Am CORPS  TM 1-320  16-16  16. Deceleration  test.-a.  Tests are 1nade frequently on full› sized airships to determine actual risistance of the airship at various  speeds.  In these tests the airship is brought to a certain velocity  and then the motors are idled, the velocity being recorded against  time as the airship decelerates.  b.  The general theory is that the resistance, or force causing de› celeration, is given by the equation :  R=Mv a,  where  ex.= (deceleration in feet per second)  z.  Mv=  the virtual mass of Lhe ship.  The virtual mass of an airship is the mass of airship and contents  plus the mass of air which is carried along with it. This latter is  computed by the Munk formula :  AMo=P1 ,  where  r  is the radius of largest cross section.  c.  Observing velocity at end of each second gives the rate of  change of velocity, or deceleration, for each second and by interpola› tion for each air speed.  Actually formulas are employed which in- .  volve calculus and are beyond the scope of this manual.  d.  These deceleration .tests are quite valuable as a check against  the resistance formulas developed in this section.  They are however  often complicated by poor instruments or faulty observation, render› ing it difficult to place a proper value on results so obtained.  For  the present more confidence is to be placed on the resistance formulas  and the power requirement formulas which will be developed in the  next section.  30  (3) Semirigids:  Percent  (a )  ~ve l o p e- ------------ ------------- ------ - --- -- ~  53  (b) Surfaces _______ _____ ____________________ ___ ____  20  (c)  Jtiggjng- -- -- -----~-------- ---- -- ---- -------- -- - 7  (d) Cars __________ _____ -----------------__ --------- 13  (e)  Accessories------------------------------------- 7  ( 4) Large rig ids :  (a)  IIull _________________________ __ ___ _____________  60  (b)  Surfaces_______________ _____ ________ _____ ____ __  15  (c)  Cars and suspensions---------------------------- 2q  (d) Miscellaneous rigging and accessories_________ ___  5 