Thanks Ed.

I guess it might be a good idea to go around with a measuring tape and look at planes with Sam James, Lu Presti and other round inlets cowls. But I guess 4.5 to 5" diameter is reasonable.

I just measured my right radiator location. As you know, it is slanted fore/aft. One side (closest to prop hub) is 6" from prop edge, and the outboard edge is 13.5" from the prop edge. Coming from a 5" diameter inlet, what should the ducting look like? Bell or trumpet shaped? Or just direct lines from each point on the radiator circumference to nearest point on the inlet circle?

Where do I find some 5" diameter tubing that will stretch to 12" diameter (or 9" x 10" square)?

Finn

Ed Anderson wrote:

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


  

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