XF6F-6 Grumman Hellcat

[Shuckins]

Could anyone direct me to some sources of information about the XF6F-6 Hellcat?

First read about the two Hellcats that were converted to prototype status in an article by Corky Meyer in the December 1998 edition of Flight Journal magazine.  From the photos that I have seen, they appear to be either converted late model -3 or early model -5 Hellcats.  Both had the rear view window behind the sliding canopy.  

According to Corky, they had the R2800-34w Pratt and Whitney engine, the same as equipped the F4U-4 Corsair and were fitted with a four-blade Hamilton Standard airscrew.  He stated that it had comparable performance to the Corsair but didn't mention it's top speed.  Some sources list top speed as 417 mph.  However, if they were converted -3 aircraft, they may have had the faulty airspeed system which had caused Grumman a lot of grief with the Navy.  If that was the case, top speed would be off by about 20 knots.  If they were built from -5 Hellcats, then the 417 mph figure would not be that big an improvement over the standard -5's top speed of 409 mph.

Grumman serious considered producing this aircraft, but decided instead to opt for production of the F8F Bearcat.  Since they were seriously considering production of the F6F-6, I assume it must have a considerable performance edge over the -5.

If anyone can clear this up for me I would be muchly appreciative!  I would also like to see some climb performance figures for this prototype.

Regards, Shuckins

[Steven]

Not sure if this helps any, but straight from Barret Tillman's "Hellcat...the F6F in WW2", pg 234.

"The last Hellcat model was the XF6F-6.  Two examples were built, and the first was test-flown by Pat Gallo in July of 1944.  The P&W R-2800-18 engine with water injection produced 2,450 horsepower which, combined with a 13 foot 2 inch Hamilton-Standard four-blade propeller, delivered a top speed of 425 mph, or 370 knots.  This was 15 mph faster than the F6F-5, and rate of climb was marginally superior.

Further testing of the -6 continued as time permitted, but by mid 1944 Grumman was building nearly 500 Hellcats per month.  With its energies devoted to production rather than additional experimentation, the factory did not put the ultimate Hellcat into manufacture before V-J day.  Presumably the Navy felt no urgent need for an improved F6F, otherwise the -6 would have progressed further than it did."

The F6F-2 strikes me as an interesting derivative as well.

[Lephturn]

I found this:

http://perso.wanadoo.fr/christophe.arribat/stoff6f.html

And this:

http://aeroweb.brooklyn.cuny.edu/specs/grumman/xf6f-6.htm

Interestingly, they seem to believe the XF6F-6 had the old pitot tube setup that was reading too slow and was actually faster than stated.  I've read something about this in the past, where they figured it out by flying side by side with Corsairs and seeing the 20Mph speed difference between the guages.

Could the Hellcat have been much faster than we thought?

[Shuckins]

Lephturn,

Thanks for the reply!  It would seem that the F6F-5 IS faster than is commonly believed.

In July of 1944 twelve captured A6M model 52s were offloaded in San Diego.  Two of these were flown to NAS Anacostia to be evaluated by the Technical Air Intelligence Center.  One was later flown to NAS Patuxent River, Maryland, where comparison flight tests were made with Allied aircraft.  Reports of these comparisons were forwarded to units in the Pacific that were having to deal with this new type of Zero in combat.  These reports covered performance trials against the F4U-1D, the F6F-5, and the FM-2.  The assessments of the performance statistics of these aircraft should be relatively free of bias, since Allied Technical Air Intelligence had only one goal;  to provide the most accurate data for the use of our combat pilots operating against the enemy in the Pacific.  They would therefore not "parrot" either Grumman or Navy propaganda. It seems that the Navy often played the various manufacturers of its combat aircraft off against each other, pressuring them to bring their product up to the "level" of their competition.  Grumman was urged to improve the Hellcat's roll rate and top speed so it would match the Corsair.
Chance Vought was urged to improve the Corsair's stall characteristics, low speed handling, cockpit layout, and it's landing gear's tendency to rebound excessively while landing on a carrier.  In other words, make it fly more like the Hellcat.

Anyway, Allied Technical Air Intelligence's wartime report stated the following:

"The F6F-5 was faster than the Zero 52 at all altitudes, having the least margin of 25 mph at 5,000 feet and the widest difference of 75 mph at 25,000 feet.  Top speeds attained were 409 mph at 21,600 feet for the Hellcat, and 335 mph at 18,000 feet for the Zero."

By the by,  one factor that may have contributed to the Hellcat's low performance reputation was that the -3 model did not have water injection for emergency power until late in the production run.  How much of a difference that would have made in top speed I don't know, but Corky Meyer asserts that both the -3 and the F4U-1 Corsair had top speeds of around 400 mph.

Now, how about HTC making use of this data, hmmm?


Regards, Shuckins

[joeblogs]

The standard aircraft characteristics report on the f6f-5 at 330 knots at 23k feet.  That's 380 MPH.  But that is with a full tank of gas (internal) coming off the ground.  I have to wonder how much fuel was in that F6 going at 406 MPH...

Tillman's book has the F6-5 at 400 MPH, but he's the only one I've seen do this.  Rene Francillon uses the more typical 380 MPH.  Each author should have enjoyed access to the same data so it's a puzzle as to why they number are off.  Then again, they are only off by 10 percent.

Given the considerable difference in the size of the wings in these two planes, and the thicker wings of the Hellcat, it would be remarkable if they attained the same top speed with the same engine and supercharger.  The only comparable experiment is from the xf6-6.  When you put the same engine used in the xf6-6 into the corsair (F4u-4), you get a plane with a top speed of 393 knots (452 MPH) at 21k feet, a difference of about 35 MPH.

-Blogs

[H. Godwineson]

JoeBlogs,

Good post!  If you would like to read a good thread line about the F6F which covers many of the points that I brought up in this one then go to the Aces High General Discussion forum and look up Fowler's thread entitled "A Few Questions about the F6 Hellcat."

Barrett Tillman's figures appear to be trustworthy.  In my opinion, he did his homework when compiling his book about the Hellcat.

Corky Meyer had a very good article about fighter performance in a special edition of Flight Journal magazine entitled "WWII Fighters" published in the winter of 2000.  Corky attended a fighter conference in October of 1944 at the Naval Air Test Center, Naval Air Station, Patuxent River, Maryland.  There he test flew many different naval and Allied aircraft, as well as a few captured Axis fighters.  The aircraft available for test flight included the F6F-5 Hellcat, F4U-1c and D Corsair, F4U-4 Corsair,
Goodyear FG1 and 1A Corsair, XF2G-1 Corsair, the Ryan XFR-1 Fireball, P-38L Lightning, P-47M Thunderbolt, P-51D Mustang, Supermarine Seafire, and several others.

He gives a very good assessment of several of these aircraft.  The Navy brass was constantly impressing Grumman with the "high performance" of XF2G-1 when Grumman was in the doghouse for one reason or another.  Sporting a Pratt and Whitney R-4360 engine with 3,000 hp, the XF2G-1 was supposed to have a sea-level speed of over 440 mph.  To make a long story short, some of the test pilots there arranged to have a "Great Race" with several of the above mention aircraft, as well as the XF2G-1, the Bearcat, and F7F Tigercat at low level to see which was the fastest.  They were sitting in their aircraft with engines running when the tower told them that the race had been cancelled.  Someone had let the cat out of the bag to the Navy brass.  Corky states that the F2G-1 had a sea-level speed of only 399 mph.

If the Navy brass was cooking the books for the F2G-1 then that makes some of the figures quoted for the F4U-4 suspect.  How does one explain a top-speed of 450 mph for this aircraft when the F8F-1, a fighter with roughly the same dimensions as the Wildcat and a much better power to weight ratio than the F4U-4 and which was at least 3,000 pounds lighter, had a top speed of "only" 450 mph?

Regards, Shuckins

[joeblogs]

I'll check those threads you mentioned.  I am intrigued about the discrepancies in the numbers.

The only thing I can say on the Bearcat is that is was supposed to take a later version of the P&W R2800.  Its power to weight ratio was terrific.  But that engine only develops about half  what the R4360 does.  Speed rises at the square root of power, so all else equal that is about 40 percent more speed.  The extra weight and possibly drag reduce that margin, but it should not be eliminated with good engineering.

-Blogs



Good post!  If you would like to read a good thread line about the F6F which covers many of the points that I brought up in this one then go to the Aces High General Discussion forum and look up Fowler's thread entitled "A Few Questions about the F6 Hellcat."

Barrett Tillman's figures appear to be trustworthy.  In my opinion, he did his homework when compiling his book about the Hellcat.

Corky Meyer had a very good article about fighter performance in a special edition of Flight Journal magazine entitled "WWII Fighters" published in the winter of 2000.  Corky attended a fighter conference in October of 1944 at the Naval Air Test Center, Naval Air Station, Patuxent River, Maryland.  There he test flew many different naval and Allied aircraft, as well as a few captured Axis fighters.  The aircraft available for test flight included the F6F-5 Hellcat, F4U-1c and D Corsair, F4U-4 Corsair,
Goodyear FG1 and 1A Corsair, XF2G-1 Corsair, the Ryan XFR-1 Fireball, P-38L Lightning, P-47M Thunderbolt, P-51D Mustang, Supermarine Seafire, and several others.

He gives a very good assessment of several of these aircraft.  The Navy brass was constantly impressing Grumman with the "high performance" of XF2G-1 when Grumman was in the doghouse for one reason or another.  Sporting a Pratt and Whitney R-4360 engine with 3,000 hp, the XF2G-1 was supposed to have a sea-level speed of over 440 mph.  To make a long story short, some of the test pilots there arranged to have a "Great Race" with several of the above mention aircraft, as well as the XF2G-1, the Bearcat, and F7F Tigercat at low level to see which was the fastest.  They were sitting in their aircraft with engines running when the tower told them that the race had been cancelled.  Someone had let the cat out of the bag to the Navy brass.  Corky states that the F2G-1 had a sea-level speed of only 399 mph.

If the Navy brass was cooking the books for the F2G-1 then that makes some of the figures quoted for the F4U-4 suspect.  How does one explain a top-speed of 450 mph for this aircraft when the F8F-1, a fighter with roughly the same dimensions as the Wildcat and a much better power to weight ratio than the F4U-4 and which was at least 3,000 pounds lighter, had a top speed of "only" 450 mph?

Regards, Shuckins [/B][/QUOTE]