Here is how I currently understand constant speed and variable pitch propellers.

In constant speed propellers, the pilot controls the governor via the prop control knob and the speeder spring, flyweights, and other parts of the system act accordingly to increase or decrease the amount of oil entering the propeller hub. This automatically changes the blade pitch in order to maintain a certain engine RPM, even in an over speeding or under speeding condition. Setting the engine at 2300 RPM will keep the engine at 2300 RPM at all phases of flight even if no adjustments to the blue knob are made.

In a variable pitch propeller, the pilot adjusts the pitch via the prop control knob for different phases of flight. However, the blade pitch doesn't automatically change in order to maintain a certain engine RPM. The pilot would need to adjust the prop control in under speeding or over speeding conditions. Setting the engine at 2300 RPM will not keep it at 2300 RPM if climb or descents are made without adjustments to the blue knob.

  1. Is my understanding of both kinds of propellers correct?
  2. Are the flyweights only found in constant speed propellers? Are there any other parts in the system that can only be found in constant speed propellers and vice versa?

1 Answer 1


Your understanding is essentially correct. A constant speed prop is governed. A variable pitch prop is not.

Constant speed props are also variable pitch.

A constant speed prop will only maintain speed if there is sufficient power from the powerplant.

Most constant speed props will require slight tweaking to maintain the rotational speed during a flight.

Constant speed props require a governor, and the flyweights are a component of a governor.

  • $\begingroup$ Can you give an example of an aircraft that uses a non- constant speed, variable pitch propellor? $\endgroup$ Commented Mar 28, 2019 at 16:50
  • $\begingroup$ The Beechcraft I discussed above. $\endgroup$
    – CrossRoads
    Commented Mar 28, 2019 at 23:02
  • $\begingroup$ I think some DC3s used variables pitch, not CS, props. The Beech electric prop is another example. It's controlled with a tiny knob similar to the panel lighting knobs. $\endgroup$
    – acpilot
    Commented Mar 29, 2019 at 16:48
  • $\begingroup$ I flew a DC-3 back in the mid-70's which had a variable pitch prop, but it had an STC, and I believe that the DC-3 normally came with a constant speed prop. $\endgroup$
    – mongo
    Commented Mar 29, 2019 at 19:15
  • $\begingroup$ @mongo - what was the benefit of the STC? Just curious. $\endgroup$
    – acpilot
    Commented Mar 31, 2019 at 18:19

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