Gliding, Props and Arithmetic

FLYING Staff

Saturday, January 12, 2008 at 10:00 AM ET

Verified

Key Takeaways:

Airplanes with controllable-pitch propellers glide significantly farther when the prop is set to coarse pitch, as fine pitch causes the engine to windmill faster, increasing drag and the rate of descent.
For modern, faster aircraft, setting the propeller to coarse pitch is generally more effective for maximizing glide distance than stopping the propeller, which can generate more drag at higher speeds.
Initial experimental results indicate that an open throttle, in combination with coarse propeller pitch, provides the optimal glide performance, surpassing other throttle/pitch configurations.

See a mistake? Contact us.

I’ve mentioned a couple of times lately that an airplane with a control-lable-pitch propeller will glide farther with the propeller in coarse pitch than in fine pitch.

These terms coarse and fine aren’t exactly intuitive, but they are analogous to screw threads of coarse and fine pitch. A screw with fine threads needs more turns to advance a certain distance; likewise, an airplane engine turns faster, at a given forward speed, when the prop is in fine pitch. Fine pitch is also called flat pitch. “Flat” may give a clearer idea of the position of the blade, but unfortunately it does not have a suitable antonym. Tilted pitch? Bumpy pitch? You hear “steep” pitch sometimes, but that’s confusing because a more steep pitch gives a less steep climb or descent.