Rudder-Bar—A control lever moved by the pilot's feet, and operating the rudder.
Surface—See “Aerofoil.”
Surface, Detrimental—All exterior parts of an aeroplane including the propeller, but excluding the (aeroplane) lifting and (propeller) thrusting surfaces.
Surface, Controlling—A surface the operation of which turns an aeroplane about one of its axes.
Skin-Friction—The friction of the air with roughness of surface. A form of drift.
Span—-The distance from wing-tip to wing-tip.
Stagger—The distance the upper surface is forward of the lower surface when the axis of the propeller is horizontal.
Stability—The inherent tendency of a body, when disturbed, to return to its normal position.
Stability, Directional—The stability about an axis which is vertical during normal horizontal flight, and without which an aeroplane has no natural tendency to remain upon its course.
Stability, Longitudinal—The stability of an aeroplane about an axis transverse to the direction of normal horizontal flight, and without which it has no tendency to oppose pitching and tossing.