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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?
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.
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.
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).One must also be careful to only compare models that were in service during the same period of the war.
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).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
The graph which compares the Fw-190, the F4U-1, and the F6F-3 leaves me with more questions than answers.A similar speed differential existed in Combat power settings as well (F4U-1A and mid-production F6F-3 are without racks, horsepower ratings unknown)
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.hey'd apparently eventually eke out speeds of around 425 mph in operational aircraft (F4U-1D
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'
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.
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).....
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).
Oh, I didn't know that...Though I have read this from time to time I haven't seen any official documentation that supports it
It almost looks like they just listed the contractor data...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
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.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.
Oh, I didn't know that...
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.
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.
Hmm, Exaggerated.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.
Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.For example, the only F4U-1 which attained 400 mph speeds without water injection was modified with the following:
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.a non-standard higher efficiency F6F propeller
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.modified cowl flaps
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.removal of tail hook with faired cut-out
removal of catapult hooks
enhanced streamlined tail wheel
shell ejector openings were taped over
After awhile, old sources become accepted without question: Sometimes, the sources weren't in context, or were based on misinterpretations of the source data.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.....
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.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.
Some questionsFor 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.
Yeah, it'd slow it down, though it'd make sense for the USMC.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.
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.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.
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?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).
Was this because of overland use or because of the turbocharger?Granted the turbocharged P-47 would tend to benefit more from increases in both boost and octane rating
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.Over 400 mph maximum speed without water injection was common for Corsair except early bardcage type.
Faulty pressurization? You mean they weren't producing an adequate boost?Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.
Hmm, Exaggerated.
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.
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.
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.
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.
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 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.
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.
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.
Birdcage Corsair's 395 mph seems from early troublesome supercharger with faulty pressurization.
I never knew the Hellcat wasn't being run at combat power settings. How did it perform when water injection was employed
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?