Arched. This term is usually applied to aerofoil surfaces which dip downwards like the wings of a bird. The curve in this case being at right angles to "camber." A surface can, of course, be both cambered and arched.
Propeller. A device for propelling or pushing an aeroplane forward or for raising it vertically (lifting screw).
Tractor Screw. A device for pulling the machine (used when the propeller is placed in the front of the machine).
Keel. A vertical plane or planes (usually termed "fins") arranged longitudinally for the purposes of stability and steering.
Tail. The plane, or group of planes, at the rear end of an aeroplane for the purpose chiefly of giving longitudinal stability. In such cases the tail is normally (approx.) horizontal, but not unfrequently vertical tail-pieces are fitted as well for steering (transversely) to the right or left, or the entire tail may be twisted for the purpose of transverse stability (vide Elevator). Such appendages are being used less and less with the idea of giving actual support.
Rudder is the term used for the vertical plane, or planes, which are used to steer the aeroplane sideways.
Warping. The flexing or bending of an aerofoil out of its normal shape. The rear edges near the tips of the aerofoil being dipped or tilted respectively, in order to create a temporary difference in their inclinations to the line of flight. Performed in conjunction with rudder movements, to counteract the excessive action of the latter.
Ailerons (also called "righting-tips," "balancing-planes," etc.). Small aeroplanes in the vicinity of the tips of the main aerofoil for the purpose of assisting in the maintenance of equilibrium or for steering purposes either with or without the assistance of the rudder.
Elevator. The plane, or planes, in front of the main aerofoil used for the purpose of keeping the aeroplane on an even keel, or which cause (by being tilted or dipped) the aeroplane to rise or fall (vide Tail).