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Originally Posted by Rotary10-RV
Additionally interesting George is that the Foil Mickey printed shows the printed Lyc fuel flows at the performance level that they print. Not casting any aspersions here, Lycoming doesn't publish the flows at higher outputs. I'm very interested in fuel flows at high outputs. The rotary is more rather than less efficient at higher HP levels. Tracy Crook has found that the rotary is very tolerant of LOP operation. He comments that he takes off LOP in his RV, as he is, "really cheap" by his own admission! The rotary's combustion chamber which contributes to higher fuel consumption numbers also seems to tolerate the LOP operation well. I guess this is a give some get some deal. Many thanks to Mickey for his tour info.
Bill
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No aspersions taken but it is kind of crazy to run the Lyc above 75% power anyway. The key to economy is get to the magic 75% and lean the **** out of it. No secret. However with that said, it does not matter if Lyc publishes FF at high output (which they do if you own official Lyc manuals with a nomagram), Mistral did publish Lyc numbers (actual or Lycoming numbers?) and they are better than the Rotary at high power.
Physics of a long skinny combustion chamber (Wankel) is such that it is inefficent. No aspersions just facts and physical limitation. I know people want it to be sooooo not true, but Wankel's are not fuel efficient, I know. Now with that said if you go right to altitude, and lean the **** out of your Mazda 13B, have good ignition, tuned intake & exhaust, you can do OK, not super great, OK. Down low on the "pipes" you are burning lots of gas, like any engine, but the Mazda does get more thirsty then pistons at high power. Wishing it was not true does not make is so. It is just the way it is. If you know that and adjust your operational techniques you can minimize the fuel penalty.
I agree with Tracy you can go LOP and believe the Mazda is tolerant of LOP, because there are only two rotors, firing more so power pulse unevenness will be less noticeable than a reciprocating engine. With 4 pistons, one pulse per two crank turns, if just one stumbles, it makes a difference. Tracy has my respect and is a straight shooter, but he is a true he is a true Disciple and believer. He is like a mad scientist in the best possible sense of the word. Also he actually flys the **** out of his own parts. Hat's off. Now can the average pilot/builder get the same LOP operation Tracy does. Yes but it will be work, by operational technique and engine tuning/tinkering. Same with Lycoming.
Depending how you fly the promised fuel economy of a Wankel may be less than realistic. Some people say they can LOP a Lycoming O320 with a carb! I find that hard to believe. A fuel injected Lyc, the bigger the better, 200hp, 260 hp, yes you can get LOP. Again its effort and you need to balance the injectors and have an engine monitor. Most homebuilders are more likely to do this. Lycoming says it is not practical on small Lycs because the GA population is not as crazy as we are, but for those willing to make the effort and tinker and fine tune, it is possible. The same applies to the Mazda or Subaru.
TURBO and SUPERCHARGING
My real feeling is with a Subaru or Mazda the best efficiency and only way to go is turbo charging (or supercharging with the Subaru). If Mazda offers a turbo and Subaru offers a super charger don't you think there is a reason? They know something. What works in a car is a real benifit in a plane.
Every engine theorist knows to best way to increase efficiency is increase compression. A turbo does that. Most of the time we are normalizing at altitude, but that is a boost, since the delta of induction to exhaust (ambient) is greater, thus a great pressure ratio.
Now a Lycoming can be turbo-ed and gain high altitude efficiency, but I think the water cooled engine has a turbo advantage. Water cooled engines are more detonation resistant and have better internal heat transfer. Air cooled Lycs can be turboed but you now need an inter-cooler and a bigger oil cooler to get rid of the extra heat of induction air compression. With water cooling you already can cool the turbo easily.
However the water cooling may be better for internal engine heat transfer it sucks for airframe cooling drag. Placing a radiators is the Achilles heal of water cooled engine installation in airplanes. I have only seen workarounds and make it works, but nothing elegant. Look at a P-51 and get back to me.
Air cooled engines in airframes designed for air-cooling are super efficient from a cooling DRAG stand point. Yes they are not as good for heat transfer of the internals but we have had 80 years of perfecting air cooled aircraft engines. The military, NASA and the who who's of 20th century industry has worked the problems of air cooled aircraft engines and installations. When some one makes an airframe just for water cooling than you will see better performance numbers. I know the Thunder Mustang set some records with a Falcon V12 (N2O) in a P-51 clone. That is my point. The Thunder Mustang airframe was made for water cooling. The RV is not.
Never the less if I had a Mazda or Subaru it would be Turboed or Supercharged. I would not mount the heat exchangers in the stock Van's cowl original air inlets, like Eggy does. That works but its draggy. Wishing it was not does not make it so. It works. It looks OK but these are inlets for AIR COOLED ENGINE. They way powersport (rotary engine kit) did it is better with the single chin scoop. It could likely still be even better, but it is a great start.
It is possible you will never get H2O engine airframe drag down to an equivalent air cooled engine. Well at least that is true unless some one comes up with some break thru exchangers, skin cooling or some cooling tunnel integral to the airframe. A stock RV airframe will not hack it. Again wish it was not so, but its true.
That big *** radiator is a bummer for you water cooled guys, and usually it is an after thought in the installation.
COOL ENGINE: Echotec $4500.00 NEW, 205 HP
http://www.crateenginedepot.com/stor...66-P826C2.aspx
Here is a hop up book:
http://greenwoodchevy.com/Merchant2/..._Code=GCGPPEDH
This might be cool for a RV-9. Yes it is 205hp, but people forget the reduction drive waste hp. Also you are not going to be winding it up 5,600 rpm. I think 160 hp at the prop flange is a realistic goal. Also with the narrow engine you can make a skinny cowl, like a P-51. While you are at it, why not a belly scoop, like a P-51? $4500 for a NEW engine. Not bad. Add an A/C compressor and have an AC RV! (kidding)
The EchoTec has a supercharger, again compression is the key, and water cooled engines are more tolerant to higher compression or "compressed induction" than air cooled engines. I would exploit the water cooling for all she is worth and turbo or supercharge. It will not help much down at low altitudes (fuel economy wise), but high altitude performance will be good; If and that is a big If, you install the radiator'(s) with min cooling drag.
COOLING DRAG
Min cooling drag is taking 200 mph dynamic air pressure, slowing it down, passing it thru the cooling core, expanding the air again and exiting the air parallel to the free air stream with min internal loss. Easier said than done. That is why the P-51 was so awesome, but to be real, it did not hurt that it had 2000 hp either.
Again I wish Mistral all the luck in the world and think their 3-rotor turbo engine might be hit, BUT they must keep cost down, weight down and have a complete low drag package. That cowl abomination of their Piper test bed Arrow is not pretty or efficient. Wishing it was not so will not make it so.
Still waiting for Arrow miles per gal VS. speed numbers. Dyno numbers mean nothing unless its in the plane.
I am looking forward to all the new Rotary engine installations to come, Mistral, homemade or other. Keep inventing but it is a big puzzle and it all has to fit. Right know weight and cooling drag are your enemies. (Not me)
George
Interesting, thanks again
That makes sense. They are very close to the Lyc below 75% power. The real key there is lean of peak Ops. That is the key. I suspect the Lyc data was at recommended best power mixture, which is totally fair. I think LOP for small Lycs can be hit or miss in practical real world application. The point is not that the Rotary is a fuel economy king but at least fuel econ with prudent power and mixture control can get decent fuel econ. 
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