F4U vs F6F & Top-Speed: Let's Settle This

[DarrenW]

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

 

[Joe Broady]

From what I gather the F4U-1 under test was an early raised cabin variant and not the later -1D as described in the narrative. Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.

Plus it must be remembered that Grumman and Vought were competing for the same navy contracts, and while I do not suggest that there was outright deception going on, it wouldn't be unusual for any manufacturer to capitalize on anomalies found with their competitor's products, especially if it could put them at a distinct advantage during competitive trials.

In this case the point of the exercise was for Grumman and Vought to steal some ideas from the other manufacturer's airplane. The Navy loaned Grumman an F4U-1D and said they wanted the Hellcat to be more like a Corsair in the matter of speed and roll rate. Vought was given an F6F-3 and instructed to improve Corsair visibility, stall behavior, landing gear oleos, and cockpit layout. It was the summer of 1943.

According to Corky Meyer, the Corsair was an F4U-1D, Bu No 17781. There are two good photos of the loaner Corsair in the book, but I'm neither knowledgeable nor interested enough to verify the number and photos are consistent with the purported Corsair model.

Grumman was not really able to get the requested improvements. As already mentioned, they "increased" the Hellcat speed by relocating the static port. In the matter of roll response, Grumman even built test ailerons which copied the Corsair profile but that didn't help. The inferior Hellcat roll rate was due to its much higher lateral stability. Meyer says it was inherent in the wing design, and a re-design was out of the question at the height of WW2. Later, the -5 Hellcat got spring tabs on its ailerons (many -3s were retrofitted too), and that did make up much of the disparity.

Vought may have gotten more from this project than Grumman. Meyer implies improved oleo action and stall behavior, raised seat, and extended tail wheel were byproducts of their Hellcat evaluation and could be incorporated in production. But he says a cockpit revision required a total redesign and had to wait until the -4.

Regarding the static pressure sensing, Meyer says it was through a "dual orifice system located way behind the lowered flaps." However, the book reproduces a diagram of external markings on the -5, one of which says PITOT STATIC LINE - DO NOT PLUG OR DEFORM HOLE. It's on the right side only, above the forward bar of the US insignia.

Reference: Corwin Meyer & Steve Ginter, "Grumman F6F Hellcat," 2012.

 

[DarrenW]

In this case the point of the exercise was for Grumman and Vought to steal some ideas from the other manufacturer's airplane. The Navy loaned Grumman an F4U-1D and said they wanted the Hellcat to be more like a Corsair in the matter of speed and roll rate. Vought was given an F6F-3 and instructed to improve Corsair visibility, stall behavior, landing gear oleos, and cockpit layout. It was the summer of 1943.

According to Corky Meyer, the Corsair was an F4U-1D, Bu No 17781. There are two good photos of the loaner Corsair in the book, but I'm neither knowledgeable nor interested enough to verify the number and photos are consistent with the purported Corsair model.

I have read Corky's book and was especially interested in what he had to say about the comparative testing performed on the "loaner" Corsair. Being that it was the summer of 1943 it would be impossible for the subject aircraft to be an F4U-1D, as they didn't arrive at units until almost a year later (during April 1944). To further add to this, Mr. Joe Baugher has an excellent website dedicated to aircraft serial numbers and has Bu No 17456 through 18121 as F4U-1As and the test aircraft falls into this block of numbers.

Navy Serial Number Search Results

It's a minor detail and this could easily have been a typo. As long as everyone understands that the F4U-1 under test didn't have the performance of the later F4U-1D everything is good....

Meyer implies improved oleo action and stall behavior, raised seat, and extended tail wheel were byproducts of their Hellcat evaluation and could be incorporated in production. But he says a cockpit revision required a total redesign and had to wait until the -4.

Again, production F4U-1Ds had all of these modifications so why would the test airplane be in need of them?

Regarding the static pressure sensing, Meyer says it was through a "dual orifice system located way behind the lowered flaps." However, the book reproduces a diagram of external markings on the -5, one of which says PITOT STATIC LINE - DO NOT PLUG OR DEFORM HOLE. It's on the right side only, above the forward bar of the US insignia.

Yes along station #97.....

 

[Zipper730]

One must also be careful to only compare models that were in service during the same period of the war.

Yeah, as there were various changes that allowed higher boost (water injection, higher octane, and the F4U-1's started using the F6F's propeller).

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

Looking at the top-speed figures, 395 mph seems a pretty common listing for earlier designs. Later figures would show around 416 or 417 mph with water injection, higher manifold pressures, the F6F-3's propeller, reconfigured cowl-flaps (I'm not sure if this had a propulsive benefit -- it's predominant goal was to keep oil from spraying over the windscreen, but tighter cowls usually do favor speed), and the gun-ports taped-over, using the same basic engine (R-2800-8). They'd apparently eventually eke out speeds of around 425 mph in operational aircraft (F4U-1D), though there was an F4U-1A that saw 431 mph in level flight (that said, the tail-hook was removed and faired over, which would be useless for carrier ops, but beneficial for land-based).

From what I recall, the normal-rated power-settings produce 2550 RPM, 2700 for military and normal-rated power-settings. The gear-ratio seems to be 0.5 regardless of propeller.

A similar speed differential existed in Combat power settings as well (F4U-1A and mid-production F6F-3 are without racks, horsepower ratings unknown)

The graph which compares the Fw-190, the F4U-1, and the F6F-3 leaves me with more questions than answers.

For starters: I'm not sure what variant of the Fw.190 is depicted. I know little information about the critical altitude figures for the Fw.190's.

As for the F4U-1A: While the aircraft could probably keep its speed slightly over 400 mph on WEP at 25000', it is not the aircraft's critical altitude in normal-rated, military-power, or WEP figures. WEP would see a critical altitude around 20300'. The curves in speed here indicate a drop off from 200'-5000', an increase from 5000'-25000'.

As for the F6F-3: The F6F's top speed usually isn't listed as being 391 mph, the F6F-5 is, but neither have critical altitudes around 25000'.

 

[DarrenW]

hey'd apparently eventually eke out speeds of around 425 mph in operational aircraft (F4U-1D

Though I have read this from time to time I haven't seen any official documentation that supports it, at least for your standard everyday carrier based F4U-1D fighter-bomber (in any condition). If you do have a credible source please let me know.

Even Chance-Vought never made this claim:

http://www.wwiiaircraftperformance.org/f4u/f4u-1d-detail-specification.pdf

 

[DarrenW]

As for the F6F-3: The F6F's top speed usually isn't listed as being 391 mph, the F6F-5 is, but neither have critical altitudes around 25000'

This is interesting to me too. Grumman also estimated the top speed of the F6F-3 to be 391 mph in a 'normal' fighter condition at 25,000 ft:

http://www.wwiiaircraftperformance.org/f6f/f6f-3-detail-specification.pdf

The specification gives two different critical altitudes while in high blower. Of course these are way above the critical altitude when using Combat power so the test aircraft in the US Navy report obviously wasn't benefiting from the added boost at 25,000 ft.

 

[DarrenW]

For starters: I'm not sure what variant of the Fw.190 is depicted. I know little information about the critical altitude figures for the Fw.190's.

I believe the consensus is that it was probably an FW 190A-5 variant. Others here could explain the supercharger/engine performance curves much better than I can.

 

[DarrenW]

Looking at the top-speed figures, 395 mph seems a pretty common listing for earlier designs. Later figures would show around 416 or 417 mph with water injection, higher manifold pressures, the F6F-3's propeller, reconfigured cowl-flaps (I'm not sure if this had a propulsive benefit -- it's predominant goal was to keep oil from spraying over the windscreen, but tighter cowls usually do favor speed).....

I fully agree. The F4U-1A was often retrofitted with the F6F's propeller because it was the better choice. Even the pilot's manual claimed it should be used whenever available:

http://www.jasonblair.net/wp-conten...Manual-for-F4U-Corsair-Aviation-Pubs-1977.pdf

 

[DarrenW]

Yeah, as there were various changes that allowed higher boost (water injection, higher octane, and the F4U-1's started using the F6F's propeller).

The rating of US aviation fuel in the Pacific theater was 130 octane for most of the war, mainly because the performance of Japanese planes (or lack there of) never warranted a push for the higher 150 octane fuel.

 

[Zipper730]

Though I have read this from time to time I haven't seen any official documentation that supports it

Oh, I didn't know that...

This is interesting to me too. Grumman also estimated the top speed of the F6F-3 to be 391 mph in a 'normal' fighter condition at 25,000 ft

It almost looks like they just listed the contractor data...

The rating of US aviation fuel in the Pacific theater was 130 octane for most of the war, mainly because the performance of Japanese planes (or lack there of) never warranted a push for the higher 150 octane fuel.

I thought they eventually did switch to 150? Regardless, it would appear they were able to bump up the manifold pressure, even if it shortened service life.

 

[DarrenW]

Oh, I didn't know that...

It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly..... but not here of course.

Some of this has to do with the misinterpretation of source data. Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a modified without equipment necessary for carrier operation, and not representative of aircraft in actual service. For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following: a non-standard higher efficiency F6F propeller, a stramlined wooden block for tailwheel, removal of tail hook, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.

In addition to this, there seems to be no F4U-1 variants tested with bomb racks installed, which will make a decent amount of difference in the testing outcome. Marine Corsairs were involved in close air support very early on so they often carried bombs in the performance of their duties. It wasn't until the Hellcat began to displace dedicated shipboard dive-bombers (like the Dauntless) that it began to do 'ground-pounder' work, so up to that point it normally flew in a 'clean' condition. FWIW there are several test reports on the site that give performance figures for the Hellcat with racks installed.

There's also the fact that the F4U is one helluva sexy airplane so it's totally reasonable to accept that it was faster than the portly ole' Hellcat, and it generally was. Problem is that this approach can lead to biased comparisons between the two, which is what we seem to have today. So when people line these two airplanes up side by side, they tend to pull out their 'favorite' performance charts and have at it, but by doing so they sometimes fail to compare them under the same set of real-world parameters. I find the biggest mistakes to be the comparison of variants from different periods of the war and their particular configuration (i.e. racks, water injection, special modifications, etc.).

So what I'm trying to say here is that yes, the Corsair WAS faster than the Hellcat, but by how much depends of a lot of considerations. Unsubstantiated information such as F4U-1Ds flying at 425 mph only leads to distorted calculations however and is something to be weary of when performing any form of genuine comparison between the two airplanes.

 

[DarrenW]

I thought they eventually did switch to 150? Regardless, it would appear they were able to bump up the manifold pressure, even if it shortened service life.

I think the trend was leading in that direction but the war ended before it became a necessity of any kind. IMHO the power ratings of both the R-2800-8W and -10W were somewhat conservative, and for the most part was implemented to keep engines healthy and happy. Nobody wanted an inadvertent engine failure due to unnecessary over-boosting, especially if it occurred over the vast expanse of the Pacific ocean. By keeping the margins wide pilots who felt compelled to exceed the nominal (and relatively safe) 52" Hg boost rating would do so only if a dire situation warranted it.

Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel). Granted the turbocharged P-47 would tend to benefit more from increases in both boost and octane rating but it definitely was on the table for both the F6F and F4U, especially if their performance ever started to lag behind the enemy aircraft that they normally encountered in combat.

 

[Dawncaster]

It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly..... but not here of course.

Some of this has to do with the misinterpretation of source data. Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service. For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following: a non-standard higher efficiency F6F propeller, removal of tail hook with faired cut-out, modified cowl flaps, enhanced streamlined tail wheel, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.

In addition to this, there seems to be no F4U-1 variants tested with bomb racks installed, which will make a decent amount of difference in the testing outcome. Marine Corsairs were involved in close air support very early on so they often carried bombs in the performance of their duties. It wasn't until the Hellcat began to displace dedicated shipboard dive-bombers (like the Dauntless) that it began to do 'ground-pounder' work, so up to that point it normally flew in a 'clean' condition. FWIW there are several test reports on the site that give performance figures for the Hellcat with racks installed.

There's also the fact that the F4U is one helluva sexy airplane so it's totally reasonable to accept that it was faster than the portly ole' Hellcat, and it generally was. Problem is that this approach can lead to biased comparisons between the two, which is what we seem to have today. So when people line these two airplanes up side by side, they tend to pull out their 'favorite' performance charts and have at it, but by doing so they sometimes fail to compare them under the same set of real-world parameters. I find the biggest mistakes to be the comparison of variants from different periods of the war and their particular configuration (i.e. racks, water injection, special modifications, etc.).

So what I'm trying to say here is that yes, the Corsair WAS faster than the Hellcat, but by how much depends of a lot of considerations. Unsubstantiated information such as F4U-1Ds flying at 425 mph only leads to distorted calculations however and is something to be weary of when performing any form of genuine comparison between the two airplanes.

There was an ongoing party.

Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service.

Hmm, Exaggerated.

There were no special modified planes used in production inspection trials for F4U-1, FG-1, F3A-1, F4U-4 and flight tests for british Corsairs. It is nonsensical to flight test with special modification configuration in a measurement to performance. I don't think the U.S. Navy wasted time and resources on such meaningless things. only few reports for special purposes used special modified planes, of course standard service conditions should not used for special purposes. and added external test devices with taped weapon holes, configuration used by most Corsairs in test, should not be treated as special modification or highly modified 'one-off' as you said, It's common for other models test reports including the Hellcat. and it had only slight effect on relative performance seems due to navy's correction. just see the below sections for details.

But before that, here is a list of all reports on the F4U page of Williams/Stirling website. only a few reports have been used special modified configuration, not many.

- ACP, SAC and British aircraft cards = official performances
- Detail Specifications = estimated performances except F4U-5's
- Maximum Speed of F4U-1 Airplane #02234 ("Cleaned-Up" Version) on War Emergency Power Ratings = clean-up test, of course standard configuration should not be used.
- Performance Characteristics of F4U-1 No. 02155 = no special modification
- Final Flight Report of Production Inspection Trials (TED No. BIS 2125) on Model F4U-1 Airplane = no special modification
- Final Flight Report of Production Inspection Trials (TED No. BIS 2121) on Model F3A-1 Airplane No. 04691 = no special modification
- Final Flight Report of Production Inspection Trials (TED NO. BIS 2122) on Model FG-1A Airplane No. 14575 = no special modification
- Final Report on Project TED No. BIS 2157 Production Inspection Trials of the Model F4U-4 Airplane =no special modification
- Flight Test of Two Model FG-1 Airplanes No. 14796 (British Corsair Mk IV KD 365) and British Corsair Mk IV KD 502 = no special modification
- Final Flight Report of Evaluation of Maximum Practicable Combat Power Rating for the Model F4U-1 Airplane Model F4U-1 Airplanes No's 55937, 50030 = overboost test, of course standard configuration should not be used, and Hellcat had similar modified planes in similar test report.
- Evaluation of Maximum Practicable Combat Rating Performance at Carburetor Impact Pressure of 32.8"- TED No. PTR 0415 F4U-1 No. 50030 = same as above report.
- Memorandum Report on F4U-1, No. 02296: Flight Tests = no special modification
- Memo. Report on F4U-1, No. 02296: Flying Characteristics and Design and Maintenance Qualities of F4U-1 = no special modification
- Corsair I JT.118 Handling trials A. & A.E.E. 30 December 1943 = no special modification
- Corsair Mk.II JT.259 Handling trials A. & A.E.E. 1 February 1944 = no special modification
- Corsair F.Mk.II JT.259 Performance trials and position error measurment = no special modification
- Corsair F. Mk.IV KD.227 (Double wasp R2800-8W) Level speed trials with and without water injection = no special modification
- Report on Comparitive Combat Evaluation of Focke-Wulf 190-A/4 Airplane NAS Patuxent River = no special modification
- Evaluation and Comparison Trials of P-51B and F4U-1 Airplanes. NAS Patuxent River = BuNo.17930 as standard but another one was overboosted.
- Flight Test of Water Injection Equipment - TED No. PTR 2105 F4U-1 No. 17930 = It seems main target, but it's corrected for standard plane by navy, see below sections.

and I've used reports of F6F-5 BuNo.58310 and F6F-5 BuNo.72731 for below drag reduction section, on the F6F page, there were only this two reports on the F6F-5.

For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following:

Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.

Officially, F4U-1 showed 407 mph without water injection and also without F6F type propeller(6501A-0). it's propeller blade design was older 6443A-21(3rd ACP pic) and 417 mph with water injection, It's standard performance for raised cabin F4U-1 without land-based configuration, many later F4U-1s were able to use this performance or even better with land-based configuration.

Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.

a non-standard higher efficiency F6F propeller

Blade design 6501A-0 was not factory installed type for F4U-1, but start service with VF-17 in solomon campaign and many F4U-1s have replaced propellers with this new type.

modified cowl flaps

It's not flapS, only top section of cowl flaps was replaced by a fixed plate completely covering the opening and It's standard improvement between early birdcage F4U-1 and raised cabin F4U-1. the Corsair that was put into battle without this was even small within the birdcage type.

It is a picture of VMF-215 on Hawaii, so it is at least before May 12. other units have different periods, but also installed within 1943, and standard for raised cabin F4U-1s.

removal of tail hook with faired cut-out
removal of catapult hooks
enhanced streamlined tail wheel
shell ejector openings were taped over

The effect of drag reduction for land-based configuration is not significant. according to Dana Bell, It was about +4 mph with hooks and folding devices removed. case for the F4U-1 BuNo.17930, folding devices remained so just +3 mph(2.4 + 0.6, see below chart) for hooks removed and faired cut-out.

High tail wheel was standard for late F4U-1s, but streamlined wooden block type was not standard. However, after take-off, it seems no way to clear effect than standard high tail wheel to performance, because after tail wheel door closed, only half of the wheel was just exposed.

both Hellcat(F6F-5 BuNo.58310/72731) and Corsair(F4U-1 BuNo.17930) taped over weapons in test, the Corsair's gun blast and shell ejector openings were taped over and the Hellcat's gun barrel openings were sealed/taped and blast tube fairing not installed. in this condition, even the Hellcat's shell ejection chutes opened, It does not seems to be special disadvantageous in terms of drag and performance compared to standard condition for both model. for example, Corsair's drag cofficient for install all six guns was just equivalent to catapult hook, so even at the worst, the effect is only slight as below chart.

Here, drag documents for F4U-1s.

These drag reductions seem to offset the drag of additional external equipment for test. however, since the drag to be reduced is different according to the added drag, the configuration would also differ to corrected for standard condition.

F4U-1 BuNo.17930's report stated several special instrument leads were carried exterrally from the firewall back to the cockpit. these were faired together to the fuselage by means of doped tape, making a half round projection of approximately 3/4" diameter. and F6F-5 BuNo.58310/72731's report also stated an outside air temperature gage of the electrical resistance type was installed for test purposes on the topside of the right wing pannel. there seems to be a slight difference in their additional drag coefficient each.

It's F4U-1 BuNo.17930, the white line is special instrument leads mentioned avobe.

As a result, F4U-1 BuNo.17930 seems appears to have achieved a drag similar to the service condition, as shown in the comparison to be described later, which is also the evaluation of the USN.

And this Navy's evaluation was evident by contrasting the F4U-1's ACP and comparison report with F4U-1, F6F-3 and Fw 190, If F4U-1 BuNo.17930 was specially modified for drag reduction, It should be clearly fast in all situations.

But compared to ACP the offical performance for service condition, the speed of BuNo.17930 was the almost identical except for the high speed high altitude range, and the comparative report explains why.

Because the F4U-1's early propeller blades showed a loss of efficiency at high speed high altitude range.

In conclusion, there was nothing so special for F4U-1 BuNo.17930's drag condition compared to standard due to navy's correction, It just seems equivalent late type land-based configuration raised cabin F4U-1. What I can say for sure is that the lots of the water injected clean wing F4U-1s with new propeller blades and land-based configuration was used in battle, and It's performance was unlikely to differ significantly from the F4U-1 BuNo.17930, basically.

However, the question arises then because the F4U-1D's top speed, which replaced the propeller blade design to 6501A-0, was still 417 mph.

From here on out, it's my guess, BuNo.17930 F4U-1's maximum speed 431 mph was for late type land-based configuration with lean mixture but F4U-1D's was not.

Look at this F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft. The report noted a loss in output from auto-rich due to caburation problems. Due to the similarity of the engine, the Corsair may also consider the possibility of experiencing the similar problem.

Compare the power curves of the F4U-1 BuNo.17930 and F4U-1 BuNo.50030, can see that a similar result is happening, despite the slightly higher manifold pressure caused by the 25 drill water jet, it shows lower altitude performance. on the other hand, it seems that the F4U-1s in early 1944 basically used lean mixture, It was a time when F4U-1's water injection had just begun to be used for battle. In the comparison report with the Fw 190 mentioned above, the F4U-1 also used a lean mixture, but experienced overheating. I guess that more detailed and practical operation restrictions have been applied over combat time increasing, for official performance, it must run for 5 minutes and the cylinder temperature should not exceed 260, as a result, it seems showed the lowered official performance. The F4U-1 BuNo.50030's report contained effort for meet the operation restrictions, However, that is not found in the report of F4U-1 BuNo.17930, perhaps this made the difference.

Back to the F4U-1D, clean wing F4U-1D with new 6501A-0 propeller blades had a top speed of 417 mph at 19,900 ft in official ACP and F4U-1 BuNo.17930 showed 431 mph at 20,300 ft with land based configuration. It shows the difference between critical altitude 400 ft and vmax 14 mph. but F4U-1D was carrier-based configuration, so need to add the drag of carrier-based configuration, references have stated that it was about 4 mph. then vmax difference is reduced to 10 mph and It can be assumed that the F4U-1D is capable of speeding 427 mph at 20,300 feet. hmm, It's similar to the number I saw somewhere. Yes, I also saw the F4U-1D's top speed of 425 mph you mentioned, in several references, It's 8 mph faster than F4U-1D ACP's 417 mph that shows a similar difference with above rich/lean graph. As explained above, if that was the F4U-1D's top speed with lean mixture, it might not be so unusual because It's also 6 mph slower than F4U-1A BuNo.17930 with same propeller, engine and clean wing, 6 mph is a convincing figure for the difference between the carrier-based configuration and the land-based configuration as above documents for drag and reference books. I really want to meet the author of the reference that first used 425 mph.

And it should be remembered that the F6F-5 also had these type of speed record - can be achieved, but unofficial. In the November 1944 TAIC test, the F6F-5 showed 409 mph. compared to F6F-5's SAC, It seems to have been a lean mixture as smiliar to above situation. I used to express the opinion that the F6F-5 was clearly a 400 mph over group aircraft, but it seemed to have little or no impact, like when I cope against biases about the Corsair.

If going to do a comparison, it would be better to distinguish between the official and unofficial performances and make comparison in the same classifications with same configuration. for example, the F6F-5 SAC's depressing official performance, Vmax 330 knots (380 mph), should not be compared to the land-based F4U-1's unofficial performance of 431 mph or the F4U-1D's ambiguous 425 mph. Since the F6F-5's that official performance was for a combat condition with three external pylon/racks installed, it should be compared to the 409 mph of the official performance for F4U-1D's combat condition with three external pylons/rack in ACP, even 417 mph cannot be compared. It's a pure fighter configuration without pylons. One interesting data is the July 1944 ACP of the F6F-5N. smiliar performance reduction I mentioned above for F4U-1s also appear in this document with F6F-5 SAC. despite the radar pod's extra drag, this F6F-5N could accelerated to 340 mph at sea level and had a Vmax of 391 mph at 18,800 feet. I felt slight more familiar with my hypothesis, and I also recalled the possibility that the 1944 ACP for the F6F-5 included a Vmax over 400 mph. have to find it. There was F6F-5N's ACP, so there would be F6F-5's.

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In addition, It should not be forgotten that maximum speed of the FG-1s and F3A-1s were lower than Vought F4U-1s.

The US service Vought F4U-1's maximum speed was almost identical at the sea level for neutral blower stage with least influence of the supercharger, is follows.

for military power

348 mph for Birdcage F4U-1 BuNo.2155
350 mph for F4U-1 ACP
350 mph for F4U-1 BuNo.17930

for combat power

363 mph for F4U-1 BuNo.49832 (2 minutes accelration time limit)
365 mph for F4U-1 BuNo.17930
364 mph for F4U-1 BuNo.50030
366 mph for F4U-1D ACP (clean wing as F4U-1 configuration)

on the other hand, for FG-1 and F3A-1, for military power

339 mph for F3A-1 BuNo.04691
332 mph for FG-1A BuNo.14575
335 mph for FG-1 BuNo.14769

Although the altitude performance varies depending on the condition of the atmosphere and the supercharger, I think that the performance at sea level can be objectively compared. As a result, Goodyear and Brewster Corsairs were slower more than 10 mph with same power setting. As far as I remember, Brewster had a problem with F3A-1's quality control and occurred accidents and through repackaging some internal components, the FG-1 was only a few inches longer than the F4U-1 and there was also Nash's R-2800 installed for some of these Corsairs. These changes may have affected but I have no specific information for it.

 

[tomo pauk]

Just dropping to say that this is one very informative thread.

 

[Laurelix]

F4U-1 - 683km/h at 7000m (WEP)
F6F-5 - 644km/h at 5700m (WEP)

At Sea Level the F4U-1 is like 50km/h faster

 

[tomo pauk]

Is that supposed to be a contribution?

 

[Zipper730]

It seems rather commonplace these days to accept without question higher and higher maximum speeds for the various Corsair variants, but if someone even mildly suggests a 400 mph F6F-5 they are called a fool and dismissed accordingly.....

After awhile, old sources become accepted without question: Sometimes, the sources weren't in context, or were based on misinterpretations of the source data.

Unlike the Hellcat, there are many Corsair test reports on the Williams/Stirling website in which the subject aircraft is a highly modified 'one-off', and not representative of aircraft in actual service.

Yeah, when I see those on WWII Aircraft Performance, I generally ignore the report. That said, the one of the F4U-1 doing 417 mph I actually dismissed because of the gun-ports being taped over, an F6F-3's propeller installed, and the top cowl-flap faired over (I mis-read as the flaps faired over -- like those on the wings). Turns out that one was actually a normal modification that was extensively employed in carrier-service.

For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following: a non-standard higher efficiency F6F propeller, removal of tail hook with faired cut-out, modified cowl flaps, enhanced streamlined tail wheel, removal of catapult hooks, and the shell ejector openings were taped over. Without a tail hook this aircraft could no longer be truly classified as a carrier aircraft. Lastly, many of the Corsairs on the site were tested using Combat power settings, which was not the case concerning the Hellcat. The use of ADI enhanced performance considerably and made an apples-to-apples comparison to planes without it impossible.

Some questions

1. Why would you cover over the shell-ejector openings? I thought the spent casing would be fairly hot after the propellant lit off...
2. I never knew the Hellcat wasn't being run at combat power settings. How did it perform when water injection was employed

In addition to this, there seems to be no F4U-1 variants tested with bomb racks installed, which will make a decent amount of difference in the testing outcome.

Yeah, it'd slow it down, though it'd make sense for the USMC.

IMHO the power ratings of both the R-2800-8W and -10W were somewhat conservative, and for the most part was implemented to keep engines healthy and happy.

I figured that, to some extent, the settings might have been conservative (I didn't consider the overwater nature). That said, I had considered that there might have been various sub-variant level changes to the engine design to allow for higher MAP.

Testing was performed on both engines using different sized water jets and carburetor impact pressure settings with very good results being obtained (up to 65" Hg was deemed safe while using 130 octane fuel).

How do you vary carburetor impact pressure? As for water-jet, I assume that sets the amount of water you can spray in at once?

Granted the turbocharged P-47 would tend to benefit more from increases in both boost and octane rating

Was this because of overland use or because of the turbocharger?

Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.

The 403 mph figure at 24800' does seem to conform with the comparison with the chart in reply #61 (Page 4), on the Fw.190 and F6F-3. I'm curious why there was such a discrepancy in listed speed (F6F: 391 mph vs. 373.5-377.5 mph; F4U-1: 395 mph versus 403 mph) and critical altitude for both.

Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.

Faulty pressurization? You mean they weren't producing an adequate boost?

 

[DarrenW]

Hi Dawncaster,

Oh boy, lots to unpack here. I'm very glad you chimed in because I consider you one of the more knowledgeable members on this site concerning the Corsair and wanted to hear what your research on this subject had to say. This wouldn't be a definitive discussion without you.

There's only a few things I need to clarify though, as I'm in agreement with the majority of the points you've made and I definitely do not agree that the Hellcat was faster than published figures due to erroneous airspeed calibration data (which was the original premise of the thread). I also have only been concerned with the performance of F4U-1s and not the F4U-4 or -5 because they are not contemporaries of the F6F-3 and -5 Hellcat.

Hmm, Exaggerated.

Sorry I misspoke here but my intent was genuine. It depends on what the word "modified" really means to an individual, so I should have worded it more clearly. There were actually two aircraft (No. 02234 & BuNo. 17930) which to me seemed to be highly modified, even if some of these modifications eventually became standard on production aircraft. Another modified aircraft that I was referring to was BuNo. 14575, which had the tail hook removed and had the bottom of the tail cone smoothly faired over. Both BuNos. 50030 and 55937 had the 13' 1" propeller and show testing at non-standard carburetor impact pressure settings so their performance would obviously be better than aircraft with the standard 13' 4" propeller and utilizing authorized impact pressure levels, but you are right that there is also a report where the Hellcat was tested at these non-standard levels too so it's partially a moot point.

And just to make clear the photo you posted of BuNo. 17930 was obviously taken at a different stage in testing than what is found in TED No. PTR 2105, as the special tail wheel faring wasn't installed at that time:

The report does state that the 'important modifications" were not standard on previous production F4U-1's, but I do agree that similar in-field modifications were being performed, if only at a localized level. From my research it looks like it wasn't until the F4U-1C/D variants that the more efficient 13'1" propeller was fitted to production aircraft so this in itself should be considered a modification for aircraft that came before it.

So the question remains, if BuNo. 17930 was indeed basically a standard land-based F4U-1 in service at the time, why would they bother mentioning those details as modifications, and why were they so interested in knowing how they effected performance? My feeling is that if those modifications were already being included in production aircraft there would be no need to mention them in the report.

The effect of drag reduction for land-based configuration is not significant. according to Dana Bell, It was about +4 mph with hooks and folding devices removed.

This is interesting as the report you referred to earlier estimated a speed gain of up to 8 mph with these modifications in place and NACA report L5A30 seems to support this conclusion as well. If we subtract 2 mph from this figure for non-smoothed surfaces and non-faired fuselage access doors (not necessary in order to make it a land-based only aircraft - reference the drag document from your previous post for this amount) we get a net gain of 6 mph with the removal of tail hook and fairing over the wing fold joints. I'm also assuming that the catapult hooks were removed to arrive at the 8 mph figure so there's no need to add that drag component back into the equation:

http://www.wwiiaircraftperformance.org/f4u/p-51b-f4u-1-navycomp.pdf

F4U-1

F6F-3

F6F-3

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf

Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.

Officially, F4U-1 showed 407 mph without water injection and also without F6F type propeller(6501A-0). it's propeller blade design was older 6443A-21(3rd ACP pic) and 417 mph with water injection, It's standard performance for raised cabin F4U-1 without land-based configuration, many later F4U-1s were able to use this performance or even better with land-based configuration.

Ok, you got me here, I never consider ACP documents as actual "test reports" so I should have been more careful with my assertion. Certainly if I was including these handy performance references I wouldn't have mentioned such things as removed tail and catapult hooks, or taped over shell ejector openings as these conditions would render an aircraft useless as a carrier combat aircraft. Be that as it may, there's no other performance figures presented on the website which have aircraft similarly configured that match what is found in this particular ACP so I'm curious which "flight tests" they are referring to.

However, the question arises then because the F4U-1D's top speed, which replaced the propeller blade design to 6501A-0, was still 417 mph.

While I don't outright question the validity of the ACP concerning the propeller blade design, could the test data presented possibly be for an F4U-1 with the 13' 1" propeller? As you said earlier it was common for this to be the case, especially by the date the ACP was published. Do you happen to have any other official performance data that show the F4U-1 with a 13' 4" propeller making that kind of speed?

Look at this F6F-5 BuNo.58310 graph, the auto-lean curve showed faster than the auto rich at altitude, the vmax was about 8 mph faster, and the critical altitude increased about 400 ft. The report noted a loss in output from auto-rich due to caburation problems. Due to the similarity of the engine, the Corsair may also consider the possibility of experiencing the similar problem.

Yes, I also saw the F4U-1D's top speed of 425 mph you mentioned, in several references, It's 8 mph faster than F4U-1D ACP's 417 mph that shows a similar difference with above rich/lean graph. As explained above, if that was the F4U-1D's top speed with lean mixture, it might not be so unusual because It's also 6 mph slower than F4U-1A BuNo.17930 with same propeller, engine and clean wing, 6 mph is a convincing figure for the difference between the carrier-based configuration and the land-based configuration as above documents for drag and reference books. I really want to meet the author of the reference that first used 425 mph.

Not quite sure what to make of your theory but I do find it interesting that engine charts differ for the two F4U-1 pilot's manuals that I have. The manual dated 1 June 1944 has an auto-rich mixture selected for everything but max cruise and minimum fuel consumption settings, while the other dated 15 March 1945 recommends it during take-off only. So it seems that auto-lean was the preferred setting for the R-2800-8W, and because of this I find it difficult to believe that the F4U-1D would be tested in auto-rich only, especially if performance suffered as a result. But I guess anything is possible.

By contrast, the three F6F manuals I have only recommend an auto-rich mixture during take-off and landing.

1 June 1944

15 March 1945

both Hellcat(F6F-5 BuNo.58310/72731) and Corsair(F4U-1 BuNo.17930) taped over weapons in test, the Corsair's gun blast and shell ejector openings were taped over and the Hellcat's gun barrel openings were sealed/taped and blast tube fairing not installed. in this condition, even the Hellcat's shell ejection chutes opened, It does not seems to be special disadvantageous in terms of drag and performance compared to standard condition for both model.

As far as shell ejector chutes go, taping them over would make the guns non-functional so besides modifying an aircraft to perform reconnaissance work I don't see a reason for the practice, which was common during the Corsair tests but not the Hellcat. Gun blast tube fairings were only fitted on the first 909 F6F-3s delivered, so I am baffled as to why they are mentioned in the case of F6F-5 BuNo.58310. Just a guess but maybe further testing was performed with this aircraft to see if they would improve performance in some measurable way???

FWIW there has been testing performed at NACA and presented in report L5A30 which found that taping over the shell and linkage ejector chutes of the P-51 under test could yield a 3 mph increase in speed. I can only assume that there would have been even a greater benefit afforded the F4U, seeing that it had more slots to be taped over:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092668.pdf

As a result, Goodyear and Brewster Corsairs were slower more than 10 mph with same power setting. As far as I remember, Brewster had a problem with F3A-1's quality control and occurred accidents and through repackaging some internal components, the FG-1 was only a few inches longer than the F4U-1 and there was also Nash's R-2800 installed for some of these Corsairs. These changes may have affected but I have no specific information for it.

Hmm, it seems that the US Navy judged the two to be generally similar to those produced by the parent company:

http://www.wwiiaircraftperformance.org/f4u/F3A-1_04691.pdf

http://www.wwiiaircraftperformance.org/f4u/kd365.pdf

I used to express the opinion that the F6F-5 was clearly a 400 mph over group aircraft, but it seemed to have little or no impact, like when I cope against biases about the Corsair.

I agree with you. Even F6F-5 BuNo.58310 reached 395 mph @ 18,750 feet while utilizing Combat power, and this was with a starboard wing pylon installed (known to reduce speed by roughly 5 mph at this height). So we have an honest 400 mph F6F-5 here in a 'clean' condition....

Back to the F4U-1D, clean wing F4U-1D with new 6501A-0 propeller blades had a top speed of 417 mph at 19,900 ft in official ACP and F4U-1 BuNo.17930 showed 431 mph at 20,300 ft with land based configuration. It shows the difference between critical altitude 400 ft and vmax 14 mph. but F4U-1D was carrier-based configuration, so need to add the drag of carrier-based configuration, references have stated that it was about 4 mph. then vmax difference is reduced to 10 mph and It can be assumed that the F4U-1D is capable of speeding 427 mph at 20,300 feet. hmm, It's similar to the number I saw somewhere.

You seem to have studied the Corsair's airframe drag extensively. Have you considered how much the glossy blue paint scheme and revised wing walkways found on the F4U-1D may have contributed to drag reduction? From what I can tell it may add about 3 mph, but this is only an estimation after looking at all the F6F test data that's available to me.

Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.

Could you tell me more about this? I mentioned this earlier in the thread but was told that due to engine similarities, whatever problems the F4U was experiencing in this regard would have manifested itself in the F6F as well.

 

[DarrenW]

I never knew the Hellcat wasn't being run at combat power settings. How did it perform when water injection was employed

Almost all F6F test data on the website shows maximum performance while in Military power. There are a few reports that show testing while utilizing Combat power but when compared to the F4U they are far fewer in number. The data I have seen varied due to height and seems to suggest an increase of about 5-20 mph from S/L to around 22k feet.

 

[DarrenW]

How do you vary carburetor impact pressure? As for water-jet, I assume that sets the amount of water you can spray in at once?

They used larger water jets and made adjustments to the supercharger fuel and water regulators which allowed for a higher flow rate to occur (hence more impact pressure), and this allowed for higher manifold pressures to be developed safely without detonation which in turn produced more power.