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

[Zipper730]

That performance report says the Hellcat engine was down on power, perhaps due to the carburetor not metering correctly. Heavy carbon deposits on the side of the plane are mentioned. It's not the first time I've see a complaint of substandard engine performance in those reports. Maybe that was the reason Grumman's tests showed Hellcat and Corsair evenly matched in speed. If the engine of their one Corsair exemplar was a little below par, that could account for the result.

Was that common with the F4U?

Another question would be claims by race pilots that claimed they were similar in speed: That said, I could see a few reasons why that could occur.

1. These designs were highly souped up with fine-tuned engines: They might not have been as equally fine tuned, which would mean the F6F could have been tuned to squeeze more power out and the F4U wasn't.
2. The F6F could turn tighter than the F4U: That would have allowed it to complete a circuit more easily. That said, I don't know how these planes compare in sustained agility, and the F4U could out-roll the F6F, which might even things up.

 

[DarrenW]

If the engine of their one Corsair exemplar was a little below par, that could account for the result.

This could definitely be the case, especially since it seems that there wasn't any critical monitoring of actual engine output, as was the norm during navy testing. 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. That's why the US Navy test results are more reliable, at least to me anyway.

 

[Conslaw]

I believe in most of what Meyer said, but his assertion that the Hellcat's top speed discrepency with the Corsair was based on a calibration error, I don't see as being credible. If you look at all the tests on ww2aircraftperformance.org, the F4U is consistently tested faster than the F6F, right until the end of the war. When I say this, I'm not knocking the F6F. It was fast "enough", and that's what matters.

 

[XBe02Drvr]

It was fast "enough", and that's what matters.

It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.
Cheers,
Wes

 

[eagledad]

Gentlemen

When the Navy tested the F6F-5 and the F4U-1D against an A6M5 and a Ki-61, the speed advantages over the 2 Japanese fighters that the F4U had was always greater than the speed advantages held by the F6F. So for me, it appears that the Corsair was faster than the Hellcat.

FWIW

Eagledad

See

http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf

and

http://www.wwiiaircraftperformance.org/japan/ptr-1111.pdf

 

[Zipper730]

This could definitely be the case, especially since it seems that there wasn't any critical monitoring of actual engine output, as was the norm during navy testing.

I'm not sure if I read that right. The USN did critically monitor or didn't critically monitor engines during their testing?

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.

I thought the F4U-1A had a higher canopy than the F4U-1 (birdcage).

Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.

I never knew the F4U-1 had any supercharger troubles...

That's why the US Navy test results are more reliable, at least to me anyway.

Less of a vested interest to fudge numbers...

It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.

Wouldn't have enjoyed the kill ratio they ended up with, now would they?

 

[wuzak]

Given the less efficient propeller and somewhat troublesome supercharger found on earlier Corsairs, what you suggest becomes even more plausible to me.

I never knew the F4U-1 had any supercharger troubles...

Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.

"Less efficient propeller"? Less efficient that what? The 4 blade propeller that came on the F4U-4, or the 3 blade propeller that the F6F stuck with?

 

[DarrenW]

"Less efficient propeller"? Less efficient that what? The 4 blade propeller that came on the F4U-4, or the 3 blade propeller that the F6F stuck with?

The three-blade variety, as this was the propeller type mounted to both the Corsair and Hellcat under comparative testing by Grumman in 1943. The four-bladed propeller didn't arrive on scene until later with the F4U-4 and the XF6F-6 prototype. From what I know Meyer never performed comparative flying tests with these two aircraft.

As far as efficiency is concerned, I was referencing a US Navy test document on F4U-1 #17930 which was fitted with a standard 13' 1" F6F-3 propeller instead of the usual 13' 4" propeller. The report clearly states that it was a "better efficiency" propeller and may have attributed to the increased level speed and climb. The various test reports that I've seen seems to support this notion (perhaps a 10 mph or more speed increase can be realized???).The slightly smaller and wider blade propeller became standard on later F4U-1Ds :

http://www.wwiiaircraftperformance.org/f4u/f4u-1-17930.pdf

...and there were other times when the F4U was "stuck" with the F6F's superior propeller:

http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf

 

[DarrenW]

I'm not sure if I read that right. The USN did critically monitor or didn't critically monitor engines during their testing?

I was referring to the testing performed by Grumman on their F4U "specimen". They apparently flew them in formation at varying throttle settings in order
to gauge speed differences between the two types. The US Navy always thoroughly monitored engine performance during testing.

I thought the F4U-1A had a higher canopy than the F4U-1 (birdcage).

I should have been more clear here. All F4U-1 sub-variants (-1A thru -1D) were known collectively as F4U-1s, as this was the major variant. When the raised canopy and other modifications were introduced the "sub-variant" became known as the F4U-1A. I will start using the correct terminology henceforth.

I never knew the F4U-1 had any supercharger troubles...

I read this somewhere but for the life of me can't find the reference for it. I was just suggesting another possibility to why this particular F4U may have been under-performing during the tests.

Wouldn't have enjoyed the kill ratio they ended up with, now would they?

Hard to say. The Japanese were already hard pressed to find competent pilots to man the J2Ms, N1Ks, Ki-100s, and Ki-84s already produced. Who would be flying these "marvels of the air" if they were made in even greater numbers? IMHO that's just as important as the planes themselves.

 

[DarrenW]

Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.

It's not that simple. The carburetor is only part of the equation, as there are many components to an aircraft induction system. In regards to the aircraft in discussion these included intercoolers, main & auxiliary stage blowers, gears & clutches, duct work and it's placement for ram air, supercharger regulator equipment, and various cockpit controls. The make-up of the induction systems found on the F6F and F4U were not identical and each had their own unique peculiarities.

 

[wuzak]

It's not that simple. The carburetor is only part of the equation, as there are many components to an aircraft induction system. In regards to the aircraft in discussion these included intercoolers, main & auxiliary stage blowers, gears & clutches, duct work and it's placement for ram air, supercharger regulator equipment, and various cockpit controls. The make-up of the induction systems found on the F6F and F4U were not identical and each had their own unique peculiarities.

The induction systems were different, including the disposition of intercoolers, but the main & auxiliary stage blowers, gears & clutches, and supercharger regulator equipment was, I'm sure, the same. Certainly the core engine was the same.

If there were problems that the F4U experienced that the F6F did not then it would likely be an installation issue, rather than an issue with the supercharger itself.

 

[Zipper730]

Given that the main difference between the engines powering the early production versions of the F6F and F4U was the way the carburetor pointed, any problems the F4U had with the supercharger would no doubt have manifested themselves in the F6F as well.

Do you mean pointed forwards/rearwards, up/down, or some mix of both? Do you have a picture or a diagram?

I was referring to the testing performed by Grumman on their F4U "specimen". They apparently flew them in formation at varying throttle settings in order to gauge speed differences between the two types. The US Navy always thoroughly monitored engine performance during testing.

Oh, okay.

I should have been more clear here. All F4U-1 sub-variants (-1A thru -1D) were known collectively as F4U-1s, as this was the major variant. When the raised canopy and other modifications were introduced the "sub-variant" became known as the F4U-1A. I will start using the correct terminology henceforth.

Ironically, I don't think the term F4U-1A was used during WWII. The British called those versions (F4U-1A/1D) the Mk.II, however.

I read this somewhere but for the life of me can't find the reference for it. I was just suggesting another possibility to why this particular F4U may have been under-performing during the tests.

Oh, okay. That makes more sense. I want to be clear, I have nothing against the F4U or the F6F. I just wanted to make sure all the information is accurate, this could affect important things, like beer-bets (i.e. "I'll bet you a round of beer that..."), and people interesting in making/modding flight-sim games. I would imagine historians would also find this to be interesting.

 

[wuzak]

Do you mean pointed forwards/rearwards, up/down, or some mix of both? Do you have a picture or a diagram?

One was an updraught and the other a downdraught carburettor.

I can never remember which had which.

There are plenty of pictures online of the F4U induction system, which was more complicated than the F6F's.

The F4U-4 used a different model R-2800 to the F4U-1, and I believe the carburettor was flipped.

Note that the carburettor on these 2 stage R-2800s was mounted on the engine stage supercharger, the first/auxiliary stage supercharger feeding the air through the intercooler system then to teh carburettor.

 

[DarrenW]

Ironically, I don't think the term F4U-1A was used during WWII.

The F4U-1A designation was recognized during the war, but it wasn't utilized very often in official documentation. Here's a British performance sheet for the Corsair Mk.II from November 1943 which includes the US version that it was based on:

http://www.wwiiaircraftperformance.org/f4u/f4u-1a-ads.jpg

It should be noted that during British tests the F4U and F6F often did not achieve the same level of performance as their American counterparts but the speed variances between the two types was still very similar to what was experienced during testing in the US, just at slightly lower values. There are a number of theories as to why this often seems to be the case, such as "possibly owing to the difficulty of reading the Standard American airspeed indicator and to the different methods of reduction " (as stated in one British test document), and that the Brits tended to monitor boost pressures (as opposed to US testing which monitored horsepower).

 

[Zipper730]

One was an updraught and the other a downdraught carburettor.

On just the F4U-1 variants? Or the F4U-1 & F4U-4?

The F4U-4 used a different model R-2800 to the F4U-1, and I believe the carburettor was flipped.

The F4U-4 had a carburetor under the chin, if I recall. If I was to make a guess, I figure it'd be an updraft simply because it's below the engine and the air would probably go up to make the engine, though it wouldn't be the first time I was wrong.

 

[wuzak]

On just the F4U-1 variants? Or the F4U-1 & F4U-4?
The F4U-4 had a carburetor under the chin, if I recall. If I was to make a guess, I figure it'd be an updraft simply because it's below the engine and the air would probably go up to make the engine, though it wouldn't be the first time I was wrong.

No, the F4U-4 had an inlet under the nose, but these fed ducts to the auxiliary supercharger, not the carburettor.

F4U-1 had an updraught craburettor (R-2800-8)
F6F-3 had a downdraught carburettor (R-2800-10/10W)
F4U-4 had an updraught carburettor (R-2800-18W)*

* description came from wiki

 

[Zipper730]

No, the F4U-4 had an inlet under the nose, but these fed ducts to the auxiliary supercharger, not the carburettor.

I was under the impression that, once you're in low blower, with both main and aux stages running, you would effectively be in a situation that would see the air go from the carburetor, to the auxiliary stage blower, and from there, to the main-stage blower, and into the cylinders?

From what I recall when in neutral blower the air came from a difference source to the main-stage blower, to the engine? I'd almost swear it came from the intercooler and, instead of going to the intercooler, it went to the engine (pretty strange, because I remember reading/hearing you'd need 2-3 times the amount of airflow through the intercooler as that used for the carburetor)

F4U-1 had an updraught craburettor (R-2800-8)

Okay, so all the F4U-1's used updraft carburetors, the F6F's used a downdraft system?

 

[wuzak]

I was under the impression that, once you're in low blower, with both main and aux stages running, you would effectively be in a situation that would see the air go from the carburetor, to the auxiliary stage blower, and from there, to the main-stage blower, and into the cylinders?

From what I recall when in neutral blower the air came from a difference source to the main-stage blower, to the engine? I'd almost swear it came from the intercooler and, instead of going to the intercooler, it went to the engine

No. There is a bypass to feed the carburetor when in neutral blower, otherwise the air enters the auxiliary blower, is compressed and sent through the intercoolers and then up to the carburetor.

This shows a cross section of the two stage supercharger, the engine being to the left and the auxiliary to the right.

Pratt & Whitney. Две ступени для "Осы" - Альтернативная История

Note the large port at the lower right. This is one of the discharge ports on the auxiliary supercharger (the other is rotate 180° around the supercharger's axis). This feeds into the intercooler on that side.

You can see the intake port to the auxiliary blower at the middle bottom. Note that there is a butterfly valve in the duct, presumably to close the duct when neutral blower is engaged. The air intake for the main supercharger, above which the carburetor sits, is at the top centre.

(There is also a picture of the R-2800-32W "sidewinder" engine from the F4U-5, which did have an updraught carburetor.
This attachment from another thread shows the layout of the -32W.
https://ww2aircraft.net/forum/attachments/p-w-sidewinder-jpg.97312/
)


This is a single stage R-2800 cutaway, which shows the carburetor feeding into the guide vanes and supercharger.

File:Pratt & Whitney R-2800-71 engine cutaway model at Archive room of JASDF Miho Air Base May 28, 2017 01.jpg - Wikimedia Commons

(pretty strange, because I remember reading/hearing you'd need 2-3 times the amount of airflow through the intercooler as that used for the carburetor)

I don't know what the excess flow capacity of the intercooler was, but it would have to be enough so that the pressure loss over the intercooler is as small as possible. It woudl be a balancing act between that, the size and weight of the intercooler and the amount of cooling air required.

Okay, so all the F4U-1's used updraft carburetors, the F6F's used a downdraft system?

 

[Conslaw]

It would be interesting to imagine what would have happened if the F4U and F6F had entered service just in time to find themselves faced with a sky full of Shidenkais, Raidens, and Reppus.
Cheers,
Wes

I think the American planes would have done almost as well as they did historically because American pilots were better trained,and they had a huge quantity advantage. The FM2 Wildcat did very well statistically despite a slight performance disadvantage to the Zero 52.

 

[Zipper730]

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?