P-40 Performance - Allison versus Merlin

FLYBOYJ · Aug 16, 2018

Big Jake said:
Firstly, if the aircraft and engine are "as built" and conform with the Type Certificate then the aircraft can be registered in Limited or Restricted categories, not necessarily Experimental. This also applies to Warbirds. Through the years, many alterations were allowed by the FAA on Warbirds.
Secondly, in Reno some Warbirds are "Stock" (certified in Limited or Restricted categories), very limited in the way of modifications, or "Experimental" (the "Big Guns".) As far as I remember, a stock one never won an un-limited race in Reno - just didn't have the performance.
Thirdly, you cannot build a P-51 or a Merlin engine from scratch unless you own the Type Certificate and have a production authorization from the FAA. All the engines and aircraft in circulation have an original placard from the original manufacturer. You can build a new aircraft around a placard but you have to be careful - you need to show the Feds that it is a "restoration" or "major repair"... In addition to a number of fighters, right now a "new" B-17 is being built basically from scratch following this method.
If you change an engine on an aircraft and that new engine is not on the aircraft Type Certificate - talk to the FAA first.
My two cents...

There is no "Type Design" for the Merlin or Allison (let alone for the P-40 or P-51), as far as I could find. While you are correct about the Limited or Restricted categories, under those categories you are "Restricted or Limited" in operations or modifications but you CAN build a P-51 or Merlin if they don't have a TC to begin with.
Again - if a former military aircraft doesn't have a T/C and you want to put a "N" number on it (and race it) more than likely the feds are going to issue that pink piece of paper that says "EXPERIMENTAL."

http://rgl.faa.gov/Regulatory_and_G...b0dbf755726862581670074666f/$FILE/8130.2J.pdf

FLYBOYJ · Aug 16, 2018

Looks like the P-51 has a "LIMITED" TCDS

http://www.calpacificairmotive.com/LTC-11__rev_5.pdf

FLYBOYJ · Aug 16, 2018

FLYBOYJ said:
Looks like the P-51 has a "LIMITED" TCDS

http://www.calpacificairmotive.com/LTC-11__rev_5.pdf

And I'll stand corrected, one for the P-40N. Both Limited

http://www.airweb.faa.gov/Regulator...90d673ee85c186257106006fd4ab/$FILE/LTC-18.pdf

Kevin J · Aug 16, 2018

MACHIA said:
From earlier reading I recall an Allison V1710 1,475 hp was used and the P-40Q and attained a speed of 422 mph in straight and level flight . The V1710's used in the P-38's were of the same horsepower . Although I'm not sure that this engine was installed in the P-63 . Anyone care to comment on that ?

You'd get an extra 20 mph out of a Spitfire without its armament, armour, rear view mirror, snow guard etc. So the speed seems plausible on the single stage engine that it was fitted with. Oops, I thought you wrote P-39Q.

FLYBOYJ · Aug 16, 2018

FLYBOYJ said:
And I'll stand corrected, one for the P-40N. Both Limited

http://www.airweb.faa.gov/Regulator...90d673ee85c186257106006fd4ab/$FILE/LTC-18.pdf

So going full circle - if you operate a P-40 or P-51 under those LTCDS and alter the type design, you'll more than likely have to certify the aircraft (to include the engine) under experimental category

Shortround6 · Aug 16, 2018

Kevin J said:
You'd get an extra 20 mph out of a Spitfire without its armament, armour, rear view mirror, snow guard etc. So the speed seems plausible on the single stage engine that it was fitted with.

trouble is that it wasn't a single stage engine and the 422mph wasn't done using 1425hp.

see:http://www.wwiiaircraftperformance.org/P-40/XP-40Q2_Eng-47-1728-A.pdf

of which this is an excerpt.

3200rpm and 75in of boost at 20,000ft were well beyond the capabilities of any single stage Allison.

P-39 Expert · Aug 17, 2018

RCAFson said:
On page 7:

http://www.wwiiaircraftperformance.org/japan/intelsum85-dec42.pdf

there's an example of a p-39 trying, and failing, to use 70in of boost, on US fuel.

Considering the takeoff rating of that engine was 44.5" it was not surprising that detonation would occur at 70". Surprised the engine didn't blow up.

GregP · Aug 17, 2018

Hi FlyboyJ,

At the Planes of Fame, we operate now four P-51s: a P-51A, two P-51Ds, and the Voodoo air racer.

To my knowledge, Steve Hinton's P-51D (N7715C) is in the Standard category, Spam Can (N5441V) is in the Limited, the P-51A (N4235Y) is in the Experimental Exhibition category, and Voodoo (N551VC) is in the Experimental Racing Exhibition category.

No point here, just FYI.

FLYBOYJ · Aug 17, 2018

GregP said:
Hi FlyboyJ,

At the Planes of Fame, we operate now four P-51s: a P-51A, two P-51Ds, and the Voodoo air racer.

To my knowledge, Steve Hinton's P-51D (N7715C) is in the Standard category, Spam Can (N5441V) is in the Limited, the P-51A (N4235Y) is in the Experimental Exhibition category, and Voodoo (N551VC) is in the Experimental Racing Exhibition category.

No point here, just FYI.

Hi Greg;

Thanks for the info - yes, looked up the N number and it is Standard which means someone holds a TC for his Mustang shown as an F-51D. I looked high and low in the TCs annd only found those for a Limited. It looks like the basis for airworthiness was the old CAR 9 which were the rules back in the 1940s!

GregP · Aug 17, 2018

If it means anything, Steve's P-51 was built up from parts of several Mustangs, but it was all done to original specs, including a propeller that still meets original diameter limits.

Old Jim · Aug 18, 2018

Here is a list of LTCs.

FLYBOYJ · Aug 18, 2018

GregP said:
Steve Hinton's P-51D (N7715C) is in the Standard category.

The cobwebs cleared on me today - He may have a "Standard" airworthiness certificate but there are 7 classes of a standard airworthiness certificate:

Normal, Utility, Acrobatic, Commuter, Transport, Manned free balloons, Special classes

Under Special Classes:

Primary
Restricted
Multiple
Limited
Light Sport
Experimental
Special Flight Permit
Provisional

I bet he's either Restricted, Limited or Experimental

GregP · Aug 19, 2018

Given your post, I'd suspect Limited. I seem to recall seeing that somewhere in the hangar. I quoted standard only because that's what an N-number FAA inquiry said. You'd think they would post the actual category, wouldn't you?

But, the FAA doesn't come across as "here to help," do they?

Also, the "Experimental Racing Exhibition" listing would then probably be simply imply "Experimental Exhibition," don't you think?

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