> This is not directly related to rotary engines, except that it's
> connected to one.
>
>
>
> I just received my prop from Catto, it's a beaut, but I
have a
> problem.
> The backing plate, where the prop contacts the prop hub, is
> aluminum. My
> spinner and it's rear bulkhead is made from carbon fiber.
Aluminum
> in
> direct contact with carbon fiber is a no-no. I was thinking of
> applying
> RTV between the bulkhead and prop just before I install it and
> torque
> the bolts down. This would theoretically insulate the aluminum
> backing
> plate on the prop from the carbon fiber spinner bulkhead, but I
> worry
> that it would mess up the friction between the prop and the
spinner
> bulhead. Any suggestions about how to approach the problem of
> insulating
> the these two components from each other in such a way as to
not
> do
> something bone- headed?
>
>
>
> Brian Trubee
>
>
> The usually way is use a thin layer of fiber glass on the
carbon
> fiber to
> electrically insulate
> the aluminum to the carbon fiber interface. I also think
titanium
> does
> more or
> less
> the same thing. Paint the bolts with a thin layer of epoxy
paint.
>
> The spinner itself has very little torque on it so friction
is not
> a
> problem
> on the outer spinner bulkhead.
>
> It is a problem if the aft spinner bulkhead is between the
prop and
> the
> PSRU
> flange.
> In that case I would make an aluminum spinner bulkhead or
contact
> Catto
> for
> their
> recommendations.
>
> --
> Paul Lamar ...No rotor no motor.
>
> Ah, very good about having an aluminum rear spinner bulkhead,
BUT, the
> spinner itself is carbon fiber. I think the best solution is to
bond a
> thin layer of fibergalss to each side of the bulkhead spinner .
Please,
> if anyone has inputs, please speak up.
>
>
>
> Thanks,
>
> Brian Trubee
>
>
> So don't believe me :). Look it up.
>
> The problem with that is the compressive strength of the epoxy
composite
> is not
> as high as aluminum and your prop may slip back and fourth. The
pulsing
> torque
> is transmitted by the friction between the parts and not the bolts
in
> shear.
> Wood props actually char under these kinds of loads.
>
> The compressive strength perpendicular to the fiber direction is
> essentially
>
> that of the epoxy resin.
>
> Paul Lamar ...No rotor no motor.
>
>
>
> Yes, that was one of the concerns- that there is friction at the
> interface between the bulkhead spinner, prop and hub. So, how about
this
> solution- an aluminum rear spinner bulkhead, with some sort of
> insulating material (RTV?) between the bulkhead and the spinner? Or, a
> layer of glass on the inside of the spinner where it meets the spinner
> bulkhead?
>
>
>
> Or conversely, does anyone want to purchase a carbon fiber spinner (16
> inch diameter by 19 long, parabolic in cross section) for $250 and I go
> with a spun aluminum spinner? I have heard of one person down in
> Portland who does aluminum spinning.
>
>
>
> Brian Trubee
>
> The friction is essential to driving the prop with out slipping back
and
> fourth each time the engine pulses. Of course the rotary is nowhere
near as
> bad
> as a four cylinder Lycoming. The Lycoming tries to back up twice per
rev.
>
> I think RTV is the wrong thing to do.
>
>
> Paul Lamar
>(At least for some applications) I recall Brian Alley (composite guru,
>pro Lancair builder) says that anodizing provides adequate galvanic
>protection for certain applications.. Is the aluminum anodized?
>Probably not.. I'd add one layup of thin fiberglass to the side of
>the spinner backing plate that contacts the prop's drive side. It
>doesn't take much to keep the carbon fibers from making direct
contact
>with the aluminum.
>Get some of the very light weight, fine weave fiberglass cloth from
>the hobby store. It's relatively easy to work with. And some slow
>cure resin/hardner. Have you worked with fiberglass much?
>I imagine that your setup uses drive lugs in the output flange? I
>think the dependence friction to transmit the torque loads is lower
>than when just mating the prop to a flat flange. The diameter of the
>drive lugs can be much larger than the bolts, and so can handle the
>shear loads much better.
>RTV would not be my choice. I suspect it would eventually cause you
>headaches with prop tracking - especially after being removed and
>installed a few times - the RTV will wad-up. It's not structural
>(soft).
>Regards,
>Matt-
Hi Brian,
Something didn't sound right about sandwiching ANYTHING between the
prop flange and the drive flange, so I went out to my workshop and
looked at my Hartzel props. Sure enough the spinner bulkhead is attached
to the OD (outside diameter) of the prop flange. Its an elaborate setup
but, the bottom line is there is DIRECT CONTACT of the prop flange and
the drive flange, no bulkhead, no RTV, no aluminum disks, no carbon
fiber or fiberglass. I have 2 props --a 2 blade & a 3 blade-- both are
done the same. Hope this helps. Dave M
Dave,
Would it be possible to send a photo?
Thanks,
Brian Trubee
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