Scott Gettings wrote:
Paul & group:
A while ago you graciously answered some early questions about 13B mounts in a Glass Goose. To recap, the Goose is a pusher with a cutout in the upper wing
for the engine and mounts, and a very narrow rear pylon. The summary of the previous thread was to have a front mount (water pump end) as wide as possible
using a 12A front cover, and some type of rear, Schertz beam.
I've obtained a 12A front cover, a 6061x1/2" plate for the front mount main beam, and a RWS motor mount plate (thanks, Bob White!). I have some crude wood
mockups of some front mount options to present.
The Goose upper wing cutout is 22" wide at its narrow point, which will just allow 20" between the front mounts. The first pix on this message show a
"horizontal tab" mount mockup, based on Paul's front mount layout.
One problem with this version is that it forces the engine about an inch aft - not good. Another is the wood/composite mount support will interfere with
the aluminum main beam, because the composite structure will need a vertical box underneath to support its horizontal part. If the horizontal aluminum tab
can only cantilever out 1", then it isn't quite long enough to allow the Barry/bolts/washers to fit within the composite structure. If the aluminum
horizontal can handle the load with the bolt hole being about 1 1/2" out from the end of the vertical metal, then it would just fit.
Perhaps a better option might be to allow the engine to move as far forward as possible, and use a piece of angle bolted on the aft surface of the primary
beam to hold the Barry mount. This would place the Barry mount behind the beam (see pic) and help the CG issue. Since an angle could be bolted with its
surface below the primary beam, there would be no interference with the composite structure underneath.
Another solution might be to place the Barry mounts vertically (see pic), but this would place all the torque on the mount's radial axis -- probably no good
(but easy to build the mount).
My specific questions on this front mount are:
2. Is a 6061 angle bolted to the back of a 6061 1/2" main beam a reasonable way to accept these loads? (this would be much easier to build and better for my
CG) If so, will a 3/8" thick 6061 90 degree angle be heavy enough? Or do I need to go with 1/2"? I'm assuming that four AN-4 bolts on each end will be more
than enough for these shear loads -- or, are AN-3 sufficient?
No need for this if you just use 3" by 3" by 1/4 inch thick angle.
You can buy this stuff at Industrial Metals Supply in San Fernando Calif.
3. What is the smallest vertical dimension for the 6061, 1/2" thick main beam in order to support the front mounts at 20"? This will need to handle some
twisting loads if an angle is used. The beam I have is 6" high, so I'll need to cut it down to the appropriate dimension.
Twisting loads will be minimal with the 22001 rubbers and 3 x 3 angle and not worth worrying about.
Paul Lamar
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