Seems like half of the air museums I go to have a model showing how a Radial engine works, but never a Rotary. Last year I was able to go to Europe (plane ticket and hotel accommodations was a gift from my mom and my aunt). The Paris Air and Space Museum, which has a fabulous WWI section (admission is free) has a model of not just a Radial Engine, but also of a Rotary engine. I took a video of the model working and just recently posted online.

Enjoy!

https://vimeo.com/groups/1minute/videos/41546699

Neat stuff.
Thanks for the video.


Wheels

I had no idea that this is what rotary engines are, as I haven't read much about the WW I planes, I always thought them like a type of Wankel. It just seems so counter intuitive(?).

The Wankel rotary engine has a triangle inside it recreating the three phases of an internal combustion engine.

It is a different system than the rotary engine you show on the vid which was created earlier in history than the Wankel and used in aviation.

The Wankel was mainly used in cars as in a Mazda

The only Wankel I saw flying was on an airplane model. It was manufactured by NSU, a subsidiary of AUDI at the time, and way before it was purchased by VolksWagen. The advantage of that Rotary Wankel on a model, was that there was not as much vibrations as there are on piston engines. The absence of vibrations (or drastically reduces) is also found on turbines engines (jet engines).

About vibrations. After first seeing an animation of how a WWI-era rotary engine worked several years ago it struck me that they should be relatively vibration-free compared to other, more traditional reciprocating engines. All the moving parts (and therefore their masses) are are prescribing perfect circles, meaning that if they're properly balanced the whole thing should run as smoothly as a bicycle tire, except possibly for a small vibration associated with the actual combustion. As this video shows, a radial, or inline for that matter, engine has the mass of the pistons and piston rods changing directions hundreds of times per minute. That's gotta add something.

And finally putting this idea in writing has just popped another into my head. The effects of gyrosopic precession on rotaries is a favorite topic of WWI simmers. I'm no engineer, but I would guess that GP could be predicted based on the mass, speed and axis of the gyro. But these engines actually had two masses of different sizes and with different axes and probably different masses creating gyroscopic forces: one for the cylinders and the other for the pistons and piston rods. I wonder what effect that might have had on GP?

Any mechanical engineers out there care to weigh in on the subject?

While the force vectors may be different when looking at the pistons/rods and the cylinders-&-everything-else separately, they still are all part of the overall rotating mass along with the propeller. This total mass is no small amount considering that lightweight alloys as we are accustomed to in modern aviation did not exist at the time. Keep in mind that any input against the gyroscopic forces is "felt" at 90 degrees to the axis of rotation and you can see why rotary engined aircraft could be unwieldy. The Sopwith Camel lost many fledgling aviators due to the effects of gyroscopic precession. These physical properties are inherent in modern day reciprocal engined aircraft, but to a lesser degree, not the least of which is the lower power-to-weight ratio. WWII prop aircraft could turn better in one direction than the other, a fact known to the opposing side and used to great benefit. What a joy the P-38 must've been with its twin counter-rotating engines. I'm no mechanical engineer and I've never stayed at a Holiday Inn Express, either.

Thanks! That really helped show how things work better than I have seen before.

I doubt it. The mass distribution on a P-38 means that it has a way bigger moment of inertia because the motors are quite some distance away from the axis of rotation. That means that it probably had some lag in both reacting to the pilot forcing it into a roll as well as when trying to stop the rolling.

Lag no, slow mass yes. But in normal flight one can take that into account and I guess Spectre was talking about hands off trimmed flight and then being able to increase/decrease throttle without having to counter forces with stick and rudder. One would only need to adjust elevator trim as the speed changes.