Engine mount design

[Bugsmasher]

After doing the calculations to compensate for gyroscopic loads and a lot of other things to be considered.... this is my mount for the 45 horse. 5/8 x .035 molly with 1/2 x .035 box tubes to close the ring behind the engine. When the rocking motion of the engine was looked at in the PC it did help take stress off things...went from reddish- yellow to a lighter stressed color in my program to static test the design. I kind of copied the bushing setup from Sam. By the way it tips the scales at 1.7 lds as seen here.

[Dave Stroud]

Nice looking mount, Gary. If you have a chance, could you please write just a bit explaining the forces exerted on the mount by the engine / flight ? I find the subject very interesting. Thanks.

[Bugsmasher]

If you want to get deep into the woods with this get a copy of Analysis and Design of Flight Vehicle structures by E.F. Bruhn. Tons of good reading and a wealth of charts to study. There are several column buckling tables for CrMo tubing. But I must confess that the math on paper was confirmed in a friends software. He has CAD programs that can emulate magnitude and speed changes of the mass in motion including gyroscopic precession loading. That's where the math gets to be pages in length... easier on PC. Let it keep up with all 12 matrices.  Basic formula starts with
"L=lw" w is frequency and l is  moment of inertia. We never could get the software to figure in uneven loading of the prop at climb angles or P factors accurately but I trust what we have done. I guess we could explain more but I don't know where you are with the math. Static loading will get you close using the cross sectional area of the tube, but it is critical that its loaded and all vectors of the design accounted for or it will be in error.