The Riddle of Takeoff Distance
Flying|September 2020
Sometimes you just have to hope for the best.
PETER GARRISON

In Spring 1927, while Spirit of St. Louis was being built by Ryan Airline Company in San Diego, Charles Lindbergh corresponded with the Standard Steel Propeller Company of Pittsburgh regarding the best pitch setting for its ground-adjustable propeller blades.

The aluminum-alloy blades were off-the-shelf items, using a Clark Y airfoil and a twist distribution suitable for Ryan’s mail planes, upon which the design of Spirit was based. The Clark Y was a profile commonly used for propeller blades, not because it had any special aerodynamic advantage but because its flat bottom made fabricating blades and measuring their pitch angles easier.

Because the propeller’s pitch could not be changed in flight, Lindbergh had a ticklish decision to make. He could pitch the prop for best efficiency in cruise, but it would then be less suitable for takeoff; or he could pitch it for maximum takeoff thrust and give up some range. The airplane would weigh around 5,100 pounds and have a static thrust of around 700 pounds. It was not going to leap forward in any case. The runway at New York’s Roosevelt Field, where the flight would begin, was 5,000 feet long, with telephone lines just beyond the departure end. The takeoff for the Paris flight would be the airplane’s first at maximum weight. For it to not succeed would be fatal to not only the project but possibly the pilot as well.

The previous fall, the French World War I ace René Fonck, eyeing the same $25,000 Orteig prize as Lindbergh, had tried to take off from Roosevelt Field in a 28,000-pound trimotor Sikorsky sesquiplane. The effort failed spectacularly, with the airplane cartwheeling off the end of the runway and killing two of the four aboard. Not that Fonck’s debacle was because of the wrong propeller pitch setting—in fact, the landing gear failed under the overload of fuel. Nor, I suppose, did Lindbergh need reminding of the likely consequences of his own fuel-filled airplane failing to get off the ground.

The propeller company advised Lindbergh that a pitch setting of 15.5 degrees would be best for takeoff, but 16.5 degrees would give the best efficiency in cruise. Lindbergh opted for cruise.

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