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Subject: [FlyRotary] Re: radiator size
I guess we are trying to find the edge of the envelope. Charlie Airesman
is using a small rad and a NACA duct with an augmenter and is doing over
200 mph with a 4 to 5g/h fuel burn. On the pusher, we can optimize the
duct length. The augmenter will be tricky with the rotary. Ed provided
some btu numbers to start with. Thanks
Joe Berki
Limo EZ
Joe, I have no problem believing that Charlie has adequate cooling at
cruise. With a 5 g/h fuel burn (if using a rotary) Charlie would be only
producing approx 55 HP. That would mean he would need to get rid of approx
1700 btu/min by radiator and approx 850 btu/min by oil cooler. Even using
only one core as radiator, at that power level, he could get adequate
cooling at airspeeds as low as 100 MPH. I suspect that at take off he is of
course producing more power and waste heat. At 200MPH at those fuel burn
rates and only one core, he would still have over 150% total reserve cooling
capacity.
Smaller power levels = smaller cooling needs. So it all depends on your
power levels and airspeeds (or more correctly mass airflow rate through your
radiators).
I think you really have to look at the btu of waste heat you need to get rid
of which is directly dependent on the power being produced and then at the
airspeed available for mass air flow through your radiators. Then you have
to decide which part of the operational regime you want to design your
cooling system for. To miminize cooling drag, you might start looking at
the requirements for your cruise regime - particuarly since you will spend
98% of your operating time there. On the other hand, if you are building a
bush plane that you expect to spend a lot of time at low airspeeds and high
power settings climbing in and out of mountainous terrain then you might
want to lean the design point more toward that operating regime (high power
low airspeed). I think that these type considerations form a reasonable
starting point.
Clearly if you don't do the radiator sizing correctly - then NACA ducts
with vortex generators or mustange like scoops or any other arrangement is
not going to make up for inaqduately sized radiators.
My 0.02 worth.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
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