If I’ve ever had to feed more than a quart of oil to a Cessna 172’s Lycoming, then I’ve blocked out that horrid memory. But there I was in Fort Worth, Texas, standing on top of the B-25 Pacific Prowler’s wing waiting for a ride, watching a mechanic dump two gallons down the throat of one of its two huge Wright Cyclone R-2600 radials. It had just flown roughly five nautical miles. The B-25 consumes up to 14 gallons of oil per hour at takeoff power and eight in cruise. You can even taste it inside the cockpit until the bomber gets airborne. Until then, you need to open a few windows.
Superficially, at least, the 172’s typical four-cylinder, 160-horse Lycoming and the 14-cylinder, 1,600-horse R-2600 are the same: They are both four-stroke engines. Fuel and air flow into the cylinder through a valve; the piston rises to compress the mixture; the spark plugs (two per cylinder in an airplane engine) ignite the compressed gasses; and boom, the piston shoves down and its connecting rod spins a crankshaft attached to a propeller, while the burnt fuel gets exhaled out a second valve and through the exhaust pipe. Both engines are aircooled. But the Lycoming has an even number of cylinders, while each bank of the Wright R-2600 is odd-numbered (and each engine has two banks). One reason: Pioneer aviators learned that to reduce vibration, every other cylinder must fire in sequence—ergo, in a seven-cylinder engine the firing order is 1, 3, 5, 7, 2, 4, 6, while the Lycoming’s firing order is 1, 3, 2, 4. If a radial’s single bank held an even number of pistons, say eight, neighboring cylinders 8 and 1 would fire one after the other, and the vibration would rattle the pilot’s dental work. I’d hate to have been the test pilot who found that out.
In the days before successful human flight, two camps emerged: With enough power a barn door can fly, or control’s the thing. The first camp was personified by machine-gun inventor Hiram Maxim, who called his barn door The Great Kite of War. Powered by a pair of two-cylinder steam engines that each generated 180 horsepower, the 7,000-pound, 145-foot-long sled had elevators for pitch and a rudder for yaw, while Maxim planned to use divergent thrust to turn the beast. During an 1894 test run on a nine-foot-gauge safety track, the Kite lifted off and broke through the guardrail placed there to, well, prevent the Kite from flying off. It floated briefly, then the rail cracked a prop before Maxim could kill the engines. The Great Kite of War settled back to the ground, never to rise again.
The other camp included birdmen like Otto Lilienthal, who, before strapping on an engine (which would flap the glider’s wings), first hoped to master aerodynamics with his gliders that he controlled by weight-shifting (see “The Aileron’s the Thing,” July 2010 Flight Training). Unlike Maxim’s Kite, Lilienthal’s series of gliders actually flew—more than 2,000 times, for a grand total of five minutes airborne—but his experiments ended in 1896 when one craft stalled and crashed, and Lillienthal died from a broken back.
And that’s when the Wright brothers got involved. Orville and Wilbur tried to solve Lilienthal’s control problems, which they perfected with movable control surfaces and keener aerodynamics derived from the world’s first wind tunnel. Only then did they attack the power problem. Instead of steam they chose a gasoline engine, which had become all the rage since Nikolaus August Otto built the first practical internal-combustion engine in 1876.
An internal-combustion engine is smaller and lighter than a steam engine because it has no boiler, no condenser, no water to turn into steam, and no constant combustion to keep up a head of steam. The Wrights’ mechanic, Charlie Taylor, built their first engine, a four-cylinder inline that generated 12 horsepower—which, to save weight, shunned the carburetor for dripping fuel. Still, it worked.
Within the decade other pioneers started using the rotary engine. Not the revolutionary Wankel Rotary invented in the 1950s, which would spew scads of power with few moving parts, weighed less, and remained whisper-quiet. (Wankels lost out to turbine engines, but they’re being kept alive in modern UAVs—and Mazdas.) No, we’re talking the old-timey rotary, built by the French companies LeRhône, Clerget, and Gnome. It resembled the radial like the B-25’s oil-sucking R-2600, except the crankshaft was fixed and the block—with a propeller bolted to it—rotated. It ran smoothly compared with typical aero-engines of the day; it was lighter since the revolving crankcase eliminated the need for a flywheel; and all that spinning helped to cool it—no need for a water jacket for this beast.
The drawbacks? That giant spinning metal plate turned into a gyroscope. Executing a left turn took muscle and time, but a right turn makes a 172’s P-factor feel like a gentle summer breeze. Like a radial, the rotary gulped oil, too, and not the Lycoming’s SAE 40 oil either—but lightweight castor oil. And as any great-grandmother knew, a dose of castor oil makes a great cure for constipation. After inhaling the fumes for a two-hour patrol, pilots tended to scramble for the head after landing.
Like rotaries, radials are aircooled. They also weigh too much for a light airplane. And smaller, civilian airplanes didn’t really need the weight nor the power. During the 1930s Clarence Taylor (no relation to Charlie) built the first Taylorcraft Cub, which came with a 65-horse Continental aircooled flat-four engine. Similar economical, horizontally opposed engines became en vogue for light airplanes after World War II. Efficient designs added horsepower without increasing weight—and given enough power, even a barn door will fly.
But you still need better aerodynamics—and control surfaces.
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