﻿AERONAUTIC 
  RESEARCH 
  AMES. 
  

  

  169 
  

  

  opposition 
  as 
  the 
  air 
  flows 
  along 
  its 
  surface. 
  Forces 
  are 
  required 
  

   to 
  move 
  the 
  control 
  surfaces, 
  i. 
  e., 
  the 
  rudders 
  and 
  elevators. 
  We 
  

   must 
  determine 
  these 
  forces, 
  and 
  must 
  investigate 
  the 
  changes 
  in 
  

   them 
  as 
  we 
  change 
  the 
  shape 
  of 
  the 
  airship, 
  e. 
  g., 
  its 
  length 
  or 
  its 
  

   cross-section. 
  A 
  great 
  deal 
  may 
  be 
  learned 
  by 
  studying 
  theoreti- 
  

   cally 
  the 
  way 
  in 
  which 
  air 
  flows 
  around 
  a 
  solid 
  body 
  shaped 
  

   more 
  or 
  less 
  like 
  an 
  airship. 
  A 
  most 
  interesting 
  mode 
  oi 
  attack 
  

   on 
  this 
  problem 
  was 
  devised 
  by 
  Admiral 
  Taylor 
  of 
  our 
  Navy, 
  and 
  

   was 
  applied 
  by 
  him 
  to 
  the 
  design 
  of 
  ocean 
  vessels. 
  The 
  drawings 
  

   illustrate 
  how 
  a 
  uniform 
  flow 
  superposed 
  upon 
  a 
  source 
  and 
  sink 
  

   produces 
  a 
  condition 
  like 
  the 
  flow 
  around 
  an 
  airship. 
  This 
  type 
  

  

  Fig. 
  

  

  -Air 
  flow 
  due 
  to 
  superposing 
  a 
  uniform 
  rectilinear 
  flow 
  upon 
  a 
  combination 
  of 
  

   source 
  and 
  sink. 
  

  

  of 
  flow 
  may 
  then 
  be 
  studied 
  mathematically; 
  the 
  pressures 
  may 
  be 
  

   deduced, 
  etc. 
  

  

  Similarly, 
  in 
  the 
  case 
  of 
  airplanes, 
  we 
  must 
  know 
  the 
  character 
  

   of 
  airflow 
  past 
  the 
  struts, 
  the 
  fuselage, 
  and 
  the 
  wings. 
  It 
  is 
  the 
  

   difference 
  in 
  the 
  pressure 
  on 
  the 
  two 
  sides 
  of 
  a 
  wing 
  that 
  produces 
  

   the 
  upward 
  force 
  required 
  to 
  support 
  the 
  machine. 
  The 
  figures 
  

   on 
  plate 
  3 
  illustrate 
  the 
  type 
  of 
  flow 
  around 
  the 
  aerofoil. 
  

  

  Great 
  progress 
  has 
  been 
  made 
  in 
  recent 
  years 
  by 
  Prandtl 
  and 
  

   other 
  German 
  physicists 
  by 
  showing 
  how 
  a 
  flow 
  of 
  air 
  around 
  

   an 
  aerofoil 
  could 
  be 
  produced 
  in 
  an 
  ideal 
  frictionless 
  gas 
  similar 
  

   to 
  that 
  observed 
  in 
  air 
  by 
  imagining 
  vortices 
  or 
  whirls 
  in 
  the 
  gas. 
  

   The 
  method 
  is 
  not 
  unlike 
  that 
  mentioned 
  above 
  as 
  useful 
  in 
  the 
  

   case 
  of 
  airships, 
  only 
  vortices 
  are 
  used 
  in 
  place 
  of 
  sources 
  and 
  sinks. 
  

  

  