APPENDIX I (continued 2)

Step: A break in the form of the bottom of a float.

Stream-line flow: The condition of continuous flow of a fluid, as distinguished from eddying flow.

Stream-line shape: A shape intended to avoid eddying and to preserve stream-line flow.

Strut: A compression member of a truss frame. For instance, the vertical members of the wing truss of a biplane.

Suspension band: The band around a balloon to which are attached the basket and the main bridle suspensions.

Suspension bar: The bar used for the concentration of basket suspension ropes in captive balloons.

Sweep back: The horizontal angle between the lateral axis of an airplane and the entering edge of the main planes.

Tail: The rear portion of an aircraft, to which are usually attached rudders, elevators, stabilizers, and fins.

Tail cups: The steadying device attached at the rear of certain types of elongated captive balloons.

Tandem: An airplane whose sets of planes are placed one in front of the other.

Tractor: See Airplane.

Trailing edge: The rearmost edge of an aerofoil or propeller blade.

Triplane: A form of airplane whose main supporting surface is divided into three parts, superimposed.

Truss: The framing by which the wing loads are transmitted to the body; comprises struts, stays, and spars.

Undercarriage: See Landing gear.

Venturi tube: A short tube, flaring at the front end, and constricted approximately midway of its length, so that, when fluid flows through it, there will be a suction produced in a side-tube opening into the constricted throat. This tube, when combined with a Pitot tube or with one giving static pressure, forms a pressure nozzle, which may be used as an instrument to determine the speed of an aircraft through the air.

Warp: To change the form of the wing by twisting it.

Wash in: See Droop.

Washout: A permanent warp of an aerofoil such that the angle of attack decreases toward the wing tips.

Weight, gross: See Load, full.

Wing: The aggregate sustaining structure on the right or left side of an airplane, comprising both planes and trussing. (Thus, “detachable wings” and “folding wings.”)

Wing flap: See Aileron.

Wing loading: The weight carried per unit area of supporting surface.

Wing mast: The mast structure projecting above the wing, to which the top load wires are attached.

Wing rib: A fore-and-aft member of the wing structure used to support the covering and to give the wing section its form.

Wing spar or wing beam: A transverse member of the wing structure.

Yaw: Yawing.—Angular motion about the normal axis.

Angle of.—The angle between the direction of the relative wind and the plane of symmetry of an aircraft.

Zero lift line: The limiting position in an aerofoil section of the line of action of the resultant air force when the position of the section is such that the lift is zero.