– 1.9 Airspeed (knots) Sink rate (knots) Ballasted lift/drag (L/D) 0 25 50 75 0 –1 –2 –3 –4 –5 –6 52 70 = :1  70 1.9 = 36:1 Ballasted lift/drag (L/D) Tangent Glider  sink rate Sink rate with water ballast Glider wings have a high aspect ratio, as shown in  Figure 3-19 .  High aspect ratio wings produce a comparably high amount of  lift at low angles of attack with less induced drag. Weight is the third force that acts on a glider in flight. Weight  opposes lift and acts vertically through the CG of the glider.  Gravitational pull provides the force necessary to move a  glider through the air since a portion of the weight vector of  a glider is directed forward. Thrust is the forward force that propels a self-launching glider  through the air. Self-launching gliders have engine-driven  propellers that provide this thrust. Unpowered gliders have  an outside force, such as a towplane, winch, or automobile,  to launch the glider. Airborne gliders obtain thrust from  conversion of potential energy to kinetic energy. The glider is maneuvered around three axes of rotation: yaw  (vertical), lateral, and longitudinal. They rotate around one  The aspect ratio is another factor that affects the lift and drag  created by a wing. Aspect ratio is determined by dividing the  wingspan (from wingtip to wingtip), by the average wing chord.  Three Axes of Rotation Aspect Ratio Thrust Weight Figure 3-18.  Calculating glide speed with water ballast. 51' wing span Wing area = 219.5 ft  2 Maximum gross weight = 1,040 lb Aspect ratio = 11.85:1 Glide ratio = 22:1 Wing area = 193.32 ft  2 Maximum gross weight = 1,808 lb Aspect ratio = 39:1 Glide ratio = 60:1 86' 11.3" wing span Chord lines 4.3 feet Chord lines 4.3 feet Chord lines 2.22 feet Chord lines 2.22 feet Aspect ratio is determined by dividing the wingspan (from wingtip to wingtip), by the average chord.  Figure 3-19.  Aspect ratio. 3-9