The alpha-beta of flying

Here’s some flying Greek from a flying geek:

α alpha Angle of attack The vertical angle between the oncoming air and the zero-lift line of the wing, as shown (partly and imperfectly) by the airspeed indicator.
β beta Sideslip The horizontal angle between the oncoming air and the aerodynamic centreline of the aircraft, as indicated (partly) by the inclinometer (the ball in the turn coordinator).
γ gamma Flight path angle Angle of the flight relative to the earth. When you fly an ILS approach, you’re following a constant gamma angle, even if your alpha and THETA vary.
Γ GAMMA Geometric dihedral angle. Vertical angle of the wings as they extend away from the fuselage. Normally the wing tips are higher than the roots, to improve roll damping, especially on low-wing planes.
δ delta Control surface deflection angle I.e. CLδe is the contribution of elevator deflection to the coefficient of lift. In a plane with direct control linkage (rods or cables), you could theoretically determine control surface deflections directly from the position of the yoke and/or rudder pedals.
ε epsilon Downwash angle The most important example is the angle of the downwash from the wings hitting the horizontal stabilizer.
θ THETA Pitch angle The aircraft’s rotation in the pitch axis, as read off the attitude indicator.
Λ LAMBDA Sweep angle Horizontal angle of the wings relative to a line perpendicular to the aircraft centreline (does that even make sense)? LAMBDA is usually close to zero on slower planes — sweep doesn’t do much until you get transsonic.
ϖ pi ~3.14 You were expecting, maybe, chopped liver?
ρ rho Air density As in 0.5ρv2 in the dynamic pressure equation you had to memorize in ground school.
σ sigma Sidewash angle The horizontal angle of air deflected to hit a surface of the plane (think of downwash, and it might make sense — I cannot think of a good example, though).
Φ PHI Airplane bank angle Rotation in the roll axis, as read off the attitude indicator.
Ψ PSI Airplane heading angle Rotation in the yaw axis, as read off the compass.

(I hope that the Greek characters show up in your browser.)

This is only a selection — if you want more (much more), grab a used copy of Jan Roskam’s Airplane Flight Dynamics and Automatic Flight Controls, part one, which I used as a reference for this list.


About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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