Un d e r t h e C o w l
Pick a Prop
Every station along a propeller has a distinctive airfoil, which
must be maintained throughout the life of the propeller.
What's best for your aircraft?
By Tim Kern
Somewhere near the end of a build/rebuild/restoration
project, or whenever an airplane changes hands, the
question of "What's the best prop?" should come up. It's
easier to answer if the theory is clear.
A propeller is the link between an airplane's engine and the
air, just as the transmission and tires link your car's engine
to the road. The right-sized tires and right gear ratio will give
a car its best performance; the right prop will allow the best
use of your airplane's engine. Also remember that like tires, a
propeller is a wear item, so frequent inspections are prudent.
For propeller choice, the aircraft's mission, the runways
it uses, and pilot preference all come into play. Because
36
Vol.2 N o.1 / January 2013
constant-speed propellers are more complicated, heavier,
and more expensive than fixed-pitch or ground-adjustable
props, and because they function quite differently, we'll
stick with the simpler designs. Fixed-pitch and adjustablepitch props are much more common among builders, and
they present a vastly wider range of choices.
Two Factors – Diameter and Pitch –
Dominate Most Discussions
A prop's diameter is governed by the engine's operating
rpm (or more precisely, by the prop hub's rpm) and the
ground clearance available. General wisdom says that
within those two parameters, "Bigger is better." General