P-40 turn rate/Flight model check

[Venturi]

Well the Boscombe Down P40E handling trials, parts 8, 10, and 17 describe the aircraft as both with and without 43gal belly drop tank and with 6 .50cal mgs as well as a gun camera fairing. They describe take off and landing trials with the belly tank off - they call it an "overload tank" - but it is a drop tank - (weight given at 8485lbs) and also with belly tank on, (8840lbs). 

 

HOWEVER, something is wrong here, because, in the weights description of the report, part 15, paragraph 4.2 and 4.4 - it breaks down like this:

 

Tare weight: 6098 - which they describe as a "light loaded condition with zero ammunition, and fuel sufficient only for 1/2hr running at max power, with a 170lb pilot."

Service load: 1358

Fuel of 123gal: 886

Oil of 17.5gal: 158

For a total weight of 8500lbs.

 

BUT, when I went to find out what "service load" was actually, I saw that "service load" as listed in the appendix that followed, included a 200lb pilot, along with other stuff like 1686rds ammo, 6x guns, etc, that were all listed as "total removable load" of 1358lbs!

 

In other words, I think they messed up on the weights! The plane was actually much lighter than the listed 8500lbs, since they started with a "tare weight" which was already a completely flyable aircraft including oil, half-hour's fuel, and 170lb pilot, then added the weight of another 200lbs for a pilot and parachute and another 158lbs for the oil! You can't fly a plane without oil or pilot! Not to mention a half-hour's worth of fuel which they double added for!

 

Additionally when I checked on the values of each individual line item like fuel, oil, guns, etc. They were all heavier in the RAF Boscombe report than the same items in the USAAF operating manual, by like 10-20% per item! I think the RAF fudged the weights!

Edited January 3, 2017 by Venturi

[Venturi]

Running a test, of 88mph (PEC of 90mph stall figure from USAAF handbook) at the weight I actually think the Boscombe Down tests were conducted at, 8000lbs or ~3630kg, a few pounds or so lighter than design weight, which accounts for fuel burn off, gives:

 

142km/h = v((3630*kg*9.81m/s2) / (1.225kg/m3*21.92m2*CLmax)) 

  142km/h=v(71221kg*m/s2 / 26.852kg/m*CLmax)

  1556m2/s2=(2652m2/s2)/CLmax

 

Gives PEC corrected CLmax of 1.70!

[unreasonable]

I've got other docs that list fully loaded weight as 8480 or 8500 pounds so something is up. Could explain the very high calculated clmax though?

 

No. Change the weight by x%, you change the Clmax by x% as well, as solving for Clmax the equation is Clmax = W / everything else. 

 

 

Yes, read again -

 

design weight + extra fuel... IE "IL2 standard load"... is listed in the operating manual as 8164lbs, and from the devs as 8420lbs!

That is assuming that "il2 standard load" isn't actually 120gal of fuel - not 100% fuel! - in which case, the actual weight listed in the handbook is 8012lbs, not 8420lbs!!

In other words, the P40 in game is being given an extra 260 - 410lbs of weight!

 

Not necessarily - it could just mean that they have a different definition of "standard".

 

Using data from https://forum.il2sturmovik.com/topic/25993-aircraft-flight-and-technical-specifications-and-operational/

 

The fuel load is given as 404 kg  = 891 lbs at about 6lbs per gallon in US convention this is 148 gallons. ie they are counting the alternate load 25.5 gal tank as standard.

 

I agree that to get close to the Il-s "standard" you have to include the alt 25.5 gallons (fair enough since this is the fuel load stated), plus oil alternative, plus the 20lb bombs (also fair enough if the plane is used as a fighter bomber) and the drop tank weight (empty - presumably most of this is in the fittings rather than the actual tank). Doing that I end up 36lbs under Il-2 standard: perhaps the Soviet pilots were actually fatter! 

 

I am fairly sure that there is a developer post somewhere that explained exactly what they included as standard.

[Venturi]

With the additional fuel tank and fuel, it should weigh ~8218lbs (need to add fuel tank weight, too!) Not 8420lbs, and that's assuming "standard load' is 100% IL-2 in game fuel!

 

Which it certainly wasn't for most P-40s! (The Boscombe P40E didn't have the extra "overload" fuselage tank, and the USAAF manual lists it as an option!)

 

Standard fuel load was 120gal or 454 L of fuel! Which with 6 guns and standard ammo is a weight of 8012lbs!

 

Why should extra oil and 6x 20lbs bombs and also a drop tank, all which aren't even an option in game, be the "standard loading" in IL2?

Edited January 3, 2017 by Venturi

[unreasonable]

IIRC it is only the drop tank fittings - presumably because the Soviet Lend Lease P-40s had them? Standard is as standard does - but in game you do not have to fly with them on, it is just an arbitrary convention they used to measure one data point in a range of weights.

 

For the purposes of understanding the Boscombe tests I agree that you need to get the weight right or the speed is meaningless (and visa versa), and the figure you come up with is pretty much what I have been using: namely the manual weights as you posted without bombs and drop tank, with a proportion of the fuel used. And I agree with your calculations. Add your PEC of 2 mph back and you get 1.63 - very close to our assumed airfoil.  

 

As an aside on the PEC I always wonder why the numbers/lines always run out above the stall speed region and we have to extrapolate. Looks like the document writers were not using the tests to calculate Clmax! Easier in a wing tunnel where you can measure the airflow directly. Presumably TAS at cruise etc is useful to know for navigational purposes so that is what is looked at.

 

The puzzle is just that the calculated Clmax at these weights is still at or above what we think the airfoil's is - subject to research - let alone the gap below this that seems to be the usual and is reflected in the Il-2 numbers.

So either there is no gap in this case or there is still a glitch with the IAS-TAS conversion.

 

For the Il-2 figures it does not matter that they are strictly comparable with the Boscombe numbers or not - what matters is pairing up Han's stall speed figures with his weight figures, as I tried to do. Without knowing the stall speed at the standard weight I just guessed it as the midpoint of the range. The minimum weight operational (not the empty weight) was paired with the lowest stall speed. But all three calculations come out within 0.02 of one another at 1.32-1.34

 

I would guess that if you ask Han why player tests show weight/speed relationships at stall that generate higher Clmax figures he will say that you were not in level flight up to the stall but descending a little, unlike his robot pilots, (which may also generally be true for RL pilots estimating IAS and altimeter by eyeball, but presumably if someone can make a cogent case to him you will get an explanation. 

[Venturi]

So, from tonight, the things I have seen are:

 

1. The weight for the configuration with extra fuselage overload tank should be 8218lbs, that includes 145.5gal of fuel, 6 mgs, 1410rds of ammo, per USAAF manual. Right now the "standard load" is 8420 pounds, so 202 lbs too heavy - of course that is assuming "standard load" in IL2 is with the extra fuel!

 

2. The actual "standard load" configuration was without extra fuselage fuel tank with 120gal fuel, and 6mgs, 1410rds of ammo, and the weight for that was 8012lbs. This should be the "standard load" in IL2!

 

3. The optional ammunition amount should not be 1686 rounds, which was an arbitrary amount of ammunition that the Boscombe trials had in their plane - but instead 1870 rounds per the USAAF manual. 1870 rounds adds 138lbs over the standard amount of ammo, not +84lbs for the 1686 rounds which we currently have as the "extra ammo" option.

 

I am still waiting on the data for the wing but I suspect we will find a CLmax for the design at around 1.6 - 1.65 at Re of 5mil, and a critical Angle of attack that is higher than 14deg, around 16deg - all based off 2212 data. But will hold off until the 2215 airfoil and P40 design data are available.

Keeping in mind the listed CLmax is around 1.33 right now, right unreasonable?

Additionally it would be good to ask him if cg changes are reflected in the CLmax of the aircraft.

I think if all these changes in the P40 were done it would really make the plane much more as it ought to be!

Edited January 3, 2017 by Venturi

[6./ZG26_Klaus_Mann]

 

 

2. The actual "standard load" configuration was without extra fuselage fuel tank, and 6mgs, 1410rds of ammo, and the weight for that was 8012lbs. This should be the "standard load" in IL2!

Extra Fuel Tank is the Barrel in the Back?

Was I correct all along then that the contradictory Reports about Spin behaviour are due to that? 

[Venturi]

So no, I do not think your theory is why the plane spins, I think it is for some other reason. Especially since the plane will spin even with little fuel on board. This behavior by the way is completely not talked about in ANY of the VERY detailed handling reports on the P40 I have recently been over. But it is a good point, that the tank should not be there in a "standard" configuration, since it is mentioned specifically as an alternate loading in the USAAF handbook.

 

Airplane has a very small stability margin in yaw. When angle of side slip is more than 12° plane becomes unstable in yaw and starts to increase the side slip angle by itself. Because of this, it is necessary to accurately operate the rudder pedals and pay attention to the side slip indicator.

Edited January 3, 2017 by Venturi

[Dakpilot]

Do not dogfight against Japanese aircraft, this is not the same operational advice that you get against German planes. In fact that thread repeatedly says you can outturn an E-3 and it's slightly faster. I don't think that the E-7 in game is substantially different than the E-3 other than a slightly more powerful engine aircraft wise?

 

It must be remembered that Erik Shilling is discussing the equivalent of P-40B Tomahawk (H81-A2) which is a very different animal, longer front end by six inches, different fuel tanks and  empty weight of 2356kg and a very different performance envelope

 

 

on a different note

 

On the first page of this thread Post #2 there is the Russian document showing weight of P-40E in 'turn comparison" as 3840kg, not reading Russian what are the specifics to that weight in the description? 

 

Cheers Dakpilot

Edited January 3, 2017 by Dakpilot

[unreasonable]

So, from tonight, the things I have seen are:

 

Keeping in mind the listed CLmax is around 1.33 right now, right unreasonable?

[ unr. edited to save electrons]

 

Correct, 1.32-1.35 assuming that my pairing of weight and speed as per the tech specs in my earlier posts is the same as theirs. 

Edited January 3, 2017 by unreasonable

[JtD]

Weight, according to the AP2014A Kitty Hawk I loading plan of August 1941, is 8492lb for the six gun version as modelled in game. The tare weight is 6081lb, the removable military load is 1365lb and consumables are 1046lb.

This is only slightly different from the part 15 of the 783 report "Weights and loading data" of a Kittyhawk I, which gives the total weight as 8500lb, tare being 6098lb, removable military load 1358lb and consumables 1044lb.

 

The tare weight is higher by about 100lb, so is the removable military load (adding items such as oxygen and ammunition boxes) and the consumables add about 200lb (full fuel and oil) compared to shown US data.

Compared to the in game standard configuration it carries 38kg of extra ammunition, but then it is 36-40kg heavier when compared to the in game 3819kg.

 

Therefore, the figure used in game is a 100% match for these two sources, but it would be interesting to know the loading details of P-40's in Soviet service, as they could have been lighter (or even heavier).

Edited January 3, 2017 by JtD

[Venturi]

Would you mind showing us the loading plan, then JtD? Since I have a handbook right here with data saying otherwise, which I have posted.

Here... from here...

P-40D E.pdf

[JtD]

Attached the Weights and loading data of the 783 report part 15.

 

The loading plan is part of the manual which you buy here:

 

http://www.flight-manuals.com/ap2014a-vol1.html

AVIA_734_Report_783__Part_15.pdf

[Venturi]

Right, you can't show us a page?

 

I have the other one already. 

 

Here is a google drive with all of the Boscombe Down docs. https://drive.google.com/drive/folders/0B4pKiKbNRE3FdWNMVEhyZU1kV0U?usp=sharing

 

appendix..

Edited January 3, 2017 by Venturi

[ACG_KaiLae]

I think we're seeing why only having limited data can cause issues. Also gentlemen, I do call your attention to this bug report which may be informative:

 

https://forum.il2sturmovik.com/topic/26074-inconsistencies-andor-errors-p-40e-1-fuel-system/?do=findComment&comment=426863

[Venturi]

I have seen that and it is confusing as both the Boscombe Down appendix and USAAF handbook I posted make mention of an additional fuel tank beyond the standard 120gal. They even go so far as to list its weight. It is not a drop tank because that too is listed separately at the same time.

 

Anyways regarding imperial vs US gallons, obviously it should be an American P40 they model, not a Brit... no offense to any Brits...

Edited January 3, 2017 by Venturi

[Dakpilot]

At this stage I would think that verifying (or at least having some consensus between 'testers') whether fuel use has an effect on change of C oF G in game, It is quite important

 

"obviously it should be an American P40 they model, "

 

I think the P-40E-1 in game is the British one sent by  lend lease,  E-1 being the export (Kittyhawk 1)

 

Cheers Dakpilot

Edited January 3, 2017 by Dakpilot

[unreasonable]

Anyways regarding imperial vs US gallons, obviously it should be an American P40 they model, not a Brit... no offense to any Brits...

 

None taken      ... but I suppose that depends on which batch they came from. Soviets had various versions some of which might have been from orders destined for the UK and then diverted - hence with Imperial instruments - and others with US instruments. Must have made life interesting for the ground crews used to metric. My guess is the devs mix and matched various instrument photos not realizing the difference, but I am sure they will dig into this and get it right in the end.

 

Great post by Cat btw as an example of how to lay out a problem.

[JtD]

At this stage I would think that verifying (or at least having some consensus between 'testers') whether fuel use has an effect on change of C oF G in game, It is quite important

Yes, it has. If you fly an aircraft with some rearward fuel tank, any 109, 190 or the P-40, this is blatantly obvious in any manoeuvre.

[Dakpilot]

Yes, it has. If you fly an aircraft with some rearward fuel tank, any 109, 190 or the P-40, this is blatantly obvious in any manoeuvre.

 

I agree but it has been said several times in this thread, that people are not sure....

 

 

 Soviets had various versions some of which might have been from orders destined for the UK and then diverted - hence with Imperial instruments - and others with US instruments. Must have made life interesting for the ground crews used to metric. My guess is the devs mix and matched various instrument photos not realizing the difference, but I am sure they will dig into this and get it right in the end.

 

Great post by Cat btw as an example of how to lay out a problem.

 

The in game P-40 is called the P40E-1 this is the Export Kittyhawk1A (H87-A4)

 

"The Kittyhawk IA was essentially the export equivalent of the P-40E. 1500 were built, primarily for the RAF, but many were diverted to Canada, Australia, and New Zealand. Following the passage of the Lend-Lease Act, all aircraft purchased with US funds had to have standard US designations and had to be issued USAAF serial numbers, even though they were never intended for service with the USAAF. Since the Kittyhawk IA was built with some British equipment, it was not exactly equivalent to the USAAF P-40E, and the Kittyhawk IA was assigned the US designation P-40E-1 (Model 87A-4) to recognize the difference.

 

Serials of the Kittyhawk IA:

41-24776/25195 c/n 18795/19214 RAF ET100/ET519

41-35874/36953 c/n 19395/19474 RAF ET520/ET999, EV100/EV699"

 

Cheers Dakpilot

Edited January 3, 2017 by Dakpilot

[unreasonable]

I agree but it has been said several times in this thread, that people are not sure....

 

 

 

The in game P-40 is called the P40E-1 this is the Export Kittyhawk1A (H87-A4)

 

Cheers Dakpilot

 

On the CoG thing is there a test that can be made where the effect can be quantified? Something like elevator trim for level flight at given speed/height etc at high vs low load outs? 

 

Presumably then the Export Kittyhawk which were mostly destined for use in the British Empire would have had Imperial instruments?

 

(Sometimes I wonder if all the low figures for stall speed are actually a typing error - the numbers are right but the units are actually knots....) 

[Venturi]

It should be asked of HAN or some other developer, to determine if the sim is taking into account rearward cg shifts. Since calculated values from the published weights are not giving large cg shifts.

The British Kittyhawks were beat to hell when the Soviets got them. The American ones were New and with support in the way of spare parts, etc.

Glad you and your elite group of crime fighters are taking it on yourselves to handle this. Hope the engine gets unlimited from being maxed at 56" at sea level, too. Details matter..

[unreasonable]

The British Kittyhawks were beat to hell when the Soviets got them. The American ones were New and with support in the way of spare parts, etc.

 

 

Yes I know, but if the "American ones" ie delivered straight from the US, were Export spec. ie P-40E-1 as Dakpilot says and I am sure he is right, they might well still have had Imperial instruments. So it is not a matter of British or American, but the spec details of American direct delivered P-40E-1s.

 

I agree details matter, BTW, the fact that they do is what makes this particular sim so interesting.

[JtD]

On the CoG thing is there a test that can be made where the effect can be quantified? Something like elevator trim for level flight at given speed/height etc at high vs low load outs?

You can literally feel it - just check out the wobbliness in flight. Additionally, try spins - the aircraft recover a load better with empty rear tanks. Or you can step on the brakes on the ground and see when it noses over. Or how easy it is to ground loop the thing.

Personally, I've checked that with the 109's, 190 and P-40, since they have large quantities of fuel to the rear of the centre of lift, and they basically handle like different aircraft if you alter between 10% and 100% fuel.

 

WRT to impact on spins:

 

https://forum.il2sturmovik.com/topic/25284-game-spinning-trials/

 

For instance, I couldn't stall a 109G with 10% fuel and full nose down trim, but could stall it with 100% fuel and full nose down trim.

[unreasonable]

You can literally feel it - just check out the wobbliness in flight.  

 

 

I will take your word for it: I would be reluctant to blame the wobbliness in my flight to anything other than my own wobbliness ....

[Sgt_Joch]

hi guys, came across these comments on the P40 in "Black Cross Red Star", vol. 2, p. 32. Thought you might find it useful.

 

"veterans...could use its advantages - maneuverability and reliable radio equipment - to compensate for its liabilities - low speed and poor climbing performance - with adequate tactics."

 

 

Edited January 3, 2017 by Sgt_Joch

[=362nd_FS=Hiromachi]

This is going so fast that its hard to follow now.

 

Sidenote:

And the conversation with Eric Shilling, who fought highly maneuverable Japanese planes, definitely brings out the point that it is the relative differences between aircraft that truly matter. In a fight against a Me109F, the P40 has a different set of advantages than over a Ki43.

I would not base any assumptions on Eric Shilling words, especially that he actually never fought any Japanese. He made quite a few flights in P-40 but no victories scored, then he spent rest of the war flying over The Hump. Most of his assumptions are purely theoretical and very subjective, based on other people experiences or intelligence reports, namely those related to A6M or to a some degree Ki-43. With first one AVG never fought, with latter one combat was sporadic. Main combat fighter of JAAF at given time was still Ki-27 Nate which is a decent factor in drawing conclusions of P-40 effectiveness and especially its maneuverability in comparison.  

Edited January 3, 2017 by =LD=Hiromachi

[Venturi]

And I think it is the height of impertinence to question the experiences and opinions of someone who was actually there and actually flew the plane, at a distance of 70+ years.

 

Saboru Sakai, maybe you've heard of him, he considered the P40 to be the among the most effective and formidable adversaries of the Allied planes he faced.

By the way, maybe you should also ask whether Chennault had any experience in dogfighting the P40. I'm sure he and Shilling swapped only a few conversational comments in passing about the P40...

http://www.chuckhawks.com/p-40_vs_zero.htm

[Crump]

Actually this part of your post is a good example of you drawing the wrong conclusions, presumably because you have not been reading the thread.  

 

What I showed was that Han's numbers had a range of weights and a range of stall speeds, and if you calculate Clmax for the stall speeds that probably correspond to the weights, you get the same answer in each case (within rounding error)  - just as you should.  See my post 320, repeated in 359. 

 

So I neither misunderstood the relationships nor drew the wrong conclusions. Do not blame me if you have not been following the thread.

 

Edit but see 369 below - the 0.03 difference I put down to rounding errors might be the CG shift.

 

 

Now you are stating it correctly and your previous statement left me confused as to whether you knew the correct relationships.  The effect of weight is change velocity not Coefficient of Lift or Angle of Attack the stall occurs.  Clmax will vary with CG position but because Velocity is squared, a small change in Velocity results in a large change in the Coefficient of Lift.

 

 

Let's examine in some detail the specific conditions being used in the NACA investigation to validate wind tunnel and flight testing methods.   These are NOT investigations to invalidate the design coefficients of lift but rather investigations to validate testing methodology.  The fact they are being misused by individuals to create the illusion it was somehow impossible to attain the design Coefficients is not only incorrect but will lead the community down a very rocky slope.  Simply put, the Devs will be modeling aircraft under testing conditions or aircraft with years of use on them and not properly constructed, finished, and delivered to the gaining service aircraft.  

 

Surface deformations from years of use do affect an aircraft.  Smoking rivets, wrinkled skins, loose fitting door, and deteriorating seals will greatly affect CLmax.  That is not representative of a properly constructed, finished, factory fresh aircraft.   Instead this is an aircraft with YEARS of service used behind it without refurbishment.  

 

 

The Last F6F-3 Hellcat was produced from 1943 until the Spring of 1944 and this report is from 1948!

 

 

That is 4 to 5 years of use compared to the fact most frontline aircraft lifecycle is measured in a months.  They note deficiencies in the rivets, access door seals, and paint deterioration.  That the surface is degraded to the point Reynolds Number has little effect is extremely telling.  Reynolds number has a large effect on CLmax with a normal finish.

 

 

In fact they not a loss of .21 in the CLmax from previous years testing all due to the poor condition of the aircraft. 

 

They note a significant loss of CLmax even from the previous year testing:

 

The report flat out states the quantitative data is not applicable to any other aircraft.  This is not a report on whether or not Grumman could achieve a design CLmax.  Achievement of the Design CLmax is an engineering norm and not something the NACA would put as the subject of an investigation.

 

 

 

It is not quantitatively applicable to any other F6F-3 because of the poor condition of the aircraft due to several years of use.  That is NOT a reason to doubt the validity of any design teams CLmax for a properly constructed and finished example.  That means Curtiss Aircraft Companies design CLmax for the P-40 is valid as it stands for an aircraft that is factory fresh.

 

Reducing that value would represent an aircraft in other than new condition and not as Curtiss intended.

[Dakpilot]

By the way, maybe you should also ask whether Chennault had any experience in dogfighting the P40. I'm sure he and Shilling swapped only a few conversational comments in passing about the P40...

 

 

 

I don't think Claire Chennault  flew any combat at all during Flying Tigers period, being nearly 50, he was a General and in charge of the whole operation not a Pilot

 

In 1937 it is said he met a few Japanese aircraft while doing a scouting flight for the Chinese Air Force in a Hawk 75, but until his death denied ever shooting one down

 

No disrespect to Gen Chennault, he achieved great success with the forces he had at his disposal

 

Cheers Dakpilot

[Holtzauge]

Surely Pilots are only interested in IAS, if they are told it stalls at 90mph in training, and it does when looking at the gauge, the PEC is irrelevant at these speeds to the operator?

 

or am I missing the point 

 

Cheers Dakpilot

 

Well as opposed to Crump, I think you are dead on when it comes to the stall.

 

However at higher speeds I guess one needs the PEC to get a correct IAS reading since without it you will mess up your TAS estimate which I assume would have been instrumental for dead reckoning navigation in those days sans GPS. At least that is my theory but you being an IRL pilot that AFAIK flies for a living can probably gauge this better.

 

 

Yes, as I have pointed out to you many times, accurate airspeed measurement was problematic at best in the 1940's. That is why normal force coefficients were used in flight testing Clmax because airspeed measurement was just too inaccurate.

No, this simply stems from confusion on your part because although it has been repeatedly explained to you, you still fail to understand how IAS can and was accurately measured at the time. So let me explain it to you again: The problem with an aircraft based IAS reading is that the near flow field varies to a large degree depending on the angle of attack which makes basing the IAS reading on a pitot and static ports attached to the plane problematic. The solution to this is the so-called trailing pitot system which is basically a pitot and static ports that can be winched out after take-off to do the reading in the so-called far field flow which is undisturbed and thus gives a very good IAS reading. This type of device is well known to people in the business who are well aware of the problem. For example, the British RAE used a trailing pitot system to derive accurate Clmax figures from flight trials both for the Spitfire and the Me-109. So no, as long as you know what you are doing, accurate IAS measuring was not even a problem back in the 1940's. So hopefully Curtis did similar measurements on the P-40 in which case we will get an accurate Clmax reading for the whole plane with warts and all. Hope it is clearer to you now? But this is kind of basic stuff so I suggest you google it to learn more. In addition, feel free to PM me if you have additional questions.

[Venturi]

Yes, my point being it is the society these men had, the conversations they had, and the responsibilities they felt for the men under their command which would have left them with a great deal of understanding

 

http://www.warbirdforum.com/dogfight.htm

[ACG_KaiLae]

I think we've probably reached the limit of what we can learn for now, until Crump goes to the smithsonian. Current items of interest:

 

1. Wing design information

2. Aircraft weight

 

I'd like to get information on Allison engines as well if there. Anything else?

[Farky]

Tare weight: 6098 - which they describe as a "light loaded condition with zero ammunition, and fuel sufficient only for 1/2hr running at max power, with a 170lb pilot."

 

Report do not describe Tare weight as a "light loaded condition with zero ammunition, and fuel sufficient only for 1/2hr running at max power, with a 170lb pilot.". It actually says -

 

"A more forward centre of gravity position of 17.1" aft may be obtained when the aeroplane is in light loaded conditions of Tare weight PLUS (!!!) a light pilot of 170 lb. and fuel reduced as in para. 4.2" i.e. "... fuel reduced to a suply sufficient for a half hours running of the engine at maximum power permissible at ground level".

 

 

In other words, I think they messed up on the weights! The plane was actually much lighter than the listed 8500lbs, since they started with a "tare weight" which was already a completely flyable aircraft including oil, half-hour's fuel, and 170lb pilot, then added the weight of another 200lbs for a pilot and parachute and another 158lbs for the oil! You can't fly a plane without oil or pilot! Not to mention a half-hour's worth of fuel which they double added for!

 

 

 

Weight in RAF report is right, because it is the result of the actual weighing. There is no room for speculations and is it fully consistent with some other data. Not all of them of course, but most of them.

 

 

Additionally when I checked on the values of each individual line item like fuel, oil, guns, etc. They were all heavier in the RAF Boscombe report than the same items in the USAAF operating manual, by like 10-20% per item! I think the RAF fudged the weights!

 

US vs. Imperial units, for sure.

 

 

Right now, IL2 dev numbers list empty weight at 6775lbs, or 3073kg!

 

Like unreasonable says - just a different definition of "empty weight". Empty weight in BoX is just fully equipped aircraft minus fuel, ammo, pilot and Vodka/Schnapps/Chianti.

 

 

Therefore, the figure used in game is a 100% match for these two sources, but it would be interesting to know the loading details of P-40's in Soviet service, as they could have been lighter (or even heavier).

 

Weight from Soviet manual for P-40E-1  - 3840 kg  (8 466 lbs.) fully loaded (100% fuel, 1560 rounds of ammo).

 

------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

 

@Farky, do you have one of those indexes as well for the Allison engine company where we could also pull documents for the V-1710-39 and -73 engines? We might as well get everything we would need once. Also, perhaps one for Bell Aircraft for the P-39?

 

Yes I have, probably, somewhere. But IMO, we do have all informations about V-1710-39 we need, no issue here. Issues are - inadequate (not detailed enough) simulation of engine use beyond official limits (this is for a long debate) and different opinions on the use of engine beyond official limits (even longer debate). Neither of these issues will be solved sufficiently for lack of hard data, such data just don't exist.

 

As for P-39 - let developers do their work first. 

 

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Stall speed - 90 mph IAS is not the only number we have in documents. For example -

RAF manual for P-40E says 92 mph IAS "clean" and 82 IAS gear down - flaps down and also "The above stalling speeds are subject to plus or minus 2 mph, depending on load.".

Same manual few pages later - "The corrections for position error are as follows: At 60 mph IAS reading subtract 3.5 mph, at 80 mph IAS reading subtract 2.0 mph, at 100 mph IAS reading subtract .5 mph ...".

My point is - calculation cannot be accurate, if basic figures are inaccurate or at least uncertain. Just my 2 cents.

[Crump]

 

 

No, this simply stems from confusion on your part because although it has been repeatedly explained to you, you still fail to understand how IAS can and was accurately measured at the time.

 

That is why the NACA published these reports because they simply do not agree with you at all.

 

 

The measurement of the airspeed of airplanes by means of instruments attached to them is an almost universal practice, but the results of such measurements are often very inaccurate, particularly with installations used for normal flight .

 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081388.pdf

 

A suspended head system is more accurate than the standard instruments.  It is hardly free from error and in fact has it's own set of limitations/error.  Stability being one of them and lag errors due to the length of the tube.  They do not do well in maneuvering flight and a much more susceptible to errors dues to atmospheric instability and gusting effects.

 

They are ideal for stall testing in comparison to other systems in that they are most accurate in unaccelerated flight at low airspeed.  Without any wind and completely smooth air they do have much smaller margin of error when compared to other forms of airspeed measurement used in the 1940's.

 

They are not accurate enough to provide any meaningful insight in CLmax in a simple lift formula analysis based on 1940's era airspeed measurements, however.

 

Which is exactly why the NACA used normal force coefficients from acceleration data to calculate CLmax in flight.  

 

Think of it like this....if airspeed was so accurate then why did they do that??  Oh yeah, because airspeed measurement was not accurate enough in the 1940's.

[Crump]

Because Airspeed Measurement was soooooooooooo accurate....they decided to ignore it and go with this other extra step....

 

 

Have I got that Right Holtzauge?

 

[=362nd_FS=Hiromachi]

And I think it is the height of impertinence to question the experiences and opinions of someone who was actually there and actually flew the plane, at a distance of 70+ years.

 

Saboru Sakai, maybe you've heard of him, he considered the P40 to be the among the most effective and formidable adversaries of the Allied planes he faced.

By the way, maybe you should also ask whether Chennault had any experience in dogfighting the P40. I'm sure he and Shilling swapped only a few conversational comments in passing about the P40...

http://www.chuckhawks.com/p-40_vs_zero.htm

There were many people there, including ground crews, intelligence officers and all kinds of others. They sure heard a story or two either. But it was proven long ago that 1st hand pilot memoirs, especially reconstructed after many years are inaccurate. They are important no doubt Venturi, but they also have to be carefully analyzed. And here we have an issue of a pilot who claims to know all the details (which he carefully expressed many years ago in one of online discussions, I have links somewhere still, also arguing with Dan Ford about overall AVG knowledge and effort) yet never flew against any of the opponents he mentions. He assumes things about a Zero against which he never flew, not to mention that AVG never encountered any Zero in direct or indirect combat. They had a chance to evaluate one captured in China but it was rebuild model with numerous limits.

 

I know very well what Sakai expressed. Keep in mind he had high opinions about most of his opponents, which also tells that he was conscious of not underestimating any opponent. He also considered the same way F4F and few other aircraft, not to mention Hellcat. Does it say anything about aircraft flying qualities ? Not exactly.

I can provide another quote from a different place, New Guinea, when recalling 1942 combat experiences of RAAF No. 75 Squadron, pilot Pete Masters said:

"There was much more we know now that we didnt know before we got to New Guinea, like the ability of Zeros to outperform us, contrary to what we had learned before we arrived. We were told that Japanese Zero was an upgraded copy of he Harvard Trainer as used by the Empire Air Scheme in Canada. It was underpowered and flimsy with very light aluminum and canvas cladding sometimes joined by canvas at the extremities. It had no armour plate to protect the pilot, and although it was reputed to fly higher than the Kittyhawk, it was also much slower and inferior in almost all its characteristics, including firepower.

 

I am now sure that all this misinformation came about because very few Allied fighters had encountered Zeros in combat proper to New Guinea and those that had in Malaysia, the Philippines, or elsewhere had never had a chance to examine the real specifications of this amazing aircraft in close quarters. In fact when I at last saw a Zero on the ground and crawled all over it I too was amazed at the rigidity of its structure and its apparent fighting qualities from the cockpit. In our combat assessments at Port Moresby during the 44 days we fought, we soon concluded that head-to-head combat between Kittyhawk and Zero was unwise, and at all altitudes above 20,000 feet was simply dangerous.

 

They were much more maneuverable and could outclimb us in the ratio of two or three to one. What they didnt have was our weight and pilot protection with 1/2 inch armour plate behind the pilot and in the firewall. Our battle plans therefore always included a desire to get above the enemy, if possible into the sun, and then to break away and come back for another shot. If we had height we could always get away from the Zero but with equal skills as pilots on both sides, the Zero always had the advantage at the same height and also could maneuver much more effectively, especially above 20,000 ft where the Kittyhawk would tend to "fall out of the sky".   

Eagles of the Southern Sky by Luca Ruffato and Michael J. Claringbould, Tainan Research & Publishing 2012, page 278.

 

I'm not even going to address that linked article, it has no sources listed and contains multiple errors. Stick to numbers Venturi, like Crump, Holtzauge or Jtd do. Second hand opinions, particularly from very different front, wont tell you much.

[Holtzauge]

That is why the NACA published these reports because they simply do not agree with you at all.

 

 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081388.pdf

 

A suspended head system is more accurate than the standard instruments.  It is hardly free from error and in fact has it's own set of limitations/error.  Stability being one of them and lag errors due to the length of the tube.  They do not do well in maneuvering flight and a much more susceptible to errors dues to atmospheric instability and gusting effects.

 

They are ideal for stall testing in comparison to other systems in that they are most accurate in unaccelerated flight at low airspeed.  Without any wind and completely smooth air they do have much smaller margin of error when compared to other forms of airspeed measurement used in the 1940's.

 

They are not accurate enough to provide any meaningful insight in CLmax in a simple lift formula analysis based on 1940's era airspeed measurements, however.

 

OK so the problem according to you is that they are unreliable in gusting and manouvering conditions? Well who would have guessed that! Maybe you should not do stall testing while manouvering and in gusting conditions? You know I think this train of thought may have occurred to those guys doing the testing back in the 1940's as well.....

 

Anyway, this method was apparently good enough for the RAE (that's the Royal Aircraft Establishment in case you did not know) who beg to differ and I'm more inclined to trust their judgement than yours and I would kind of trust them NOT to publish Clmax figures derived during gusting and manouvering conditions but that's just me.....

 

Crump: BTW I think I'll quote you on this one though: "They are ideal for stall testing in comparison to other systems in that they are most accurate in unaccelerated flight at low airspeed"!

Edited January 3, 2017 by Holtzauge

[Crump]

Quote it all you want.  

 

 

 

Anyway, this method was apparently good enough for the RAE (that's the Royal Aircraft Establishment in case you did not know)

 

 

Probably why the RAE whined so much when the NACA said the Spitfire Clmax was so much lower than the RAE "measurement", LMAO!!

 

[Venturi]

"A more forward centre of gravity position of 17.1" aft may be obtained when the aeroplane is in light loaded conditions of Tare weight PLUS (!!!) a light pilot of 170 lb. and fuel reduced as in para. 4.2" i.e. "... fuel reduced to a suply sufficient for a half hours running of the engine at maximum power permissible at ground level". Ok - so then oil, which is 158lbs? That magically disappeared from the "empty" aircraft which flew? What other things were double-counted for?

 

Weight in RAF report is right, because it is the result of the actual weighing. There is no room for speculations and is it fully consistent with some other data. Not all of them of course, but most of them. So then how is there not room for speculation? You realize this means CLmax must be around 2.0... show us some data before concluding this because I for one have one USAAF source saying one thing, and another saying something different.

 

By the way, the guns weight varies too, RAF report - 463lbs for 6x .50cal... USAAF report - 384 lbs

So does the oil, RAF report - 17.5gal, 158lbs ... USAAF report - 16gal, 120lbs (1.5gal of oil does not weigh 38lbs!)

Wireless... RAF report - 160lbs plus another 147lbs for accessories, USAAF report - already has radio in "empty" or "tare" weight of 5982lbs!

Gun camera... RAF report - 10lbs, USAAF report - ABSENT in standard load, but when present, 3lbs!

 

Etc, etc, etc.

 

So who is right? More importantly, which is the "standard" load and what is that load in the game? 100% fuel? You do not know so it is premature to assume.

 

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Yes I have, probably, somewhere. But IMO, we do have all informations about V-1710-39 we need, no issue here. Issues are - inadequate (not detailed enough) simulation of engine use beyond official limits (this is for a long debate) and different opinions on the use of engine beyond official limits (even longer debate). Neither of these issues will be solved sufficiently for lack of hard data, such data just don't exist. Sure it does. It just isn't in the format that computer game-players and software developers trust.

 

As for P-39 - let developers do their work first. It will be easier since it is MAP-regulated.

 

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Stall speed - 90 mph IAS is not the only number we have in documents. For example -

RAF manual for P-40E says 92 mph IAS "clean" and 82 IAS gear down - flaps down and also "The above stalling speeds are subject to plus or minus 2 mph, depending on load.".

Same manual few pages later - "The corrections for position error are as follows: At 60 mph IAS reading subtract 3.5 mph, at 80 mph IAS reading subtract 2.0 mph, at 100 mph IAS reading subtract .5 mph ...".

My point is - calculation cannot be accurate, if basic figures are inaccurate or at least uncertain. Just my 2 cents.

 

 

It still gives a ballpark of CLmax of approximately 1.8-2.0 with the weight you listed. Even at 8000lbs, which I think much more likely the explanation, it is 1.7.

Edited January 3, 2017 by Venturi