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-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of John Slade
Sent: Sunday, August 24, 2003 2:26 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: cooling and radiators
Re; Al Wicks radiator
It's good that he got it to work well. He has enough radiator for the hp,
and both some vg's before the duct entrance, and exhaust augmention will
help the air flow. That's all good, but I'm put off by statements such as:
"The first thing to keep in mind is that heat transfer with coolant is
substantially more efficient than an air cooled engine. Why is that?
The specific heat of water is 1.0, meaning it is extremely effective at
grabbing and releasing heat. Air and oil are insulators in comparison. Oil
has a specific heat of 4/10. So oil is 40% as effective. Air is even worse
at .24. The conclusion? It should be easy to use the same ducting as the
Lycoming engines."
which is incorrect. Of course water is more effective than air in carrying
heat, and it carries it from the engine to the radiator. Now what? Now we
have to reject to air, just like a Lyc, except we have to do it at a lower
temperature; so it is less efficient, and will need more airflow.
Fortunately a radiator has better volumetric heat transfer efficiency to
help make up for it.
Then he says:
As a result, I don't need an oil cooler (less drag, complexity). My oil
temperature follows coolant temperature then peaks at 237F. Well within
normal operating temp.
237 is well within the operating temp? Well, yes; it is below the upper
limit on a piston engine, but not something you want to do on a regular
basis with a rotary.
Al
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