Ending the Argument

[DogMD11]

Hello everyone! First time posting here, but long time lurker. Lots of great info on this forum; I have learned so much about a subject I thought I knew pretty well!

In June 1990, the EAA's magazine Sport Aviation published an article called "Flight Test Comparison...Ending the Argument" by John Ellis and Christopher Wheal. The article was a modern-day performance comparison between a P-47D Thunderbolt, P-51D Mustang, FG-1D Corsair, and F6F-5 Hellcat. This was not an analysis of WWII-era data but rather an actual flight test of the four aircraft which compared their performance and flight characteristics.

It's an interesting article and thought everyone here would enjoy reading/discussing it. I recently obtained a copy of it through EAA's archive and can provide scans of the article if requested. I did a search for this article on this forum but did not find anything; if it has been discussed before then I apologize and ask if someone could provide a link to the appropriate thread.

You can find an online copy of the article at www.coursehero.com but you have to sign up to be a member (don't know if it costs anything or not). I'd be happy to post scans of the article here, but I'm not sure how to do it and don't want to get into any trouble with copywriting or anything like that. Some help would be appreciated!

 

[soulezoo]

How about a reader's digest conclusion in the mean time?

 

[pbehn]

No argument is ended that easily. No aircraft is as they were in WW2, did they have guns ammunition armour and all the other gubbins.

 

[vikingBerserker]

and the same fuel, same oil etc etc

 

[pbehn]

and the same fuel, same oil etc etc

Paint preparation, radiosssssszzzzzzzzzzzzzzzzzzz

 

[soulezoo]

Of course, for all those reasons and many, many more, there will never be an "Ending Argument"

Look at all the fun we'd be missing here amongst ourselves were that so!

 

[Elmas]

Ground control, Pilot's skill...

 

[DogMD11]

As far as a "readers digest" summary goes, it's a little hard to define. From the article: "...Unfortunately, the title we chose for the paper turned out to be rather ambitious as the test program actually raised more questions than it answered."

The performance section of the article was -in my opinion- tough to draw any meaningful conclusions. Because of the use of 100LL fuel, the radial engined fighters were required to reduce manifold pressure by 4 inches, while the Mustang was able to use full power settings. There was no explanation as to why this was (compression ratios?), and it was not stated as to whether the P-51's power was reduced accordingly to compensate. Despite this, the performance of the four aircraft was very similar and there were no real surprises in the categories tested: time to climb (10,000 feet), level acceleration (10,000 feet), turn performance, roll performance, and diving accelerations.

The most interesting aspect of the article was an attempt to quantify handling by measuring maneuvering stability and performing "simulated mission tasks and agility testing". The later consisted of air-to-air and air-to-ground tracking, 180 degree course reversal, and target tracking. It was here that the Corsair and Thunderbolt shined, both with very nice handling near the stall limit and low control forces. The Hellcat had high stick and rudder forces throughout its envelope and the Mustangs' very high stick forces and zero stall warning/vicious departure made it difficult to fly near the limit. Lots of good stuff here about the handling of each aircraft.

I suppose none of this is any real news to those of us who are knowledgeable about these aircraft. However, to have one person fly and try to objectively evaluate these aircraft was the most interesting part - very different from reading combat reports and memoirs with their subjective evaluations.

Also, too bad they couldn't have tested a P-38.

 

[GregP]

The leading world designers were striving to make the best fighter. It isn't the least bit surprising to me to see that they all got pretty close to one another with wildly different designs.

Al lot of time, when the power is similar, the performance is similar since everyone is trying to be light and fast with about equal power.

 

[wuzak]

The performance section of the article was -in my opinion- tough to draw any meaningful conclusions. Because of the use of 100LL fuel, the radial engined fighters were required to reduce manifold pressure by 4 inches, while the Mustang was able to use full power settings. There was no explanation as to why this was (compression ratios?), and it was not stated as to whether the P-51's power was reduced accordingly to compensate. Despite this, the performance of the four aircraft was very similar and there were no real surprises in the categories tested: time to climb (10,000 feet), level acceleration (10,000 feet), turn performance, roll performance, and diving accelerations.

Do you know what the manifold pressures used were?

It could be that the MAP the P-47 was reduced from was for a higher grade of fuel, while the MAP used in the Mustang was for a similar grade (standard was 100/130).

 

[pbehn]

Great to see that the test has ended all the arguments

 

[DogMD11]

Here is the article, I divided it into two parts. Part 1:

 

[DogMD11]

Part 2:

 

[Dawncaster]

Weight and drag conditions also be considered.

P-47D : 80% of 14500 lbs gross weight, two wing pylons installed.
F6F-5 : 86% of 12480 lbs gross weight.
P-51D : 88% of 10100 lbs gross weight.
FG-1D : 92% of 12028 lbs gross weight, two stub pylons installed.

Compared to gross weight for military service condition, best condition for Thunderbolt and worst condition for Corsair.

ps. gross weight from tactical chart for Thunderbolt and Mustang and from pilot's manual for Corsair and Hellcat.

 

[DogMD11]

Whoops, here is the rest of Part 2:

 

[pbehn]

Did I read correctly that the turbo had been disconnected on the P-47?

Much as I love the Merlin , as I understand it if you only want performance up to 10,000ft then an Allison powered Mustang I would be better.

 

[Shortround6]

Anybody notice the engine in the Mustang is listed as a V-1690-9 which is the engine usually associated with the P-51H?

Granted many P-51Ds were re-engined with -9 (or -9A) either near the end of the war or post war in US service.

Perhaps it is a typo and they meant the -7?

There is a difference in the supercharger gears, the -9 went back to the same gears as the -3 used on most of the P-51Bs & Cs.
A bit less power at low altitude but a bit more around 10,000 ft than the -7 engine in low gear?

Without pressure used in the test being given it is an unknown. The -3 and -9 could hold 60-61in to 10,000ft and that was Military power, not WER. METO might be 2700rpm and 46in which is actually quite a change from take-off or military power.

I would note that in the Corsair's pilots manual the chart for take-off is given at 32 degrees F (0 degrees C ) and says to add 10% for every 20 degrees F (10 degrees C) to the distance and that is at 54" of MAP. Corsair take-off (and climb?) test was done at 15 degrees hotter than the F6F and P-51, climb may have gone closer to average as the cooler air at high altitude may have been closer than the runway temperature.

The R-2800 engines, without using auxiliary superchargers (or turbo) start falling off in power between 1500-3500ft depending on the RAM and in climb that is a lot less than full speed level flight. An R-2800 was lucky it was making 1600hp at 10,000ft in low gear without ram.
The sea level 54in for take-off had fallen to about 40in of MAP without ram. Now if you limit the engine to 50in for take off and the first 3-4000ft it doesn't change the climb much (if any) after that.
P-47 could hold any pressure desired under the Max limit to 10,000ft with ease. F4U and F6F would have engaged the auxilary supercharger in low gear at somewhere between 4000-5000ft if making a maximum effort climb. See climb charts.
perhaps the 100LL would not allow the higher temperatures that go with the use of the auxiliary supercharger?

 

[pbehn]

I have a feeling that if this test was done for real during the period 1943 to 45 it still wouldn't answer any questions. Any aircraft that was available to test was already scheduled to have changes and improvements if they weren't already being done on the production lines.

 

[pbehn]

For my two pence there were and always will be serious issues with any such test.

Firstly the planes took off and landed from land. Two of the aircraft were specifically designed for carrier operations. Operating from a carrier means a lot of penalties in weight and structure so the Hellcat and Corsair should get some credit for that.

Stall speed, as an absolute minimum in level flight is of great interest for carrier operations but for little else. Stall at other speeds was important for pilots as was how predictable and controllable the stall was. The P 47 gets no marks in the test for its stall speed, but it could out turn a 109 at 30,000ft because of its wing loading and the power generated at that height by its turbo engine, that is another expression of "stall characteristics"

The P 51D was not a peak performance aircraft in 1944, it was just a very good aircraft that could carry a huge internal an external load of fuel and so project a good performance over most of Europe. If ultimate performance was the aim then the P51 would have been fitted with a Griffon, as later racers were. However a Griffon engine P51 wouldn't have reached Berlin and returned to base. The US air force could have coped with a lower top speed rate of climb etc on the P51 they could not have coped with a reduced range.

If you ask me to choose, I will have one of each thank you. A Tempest for Fridays a Spitfire for Saturdays and a Mosquito to go to church on Sundays.

 

[Shortround6]

I have a feeling that if this test was done for real during the period 1943 to 45 it still wouldn't answer any questions. Any aircraft that was available to test was already scheduled to have changes and improvements if they weren't already being done on the production lines.

It would answer more questions than this test. At least they might have written down what boost pressures were actually used on the Mustang? Comparing climbs using unknown power settings and somewhat less than gross weights doesn't really give good answers.

I understand the constraints of the test. No 100/130 fuel, which may have hurt the radial engines more than the Mustang, radials being a bit more sensitive to fuel usually.
Getting combat equipped aircraft is almost impossible at this point in time (or in the 90s) so gross weights are going to be lower and trying to ballast borrowed aircraft up to WW II weights in a short space of time and have the ballast stay in place and not damage the aircraft was probably out of the question. How close they could get by juggling the fuel load (and stay in CG) I have no idea. But having one aircraft operating at 80% of gross and another operating at 92% is going to skew the results as you noted earlier.
Cutting the manifold pressure by about 4in in the case of the radials due to the fuel is understandable but allowing the Mustang to use full boost until rough running forced a reduction in throttle doesn't seem right? Mustang should have been cut by 4 to 4.5in to keep things in proportion?
Max continuous is stated as being used for the other parts of the test but this varies with altitude considerably for the radials also. Their superchargers are NOT going to hold a given pressure in the manifold at a reduced RPM anywhere near 10,000ft while it is not a great trick for the 2 stage supercharger in the Mustang to do so. In fact the Mustang might be able to hold the 2700rpm/46in max continuous to 15,000ft or better? (at least in level flight?)

Maybe the loss in power matches the lighter weight to some extent?