roadtrip

I have an old OS 60 FP with a DU-Bro spinner with an aluminum backplate. I know the prop should not touch the spinner, but is it ok for the prop to contact the backplate?

Rodney

Yes, in many if not most cases, the prop rests on the spinner backplate.

52larry52

My Feedback: (1)

Only the center hub area of the prop should contact the spinner back plate, not the blades of the prop. If they do, use a different prop. The backside of the prop contacting the lip of the spinner back plate will create a prop failure point. A minor notching of the back plate lip might be OK, but never notch or modify the prop to clear, modify the spinner openings, or use a different prop. (or a different spinner)

Jennifer Curtis

Use a washer or disk of lite-ply as a spacer between
the back of the prop and the backplate. Trim the
openings as needed for the prop blades. Balance
the spinner assembly alone, then balance it with the prop.
Mark the prop and spinner so you put it on the plane the
same as it was balanced.

Jenny

52larry52

My Feedback: (1)

Jenny is right, a thin spacer washer behind the prop hub will also solve the problem.

roadtrip

The problem I just realized, may be that the spinners I have may be the problem here as they may be for electric only. They are plastic with aluminum backplates and have no raised center where only the prop hub would contact the backplate as in a plastic Du-Bro backplate/spinner. The props I just got are all XOAR wood props, very popular with my club and others. Having just got these, I'll ask around the club to see if there's a difference between electric backplates and nitro/gas backplates. So far I haven't found much on the net to clarify that other than some "electric only" spinners for sale. This is what got me to wondering.

jester_s1

Every prop I've ever owned has been raised at the back so that it doesn't touch the backplate. Nearly every plane anyone ever built winds up with a spinner on it, so the prop manufacturers design their props to work with them.

roadtrip

Could it be that all of your props are nylon? I have a Great Planes spinner with aluminum backplate that contacts all of my wooden props, regardless of brand, from the center of the backplate to the outer edge of the backplate. I have noticed that nylon props have about a 1/32" clearance with this backplate. Maybe with wooden props, the center of the backplate hub essentially extends to where the trailing edge of the prop curves away about half way down the total length of the prop?

jester_s1

True, the only wood prop I've ever bought was for my Cub which has a spinner nut. To get back on topic and contribute something, any spacer a person uses needs to be a high friction material so the props don't slip. A smooth washer is not sticky enough generally. An easy fix though is to get a sheet of the open mesh sandcloth for drywall. They sell it in a roll for plumbing too. You want the kind that you can see through; it looks a lot like screen material for your windows. It's very coarse and is rough on both sides. It will bite into the surfaces you put it between and won't let them slip.

Gray Beard

My Feedback: (-1)

This is what Jenny mentioned, it's just a 1/16 piece of ply that was used to keep the prop off the back plate.

roadtrip

Makes you wonder why Great Planes doesn't make their aluminum spinner backplates with a raised, knurled center so that only the hub of the prop comes in contact with the backplate. I haven't found any other brand of spinner that doesn't do this.

Gray Beard

My Feedback: (-1)

I gave up using the GP spinners long ago due to them breaking at the center, it was probably me over tightening them but the only ones I have broken were the GP spinners. My LHS started selling the Magnum spinners and when they came out they were a bunch cheaper so I started using them. Now there isn't a big price difference but I haven't bought a new spinner in a few years. I still have several of them I keep using.
The quality of the Magnum is as good as any.

52larry52

My Feedback: (1)

Gray Beard didn't give away his secret of where he gets those plywood spacer washers from but I'll take a guess.....get out a hole saw with an I.D. about the size you need for a spacer washer O.D. and after cutting a hole in the plywood, you clean out the "scrap" that is left stuck inside the hole saw, sand the edges a little to clean them up and there is your plywood spacer washer. Don't tell G.B. I gave his secret out!

Gray Beard

My Feedback: (-1)

Larry, what was it that gave it away?? The size perfection or the perfectly centered hole?? Yes, I have the hole saw in several sizes and that's exactly how I make them. The big trick is using a back board when drilling them so the wood doesn't split.

52larry52

My Feedback: (1)

G.B., MAN, I told those guys not to tell you it was me that gave your secret away! What's the matter with them? Can't anyone keep a secret anymore? It wasn't me, you can't prove it. OK, maybe I also made some that way. OK, maybe I also made some out of plastic that way but you can't prove it.

Gray Beard

My Feedback: (-1)

I made a couple from the clear plastic from a CD case and it melted enough to stick onto the thrust washer grooves and I had to peel it off. My problem isn't usually the prop hitting the back plate but the back plate hitting the cowl. My measurements are good during the build but that dumbass married to my wife tends to forget about the engine thrust angle. I always start out at zero thrust then add thrust as needed during the trim flights. That kind of messes with my measurements!!
I have noticed that during the prop testing the smaller pitched props will touch the back plate.