Occasional adjustments are required in the tension  of the control lines of the major controls to compensate  for slight changes in the shape of the envelope with vari› ations of the pressure and of the loading.  Tension varies  particularly with the fullness of the aft ballonet, a large  amount of air in this ballonet causing the cables to slacken.  An  automatic tensioning device located in the aft  portion of the car between frames 1 and 2 takes care of  part of these variations.  In addition, the tension can  be adjusted from the pilot’s compartment.  The crank on  the port side is for the elevator lines, and the one on  the starboard side is for the rudder lines.  The tension  of the controls should be checked from time to time in  flight.  A check should always be made immediately after  a heavy take-off, because of the added sagging of the en› velope caused by the dynamic lift.  Occasional adjustments may also have to be made in  flight.  -J,q_  CAUTION:  It is particularly important that the pilot  check the controls and adjust the tension  of the lines as required before take-off and  before landing otherwise he may find himself  without enough control in an emergency.  C.  MAJOR CONTROLS 