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The Truth about “Wing Incidence”

Gemini Sparkle

Key Takeaways:

  • The article argues that "wing incidence" is a misnomer, proposing "fuselage incidence" as the more accurate term, which is primarily optimized for minimal drag and practical considerations like cabin comfort, rather than controlling the wing's lift.
  • An airplane's lift and attitude are dynamically controlled by the wing's angle of attack, independent of the fuselage's fixed attachment angle, as the fuselage is largely a minor aerodynamic player.
  • Decalage, the angular difference between lifting surfaces, is crucial for longitudinal stability but is a complex, non-fixed value influenced by adjustable control surfaces and varying airflow.
  • While conventional aircraft can tolerate non-ideal incidence or decalage, incorrect decalage in canard designs can lead to dangerous, unrecoverable stalls, making conventional configurations safer for amateur builders.
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(February 2012) Books about airplane design often mention wing incidence as if it were a parameter of some importance. It isn’t. In fact, “wing incidence” is a misnomer. I propose — and fully expect my proposal to have no effect — that the term be abandoned, and that we speak of “fuselage incidence” instead.

The so-called angle of incidence is the angle between the chord line of the wing at the fuselage and the fuselage’s longitudinal axis. Now, this sounds as if it ought to matter, because after all, if the wing is not at the correct angle it will not have enough lift, or will have too much, and the airplane will mush, or plow, or otherwise behave inappropriately. But to think that way is to slip into the mindset of the lubber who says, “The airplane flew into a storm and the wings fell off.” Wings never fall off. It is the fuselage that falls off the wing.

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

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