Well as promised here are the drawings on the Lancair/Kis cruiser type of
motor mount. The neat thing about both composite airplanes is you have
considerable
choice about where to put the hard points on the firewall as long as they
are out near the skin. This is ideal for this type of dual tripod mount.
You want to space them as far apart as possible while keeping them near
the fuselage skin. The exact locations is not all that important.
The other thing shown here is my motor mount bracket made from 1/2 AL
plate.
The trick is the plates are notched to fit close together. This takes
most of the bending loads and shear from a six G pull up. About 900 pounds
per mount. The area in contact is about 1/4 square inch so the compressive
stress in the plate is only about 4000 psi which is a piece of cake for
6061 T6. the quarter inch bolts only hold things together with almost
no shear load. These plates are sandwiched between Tracy's redrive spacer
and the engine back end plate. Tracy's spacers will have to be cut down
about 1/2 inch in length.
BTW the large holes called out at 1/2 inch are really 10 MM. Same as
the transmission bolts on a rotary.
These motor mount brackets could be made with nothing more than
a band saw, drill press and a file.
The steel cup at the bottom of the rubber bushing does double duty as a
thick
washer for the Barry Mount and a weldable end for the tripods. It keeps
the weight and length of the 1/2 inch bolt down.
Notice all the room under the engine between the pan and the rad.
Squeezing a rotary into a low height cowling like the Lancair
and kis cruiser is not easy. Plenty of room from side to side
but the height is the problem. I think this is a minor break through
in that regard.
Paul Lamar
Paul,
Ken Gillanders wrote:
I like the brackets much better than the 2" OD 4130 tube. Easier to
fabricate, no welding.
Ken Gillanders
BD4 rotary powered
Thanks Ken.
Inventive minds don't always do what you want them to do when you want them to
do it. They also work in mysterious ways.
I am kind of proud of that design. Reminds me of those old toy cars that
you put together by inserting tab A into slot B and bending it over.
Paul Lamar
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