Learning to fly in the U.S. Army

by E. N. Fales

52. Lift.—(See 50). The upward or vertical part of the air pressure acting against the wings, and which is utilized to lift or support the airplane.

53. Center of Gravity.—The point of balance of an airplane which may be otherwise defined as the point through which the mass of an airplane acts. If the weight is too far forward the machine is nose-heavy. If the weight is too far behind the center of lift the machine is tail-heavy.

54. Aspect Ratio.—The ratio of span to chord of a wing or any other aerofoil.

55. Gliding Angle (Volplane).—The angle made to the horizontal by the flight path of an airplane with the engine shut off; e.g., an airplane is 1000 ft. high, when its engine fails. Suppose its gliding angle is 1 in 6. Therefore, in still air it can glide 6000 ft. forward. The general term glide refers to flying without power.

56. The Angle of Best Climb.—The steepest angle at which an airplane can climb.

57. Stability.—The property of an airplane to maintain its direction and to return easily to its equilibrium or balance with a minimum of oscillation. This is sometimes called dynamical stability. An airplane may have (first) inherent stability, which is the stability due to the arrangement and disposition of its fixed parts. It may also have stability with regard to any one of the three directions in which it may move. These are named as follows: (1) directional stability, with reference to the vertical axis; (2) lateral stability with reference to the longitudinal (or fore and aft) axis; (3) longitudinal stability, stability with reference to the lateral (or thwartship) axis.

58. Flying Position.—Refers to the position of the fuselage when flying. With the Curtiss JN-4 machines in this position the top longerons are horizontal and level both ways. The engine bearers are also level, and the wings have an angle of incidence of 2°.

59. Capacity.—The weight an airplane will carry in excess of the dead load (dead load includes structure power plant and essential accessories).

60. Flight Path.—The path of the center of gravity of an aircraft with reference to the air.

61. Stalling.—A term describing the condition of an airplane which from any cause has lost the relative speed necessary for support and controlling, and referring particularly to angles of incidence greater than the critical angle.