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Propellers are made in varying pitch angles, and the angle can be optimized for a specific mission. Generally, a coarse pitch (high angle) lets the propeller take a larger bite out of the air with each revolution, which tends to slow the RPM but increase cruise speed. A fine pitch (low angle) permits higher RPM, generally improving takeoff and climb performance, at the expense of cruise speed.
Pilots of fixed-pitch propellers often specify the pitch angle they want for their specific mission. Many antique aircraft were offered with your choice of a "cruise prop" or a "climb prop," and many owners bought one of each, swapping them out as requirements dictated.
With an in-flight variable pitch propeller, the pilot sets the angle to fine for takeoff and climb, and then to coarse for cruise flight. We in the LSA universe aren't given this option, as the ASTM standard specified fixed pitch or ground-adjustable. * But, we can loosen up about a dozen screws on the ground, and reset the blades to whatever angle we want. So, if we're going in and out of short fields, and want our plane to have STOL characteristics, we might set the pitch fine, as a climb prop. If we're taking a long XC and want to go fast, we might set the pitch more coarse, making it into a cruise prop. For flight training, we might compromise halfway between these extremes.
Most SLSA manufacturers have already decided what prop pitch they consider optimum, and if that's what they put in the manual, that's what we have to use (unless the manufacturer specifies a range, or gives the owner/operator a Letter of Authorization to deviate from the book value). For example, the Evektor SportStar says to set the pitch at 17 degrees, and does not authorize any other value. Anyone with an ELSA is free to -- well, experiment.
* One exception is LSA motorgliders, where prop pitch is allowed to be in-flight variable, so the engine can be shut down and the prop feathered for gliding flight.
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Prof H Paul ShuchPhD CFII DPE LSRM-A/GL/WS/PPC iRMTAvSport LLC, KLHVAvSport.orgfacebook.com/SportFlyingSportPilotExaminer.US
We hand-craft powered paraglider propellers! GSC Systems is one of the oldest and most globally-renowned propeller manufacturing companies for the light aircraft and airboat industries today.
We began with handmade hardwood fixed-pitch propellers and also developed the ground adjustable TECH II and TECH III. With the TECH series, customers are able to replace single blades rather than changing the complete propeller.
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