Warbird Information Exchange

Why did Allison use all of the different exhaust manifold types?

P-39's used 12 tube fish tail, 12 tube round & 24 tube oval. P-63's used both 12 & 24 tube.

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45-47=-2

Mike - do you have access to a copy of "Vee's For Victory!" by Daniel D. Whitney? The discussion of War Emergency Ratings on pages 165-169 includes on page 168 a discussion of at the increased setting, Allison found "their previous recommendations on the size of the ejector jet nozzle was inadequate to pass the additional exhaust flow without creating excessive back pressure and potentially causing detonation". The recommendation changed from 3.2-3.6 square inches per cylinder to 4.2-4.4 square inches per cylinder.

I'm not an engineer but this sounds like a clue to your question. If you don't have access to the whole text, PM me and I'll see if I can help.

Randy

I don't have that book, but thanks for the explanation.

I just found it odd that while early P-39's could have either 12 or 24 tube manifolds the majority of mid/late P-39 production used the 12 tube manifolds and as P-63 production progressed they went back to the 24 tube manifolds. Presuming each new engine development was increasing HP.

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45-47=-2

Likewise, Marlins exhaust arrangements evolved over time.
Early engines had three tubes per side, leading some to think it had a six cylinder engine.
NACA did a lot of research on the topic in 1942, using a Spitfire for tests.

https://ntrs.nasa.gov/search?reportNumb ... BRIT%20%20)

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Remember the vets, the wonderful planes they flew and their sacrifices for a future many of them did not live to see.
Note political free signature.
I figure if you wanted my opinion on items unrelated to this forum, you'd ask for it.

John, that link does not work but I found this, which is probably the document:

https://ntrs.nasa.gov/api/citations/19930093540/downloads/19930093540.pdf

Randy

There's a good thread over on the Secret Projects forum that might have some answers.

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