Simanaitis Says

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ROTARY ENGINES: HOLD THE CRANK, SPIN THE REST

I’M TALKING about a rotary engine in the traditional sense, its crankshaft firmly fixed to the frame, its engine block with radially aligned cylinders spinning around and producing power. (By contrast, the Mazda automotive rotary is an entirely different concept, a Wankel engine.)

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A rotary engine’s crankshaft is fixed; the rest of it spins. Animation at http://goo.gl/KrxGB (not available on all devices).

At first, this may seem like a screwy idea, but in the early days of internal combustion, the rotary had benefits not offered by a conventional piston engine. Its lack of conventionally reciprocating elements made for very smooth operation. In fact, the block’s rotating mass acted as a big flywheel enhancing smoothness between firing strokes.

Since it had no added flywheel, a rotary engine was comparatively lighter than a conventional one. Early rotary aircraft had a substantial advantage in power-to-weight ratio.

Last, the spinning cylinder block generated its own flow of cooling air. Most early rotaries were air-cooled.

In fact, the first engine specifically intended for an aircraft was a five-cylinder rotary designed by Stephen M. Balzer in 1899. It proved underpowered for Dr. Samuel P. Langley’s Great Aerodrome being developed at the same time as the Wrights’ Flyer. Charles M. Manly transformed the Balzer into a (non-rotary) radial.

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1903 Manly-Banzer radial (note, not a rotary) powering Langley’s Great Aerodrome in its two configurations.

This Manly-Balzer was the engine of the Great Aerodrome when it catapulted itself into the Potomac River on December 8, 1903.

The Wrights flew successfully only nine days later at Kitty Hawk, North Carolina. The Manly-Balzer engine finally did become airborne when Glenn Curtiss was given the task of evaluating Langley’s concepts in 1914. Details are given in “The Wright Bros. vs. Glenn Curtiss” at http://wp.me/p2ETap-zA.

The Sopwith Camel (Snoopy’s craft) and Avro 504 were among many early rotary-powered aircraft.

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A Sopwith Camel with a familiar pilot. Image from http://goo.gl/A2ZQuh.

See http://goo.gl/LCHFE9 for a beautiful example of the Avro and its rotary power—in 1/4 scale. Also, check out http://goo.gl/WQ0TeK to see the prudence taken in firing up a full-size Camel.

Having the rotary in the aircraft nose, in a tractor-type layout, put the engine directly in the cooling airflow. However, even some pusher aircraft had rotaries, the Borel Monoplane and Farman Biplane being two examples. (See http://wp.me/p2ETap-fB.)

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My 1912 Wake Up, England! Farman model for Microsoft Flight Simulator. Note the oddity of its prop and rotary engine placement.

In fact, the Farman’s rotary powerplant resided aft of its pusher propeller, possibly to enhance its cooling, possibly for matters of weight distribution.

Both of these were seven-cylinder rotaries. In fact, for reasons of alternating-cylinder firing order, most radial engines—rotaries and non-rotaries alike—had odd numbers of cylinders, typically seven or nine.

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An 80-hp Gnome Monosoupape rotary powerplant. Image from Aviation Archive: Aeroplanes of World War I. See http://wp.me/p2ETap-1RL.

Some rotaries were of the Monosoupape type, with a single valve per cylinder for both intake and exhaust. Most had separate intake valves. Cam actuation of the valves was another rotary oddity: The engine had no rotating camshafts; rather, a stationary annular ring took the place of camshaft lobes. Rollers on the ends of the rotating pushrods followed the contouring of this single cam ring.

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The annular ring with contoured circumference is a radial engine’s cam. Several of its pushrod rollers can be seen.

Rotary engines had different schemes to control engine speed and power. Some used a hit-and-miss switch that fired cylinders only every second or third power stroke. Others interrupted ignition by means of a “blip” switch. Still others interrupted the fuel flow.

The rotary engine’s spinning mass acted as a giant gyroscope which dramatically affected maneuvering of the aircraft. A brief physics lesson on gyroscopic precession of a Sopwith Camel can be seen at http://goo.gl/BBSaQ2.

Turning a Sopwith Camel to the right inherently caused a dive as well; turning to the left, a climb. This made the aircraft highly maneuverable to the adept—and deadly to the inexperienced, particularly on takeoffs or landings. The simulation game Ace of Aces built this into the craft’s flight dynamics (see http://wp.me/p2ETap-1H9).

By the end of World War I, the power advantages of water-cooled inline powerplants overtook the benefits of the rotary concept. See Aviation Archive: Aeroplanes of World War I, http://wp.me/p2ETap-1RL, for this and other aspects of WWI aircraft engineering.

In a coming item, we’ll see rotary engines finding their way into road vehicles. Consider the logic of this: Road wheels spin; they don’t reciprocate. ds

© Dennis Simanaitis, SimanaitisSays.com, 2014

2 comments on “ROTARY ENGINES: HOLD THE CRANK, SPIN THE REST

  1. Bill Urban
    May 2, 2014

    Thanks Dennis, more fascinating stuff. That Megola offers both “revolutionary” propulsion and eye pleasing style, definitely Guggenheim material. (But can’t say much for the unsprung weight.) An artistic study for future electric power?
    Were any of these two-cycle, given the intake charge coincidentally via the crankcase? That piston mounted valve is interesting, but there’d be a lack of vacuum to act on it.
    Could the automobile rotary have been an effort to avoid Selden?

    • simanaitissays
      May 2, 2014

      Hi, Bill,
      To my knowledge, all here were Otto 4-strokes. Note, the Adams-Farwell video states this explicitly.
      Hub motors have been used in EVs; fine where unsprung weight isn’t a huge problem (in heavy vehicles, or when ride/handling aren’t crucial).
      Interesting question concerning the Selden Patent. I suspect he would have harrassed them anyway.

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