XF6F-6 performance

[Trilisser]

Generally available data for the F6F-5 and XF6F-6 suggest a very significant increase in performance, way beyond the power increase alone. How much was due to the new propeller?

 

[tomo pauk]

The main reason was the greatly increased full throttle height of the new engine (similar/same? as used by F4U-4), by some 6500 ft (I do not have my ATH, so that's from memory). It basically enabled the plane to fly with same/greater power at higher altitude (thinner air = less drag) - basically the same story when comparing the F4U-1 and U-4. The increased engine power and 4-bladed prop were certainly another ingredients of the increased performance.

 

[Trilisser]

The SAC sheet for the F6F-5 states max. speed as 380 mph (330 kts) at 23,400 ft while I recall AHT mentioning 417 mph for the -6 at 25,000 ft. That is too little a difference to account for much.

 

[tomo pauk]

By looking at the graph at the ATH, the 380 mph @ 23400 ft figure corresponds with engine running at military power (1650 HP). Ram effect is elevating the full throttle height (for military power setting) from 22500 ft to 23400 ft.
The R-2800-18W, used at the XF6F-6, makes 2080 HP @ 23300 ft, war emergency power. Ram effect should elevate the FTH (for WEP setting) for maybe another 1000 ft, so the prototype should have more than 400 HP more than the F6F-5, at some 1000 ft greater altitude.

One thing I have not mentioned is the exhaust thrust - while the Hellcat is hardly some great example of harvesting upon that effect, more exhaust gases, on a tad greater altitude, should provide more exhaust thrust, and again some added speed.

 

[Jabberwocky]

The SAC sheet for the F6F-5 states max. speed as 380 mph (330 kts) at 23,400 ft while I recall AHT mentioning 417 mph for the -6 at 25,000 ft. That is too little a difference to account for much.

There's a bit of conjecture as to how fast the F6F actually was, as the -3 had problems with its pitot tubes giving bad readings and there is plenty of conflicting data.

Grumman and NAS Patuxent River testing in 1944 showed the -5 aircraft was capable of about 391 mph at 23,000 ft.
UK FAA Hellcat II data sheet for 1945 gives 392 mph at 19,500 ft as best speed with water injection (60" MAP)
There is also a TiAC test showing 406 mph for -5 at 21,600 ft with water injection and 58" MAP.

On the opposite side of the coin, FAA, Grumman and NAS Patuxent River testing in 1945 show about 385-387 mph as top speed for -5 airframes, but that could simply be degraded performance from wear and tear or due to external equipment like bomb shackles.

The -6 had the following going for it:

R-2800-34W with 2450 hp and critical alt of 26,500, compared to 2250 hp and 23,900 ft for the R-2800-10W or -18W in the -5
Four bladed Hamilton Standard prop of 13' 2", compared to the 13' 1" three bladed prop on the -5.
Minor clean up around canopy and cowl

There is also a Grumman report that indicated the XF6F-6 made 425 mph at 25,000, but as it was a prototype this might not be representative of the performance of a combat laden aircraft.

 

[Trilisser]

Jabberwocky, the -6 Hellcat had the -18W variant, not the -34W.

 

[tomo pauk]

There's a bit of conjecture as to how fast the F6F actually was, as the -3 had problems with its pitot tubes giving bad readings and there is plenty of conflicting data.

Grumman and NAS Patuxent River testing in 1944 showed the -5 aircraft was capable of about 391 mph at 23,000 ft.
UK FAA Hellcat II data sheet for 1945 gives 392 mph at 19,500 ft as best speed with water injection (60" MAP)
There is also a TiAC test showing 406 mph for -5 at 21,600 ft with water injection and 58" MAP.

On the opposite side of the coin, FAA, Grumman and NAS Patuxent River testing in 1945 show about 385-387 mph as top speed for -5 airframes, but that could simply be degraded performance from wear and tear or due to external equipment like bomb shackles.

Thanks for the data

The -6 had the following going for it:

R-2800-34W with 2450 hp and critical alt of 26,500, compared to 2250 hp and 23,900 ft for the R-2800-10W or -18W in the -5
Four bladed Hamilton Standard prop of 13' 2", compared to the 13' 1" three bladed prop on the -5.
Minor clean up around canopy and cowl

IIRC the -18W was never installed in the F6F-5. Also, the -10W was capable for 1975 HP w/ water injection @ 20000 ft, while the -18W was managing 2080 HP @ 23300, water injected. Per AHT.

There is also a Grumman report that indicated the XF6F-6 made 425 mph at 25,000, but as it was a prototype this might not be representative of the performance of a combat laden aircraft.

That might be very true.