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