F4U/P47 Drag coefficients

[wells]

Hmm,

The F4u and P-47 are 'optimized' for a speed of about 165 mph IAS.  The lift coefficient being roughly 0.55 for the F4u and 0.69 for the P-47 at that speed.  Now, if you keep that optimum lift coefficient (angle of attack) at other speeds, you could get something like an optimum G-load.

200 mph = 1.5 g
250 mph = 2.3 g
300 mph = 3.3 g
350 mph = 4.5 g

If you pull more than that, you would be on the 'backside' of the L/D curve, wasting energy.

[drgondog]

I just saw this and have a couple of thoughts on this subject.

First, the CDo of .0213 posted in Dean's America's 100K for the P-47 is for the XP-47 on page 113. The CDo .0251 he posts on page 598 is for P-47D.  The CDo for the F4U-1D is .0267.

Second, those CDo values are for 250 mph at SL.  Between RN=2x10^^6 and about 20x10^^6 the CDo values steadily decrease, stabilizing to a constant (but uncorrected for compressibility). Look to pg 112 for the example of P-51D CDo vs RN.

q= Dynamic Pressure = Rho*V^^2 = 160 #/sq ft

At 250mph TAS at SL, RN for P-47D = ~ .00237x250x1.467X(7.29)/(3.7373x10^^-7)= 16.9x10^^6

For the F4U, RN at 250mph at SL =~ .00237x250x1.467x(8.12)/(3.7373x10^^-7) = 18.3x10^^6

For the P-51D, RN = .00237x250x1.467(6.63)/(3.7373x10^^-7) = 15.4x10^^6

Go back to pg 112 and pick off CDo for RN=15.4x10^^6 to find .0176.  At 10^^20 the CDo (uncorrected for M) is .0156. At that RN, the P-51D is going about 324mph TAS and about 0.42M

Back to your question "what is going on about relative Drag?"

First the Drag(total) = Drag(parasite) + Drag (induced)

Induced Drag CDi= (CL)^^2/(Pi*AR*e); Assume as Dean states e=.85, P-47 AR=7.29, GW =14411; F4U AR=7.83, GW=13698

P47 CL= W/q*S=13698/160*300 = .285; CDi= (.285)^^2/(3.14*5.61*.85) = .00544
P-47 Total Drag Coefficient at 250mph, SL= .0251+.00544 = .03054
 
Total Drag47 in pounds= CD*q*S = .03054*160*300 = 1466 # (Dean Table 104 has 1485)

F4U CL = 12694/160*314 = .264; CDi= (.264)^^2/(3.14*5.35*.8) = .00488
F4U Total Drag Coefficient at 250mph, SL= .0267+.00488 = .0315

Total Drag4U in pounds= CD*q*S = .0315*160*314 = 1586 # (Dean Table 104 has 1580)

The F4U with 2000HP at SL at 250mph and 80% efficiency has Thrust=.80*2000*550/367.5
F4U Thrust in # = 2394 # (excluding exhaust) (Dean Table 104 has 2400)

The P-47 with same HP at SL has the same Thrust = 2394 # so the delta excess thrust for the P-47 over the F4U is (2394-1466=928# P-47) vs (2394-1586=808# F4U)

So, for these weights and HP and engine and Oswald efficiencies, relative aspect ratios and wing loadings - the Jug should be faster through the M=.55 range.  Above that, you will have to look at CD vs RN and the Compressibility Drag rise curve.

Additionally Dean did not look into the relative CD vs CL Form Drag due to Angle of Attack.

For a P-51D at CL=10208/160*233.2 = .27, the Delta CD is .00018

Hope this helps.

[The Fugitive]

Holy Necro Bump Batman!

[drgondog]

Gents,

I am researching this right now because some issues in the game got me looking at actual flight characteristics of these two A/C in contrast to one another.

Does anyone have drag data IE NACA reports of the Drag coefficients of these two A/C. I have "America's Hundred Thousand" and I believe the information there may be a bit misleading based on the varying speeds the Cdo's were calculated.

The Parasite Drag Coefficients were extracted from the cited References on page 113 of Dean's book for the speeds and SL at the associated RN's. The P-51D data is in fact as it should be for RN=15x10^^6 at 250 mph @SL - namely .0176.

Based on that text the P-47 had a lower drag Airframe than the F4U. I believe this is wrong based on performance data of the A/C in or out of the game.

The game performance may not match real life for a variety of reasons. First, the Oswald efficiency given for the P-47D per flight test report was nearly .9 whereas Dean uses .85 for all (including F4U-1 and F4U-4), so the Induced Drag values for the P-47D will be about 5% less in real life than Dean's calculations.

Second, all Parasite and Induced and Form Drag Coefficients are referenced to each individual wing area. The P-47B (.0215) and P-47D (.0251) have CDo less than the F4U AND have 95% of the wing area. Net Result? Less Parasite Drag in pounds for the P-47's even if CDo was exactly the same.

In AH currently the F4U-1D out accellerates the P-47 to 300MPH and is equal to it or better at lower speeds with WEP. Also it is faster at sea level with WEP by a full 20MPH 360MPH to 340MPH. These speeds correspond to the actual perfromance data exactly. Why then is it assumed that the P-47 had a lower drag Airframe? It had 14FT less wing area(314Sq Ft vs 300Sq Ft) and a much larger cowl intake compared to the F4U creating allot of additional drag. This is because the F4U had it's oil cooler intakes in the wings.

If the F4U had 350HP(2250HP vs 2600HP) less than the P-47D30 then why is it 20MPH faster at the same Alt?
The P-47D30 weighed 2400lbs more but weight is not as limiting a force in top speed as drag. In fact weight can assist top speed because of the force of momentum.

Too many unknown variables to deal with.  First, Dean's calculated values are at P-47D GW=13698 which is just about right for a P-47D model lower than P-4D-25. Full internal fuel and ammo, no external wing pylons, 305 total gallons. The Combat Power at SL=2300HP

Second, for that model series, 2300HP was Combat Power and remained constant through 27000 feet. The F4U did not have a Turbo so its power fell off considerably with altitude.

Both the F4U-1 and -4 in Dean's book had .0267 CDo at 250mph SL. The Combat Power of the R2800-8W was 2135 from SL to 12000 feet, and for the F4U-4 the 18W started at 2380 and dropped to 2080 at 23000ft.

The GW of the fully loaded F4U-1 with both Fuse and wing internal tanks plus full ammo was 12,676 pounds. 

So, the GW difference between the P47D through the P-47D-20 and the F4U-1 was about 1000 pounds more for the Jug. The Combat Power of the P-47D was 165 HP More than the SL 2135 for the F4U-1. The actual Thrust difference in Pounds was 2300/2135 = 1.077 factor in favor of the Jug. The actual Drag difference in pounds based on the above analysis was ~1470 # for the Jug and 1584 # (CRS from earlier calcs) for the F4U-1 so:

The Jug was a.) faster and b.) had slightly more acceleration than the F4U-1 by the numbers



Does anyone have data or an explanation for this or any NACA data? Pyro/HT?

Thanks F4UDOA

The challenge is to find Performance Reports published by Republic and Vought which have the detailed Drag estimates as f(CD, RN, CL), as well as Power Available and Power Required as f(height, boost, RPM). Then go to the Spitfireperformance threads and gather Flight Test data with given results including references to external racks, GW, etc.

I have the NAA P-51D and P-51H reports

[FLS]

Thanks for posting.