Bud,
I'm in the process of converting my Classic to XS firewall forward and keeping
the Rotax 912S with Airmaster CS prop. You recently wrote an interesting
treatise
on various causes of drag and I was particularly intrigued by your explanation
of cooling drag.
Now I better appreciate the need to seal the cooling duct effectively and how
important
the bubble of pressure at the cowling intake is to encourage unneeded
air to slip past the outside of the cowling. This raises the notion in my mind
of encouraging some back pressure.
The pictures I've seen of other XS installations show the radiator extending
across
the duct and hanging down more than halfway. Behind that hangs the oil cooler,
often extending a bit lower than the radiator, but never all the way down
to the cowling.
The question I ask is whether there would be a drag-reducing improvement by
reducing
the outflow of air from the tunnel with say metal plates partially blocking
some of the gap, or perhaps this would simply cause oil and water temperatures
to rise.
I've also heard that the duct exit at the rear of the bottom cowling is the
cause
of a low pressure thereby increasing drag, so some outflow of air from the
duct could help to reduce this effect.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=465772#465772
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