Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: oboe on March 03, 2001, 08:00:00 AM
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Does anybody have a good method of establishing turn performance numbers for AH aircraft?
I'm interested in testing the a/c but a little unsure how to measure instantaneous turn rates, corner velocities, etc. I've checked over Iddon's turn methods for WBs a/c testing, but at 6g in AH I am blacked out and can't see the instruments...
Thanks!
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Originally posted by oboe:
Does anybody have a good method of establishing turn performance numbers for AH aircraft?
You can use the minimum turn radius "index number" method. To use this method, you need to know the following:
Gross Weight.
Wing Area in Square Feet.
Maximum Lift Coefficient.
Finding or determining the lift coefficient will be your biggest challenge.
Here's how it works:
Gross weight/wing area/lift coefficient= turn rate index.
Here's the calculation for the P-38L:
Without 8 degrees of Fowler flaps.
17,100/327.5 = 52.21/2.17 = 24.06
With maneuvering flaps deployed:
17,100/369.8 = 46.24/2.73 = 16.93
Let's compare the P-38L to the F4U-1:
11,800/314.0 = 37.58/1.48 = 25.39
The F4U performs so badly due to the spoiler added to the right wing (to cure the wing drop in a stall condition), which kills the lift coefficient.
On the other hand, the big P-38 turns remarkably tight if the pilot sets the flap handle to the 'maneuver' position. By doing so, the P-38 can turn with the Hellcat and run rings around the P-51 and any Luftwaffe fighter. The P-38 pilot could briefly tighten his turn by deploying his dive recovery flaps in the turn, which would pitch up the nose. Amazingly, the huge P-61 Black Widow can turn tighter than all the above with a 16.0 index #.
Finally, lets look at the index # for the A6M5:
6,025/229.3/2.46 = 10.68
Here's some index numbers for some AH aircraft:
F6F-5: 16.52
P-38L: 16.93
P-51D: 21.49
F4U-1D: 25.39
P-47D-30: 24.68
A6M5: 10.68
Others:
FM-2: 11.99
P-63A: 14.87
P-40B: 15.30
So, let's put them in order of turn index:
1) A6M5
2) FM-2
3) P-63A
4) P-40B
5) P-61B
6) F6F-5
7) P-38L
8) P-51D
9) P-47D
10) F4U-1D
If you locate the Lift Coefficients of the other aircraft in AH, you can calculate their turn index relative to each other.
My regards,
Widewing
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One additional note: Forget calculating the coefficient of lift. The formula is extremely complex and requires data that can only be determined emprically. As a rule, this is determined experimentally in a wind tunnel.
My regards,
Widewing
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Do I read correctly? you say that the F4U1-D should turn worse than the P51D?
I find that hard to believe.
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Widewing,
F4U max Cl with 50 degrees flap is 1.88.
I will post the naca doc with max cl's all birds.
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Originally posted by Widewing:
emprically??!!
Empirically....... I should have used the spell check button.
My regards,
Widewing
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Originally posted by R4M:
Do I read correctly? you say that the F4U1-D should turn worse than the P51D?
I find that hard to believe.
Both aircraft, no flaps, the Mustang wins. Also, the Mustang had a maneuver setting for the flaps, which tightens the turn radius further.
My regards,
Widewing
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Originally posted by Widewing:
Both aircraft, no flaps, the Mustang wins. Also, the Mustang had a maneuver setting for the flaps, which tightens the turn radius further.
My regards,
Widewing
well that now really **really** surprises me...from my experience, in AH, Corsair turns better than P51D, with or without flaps.
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And the USN thought so too I believe...
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Originally posted by F4UDOA:
Widewing,
F4U max Cl with 50 degrees flap is 1.88.
I will post the naca doc with max cl's all birds.
I would expect that the flaps would increase the Cl by as much as 50%. However, flying in combat with the flaps deployed at 50 degrees isn't recommended.
I assume you will be referencing NACA report #829?
My regards,
Widewing
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A pity that Cl numbers are variable with the conditions they are measured under... (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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Turn radius = V^2 / G load / g
with V in ft/sec and g = 32.2 ft/sec^2, answer in ft.
In a level turn, the radius will be a bit bigger than that, cause you won't be banked 90 degrees. You can find the bank angle by
cos^-1(1/G), so for 3g, the bank angle is 70.5 deg.
Then take the inverse sine of the bank angle to modify the radius, so that
1/sin(70.5) = 1.06
This means that the radius will be 6% greater than calculated above. Reason # 829 why one should use the vertical for turning! (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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Widewing,
You mentioned.
One additional note: Forget calculating the coefficient of lift. The formula is extremely complex and requires data that can only be determined emprically. As a rule, this is determined experimentally in a wind tunnel.
Here is a simple calculation for max CL as long as you know the 1 G stall speed.
Here is the F4U-1D from the pilots manual stall at 96MPH IAS clean power on 11,300lbs
Cl = Lift * 391 / (V^2 * Area)
Cl = 11,300lbs * 391 / (96.66MPH^2 * 314)
Cl = 1.50
BTW the F4U also had a maneaver flap setting of 20 degrees.
Here is the P-38L from the pilots manual the 1G stall at 17,000 is 100MPH IAS, however the correction table for airspeed IAS to CAS(calibrated air speed) shows that the 106MPH IAS is actually 120MPH CAS. Meaning that an indicated stall of 100MPH is really closer to 114MPH. So using 114MPH as the 1 G stall number here is the max Cl.
Cl = 17,000LBS*391 / (114MPH^2 * 327.5)
Cl = 1.56
Which falls more clearly into the range of most WW2 fighters, being between 1.40 and 1.60. You may say that the P-38 had a high aspect ratio wing giving it more lift, however it had two large engine nacelles breaking up the lift generating part of the wing. When you consider that it only had 327 sq. ft of wing at a loaded weight of over 17,000lbs (wing loading over 50lbs per sq foot) it is easy to see why it required fowler flaps to maneuver effectively in the horizontal plane.
compare it too these landing weight wing loading numbers
F6F-5 = 32.2
F4U-1 = 33.3
P-51B = 35.3
P-47D = 39.7
P-38J = 44.4
Regards
F4UDOA
[This message has been edited by F4UDOA (edited 03-03-2001).]
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You can also use the Russian method, by measuring the time it takes to turn 360 degrees without losing or gaining any altitude. They called it "Turn Times".
Of course this is sustained turn rates, rather than instantaneous turn rates.
Easy to test in the game if you have some time and stopwatch. Best to repeat the test 5 times for each aircraft and take the average.
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Vermillion
**MOL**, Men of Leisure
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Ah, Verm's getting at more of what I'm after - a way to measure in-game performance of the aircraft as AH as them modelled. Sorry if I was unclear. Those equations are interesting but I don't have accurate, consistent weight figures for the aircraft, let alone wing area and Cl.
Verm, doesn't every aircraft maximize its turn rate at corner velocity? And every aircraft has a different corner velocity doesn't it? How do I determine at which speed to enter the turn, and how many G's I can pull?
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Originally posted by F4UDOA:
Cl = Lift * 391 / (V^2 * Area)
Cl = 11,300lbs * 391 / (96.66MPH^2 * 314)
Cl = 1.50
Don't you mean:
L X 391 / V^2 / A
11,300 x 391 / 96.66^2 / 314 = 1.506
This is a bit higher than the NACA number of 1.48
Let's try you formula for the F6F-5, power on, clean:
12,500 x 391 / 75.2^2 / 334 = 2.588
This is a lot higher than NACA's 2.27 for this aircraft.
BTW the F4U also had a maneaver flap setting of 20 degrees.
This wasn't really a 'maneuver setting', but rather being able to lower the flaps to about 20 degrees max. However, there are speed restrictions for the F4U. There are no speed restrictions placed on the P-38 for the 8 degree Fowler setting. At least, I can't find any. Any fighter can lower its flaps to increase lift and tighten the turn radius in a combat situation. Only the P-51 and P-38 have a flap system specifically engineered for that purpose.
By the way, you are using the power-off stall speed for your calculation. Power-on is typically 6 mph less (according to Stan Richardson, P-38 instructor).
Cl = 17,000LBS x 391 / (108MPH^2 / 327.5) = 1.74, which is well below the 2.17 number from the NACA data.
The problem with this calculation is that it ignores the many factors that contribute to, or take away from the maximum lift coefficient. That is why many hundreds of hours were spent in the wind tunnel. If it came down to a simple calculation, why would NACA have spent such enormous resources to determine it empirically? This calculation does not factor in assymetical wash from the propeller. Nor does it account for the fact that more than 50% of the P-38's wing is blown by the prop wash. Nor does it account for the P-38's center wing sections being in what is, essentially, a channel. This prevents cross span flow and significantly increases lift.
If you don't already have it, go up to the NACA server and download a copy of Report No. 829, Summary of Measurement in Langley Full-Scale Tunnel of Maximum Lift Coefficients and Stalling Characteristics of Airplanes.
Also go up to:
http://www.lerc.nasa.gov/Other_Groups/K-12/airplane/foil2.html (http://www.lerc.nasa.gov/Other_Groups/K-12/airplane/foil2.html) and have a try at their FoilSim program. It's an interesting diversion.
Diz Dean publishes the clean Cl for the following aircraft:
FM-2: 2.38
P-63A: 2.38
P-61B: 2.54
F6F-5: 2.27
P-51D: 1.89
P-38L: 2.17
P-47D: 1.93
F4U-1D: 1.48
My regards,
Widewing
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Don't you mean:
L X 391 / V^2 / A
Same thing! You know, when dividing by a fraction, you invert and multiply? Note the brackets in DOA's equation.
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Originally posted by wells:
Same thing! You know, when dividing by a fraction, you invert and multiply? Note the brackets in DOA's equation.
I suppose that being up since O-Dark Thirty this morning has been dulling my mind a bit. No, I completely missed the brackets in the equation. That's it, it's time to get some sleep. This staying awake for 20 hours, two days in a row is too much. I've been trying to finish an editing job due by Wednesday, so I've been working since the wee morning hours, taking time to visit here for a break. I should finish up by tomorrow night. I hope so, 'cause it's looking like I'll be sending Monday shoveling snow.
My regards,
Widewing
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Diz Dean publishes the clean Cl for the following aircraft:
FM-2: 2.38
P-63A: 2.38
P-61B: 2.54
F6F-5: 2.27
P-51D: 1.89
P-38L: 2.17
P-47D: 1.93
F4U-1D: 1.48
Oh toejam, not this again!!! (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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Widewing,
You used the F6F as an example
Let's try you formula for the F6F-5, power on, clean:
12,500 x 391 / 75.2^2 / 334 = 2.588
This is a lot higher than NACA's 2.27 for this aircraft.
That is too high, but for two reasons.
1. The F6F does stall at 75MPH but not at 12,500lbs. I don't have a pilots manual for that A/C but I know that listed stall speed is for a landing condition just as the 11,300 is for a less than full load for the F4U and the 17,000lbs is for the P-38. The actual weight would probably be just under 12,000lbs.
2. The equation I used is not in metric units. If you use this equation which compensates more accurately for air density at sea level it is more accurate.
Lift (N) = Cl * wing area (square meters) * density (kg/m^3) *
velocity^2 (m/s) / 2
Which is
Cl = 2 * 53410 / (29.19 * 1.225 * 45^2)
= 106820 / 72409
= 1.48
The F4U flaps were not designed to be operated beyond certain restrictions but were however labeled as maneuver flaps at 20 degrees or less below speeds of 230MPH.
Francis Deans numbers are taken from different sources. The F4U stall is obviously without flaps and meets the NACA recorded number, the rest do not. In fact the P-51 appears to be 1.44 no flap. Most WW2 fighters had max Cl's of between 1.4 and 1.8 no flap with few exceptions.
http://naca.larc.nasa.gov/reports/1945/naca-report-829/ (http://naca.larc.nasa.gov/reports/1945/naca-report-829/)
Notice even the F6F max Cl listed as A/C number 5 in the back of the report(pg 35) is well under 2.0 with the P-39 approx 1.5.
The pilots manual is usually the best guide to stall speeds and operating limits. If the book says she stalls at 108MPH then it's probably not to far off. The document I recently listed from Vought list A/C stalls, apparently with flaps and weights listed. The order of finish seems to indicate a clear advantage for Naval birds beginning with the F8F and F6F based on the requirement for low landing speeds and handling qualities. The F4U is no exception.
Thanks
F4UDOA
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Widewing,
Do you have a NACA doc with the P-38 Max Cl listed??
I could use that one.
Thanks
F4UDOA
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there exist two american fighter aircrafts which were hardly tested by the independend (!)NACA (at least i´ve seen almost no reports), but where you can read the wildest performance claims:
The F4U and P38
niklas
[This message has been edited by niklas (edited 03-04-2001).]
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Originally posted by F4UDOA:
Widewing,
Do you have a NACA doc with the P-38 Max Cl listed??
I could use that one.
Thanks
F4UDOA
No, I don't. I have been forced to rely on data compiled by others. One other note: Dean seems to have applied 3g stall speeds to arrive at his max lift coefficients. If you're interested in his 3g stall numbers, I will post them.
My regards,
Widewing
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Niklas,
That is comical considering your favorite source of information is the Propaganda office of the Third Riech. Herman Georing was famous for his honest evaluations of the abilities of his Air Force (http://bbs.hitechcreations.com/smf/Smileys/default/rolleyes.gif)
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No thanks Widewing, I have them.
He took them from the "Report of Joint Fighter Confernace" Oct 1944. During the inter-service evaluations of different A/C average 3G stall speeds were measured. Dean based his Coefficients from those numbers. The problem with those numbers is that they are an average of results. For instance the F4U-1D had a range of 3G stalls from 130Knots to 190Knots. So based on those results the average was 150knots. However that is really not any basis for determining 3G stalls. The FG-1 was also tested at that meet and had an average of 130Knots. This is the same airplane!! Evaluating stall speeds was not the purpose of the meet and the scattered results show different stalls from different pilots and conditions.
Probably the most notable irregularity in stall speeds that Dean did not publish was the result of the F8F-1 in 3G stalls. It had an average stall of 170Knots to the left and 150knots to the right. The F8F had turning capability on par with the Spitfire, but according to the indicated results would have been out turned by the P-47.
Do you have a copy of this report?? It was also published by F. Dean through Schiffer Books. Here is a link to order. All in all it is a very interesting book.
http://www.schifferbooks.com/military/aviationwwii/0764304046.html (http://www.schifferbooks.com/military/aviationwwii/0764304046.html)
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F4U - isnt the max CL you speak of taken in level flight or near level flight?? you said it is typicaly 1.4-1.8 for almost all ww 2 a/c. and the higher ones widewing speaks of are taken at a higher angle of attack and the CL rises with the angle of attack until it peaks out at about 14-17 degrees not??? purely questions by the way.
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Originally posted by F4UDOA:
Niklas,
That is comical considering your favorite source of information is the Propaganda office of the Third Riech. Herman Georing was famous for his honest evaluations of the abilities of his Air Force (http://bbs.hitechcreations.com/smf/Smileys/default/rolleyes.gif)
BS - my informations were written down by ENGINEERS from Messeschmitt or Focke Wulf.
Are you really so naive to believe that german propaganda said something in the radio like "Our engineers prooved that CLmax of our aircrafts is way better, and drag a lot lower, and according to the results from certain forumlas, including oswald efficiency and propeller efficiency, we germans demonstrated again our superiority ...." ????
Messerschmitt was untouchable as a fighter designer - there was no need for his team to lie, because the next order for fighters was sure for him. Heinkel was "out", Focke Wulf was "in".
This situation was a little bit different in america, right? Which company will get the next order for 10000 fighter aircrafts? Well, i´d say the company who can "proove" that their product is the best (really? (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
niklas
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Niklas,
The Germans proved themselves by loosing the air war with a resounding thud, both by tactics and a miscalculation of the capabilities of their men and machines.
You prove yourself by saying things like this.
there exist two american fighter aircrafts which were hardly tested by the independend (!)NACA (at least i´ve seen almost no reports), but where you can read the wildest performance claims:
The F4U and P38
There is more documantation available for these A/C than many A/C manufactured today. Can you provide Max Cl data for the 190 or 109? Can you provide detailed drag info for these birds? Are there any claims of performance from either of those two A/C that can't be substantiated?
Don't just pop in and say that there are "wild peformance claims", be specific.
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bolillo_loco,
It is my understanding that there is a constant used in determining Max Cl. Generally I believe it is the steepest angle an A/C can remain flying at a given air speed just above or during stall. The stall speed varies with different A/C but the AOA remains somewhat consistant in most conventional A/C.
This is my opinion, I do not no what the specific technique is. I'm sure Wells could provide insite into that arena.
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Can you provide Max Cl data for the 190 or 109? Can you provide detailed drag info for these birds? Are there any claims of performance from either of those two A/C that can't be substantiated?
ok you force me to do it: www.freenet.de/luftwaffeln/fw190drag.gif (http://www.freenet.de/luftwaffeln/fw190drag.gif)
now i want from you the same for the P38 and F4U please!
niklas
[This message has been edited by niklas (edited 03-05-2001).]
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Here ya go.
http://members.home.net/markw4/MSWF4UDATA.pdf (http://members.home.net/markw4/MSWF4UDATA.pdf)
Which line item is drag data? I can only guess so much.
[This message has been edited by F4UDOA (edited 03-05-2001).]
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Niklas,
Don't disappear now.
Translate that bowl of schnitzel you posted.
Which lines list Cd, Cdo and Cdi??
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ok here i am - i just needed a little bit time to study your documents.
ahhhaa Cd0 = 0,02 - now this sounds a bit more realistc ....
when "Flugzeugmuster" is line 1, then drag is line 10 (Schnellflug = fast flight) and 11 (Steigflugflug = climb). It´s dragarea (cw0F = cd0*wingarea , wingarea in m^2). K in the same line is the factor for induced drag (k*cl^2). K also includes wingarea (i.e 18,9 m^2 for the A-8).
niklas
[This message has been edited by niklas (edited 03-06-2001).]
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Thanks Niklas,
I hardly ever agree with you, but you have some great documents.
<S>
F4UDOA
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F4UDOA,
Somewhere on this BBs you asked where I obtained the roll data for my chart. The answer is: The NACA server. Go to:
http://naca.larc.nasa.gov/reports/1947/naca-report-868/ (http://naca.larc.nasa.gov/reports/1947/naca-report-868/) and download a .pdf copy of report #868, Summary of Lateral-Control Research. The aircraft defined are as follows:
Fw-190A (I believe this was a captured A-4)
Typhoon
Spitfire (standard wing)
Spitfire (clipped wing)
F4F-3
F6F-3
P-39D
P-47C
A6M
XP-51
P-51B
P-63A
P-40F
The P-38L is not found on that report, but is found in a test report authored by Ben Kelsey. I have a portion of this report and will post the data tonight, after I dig it from my files.
My regards,
Widewing
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I have received permission from the owner of this document to post limited portions of it here.
P-38L roll data follows:
(http://home.att.net/~historyzone/KelseyRoll.JPG)
My regards,
Widewing
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Great document Widewing! Looks like wing twisting becomes a factor over 300 mph as the roll rate starts to level off.
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Just digging this up again ... does anybody have any CLmax data or stall data for the 109? How about for the Ki-84? Thanks in advance.
Sable
352nd FG