DarrenW
Staff Sergeant
So, provided the engines were in proper shape, as was the plane: The speed figures for the F4U & F6F were indeed accurate? When it came to race planes, the fact that they were so modified made it difficult to determine the exact performance they were capable of when used in typical 1940's era combat-trim?
I happen to trust the wartime test results and they can be compared without reservation, as long as the aircraft were flown in similar power settings and were equally configured (i.e. clean or with wing racks/ fuselage bomb shackles/rocket launchers, ect.). The instrument correction tables found in ordinary pilot manuals of the day were generally ignored by the USN and USAAF flight testing facilities, as it was customary to first perform several runs over a predetermined speed course for accurate pressure and temperature readings and then use this data to correct for instrumentation error before actual flight tests were commenced. After this is accomplished the aircraft is ran at various power settings along the marked course and timed. Pacer aircraft with highly accurate recording equipment was yet another means to find these discrepancies and correct inaccurate readings accordingly.
One must also be careful to only compare models that were in service during the same period of the war. Here is an example of testing performed on an early F4U-1 'birdcage' and two early production F6F-3s. All aircraft developed the same horsepower during the tests and were without wing or fuselage racks:
F4U-1 'birdcage' in 'normal' condition, gross weight = 11,194 lbs:
http://www.wwiiaircraftperformance.org/f4u/f4u-1-02155.pdf
F6F-3 in 'normal' condition, weights as shown:
http://www.wwiiaircraftperformance.org/f6f/f6f-3-02982.pdf
A similar speed differential existed in Combat power settings as well (F4U-1A and mid-production F6F-3 are without racks, horsepower ratings unknown):
http://www.wwiiaircraftperformance.org/fw190/ptr-1107.pdf
Now if we compare the later F6F-5 to an earlier Goodyear FG-1A (same as Vought F4U-1A) we start to see this speed gap at high blower critical altitude close to almost a dead heat:
F6F-5 with one wing mounted pylon @ 1655 hp:
http://www.wwiiaircraftperformance.org/f6f/f6f-5-58310.pdf
FG-1A @ 12,057 lbs 'clean' and WITHOUT external pylons):
http://www.wwiiaircraftperformance.org/f4u/FG-1A_14575.pdf
In the previous example we can see the danger in comparing aircraft from different periods of the war. The F4U-1D was the contemporary of the F6F-5 so it would be logical to look at these two aircraft when making performance comparisons. Due to modifications the F6F-5 was on average 10-15 mph faster than the F6F-3 under similar circumstances so this helped erase some of the speed advantage held by earlier F4U variants. I'm positive that Vought worked tirelessly and made incremental improvements along the way just like Grumman, which resulted in increased speeds for the later F4U-1D variant (such as the aforementioned revised propeller).
Here is a comparison that I used earlier in this thread to show the maximum speed difference between the F6F-5 and F4U-1D:
F6F-5 @ 1940 hp with two wing pylons and fuselage bomb shackles (330 knots = 380 mph):
http://www.wwiiaircraftperformance.org/f6f/f6f-5.pdf
F4U-1D @ 1975 hp with two capped wing pylons and fuselage drop tank rack in place (subtract a further 8 mph when pylons are uncapped) :
http://www.wwiiaircraftperformance.org/f4u/f4u-1d-acp.pdf
I believe the altitude given for the F6F-5 in combat power was a typo and should actually read 18,000 ft. This is unimportant however as a maximum of 380 mph was reached at both auxiliary blower critical altitudes. It's very easy to see that later F4U-1Ds were faster than earlier variant F4U-1s and thus maintained a similar margin of speed over the F6F-5 as earlier variants had over the F6F-3.
Finally, (as eagledad already pointed out) comparative testing of the F6F-5 and F4U-1D against captured Japanese aircraft always gave the Corsair an edge in speed over the Hellcat (between 5 - 17 mph depending on altitude):
http://www.wwiiaircraftperformance.org/japan/ptr-1111.pdf
http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf
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