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Engine and
fan.
The
engine and fan were selected in a compromise between power
and cost. The O.S. .91 fan engine was chosen because
of our experience with O.S. engines and a recommendation
from a user. The engine uses a tuned pipe for
exhaust. The fan chosen was a 6", 8-blade
Hurricane custom unit. The fan has a machined aluminum
engine mount and hub. The blades are of
carbon/composite construction. In the UAV the
engine/fan function in the tractor configuration, with the
pipe sticking out behind. The
engine and fan were mounted in the Kevlar joiner just aft of
the wing. The stiffness of the Kevlar coupler allowed
the blade to shroud clearance to be very small. 
To
supply the fan with air, two large intake ducts were built
into the top and bottom of the fuselage. The duct
configuration chosen was believed to offer the large supply
of air needed by the fan even in side slip and at high
alpha. The tail pipe size was selected based on
recommendations from the fan manufacturer. 
Starting
the engine (note ear protection, safety glasses). To
start the engine, a model engine starter was used with a
homemade belt. A plywood piece slipped over the fan
hub to keep the belt out. A dowel was used to keep the
belt from getting sucked in. Because stuff like belts
and plywood tended to come flying out of there, the crew
wore safety glasses. Anyone involved with starting the
engine had to wear ear protection because the sound was
quite loud. The
propulsion system worked well. It put out about 11 or
12 lbs of thrust, which was good enough for the task at
hand.
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