Re: Bernard Hunt EZB Pitch Specifications

From: <mkirda_at_sbcglobal.net>
Date: Mon, 09 Sep 2013 03:18:57 -0000

Here are the numbers.

        22.5 26
        Angle 3.5 Angle
1 74.4 77.9 76.4
2 60.8 64.3 64.2
3 50.0 53.5 54.1
4 41.8 45.3 46.0
5 35.6 39.1 39.6
6 30.8 34.3 34.6
7 27.1 30.6 30.6
7.5 25.5 29.0 28.9
8 24.1 27.6 27.4
9 21.7 25.2 24.7
10 19.7 23.2 22.5
11 18.0 21.5 20.6
12 16.6 20.1 19.0

Column one: At each inch station
Column 2: 22.5"P helical block
Column 3: Same 22.5" blade rotated +3.5 degrees
Column 4: 26" helical block

Note nearly +2 degrees AoA at 1". Move in a bit and there is a bit of wash-out in the middle of the blade. At around the tip of an F1L prop (7-7.5") there is no difference. Only when you get further out do you see the wash-in again.

At the risk of oversimplification, I see someone who has a block that is pretty close in pitch to what they needed, made a blade and mounted it to the spar rotated to the pitch they needed. As you can see, rotating the blade a couple of degrees makes very small differences in AoA over the blade overall.

I suspect it will be far more important to have the prop spars with equal torsional rotation when loaded and blades that flex similarly.

Regards.
Mike Kirda
Received on Sun Sep 08 2013 - 20:18:59 CEST