Calculating Pitch on Existing Propellors

[Sooty]

Hi

I have a bunch of race propellors, but don't have any information on them.

I can obviously measure stuff like diameter and blade angle.

What I need is the calculation or method of working out the pitch of the propellors.

When measuring diameter of of props, do you measure the actual outside diameter? or do you measure at a different point on the blade? I ask as I have two different types, standard curved tip blades and cleaver blades.

When measuring blade angle of a cupped blade, where do you measure? Mid way across blade or between leading & trailing edge?

Any help appreciated.

Sooty

[flyguy]

Hi

To Measure Pitch, Put A Dial Indicator On Blade At 75% Of Dia. Then Index Prop 1 Degree. Read Indicator Movement And Multiply By 360 Degrees.

As For Blade Angle, A Sine Plate Or Machinist Protractor Should Work.

Good Luck

[DMacPherson]

Try to find a local propeller shop that has a propeller scanning device, such as a Hale MRI or a Prop Scan. These devices can provide a full blade scan with local pitch at various radii at points from trailing edge to leading edge. (However, the local measurement of the cup can sometimes be a bit difficult.)

Depending on your requirements, this data can also be further evaluated with to provide chord lengths (outline), rake, skew, full pitch distribution. (The Scan Converter add-on to our PropCad propeller design software is commercial utility for this purpose.)

Regards,

Don MacPherson
VP Tech Dir
HydroComp, Inc.

[Poida]

Measuring the pitch of a prop.
That was a good question, wouldn't have a clue, but I thought how would I do it if I had too.

Put the blade on a flat surface and measure the distance from the two edges of one blade.

Put a protractor on the end of the prop with each arm of the protractor in line with the front end back edge of the prop. This will tell you how many degrees the prop blade is wrapped around the hub, say the angle is 40 degrees.

Divide 360 degrees by the 40 degrees and this gives you 9.

Multiply the first distance you got from measuring the distance from the edges of the blade and multiply it by 9.

Unless I am mistaken, and someone will soon point this out if I am, this will give you the distance that a point would have travelled around the hub at an angle subtended by the blade ie the pitch.