NACA 63(420)-422 and NACA 63(420)-517.- The a d d i t i o n
of t h e number 20 e n c l o s e d i n p a r e n t h e s i s w i t h t h e lowdrag-
range i n d e x f o r t h e s e c t i o n d e s i g n a t i o n i n c h a r t s
NACB 63(420)-422 and NACA 63(420)-517 i n d i c a t e s t h a t t h e s e
s e c t i o n s were o b t a i n e d by s c a l i n g t h e o r d i n a t e s of t h e
NACA 63,4-020 b a s i c s e c t i o n . Thus, t h e s e c t i o n d e s i g n a -
t i o n NsCA 63(420)-517 may be i n t e r p r e t e d a s f o l l o w s : The
NACA 63,4-517 a i r f o i l d e r i v e d from t h e NACn 63,4-020 b a s i c
s e c t i o n . The a l t e r e d t h i c k n e s s of t h e d e r i v e d s e c t i o n
l e a d s , as one would e x p e c t , t o a change i n t h e low-drag
range of t h e d e r i v e d s e c t i o n as compared with t h a t of t h e
b a s i c s e c t i o n . The 4 i n d i c a t i n g t h e low-drag range i n
t h e o r i g i n a l d e s i g n a t i o n i s r e p l a c e d by (420) i n d i c a t i n g
t h a t t h e low-drag range was k0.4 when t h e t h i c k n e s s was
20 p e r c e n t . The p a r e n t h e s i s i s employed t o emphasize t h e
I f a c t t h a t t h e low-drag range index does not apply t o t h e
a l t e r e d a i r f o i l . For t h e example mentioned, NACA 63(420)-
5 1 7 , the Bkee~eticall ow-drag r a n g e i s p r o b a b l y l e s s t h a n
~0.3.
This e x t e n s i o n t o t h e numbering system w i l l be generally
mploysd h e n c e f o r t h t o design~te such a l t e r e d a i r -
f o i l s .