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SESK: Stuff Everyone Should Know · sesk.info/comm-cs-prop-two-controls

With a constant-speed propeller, which control sets power output and which sets rpm?

The throttle sets power; the prop control sets rpm.

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  1. Throttle sets rpm, prop control sets power
  2. Throttle sets power, prop control sets rpm ✔
  3. Mixture sets rpm, throttle sets blade angle

Why: The throttle controls manifold pressure, which indicates power. The propeller control selects the engine rpm that the governor will hold. A manifold pressure gauge shows power output.

Huh, didn't know that: A constant-speed prop lets an engine reach its maximum rated horsepower while the airplane is still sitting on the runway.

The dad joke
Why did the prop control feel important? It was in charge of the revolution.
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References

Answer: Throttle sets power, prop control sets rpm. The throttle controls manifold pressure, which indicates power. The propeller control selects the engine rpm that the governor will hold. A manifold pressure gauge shows power output.

  1. PHAK ch 7, Aircraft Systems (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/09_phak_ch7.pdf
    The throttle controls power output, and the propeller control regulates engine rpm.
    Checked 2026-10-10.
  2. Airplane Flying Handbook ch 12, Transition to Complex Airplanes (FAA-H-8083-3C) www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/13_afh_ch12.pdf
    with a constant-speed propeller, an airplane can develop its maximum rated horsepower (red line on the tachometer) while motionless.
    Checked 2026-10-10.
  3. PHAK ch 7, Aircraft Systems (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/09_phak_ch7.pdf
    converts a high percentage of brake horsepower (BHP) into thrust horsepower (THP) over a wide range of rpm and airspeed combinations.
    Checked 2026-10-10.

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