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Method of determining a clean propeller pressure signal from a propeller/engine exhaust combined signal measured in flight with a microphone arranged on a propeller-driven aircraft

  • US 4,607,528 A
  • Filed: 03/11/1985
  • Issued: 08/26/1986
  • Est. Priority Date: 03/15/1984
  • Status: Expired due to Fees
First Claim
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1. A method of determining the propeller pressure signal of a propeller-driven aircraft powered by a four-stroke internal combustion engine comprising:

  • a. recording a combined propeller and exhaust signal from said aircraft during the flight of said aircraft, said combined signal consisting of a series of successive propeller signals and a series of successive combustion signals from individual cylinders of said engine;

    b. simultaneously recording an exhaust signal from said aircraft, said exhaust signal consisting of a series of successive combustion signals from individual cylinders of said engine and being measured adjacent the exhaust pipe of said engine;

    c. adjusting the amplitude of at least one of said combined signal and said exhaust signal so that the amplitude of said exhaust signal is substantially the same as the amplitude of the exhaust signal portion of said combined signal;

    d. adjusting the phase of at least one of said combined signal and said exhaust signal so that said combined and exhaust signals are in phase with each other; and

    e. thereafter subtracting said exhaust signal from said combined signal to determine said propeller pressure signal.

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