﻿228 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  dining 
  it 
  backward. 
  The 
  pull 
  of 
  the 
  first 
  case 
  and 
  the 
  additional 
  

   drag 
  in 
  the 
  second 
  would 
  eventually 
  cancel 
  out, 
  if 
  they 
  were 
  of 
  equal 
  

   magnitude. 
  However, 
  in 
  the 
  rising 
  phase 
  the 
  angle 
  of 
  attack 
  and, 
  

   consequently, 
  the 
  lift 
  are 
  increased, 
  in 
  the 
  descending 
  phase 
  they 
  are 
  

   decreased. 
  Therefore 
  the 
  forward 
  component 
  wins. 
  Lift 
  is 
  auto- 
  

   matically 
  concentrated 
  during 
  the 
  period 
  when 
  power 
  is 
  transmitted 
  

   from 
  the 
  air 
  to 
  the 
  machine. 
  The 
  airplane 
  combs 
  the 
  fluctuation. 
  

   We 
  often 
  call 
  this 
  phenomenon 
  the 
  " 
  Knoller-Betz 
  " 
  effect, 
  after 
  the 
  

   names 
  of 
  two 
  scientists 
  who 
  independently 
  published 
  the 
  first 
  explan- 
  

   ations 
  in 
  1912 
  and 
  1918. 
  It 
  may 
  be 
  that 
  this 
  is 
  tlie 
  same 
  phenom- 
  

   enon 
  which 
  causes 
  discrepancies 
  between 
  the 
  results 
  of 
  wing-model 
  

   tests 
  conducted 
  at 
  various 
  laboratories 
  or 
  under 
  difTerent 
  conditions 
  

   of 
  turbulence. 
  

  

  Flying 
  through 
  vertically 
  pulsating 
  air, 
  the 
  operation 
  of 
  the 
  

   elevator 
  in 
  a 
  certain 
  rhythm, 
  would 
  yield 
  an 
  optimum 
  power 
  gain 
  

   a 
  little 
  in 
  excess 
  of 
  that 
  natural 
  gain 
  which 
  would 
  be 
  derived 
  from 
  

   inertia 
  alone. 
  However, 
  there 
  is 
  no 
  conspicuous 
  periodicity 
  in 
  the 
  

   vertical 
  wind 
  fluctuations 
  and 
  it 
  would 
  be 
  extremely 
  difficult 
  for 
  the 
  

   pilot 
  to 
  estimate 
  their 
  harmonic 
  constituents 
  aiid, 
  above 
  all, 
  to 
  dis- 
  

   criminate 
  in 
  time 
  between 
  vertical 
  and 
  frontal 
  gusts. 
  

  

  The 
  utilization 
  of 
  the 
  latter 
  is 
  a 
  dift'erent 
  proposition 
  and 
  leads 
  us 
  

   to 
  dynamical 
  soaring 
  proper. 
  It 
  is 
  obvious 
  and 
  well 
  known 
  that 
  

   the 
  horizontal 
  mean 
  velocity 
  component 
  of 
  the 
  wind 
  can 
  not 
  be 
  

   captured 
  from 
  any 
  free-flying 
  vehicle. 
  It 
  can 
  be 
  by 
  a 
  kite 
  which 
  is 
  

   connected 
  to 
  the 
  solid 
  ground 
  by 
  a 
  cord. 
  

  

  Soaring 
  flight 
  is 
  in 
  some 
  languages 
  called 
  " 
  sailing 
  flight." 
  The 
  

   comparison 
  with 
  sailing 
  does 
  not 
  lack 
  some 
  justification. 
  The 
  sailing 
  

   vessel 
  depends 
  upon 
  its 
  simultaneous 
  contact 
  with 
  two 
  mediums, 
  

   the 
  sail 
  with 
  tlie 
  air, 
  and 
  the 
  keel 
  with 
  the 
  water. 
  Without 
  the 
  keel 
  

   part 
  it 
  would 
  be 
  helpless. 
  A 
  round 
  nutshell 
  without 
  a 
  keel 
  would 
  

   drift 
  uncontrollably 
  with 
  the 
  wind. 
  So 
  would 
  a 
  sailed 
  ice 
  sled 
  put 
  

   on 
  balls. 
  Furthermore 
  it 
  is 
  only 
  tlie 
  relative 
  motion 
  between 
  these 
  

   two 
  mediums 
  that 
  can 
  be 
  utilized. 
  When 
  the 
  wind 
  blows 
  with 
  the 
  

   same 
  velocity 
  and 
  direction 
  as 
  the 
  river 
  flows, 
  sails 
  are 
  dead 
  and 
  

   worthless 
  to 
  the 
  river 
  craft. 
  

  

  Now, 
  where 
  is 
  the 
  other 
  medium 
  to 
  lean 
  against 
  from 
  an 
  aircraft 
  

   totally 
  surrounded 
  by 
  nothing 
  but 
  the 
  wind 
  ? 
  It 
  can 
  only 
  be 
  portions 
  

   of 
  the 
  v/ind 
  which 
  move 
  at 
  velocities 
  different 
  from 
  the 
  average. 
  

   The 
  wind 
  is 
  almost 
  never 
  uniform. 
  In 
  one 
  place 
  and 
  at 
  one 
  instant 
  

   it 
  moves 
  faster 
  than 
  at 
  another. 
  It 
  is 
  these 
  irregularities 
  from 
  which, 
  

   in 
  dynamic 
  soaring, 
  energy 
  is 
  drawn. 
  Conventional 
  types 
  of 
  air- 
  

   craft, 
  contrary 
  to 
  naval 
  craft, 
  lacking 
  the 
  advantages 
  of 
  maneuvering 
  

   at 
  the 
  contact 
  surface 
  of 
  two 
  media, 
  can 
  not 
  get 
  hold 
  of 
  them 
  simul- 
  

   taneously. 
  Thus 
  we 
  have 
  to 
  merge 
  into 
  each 
  of 
  them 
  alternately, 
  

   relying 
  on 
  inertia 
  as 
  a 
  substitute 
  for 
  the 
  mast 
  and 
  rigging. 
  

  

  