Although the effect of wind is not covered in this section, it  is a very prominent force acting on the gliding distance of the  aircraft in relationship to its movement over the ground. With  a tailwind, the aircraft glides farther because of the higher  groundspeed. Conversely, with a headwind the aircraft does  not glide as far because of the slower groundspeed.  Variations in weight for an aircraft with a rigid wing  do not affect the glide angle provided the pilot uses the  correct airspeed. Since it is the lift over drag (L$_{D}$) ratio that  determines the distance the aircraft can glide, weight does  not affect the distance. The glide ratio is based only on the  relationship of the aerodynamic forces acting on the aircraft.  The only effect weight has is to vary the time the aircraft  glides. The heavier the aircraft, the higher the airspeed must  be to obtain the same glide ratio. For example, if two aircraft  having the same L$_{D}$ ratio but different weights start a glide  from the same altitude, the heavier aircraft gliding at a higher  airspeed arrives at the same touchdown point in a shorter  time. Both aircraft cover the same distance, only the lighter  aircraft takes a longer time.  However, the WSC aircraft has different characteristics  because it has a flexible airframe. As more weight is added  to the WSC wing, it flexes more creating more twist in the  wing decreasing aerodynamic efficiency, as discussed in  chapter 2. For example, a pilot is accustomed to a glide ratio  of 5 to 1 flying solo; a passenger is added, and this glide ratio  may decrease to 4 to 1. This decrease in glide ratio for added  weight is true for all descent speeds. The amount of decrease  in glide ratio varies significantly between manufactures and  models because each wing flexes differently. The more  flexible the wing is, the greater the decrease in glide ratio.  Pilots should become familiar with glide ratios for their  aircraft at all speeds and all weights. Although the propeller thrust of the aircraft is normally  dependent on the power output of the engine, the throttle is  in the closed position during a glide so the thrust is constant.  Since power is not used during a glide or power-off approach,  the pitch attitude must be adjusted as necessary to maintain  a constant airspeed.  The best speed for the glide is one at which the aircraft travels  the greatest forward distance for a given loss of altitude in still  air. This best glide speed corresponds to an angle of attack  resulting in the least drag on the aircraft and giving the best  lift-to-drag ratio (L$_{DMAX}$).  [Figure 6-16] Any change in the gliding airspeed results in a proportionate  change in glide ratio. Any speed, other than the best glide  speed, results in more drag. Therefore, as the glide airspeed  is reduced or increased from the optimum or best glide speed,  the glide ratio is also changed. When descending at a speed  below the best glide speed, induced drag increases. When  descending at a speed above best glide speed, parasite drag  increases. In either case, the rate of descent increases and the  glide ratio decreases.  This leads to a cardinal rule of aircraft flying that a student  pilot must understand and appreciate: the pilot must never  attempt to “stretch” a glide by applying nose up pressure and  reducing the airspeed below the aircraft’s recommended best  glide speed. Attempts to stretch a glide invariably result in an  increase in the rate and angle of descent and may precipitate  an inadvertent stall.  To enter a glide, the pilot should close the throttle and  obtain the best glide speed. When the approximate gliding  pitch attitude is established, the airspeed indicator should  be checked. If the airspeed is higher than the recommended  speed, the pitch attitude is too low; if the airspeed is less than  recommended, the pitch attitude is too high. Therefore, the  pitch attitude should be readjusted accordingly by referencing  the horizon. After the adjustment has been made, the aircraft  should be retrimmed (if equipped) so that it maintains this  attitude without the need to hold pitch pressure on the control  bar. The principles of attitude flying require that the proper  flight attitude be established using outside visual references  first, then using the flight instruments as a secondary check.  It is a good practice to always retrim the aircraft after each  pitch adjustment.  Increasing Lift-to-Drag Ratio Increasing Speed Stall L D- MAX V$_{NE}$ Figure 6-16.  L$_{DMAX}$. 6-15