Prop Blade to Cowl Clearance?

[moodyjr]

I'm in the process of modifying a standard Vans IO-360 cowl to a James style cowl using some new inlet rings I had made by a metal spinner.

To get a reasonable transition to the new inlets they protrude about 3/4 in forward of the spinner ring. Minimum clearance to the aft edge of the prop blade is about 1-1/2 in (coarse) to 2-1/8 in (fine). Prop clearance on the original cowl was about 3 to 3-1/2 in.

Does anybody know of any research, theory, opinion or just wild speculation about optimum/ minimum clearance between prop & cowl?

A/C is RV-8A with supercharged Subaru/ 3 blade MT prop.

thanks

John Moody
Melbourne

[joeboisselle]

Originally Posted by moodyjr

Does anybody know of any research, theory, opinion or just wild speculation about optimum/ minimum clearance between prop & cowl?

I've seen aircraft with a 1/4 inch of clearance. A near miss is still a miss.