This is a modified sketch of Leonard's motor mount bracket. Front view.
It is intended to be bolted to the side of the block with four large
bolts.
There are two ways to approach this. The sledge hammer approach is beef
up this bracket and make it take all the bending loads due to dropping
in the airplane or pulling six G's. Six times 390 pounds is 2340 pounds.
That is what the engine weighs during a six G pull out. Since this
bracket is eight inches long and it takes half the load that would be
about
9400 inch pounds or about 780 foot pounds. If you could beef the bracket
up to take those kinds of bending loads it would probably crack the
block.
The better way is shown in the sketch. Brace the bracket to the bottom
of
the pan with a bolt on 1/2 square .049 4130 steel tube.
This will easily take the vertical loads in tension. A 1/16 thick
4130 steel strap one inch wide should be welded across the bottom of
the pan to take the transverse side to side tension load. Assuming of
course
the pan is a stock steel oil pan. The 1/2 inch square tube can be
welded or bolted to this strap.
The bracket should also be braced fore and aft with a 1/2 square tube
to take the thrust loads.
Most of the bracket is made from thick aluminum plate. You will need to
find someone with a 400 amp tig welder to weld aluminum plate this
thick.
You could also fabricate it from much thinner sheet steel and use a
large
aluminum washer bolted to the steel with flat head screws to act as a
seat
for the Barry rubber bushings.
Paul Lamar
Todd Carrico wrote:
Todd Carrico:
I would not use Aluminum for the motor mount. Burns easily in case of
fire. An inflight fire is bad enough with out having to deal with
lossing your CG as well.
It will also fatigue eventualy.
I also don't see enough firesleeve in these installations.
tc
Todd just about all aircraft engines use aluminum for motor mount brackets.
The O-470 in my 182 uses four aluminum motor mount brackets.
Bonanzas and several models of Cessna motor mounts are made from thin sheet
aluminum. Frequently the blocks of automotive piston engines used in AC are
also aluminum.
This aluminum bracket is made from bar, 1/2 inch thick by two inches wide.
It is unlikely that it will be weakened enough to fail before something else
seriously happens. If properly braced the stress level is very very low.
These two brackets are not the only things holding the engine in. The rear
steel bracket could hold the engine by itself.
I think the weight of a steel bracket should be put into an engine
compartment fire extinguisher system instead.
Paul Lamar
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