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I have a 2 1/2" by 1" outlet just behind the canopy on the
top of the fuselage. At the forward end, just behind the roll-over rib is the
inlet which is a 4" square muffin fan. This fan is powered by a solar cell in
the back-top of the canopy to provide airflow on the ground with the canopy
closed. Since a very large portion of your body's heat rejection is in your
head, it is important to have the air flow up your body and past your head. This
outlet is fitted with a counter-weighted door that is flanked by triangular
side plates about 1 1/2' high at the back end with turned-inward
top edges to restrain the door's opening range; the door prevents rain from
entering when on the ground. This opening is in a low pressure region which
promotes the flow and is open during flight.
If your curved-divergent submerged
inlets, NACA ducts, are located above the first third of the leading edge of the
wing you will have minimal flow since that is a low pressure region. To increase
the flow, place toed-in triangular VGs at the forward end of the duct, about 1"
long and 3/8" at the back high with their forward, pointy-ends about 3/8"
apart, angled inward at about 15 deg. each. Or you can do like I did and put a
1" diameter hole at the base of your windshield and feed that into your cabin
outlets. Mine, after diverging, goes into a Lancair-purchased 105 CFM
blower before exhausting through large, plastic eyeball vents at the bottom of
the instrument panel. I get flow through these on the ground when my fixed-pitch
rpm is above 1000. I have the blower tied into a circuit that turns it on when
the gear is down and the canopy is closed and a three-position switch is in
AUTO. The switch also turns it OFF or ON.
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