The Wright stuff

In 1902, the Wright brothers sent out a request for bids to several engine makers for an 8-hp, "vibration-free," gas-fueled engine that would weigh no more than 200 lb. No one took them up on the offer. Having successfully built a one-cylinder, 3-hp, cast-iron engine the year before to power their machine shop, the brothers decided to design and build the engine for their aircraft as well. They finished it eight weeks later with the aid of Charles Taylor, a mechanic and machinist, but without drawings. The 12-hp, four-cylinder engine weighed 170 lb, including the radiator, water and fuel tanks, and 1.5 gallon of gas. It had no throttle. The four-stroke engine always ran at about 1,000 rpm. But output could be somewhat controlled by retarding or advancing the spark timing. Other engine features included:

• Noninterchangeable components. Each was hand fitted. A piston, for example, only fit in the cylinder it was built for.
• The crankcase, cylinder water jacket, mounting lugs, and part of the intake manifold were cast as a single piece of aluminum.
• Valves were cold-rolled steel and of the poppet type. Piston suction opened the inlets and exhaust valves operated on a bicycle chain and sprocket-driven camshaft.
• Fuel dripped into the intake manifold where it was vaporized by the hot water jacket and sucked through the inlet valve and into the cylinders.
• Time between overhauls was about 12 hr.

The brothers also had to design their own propeller. They initially thought they could use information on maritime props, but found little useful data. Besides, they needed a prop with 66% efficiency, and ship props were considered acceptable if they were 50% efficient. So the brothers developed a theory of prop design in which the prop is thought of as a rotating airfoil. They designed an 8.13-ft propeller that was later found to be 66% efficient.

The Wright Brother's Flyer relied on this four-cylinder engine they built themselves. By 1910, they were using a V8 in their "Baby Gran