till I'm blue in the face and gotten it to within 1/16 or less turning by hand
but the darn thing still wobbles. I'm sure yours runs perfect, so how did you
do it?
Gave up and made a new back plate, 2 in fact. The first just had a ply of carbon
fibre BID vac bagged to front and back. That helped a bit. Then I turned up a
steel mould with a double cone section and a centre hole exactly the size of the
central boss on the Rotax. The backplate is a single ply of carbon between 2
plies of glass and it's rigid and dead true. Not quite so easy to idealise the
front bulkhead. I made a foam double cone about 1/2" deep, bonded it to the
front of the old jelly front plate and put a single ply of glass BID on it.
Rigid enough. Centering was not so easy. I may make a mould for the front if
enough interest. The problem is that with different prop thickness the front
plate is a different diameter.
One way to center might be to make the front plate small, put flox on the rim,
fit the spinner (waxed) center it by turning the engine by hand, ( with oil in
the engine, plugs out ) then let it cure. You will, of course find that the
spinner itself isn't quite true. Ah well, never mind, it was worth a try.
Seriously though, you will get some vibration with an of true spinner and it
will eventually wind you up. The degraded laminar flow will cost you a knot or
three.
I can make backplates for L55 plus shipping.
One further thought, don't forget that glass or carbon backplates will compress
slightly under the heat and pressure that exists on the end of the crankshaft.
Epoxy more than polyester I suspect. You need to check your prop bolt torque
periodically just like you would with a wooden prop.
Graham
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