It looks like a K&L wedge diffuser will work best for my application. I am working the cowl design and I am trying to determine the optimum opening area for inlet air. I have your book but I cant seem to find the answer. Some time back there was some discussion about this. If I remember correctly the consensus was 15 percent of rad area was too much. Is this correct. If so, what is a good area for inlet air?

    Paul Shamlian

    I suspect it depends on the thickness of your core.
    What are the dimensions of the core you plane to use?
    I suspect if the core is large in area and thin 10% might work.
    Large area thin cores have lower cooling drag.

    The other factor is movable louvers aka cowl flaps. If you can close the louvers,
    assuming the engine is cooling adequately, the drag of an overly
    large opening, say 20%, is reduced by external diffusion.

    If the core is thin 10% might work.

    It is a good idea to use louvers or cowl flaps in any event.

    Also it is a good idea to have the opening in the prop slip
    stream so it will cool waiting to take off.

    We are still over cooling the 650 HP TTC with 20% opening
    on the ground no less.

    The cross counter flow heat exchanger consist of two .75" cores
    20" by 30"  back to back.   No cowl flaps but a very nice set of curved louvers.

    Start with 20% and see what happens. Design the opening so it can
    be closed down later. Maybe you can run it with out the final cowl.

    Do you have any recent pictures of your Bear Hawk patrol Paul?
    Is the core on the cool side of the engine? Does it exit through
    the side of the cowl?

    Paul Lamar

The radiator I am looking at has a core that is 17 X 14 with a thickness of 2.7 inches. 642 cubic inches. I am only measuring the core, not the overall dimensions. The best source I could find for radiators was Summit racing. They are the same radiators we use in circle track racing. I am modeling the firewall forward in Rhino and trying different arrangements. There isnt room on the cool side to make it work without a large boxy nose bowl. The rad fits under the engine nicely and maintains a nice cowl. There isnt enough room to have both the oil cooler and rad under the motor so the oil cooler has neen moved to the cool side. The plan is to try to build louvers on the bottom of the cowl for the radiator. Not yet sure how to exit the air from the oil cooler. Hopefully just an exit duct but might be a cowl flap
Paul Shamlian


That is not going to work well. First a core that size full of water is very heavy.
Second the air has a hard time going through a core that thick. Most car racers
have not caught on yet. Dodge and Honda are the leaders in cooling efficiency.

You have a engine weight problem already unless
you are going to aluminum end housings.

Shop this company by rad size.

https://www.radiatorexpress.com/category.asp?cat_id=R026

Here is the 20" by 30" by 3/4 inch thick Dodge truck rad underneath
Bear Hawk Patrol 3D's. It is always harder to fit the 13B in a tandem
airplane. The RV4 is even narrower than the 32 inch wide Bear Hawk Patrol.

I'll get the year and make so you can order year and make.
It will be about $130.

Where are you Paul?

Paul Lamar

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