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The Allison "V-3420"

Old 25th Mar 2010, 01:21
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The Allison "V-3420"

I've been doing a lot of reading about the B-29, for a magazine article I'm working on, and I'm stunned to find how many assumedly authoritative sources (including William Wolf's exhaustingly comprehensive tome "Boeing B-29 Superfortress") confidently explain that the Boeing XB-39, which was to be an up-rated B-29, was powered by four Allison "V-3420 engines, which were each a pair of V-1710s on a common crankshaft, thus creating a V-24."

Lovely. A crankshaft as long as a standard 2x4 stud, harmonics like nodes on a guitar string, and a block the length of half a P-51...

Fortunately, the "V-3420" was actually what Volkswagen/Audi would today call a W-3420--two 1710 V-12s on a common crankCASE. It in fact had two crankshafts, geared together within that crankcase.

Even right now, you can Google "Allison V-3420" and get numerous hits. Google "Allison W-3420" and there's almost nothing.

Sorry for the rant, but it just bugs me that a lot of aviation history seems to be written by people who don't know the difference between a crankshaft and a crankcase. I'll go home now.
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Old 25th Mar 2010, 01:43
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Confusion probably arises because it was designated "V" and hence the erroneous assumption of a single crank. Would not expect to find anything under W-3420 because that is not what it was designated. Powered the XB-19A, XB-39, XP-58, XP-75 and PT-8 patrol boat. A reliable and excellent performer. The proposed DV-6840 would have been something else again - two 3420s on a common crankcase - one upright, one inverted.

Last edited by Brian Abraham; 25th Mar 2010 at 01:54.
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Old 25th Mar 2010, 04:12
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Some time ago I was browsing a bookshop in Vancouver BC and found a book about the failure of materials in aircraft written by some professor in a mid Western university with a list of qualifications up his ying and yang. Looked interesting so I checked some pages. About halfway through I read that the Spitfire amongst others suffered from a high fire risk because it was made of wood.

Didn't buy the book.
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Old 25th Mar 2010, 08:58
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I recently read the book - The Michigan madman - EJ Potter. He used this engine and refered to them as a W-24 engine. Nice picture in the book of one sat on a pallet...
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Old 25th Mar 2010, 10:47
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My guess is that the system of engine designators didn't have a 'W' in it at the time. Because of that they chose a 'V-' designation since it was a variant of a V-shaped engine. Now if Allison themselves chose to call it a V-3420, shouldn't we continue to use that name? With that in mind the author of the book you read was correct in one way, but he failed to research the engine in question and therefore misinterpreted the designation.
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Old 25th Mar 2010, 14:24
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E J Potter - remember him well. Mid 60s, Santa Pod raceway, he ran a motor bike powered by a 327 cu in Chevrolet V-8.
Quaint start procedure: Stage, then put the bike up on its prop stand; release the clutch so the back wheel was turning; on the 'green', rock it forward off the stand at the same time opening the throttle wide. The back wheel spun for the whole quarter mile!!
On his second run, he came off the line a bit sideways, veered across the track, hit the crash barrier just in front of where I was standing, then cartwheeled.
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Old 25th Mar 2010, 20:05
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Other exploits included runnning a allison in a Plymouth fury.......got badly burnt in that when the supercharger let go.....
Got himself into a spot of bother when the US authorities found out he was buying up surplus USAF scrap and rebuilding the jet engines as pumps for a natural gas line in China
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