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```NOMENCLATURE FOR AERONAUTICS 7

[Column 1]
angle - continued.
flight-path angle - The angle between the flight path of the aircraft and the horizontal.
gliding angle - The angle between the flight path during a glide and a horizontal axis fixed relative to the air.
landing angle - The acute angle between the wing chord and the horizontal when the airplane is resting on level ground in its normal position; also called "ground angle."
minimum gliding angle - The cut angle between the horizontal and the most nearly horizontal path along which an airplane can descend steadily in still air when the propeller is producing no thrust.
rudder angle - The acute angle between the rudder and the plane of symmetry of the aircraft. It is positive when the trailing edge has moved to the left with reference to the normal position of the pilot.
trim angle - The angle between the horizontal and the longitudinal base line of a seaplane float or flying-boat hull. It is positive when the bow is higher than the stern.
zero-lift angle - The angle of attack of an airfoil when its lift is zero.

angle of attack - The acute angle between a reference line in a body and the line of the relative wind direction projected on a plane containing the reference line and parallel to the plan of symmetry. (See fig. 9.)
absolute angle of attack - The angle of attack of an airfoil, measured from the attitude of zero lift.
critical angle of attack - The angle of attack at which the flow about an airfoil changes abruptly as shown by corresponding abrupt changes in the lift and drag.
effective angle of attack - See ANGLE OF ATTACK FOR INFINITE ASPECT RATIO.
induced angle of attack - The difference between the actual angle of attack and the angle of attack for infinite aspect ration of an airfoil for the same lift coefficient.

angle of attack for infinite aspect ratio - The angle of attack at which an airfoil produces a given lift coefficient in a two-dimensional flow. Also called "effective angle of attack."

angle of dead rise - The angle with the horizontal made by a transverse line joining the keel of a hull with the chine.

angle of heel - The angle between a horizontal plane and the lateral axis of a seaplane on the water.

angle of incidence - Same as ANGLE OF WING SETTING. In British terminology the angle of incidence is equivalent to the American term "angle of attack."

angle of pitch (aircraft) - The acute angle between two planes defined as follows: One plane includes the lateral axis of the aircraft and the direction of

[Column 2]
the relative wind; the other plane includes the lateral axis and the longitudinal axis. The angle is positive when the nose of the aircraft is able the direction of the relative wind. (In normal flight the angle of pitch is the angle between the longitudinal axis and the direction of the relative wind.)

angle of pitch (propeller) - Same as ANGLE, BLADE.

angle of roll (or angle of bank) - The angle through which an aircraft must be rotated about its longitudinal axis in order to bring its lateral axis into the horizontal plane. The angle is positive when the left side is higher than the right.

angle of stabilizer setting - The acute angle between the longitudinal axis of an airplane and the chord of the stabilizer. The angle is positive when the leading edge is higher than the trailing edge. (See fig. 5.)

angle of wing setting - The acute angle between the plane of the wing chord and the longitudinal axis of the airplane. The angle is positive when the leading edge is higher than the trailing edge. (See fig. 5.)

angle of yaw - The acute angle between the direction of the relative wind and the plan of symmetry of an aircraft. The angle is positive when the aircraft turns to the right.

antidrag wire - See WIRE (AIRPLANE), ANITDRAG.

appendix - The tube, usually located at the bottom of a balloon, used primarily for inflation and deflation. In the case of a free balloon it may also serve as an automatic-discharge opening. The term should be restricted to the various types of balloons and should not be applied to airships.

approach light - See LIGHT, APPROACH.

area, equivalent flat-plate - The area of a square flat plate, normal to the direction of motion, which offers the same amount of resistance to motion as the body or combination of bodies under consideration.

area, measurement of (performance calculations):
control-surface area, trailing - The area of a trailing control surface is the area of the actual outline projected on the plane of the surface, except that any portion of the movable surface lying forward of the hinge axis and within the fixed surface is included in the fixed surface. Auxiliary or paddle-type balance surfaces shielded by and lying outside of the fixed surface are no included in the area of either the fixed or the movable surfaces.
horizontal tail are - The horizontal tail are is measured in the same manner as the wing area, that is, with no deduction for the area blanketed by the fuselage, such blanketed area being bounded within the fuselage by lateral straight lines that connect the intersections of the leading and trailing edges of the stabilizer with the sides of the fuselage, the fairings and fillets being ignored. ```