Clearance with an 80" Prop

[JimParker256]

...you won't have an issue from a regulatory standpoint...

That's a true statement, since those requirements for Part 23 certification absolutely do not apply to Experimental Amateur Built aircraft. It was offered in the interest of perhaps providing a "reasonable guideline" for us to consider. As the builder, it's your call.

[whee]

Oh, I agree Jim, it is definitely a good guideline. I'm told that the DAR the used around my area checks things like this and if it is way outside the norm then he won't issue an airworthiness cert. That's the kind of situation I was referring to.

[JimParker256]

Finally found the reference for the prop clearance design standard, although it's the older CAR 3 version. Still probably good to think about with longer props...

23.925 Propeller clearance.
Unless smaller clearances are substantiated, propeller clearances, with the airplane at the most adverse combination of weight and center of gravity, and with the propeller in the most adverse pitch position, may not be less than the following:
(a)Ground clearance. There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level, normal takeoff, or taxing attitude, whichever is most critical. In addition, for each airplane with conventional landing gear struts using fluid or mechanical means for absorbing landing shocks, there must be positive clearance between the propeller and the ground in the level takeoff attitude with the critical tire completely deflated and the corresponding landing gear strut bottomed. Positive clearance for airplanes using leaf spring struts is shown with a deflection corresponding to 1.5g.

I had not known about the clearance being measured with the "landing gear strut bottomed" part, until I read this. But the clearance requirement is 9 inches in normal level takeoff position, and "positive clearance" with that the critical tire (main, for us) flat and that same. strut bottomed out, and the airplane in "level" attitude.

Since this is for "thought guidance" only for us experimental builders, I'm probably going to just leave it at this, and not try to find the Part 23 version... Hope this is helpful