I agree that the "depth" of this mount looks too thin just behind the
engine. The uppermost tubes are not far above the lowermost tubes.
With
some sort of downward (or upward) force on the engine CG, these tubes
would be under a lot of compression and tension.
Also, the lower tubes look _REALLY_ long. They don't have any
sort
of brace in the center. Again, with a downward force on the engine,
these tubes might well buckle. What exacerbates this is that they
might
also be subjected to bending as the engine flexes downward.
It may be the perspective in the picture, but this mount looks
like
trouble to me as well.
If you are emotionally attached to this mount, and aren't
willing to
give it up just on the speculation of others, you should at least
proof
load it downward. This would not be terribly difficult to do.
Bill D.
Thanks Bill. I particularly like the "emotionally attached"
part. :)
Paul Lamar
Paul, Bill,
Thanks for the input. I do know a couple of very talented ME's here in
Austin that came out of the UT think tank a few years back. I will
have
one of them run an analysis using the tube specifications, angles and
weights. It may be a few weeks since these guys are involved in one
of a
kind projects for some major companies involving robotics, etc. I will
let the group know one way or the other what the estimates are. I am
emotionally attached enough to the mount that I will not do
destructive
testing :) One of the engineers is also a pilot so after his
analysis I
see if he would fly it.
This mount was made a little different than Freds other mounts because
of the complexity of the RV10 noise wheel. If modification are
required
they will be done before flight.
Bobby
Bobby (or anybody else building an RV10) what is the vertical
position of the thrust line relative to the top motor mount
hard points on the firewall. Also as a double check what
is the distance between those two hard points?
Paul Lamar
OK given the thrust line is 10 inches below the top of the
cowl and other RV10 firewall dimensions and assuming 3/4"
0.049" wall tubes my estimate on the total compressive load
on the four lower tubes is as much as 8,000 pounds. If you
assume the load is equally proportioned between all four
lower tubes each tube is seeing 2000 pounds of compressive
load. Since the lower tubes are about 40 inches long, unsupported,
buckling is likely. A simple fix is to weld in three supporting
half inch diameter tubes between the two lower tubes on each
side and the aft tube cluster. An even better fix is do that
and add two long tubes from the outer reaches of the motor
mount back and up to the upper hard points on the firewall.
--
Paul Lamar ...No rotor no motor.
Very clever with the triangulated 1/2" braces. Jerry
Thanks Jerry.
Paul Lamar
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