F4U Corsair vs P-51 Mustang

[Dawncaster]

For topical contrast, in April `43 C-V gave figures for their F4U as: sea level - 311mph, & 7,500ft - 336mph..

it's not factual and maximum speed.

That figures from F4U-1's Detail Specification was not actual test result.

see 113a, it's estimated performances and level speed with 'normal power'.

from Production Inspection Trials, one of the first batch(BuNo 2xxx) early birdcage F4U-1's level speed with military power was follows

sea level - 348 mph, 7500ft - 354 mph, maximum - 395 mph.

 

[J.A.W.]

Yeah, I had my doubts, but maker's figures are usually not less than service tests..
Got a date for those early F4U test numbers?

 

[Shortround6]

Spit XII with Griffon IIB 372 m.p.h. at 5,700 ft. Nov 1942
Spit XII with Griffon IV 375 m.p.h. at 4,600 ft. Aug 1943

 

[Dawncaster]

Yeah, I had my doubts, but maker's figures are usually not less than service tests..
Got a date for those early F4U test numbers?

it's not maker's figures, 'Production Inspection Trials' by US Navy

http://www.wwiiaircraftperformance.org/f4u/f4u-1-02155.pdf

 

[J.A.W.]

Yeah, early Griffon-Spit, what was the saying.. 'a day late, and a dollar' short?
By then, high-boost LF Mk IX's - pretty much made the Mk XII needless..

 

[J.A.W.]

it's not maker's figures, 'Production Inspection Trials' by US Navy

http://www.wwiiaircraftperformance.org/f4u/f4u-1-02155.pdf

Ok ta for that, F4U - 335mph at 6,000ft on test ( mil-power Vmax) - in mid 42..

 

[wuzak]

Yeah, early Griffon-Spit, what was the saying.. 'a day late, and a dollar' short?
By then, high-boost LF Mk IX's - pretty much made the Mk XII needless..

LF.IXs didn't appear until late 1943 - after Spitfire XII production had been completed.

 

[J.A.W.]

LF.IXs didn't appear until late 1943 - after Spitfire XII production had been completed.

Ta for that correction W, maybe I was thinking of 'clipped, cropped & clapped' low-level Mk V's, instead.

 

[Dawncaster]

hey, you wrote 10 mph less or more some figures.

Ok ta for that, F4U - 335mph at 6,000ft on test ( mil-power Vmax) - in mid 42..

it's 345 mph not 335.

http://www.wwiiaircraftperformance.org/f4u/02155-level-a.jpg

From the service tests on wwiiaircraftperformance site: Spitfire (Oct `42)
Max speed at sea-level, Spit IX - 335mph
Max speed at 6,000ft, Spit IX - 348mph..

it's 338 mph at 6000 ft, and also sea-level speed was bit lower than 335 mph.

Spitfire F Mk IX BF274 Test
http://www.spitfireperformance.com/bf274speed.jpg

 

[J.A.W.]

Ta for the correction re: F4U..
& true, Spit performance did vary, quite a bit, even in the same Mk, as engine specs changed..

 

[Dawncaster]

Ta for the correction re: F4U..
& true, Spit performance did vary, quite a bit, even in the same Mk, as engine specs changed..

yeah, but that was only oct 1942 report for Spitfire IX.

I think that 335 mph sea level speed corresponds to that of Spitfire LF IX with 18 lbs boosted Merlin 66.

Spitfire LF & HF Mk IX Test

 

[J.A.W.]

The Brits used their Mustangs running on high boost, in mid `44 to intercept Nazi V1 cruise-missiles,
& while they also had the Corsair on hand, in mid `44, the F4U could not make enough speed to do that job..

 

[Dawncaster]

Carrier Task Force for V1 Intercept?

Interesting....

and when Spitfire XIVs equipped 25 lbs boosted griffon engines in field?

 

[J.A.W.]

AFAIR, running the Griffon that hard - was deemed permissable, due to the pressing situation,
but the early Mk Griffons showed some durability 'bugs' from being pumped that hard,
so were backed off to +21lb, & only later units ( also on the hi-test juice) were cleared for +25lb.

No carrier fighters could make those speeds at low-level in mid `44..

& while the Brits had all 3 R-2800-powered US fighters on hand, not even their
turbo-boosted P-47D Thunderblots were fast enough - at the heights V1s came in on..

 

[GregP]

P-47s did not use the turbo at low altitudes ... the turbo was a high-altitude boost system only.

The P-47 was so good up at high altitude specifically because the boost system allowed it to maintain high power levels way up high. Down low, it was basically supercharged only.

 

[Shortround6]

To get to the WEP settings using water injection some assistance from the turbo may have been necessary. Perhaps more in climb than in level flight?
Looking at tests where they give turbo RPM and back pressure numbers.
At 5,000ft the P-47D was using a bit more turbo RPM and had a bit more back pressure when climbing than when flying at high speed level with the same Engine power inlet manifold pressure.
Turbo rpm and back pressure increased as the altitude went up.

 

[GregP]

Because the waste gate closed as the altitude went up. When it was fully closed, that was all the turbo was going to give.

When the turbo was not in use, it idled at about 2,000 rpm. Max rpm was 22,000. That is a P-47N. The turbosupercharger control knob was located on the throttle quadrant. outboard. The throttle as in the middle and the prop knob was inboard.

The control COULD be left on "Automatic," and that setting had overboost control. Or, you could control the turbo manually.

I'm sure you could overboost the engine, but that wasn't normally on the mission profile. If you were about to die, all bets were off. Otherwise, the turbo was idling at low altitudes.

 

[J.A.W.]

I recall reading that really heavily loaded late model Jugs needed a fair bit of strip - to get enough speed to unstick,
& some nervy pilots would overdo the 'throttle jockey - whip hand' routine, & get a compressor feedback surge..
Not a good situation if you were running out of strip & you are aboard a fast gas-filled wagon/rolling crematorium..

Having red glowing hot exhaust manifolding reaching right through to the turbine, must've been a real fire-lighter,
- for all that gas cascading out - in a too-late take-off abort, wild bull rodeo ride - too..

 

[Shortround6]

Test numbers from a few different P-47s.
altitude.....rpm.....intake pressure...........turbo rpm............back pressure.............HP...........speed
P-47B
C 0000......2700..........52.7..................... 5,600.............................................. 2000...........172
L 5,000.....2700..........52.0.....................6,800...............................................2000............352
C 5,000......2700........ 51.6......................8,200...............................................2000............183
P-47D
L 5,500......2700..........53.5....................14,400...................32.4.....................2000..........329.5
P-47D-10
L 0............2700...........56........................7,200...................36.0.....................2210............333
C 0............2700..........56........................7,300...................37.0......................2200.................
L 5,000......2700..........56........................9,400...................33.2..................... 2265............353
C 5,000......2700......... 56......................10,400...................35.5......................2285.................

I have no explanation for the 14,400rpm for the P-47D
C stands for climb and L stands for level flight. I think we can see that ram air in level flight requires a bit less work from the turbo.
Turbo is certainly not working very hard as power required goes up with the square of the RPM. Maxed out turbo at 22,000rpm is making/using over 9 times the power that it is at 7200rpm. It may not be idling but it is very far from being even pushing hard.
These planes did NOT use the same turbo and turbo controller. P-47B and the D had a max turbo speed of 18,250rpm and the P-47D-10 had a max of 22,000rpm.

 

[GregP]

None of the P-47 pilots I have spoken with (maybe 15) said the turbos were operating at low altitudes, and I have asked a few.

The 2,000 rpm turbocharger idle is straight from a P-47N Pilot's Operating Handbook. Last time I asked was the first week of April, and I spoke with Neal Melton, who operates two P-47Ds, one of which has a P-47D with an operational turbo. If anyone wold know, it's a guy flying one right now, in stock form. Of course, he is NOT hauling ordnance or ammunition!

Now I'm getting curious about the P-47D and forward.

Hey J.A.W.,

The turbocharger is located behind the cockpit, in the rear fuselage, about where the U.S. star insignia is located. It is very far from red hot when it gets anywhere near the turbo, being in a 170+ mph slipstream and having a stainless steel cover on it. After the turbocharger, it goes through an intercooler and then routes forward alongside the pilot on either side of the cockpit to the carburetor. It's cool enough for almost the entire trip so you can lay aside the fears of fire from it, even with some battle damage in the form of bullet holes.

Neal's T-bolts operate from a 5,500 foot runway at 1,013 MSL ... though they fly light when compared with a wartime load. Standard S.L. ground run on takeoff was 4,600 ft, but they had fuel, probably drop tanks, ammo, bombs, all armor, etc. So, a private T-bolt is probably flying at somewhere near 11,500 - 12,000 pounds or so, give or take a bit. The ground run will be correspondingly less, and Neal has been flying out of Sevierville, TN for a long time without any trouble.

At the Planes of Fame, our P-47 is a P-47G and it has no turbo, no armor, no guns or ammo, and is very light when compared with a wartime Thunderbolt.