The Riddle of Takeoff Distance

Not all performance calculations are as specific as we think.

Peter Garrison

Thursday, November 19, 2020 at 04:08 PM ET

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For the historic flight, takeoff distance was merely an educated guess. American Stock Archive

Key Takeaways:

Charles Lindbergh made a critical decision to optimize his Spirit of St. Louis's propeller pitch for cruise efficiency over maximum takeoff thrust, accepting significant risk for his heavily loaded aircraft.
Predicting takeoff distance was highly imprecise and challenging in Lindbergh's era, leading to considerable anxiety as calculations often failed to reflect practical reality.
Later research, like Edwin Hartman's 1936 NACA study, debunked misconceptions, showing that overall propeller efficiency during the later stages of takeoff roll is more crucial than initial static thrust.
Modern computational methods can now accurately model takeoff performance, demonstrating that Lindbergh's intuitive "guess" regarding his flight's critical initial phase was remarkably successful.

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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.