﻿224 
  ANNUAL 
  REPORT 
  SMITIiyONIAN 
  INSTITUTION, 
  1927 
  

  

  mental 
  means, 
  as 
  a 
  full-size 
  flying 
  laboratory, 
  for 
  investigating 
  

   problems 
  in 
  which 
  the 
  elimination 
  of 
  interference 
  of 
  a 
  propeller 
  

   slip 
  stream 
  with 
  the 
  lift 
  of 
  wings, 
  stal?ility, 
  and 
  control 
  is 
  essential. 
  

  

  A 
  third 
  field 
  wherein 
  the 
  glider 
  is 
  useful 
  is 
  in 
  the 
  abundance 
  of 
  

   opportunity 
  it 
  affords 
  for 
  acquiring 
  aerial 
  experience 
  which 
  is 
  of 
  

   unlimited 
  value 
  in 
  the 
  training 
  of 
  future 
  commercial 
  and 
  private 
  

   flyers. 
  Glider 
  champions, 
  as 
  a 
  rule, 
  afterwards 
  became 
  superior 
  air- 
  

   plane 
  pilots, 
  whereas 
  the 
  reverse 
  did 
  not 
  hold 
  so 
  generally, 
  although, 
  

   of 
  course, 
  many 
  of 
  the 
  new 
  pioneers 
  of 
  soaring 
  flight 
  were 
  much 
  

   benefited 
  by 
  their 
  previous 
  extensive 
  motor 
  flying 
  experience. 
  No 
  

   doubt, 
  gliding 
  constitutes 
  an 
  excellent 
  means 
  of 
  initial 
  aviatic 
  train- 
  

   ing 
  and 
  has 
  thereby 
  already 
  done 
  much 
  to 
  make 
  aviation 
  popular 
  

   and 
  to 
  promote 
  air-mindedness. 
  

  

  In 
  fact, 
  any 
  motor 
  flight 
  is 
  terminated 
  by 
  gliding 
  down 
  to 
  land. 
  

   Of 
  course, 
  the 
  idea 
  of 
  soaring 
  flight 
  is 
  to 
  glide 
  not 
  down 
  but 
  level 
  or 
  

   even 
  to 
  gain 
  altitude. 
  Now 
  let 
  us 
  see 
  how 
  this 
  is 
  done 
  without 
  a 
  

   motor. 
  

  

  Theoretically, 
  we 
  may 
  distinguish 
  between 
  " 
  static 
  " 
  soaring 
  flight 
  

   and 
  " 
  dynamic 
  " 
  soaring 
  flight, 
  although 
  in 
  practice 
  they 
  m.ay 
  over- 
  

   lap 
  or 
  blend. 
  

  

  The 
  principle 
  of 
  static 
  soaring 
  is 
  trivially 
  simple. 
  It 
  consists 
  

   in 
  gliding 
  down 
  in 
  a 
  rising 
  current 
  of 
  air. 
  Provided 
  the 
  vertical 
  

   velocity 
  component 
  of 
  the 
  air 
  current 
  exceeds 
  the 
  minimum 
  rate 
  

   of 
  descent 
  of 
  the 
  machine, 
  any 
  airplane 
  can 
  climb 
  without 
  a 
  motor 
  

   at 
  a 
  rate 
  of 
  ascent 
  equal 
  to 
  that 
  excess. 
  A 
  wind 
  blowing 
  over 
  a 
  vast 
  

   plain, 
  suddenly 
  confronted 
  with 
  a 
  large 
  mountain 
  range 
  extending 
  

   across 
  its 
  path, 
  would, 
  of 
  course, 
  be 
  deflected 
  upward. 
  A 
  wind 
  

   blowing 
  at, 
  say, 
  32 
  feet 
  per 
  second 
  up 
  a 
  slope 
  1 
  : 
  4 
  would 
  furnish 
  

   8 
  feet 
  per 
  second 
  lifting 
  component. 
  An 
  airplane 
  flying 
  at 
  60 
  feet 
  

   per 
  second 
  and 
  having 
  a 
  gliding 
  angle 
  of 
  1 
  : 
  8, 
  thus 
  a 
  natural 
  rate 
  

   of 
  descent 
  of 
  7^2 
  feet 
  per 
  second, 
  would 
  still 
  be 
  carried 
  up 
  at 
  i/^ 
  foot 
  

   per 
  second 
  and 
  yet 
  proceed 
  at 
  28 
  feet 
  per' 
  second 
  against 
  the 
  wind. 
  

   However, 
  this 
  would 
  soon 
  carry 
  it 
  too 
  far 
  upwind, 
  out 
  of 
  the 
  zone 
  of 
  

   vertical 
  deflection. 
  This 
  is 
  why 
  the 
  soaring 
  birds 
  and 
  experienced 
  

   glider 
  pilots 
  cruise 
  weaving 
  to 
  and 
  fro 
  along 
  the 
  mountain 
  ridges, 
  

   always 
  trying 
  to 
  keep 
  within 
  the 
  zone 
  of 
  strongest 
  lift. 
  

  

  Of 
  course, 
  the 
  wind 
  does 
  not 
  exactly 
  follow 
  the 
  contour 
  of 
  the 
  

   hillside 
  in 
  equidistant 
  flow 
  lines. 
  As 
  far 
  as 
  the 
  windward 
  side 
  of 
  

   the 
  wind 
  obstruction 
  is 
  concerned, 
  model 
  experiments 
  in 
  wind 
  tunnels 
  

   have 
  given 
  interesting 
  results 
  and 
  perspicuous 
  flow 
  pictures 
  can 
  be 
  

   derived 
  by 
  calculation, 
  using 
  the 
  method 
  of 
  sources 
  and 
  sinks. 
  A 
  

   combination 
  of 
  sources 
  and 
  sinks 
  is 
  so 
  chosen 
  that 
  the 
  fictitious 
  fluid 
  

   produced 
  by 
  these 
  sources 
  and 
  washed 
  leewards 
  by 
  the 
  flow 
  represent- 
  

   ing 
  (he 
  wind 
  is 
  completely 
  housed 
  within 
  a 
  shape 
  that 
  coincides 
  with 
  

  

  