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Old 03-22-2009, 08:07 PM
  #253  
butlern
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Join Date: May 2003
Location: Iowa City, Iowa (again!)
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Default RE: Charlie Kellogg's TBM Avenger Build

Another update:

I have been working on the Avenger on and off for the past 2 weeks, and most of that time was spent considering the installation of the engine. Because the Moki 150 has a rear carburetor, and because the cylinder bank is very hard or often impossible to work around, I decided to mount the motor to a false firewall.

The false firewall (which I call F-0) will be bolted to F-1 (1/4-20 and blind nuts). The bolts will be numberous and each will be placed such that I can get a T-handled allen wrench on them easliy front the front, between and around the cylinders.

Anyway, the original F-1 was discarded and I made a new F-1 because the motor depth required that I shift the position of F-1 back about 12mm on the crutch. Shifting the original F-1 rearwards moved it out of the isometric taper built into the top half of the fuse front, so the new F-1 had to be oversized a bit so that the taper from F-4 to F-1 would remain intact. Not sure if that was clear. It’s hard to explain because I’m probably not using the right words.

The other thing I did was to cut a new F-3. My plan is to tie together F-1 through F-4 with hardwood dowls to help distribute the forces (torque and weight) of the radial engine. The original F-3 was, in my opinion, too thin for this particular motor installation. For those keeping score, there is no F-2. Not sure why that number was omitted from the plans and drawings.

Back to F-0… Attached to the front of F-0 is the engine, and attached to the back of F-0 is the throttle servo, choke servo and the ignition module. Again, because there is no room to work around this motor, all of these units needed to be mounted to the back of F-0. In this way, all connections to the engine (except fuel) are already in place which obviates the need to gain access to the rear of the motor through the bombay doors or through a hatch cut in the side of the fuse front. In theory this will make the engine that much easier to install, remove and service.

The other thing that I did was to position F-1 so that it has 1.5 degrees of down and 1.5 degrees of right thrust. The original plans had the thrust built into a motor box, but it was too complicated to introduce these angles with shims between F-0 and F-1. So, to make it simple I just glued F-1 to the crutch with the appropriate down and right thrust built in. Last picture shows the down thrust when the fuse is viewed from the side. All of this F-1 modification has changed the layout of the bombay. The new bombay will be at least 2-3 cm shorter, as a consequence of shifting F-1 back on the crutch. Because I also angled F-1 (1.5 degrees down and right thrust) I need install a new bulkhead behind F-1. I may also be out of luck when it comes to fitting Charlie's fiberglass torpedo in the new, shorter bombay. Anyway, all that can be worked out when I get the plane inverted on the building table.

Lastly, I had to determine where to bolt the engine to F-0. Because there is 1.5 down and 1.5 degrees of right thrust, and I wanted the prop hub to exit the center of the cowl, I had to use a little bit of trigonometry to determine how off-set the engine thrust line should be with regard to the center of the firewall. Pictures appear below. I just marked where the engine would be mounted if there was 0 degrees thrust, then used the math to determine where the mounting needed to be given 1.5 of down and right. Easy.
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