From: "Charlie England" <flyrotary@lancaironline.net>
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Date: Sun, 11 Jan 2015 10:15:28 -0600
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] cowl temps
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On 1/11/2015 7:24 AM, steve Izett wrote:
> Hi Guys
>
> Ive finally got the engine (Renesis) and cowl complete on the Glasair.
> Now without a prop I can run her (1500rpm, 90 deg F ambient) for about 10 mins before water temps teach 200 deg F.
> Hoping that with the prop she will keep her cool.
>
> We have sought to protect the inner cowl surfaces from exhaust radiant heat and this appears to be functioning
> however I’m surprised at the upper cowl external surface temps after shut down getting to hot to touch.
> What are your experiences of cowl temps after shutdown?
> If air-cooled engines run up to 400 deg F CHT’s how do they go?
> I take it we all have glass cowls!
>
> Steve Izett
>
The only place an air cooled engine is that hot is the head metal 
adjacent to the combustion chamber. If you could measure a water cooled 
engine's head temp between the combustion chamber and water jacket, it 
would probably be pretty high, too (the fire in the combustion chamber 
is the same temp in both, right?).

I've never measured the temp, but my Lyc powered RV-4 cowl gets too hot 
to touch after shutdown. Googling for human pain threshold temps returns 
answers from 43-54 degrees C; much lower than the 200 degree engine 
temp, and much cooler than the threshold for fiberglass damage.

Radiant heat from the exhaust will obviously be much higher, and can 
easily melt (or burn) fiberglass if it isn't protected by a radiant 
barrier and/or supplied with adequate cooling air flow.

Don't know if that helps, but there you go....

Charlie