the 'prop' shaft is bolted to the airframe.
I think that we're having a terminology problem. Do you actually mean the stationary crankshaft? Unlike stationary aircraft engines, in which a turning crankshaft drives the propeller, in rotaries the whole engine spins around a
stationary crankshaft. The
prop is bolted directly to the engine and spins with it. The primary reason for the rotary configuration was to provide adequate cooling. Because the cylinder heads are perpendicular to the slipstream and whirling through the air, the engine stayed within safe temperature limits. Engine cooling was a challenge in the first decade of the 20th century, even with water-cooled engines, and rotaries presented a viable solution to the problem.
There are also a number of fallacies concerning rotaries that keep getting printed: #1.They were two-stroke engines that mixed the oil and fuel, #2. They did not have throttles and, #3. they were tricky to fly because of the gyroscopic and torque forces from the spinning engine.
#1. Regardless of configuration, all rotaries are four stroke engines. A common fallacy about rotaries is that they are two-stroke. That misconception probably arises because of confusion over how they are lubricated. Regardless of make, rotaries share a total-loss oil system. The air, fuel and oil are delivered to the engine through a hollow crankshaft, creating the impression that the oil mixes with the gas as in a two-stroke. In fact, the oil and fuel do not mix. Castor oil, often the famous Castrol brand, was the preferred lubricant precisely because the oil maintained its lubricating qualities even under pressure and high heat. It did not ignite with the fuel as it passed through crankcase, cylinders and out the exhaust.
#2. Many books on WWI aviation state that rotaries had no throttles and always ran at full speed; the only way to slow them was to temporarily turn them off via a coupez or "blip" switch that cut the ignition. While this is semi-true in fact all rotary engines had a way to control [engine speed] except the 100-hp Gnome. All had carburetors except the 100- and 160-hp Gnomes.
So if you limit your discussion to the 100-hp Gnome it fits the typical description. Naturally it proved very unpopular with pilots, since they couldn't adjust speed by increasing or reducing power. Canadian born ace and 1st Pursuit Group commander Harold Hartney, who flew various planes powered by the 100-hp Gnome, stated in his memoir Up and At 'Em that it was a horrible engine.
Manufacturers quickly developed ways to regulate engine speed by manipulating the relationship among the carburetor, mixture control (or fine adjustment as it was called at the time) and sometimes the ignition. Different types of engines used different systems. Only the Gnome engines did not have carburetors or throttles. The only direct control pilots had over the fuel and air mixture was the fuel flow fine adjustment lever in the cockpit. Gnomes were often called Monosoupape engines, French for "single valve." The single valve both induced air for the fuel/air mixture and vented the exhaust after the mixture ignited. In place of a valve for inletting fuel, the 100- and 160-hp Gnomes had inlet ports toward the bottom of the cylinders. Because the Gnome power plants did not have a throttle or carburetor, pilots could vary the speed of the engine only by interrupting the ignition. The 160-hp Gnome improved on the 100-hp version's simple on/off switch by providing a variable ignition timing selector.
#3. According to pilot memoirs and modern pilots flying exact replicas , the often-repeated tales about tricky aircraft handling due to the gyroscopic and torque effects of rotating engines—that the spinning mass of the engine made for very quick turns to the right and slow turns to the left—are exaggerated. "When you hear the stories about rotary engines being hard to fly, the problem was with the inexperienced people flying them," stated one pilot. "When I made my first flight in a rotary-powered aircraft, I landed and then realized that I hadn't noticed any gyroscopic effects. An experienced pilot automatically compensates for those things. Turns to the right might be a little quicker, but that is because the rotary engine tends to pull the nose down [in that direction], and you make a quicker descending turn than you make a climbing turn."
Others agreed: "There are small gyroscopic effects but nothing close to the exaggerated tales often repeated in print and in documentaries. You adjust for them much the same way you would if you were flying in mildly gusty conditions. The torque reactions are most notable during takeoff and gliding in for landing when 'blipping' the engine."
Other factors had a more pronounced effect on aircraft handling. Pilots noted that all the early rotary-powered planes had a lot of adverse yaw (the tendency of the plane's nose to point in the opposite direction of a bank when starting a turn), and all were tail-heavy, leading to a certain amount of instability in their handling.