For what it's worth, I have not put the NACA vent for the cold air plenum
into the top cowling, but have installed such a vent with a 3" stub glassed
into the cowling on the right lower side. From there a 3" scat tube takes
the ram air into a bell-shaped auxiliary airbox bolted on top of the plenum
chamber, which has two bowden-cable operated aluminum flap valves, connected
to each other with a straight rod on the inside opposite each other.
The right side opening has a 3" stub for the Scat Tube for the cold air
whereas the left side flap valve opens up into the inside of the cowling for
carb heat. When one side is open, the other one is closed. I used to have a
Scat Tube from the original heat exchanger on the exhaust leading into the
carb heat side of this box, but found the temperature under the cowling to
be much higher. I cut the heat exchanger off, saving weight and clutter. The
auxiliary air box is made of fiber-glass laid up over a foam plug and has a
flat flange around the open bottom for mounting on top of the plenum box.
Come to think of it, I actually made the lay-up on top of the plenum box
with the filter in place and a 1" wrap-around lip under the front of the
plenum box. I also manufactured a 3" x 2" Y and fit it into the 3" Scat
Tube, to supply cold air to two ball vents in the low center of the
instrument module with a 2" tube.
All these mods. work extremely well in our climate and we have crossed the
Canadian Rockies 6 times, and have flown from Vancouver to the Atlantic and
back, encountering all kinds of conditions.
Peter Timm,U.K. 110
Europa Classic Mono (upgraded to XS standard), 200 hrs, Rotax 912 S
Hi all,
Installation - 80hp 912 in 'Classic' airframe with cold air plenum. Has
anyone worked up a carb hot air system taking warm under-cowl air into the
carbs when required at the same time as blocking off the cold air delivery
through the air filter?
I am working on such a system - subjec to PFA approval - but don't want to
re-invent the wheel if someone has already gone down this path.
I know it sounds like I'm reverting to 40s technology but I don't have room
for the Rotax system (only 10mm between rear of air box and firewall) and
anyway, I love a challenge!
Regards,
Peter
mailto:pm.davis@ntlworld.com
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Cheers,
Chris
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