Corsair vs. Lightning Flaps

[Brooke]

I'll plug in P-38 data into all the math I just did for the F4U.

I've got data for v_stall with and without flaps, prop diameter, HP, weight, dimensions, etc.  I can estimate the P-38's C_D_min and e, but I'd be happier if I got a reference for them.

Does anyone know of a good reference for C_L and C_D for the P-38 (say, for wind-tunnel data on a scale model)?

[Benny Moore]

I'm dying to know the answer to this, and have been for a very long time.  Based on everything I know, Aces High II's P-38 is very accurate, but I've always wondered if the Fowler flaps should work a bit better compared to conventional flaps.  I look forward to your results.

[Raptor]

Good point Saxman.
I had dropped my tanks prior to engaging him, but the F4u does burn fuel at a faster rate than the P38. He started with more (75% over 50%). This was his first engagement after landing a sortie so that would say he burnt more than 25% of his fuel in the time it took to climb to 8k? Or do you not consider proportions in this kind of situation. (Thinking if both planes at roughly the same fuel % load will that have a significant difference in results?)
His corsair was flying close to vertical while he was rolling though, and I flew straight angling into the vertical so I am not sure.

[TequilaChaser]

Raptor,
you quoted Widewing in regards to heavy fighter & Inertia.

but  Widewing is talking Zoom climbs, where one is at speed and has the mass a haulin tail......so the inertia kicks in.....

this is apples to oranges comparing it to starting a vertical climb at 125 & 130 mpph respectively, you have no speed for the inertia to be of any use  in this reference....at this speed  one would probably be looking for shear Thrust output when beginning a vertical maneuver so slow.  so it is back to power to weight ratio....( & flaps efficiency?.....  you both are close in the caliber of fighter in my book )


edit: knowing AKDogg in the Hog, if he was rolling he was using the torque of the Hog to roll the plane and reduce fighting it ( fighting it meaning: holding aileron straight - ie....increasing drag? and also using the rolls to look back over his shoulder to keep you in site )

[AKDogg]

When I fly the -1 hog, I always use 75% fuel.  To me it gives the plane better balance.  I don't burn the wing tanks at all on the -1.  Those tanks are my reserve to get home.  When u load 75% fuel in the -1 it puts 25% fuel in each wing and 100% in main.  When we engaged raptor on that fight, I had approx 7/8 of a tank left in main as I just upped from the CV and got to 8k.  75% fuel in a -1 hog gives u 39mins of flight time from take off at full throttle.

Now for having control at the top of my stall, what I did there raptor was use the torque of the engine to put my nose on ya.  What I mean is where u were located at that time, I rolled the plane so that the torque would help me point the nose to u.  This is how I get alot of people in stall fighting by using the torque of the engine to help me turn in the vertical.

Now for the flaps that i used to do that manev on ya.  I had only 1 notch of flaps just before I started that and when I did start the pull up, I went to 3 notchs to give me that extra nose quickly then pulled my flaps back to 1 notch to close to the top of vertical then went full flaps just before the nose over.  The p38 should have still out climbed me but like AKAK said, U used the flaps somewhat wrong in that situation or leading to that stituation.

Now keep in mind the other fights we had that night, I was getting lighter each time we engaged via ammo load/fuel load going down which we all know make the plane even more incrediable.  When I usually rtb its either ammo or my fuel goes to wing tanks.  The wing tanks at 25% each will get me about 40 miles if i go economy mode but at full throttle will go about 20-25 miles which is about the distance to any airfield.

Lately I been flying stupid when AKAK is around and I sometimes just go vertical with him and I usually die.  Alot of it maybe i get to confident or I don't really care.  I do get in those moods quite often,lol.

[TequilaChaser]

heh, AKDogg answers as I edited same about the roll & Torque......

Afternoon Dogg ~S~

[Raptor]

Dogg
When we were discussing it on 200 you said you went full flaps and I assumed you stayed at full flaps. That threw me off the most. That's enough evidence for me as I was thinking before you replied "in a pure vertical climb would it not be better to use less flaps and rely on the engines?"

[AKDogg]

Well raptor, I did hit my flap button multiple times but we both know that flaps don't deploy that quickly.  I might have selected full flaps but by the time they would have got to full flaps I would have been alrdy verticle.  So as the flaps were going down and I was pulling up, at about 75% of the pull up I was alrdy putting flaps back up if u know what I mean.

back to ya

[Brooke]

I put the P-38J numbers into the model and got the following (in the Appendix:  P-38J):

http://www.electraforge.com/brooke/flightsims/aces_high/stallSpeedMath/turningMath.html

It seems the model agrees pretty well with AH, although not as well as with the F4U-1.  The model predicts about 10% better turning performance for the P-38J.  However, I had to estimate e_clean, e_flaps, and C_D_min_flaps.  Also, I was using stall speeds for power off.  For the F4U, I was using stall speed power on, which is lower and results in estimates of C_L_max being larger.  If I used power-on stall speeds for the P-38J, the model would predict still a little better turn rate.  (I don't have a good reference for power-on stall speed for the P-38J, which is why I didn't use it.)

[Widewing]

Originally posted by Brooke
I put the P-38J numbers into the model and got the following (in the Appendix:  P-38J):

http://www.electraforge.com/brooke/flightsims/aces_high/stallSpeedMath/turningMath.html

It seems the model agrees pretty well with AH, although not as well as with the F4U-1.  The model predicts about 10% better turning performance for the P-38J.  However, I had to estimate e_clean, e_flaps, and C_D_min_flaps.  Also, I was using stall speeds for power off.  For the F4U, I was using stall speed power on, which is lower and results in estimates of C_L_max being larger.  If I used power-on stall speeds for the P-38J, the model would predict still a little better turn rate.  (I don't have a good reference for power-on stall speed for the P-38J, which is why I didn't use it.)

I have the P-38J/L manual and it provides only power-off stall numbers. For example, for a P-38J at 15,000 lbs stall occurs at:

Clean: 94 mph IAS
Landing config, full flaps: 69 mph IAS

These numbers require adjustment due to pitot tube position error, and there's a rough chart for this provided. In the P-38's case, the error is less when full flaps are used. I suspect this is due to reduced AoA.

I have found numbers for power-on stall from the Joint Fighter Conference. Unfortunately, they are all over the place, depending upon the pilot. In some cases, as much as a 15 mph difference can be seen.  Some pilots reported a higher stall speed using full flaps, which is at odds with Tony LeVier's comments. LeVier stated in an interview that stall speed clean was reduced by 5 mph with power on. I tend to lean towards LeVier as he was the lead test pilot on the P-38 program from 1944 on, and had nearly 4,000 hours in the type.

In game, stall speeds are as follows from testing for P-38J at 15,464 lb.

Power off-
Clean: 104 mph TAS
Landing: 88 mph TAS

Power on-
Clean: 100 mph TAS
Landing: 79 mph TAS

Flap drag is another factor that can be measured in terms of speed bleed-down. Power off with full flaps, the P-38J requires 8.31 seconds to bleed down from 150 mph TAS to 100 mph TAS.

Compare this to the F4U-1D, which with full flaps requires 6.03 seconds to bleed down from 150 mph TAS to 100 mph TAS.

In addition, with full flaps and MIL power, level flight, the P-38J will accelerate past 150 mph TAS with ease, eventually gaining enough speed to blow up the flaps. On the other hand, the F4U-1D cannot exceed 144 mph in MIL power with full flaps (after 3 minutes at 144 mph). To obtain enough speed for testing, flaps had to be raised one notch and then dropped at 155 mph to begin timing at 150 mph. The drag increase with that final notch of flaps is huge, and demonstrates why flying around with more flaps than needed is detrimental.

So, the P-38J's Fowlers generate much less drag than the F4U-1D's flaps, which should be the case. Both aircraft were loaded with 25% fuel, zero burn.

As far as I can tell, the flaps on the P-38s seem to perform as they should (except for blowing up, P-38 flaps could not blow up, but would just jam in the roller tracks).

My regards,

Widewing

[Benny Moore]

On Mike Williams' excellent site, some of the documents give power on speeds as low at 53 M.P.H. with full flaps.  Obviously, that's not calibrated, but still ...

[Widewing]

Originally posted by Benny Moore
On Mike Williams' excellent site, some of the documents give power on speeds as low at 53 M.P.H. with full flaps.  Obviously, that's not calibrated, but still ...

Thanks for reminding me Benny.

I think it is calibrated, or at least corrected for error...

Flight Test Engineering Branch
Memo Report No. Eng-47-1706-A
4 February 1944

FLIGHT TESTS
OF A P-38J AIRPLANE

Flight tests have been conducted at Wright Field on the P-38J Airplane, AAF, No. 42-67869, at the request of the Fighter Branch, Experimental Engineering Division. These tests were made on this airplane primarily to obtain comparative performance data with similar tests on a P-47D-10, a P-39Q-5 and a P-51B airplane. The performance should be that of a typical production model as it was selected at random from airplanes which had been delivered from the factory. From 2 December 1943 to 21 January 1944 approximately 30 hours were flown on this airplane by Capt. G. E. Lundquist, Capt F. C. Bretcher, and Capt J. W. Williams.

Condition of Aircraft Relative to Tests:
 
A. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 16,597 pounds with the c.g at 24.75 m.a.c., gear down; and 28.5% m.a.c. , gear up. Gross weight included 300 gallons of fuel, 26 gallons of oil, 457 lbs. of ballast for ammunition, 100 pounds of ballast in the nose to locate the center of gravity within the allowable range, and automatic observer, complet radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photgraphs which are included at the end of the report.

Skip down to......

F.    Stalling Speeds

Indicated airspeed corrected for instrument error

Landing gear up, flaps up.
Power off: 99 mph
Power on: 74 mph

Landing down, flaps up.
Power off: 95 mph
Power on: 73 mph

Landing gear down, flaps down.
Power off: 78 mph
Power on: 53 mph

*Power on was at 54" Hg manifold pressure and 3000 rpm

There you go Brooke, real, reliable test data from the Fighter Branch, Experimental Engineering Division at Wright Field. Plug these numbers into your calculations and maybe we'll get a better understanding of the AH2 flight model.

My regards,

Widewing

[Widewing]

Also interesting is this chart that shows how much the boosted ailerons increased roll rate, even at low speeds around 125 mph...



My regards,

Widewing

[Brooke]

Originally posted by Widewing
I have the P-38J/L manual and it provides only power-off stall numbers. For example, for a P-38J at 15,000 lbs stall occurs at:

Clean: 94 mph IAS
Landing config, full flaps: 69 mph IAS

These numbers require adjustment due to pitot tube position error, and there's a rough chart for this provided. In the P-38's case, the error is less when full flaps are used. I suspect this is due to reduced AoA.

Yep, those are the numbers I used, and I corrected them to CAS using linear regression on the values in the table.

I have found numbers for power-on stall from the Joint Fighter Conference. Unfortunately, they are all over the place, depending upon the pilot. In some cases, as much as a 15 mph difference can be seen.  Some pilots reported a higher stall speed using full flaps, which is at odds with Tony LeVier's comments. LeVier stated in an interview that stall speed clean was reduced by 5 mph with power on. I tend to lean towards LeVier as he was the lead test pilot on the P-38 program from 1944 on, and had nearly 4,000 hours in the type.

I'll plug in stall speeds that are 5 mph lower and see what that does to C_L_max and thus the other stats.

Flap drag is another factor that can be measured in terms of speed bleed-down. Power off with full flaps, the P-38J requires 8.31 seconds to bleed down from 150 mph TAS to 100 mph TAS.

Compare this to the F4U-1D, which with full flaps requires 6.03 seconds to bleed down from 150 mph TAS to 100 mph TAS.

In addition, with full flaps and MIL power, level flight, the P-38J will accelerate past 150 mph TAS with ease, eventually gaining enough speed to blow up the flaps. On the other hand, the F4U-1D cannot exceed 144 mph in MIL power with full flaps (after 3 minutes at 144 mph). To obtain enough speed for testing, flaps had to be raised one notch and then dropped at 155 mph to begin timing at 150 mph. The drag increase with that final notch of flaps is huge, and demonstrates why flying around with more flaps than needed is detrimental.

So, the P-38J's Fowlers generate much less drag than the F4U-1D's flaps, which should be the case. Both aircraft were loaded with 25% fuel, zero burn.

Good points on the flaps.  The P-38 has more weight and thrust than the F4U (W = 16,462 vs. 11,300 lbs, and T = 4650 vs. 3600 lbs at 150 mph).  The extra weight could cause it to decelerate more slowly and the extra thrust could be enough to pull through to higher speeds even if full-flap C_D_min for the P-38 is similar to the F4U.  I'll play around with the models some.  I wish I could find a C_L and C_D vs. alpha graph for the P-38 with and without flaps.

Do Fowler flaps give less drag?  They generally give a higher C_L_max and so perhaps a higher L/D that for, say, split flaps, but I don't know if they have a lower C_D_min.

One thing about P-38 vs. F4U flaps.  P-38's have Fowler flaps in that the flaps extend backward.  However, they are also somewhat like split flaps in that the leading edge of the flap is still forward of the trailing edge of the wing during full-flap deflection -- or so it seems to me.  The F4U does not seem to have plain flaps, but slotted flaps, which are more efficient than plain flaps.  So, it might be that the P-38 flaps (sort of Fowler/split combo) are not a lot more efficient than the F4U flaps (slotted).  Power-off stall C_L_max with and without flaps might be one way to judge.  I'll look at that, too.

[Brooke]

Originally posted by Widewing
Thanks for reminding me Benny.



There you go Brooke, real, reliable test data from the Fighter Branch, Experimental Engineering Division at Wright Field. Plug these numbers into your calculations and maybe we'll get a better understanding of the AH2 flight model.

My regards,

Widewing

Many thanks, guys!  I will start some calculations.