Launching of Foamed Plastic Models with a Two - Stage Light - Gas Gun

T e c h n i q u e s have b e e n d e v e l o p e d to l a u n c h u l t r a l i g h t w e i g h t m o d e l s (i. e . , d e n s i t i e s on the o r d e r of 1 l b / f t 3) f r o m a t w o s t a g e l i g h t g a s gun. To date , s p h e r e s and c o n e s have b e e n l a u n c h e d wi th s o m e s u c c e s s . The p u r p o s e of the d e v e l o p m e n t was to d e t e r m i n e w h e t h e r u s e f u l a e r o d y n a m i c da ta (e. g . , s p h e r e d rag ) cou ld be ob ta ined in a s h o r t a e r o b a l l i s t i c r a n g e at p r e s s u r e s on the o r d e r of 0 .01 m m Hg. A n u m b e r of s p h e r e s have b e e n l a u n c h e d in s u p p o r t of th i s e f fo r t , s o m e at p r e s s u r e s as low as 0 .03 m m Hg. T h e r e is good a g r e e m e n t b e t w e e n t h e s e m e a s u r e m e n t s of s p h e r e d r a g c o e f f i c i e n t and those p r o d u c e d in l o w d e n s i t y wind t u n n e l s . The a p p l i c a t i o n of th is t e c h n i q u e to a l o n g e r r a n g e hav ing a l o w e r p r e s s u r e c a p a b i l i t y , say , 0. 001 m m Hg, would p e r m i t m e a s u r e m e n t s to be m a d e in the n e a r f r e e m o l e c u l e f low r e g i m e .