Bizarre Powerplants

When two engines are better then one – The Allison V-3420

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Allison V-3420

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Keeping up with the Jones during war time isn’t easy when they are the Germans and the British. We needed more power and we needed it now. So going with what we know we took two Allison V-1720’s and connected them together.

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Fisher P-75 with Allison V-3420

During the beginning of World War II the Allison V-1710 12 cylinder was the best liquid cooled inline engine the American’s had but we learned that it wouldn’t be enough. Put this with the fact that the air cooled radial was creating far more horsepower with greater reliability. Creating a new engine was going to take to long so we needed a quick option and we needed yesterday.


Allison V-3420

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Allison gave us the quick and dirty solution in the Allison V-3420. Take two Allison V-1720’s and join them together using a common crankcase. This created a 2600 horsepower 24 cylinder water cooled beast of an engine. Supporting it was easy since it shared parts with the Allison V-1720.

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Allison V-3420

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Unfortunately for Allison none of the aircraft that the engine was installed in ever went into production. Whether that was the Fisher P-75 Eagle that, itself, was made of parts of four other aircraft or the Lockheed P-58 Chain Lightning bomber destroyer listed below. It wasn’t so much a jinxed powerplant as much as one that just never fit into role it was designed for. The reason for this was that none of these aircraft started out with the V-3420 as part of their design. They all fell back onto it after their engine of choice failed to materialize.

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Lockheed XP-58 Chain Lightning

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In the end it was the right engine for the wrong time. The Germans would experiment with mated Daimler engines but these two would fail due to heating issues. The design was far more successful in tanks and on the automotive side then it was in aviation.

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  • theTokenGreek

    I think I desperately need to know more about this "Chain Lightning"…

    • fodder650

      The Chain Lightning was one of many bomber destroyer prototypes developed at the time. Plus one of several P-38 upgrades that was proposed. Let me go put something together on it

      • theTokenGreek

        sweet, thanks! I may be an aviation buff, but my focus is quite narrow these days, and quirky/awesome stuff like this has an easy time escaping my attention

  • Abe

    Seeing a piece of history rust like that irritates me to no end.

    • fodder650

      In this case I am just happy that someone saved one actually since it's such a side note in aviation history

  • The Professor

    Somebody needs to stick it in an old style Unlimited racing boat.

  • texlenin

    Ok. I'm the dumb one here, so I'll ask.
    If it's on a common crank, why are there
    two output shafts? The Chrysler only had
    Xplain me, please.

    • fodder650

      I've been sitting on this article for a week because of that very question. I need to go find the wording of the answer but it comes down the bell housing the driveshats plug into at the end of the propshafts. Because, like you, I said the same thing.

      Oh and they share a common crankcase not crankshaft. I need to check to see if i have that wrong above

      • Judging from the relative positions of the cylinder banks, the answer is indeed a common crankcase which contains two crankshafts. They could have geared the cranks together to produce a single output shaft, as in the King-Bugatti U-16:

        <img src="; width="300">

        but that's self-defeating if the purpose is to drive a set of coaxial counter-rotating props.

      • texlenin

        "down the bell housing the driveshats plug into at the end"
        WOW. Two street-legal William Shatners!?! Cool.
        I'm thinking two cranks with a planetary/idler between
        in a common case. Imagine if they'd continued the
        theme and used 4 1720's?

        Edit(1:34am)Nope, Doc, I think that's exactly
        the reason for the two shafts. And they didn't
        have to reverse one of the crankshafts for it
        to work.

        • CaptianNemo2001

          If you have ever heard of a Twin-Six of the 1910's, '20's, and '30's its the same set up. 2 cranks geared to one output shaft. Thus making a V-12 of sorts…

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