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Date: Mon, 13 Mar 2006 17:33:56 -0500
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] heat output
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M Roberts wrote:

> Here's an interesting question. Considering the exhaust heat of the 
> rotary is so much higher than a Lycoming, if doing a side-by-side 
> comparison of the two with equal fuel burn rates, wouldn't the 
> Lycoming have more engine heat to remove from under the cowl than the 
> rotary?
>
> I think this one is a no-brainer, but my mother often said the same 
> about me...
>  
> Ernest,
>  
> Not necessarily.
>  
> The conventional wisdom:
>  
> The Wankel has a higher exhaust temp because of uncombusted 
> hydrocarbons (due to the flat combustion chamber) and possibly a lower 
> expansion ratio (depending on which engine you may be comparing it 
> to). So the Lycoming may make more power for the same fuel flow with 
> less heat rejection. The Wankel also has a lot more surface area for 
> the combustion chamber and rotors so the heat rejected to the coolant 
> will be more. You never get something for nothing and giving up all 
> those valves, push-rods, lifters, ad nauseum, comes with a price. The 
> price is slightly higher cooling load and egts.
>  


Conventional wisdom has me confused.  Is it saying that the piston 
engine does a better job at converting the fuel to work, and the Rotary 
wastes a lot of fuel to heat the engine?  But haven't we had reports of 
Rotaries flying formation with Lycs with equivalent airframes and 
getting effectively the same fuel burn, thus blowing a whole in this 
whole BSFC argument? 

Would the answer to  my question be that at equal burn rates, the Rotary 
would spit more heat out the exhaust and have less to reject through 
other means, but it also wouldn't be producing as much power?

-- 
         ,|"|"|,               Ernest Christley     |
----===<{{(oQo)}}>===----     Dyke Delta Builder    |
        o|  d  |o          www.ernest.isa-geek.org  |