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Here are some pictures of my cabin
ventilation. There is a 1" dia. hole at the base of the canopy that feeds into
an expansion duct. This duct turns 90 deg into a 105 CFM blower from Lancair.
The output of the blower goes into a duct that divides and goes to nozzles
centered on each side at the base of the instrument panel. The blower has a
three-way switch; OFF, ON, AUTO. In AUTO mode a switch is closed when the canopy
is shut so that when the Master is turned on, with the gear down, the blower
starts. When the gear retracts, the blower is turned off. Friends always
comment about the comfort on the ground with the canopy closed. That 1" hole
even provides airflow without the blower with the fixed-pitch prop
turning at or above 1100 rpm, and more than enough flow in cruise.
A cabin air outlet is provided on top
of the fuselage just behind the canopy. It is fitted with a lid that is closed
when no air flows. By having the outlet up there, the air flow is up past your
head where it gives the best "feel". The outlet is also fitted with a 4" fan at
the forward end inside the cockpit which is powered from a solar cell in the top
of the canopy. This solar cell makes contact when the canopy is closed, and
connects to the battery to give it a trickle charge. As soon as the charge
current exceeds 80mA, the battery is momentarily connected to the fan to start
it, and then any solar output above 80mA keeps it running. This keeps air
mildly flowing from inlet to outlet on sunny days when parked with the
canopy closed to help hold down temperatures.
Submerged, curved-divergent (NACA)
ducts work very poorly if on the side of the fuselage anywhere back of the
leading edge of the wing where a low pressure region exists. Either have them
well forward of the LE, or if you already have them above the wing and your
airflow is pitiful try this: put two small triangular VGs, 1" L by 1/2"
H, 1/2" to 1" ahead of the start of each duct, canted inward about 30
deg. so that the LEs are about 1/2" apart and the TEs are about 1
1/2" apart. These will generate inward-curving vortices which will enter the
NACA duct. You'll be surprised at how much more airflow you'll
get!
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