| Gary,
You've hit on one of the main advantages of the rotary engine... that it is failure tolerant. Generally speaking, if it is running, it will continue running until shut down where it will likely not restart. But it typically won't freeze up and quit while running.
I'm sure you've heard of the smoothness of the rotary engine. I've enclosed two charts which compare vibrations of the 2-rotor wankel to a 4-cylinder reciprocating piston engine. The difference is very apparent.
To control cooling I use a cowl flap, simple, light weight, and effective. Another solution might be to add a spray bar, often used in racing applications. I have found that at low power settings I have no cooling problems during ground ops. However, I am cooling limited when doing full-power ground runs above 80*F OAT.
Mark
On Tue, Jun 7, 2011 at 1:18 PM, Gary Casey <casey.gary@yahoo.com> wrote:
Ted, Yes, it is a fun conversation and could go on forever :-) Sorry about the various text colors - I don't know how to fix all that stuff. My comments are based mostly on a narrow horsepower range of about 350 that I targeted for
my ES, so they may not be valid for other hp ranges (like the 600 hp Eagle). But: Matching the air-cooled engines BSFC is difficult - it is a low friction, low surface-to-volume ratio engine running reasonably hot (hot internal surface temperatures reduce heat rejection and improve BSFC). I doubt that a liquid-cooled engine could match the BSFC of a modern air-cooled engine running LOP.
I designed a direct-drive V-8 installation, and at the hp target I was (and am) convinced it was a better choice than a package with a speed reduction. A V8 can tolerate a lot of boost so a 400 cu.in. Chevy running about 50 inches manifold pressure can produce a reliable 350 hp at 2800 rpm.
I agree with the comments on rotary
engines. They have one advantage, which I consider important, and that is that they can continue to produce power with substantial damage. This would include apex seal failure and loss of coolant. I piston engine will likely not last long without coolant. But as for parts count, I once counted 50 parts in a single rotor. Production rotary engines, to my knowledge, are not tolerant of crankshaft (oops, "e-shaft", pardon me) thrust, so allowances have to be made. Yes, the noise level can be tolerable with an added turbocharger, but the high exhaust temperatures require a high-temperature turbine housing (and probably a liquid-cooled center section) and even then it can be marginal.
One advantage of air-cooled engines is that they have a gradual over-temp limit, while liquid-cooled engines have an absolute limit (boiling).
With an absolute limit you have to go to great pains to stay away from the limit, even for a short time. This might have to include an electric cooling fan for ground operation, but what do you do in the air? Most likely oversize the cooling system to maintain an adequate margin, and this adds weight and cooling drag.
Gary Casey
From Ted:
This is a fun conversation.
On 6/4/2011 9:52 AM, Gary Casey wrote:
My conclusions - opinions of the disadvantages:
V-8 with reduction gear: Heavy - about 150 pound penalty Complex installation and systems
Slight fuel consumption penalty
weight, 400 HP. Eagle 540 700# wet, 600 hp. A comparably sized automotive derivative engine can easily be lighter hp for hp. Because of internal design elements (advances in design possible because of liquid cooling, i.e. no gas used for cooling) modern liquid cooled engines can easily match or improve on air-cooled gas consumption.
V-8 engine direct drive turbocharged: Heavy - about 75 pound
penalty Complex installation and systems
No information, so I can't comment. The only one I could find was the WW1 Hispano-Suiza. Hardly relevant to the conversation.
Rotary engine: Very complex installation and systems
Heavy - up to 50 pound penalty Potentially fragile apex seals
Hgh cooling drag Noisy
Significant fuel consumption penalty increases the weight penalty
Mazda 13B engine FWF weight 325 # all up (200 HP. I couldn't find the 20B data quickly) The equivalent engine is the Lycoming IO-360 at 324-335 #. Sounds like a wash, or maybe a slight win for the rotary. Yes, the rotary is slightly thirsty, but the gap seal issue is ancient history. The newer engines have been bulletproof.
Turbine engine: High initial cost
High fuel consumption negates any weight savings
Amen.
Misc. opinions: The liquid-cooled
V-8 dates back to about 1918 when Chevrolet built the first mass-produced one, so it's technology is even older than the air-cooled engine's "30's technology" that someone mentioned.
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