vjaqua wrote:

Pine - The center 20 percent radius portion of the propeller has almost

no impact

on performance, and in many cases is almost, if not completely,

encompassed by

the spinner. My programs essentially ignore this area, especially since

true

helical pitch would usually result in very steep angles for these points.

I can

give you a starting point prop configuration with data on engine shaft
horsepower, prop shaft rpm at that power,and a realistic value for

airplane top

speed at that power. If you have some diameter limitations based on gear
clearance, that can be considered also. in most cases optimum performance

is

realized with the maximum diameter allowed by tip speed and clearance.
Vance

Pine Pienaar wrote:

Hi Vance

This prop is for my Weight shift trike, powered by a Rotax 503 and B box.
The current wood prop is a 64X32 and at 6400 engin 2480 prop rpm I'm seeing
64.5 Mph this is top speed for this prop. Max engin rpm is 6800. With 5200
rpm (cruise) 2015 prop rpm I;m getting 46 Mph

This engine is rated at 52 Hp max with 39 Hp calculated in the cruise.

Although the airframe can and do take a 72" prop its not used with this
engine and B box 2.58:1 ratio. For some reason they only use it with a C or
E box that has a 3.47:1 ratio.

I would like to use a Naca 16 series or the ARA D series airfoil as I'm
planning a solid Carbon blade, and can use CNC machines to cut the moulds.

Many many Thanks

Pine

My program seems to favor a 70 inch diameter with roughly 34 inch pitch. Pitch is
based on flat bottom measurements with foils similar to Clark Y and RAF sections
frequently used for props. I could find no info on the 16 series in Abbott and Von
-- , and I am not familiar with the ARA D you referenced. Propellors are much more
forgiving of airfoils than wings. Dowty, I believe, uses undercambered foils on
some of their props, but really fast planes use sections with very littls camber,
and thin sections. With your gear ratio 70 in dia is pushing the limits for wood
blades, but with the carbon you can use metal  thickness practice. With thin
carbon sections I would use some Bi-directional for torsion, you will not need UNI
for the centrifugal, the stresses usually are less than you first think. The
program uses true helical pitch, and the angles and suggested blade widths (2
blade use 2/3 for 3 blade) are 0.9R 2.8in 9.8deg. 0,7R 3.7in 12.6deg  0.5R 5.0in
17.4deg  0.3R 6.0in 27.5deg.  I do not know what your power curve for that engine
looks like, so I cannot estimate static rpm and thrust.

Your application is a natural for props like the ground adjustible Warp drive, but
I can certainly identify with your desire to do your own design.

Your spread between cruise and top speed seems too wide, you are probably cruising
well below 70 percent power.Vance

 
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