[quote:022580b62a="Jeff Roberts"]Since I struggled with the cooling on my 912-S
Tri gear for so very
long I thought I'd throw my thoughts into this subject. I have found
the air cooling of the fins to be inadequate. If you look at the round
inlets in relation to where the top of the engine sits you will find
they are too low and too outside.[/quote:022580b62a]
While fitting the cowling and planning some modifications to the lower cowling,
I was also not happy about the position of the forward inlets. Thinking about
it I got the idea to make Naca inlets in the top cowling, with a air flow
promoting
shroud, just above the fins, and close off the standard forward inlets.
(I do not literally mean just putting some bid over it, but these positions can
be used for other purposes, like landing lights.)
These naca inlets in the upper cowl and closing off the standard inlets would
have
the following advantages:
1) No path for the air to escape directly under the engine (instead of over the
engine). This air is not just lost, but also increases the pressure under the
engine, hindering the air flow through the fins.
2) During flight, air will enter here and finds its way down through the fins to
the exit at the rear of the lower cowling.
3) No more need for the (expensive?) Rotax shroud and the third nostril (another
drag creating hole).
4) No more need for the gills on the side. The naca inlets are in the top, just
above the fins, so warm air will escape naturally there once the engine is shut
down. The cowling won't heat up.
5) From the naca shroud It is easy to make a small bypass to cool things like
alternator
regulator. There are direct and straight ways in the top cowling to
almost every part that needs to be cooled. All these ducts can be glassed in the
top cowling.
6) Lower drag. I believe the standard inlets are very draggy, with their sharp
endings, and there is no room to make a ramp to slow the air down before letting
it loose in the engine bay. With the naca inlets, there is sufficient room
to make a rounded expansion where the air can slow down and expand, without
creating
much turbulence.
7) Easy to implement. Naca inlets can be bought, closing off a hole is easy too.
I have yet to start with implementing this. Comments please, before I start
cutting
something that I'm going to regret later. ;-) Do I oversee something?
Frans
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