If the glider is loaded so the CG location is behind the aft  limit, handling is compromised. The glider is said to be tail  heavy. Tail heaviness can make pitch control of the glider  difficult or even impossible. The fundamental problem with a CG aft of the aft limit is the  designed function of the horizontal stabilizer and elevator.  Fixed wing aircraft are generally designed so that the horizontal  stabilizer and elevator provide a down force to counter the  slightly nose forward CG such that the aircraft tend to resume  a level pitch attitude after an upset about the lateral axis. As  the airspeed changes, the pilot changes the trim or trims the  aircraft so the down force exactly balances the forward CG  within limits. Should the aircraft be upset and the nose pitches  upward, the resultant slower airspeed results in less down  force produced by the horizontal stabilizer and elevator. This  decreased down force lets the nose lower so the airspeed  retains to the pre-upset value. This is called positive stability.  Conversely, if the upset places the aircraft in a nose down  attitude, the increased airspeed will increase the down force and  raise the nose to the pre-upset balanced condition. However,  if the control surface is in a stalled condition, this stabilizing  action will not begin until the control surface regains un-stalled  airflow and begins producing down force again. the glider load is within the envelope and is safe for flight. If  each pilot weighs 225 pounds, the rear seat maximum load  is exceeded, and the glider load is outside the envelope and  unsafe for flight. The CG position can also be determined by calculation using  the following formulas: The following are the most common reasons for flight with  CG located behind permissible limits: The computational method involves the application of  basic math functions. The following is an example of the  computational method. Given: To determine the loaded weight and CG, follow these steps. Some glider manufacturers provide weight and balance  information in a graphic presentation. A well designed graph  provides a convenient way to determine whether the glider  is within weight and balance limitations. In  Figure 5-19 , the chart indicates that the minimum weight  for the front seat pilot is 125 pounds, and that the maximum  is 250 pounds. It also indicates that the maximum rear seat  pilot weight is 225 pounds. If each pilot weighs 150 pounds,  the intersection of pilot weights falls within the envelope;  Maximum gross weight....................1,100 lb Empty weight.......................................600 lb CG range....................................14.8–18.6 in Front seat occupant..............................180 lb Rear seat occupant...............................200 lb 4.  To determine the CG, divide the moments by  the weight. 3.  Total the weight and moments. 2.  Enter the moment for each item listed. Remember,  weight × arm = moment. To simplify calculations,  the moments may be divided by 100. 1.  List the empty weight of the glider and the weight of  the occupants. •  A heavy, non-approved tailwheel or tail skid was  installed on the aft tail boom of the glider. •  Foreign matter or debris (water, ice, mud, sand, and  nests) has accumulated in the aft fuselage of the glider  and was not discovered and removed prior to flight. •  Tailwheel dolly is still attached, far aft on the tailboom  of the glider. •  Pilot weight is less than the specified minimum pilot  seat weight and trim ballast weights necessary for  the lightweight pilot are not installed in the glider  prior to flight. •  Weight × Arm = Moment •  Total Moment ÷ Total Weight = CG Position (in inches  aft of the reference datum) 5-13 Sample Weight and Balance Problems Figure 5-19.  Weight and balance envelope. Problems Associated With CG Aft of Aft Limit Rear seat pilot weight (lb) 225 200 150 100 50 0 Front seat pilot weight (lb) 125  150  175  200  225   250 Within weight and balance limits Out of weight and balance limits