From Nigel ( on 5/20/99:

>Been helping Gilles Graton ( make a prop for his Velocity
>173 Elite powered with a 225 HP Franklin 6 cyl. This is the first higher HP
>prop that I have been directly involved with and we learned a few things.
>Thought I would pass this on.
>The prop is a 3 blade 67 inch dameter constructed with pine core with glass
>spars and skins with carbon re-inforced tips, same as the ones we discussed
>on the mail list. We used a carbon tube insert in the centre to fit the
>centering boss on the prop extension. There was room to loop the spars
>around this tube and between the bolt holes.
>The prop came out at 10 lbs and quite flexible in torsion, I was concerned
>but we decided to run it anyway to see what it would do. It was great until
>2000 RPM when it went into flutter and howled. The tip path made a blurred
>pattern about 4 inches wide. No damage to the prop so we stripped off the
>primer and added 2 bias plies at + and - 45 degrees of uni glass right up to
>the hub full span of the blades. This really stiffened up the blades in
>torsion. The added blade weight was not a concern as we used large spars
>with a calculated centripital blade load safety factor of 7 at 3000 RPM
>It now runs perfectly giving 2750 static which was our design objective.
>The aircraft will soon have its final inspection and then go on to flight
>testing where we can further evaluate propellor flight performance.
>So what did we learn? The spars can be fitted around a centering boss
>insert, we used carbon but machined aluminum would be easier. The higher HP
>props with longer blades need a 2 ply torsional bias layup of + - 45 degree
>uni to ensure sufficient blade stiffness to prevent blade flutter.
>Hope this is usefull,