Using my eyeball-caliper, I think this little model-airplane Wankel engine is also rated according to a single side of the rotor. It's rated at 4.9cc, which looks like a reasonable estimate for the maximum volume of one combustion chamber. What that means is, it's actually a 14.7cc engine, which is ENORMOUS displacement for a nitromethane/methanol powered engine of this class. However, the 4.9cc rating may actually be an appropriate comparative rating in this case, because normal RC engines are 2-stroke piston engines, which require only 1 crankshaft rotation to complete a combustion cycle -- the same as this engine. However, this engine is a 4-stroke, meaning that it separates the intake and exhaust cycles from each other, minimizing the amount of fuel wasted out the exhaust -- but at the same time, it constantly has one combustion chamber actively combusting while the other two are preparing for combustion or venting exhaust, so like a 2-stroke piston engine it doesn't waste any of its momentum preparing for combustion or venting exhaust. In fact, it's even better than a 2-stroke piston engine in that regard, because even a 2-stroke piston engine is running on its own stored momentum for half of each crankshaft rotation.
It's just a shame that Wankel engines are so hard to seal properly, and have such poor volumetric efficiency, or they would be indisputably the best form of positive-displacement combustion engine ever invented.