Hi, Gents – sorry for the delay in responding but some other aspects of “life” got in the way.
Putting my ALFA Romeo back together, designing and building some new type window latches for my Swift, doing the annual inspection on my Cessna 120, landscaping, new model airplane work and ------------ well, you get the picture.
Anyhow, thanks for the many kind and inquisitive comments about my engine mount system.
Allow me to address a few.
Keeping the engine from rotating: Although I’m positive that the friction will prevent this from happening, there will be four pointed pins protruding from the rear of the plate. They will sink into the firewall.
I know that backplate mounting has been done before (using the backplate mounting bolts) but with my method, it will be very easy to swap engines should it become necessary.
Someone said that the 6061-T6 “will deteriorate and pull out.”
Nonsense! When I was designing linear and rotary actuators for the aerospace divisions of Northrop-Grumman and Moog, many of our customers specified the materials to use. A Swiss company in particular specified 7MM x .75MM thread x 13MM WAF nuts be made from 6061-T6 hexagonal stock. We had the stock custom-machined from 6061-T6 barstock. Minimum order two five-foot lengths. We needed a total of 14 inches, so the rest was to be scrapped. I was able to rescue one three foot length and I’ve made around twenty five prop nut of different lengths – not one has failed.
As extra insurance however, there is as steel nut in the cavity forward of the mounting plate.
A concern about cooling: I have added two large holes in the firewall since my original post, and there is a 3/8 x 2 inch slot above the firewall. Also, the outboard cheek cowl is an air scoop that ducts air in directly at the bypass. Four large holes on the cowl allow plenty of room for cooling air to exit. And, of course, the head will be exposed.
“Using one fastener in a bolted joint to hold anything important onto a full-sized airplane is very rare. For good reasons....”
Good point – both my full-scale planes have six bolts holding the propellers on BUT, all of my model airplanes have ONE bolt (or nut) holding the propeller on. Consider the amount of power being transmitted through the thrust washer/propeller interface as well as the RPMs. My mount will not be compromised.
Furthermore, my firewall is made from white birch plywood and carbon fiber/epoxy. It WILL NOT compress.
Will my firewall come loose from the fuselage? It is epoxied to the plywood doublers. Also, six small hardwood dowels pass through the doublers and around ¼ inch into the firewall edge. And finally, two small gussets will be added to the rear of the firewall where it joins the doublers.
Why am I doing all this? It’s the only question I can’t answer but I’m sure having FUN!!!
If anyone is interested, I’ll post some photos of the plane as it’s coming together.
Bob Z.