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Wright's original angle of attack indicator

A great idea took time to take hold

Modern angle of attack indicators for general aviation were generally derived from sensors deployed first on commercial and military aircraft, yet to suggest that the importance of this uniquely informative instrument was overlooked at the dawn of powered flight would give Orville and Wilbur Wright an undeserved slight.

Photo by Mike Fizer.

The brothers' penchant for aeronautical invention did not begin with their first powered flight on December 17, 1903, nor did it end on that auspicious date: Orville Wright (who took over the family business after Wilbur's death in 1912) patented and sold an angle of attack indicator suitable for any airplane.

Aero and Hydro, a weekly aviation newspaper published in Chicago, reported on the invention of the Wright Incidence Indicator in August 1913: "A new instrument for the use of aviators, which is of considerable interest, has been brought out by the Wright Company at Dayton, Ohio. Orville Wright has for a long time strongly advocated the use by aviators of an instrument, showing the angles of incidence in the air."

Wright used the British term "angle of incidence," though "angle of attack" became the favored term in the United States. Each variant describes the same thing: the angle between the relative wind and the chord of any airfoil.

"On climbing, if the machine is set at too great an angle, the lift falls off, the drift decreases, and the machine first begins to sink and then in losing headway to 'stall.' ...the angle of the machine with the horizontal, which is registered by the ordinary gravity clinometer, does not represent the angle of the [airplane's wings] to the air, or relative wind," the magazine reported. "This latter, however, is the important thing to know, and as no such instrument was on the market, the Wright company proceeded to turn one out on their own..."

The Wright Co. was incorporated in 1909 with Wilbur Wright as president and Orville Wright as vice president. The company built the United States' first aircraft factory in Dayton, Ohio, in 1910 with a flight school and test flight airfield 10 miles east of the factory at Huffman Prairie, adjacent to today's Wright-Patterson Air Force Base. The company's headquarters was in New York City, the nation's business center. Above all else inventors, the brothers developed the Wright Incidence Indicator that reached the market in 1913. As neither of the brothers ever had much interest in being businessmen, Orville sold the company in 1915, took the money from the sale and his royalties, and retired to his mansion in Dayton.

The incidence indicator was a flat, round, metal device, about eight inches in diameter and one inch thick, which "consists of a light air vane which operates a pointer on a dial by a special mechanical contrivance overcoming any gravitational influence." The dial was marked in degrees of angle (of attack). As the Aero and Hydro article stated, “the pointer indicates at any time the angle of the chord of the [airplane's wings] with respect to the air currents through which the machine is flying..."

The device could be attached to any biplane's wing strut or "on a monoplane can readily be fitted to one of the cabanes, or to some member of the chassis." Merriam-Webster defines a cabane as "a framework supporting the wings of an airplane at the fuselage." The Wright indicator weighed 2.25 pounds and the dial could be "read clearly at a distance of 10 feet." It sold for $50, which in 2022 dollars would be about $1,400.

Coincidentally, today's AOA indicator systems for GA aircraft sell for a similar amount. For example, the Garmin GI-260 AOA Indicator System lists for about $1,600. It does require more installation than just bolting it to a wing strut. An air data probe must be mounted on the wing and air pressure tubing connected to an air data sensor unit, which is usually installed under the instrument panel. That sends an electrical signal to the indicator mounted in the cockpit where the pilot can readily view it. That's the price for a stand-alone system. If you have a compatible electronic flight information system, you can purchase an AOA probe that will transmit the data to be displayed to the EFIS, for $600 to $700.

In 1913, "a pilot, who knew his machine's limiting range of angles could be sure of remaining within safe flying positions." It's a pity that it took more than a century for Orville's pitch to stick.

Dennis K. Johnson

Dennis K. Johnson is an aviation writer and pilot living in New York City.
Topics: Gear, Technology

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