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span loading- See LOADING, SPAN. 

spar, wing- See WING SPAR. 

  air speed- See AIR SPEED.
  get-away speed- The air speed at which a seaplane becomes entirely air-borne. 
  ground speed- The horizontal component of the velocity of an aircraft relative to the ground. 
  hump speed- The speed of a seaplane during take-off at which the float resistance reaches a maximum. 
  landing speed- The minimum speed of an airplane at the instant of contact with the landing area in a normal landing. 
  minimum flying speed- The lowest steady speed that can be maintained, with any throttle setting whatsoever, by an airplane in level flight at an altitude above the ground greater than the span of the wings.
  operating speed- The speed in level flight corresponding to 87.5 percent of the rated speed of the engine. 
  pitch speed- The product of the mean geometrical pitch and the number of revolutions of the propeller in unit time. 
  rated engine speed- The rotative speed of an engine at which its reliability has been determined for continuous performance. 
  sinking speed- See SINKING SPEED. 
  slip speed (supercharger)- The supercharger speed necessary to maintain a given pressure difference between intake and discharge when there is no air delivery. 
  stalling speed- The speed of an airplane in steady flight at its maximum coefficient of lift. 
  take-off speed- The air speed at which an airplane becomes entirely air-borne. 
  terminal speed- See VELOCITY, TERMINAL. 

spin- A maneuver in which an airplane descends along a helical path of large pitch and small radius while flying at a mean angle of attack greater than the angle of attack at maximum lift (cf. spiral). 
  flat spin- A spin in which the longitudinal axis is less than 45° from the horizontal. 
  inverted spin- A maneuver having the characteristics of a normal spin except that the airplane is in an inverted attitude. 
  normal spin- A spin which is continued by reason of the voluntary position of the control surfaces, recovery from which can be effected within two turns by neutralizing or reversing all the controls. Sometimes called "controlled spin" (fig. 8).
  uncontrolled spin- A spin in which the controls are of little or no use in effecting a recovery. 

spinner- A fairing of approximately conical or paraboloidal shape, which is fitted coaxially with the propeller hub and revolves with the propeller. (See fig. 5.)

spiral- A maneuver in which an airplane descends in a helix of small pitch and large radius, the angle of attack being within the normal range of flight angles (fig. 8) (cf. spin).

split S- A maneuver consisting of a half snap roll followed by a pull-out to normal flight, thus obtaining a 180° change in direction accompanied by a loss of altitude (fig. 8). 

spoiler- A small plate arranged to project above the upper surface of a wing to disturb the smooth air flow, with consequent loss of lift and increase of drag. (See fig. 1.) (cf. interceptor.)

squat- A downward, or negative, displacement of the center of gravity of a seaplane while running on the water.

spray strip- A strip projecting from the hull of a seaplane to change the manner in which the spray is thrown. 

sponson- A protuberance from a seaplane hull designed to increase the beam or give lateral stability at rest. 

stability- That property of a body which causes it, when its equilibrium is disturbed, to develop forces or moments tending to restore the original condition.
  automatic stability- Stability dependent upon movable control surfaces automatically operated by mechanical means. 
  directional stability- Stability with reference to disturbances about the normal axis of an aircraft; i.e., disturbances which tend to cause yawing. 
  dynamic stability- That property of an aircraft which causes it, when its state of steady flight is disturbed, to damp the oscillations set up by the restoring forces and moments and gradually return to its original state. 
  inherent stability- Stability of an aircraft due solely to the disposition and arrangement of its fixed parts; i.e., that property which causes it, when disturbed, to return to its normal attitude of flight without the use of the controls or the interposition of any mechanical device. 
  lateral stability- Stability with reference to disturbances about the longitudinal axis; i.e., disturbances involving rolling or sideslipping. The term lateral stability is sometimes used to include both directional and lateral stability, since these cannot be entirely separated in flight. 
  longitudinal stability- Stability with reference to disturbances in the plane of symmetry; i.e., disturbances involving pitching and variation of the longitudinal and normal velocities. 
  static stability- That property of an aircraft which causes it, when its state of steady flight is disturbed, to develop forces and moments tending to restore its original condition.