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Thread: P-38 Prop rotation question

  1. #1
    gmelton's Avatar
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    Question P-38 Prop rotation question

    The Lockheed P-38 was designed with both engines critical with respect to engine out during takeoff unlike current light twins with C/R props. The down blade on both P-38 engines is outboard rather than inboard. Perhaps a number of P-38 pilots would have survived their engine outs had the engine rotation been reversed. What was the intended design advantage? Have any of the remaining P-38's had engine rotation swaps and if so, were there any changes to the flight or ground handling characteristics?

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    Mike Switzer's Avatar
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    I can't remember the specifics, but this was done for a specific reason. I have it in a book somewhere, I will try to look for it later.

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    If the props are counter rotating, there is no critical engine. Failure of either engine has the same effect on performance and handling - at least in theory the effects of torque and p-factor are equal. Perhaps Vmca would have been reduced had the props counter-rotated in the other direction but as long as they rotate in opposite directions with respect to each other, there is no "critical engine" IAW the commonly used definition.

    I have seen internet claims that the with outward rotating props, the airplane was a more stable weapons platform. Not sure it that is true or not.

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    Just a guess, but if the 38 was designed with this known defect, it might have been to offset some other problem such a possibly not getting sufficient airflow past the booms and over the tail or tails.

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    Mike Switzer's Avatar
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    On the XP-38 the propeller rotation was initially inward, elevator buffeting began to appear & the rotation was reversed to outward rotating to try to alleviate the problem.

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    I regret that I don't have any P-38 time, but some years ago, I was a patient in a Navy Hospital and my room mate for several weeks was a USAF Colonel. With a lot of time to kill, we talked a lot. He flew P-38s in the Big One, F-82s in Korea and B-58s in the cold war.
    He said that the P-38 was intentionaly configured to be unstable. A high Vmc was an accepted trade off. On the other hand, The F-82's props swung the other way like Piper twins. It was configured for stability. Missions were long.Lots of gas on board. He said that it was a gentleman's plane. Low Vmc. An engine cut was a non event.
    A few years later, I went to an air show at San Marcos. Lefty Gardner flew an aerobatic routine in CAF's white P-38, "Scaterbrained Kid". Awsome. Then he feathered one and did the whole thing again. @#& Awsome!
    As for the B-58, he said that if you were clumsey and supersonic you may not come home.
    Bob

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    The reason for making both engines critical on the P-38 was performance. I can't provide a reference right now, but I recall reading that the inward to outward rotation boosted the P-38's top speed by 20-30 kt over running the props the other way. The reason for this is that the propwash has a spiral component. As designed, the upwards component of the spiral propwash is channeled under the inboard wing between the engine nacelle and fuselage, giving additional lift and thrust as the air is deflected straight back.

    - Andy

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    Quote Originally Posted by Mike Switzer View Post
    On the XP-38 the propeller rotation was initially inward, elevator buffeting began to appear & the rotation was reversed to outward rotating to try to alleviate the problem.
    This was the explanation in Lockheed's newsletters and publications that my Dad (a longtime employee) brought home from work.

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    FlyingRon's Avatar
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    The critical engine is the one still running

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    gmelton's Avatar
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    Gentlemen,
    Thank you for the answers. Increased performance and tail feather buffet make sense.
    Yes the critical engine is still the one running. However, some engines are still more critical than others when one quits.

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