I tried extending the carb air inlet on my -6A to within 1/4" of the prop,
as I have seen done on formula 1 race planes at Reno.  I guess there is a
reason everyone doesn't do it.  I saw no rise in manifold pressure, but did
have engine coughing taking place at steep angles of attack, so I chopped it
back to its current distance of, oh, 3-4", and don't seem to be able to make
the engine cough now.  I realize that some of this could also simply be
caused by the sharp, thin edge I have around the inlet opening.  ideally I
would have a wing shape cross-section I guess, but it didn't come out that
way, and I haven't been well enough to mess with it more.
my round cooling inlets were a result of having to fix a cracked cowl so
many times that there was little fiberglass left to work with.  my design is
far stronger than stock, since the opening is wholly contained in the lower
cowl..  bill once told me that they tufted the inlets and found air actually
flowing forward towards the prop end of that rectangular opening they use.
Kevin Lane  Portland, OR
e-mail-> n3773@comcast.net
web-> http://home.comcast.net/~n3773
(browse w/ internet explorer)
----- Original Message -----
From: "Finn Lassen" <finnlassen@netzero.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, January 10, 2004 9:16 AM
Subject: [FlyRotary] Radiator ducting


> Hi Ed,
>
> As usual I didn't pay attention when I should have.
> I'm now replacing the right radiator for the 2nd time (this time with a
> new one) and am starting to look at proper ducting.
>
> Bernie Kerr suggested pointing the inlet in the direction of the
> slipstream from the prop to increase ram effect.
> Looking the the inlets on some turboprop installations it seems the
> clearance between rear side of prop and tip of inlet lip is quite small.
> My RV-3 cowling tapers back from the center to maybe 5" at the outside
> of the cowling.
> Would there be any negative effect on prop efficiency if one were to
> extend the outside of the cowling out close (1" or less) to the trailing
> edge of the prop?
>
> Which brings me to the next question: With proper ducting, what is your
> currently recommended mininum inlet area? I'm considering a circular
> inlet as in Dave Anders RV-4 (see the Mustang II in Feb 2004 Kit Planes").
> The advantage of moving the inlet forward would be a longer duct, closer
> to the optimal 7 degree maximum.
> Would having the inlet real close to the prop also increase pressure in
> the duct?
>
> Others are welcome to chime in here too :)
>
> Finn
>
>
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