Comparative turn performance

[Widewing]

 

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  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

[wells]

 

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.

[Widewing]

 

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

[juzz]

 

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!!!  

[F4UDOA]

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/

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

[F4UDOA]

Widewing,

Do you have a NACA doc with the P-38 Max Cl listed??

I could use that one.

Thanks
F4UDOA

[niklas]

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).]

[Widewing]

 

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

[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  

[F4UDOA]

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

[bolillo_loco]

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.

[niklas]

 

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  

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?  

niklas

[F4UDOA]

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.

[F4UDOA]

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.

[niklas]

 

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

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).]