﻿238 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  soaring 
  flight 
  it 
  becomes 
  quite 
  an 
  indefinite 
  fiction 
  bare 
  of 
  sensible 
  

   qualities. 
  The 
  reason 
  for 
  it 
  is 
  that 
  all 
  dynamical 
  maneuvers 
  involve 
  

   actions 
  of 
  inertia, 
  and 
  it 
  is 
  just 
  the 
  task 
  of 
  the 
  dynamically 
  soar- 
  

   ing 
  machine 
  to 
  steer 
  in 
  such 
  a 
  way 
  that 
  the 
  inertia 
  forces 
  do 
  not 
  on 
  an 
  

   average 
  cancel 
  out, 
  with 
  respect 
  to 
  axes 
  inherent 
  to 
  the 
  craft. 
  Thus, 
  

   dynamical 
  soaring 
  is 
  the 
  true 
  materialization 
  of 
  Einstein's 
  famous 
  

   fictitious 
  box 
  within 
  which 
  all 
  mechanical 
  means 
  completely 
  fail 
  to 
  

   distinguish 
  any 
  essential 
  difference 
  between 
  inertia 
  and 
  gravity. 
  

   Once 
  the 
  two 
  are 
  entangled 
  they 
  can 
  not 
  be 
  separated 
  by 
  instruments. 
  

  

  In 
  order 
  to 
  describe 
  fully 
  the 
  status 
  of 
  motion 
  of 
  a 
  body 
  freely 
  

   moving 
  in 
  space, 
  we 
  have 
  to 
  state 
  six 
  elements, 
  the 
  three 
  components 
  

   of 
  velocity 
  and 
  the 
  three 
  components 
  of 
  rotation 
  in 
  space. 
  All 
  

   mechanical 
  instruments 
  based 
  on 
  the 
  principles 
  of 
  masses, 
  springs, 
  

   liquids, 
  pendula, 
  and 
  gyroscopes 
  combined 
  and 
  carried 
  on 
  board 
  the 
  

   aircraft 
  are 
  subject 
  to 
  the 
  combined 
  influence 
  of 
  both 
  gravity 
  and 
  

   inertia, 
  too. 
  So, 
  in 
  order 
  to 
  determine 
  the 
  vector 
  of 
  gravity 
  we 
  have 
  

   to 
  subtract 
  from 
  the 
  resultant 
  the 
  vector 
  of 
  inertia. 
  We 
  can 
  meas- 
  

   ure 
  by 
  six 
  aerodynamical 
  instruments 
  such 
  as 
  anemometers 
  and 
  wind 
  

   vanes 
  the 
  six 
  equivalent 
  data 
  about 
  the 
  relative 
  motion 
  of 
  the 
  ship 
  

   in 
  the 
  surrounding 
  air. 
  This 
  suffices, 
  evidently, 
  in 
  calm 
  air. 
  

  

  However, 
  as 
  soon 
  as 
  I 
  suspect, 
  or 
  know, 
  that 
  the 
  atmosphere 
  

   is 
  involved 
  in 
  an 
  irregularly 
  accelerated 
  motion 
  with 
  reference 
  

   to 
  the 
  earth, 
  I 
  am 
  at 
  a 
  complete 
  loss 
  to 
  determine 
  the 
  amount 
  of 
  

   the 
  influence 
  of 
  this 
  fact 
  by 
  means 
  of 
  any 
  instruments 
  of 
  mechani- 
  

   cal 
  or 
  aerodynamical 
  kind 
  carried 
  aboard. 
  The 
  unknown 
  data 
  

   must 
  be 
  supplied 
  by 
  having 
  recourse 
  to 
  other 
  physical 
  fields. 
  In 
  

   practice, 
  I 
  mentioned, 
  it 
  is 
  the 
  field 
  of 
  vision. 
  To 
  do 
  that 
  auto- 
  

   matically 
  by 
  means 
  of 
  instruments 
  is 
  at 
  present 
  pretty 
  well 
  beyond 
  

   available 
  instrumental 
  facilities. 
  Theoretically, 
  instruments 
  utiliz- 
  

   ing 
  such 
  extraneous 
  fields 
  as 
  the 
  magnetic 
  field, 
  the 
  dielectric 
  field 
  

   or 
  the 
  air-density 
  gradient 
  may 
  be 
  given 
  consideration, 
  but 
  whether 
  

   sufficient 
  accuracy 
  and 
  quick 
  response 
  will 
  ever 
  be 
  attained 
  is 
  hard 
  

   to 
  fancy. 
  Besides, 
  weight, 
  bulk, 
  and 
  complication 
  are 
  big 
  handicaps 
  

   for 
  the 
  use 
  of 
  automatic 
  apparatus 
  and 
  even 
  instruments 
  in 
  general. 
  

  

  Just 
  the 
  same 
  it 
  is 
  of 
  great 
  scientific 
  interest 
  to 
  investigate 
  with 
  

   whatever 
  instruments 
  are 
  feasible, 
  into 
  the 
  details 
  and 
  intricacies 
  

   of 
  soaring 
  flight. 
  Recording 
  altimeters, 
  air-speed 
  meters, 
  and 
  so- 
  

   called 
  accelerometers, 
  which, 
  however, 
  are 
  really 
  not 
  indicating 
  

   acceleration 
  proper, 
  but 
  a 
  component 
  of 
  the 
  resultant 
  air 
  force, 
  have 
  

   been 
  of 
  great 
  assistance 
  to 
  both 
  pilots 
  and 
  students. 
  You 
  can, 
  while 
  

   flying, 
  by 
  watching 
  these 
  instruments 
  simultaneously 
  with 
  the 
  hori- 
  

   zon 
  and 
  the 
  other 
  physical 
  sensations, 
  interpret 
  much 
  better 
  whether 
  

   you 
  are 
  gaining 
  or 
  losing 
  energy, 
  in 
  every 
  phase 
  of 
  the 
  gust. 
  Angle 
  

   of 
  attack 
  and 
  yaw 
  meters, 
  however 
  primitive 
  they 
  may 
  be, 
  are 
  also 
  

   a 
  valuable 
  asset. 
  A 
  wealth 
  of 
  information 
  has 
  been 
  accumulated 
  

  

  