We are in the process of attempting to manufacture a plenum chamber as
our Rotax 912 engine is one of the early models with a bulky ignition
box bolted to the centre bulkhead and the factory model does not fit.
At the moment we have a large piece of blue foam which we have managed
to shape around the various obstacles in the engine compartment. This
will be glassed over as a former when we are happy with the finished
shape.
Our aim is to take cold air from a scoop on top of the engine cowling
and when warm air is needed to take ducted air from behind one of the
radiators. Hot or cold air is selected via a flap mounted inside the
plenum chamber.
We are intending to use the original air filters which will just fit
into the chamber (one on each side turned through 90 degrees - upright
instead of horizontal) unless someone has a better suggestion.
What we would like to know is if it is ok to fit a ram air scoop on top
of the cowling to feed pressurised air into the carburettors and
hopefully gain a couple of hp in the process. We have assumed that the
engine compartment is normally pressurised anyway due to air being
forced through the front of the cowlings. The pressure equalising tubes
would have to be connected to the inside of the plenum so as to be at
the same pressure as the incoming air supply.
We were also considering piping the air from behind the radiators for
heating the cabin. Presumably this is fairly clean air (ie- free from
Carbon Monoxide or other fumes). From what we have heard, the heat
exchanger on the silencer box tends to make the air too hot which then
needs to be mixed with cool air to heat the cabin.
Has anyone been down this route before. Any suggestions would be
welcome.
Carl Pattinson
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