Prop to pole clearance

[windstuffnow]

   There was a post sometime back about the direction the blade spins and clearance between the prop and the pole.   I never gave it much thought and have run the props in either direction.   A couple times it wasn't by choice but by mistake in carving.   I really never gave it much thought.

   I just finished rebuilding an old aermotor tower and got it up which will need a larger offset to get the clearance I need.   In the past I've always used the 5 inch rule, something I picked up while building airplanes.  We used composite props and they were fairly flexible but the wood props didn't require as much clearance although I still mounted the engine with the same clearance.

    Dan had mentioned a little trick using a bike wheel to see which way the prop should turn to get the blades to pull away from the tower instead of into it during yaw.   I decided to try it out.   Here is the thing, when it yaws one way it will smack you in the forehead but when it yaws back it bops you in the knees.  This occurs in either direction of rotation but in reverse.   So, rotation doesn't matter and the clearance has to be built in.

    I guess I'll stick to the 5" rule...

Have Fun

Windstuff Ed

[Garry]

Ed,

My twelve footer yaws much more quickly when the gust hits than when the gust subsides. At night with a flashlight the tips almost like they move in a figure eight when a gust hits.

Garry

Yea I know... Who is nutty enough to be standing out in storm watching blades dance??

[Norm]

   I can't recall anyone even mentioning using a small prop at 90 degrees to the main and driving a reduction gear instead of a tail would give a delayed action. I remember seeing old windmills that had them of course for a different reason but still it did give a delayed action even tho' none of this was a concern with large rigid blades, but they even tilted the blades for tower clearance didn't they?

                random thoughts.....haven't had my morning quota of coffee yet!

              Fun   ( :>) Norm

   

[Ungrounded Lightning Rod]

I take it the most abrupt yaw is when the mill feathers, so there WOULD be a preferred direction?

[Ungrounded Lightning Rod]

I can't recall anyone even mentioning using a small prop at 90 degrees to the main and driving a reduction gear instead of a tail would give a delayed action.  I remember seeing old windmills that had them of course ...

Some of the mills at Altamont Pass had a system like that.

[Victor]

 The old (80's) Whirlwind 4kw machine operated like that. Whirlwind became World Power Technology and  started making the Whisper series and was then sold to Southwest Windpower.

Victor

[SmoggyTurnip]

What is the 5 inch rule.