P-40 turn rate/Flight model check

[Crump]

 

 

Yes 1.82 is with power on. The 1.36 is with power off. This is kind of basic Crump and something you learn rather early on in aerodynamics classes. I'm sure if you google it you can find some more info. Try also googling slipstream effects. That should point you in the right direction.

 

Thank you for that but I do not need it.  Again, still looking at where you are getting the 1.36 as the design Clmax......

 

Why don't you stop trying to get the thread locked and playing games.  Just answer the question!

Oh...you want the thread locked because it is getting uncomfortable as the details come out.  You got nothing to fear Holtzauge, right?

[Holtzauge]

I already told you: The Clmax for the Spitfire comes from Royal Establishment report TN 1106. In it the British aerodynamicist M. B. Morgan states that the Clmax of the Spitfire is 1.36. If you have issues with that then I suggest you start your own thread and explain why he got it wrong and stop derailing this thread.

[Crump]

 

 

Royal Establishment report TN 1106. In it the British aerodynamicist M. B. Morgan states that the Clmax of the Spitfire is 1.36

 

RAE TN 1106 is about the Avro Vulcan and nothing to do with the Spitfire....

 

http://naca.central.cranfield.ac.uk/reports/arc/cp/1106.pdf

Just post a copy of the report you are referencing so we can see the details.

[Holtzauge]

Sorry Crump but what you refer to as RAE TN 1106 is RAE C.P. 1106 which is not the same as TN 1106: TN 1106 was authored by M. B. Morgan in March 1943. TN is the abbreviation for Technical Note and I have no idea what C.P. stands for but as you say it seems to be about the Vulcan and appears to be from April 1960.......

 

Still, this has nothing to do with the P-40 so you are continuing to derail.

[Crump]

Wow....

 

 

 

ust post a copy of the report you are referencing so we can see the details.

 

Missed that part huh?     

[unreasonable]

The National Archives has it  (TN 1106 - Stalling characteristics of Supermarine Spitfire VA airplane, and measurements of flying...), but not online, so I have paid the fee to find out how much it will cost to get a digital or photocopy done.  Might be amusing to have to hand when the Spitfire makes it to BoX for the next round of the endless struggle.

 

The relevance to P-40 FM? Simply that there is a generic problem of measuring CLmax and relating it to wing/airfoil CLmax, so it is instructive to look at as many cases as possible before interpreting the data for any particular plane.

[JG13_opcode]

It's on Mike Williams' site in .pdf

[unreasonable]

Is it? Could you link to it please.

 

All I can find there is the NACA report on the subject, not RAE TN 1106 which Holtzauge reports has different conclusions, plus a bunch of other MkV material none of which mentions stall speeds. 

[Kurfurst]

Is it? Could you link to it please.

 

All I can find there is the NACA report on the subject, not RAE TN 1106 which Holtzauge reports has different conclusions, plus a bunch of other MkV material none of which mentions stall speeds. 

 

Could have spared the coin, but thanks for your efforts, I could have sent it to you. The title was suspicious anyway, its about a Mark VA that NACA tested in late 1942, and there is a RAE doc on it in early 1943. And its known the UK guys did not fully endorse and commented on the NACA trials (which are much hated in certain communities to this day, as they are quite professional and objective )

[unreasonable]

Could have spared the coin, but thanks for your efforts, I could have sent it to you. The title was suspicious anyway, its about a Mark VA that NACA tested in late 1942, and there is a RAE doc on it in early 1943. And its known the UK guys did not fully endorse and commented on the NACA trials (which are much hated in certain communities to this day, as they are quite professional and objective )

 

You could still send it to me - all I have done so far is ask for a quotation! 

[Kurfurst]

You could still send it to me - all I have done so far is ask for a quotation! 

 

Great! Will do! 

[ZachariasX]

http://www.wwiiaircraftperformance.org/NACA-Spitfire-V-Stalling.pdf

 

This report?

 

On page 7 they give it a

 

power off Clmax of  1.15 - 1.18

power on                 1.63 - 1.68

 

As well as a funny comment after that table. That one comes rather close to trolling, as far as official reports go. Starting a concluding sentence with "Apparently... " and then poo-poo on the "apparent" design choices. Priceless. Imagine they had a forum instead of exchanging official reports.

 

I hope that there's more than this report about the Spitfire. What I find telling is their laconic indifference about finding something that should be somehow surprising given even the wing profile should have a much higher Clmax.

[unreasonable]

No, not that one. That is the NACA report that Holtzauge says the RAE did not like. That is just a couple of Yanks being sniffy: NIH.

[Venturi]

Be definition, aircraft CLmax can be calculated at the level flight stall speed, if weight is known for that particular loading. The only limits on that are measurement errors.

 

Clean stall speed of P40E at 86-90mph with 8500lbs gives CLmax of 1.7 to 2.0.

[Kurfurst]

No, not that one. That is the NACA report that Holtzauge says the RAE did not like. That is just a couple of Yanks being sniffy: NIH.

 

If you mean the RAE response to that, IIRC the whole paper is a single page or two along the lines 'we don't like some of NACA conclusions' - of which perhaps a single short paragraph is dedicated to the Spitfire's Cl and disagreement in its calculation methods.

 

That is, a short a memo. Nothing that would merit this discussion dedicated to it IMO, but I guess other personal factors have intervened in that as well.

[ZachariasX]

 

 

That is, a short a memo. Nothing that would merit this discussion dedicated to it IMO, but I guess other personal factors have intervened in that as well.

 

See, forists are nothing new to this world. They just were not called that way back then.

 

But I shall be happy to see some further good documentation on the P40 (as well as on the Spit).

[Holtzauge]

At work now but I'll post RAE TN 1106 when I get home this evening ;-)

[Farky]

http://www.wwiiaircraftperformance.org/NACA-Spitfire-V-Stalling.pdf

 

This report?

 

 

No, this Technical Note - http://www.spitfireperformance.com/rae1106.pdf

[Kurfurst]

It seems Farky beat me to it! 

[JG13_opcode]

 

 

Is it? Could you link to it please.

 

Thread's already well off topic.  Spitfire has nothing to do with the P-40 and I'd rather not contribute to more red herrings. 

[ZachariasX]

Thread's already well off topic.  Spitfire has nothing to do with the P-40 and I'd rather not contribute to more red herrings. 

Yes, it is. But I had a good laugh again reading through the document. I quote:

 

[...] The conclusion that "the excellent stall warning is obtained at the expense of a high lift coefficient" is not borne out by the Royal Air Establishment measurements quoted above. [...]

 

What a nice way to phrase "F*** YOU, amateur!" and really matches the laconic tone of the previous report. Now, what the reality really is and who is actually somehow amateurish remains to be seen.

 

 

Back OT: I think this is very instructive that even "scource data" has to be taken with a grain of salt, wherever it comes from. This also in the case of the P-40. All we can do is look up different tests, do some sanity check on the results, try to understand what exactly they did as experiments, how they performed it as well as for what purpose they did the individual report.

[unreasonable]

Thread's already well off topic.  Spitfire has nothing to do with the P-40 and I'd rather not contribute to more red herrings. 

 

Of course it is on topic, if the topic is the reliability of measurements in stall testing determinations of CLmax, which it has to be given that, as Venturi posts, the P-40 stall speed numbers on the face of it give a CLmax considerably higher than that of the wing (or at least than an airfoil that is only marginally different), which seems to be physically impossible, or at least in need of explanation.

 

One possible type of explanation relates to the technical specifications of the P-40. Perhaps someone will discover some relevant data, perhaps not. I am not holding my breath.

 

The other possible types of explanation is completely general: perhaps there is a factor that the lift equation does not include. Perhaps there are systematic problems with measurements.

 

The NACA/RAE dispute (thanks Farky) suggests the latter.

 

Looking at the NACA data is interesting, since there must be information missing in the report. Using their stated numbers for stall speed and weight gives you a CLmax of 1.21 (F up), so I assume there is an undocumented speed adjustment of about +2mph addded to the stated 91 mph to give CLmax 1.16 (or that their formula includes something else).

 

In contrast, suppose you accept the RAE figure of 1.36: in that case, at the NACA test weight the stall speed (EAS) must have been  85.7mph 

 

So that is a 7.3mph difference - 8.5% of the RAE number.

 

So if even NACA and the RAE disagree about the stall speed of the Spitfire by as much as 8%, why should we have strong faith in the numbers for stall speeds in the P-40 manuals?

Edited January 9, 2017 by unreasonable

[JG13_opcode]

It's a document about the spitfire.  This is a thread about the P-40.  Any relevance is tangential at best and should be split off into its own thread.

[unreasonable]

I strongly disagree, because it is speaks to a completely general problem about using stall speeds from manuals that has just happened to rear it's ugly head in the case of the P-40.

 

Perhaps a more general thread is required: but you cannot solve the "P-40 problem" in isolation, since it is not an isolated example of the problem.

 

The same CLmax/ manual stall speeds issue arises in the Spitfire.

 

From Spitfire II manual (from here http://zenoswarbirdvideos.com/Images/spit/Spit2Manual.pdf)

 

"Approximate stalling speeds when loaded to about 6,250lbs are: Flaps and undercarriage up, 73 mph ASIR"

 

Stick those numbers in with a Spitfire wing of 22.5m^2 gives you a CLmax of 1.90    Yet the RAE is saying (for a MkI) 1.36

 

That is equivalent to a 13mph difference in stall speeds from the RAE figure, and 20mph from the NACA figure.  Both NACA and RAE must have come up with a stall TAS considerably higher than the manual's suggested AIS - not somewhat lower, as Venturi suggests should be the case in the P-40. Why is this? They either measured the AIS differently from eyeballing it in flight (as discussed in the NACA document) and/or applied different PECs.

 

This is clearly relevant.

[Venturi]

It's not I who suggests, it's the USAAF and RAE PEC reports, as well as the technical theoretical explanation listed previously..

[Venturi]

However the point is being made, that if the same lift equation as I used in the P40s case to illuminate the difficulties, is also used in the Spitfire's case to determine empirical aircraft CLmax...

 

...then we also have the same problem as with the P40, that is, an aircraft whose CLmax is far in excess of the plain wing CLmax.

[unreasonable]

However the point is being made, that if the same lift equation as I used in the P40s case to illuminate the difficulties, is also used in the Spitfire's case to determine empirical aircraft CLmax...

 

...then we also have the same problem as with the P40, that is, an aircraft whose CLmax is far in excess of the plain wing CLmax.

 

Or, that the AIS-TAS conversion is problem in both cases, if you start from the manual's numbers rather than from carefully calibrated flight tests.  

 

In the Spitfire, you have both NACA and RAE agreeing that the plane's CLmax is well below that of the wing/airfoil. It seems far more probable to me that the case of the P-40 is similar, for similar reasons, rather than that the P-40 had some strange individual characteristics that allow it to outperform it's theoretical wing limit.

 

The only thing that will solve this to everyone's satisfaction (perhaps) would be a  whole plane wind tunnel test.

[ACG_KaiLae]

It's a document about the spitfire.  This is a thread about the P-40.  Any relevance is tangential at best and should be split off into its own thread.

 

I'd agree that discussion about this is roughly about 6 months too soon. As for how accurate the data is: You can only use the data you have, not the data you wish you had. Meaning, that if you suspect there was instrumentation error, how much? More to the point, exactly how much so it can be precisely defined and accounted for. I very much doubt you can say with absolute precision if this is the case. In probably every case there is some error that is in the measurements, but it's the best information we have or are going to get, so it's what we'll have to go with. Unless you want to get an actual P-40E and stall it on a radar range. 

 

Again, I doubt anything useful will be learned with regards to the P-40 until we get the manufacturer's documents. 

Edited January 10, 2017 by Kai_Lae

[unreasonable]

Well, Kai_Lae it is your thread so I make a final comment and then leave it at that.  (edit V. Interesting thread, BTW, thanks for "curating").

 

I forecast that the Spitfire threads will be exactly the same, because it is the same problem. 

Edited January 10, 2017 by unreasonable

[JG13_opcode]

It seems far more probable to me that the case of the P-40 is similar, for similar reasons, rather than that the P-40 had some strange individual characteristics that allow it to outperform it's theoretical wing limit.

If by "theoretical limit" you mean the airfoil data, then you are correct. Not a single real wing achieves a CLmax equal to the sectional airfoil clmax. To do so would violate the laws of physics.

 

I forecast that the Spitfire threads will be exactly the same, because it is the same problem.

I actually think they'll be more civil without Crump's constant belligerence and derailment of threads. He's a reasonably knowledgeable guy; just not as knowledgeable as he portrays himself. I don't think he's an engineer. His degree is in "Aeronautical Science" which is not an accredited engineering program. (Not to say that you need to be an engineer to know things)

Edited January 10, 2017 by JG13_opcode

[ZachariasX]

As long as we keep on are discussing data istead of "truth", we shall be fine.

[Sgt_Joch]

so more on the P40s wing warp. This quote from a RAF Kittyhawk pilot gave me the idea:

"... not an easy aircraft to fly properly and as a result, we lost a good number of pilots while training."

"In the first few months after conversion to Kittyhawks, all the squadrons lost heavily to the 109s."

"I found that one had to have a very strong right arm to fly the Kittyhawk I during most maneuvers. In dive-bombing, the aircraft would pick up speed very quickly in the dive, but it had a great tendency to roll to the right. One could trim this out reasonably well with the left hand, but even then when one pulled up, it wanted to roll to the left quite viloently. So I learned to trim about halfway in the dive and hold the control stick central by bracing my right elbow against my right leg and the right wall of the cockpit. It was also distracting to have one's left hand on the trim all the time, when it should be on the throttle."

"In a dogfight, with violent changes of speed, it was all one could do to fly the aircraft."

"Kittyhawk II... was a definite improvement in lateral stability over the Kitty I."

"Eventually, with the Mk IIIs, the Kittyhawk became a good, stable fighting aircraft, although it never did have enough power or climbing ability compared to the 109s or the Spitfire."

https://ww2aircraft.net/forum/threads/p-40-vs-me-109.12342/#post-333491

 

I tried this out in QMBs against AI 109F2, if you use a lot of positive elevator trim, i.e.+ 50%, while maneuvering you can out turn the 109 a lot more easily and then return to a more normal -10-20% negative trim when in firing position.

 

In fact, if while holding the turn, you bring the trim back to a more neutral position, you will see the 109 start to out turn you.

Edited January 10, 2017 by Sgt_Joch

[Venturi]

Or, that the AIS-TAS conversion is problem in both cases, if you start from the manual's numbers rather than from carefully calibrated flight tests.

 

In the Spitfire, you have both NACA and RAE agreeing that the plane's CLmax is well below that of the wing/airfoil. It seems far more probable to me that the case of the P-40 is similar, for similar reasons, rather than that the P-40 had some strange individual characteristics that allow it to outperform it's theoretical wing limit.

Don't forget the Spitfire which has the same problem. It would be instructive to do more of the IL2 simulated aircrafts' empirical CLmax'es. I've already done the 109E7 and found that its calculated CLmax from the dev numbers is very similar to the measured value of CLmax that the RAE aircraft tests determined from the trailing pitot method.

[Holtzauge]

I did some new C++ simulation estimates on the P-40 but this time at sea level (the previous were at 1 Km) but since it seems unclear if the IL-2 P-40 turn times given by the developers are at maximum or combat power I did two simulations:

 

My sea level estimates                                         Il-2 new estimate                       Difference %  

 

P-40E with 1150 hp: ca 24.5s                              24.3s                                             -1%

 

P-40E with 1470 hp: ca 20.9s                              24.3                                               +16%

 

Anyway, I would assume that the 24.3 s turn time number for the IL-2 P-40 at 270 Km/h is for the combat power 1150 hp since AFAIK the turn times posted by Han for the other planes are also given at combat power? If that is the case then it looks like the IL-2 model is spot on.

 

Of interest here is that at 270 Km/h the P-40 is engine power limited in both simulations: With 1470 hp the engine power manages to pull the P-40 around with a Cl of circa 1.2 and with 1150 hp it can manage a Cl of 1.1. So even if the Clmax of the P-40 is higher than the 1.35 I have assumed it’s not going to help: The P-40 is simply power limited and would not be able to utilize a higher Clmax to improve the stationary turn rate.

 

So IMHO there is nothing strange about the 24.3 s turn time in IL-2 since the P-40 is simply hampered by the laws of physics: It’s a pretty heavy plane compared to the engine power.

[Holtzauge]

Another thing to bear in mind regarding the Spitfire Clmax when it comes to judging how NACA did it compared how the RAE did it is that NACA calibrated by flying in formation with another aircraft (which I have to agree with the RAE seems like a rather coarse method) and the RAE used a rather cumbersome approach which involved winching out the IAS measuring device to get it out of the flow field disturbed by the airplane. There is a reason they went to all that trouble and that is that in theory that should provide a much more accurate estimate than measuring in the near field where flow conditions vary a lot between high speed flight and stall. So with that in mind I would be more inclined to believe the RAE measurement. In addition, remember that the RAE also measured the Clmax of a captured Me-109 using the very same method to 1.4 and that the Germans themselves estimated the Me-109 Clmax to.........you guessed it.....1.4.

[ACG_KaiLae]

Well, since Crump got banned, we'll need another person to see about going to the Smithsonian to get the docs we need. I'll see about finding someone else in the area that might be willing. Is there a charge for accessing the documents we need?

[6./ZG26_Klaus_Mann]

Well, since Crump got banned, we'll need another person to see about going to the Smithsonian to get the docs we need. I'll see about finding someone else in the area that might be willing. Is there a charge for accessing the documents we need?

It's the Internet dude, and we are all just human. It may be frowned upon, but if you have a really important message that can't wait the month or so of being banned just create a Second Account with a different Email. 

I do get carried away sometimes, and that gets me bans all the time, which I tend to respect. 

[-WILD-AlbinoHA5E]

It's the Internet dude, and we are all just human. It may be frowned upon, but if you have a really important message that can't wait the month or so of being banned just create a Second Account with a different Email. 

I do get carried away sometimes, and that gets me bans all the time, which I tend to respect. 

But just as often there is need for positive Content out there and the Ban is there to restrict negative behaviour, but just like Prisoners working outside Prison, good content doesn't have to be crippled by Restrictions set upon you through negativity.

[BlitzPig_EL]

Kai_Lae, yes the NASM charges for documents.

 

As I recall it's by the page, but I don't remember how much they charged me to photocopy the P36 docs that I got years ago.

[6./ZG26_Klaus_Mann]

But just as often there is need for positive Content out there and the Ban is there to restrict negative behaviour, but just like Prisoners working outside Prison, good content doesn't have to be crippled by Restrictions set upon you through negativity.

And a Second account can also help keeping your Main Account to Positive Content and if you are part of a Squad it really helps you image not being a Male Donkey all the time.