Al O’Donnell:
I have seen 3 (three) blade props on Sierras. What is the performance difference etc with the two verses the three blades?
Can’t give you hard data for a specific plane. Here’s what it all boils down to, in my opinion:
3-blade costs less (!) if you have to have a new prop. Usually includes a new spinner.
3-blade feels smoother, due to the higher signature frequency (less “drumming” effect).
3-blade is sometimes claimed to make a slight improvement in takeoff acceleration and climb. I have yet to see a good explanation for this claim, or to see it quantified. And I have never seen a recommendation, for any plane, to switch from a 2-blade to a 3-blade to improve high density altitude performance (like out West).
3-blade will reduce cruise speed slightly. While some people have said “no change”, I think they had rose-colored glasses on. Most people have reported loss of 2 to 5 knots. Planes like the Malibu have a 2-blade prop for a reason. The only good reason for more than two blades in a new aircraft design, is insufficient ground clearance for a large enough 2-blade prop.
3-blade is markedly heavier, at a point where it has the most ill effect. It will shift CG forward, requiring more attention to loading, and possibly ballast, to prevent excessive nose-up trim drag. There is a net reduction in payload.
Every technical analysis I have ever read on the subject clearly explains why a 2-blade is more efficient than a 3-blade. One major reason, in simple terms, is that the last 1/3 of the blade does nearly all the work, while the inner 1/3 contributes mostly drag. The 3-blade has less “outer 1/3” and more “inner 1/3”.