The Aeroplane Speaks. Fifth Edition

=Roll, to=--To turn about the longitudinal axis. =Rib, Ordinary=--A light curved wooden part mounted in a fore and aft direction within a surface. The ordinary ribs give the surface its camber, carry the fabric, and transfer the lift from the fabric to the spars. [23] =Rib, Compression=--Acts as an ordinary rib, besides bearing the stress of compression produced by the tension of the internal bracing wires. [24] =Rib, False=--A subsidiary rib, usually used to improve the camber of the front part of the surface. [25] =Right and Left Hand=--Always used relative to the position of the pilot. When observing an aeroplane from the front of it, the right hand side of it is then on the left hand of the observer. =Remou=--A local movement or condition of the air which may cause displacement of an aeroplane. =Rudder-Bar=--A control lever moved by the pilot's feet, and operating the rudder. [26] =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.