TM 1-320  14-15  AIRSHIP AERODYNAMICS  b.  The theory of dimensions shows that the coefficients of resistance.  b.  Total resistance of airships may be subdivided approximately as  follows for- 15. Resistance of completely rigged airship.-a. There are•  very little data available showing the relative resistance of the various  parts combining to produce the total resistance  of  a completely rigged  airship due to the difficulty in obtaining dynamic similarity between  the model tested and the full-scale airship.  e.  To overcome the effect  of  this difference a wind tunnel has been  built at Langley Field in which  p  may be sufficiently increased  to  make the product  pL  for the model equal that of the full-sized small  nonrigid airship, thus eliminating scale effect.  1’L  vary directly as -;-• where  a. v,  the kinematic viscosity coefficient, is defined as the ratio be› tween the absolute viscosity coefficient and the atmospheric mass  density.  Hence- e - vL  d.  -;’  called the Reynolds number after Professor Reynolds,  depends on three variable quantities,  p,  v,  and  L :  To predict full› scale performance from the model tests, allowance must be made for  the fact that the  L  in the full-sized airship is very different from the  L  in the model, and consequently the co-efficient of resistance will be  different.  v=~'  where  v  1s  the absolute viscosity coefficient of the air and is a  constant.  v=velocity in feet per second.  L=some convenient linear dimension of the body such as the  diameter in the case of a cylinder.  v=  kinematic viscosity coefficient of the fluid.  29  (1) Large nonrigids with closed cars:  Percent  (a)  ~n velope_____ ____ ____ __ ___ ___ _ _ _ ____ _ ______ ___ _  45  (b) Surfaces---------- -------- ------ - ------ ----- --- 20  (c) Rigging and suspension cables__ __ ________ _______  15  (d) Cars_______________ ___ ___ ___ _______________ ____  15  (e) Accessories --- ---------------------------------- 5  (2) Small nonrigids with open cars :  (a)  ~nvelope  ____ --------_ ----•• _______ -•- ------_____ .  35  (b) Surfaces-------------------------------------- •  25  (c) Rigging and cables __ __ __________ _________ ____ ___ 20  (d)  Cars--------------------- --------------------- _  15  (e) Accessories------------ ... _ ------------------- 5 