Tl4 1-320  87  AIR CORPS  trim  is given this type of airship during initial inflation by proper  adjustment of car suspension rigging.  c.  It is customary to take off large semirigids and rigids statically  light, but nonrigids are taken off as much as 6 or 7 percent heavy.  (1) The light take.-off may be made with the airship in any trim  from tail heavy to a few degrees nose heavy.  In the latter case the  airship should be free-ballooned to a safe altitude before the motors  are opened. The light take-off presents little difficulty.  (2) For the take-off when the airship is in static equilibrium the  trim should be neutral or a few degrees tail heavy, preferably the lat› ter. In this case the car party of the maneuvering crew gives the air› ship a toss upward, the men on the nose of the car throwing their end  up first, then the men to the rear throwing up their end.  This gives  FIGURl’l 25.- Flight at constant alt itude (airsbip statically Hght, trimmed nose heavy,  elevators ne\ltral).  t.he airship an initial angle of attack to the air stream.  When clear  of the party the pilot opens his motc•rs and raises his elevators slightly.  The thrust of the propellers assisted by the slight force on the eleva› tors will further raise the nose of the airship and it . will climb  rapidly.  (3) For the heavy take-off the ajrship must be carefully trimmed  tail heavy.  The amount of the trim varies with degree of heaviness,  type of airship, and wind velocity.  If  there is a good wind blowing it  gives the airship an initial air speed to assist the ascent. Experience  has shown that an airship of the TO type with a trim of 9°  tail heavy  will take off 700 pounds heavy in still air. For this degree of heavi› ness the car party should be augmented to at least  20  men and 4 men  should be assigned  to lift on the tail surface.  At the proper signal  the car is thrown up, nose first as before.  The elevators should be  depressed about 10°  and as the pilot opens his motors he will find it  necessary to depress the elevators fully to keep the tail from striking  the ground. Action of the airship in rising is a pure case of reverse  control.  The air from the slipstream of the propellers strikes the  54 