Performance of XF6F-1

[Hardrada55]

I read somewhere that the prototype XF6F-1 was marginally slower than the captured A6M2. For that reason the engine was changed from the R-2600 to the R-2800. Is this true? I find it hard to believe the performance between the R-2600 and the R-2800 powered F6F was that different. What was the performance of the XF6F-1? What was the reason for the change of engines if it wasn't to up the performance of the F6F?

[Twitch]

Well here's what I got on the subject. The XF6F-1 had a 1,600 HP R-2600-16 and flew in June 1942. The XF6F-2 was supposed to fly with a turbo-supercharged R-2600 but never did. It was actually completed at the XF6F-3 with the R-2800-10 using a 2-stage blower putting out 2000 HP.

This plane did 315 MPH at sea level and 380 at 23,400 feet. The A6M2 and similar did 332/334 MPH @ 16,570 feet and 336/338 MPH @ 19,685 feet. Seal level max was about 275 MPH.

The only reason for upgrading to the R-2800 was simply because they could. Engine tech changed fast in WW 2 when as a plane was designed with an engine in mind developments improved so quickly that subsequent models had more power from the same physical size.

Certainly the XF6F-1 was not slower than the A6M2. The F4F-3 did 281 MPH @ sea level and 328 MPH @ 21,000 feet. The F4F-4 did 275 MPH and 318 MPH at the same altitudes.

The bottom line was why use an engine with less HP versus one with more for the same weight?

[R Leonard]

Also, remember that the Grumman XF6F-1 first flew on 26 June 1942. Even at that time, it was already obvious that the 1600 hp R-2600, in either its R-2600-10 version in the XF6F-1 or its R-2600-16 version in the XF6F-2, was not going to provide the speed desired for the airplane. The solution, which Grumman had already identified, was a switch to the 2000 hp Pratt & Whitney R-2800 engine. The XF6F-1 flight with the R-2600-10 was essentially a test to verify what Grumman and the Navy already suspected - the need for more power. The XF6F-3, the re-designated XF6F-1 now mounting the R-2800 engine, first flew on 30 July 1942.

Up to that point the USN had only observation estimates of the A6M2’s speed performance. Twenty days later, the Koga Zero arrived in San Diego, and after about a month’s restoration, A6M2 #4593 finally got in air over North Island. The results of the tests conducted between 20 September and 15 October by gave the Navy a definitive picture of the airplane’s capabilities and weaknesses. Speed wise, taken directly from the Sanders initial evaluation report of September 29, 1942:

Maximum speed.. Sea level.........270 (m.p.h.)
.........."..........."........5,000 feet.…..287......"
.........."...........".......10,000..."........30 5......"
.........."...........".....*16,000..."........326 ......"
.........."...........".......20,000..."........32 1.5..."
.........."...........".......25,000..."........31 5......"
.........."...........".......30,000..."........30 6......"

As you can see, and as Twitch noted, the XF6F-1 with the R2600 was faster a sea level (315 v 270) and generally faster than the A6Ms best reported speeds. What the Navy wanted was ‘more speed” and the R2800 gave that to the F6F-3. The Navy, with remarkable prescience, placed its first order for the F6F-3, with the R2800, on 23 May 1942, before any version ever got in the air (and a scant two weeks after USN fighter pilots had encountered the A6M2 for the first time at the Battle of the Coral Sea).

R

[chris mcmillin]

This is great stuff. Thanks for the tech notes.
Chris...

[helmitsmit]

It is the same reason they stuck a Griffon on a Spitfire Mk V111 they didn't need to as such but they couldn't resist the 40mph increase and altitude performance.

[plan_D]

The Spitfire VIII never had a Griffon engine, they were fitted with the Merlin 60 series engines. The Spitfire IV was the first to fly with a Griffon engine, in November 1941. It was a modified Spitfire III with the 1,735-hp Griffon-IIB. The first operational Griffon Spitfire was the Spitfire XII, which equipped No.41 and No.91 Squadrons in low-level defence against the Fw-190 hit and run raiders.

[helmitsmit]

They first tried the griffon 60 series on a mk 8 which became the mk14 prototype.

[Hardrada55]

"It was actually completed at the XF6F-3 with the R-2800-10 using a 2-stage blower putting out 2000 HP.

This plane did 315 MPH at sea level and 380 at 23,400 feet"

OK, so we all know the XF6F-3 would perform as above cited and the F6F-3 itself would do 376mph @ 17,300 ft. What about the performance of the
XF6F-1? If it is benig said that the XF6F-1 would do 380 @ 23,400ft with the R-2600, why would Grumman switch to an engine that produced LOWER performance?

[helmitsmit]

Think about the combat loadings (ammo etc.) Much more weight. so they needed a more powerful engine

[R Leonard]

The point was that the XF6F-1 with the R-2600 engine did not generate the speed or rate of climb that the Navy wanted, as both Grumman and the Navy suspected, hence the step up to the R-2800. And the change had nothing to do with any known speed of the A6M because the Navy had not yet tested Koga's mount when the XF6F-3 first flew. The performance of the XF6F-1 was OBE and never mattered as the principals already knew they were not going to use the R-2600 . . . remember, before the XF6F-1 ever got in the air the Navy had already placed an order for what became the F6F-3, stipulating the R-2800 engine.

Almost anywhere you go you'll run across some variation of the F6F development resulting from the recovery of Koga's A6M from Atukan . . . or based combat results of F4Fs against A6Ms and so on. None of which are true. A careful examination of timelines, a reading of combat reports, in other words, all the real information and not conjecture, bear out the development of the F6F being independent of the any information on the A6M.

R