Here is a side video of the propeller on W7's number 1 engine during the propeller governor test. If you watch close you can see the width of the blade change when the propeller control is moved. When it looks wide it is at the 'Low' RPM position (taking a bigger bite of air so more load slows the engine) and when it looks thin it is in the 'High' RPM position (smaller bite is a lower load and the engine turns faster). Can you hear and see the change? | National Warplane Museum - Geneseo Airshow