F4U Corsair vs P-51 Mustang

[airminded88]

Does that mean on a sustained straight level flight going more or less at the same speed the P-51's substantially less parasitic drag would enable it to outpace the Thunderbolt with much more raw hp?

 

[CORSNING]

With the same amount of fuel, yes.

 

[airminded88]

Very interesting.
Thanks Corsning!

 

[CORSNING]

You are very welcome AM88. The truth is, I digress, there are members on this site
that are way more adverse in this area than I. Just wait until drgondog gets a chance
to see your post. He can give you way more information than I.

 

[drgondog]

Does that mean on a sustained straight level flight going more or less at the same speed the P-51's substantially less parasitic drag would enable it to outpace the Thunderbolt with much more raw hp?

Force=Mass*acceleration;

F=Thrust. At equilibrium T=D; When T>D, the aircraft accelerates.

Simplest answer - The Mustang will always 'out accelerate' and continue to accelerate when the P-47 reaches equilibrium, when they both have the same THP.

Because the Full throttle height of the P-51D was 24000 feet/1390HP for 1650-7 and 29000 feet/1290HP with the 1650-3, the Hp reduced steadily as a function of altitude from whereas the P-47D with turbo continued to produce 2300HP until about 32,000 feet.

The Drag advantage over the P-47D that enabled a faster P-51 at just over 1/2 the HP crossed over about 30-31000 feet

 

[Peter Gunn]

Force=Mass*acceleration;

F=Thrust. At equilibrium T=D; When T>D, the aircraft accelerates.

Simplest answer - The Mustang will always 'out accelerate' and continue to accelerate when the P-47 reaches equilibrium, when they both have the same THP.

Because the Full throttle height of the P-51D was 24000 feet/1210HP for 1650-7 and 29000 feet/1330HP with the 1650-1, the Hp reduced steadily as a function of altitude from whereas the P-47D with turbo continued to produce 2300HP until about 32,000 feet.

The Drag advantage over the P-47D that enabled a faster P-51 at just over 1/2 the HP crossed over about 30-31000 feet

So if the Mustang had the same amount of continuous power the way the Thunderbolt did, say 2300HP to approx. 32,000 feet, it seems you'd have one speedy little aircraft. I realize that'd be a tall order but if I'm understanding this correctly, the lower drag P-51 would be a real scorcher with that type of powerplant.

I guess my question is if you keep the same physical shape of the Mustang with this type of constant power, how fast is this fantasy plane theoretically going to go?

 

[CORSNING]

Wow drgondog, you never cease to amaze me.

 

[grampi]

So if the Mustang had the same amount of continuous power the way the Thunderbolt did, say 2300HP to approx. 32,000 feet, it seems you'd have one speedy little aircraft. I realize that'd be a tall order but if I'm understanding this correctly, the lower drag P-51 would be a real scorcher with that type of powerplant.

I guess my question is if you keep the same physical shape of the Mustang with this type of constant power, how fast is this fantasy plane theoretically going to go?

The unlimited versions of the Mustangs at the Reno Air Races have 3600+ HP and they do well over 500 MPH, and that's near the ground...imagine how fast they'd go at altitude...

 

[drgondog]

Grampi answered the question.

 

[gjs238]

The unlimited versions of the Mustangs at the Reno Air Races have 3600+ HP and they do well over 500 MPH, and that's near the ground...imagine how fast they'd go at altitude...

Pretty quick

 

[BiffF15]

Pretty quick

Reminds me of my first afterburner takeoff in the Eagle!

 

[wuzak]

Because the Full throttle height of the P-51D was 24000 feet/1210HP for 1650-7 and 29000 feet/1330HP with the 1650-3, the Hp reduced steadily as a function of altitude from whereas the P-47D with turbo continued to produce 2300HP until about 32,000 feet.

The Drag advantage over the P-47D that enabled a faster P-51 at just over 1/2 the HP crossed over about 30-31000 feet

Small correction there Bill. You obviously meant the V-1650-3.

Is there another cross-over point for the Mustang and P-47? As the altitude increases, the Mach number increases for the same TAS which will increase the drag significantly. The P-47 must be relatively worse due to its lower critical Mach.

The Spitfire XIV was faster at 37,500ft than the P-47D was at the same altitude. The Spitfire XI ~430mph TAS vs the P-40D at around 400mph.

http://www.spitfireperformance.com/JF319_Report_P-3792_level-speeds.jpg
http://www.wwiiaircraftperformance.org/p-47/P-47D_43-75035_Eng-47-1652-A.pdf

The P-51D was 407mph at 35,000ft with the -7 engine.
P 51D Performance Test

 

[drgondog]

Wuzak - yes to 1650-3.

Is there another cross-over point for the Mustang and P-47? As the altitude increases, the Mach number increases for the same TAS which will increase the drag significantly. The P-47 must be relatively worse due to its lower critical Mach.

Wuzak -the Mcr isn't quite reached by either ship although both are well immersed in the 0.6 to 0.65 M range

The Parasite Drag in that range would need a compressibility factor applied to the base RN=9x10^^6 estimates for both. I haven't looked but there might be a cross over point above 35K because the power loss on the P-47's R2800 is a pretty steep gradient from 31K, moreso than the 1650.

I haven't seen the CDp vs M for the P-47 but for the P-51 it is around 1.25 for .65M

 

[Zipper730]

As a Mustang admirer, I have to note that the F4U-4 &5 and the P-51H were at the peak of 1945 US Fighters.

The F4U-5 didn't fly until the war was over, though there was the F8F, which did...

The F4U-5 should always out turn and out roll a P-51H through ~ 22000 feet based on the relative wing loadings and the P-51H standard rigging of 10 degrees aileron throw.

Don't forget the difference in the wing cross-section: The F4U has a lower stall-speed than the P-51.

They, however had far less escort radius for high altitude penetrations as they had much less internal fuel than the F4U-1

Tue F4U-4 could carry more fuel than the F4U-1 in the normal configuration, in overload the F4U-1 had a higher fuel-fraction, though a lower total load

F4U-1 (Fighter Normal): 178 gallons, fuel fraction: 9.59%
F4U-1 (Fighter-Overload): 363 gallons, fuel fraction: 17.21%
F4U-4: 384 gallons, fuel fraction 15.82%

 

[wuzak]

The F4U-5 didn't fly until the war was over, though there was the F8F, which did...

The F8F, particularly the F8F-1 which flew before the end of WW2, was not in the same league as the P-51H or F4U-4 in terms of high altitude performance nor range, certainly compared to the P-51H.

 

[drgondog]

The F4U-5 didn't fly until the war was over, though there was the F8F, which did...

Don't forget the difference in the wing cross-section: The F4U has a lower stall-speed than the P-51.

Easy to 'not forget'. The T/Cmax was near same but the NACA 23xxx had a better CL to AoA that the NACA/NAA 45-100 airfoil. But the F4U drag penalty was about 40% more parasite drag not to mention that the F4U had 314 sq feet of wing to 233 sq feet on the P-51D for a WL advantage of 39 to 41 for a Combat Load Fighter with no external tanks.

Tue F4U-4 could carry more fuel than the F4U-1 in the normal configuration, in overload the F4U-1 had a higher fuel-fraction, though a lower total load. No. Not for FIGHTER Combat load. The F4U-1 carried 361 gallons while the F4U carried 234 gallons (both internal - max. This is the reason that ONLY the F4U-1 series might have been able to perform escort comparable to P-47D but well short of P-38J/P51B/D

Note: INTERNAL fuel is King in Combat Radius. The F4U-1 was King of the Corsairs in context of escort radius with 361 gallons ~ about the same as the P-47D-25 with the extra internal fuselage tank. The rest of the F4U's (-1D, -2, -4) as well as F6F (250 gallons) were all less than the ETO inadequate 305 for P-47C/D below the D-25.

The external fuel fraction is interesting but not for worst case planning of being forced to punch external tanks in 'premature' combat engagement. Ya gotta get home with what ya got internally after 15 minutes Military/ 5 minutes Combat Power

F4U-1 (Fighter Normal): 178 gallons, fuel fraction: 9.59% (361 internal)
F4U-1 (Fighter-Overload): 363 gallons, fuel fraction: 17.21% (361 internal/175 external)
F4U-4: 384 gallons, fuel fraction 15.82%

F4U-4 234 internal 150 external for fighter w/2 external 75's or one c/l 150. For Fighter role - fleet protection - the internal fuel load is the one calculated for mission fuel ftraction

Fuel Fraction is usually expressed in internal fuel weight to Gross weight -Fighter role- - take Off - clean but when doing the Fighter mission plan for which bomb/rocket load is not a factor, your definition is OK.

 

[wuzak]

Bill, would it be fair to say, simplistically, that external tanks got the aircraft to the fight and internal tanks got them home?

And if external tankage is much, much greater than internal tankage that the configuration is for ferrying?

 

[Zipper730]

F4U-4 234 internal 150 external for fighter w/2 external 75's or one c/l 150. For Fighter role - fleet protection - the internal fuel load is the one calculated for mission fuel ftraction

I didn't know that was counting drop-tanks. The F4U-1's 363 gallon overload was internal or with drop-tanks?

Fuel Fraction is usually expressed in internal fuel weight to Gross weight

I just didn't know that factored in drop-tanks

 

[drgondog]

I didn't know that was counting drop-tanks. The F4U-1's 363 gallon overload was internal or with drop-tanks?

The 361 gallons for the F4U-1, 1A, 1C is maximum internal fuel for Fuselage and wings - not an 'overload' condition. This is primary Gross weight and for most combat airframes the basis for calculation of Design Limit and Ultimate stresses for 8G and 12G loading respectively

The 237 gallons for F4U-1D is maximum internal fuel load - all fuselage. It and the F4U-4 differed from the F4U-1 by Not having internal fuel stored in the wing of the F4U-1.

These full ammo and full internal fuel conditions are really not overload as they generally are the Gross weight for design purposes. Anything less than full internal load should probably be called 'Light'.

Dean does call max internal fuel Overload 1, and Normal vs Overload is defined by him as 60 gallons less than full internal fuel.

The Maximum Overload condition is a Basic Overload Mission Loadout for full internal fuel and ammunition but zero stores on pylons (no rockets, bombs or external fuel tanks).

The Max Gross Weight is the same as above plus maximum stores on the pylons

I just didn't know that factored in drop-tanks

Suggestion - get Dean's America's Hundred Thousand for the best (IMO) central set of physical data on all the WWII US fighters.

On Design criteria and stages and metrics used in Preliminary design, you might get AIAA series Raymer's "Aircraft Design - A Conceptual Approach" or Nicoli's Fundamentals of Aircraft Design. Both have excellent reference "Mission Profile" in depth discussion of weight fractions and comparisons against other similar mission aircraft for assessment and comparisons.

 

[drgondog]

Bill, would it be fair to say, simplistically, that external tanks got the aircraft to the fight and internal tanks got them home?

Yes and as the war progressed, particularly in the PTO, some drastic external fuel stores were used by 5th AF that risked not getting home. For example Kenney had 300 and 160 gallon tanks fabricated in Australia (with high quality) because the AAF Material Command was slow to deliver. I know of some missions in which P-47D's with 305 gal internal plus a 300 on one pylon and 160 on the other were used to try successful mixed target escort with P-38s. The resultant drag from those big external honkers balanced out the range for the 460 outbound versus the 305 internal for clean configuration.

And if external tankage is much, much greater than internal tankage that the configuration is for ferrying?

Yes, save the example above.