Paul, I have your "how to cool a wankel" book and didn't know if this question is for the general newsletter or not since I'm attaching a picture right from it.

The picture of page 37 is of Kays and London diffuser. Is there a formula for U, A, Vm, etc?

I remeber hearing, the opening is 20% or 15% of your surface area. Or I could be getting confused with Kuchemann and Weber.

- Matt Boiteau


We first said in the book  but later experience has shown in the TTC and Neil's Glastar 15% is too big,
It is more like 7.5%. One reason for that  is.....it is  always in the prop blast. Surprisingly, with a 15%
opening in the TTC, it never gets above 120 degrees F :-) I am stupefied by that :-)

That Kay's and London wedge diffuser works extremely well. In the TTC we  also have
very good venetian blind cowl flaps that are fixed open. These cowl flaps
are a 90 degree arc shaped. I am sure that is helping a bunch to draw the air
through  the rad. Neil's are flat but adjustable.

If you want it to work even better... Ian Beadle in OZ used the K & L.... S shaped diffuser and made
the opening even smaller. Here is a shot of his airplane. It is hot in the outback and this works.
I went for a ride. This cools both water and oil.

Paul Lamar


I'm starting to really like the idea of having adjustable louver flaps directly under the rad instead of ducting the air to follow the bottom of the cowl to exit at the back with exhaust / oil / radiant cowl air.
The front opening of the rad to the front of the cowl is only 4.5 inches. So I'm going to have a tight squeeze to come up with an S-shape / K&W diffuser. Too bad we didn't have more pictures and info on Ian's setup. I have pictures saved from a few months ago when his plane popped up on here.
This is my math so far.
  Rad is 18.75"W x 24.25"L = 454sq inch.
  Using 10% to find the height, the K&L opening is 2.4"H x 18.75"W
Paper towel roll gives me a good reference for the angle. It's hard to take good pictures when there is so much crap in the background.
- Matt Boiteau

Nice welding on the motor mount Matt.

The trouble with a duct under the rad ( unless it is very deep) back pressure will be built up
in the duct and the flow will be reduced. See page  46, 47, 48 and 49 in my book.

Some sort of louvers are essential.

Paul Lamar

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