﻿174 
  ANNUAL, 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  certain 
  properties 
  studied 
  and 
  observed 
  in 
  ordinary 
  wind 
  tunnels 
  

   at 
  atmospheric 
  pressure 
  may 
  hold 
  also 
  for 
  actual 
  airplanes, 
  but 
  one 
  

   can 
  not 
  be 
  certain 
  of 
  this 
  until 
  the 
  question 
  is 
  investigated 
  in 
  a 
  com- 
  

   pressed-air 
  tunnel. 
  In 
  view 
  of 
  the 
  great 
  importance 
  of 
  this 
  matter, 
  

   the 
  National 
  Advisory 
  Committee 
  for 
  Aeronautics 
  has 
  designed, 
  

   and 
  has 
  now 
  under 
  construction 
  such 
  a 
  tunnel, 
  in 
  which 
  the 
  air 
  may 
  

   be 
  compressed 
  to 
  25 
  atmospheres. 
  When 
  completed 
  it 
  will 
  be 
  the 
  

   only 
  one 
  in 
  the 
  world; 
  and 
  it 
  is 
  expected 
  confidently 
  that 
  a 
  great 
  

   amount 
  of 
  useful 
  information 
  will 
  be 
  obtained. 
  

  

  I 
  have 
  outlined 
  the 
  experimental 
  methods 
  available 
  for 
  aero- 
  

   nautical 
  investigations, 
  and 
  wish 
  now 
  to 
  state 
  briefly 
  some 
  of 
  the 
  

   more 
  important 
  ones 
  which 
  occupy 
  our 
  thoughts 
  : 
  

  

  1. 
  Everyone, 
  the 
  world 
  over, 
  is 
  interested 
  in 
  designing 
  a 
  heli- 
  

   copter; 
  but 
  before 
  this 
  can 
  be 
  done 
  we 
  must 
  have 
  knowledge 
  of 
  the 
  

   properties 
  of 
  a 
  propeller 
  whose 
  shaft 
  is 
  very 
  oblique 
  to 
  the 
  flight 
  

   path, 
  and 
  we 
  probably 
  shall 
  have 
  to 
  design 
  a 
  new 
  type 
  of 
  propeller. 
  

  

  2. 
  A 
  greater 
  range 
  of 
  speed 
  for 
  any 
  one 
  airplane 
  is 
  desirable, 
  so 
  

   that 
  it 
  may 
  attain 
  a 
  great 
  flying 
  speed 
  and 
  yet 
  have 
  a 
  slow 
  landing 
  

   speed. 
  In 
  order 
  to 
  secure 
  this 
  possibility, 
  modifications 
  of 
  the 
  wing 
  

   are 
  essential 
  ; 
  and 
  the 
  most 
  promising 
  form 
  at 
  the 
  present 
  time 
  is 
  the 
  

   Handley-Page 
  slotted 
  wing. 
  Much 
  more 
  research 
  is, 
  however, 
  neces- 
  

   sary. 
  

  

  3. 
  Great 
  improvements 
  may 
  be 
  expected 
  in 
  reducing 
  the 
  drag, 
  or 
  

   resistance, 
  of 
  aircraft, 
  and 
  many 
  researches 
  are 
  now 
  in 
  progress 
  as 
  to 
  

   the 
  effect 
  of 
  putting 
  the 
  engine 
  and 
  the 
  propeller 
  in 
  different 
  posi- 
  

   tions, 
  of 
  changing 
  the 
  position 
  of 
  the 
  fuselage, 
  etc. 
  

  

  4. 
  Over 
  100 
  different 
  wing 
  forms 
  have 
  been 
  investigated, 
  but 
  our 
  

   practical 
  knowledge 
  is 
  far 
  from 
  satisfactory, 
  largely 
  owing 
  to 
  the 
  

   fact 
  that 
  the 
  tests 
  have 
  been 
  made 
  in 
  different 
  laboratories 
  and 
  at 
  

   different 
  air 
  velocities. 
  Further, 
  of 
  course, 
  the 
  Reynolds 
  number 
  in 
  

   all 
  tests 
  has 
  been 
  too 
  small. 
  When 
  the 
  compressed-air 
  wind 
  tunnel 
  

   at 
  the 
  Langley 
  Memorial 
  Laboratory 
  is 
  finished, 
  we 
  will 
  be 
  able 
  defi- 
  

   nitely 
  to 
  say 
  what 
  wing 
  is 
  best 
  for 
  any 
  specific 
  purpose. 
  

  

  These 
  are 
  simply 
  illustrations 
  of 
  the 
  type 
  of 
  investigations 
  now 
  

   engaging 
  the 
  attention 
  of 
  aeronautical 
  laboratories, 
  but 
  they 
  serve, 
  

   I 
  hope, 
  to 
  make 
  clear 
  Jiow 
  interesting 
  the 
  subject 
  is 
  to 
  the 
  scientist 
  

   and 
  how 
  important 
  to 
  the 
  designer 
  of 
  aircraft. 
  

  

  