From Bollyprops


1, 3 AND 4 BLADE PROPELLERS

The rules vary when dealing with single blade and racing propellers. A small 2 blade 5.8 x 5.8 with 12mm chord is equivalent to a single blade of 6.2 x 5.7 with 17mm chord. The single blader is more efficient due to the extra diameter and chord (much higher Reynolds number). Large diameter single blade propellers are not practical due to the high weight of the counterbalance required.

For some racing applications a high aspect ratio blade is not possible due to the extreme loads imposed at high RPM, especially if the tip is expected to exceed mach 0.7.

Contrary to popular belief, multiple-blade propellers do not operate in severely disturbed air from the previous blade (when in forward flight). The reason multi blade propellers often appear inefficient is the need to use considerable lower diameter propellers (in comparison to 2 blades), for the same horsepower available. Diameter for diameter a well designed 4 blade prop will in some circumstances perform better than the equivalent 2 blade propeller.

It is rare to find an efficient 3 or 4 blade propeller manufactured from nylon based materials. The reason for this is the most efficient shape (thin, narrow blades) for these propellers is difficult to produce in anything but a carbon or glass composite construction. For this reason Bolly have one of the best and most efficient ranges of 3 and 4 bladed propellers in the world.



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