> > 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
> >
Finn,

    I would not go below about 18 square inches initially.  I did reduce one
of my duct openings to around 9-10 square inches, but left the other one at
24 square inches.  Cooling is still fine (increased coolant temp by 5F), but
I suspect the 24 Square inche one is carrying more of the load.   K&W
indicates that if your inlet opening is below a certain critical ratio then
the losses go way up.  Using the 95 square inches of the cores I calculated
that 18 square inches was a good minimum.  If you duct shape and outlet are
close to optimum you could go smaller, but then things have got to be just
right.  I know that 24 square inches per core works great, and my total
coolant inlet are is now at 33 square inches and still cooled on 90F day.  I
would pay particular attention to the lower lip of your inlet making certain
it has a sort of airfoil curve to it so that air will find an easy path when
the nose is up relative to the airstream (like during your climb).

Don't have a clue as to whether the "round" inlets are better, some folks
believe so.  Van sort of poop pooed the idea at one dinner.


Ed Anderson