Slip factors

daiquiri · Feb 5, 2015

I will send you a PM.

sandhammaren05 · Mar 10, 2015

daiquiri said: ↑

Thanks for all that info, very interesting indeed.

Now sorry for the pedantry, but:

Expressed in common aerodynamic terms, looks like you have described a situation which the thin airfoil theory calls "ideal angle of attack". It is the angle of attack which aligns the camber line at the leading edge to the local inflow. This, imo, confirms that you are using the word "pitch" as a synonym for "camber". Which, strictly speaking, is incorrect - besides imo being unnecessary, since it is evidently perfectly describable by using standard airfoil terminology.

But ok, now I do understand where it comes from. You folks use the pitch gauge for prop tuning, so I guess it comes naturally to call the measured quantity "pitch".
However, it is indeed a pitch only for surface-piercing propellers, on which the pressure side of blades govern prop's characteristics.
In case of other types of marine propellers and aeronautical propellers what you measure is not a blade pitch but just a twist of one side of the blade. In order to arrive to the true propeller pitch (as conventionally defined), one also needs a thickness distribution and some math, as explained here: http://www.mh-aerotools.de/airfoils/propgeo5.htm#UsingABench

Cheers
Click to expand...

Having reviewed the terminology in Newman, and in Breslin and Andersen, I agree that my terminology is nonstandard in marine engineering. However, my terminology, not that of marine engineering, will be understood in prop repair shops. Pitch (angle of attack) is indeed measured from leading to trailing edge, but this is the same as the local pitch measured over a small chord near mid-blade, so we're talking about the same thing. What I call pitch distribution, or local pitch varying from leading to trailing edge over small chords, is simply the correct way to describe camber piece-wise (as I knew before). I've made a correspondence between propshop and engineering terms in the revised ms. Thanks for your help, I want the ms to be widely readable without confusion!

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Slip factors

daiquiri Engineering and Design

sandhammaren05 Senior Member

Slipway launching calculations

Resistance factors, planing hull at low speed