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Scott,

The doublers were mounted on the aft side of the back plate.  Each hole was carefully drilled while clamped with a bolt thru both pieces and clecos used as each hole was drilled.  The rivet heads are pointed aft and were installed with a rivet squeezer.  This was done at about 60 hours tach time.

When I had the prop balanced (about 90 hrs tach time), three of the four outer most rivet heads had snapped off.  The shop air-hammer bucked replacement rivets with the heads facing forward because that could be done without removing the back plate.  The shop's comment was that bucked rivets were less likely to fail this way while their experience was that squeezed rivets were weaker.  At about 130 hours, the bucked rivets were holding up while the fourth original outermost squeezed rivet had popped off its head.

If the opportunity arises or more rivets break, I will have them all bucked.  If my spinner shows signs of cracking more than just cosmetically, I will replace the spinner and use the new (?) carbon backplate.

Perhaps some engineer could suggest whether more rivets or a different pattern (other than the four corners of each rectangular doubler) would be better.

The backplate and the spinner are apparently subject to a great deal of flexing (ergo, the need for the doublers).  Remember that the nuts holding the spinner backplate on the Hartzell prop should be torqued to only 22 ft lbs.

So, to actually answer your question, since you have all the materials in hand, certainly buck the rivets.  If you have not yet fitted the spinner or drilled the holes and mounted the nutplates, go with the carbon backplate.

Scott Krueger
N92EX
 

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