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----- Original Message -----
From: "Joseph M Berki" <Joseph.M.Berki@grc.nasa.gov>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, December 01, 2003 6:26 AM
Subject: [FlyRotary] Re: radiator size
I am glad someone brought up cooling vs expected horsepower. George was
running three rads at one time and found that he had to pumb the rear
heater (in the car) connection into the system. His cooling problems went
away. Another successful rotary was Greg Riechters Cozy III. He elected
to go with jet power so we have not heard a lot about performance. John
Slade probably has numbers. I believe Gregg was running over 488 cubic
inches of cooling volume. Right now I am leaning toward two of the large
GM evaporator cores fed by a scoop under the belly that starts at 46
inches
from the rad face and expands from the inlet opening to the rad face. I
thought K&W curve at the rad face would help. The oil cooler will be in
the strake closeout fed by another small scoop and will exhaust to the
augmenter or overboard. I wanted to use a single scoop to feed everything
but i think it generates more air flow problems.
Joe Berki
Limo EZ
Joe, There's no question in my mind that your cooling system design needs to
start with the expected HP(and therefore waste heat) AND flight Regime (and
therefore airspeed) you expect to operate in. For an aircraft that spends
most of its time at cruise (and don't most?) with an NA 13B engine, a range
of from approx 80 - 100HP (7.5 -11GPH) is probably a good figure to plan on.
That would mean you need to get rid of from 3800 - 5500 total BTU/Min at
cruise airspeed.
Now, you would undoubtedly (hopefully) produce more power for takeoff and
climb. So now you are faced with the challenges of a different cooling
regime. High power (and lots of waste heat) and low airspeed (minimal
cooling airflow available). If you design for this regime (successfully)
then you will certainly have taken care of your cruise regime. On the other
hand, you may well be incurring more cooling drag penality at cruise (where
you will spend most of your flying time) than necessary.
Again, I think you need to consider your aircraft and operating situation.
If you spend most of your time at high speed cruise (such as most carnard
types are likely to do) then perhaps optimizing for cruise is the way to go.
If a "bush" plane climbing in and out of valleys at high power settings,
then perhaps the high power, low airspeed is the design point to shoot for.
Perhaps cowl flaps or fans could bridge the gap.
Anyhow, I think we understand that like most other decisions on an aircraft,
cooling is another compromise.
Be realistic! For an 13B NA engine, probably the person getting the most
out of an engine is Tracy Crook producing a bit over 180HP. For most of us,
its probably closer to 160HP and a few range in the 120-150HP range for max
power such as take off. Cruise is probably no more than 75% of that and
probably closer to 50%.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
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