12" Spinner Woes

We have a bit of a unique problem. We have an Ed Sterba prop vintage 1991 with a hub thickness of 4.44" or a fraction over 4-7/16". The front bulkhead of the spinner fatigued and cracked around the perimeter. I bought a new front bulkhead from Vans, but it is of a different spinner than was originally installed and thus does not fit the existing spinner. The rear bulkhead also had a fatigue cracking around the bend for the mounting flange,so now need a new 12" spinner with front / rear bulkheads to accommodate current prop hub thickness. The current Vans 12" fiberglass spinner will only accommodate a hub thickness of 4-1/4" (as i was told by the Vans tech assistance) which will not work for the front bulkhead on that spinner. We have an RV-4 built in 1991 which has the cowling with a 12" diameter front. Vans went to 13" cowling interface in 1994 to accommodate CS prop hubs and standardize all kits around the 13" interface. Their current 12" fiberglass spinner kit will not likely work for our Sterba prop.

I was looking for recommendations on a way forward with the current prop and any 12" diameter prop spinner options. The prop goes on a Lycoming O-320. I've emailed ACS products in Lake Havasu to see what they may have.

Any suggestions would be welcome.

Way back, when the majority of flying RV's used wood props (there weren't many metal prop. options), this was a common problem.
The reason was that wood prop makers hadn't agreed on a thickness standard.
It was common practice to make a spacer to go between the fwd face of the prop. and the fwd spinner bulkhead.

Get a new 12 inch spinner.

Fit both bulkheads into it and carefully measure what the spacing is between them.
Carefully measure the thickness of your prop.
Get a spacer made with a thickness equal to the difference between the bulkhead spacing and the prop. thickness.

Any machine shop with a CNC mill should be able to make/drill you one for a relatively low cost. Just give them your crush plate and ask them to make you another from aluminum (at the thickness you already determined). If your crush plate has an anti rotation grove for the bolt heads, tell them not to put that into the spacer (leave a a flat circular plate).

Thanks for that, but I have the opposite problem. The Vans 12" spinner only accommodates prop hubs up to 4-1/4" thick. The Sterba prop is 4-7/16" which places the back of the spinner 3/16" forward of the rear bulkhead. Vans does sell spacers for the case where you have to build up the prop thickness. I'm trying to find a 12" spinner that can accommodate a wide prop hub base.

I recently went through the same type issue (different brand prop). This is what worked for me:

I took a look at the hub area of the prop, & determined that I could remove enough thickness from the front face of the hub to make the prop the same thickness as the prop I was replacing. I'm fortunate that my neighbor has a Bridgeport mill. It was a very simple process to just clamp the prop in the mill, & remove the unneeded material with an end mill. This left small areas that got milled off that were outside the spinner coverage area, but after refinishing, you'd never know it had been modified.

Obviously, you'd need to deal with the extra bolt length after doing this, but you can use bushings to take up the extra length.

You might be able to achieve the same result using a table saw, but I'm not sure I'd want to try it because it would be pretty difficult to keep the new face perfectly parallel to the back face of the prop.

Charlie

Have you called Ed Sterba? I believe he is still around. Should be simple for him to reface the prop for a small charge. This will assure the tracking is maintained.
Charlie has the right idea. Just take care with the surface, Some of the past Wood prop Mfgs would drill a hole in the hub to add weight for balance( I'm NOT sure if Sterba did this). But, if so, It could make a mess of your prop.

Silent_Flyer said:

Thanks for that, but I have the opposite problem. The Vans 12" spinner only accommodates prop hubs up to 4-1/4" thick. The Sterba prop is 4-7/16" which places the back of the spinner 3/16" forward of the rear bulkhead. Vans does sell spacers for the case where you have to build up the prop thickness. I'm trying to find a 12" spinner that can accommodate a wide prop hub base.

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Sorry about that, I turned you numbers around in my mind.
Refacing the hub area is the only way to fix it. Just about any of the popular prop. makers could do it for you.

Second on contacting Ed Sterba

A friend and I both have Sterba props on our RV-4's. Earlier this year we sent them to Ed for refinishing. He checked balance and tracking and refinished for $50 plus shipping. I thought that was an outstanding deal.

I feel confident that he can help you with your particular situation.

That is outstanding. He must use varnish. I have that much in materials(PPG high solids Clear) on a refinish.

ccsmith51 said:

A friend and I both have Sterba props on our RV-4's. Earlier this year we sent them to Ed for refinishing. He checked balance and tracking and refinished for $50 plus shipping. I thought that was an outstanding deal.

I feel confident that he can help you with your particular situation.

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