I just finished modifying my old spinner to fit over my new-to-me (used) Catto Prop. There is a gap between the spinner and the prop, see photos. I have a couple of questions:
Will this much gap be unsafe to fly in any way?
If not unsafe, how much efficiency will I lose?
(The gap looks larger in these photos than it does in "real life")











Thanks, as always!

Fly on, Pete!
 

My buddy doesn't even have that plate on his -4. His gap is over an inch on the back side.

Ellipse, (the prop guy) says to have as close as possible fit for efficiency's sake, less drag but I figure that you can make a new, tighter fitting piece later on.

Regards,

Pete,
The only problems you will have with this kind of a gap is cosmetic and a little extra drag. The airplane will fly just fine.
But, hey, it's fiberglass. Put on your boat builder's cap and fix it.

Pete, hang loose a few days. I'm fitting a new spinner and expect to start on some glass cover plates with built-in joggles tonight. I can probably post a photo how-to, assuming you're ok with a little glass work. I think you can close your gaps with new cover plates.

Dan, thanks. I'll be interested in what you come up with.

Ok Pete, let's get you going. Pull your spinner and clean up the edges of the cutout; straight (where desired) and sanded smooth.

First we make a quick mold shell. Tape off the outside of the spinner from one opening to the other:



Paint on some PVA mold release, let it dry, and lay up three plies of 9 oz glass, extra wet and no bubbles because we want the inside to be slick:



When cured, pop it off and trim the loose edges:



Cut it in half, then tape a section firmly over each blade cutout:



Flip it over and apply two coats of PVA to everything in the area. Let it dry between coats.



To be continued. No, yours won't have the flanges.

The mold shells mean the new gap plates will match the curvature of the spinner, precisely match the shape of the opening, and will have integral flanges.

Get out the cutting board and prepare 8 identical pieces of 9 oz fabric. These were 5 x 6, but you may need a different size depending on your cutout. Stack four each on two sections of plastic sheet. Cut a plastic cover sheet too. Mix about 50 grams of epoxy. Pour a little of it in another cup and set it aside. Pour the rest on the two fabric stacks:



Ignore the small stacks in the above picture; more flange material for my installation.

While the resin is soaking the stacks, grab the other cup you previously set aside and mix in some micro, plus just a pinch of flox. Make it about like peanut butter. Wipe in a small fillet around the edge of the prop cutout:



Fabric can't fill this joggle; if you try you'll wind up with a trapped air bubble. The fillet material allows the fabric to smoothly lay over the joggle without trapped air, and it will precisely define the cutout edge on the finished part.

Go back to the fabric patches, add resin to any dry spots, and lay a plastic sheet on top of the pile. Roll or squeegee to fully saturate the fabric and remove excess resin, plus any trapped air:



Cut right through the plastic to trim the saturated fabric stack to the desired final size. Carefully peel the plastic off one side, and place the stack:



In my case I had to trim around the flanges, but you won't. Smooth it down, starting from the center and working outward to remove any trapped air bubbles. Now carefully peel the plastic sheet off the top. Use a cheap chip brush to stipple down any disturbed fabric and remove any remaining air.

Add a flange to the wet fill plate by clamping something slick to the existing spinner flanges, wiping in a small flox filet, and adding layups for the necessary flange thickness.



More tomorrow.

BTW, if you're wondering about the glass flanges on the inside of the above spinner, here's the rest of the deal:





The spinner screws go in from the back when the cowl is removed. No exposed screws; a "screwless" spinner. I've seen it elsewhere done a few different ways, so....

About 8 hours since layup. The new part is "green", not fully cured but hard enough to pretty much do as you please. The green stage is handy; you can abuse the part to get it out of a mold (within reason, because it is not brittle), you can easily trim with scissors, etc. Still not cured enough to sand very well.

Pull all the tape off the shell mold and remove the shell:



Flip it over and slide a sharp flat tool up under the flanges:



Pete, your plate will probably fall right out at this point, but if not just give it a sharp rap on the outside with a small ball peen. Mine needed the rap because of the additional backplate flange.

Here's the rough trimmed filler plate with flanges. Since it was molded in the spinner cutout, it will perfectly match whatever cutout shape you might have, and that should fix your problem. From here it's just trim to fit around the prop blade, add nutplates if desired, and surface finishing.



Good luck!

Fantastic tutorial!
 

Dan- that's a fantastic tutorial! I have not done any fiberglass work, but I have a buddy at the airport that is a pro. Your postings have given me the knowledge to have a go at it, and I'm sure my buddy will help.

Greatly appreciated!:)