Flying at 7000 rpm (or less) is a lot different than racing at 9500 rpm of course.
But, flying is very close to a 100% duty cycle while racing is closer to 60%.

Lynn E. Hanover


I'm going to step in a pile of doo doo and put on my heretic hat here. Everybody always makes the 100% duty cycle argument, but it simply is not so. The only application where this is correct is when you turbo normalize the engine and use a CS prop.

In a NA, fixed pitch prop application, you will never see 100% duty cycle. You will never even see full MSL power. The prop limits your  rpm on takeoff. Then you gain altitude. The power output decreases. Then you bring the throttle back and lean the engine. It will not be making anywhere near 100% MSL power. Cruise will be 75% of whatever fractional power you make at cruise altitude, LOP. Way below max. Probably closer to 60%

If you build a special STOL airplane with a climb prop and operate as a banner tug....then you may see 100% duty cycle. None of us do this.

The one thing that is true is that there is never a chance for the engine to cool off. The heat flux is constant. This of course relates directly to spark plug heat range.

The Achilles heel of the rotary for continuous power output is the fact that it has essentially only one combustion chamber for three events. This means that chamber must move all the waste heat for 3 cycles with no breaks. Mechanically a great package and a very good effort at fitting the proverbial 10lbs of poo in a 5lb bag (well actually 15lbs in a 5lb bag). Unfortunately the cooling load is concentrated as well.

No free lunch.

So I guess if you are referring to a cooling duty cycle of 100% I would agree. There is no chance for the combustion chamber/spark plugs to cool between shifts or into corners as in the car.

But the often and reflexively touted 100% mechanical/power duty cycle is incorrect.

This actually favors piston engines. The cooling load is spread around and the chamber gets to rest between combustion events. Whether or not the mechanical complexity and additional weight/volume is worth this advantage is something we all have obviously made a decision on.


Monty