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Old 02-28-2018, 06:09 AM   #11
Dbahnson
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Quote:
Originally Posted by GRB81 View Post

I know it might be a silly question but what does L.H. stand for after the drawing number?

Kind regards,

Graham
LH is the direction of the thread, i.e. "left hand". Propellers are really just sections of a screw device ("airscrew") and will have a thread direction and a pitch, even though all you see of it is the one section that forms the blade. By convention (at least British, U.S., French, and others) as you look at the propeller from behind when it turns, if it moves forward by turning clockwise it's a right hand thread, just as turning a right hand threaded screw clockwise pulls it forward. The pitch is the distance between threads and similarly can be visualized as fine thread or coarse thread - and everything in between.

Most aircraft engines rotate in a direction such that a right hand propeller provides a tractor configuration. If the engine is mounted backwards, the thread needs to be reversed and acts as a pusher.

Some engines were configured to rotate in the opposite direction, and some engines were geared, which reversed the direction, and those also used left hand threaded propellers. The photo on your initial post shows a left hand thread.
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