Re: aluminum spinner - ACS SN-4?


One Sky Dog
 

In a message dated 1/12/2006 10:52:50 AM Mountain Standard Time,
bfarnam@pacbell.net writes:

As another point of info regarding the use of tubing on the front spinner
bulkhead, I also had failures when I used Tygon tubing. When I switched to
polyurethane tubing, the problems went away. Urethane has much higher cut
and abrasion resistance. I have about 250 hours on the urethane and it still
looks good.

Bob F.
N200QK
EAA Flight Advisor



.
As another point no matter what you do there will be relative motion between
the two pieces. The Tygon tubing cannot move or strain to absorb this
motion. The urethane and other softer elastomers can absorb the strain and if the
hysteris of the material is low then internal heating will be small. Caution:
Some rubbery materials suffer from internal heating when constantly strained.

I have limited experience with spinners my aluminum one and backplate were
cracked when I bought the plane. I bought a composite spinner and backplate
from A.S.& S. and could not bring myself to put it on my airplane. I made my own
backplate and spinner out of carbon\epoxy. The back plate has the 2" offset
conic taper from the hub to the rim of the spinner which stiffens the
backplate. I ran a front bulkhead with a tube around the perimeter and it would not
stay on the rim because the plate was not restraned in rotation. I do not
endorse this across the board but I have not run a front bulkhead for 300 hours
with my setup.

As for material choice IMHO: Glass is strong in tension and compression but
it is not stiff so it moves around a lot under low loads. Kevlar is excellent
in tension but poor in compression and wicks moisture. It is extremely tough
and fairly stiff, finishing is a real pain but can be done. Carbon fiber is
strong in tension and compression usually at least as stiff as aluminum in a
laminate and does not suck up water. Down side is cost and when it is
electrically coupled to aluminum it makes a battery, but can be isolated to mimimize
the problem.

Regards,

One Sky Dog

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