F4U-4

[Nashwan]

What was the power output used by the F4U-4 in it's wartime service?
I just spotted a reference elsewhere that got me checking. In the pdf posted by F4UDOA some time ago, it lists the F4U-4 with one set of performance figures at 70" WEP, 2650hp, and later revises them down to 2450hp, with a corresponding drop in climb rate and speed.
The revison downwards is dated April 45, but what I'd like to know is did the 2450hp figure stick, or were the engines re rated again before the end of the war?
If anyone has got any info on this thanks for the help, and thanks to F4UDOA for posting the docs in the first place.

[F4UDOA]

Nashwan,

Actual production in WW2 F4U-4's used the PW-R2800-18W as well as the 34W. The -18W which was in the WW2 varient could be run at higher manifold pressures than used in normal service that would increase HP as well as using higher octane fuel which also increased performance. In fact this could be done with any of the wartime F4U's much the same as any Two stage mechanicaly Turbo-charged engine such as the F4U or F6F. The F4U could be flown in Nutural blower, Low blower or high blower stages. All designed to increase or maintain MAP up to alt. In fact Grumman test pilot Corkey Myer swears the only reason the F4U-1 was 30knots faster at sea level than the F6F was the efficiency of the Vought air intakes for the Low blower stage of the F4U's R2800. They both had the same engine but different means of air intake.

Remeber this was only possible because most American A/C with the PW had manual control over high blower and low blower and nutural stages. This was not so in the FW190 series which was done automatically without pilot control. It was also possible to use high blower at low alt but would have caused a massive engine failure for sure. So the F4U-1 and 4 could be flown at different maps. However the production numbers are 2450HP with a 4K per minute climb at sea level combat power and a 3600fpm at Mil power. And a speed of 440mph at 18K and 450+ at 25K standard 100octane av gas.
Quite the beast.

[ 07-10-2001: Message edited by: F4UDOA ]

[Nashwan]

Thanks for the clarification, and as I said for the original data.

[Razzor]

Are you sure about that 100 octane? I thought they used 115/145 octane. Those engines were designed for the higher octane fuels, and although they will run on 100/130, they wouldn't develop near the HP that they could on 115/145. Now, with only 100LL available, those Pratts and Wrights are really hog tied. Pun intended  

Razzor

[Bodhi]

Best gas we could attain during the war was 120 octane, unless it was the states.  Do not let the higher statements fool you.

[ 07-14-2001: Message edited by: Bodhi ]

[Karnak]

Bodhi,

I understand that the British use 150 Octane fuel in some Spitfire LF.Mk IXs.

[gripen]

Originally posted by Karnak:
Bodhi,

I understand that the British use 150 Octane fuel in some Spitfire LF.Mk IXs.

AFAIK the RAF used 150 octane fuel on the Buzz Bomb (V-1) intercepting missions and not just in the Spitfires but in the Tempests, Mosquitos and Mustangs too.

Gripen

[gripen]

Originally posted by F4UDOA:


It was also possible to use high blower at low alt but would have caused a massive engine failure for sure. So the F4U-1 and 4 could be flown at different maps.

QB]

Hm, AFAIK the R-2800 had automatic pressure controll. So there was no sense to use high blower at low altitude, low blower could certainly do max possible manifold pressure (say 60-70"). Using high blower at low altitude would have resulted lower performance than low blower, because low blower was more efficient at low altitude.

Gripen

[F4UDOA]

Gripen,

What was it called? I know the high and low blower were manually operated on the F4U until the F4U-5 which was post WW2. Why would low blower be less efficient than the high blower? It seems to me that they are called low and high because of the need to develope higher boost at high alt. At lower alt I cannot see why high blower would not overboost the engine. I think I have read something about this somewhere. Could you help "fill in the blanks"?

Also this test on the F4U-4 that I am quoting from is not the 120octane test. It was a wartime test done with 100octane gas. The 120 octane gas gave the F4U-4 a climbrate of 4900+fpm. The 100 octane it is a 4000fpm.

Here is a link to the data I posted on my webpage. It is a 30 page doc and 6 meg. There are two test of the -4. One is at 70inches of MAP anf the other is 60inches. I reccomend down loading this doc first and NOT trying to read it from it's location.

here it is

MyF4Udata

[Nashwan]

I know most British engines used automatic boost control. I tried to come up with an explanation but found this one which is much better
"The throttle lever was connected to the automatic boost control which, in turn, controlled the opening of the throttle butterflies. Manifold pressure was boosted by the supercharger up to 18 lbs/sq.in above atmospheric pressure in the Griffon and 9 lbs in the Centaurus. [American practice is to measure boost as absolute pressure, expressed as inches of mercury, thus manifold pressure 30 ins.hg in American engines equals zero boost in British]. The pilot sets the climbing power needed, for example, in the Seafire, maximum rate of climb 150 knots IAS , power +9lbs and 2600 rpm , and the automatic boost control progressively opens the butterflies in the climb until the full throttle height, for that boost and rpm setting, is reached and boost begins to fall. Shortly after, the altitude switch should change the supercharger to high gear, boost increases, throttle opening is consequently reduced and, as the climb continues, progressively re-opened until a second full throttle height is reached, then boost again falls." http://www.auf.asn.au/magazine/seafires1.html
As far as I know British twin supercharged engines had a 2 position blower switch, which allowed selection of medium supercharger or auto, there was no option to select full supercharger.

Do you know when the US navy begin using the higher octane fuel, and were F4U-4s in service adjusted to make use of the higher power available?

[ 07-16-2001: Message edited by: Nashwan ]

[F4UDOA]

Nashwan,

I haven't seen any test documents that specifically refer to higher octane fuel before the end of WW2. However I do have test records of higher manifold pressures used on F4U's. Up to 72 inches in the F4U-3 which was the Supercharged version of the F4U-1. How these pressures were achieved I do not know. In the test of a F4U-1A and F4U-1(modified) the F4U-1 was run at 65inches of MAP while the F4U-1A was at 60.

Here is that test.

P-51B vs F4U-1/1A

[gripen]

F4UDOA,

The R-2800 in the F4U had two stage system which could be operated:
1. Neutral Blower, this is engine stage alone. This could do about 60" up to about 4-5k. I quess WER rating of the F4U-4 did not use this setting att all because neural blower could not do 70" at sea level.
2. Low Blower, this is auxiliary stage at low speed. This could do 70" up to about 7-8k (see page 2 in your source), that is critical altitude of the Low blower.
3. High Blower, this is auxiliary stage at high speed. This could do 70" up to about 16k (see page 2 again) and that is critical altitude of the high blower

The automatic pressure control keeped MAP constant 70" below these critical altitudes (just like Nashwan told). Both blowers could be used at low altitude for 70" but difference is that low blower consumes power about 100-150 hp less than high blower (see again your source). This is why low blower is more efficient than high blower at low altitude.

Gripen

[F4UDOA]

Gripen,

The 70inches of MAP shown in the beggining of my document is from the XF4U-4. Check the last page of the doc and you will see that the critical alt. of the engine has gone up from 16,000ft to 26,000ft. This reduced max HP from 2650 to 2450HP but gave it a better performance curve at alt while maintaining a 376mph speed on the deck. But the production F4U-4 never ran higher than 60inches with 100octane fuel.

[gripen]

Originally posted by F4UDOA:
Gripen,

The 70inches of MAP shown in the beggining of my document is from the XF4U-4. Check the last page of the doc and you will see that the critical alt. of the engine has gone up from 16,000ft to 26,000ft. This reduced max HP from 2650 to 2450HP but gave it a better performance curve at alt while maintaining a 376mph speed on the deck. But the production F4U-4 never ran higher than 60inches with 100octane fuel.

My Mistake, I just took first F4U-4 graph what I saw for an example. I did not know what was the WER rating MAP of the production F4U-4 (that is why used, say 60-70" in my first post).

Anyway, critical altitude depends also on MAP, if the production F4U-4 had had 70" WER then critical altitude would have been about same as in the XF4U-4 (around 16k). It should be also noted that those critical altitudes in last pages of the document are rammed, so comparable rammed critical altitude for the XF4U-4 and 70" is around 20k (see page 20).

That P-51 vs F4U comparison in your web pages is pretty interesting. Seems that navy testers wanted to show F4U in the best possible light because they used that special WER for that another F4U.

Gripen

[F4UDOA]

Gripen,

The Navy was actually doing testing with the P-51 at the time for carrier trials. The F4U-1A was the representation of the actual service F4U and the modified F4U-1 was supposed to be a mock-up of a F4U-4. I have some pics of a P-51D being flown off of carriers. It was to be designated the SeaHorse. However it didn't have the low speed control neccesary for carrier duty.

Later
F4UDOA