WW and other documents guys: F4U-1A Climb Discrepancy

[Saxman]

This performance report was posted in the B-29 thread:

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

What really jumped out at me is the HUGE difference in climb chart on page 23 between the "F4U-1" used in the test (from it's BuNo a later-production F4U-1A equivalent to what we have in the game) and the performance of our F4U-1A.

This chart places the 1A as exceeding 3500fpm rate of climb at combat power PAST 10,000ft, and meeting 3000fpm up through 16,000ft. The rate of climb peaks at ~3700fpm ASL. Climb speed was given throughout the document at ~170-190kts, so this appears to be SUSTAINED rate of climb. The engine is tuned at 33.9" HG carburetor impact pressure.

These numbers are at least 1000fpm higher than what our F4U-1A is capable of achieving, and if I'm reading the report right, the aircraft was flown at LEAST at maximum combat weights, if not somewhat overloaded.

Anyone have thoughts as to why there's so such a discrepancy between this and our 1A?

[Stoney]

Yeah, it was a test profile.  Just like it was poor evidence of cooling problems on the R-2800, its poor evidence of a F4U-1 that could achieve a 3500 fpm rate of climb.

[Saxman]

Thing is, if this test was rigged by the USAAF so they wouldn't have to order the Corsair as you suggested in the other thread, I would think they'd have fudged the rate of climb numbers DOWN rather than UP.

[Stoney]

Thing is, if this test was rigged by the USAAF so they wouldn't have to order the Corsair as you suggested in the other thread, I would think they'd have fudged the rate of climb numbers DOWN rather than UP.

Did you not read that the test in this document was conducted by the Navy for purposes of determining whether or not they could run higher power WEP settings?  RTHolmes posted it to support his "R-2800 had cooling problems" argument...  The USAAF test he mentioned was from another document.

[Saxman]

I skimmed ahead to get to the results data, as I assumed this WAS the document Holmes mentioned (seeing as I'd requested he post it) so I didn't pay attention to who was actually running the test and why.

That would explain the climb rate, tho, if these engines were modified to run at higher power than standard.

Of course it invalidates his entire point for posting it in support of his argument in the first place considering these engines were being operated at settings OUTSIDE their normal operating conditions...

[Stoney]

Of course it invalidates his entire point for posting it in support of his argument in the first place considering these engines were being operated at settings OUTSIDE their normal operating conditions...

My point exactly. 

[RTHolmes]

Of course it invalidates his entire point for posting it in support of his argument in the first place considering these engines were being operated at settings OUTSIDE their normal operating conditions...

My point exactly. 

  read it again, 1/3 of the test flights were using the normal 31.5" impact pressure as a control reference, the others used increasing pressures of 32.8" 33.9" and 35" (untested due to failures at lower settings) to see what difference increasing impact pressure would have on performance and reliability.

must be nice to be able to selectively choose which evidence you want to use to support a hypothesis. sadly ive been burdened with objectivity by rigorous training in the scientific method, which means I have to look at all the evidence and accept whatever it supports, whether I want that outcome or not.

[RTHolmes]

anyways, back to the data. the dashed line shows a climbrate of over 3400fpm up to ~11k using WEP and 31.5" which doesnt look right to me as it doesnt match any of the other charts ive seen. the chart states the test ran at 33.8", perhaps the lower settings are calculated/interpolated rather than tested?

[texastc316]

Can you imagine the whines if the f4 could climb like that in game? Lol

[Stoney]

read it again, 1/3 of the test flights were using the normal 31.5" impact pressure as a control reference, the others used increasing pressures of 32.8" 33.9" and 35" (untested due to failures at lower settings) to see what difference increasing impact pressure would have on performance and reliability.

must be nice to be able to selectively choose which evidence you want to use to support a hypothesis. sadly ive been burdened with objectivity by rigorous training in the scientific method, which means I have to look at all the evidence and accept whatever it supports, whether I want that outcome or not.

Its a test regime.  They were purposefully flying the aircraft into high manifold pressure situations, using water, with gear and flaps down, at climb angles with manual cowl flap settings.  Heck, the planes weren't even running on Avgas--they were running an ADI mixture to prevent detonation.  The whole thing basically boiled down to whether or not use of higher WEP power settings overheated the engines, so they could determine whether or not they could raise the WEP rating of the plane.  As they could not keep the planes from overheating, the conclusion states they couldn't support raising the WEP setting to something higher.  That is completely different from saying that R-2800's had cooling problems...  For you to pull that conclusion from that report is truly laughable...

But, I know I won't get the last word with you, so I'll just read the rest of this one...

[RTHolmes]

indeed the climb section of the tests were conducted "under the most adverse conditions possible", but still within the operating limits. however, the 5min WEP then 15min Mil sections of each test were conducted after 30mins of level cruise (ie. ideal conditions.) neither of the engines tested using normal operating settings (P-12771 and P-16219) completed the tests successfully.

excess temperatures are a consistent theme in this report and the limiting factor in all of the tests. one of the report recommendations is the fitment of a carb air temp warning light, why would this be necessary if overheating wasnt a problem?

Heck, the planes weren't even running on Avgas--they were running an ADI mixture to prevent detonation.

Talk about laughable, I'd like to see how far you get by filling your fuel tanks with a 60% alcohol/40% water mix. Personally I'd fill the tanks with avgas and put the AD mix into the water injection tank.
 

[Stoney]

Talk about laughable, I'd like to see how far you get by filling your fuel tanks with a 60% alcohol/40% water mix. Personally I'd fill the tanks with avgas and put the AD mix into the water injection tank.

Poorly worded sentence on my part.  All I meant was that the mixture they were using wasn't a stock gas/water mixture purposefully because they knew they were going to operate the engines at power settings that would lead to detonation.

one of the report recommendations is the fitment of a carb air temp warning light, why would this be necessary if overheating wasnt a problem?

Induction air temperature is always a consideration when using supercharged or turbocharged induction systems.  But, its an induction temperature issue, and not one of cylinder cooling.

This report does not support your statement that the R-2800 was difficult to cool.  It does support not using higher than rated WEP settings on the F4U-1.

[F4UDOA]

Stoney,

Does it actually say in the report that they used a higher octane fuel or additional ADI other than what is normally used? I don't think I have ever seen an F4U-1 series test with anything other than 100 octane avgas and standard ADI at WEP.

I think the most critical modification made for this test was the carburetor pressure and jet size that increased MAP. If you look at the lowest Carb Pressure setting tested it seemed to match the standard F4U-1A performance charts (3400FPM SL and 420MPH at 20,000).

Also this aircraft had 237 gallons of fuel and 2400 rounds of ammo which was a full load and weight of over 12,000lbs. It was not loaded for "max performance" testing.

[Stoney]

Stoney,

Does it actually say in the report that they used a higher octane fuel or additional ADI other than what is normally used? I don't think I have ever seen an F4U-1 series test with anything other than 100 octane avgas and standard ADI at WEP.

No.  I only mentioned the ADI use as a illustration of how hard they were pushing the engines.  I don't know enough about carburetor impact pressure to know how adjusting that impacts the engine.  What is evident to me is that entire test was designed to see if the U.S. Navy could raise the WEP settings on the F4U-1 series aircraft, and the conclusions were no. 

Ultimately, this report was posted as evidence that the R-2800 had cooling problems.  Some test regime designed to stress the engines at higher than normal power settings doesn't seem suited to prove the R-2800 series engines had chronic cooling problems.

[Hooligan]

It looks like it was loaded with 1383 rounds of ammunition and had the single 237 gallon fuel tank rather than the 361 gallons/3 fuel tanks that the AH -1A comes with.

Hooligan