Subject: [FlyRotary] Re: rule of thumb and RV-3 sizes- was Cooling Inlet Areas/Bernie's RV9

Bill, would you agree that more air is more important than more radiator? This would explain why smaller systems are functioning better than predicted. Given the space available in most aircraft down sizing the radiator is important. How small can we go? Jerry

Jerry;

Like most things; it’s a tradeoff.  Generally more cooling air flow equals more drag.  Somewhere in there one would hope there is an optimum; but everyone’s criteria for trading configuration needs for drag reduction is different.  The attached chart shows radiator cooling drag as a function of area (actually height for a given width, but same idea) for a fixed amount of heat rejection.  Larger area gives less drag, and vice-versa.

Sorry, best quality I could achieve scanning a scan, and keeping a manageable file size.

Al

On Thursday, April 7, 2005, at 06:33 AM, William wrote:

The amount of heat rejected is very similiar, however the delta-T available to drive the heat into the air is less for the Rotary than for the air cooled engine because of the temperature limitations of the water cooling circuit. Therefore we cannot heat the air as hot, and therefore need more air than for a direct air-cooled engine.
Bill Schertz
KIS Cruiser # 4045

----- Original Message -----
From: rijakits
To: Rotary motors in aircraft
Sent: Wednesday, April 06, 2005 9:43 PM
Subject: [FlyRotary] Re: rule of thumb and RV-3 sizes- was Cooling Inlet Areas/Bernie's RV9

snip

I mentioned that on the other list, but I was dismissed as " you can't compare aircooled engines with a rotary".
I don't think there is a great difference on the amout of cooling necessary, as the efficiency of both engines are fairly close. So some heat goes out the exhaust and the rest has to be cooled. For sure you need different ducting, but the amount of heat energy should be about the same and you want to get rid of it with the least drag, either way.
 
 
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