Rob,

 

The use of an aerodynamically tight cowl requires the prop hub extension so that the face of the cowl is not flat.  If you use the long engine mount and an original cowl, the aft portion of the cowl will have to be extended about three inches as that is the distance the entire engine is moved forward.

 

Here is a picture of a 320 with the standard cowl and a Hartzell prop with the standard engine mount.  Note the prop hub extension at the left.

 

 

Scott Krueger

 

Another query for those out there who have completed your build.

 

I read in the construction manual, that there should be a 4 inch prop shaft extension between the engine and the prop hub. Presuming that the manual was written for the short engine mount, I am wondering whether the prop extension is the same for the long mount.

 

Further, does the length needed depend on what prop I fit? (I am planning to fit a two bladed metal constant speed prop, although I haven’t decided what brand yet.)

 

Thanks again.

 

Rob Stevens

Perth, Western Australia