some information. In the second part of January, I will be at the Smithsonian archives looking for the information we need on the P-40E.

[ACG_KaiLae]

Second phase of tests, ran run at 284 IAS. Results by testing, 458.515 KPH, which is 284.908 MPH. 

 

How necessary is the slower speed run? It's proving quite difficult to get this, because anything under about 50% throttle causes AOA to rise, which increases drag, which decelerates the plane more, needing more throttle - which then speeds up the plane. I can probably get one at about 150 MPH but not slower than this reliably because of constant throttle manipulation needed.

[Willy__]

 

 

How necessary is the slower speed run? It's proving quite difficult to get this, because anything under about 50% throttle causes AOA to rise, which increases drag, which decelerates the plane more, needing more throttle - which then speeds up the plane. I can probably get one at about 150 MPH but not slower than this reliably because of constant throttle manipulation needed.

 

Do you need to stay at a constant RPM ? If the answer is "no" you can try changing the RPM, so the plane will acelerate slower, making it easier on the throttle.... I guess... ? 

 

Anyways, good luck with testing. 

[ACG_KaiLae]

Ok, so ran run at 158 MPH, which is about as reliably slow as I can get it. Results, completed course with TAS of 255.268 KPH, which is 158.616 MPH.
 

From what I can see, difference at sea level between IAS and TAS is less than 1 MPH indicated, being between .6 to .9 MPH. Because it's not really possible to determine if the speed was actually a fraction between say, 158 and 159 MPH by reading the speedometer, it's actually likely less than that.

[Venturi]

In other words, CLmax is way off...

Clean stall of 96mph in game, should be 90mph. I've got a couple inquiries out on this, too.

[ACG_KaiLae]

I got 95 by my testing, which matches the official data. That is still a 6% variance.

[JG13_opcode]

In other words, CLmax is way off...

Clean stall of 96mph in game, should be 90mph. I've got a couple inquiries out on this, too.

 

6.6% error seems pretty good to me.  Certainly I would not call it "way off".

 

Wasn't Oleg's standard in the old sim 10%?

Edited December 28, 2016 by JG13_opcode

[Solty]

6.6% error seems pretty good to me.  Certainly I would not call it "way off".

 

Wasn't Oleg's standard in the old sim 10%?

10% can a be a big number at times.

[ACG_KaiLae]

6.6% error seems pretty good to me.  Certainly I would not call it "way off".

 

Wasn't Oleg's standard in the old sim 10%?

 

The max amount that they state as allowable is 5%. However, that's stall speed. I'm going to guess that the lift coefficient is off and causing the issue. Do we have enough data to calculate what the clmax in game is?

 

Ideally, obviously, the error should be 0. Considering the importance of having the wings set up right - see FW-190 - if this is off a correction should be looked into.

[Venturi]

6.6% difference at stall speed induces a large difference in stall speed as g increases, since it is in the denominator...

 

V(g) = √( 2*W*g / ρ*S*CLmax ) 

Where,
V(g) = Stall Speed at (x)g
W = Weight of the aircraft
g = acceleration at (x)g, for 1g it is 9.81 m/s²
ρ = Density of Air
S = Wing Area
CLmax = Coefficient of Lift at Stall

 

 

Example A (from in game testing)

155km/h = √((2*2880kg*9.81m/s²) / (1.225kg/m³*21.92m²*CLmax)) 

  155km/h=√(56505.6kg*m/s² / 26.852kg/m*CLmax)

  1854m²/s²=(2104m²/s²)/CLmax

  

  gives CLmax of 1.13!

 

 

Example B (from Boscombe trials)

145kph = √((2*2880kg*9.81m/s²)/(1.225kg/m³*21.92m²*CLmax))

  145km/h=√(56505.6kg*m/s² / 26.852kg/m*CLmax)

  1622m²/s²=(2104m²/s²)/CLmax

 

  gives CLmax of 1.30!

 

 

But actually, what we are really looking for, is stall speed at any given acceleration (g loading). Obviously, as g increases, so too does the airspeed at which the aircraft will stall.

 

Let's see...

 

Example A (current in game) CLmax, for stall speed at 5g

  Stall @ V km/h = √((2*2880kg*49.05m/s²) / (1.225kg/m³*21.92m²*1.13))

  Stall @ V km/h = √(282528kg*m/s² / 30.343kg/m)

 

  gives 5g stall at 347kph!

 

 

Example B (Boscombe trials) CLmax, for stall speed at 5g

  Stall @ V km/h = √((2*2880kg*49.05m/s²) / (1.225kg/m³*21.92m²*1.30))

  Stall @ V km/h = √(282528kg*m/s² / 34.91kg/m)

  

  gives 5g Stall at 324kph!

 

 

Now, imagine a 20% relative simulated inaccuracy in favor of one aircraft over another, as we have currently, between the P40E and the Bf109...

Edited December 29, 2016 by Venturi

[ACG_KaiLae]

I'd prefer to leave out the 109; that's a topic for a later time. Still if what is above is correct it's basically the same difference in the 190 that is due to be fixed.

[JG13_opcode]

Look, the nature of floating point mathematics in x86 processors ensures that it is 100% impossible to ever get an exact match.

 

Some error is strictly unavoidable due to the way computers represent numbers internally.

 

At some point we need to accept a result as reasonable. 6.6 % error in stall speed between the game and historical tests is acceptable in my book.

The max amount that they state as allowable is 5%.

Ambitious. Got a link for that statement?

[ACG_KaiLae]

I thought I did, but offhand, I can't find it at the moment. 

 

Is the math correct above for clmax?

[Venturi]

Look, the nature of floating point mathematics in x86 processors ensures that it is 100% impossible to ever get an exact match.

 

Some error is strictly unavoidable due to the way computers represent numbers internally.

 

 

 

Baloney.

[Venturi]

The other thing to consider is theoretical WING CLmax vs empiric AIRCRAFT CLmax.

 

Personally, I would take empiric data over theoretical data any day, because it is derived from actual flying aircraft and thus encompasses all variables.

 

It would be great fun to do a testing and calculation of ALL aircraft empiric CLmax, derived from their published stall speeds, wing areas, and weights, and see how it matches the CLmax in game... no wing polars or other elusive data needed.

 

Or I guess we could just fix the P40? 

Edited December 29, 2016 by Venturi

[JtD]

The P-40 used a NACA 22xx series airfoil, which for instance was also used on the Spitfire. It should have a similar maximum lift coefficient, and that of the Spitfire was tested to be 1.36 (power off). With the Yak-1 modelled at 1.33, the P-40 should end up in that region, too.

 

Venturi, I'm curious why you calculate the in game lift coefficient with a weight of 2880kg, considering that "Minimum weight (no ammo, 10% fuel): 3264.2 kg" is stated by the developers. In what condition did you test?

[Venturi]

Yes, I was making a point by being conservative.   

 

Fully loaded for the P40E, as I assume Boscombe 90mph stall test was from, is 3,760kg.