[jcaplins]

I purchased the spinner, cowl, engine, prop, etc.. secondhand and I do not have any parts to screw to the spinner bulkhead to fill the gap behind the prop blades.

Is there a specific name for the piece that would back-fill the cutouts in the spinner?

Are they required, or just a cosmetic option?

I suspect they are made when someone cuts the spinner for their prop, and perhaps I can make my own from scratch.

Thanks,

 

[Auburntsts]

Your suspicion is correct. You normally fab the gap fillers after you cut the Spinner. On the RV-10 you make them and their associated backing plates out of AS3-063 alum sheet ensuring there's a 1/16" to 1/8" clearance between the fillers and the prop blades.

As to whether you really need them or not, can't say.

 

[rightrudder]

I've heard that they help to smooth the cooling flow into the inlets, more than anything. Maybe someone who actually knows about aerodynamics will chime in )) but on a gut level this makes sense.