NAVWEPS 00-801-80  HIGH SPEEO AERODYNAMICS  Once the configuration of a transonic air-  craft is fixed, the pilot must respect the effect  of angle of attack and altitude.  The local flow  1 velocities on any upper surface  increase  with an  increase  in angle of attack.  Hence, local sonic  flow and subsequent shock wave formation  can occur at lower free stream Mach numbers.  A pilot must appreciate this reduction of force  divergence Mach number with lift coefficient  since maneuvers at high speed may produce  compressibility effects which may not be en-  countered in unaccelerated flight.  The effect  of altitude is important since the magnitude  of any force or moment change due to com-  pressibility will  depend upon the dynamic  pressure of the airstream.  Compressibility  effects encountered at high altitude and low  dynamic pressure  may be of little consequence  in the operation of a transonic aircraft.  How-  ever,  the same compressibility effects en-  countered at low altitudes and high dynamic  pressures will  create greater trim changes,  heavier buffet, etc., and perhaps transonic  flight restrictions which are of principal inter-  est only to low altitude.  can be quite weak, the pressure  waves can be  of sufficient magnitude to create an audible  disturbance. Thus, “sonic booms” will be a  simple consequence  of supersonic  flight.  The aircraft powerplant: for supersonic  flight  must be of relatively high thrust output.  Also, in many cases it may be necessary to  provide the air breathing powerplant with  special inlet configurations which will slow  the airflow to subsonic prior to reaching the  compressor  face or combustion chamber. Aero-  dynamic heating of supersonic flight can pro-  vide critical inlet temperatures for the gas  turbine engine as well as critical structural  temperatures.  The density variations in airflow may be  shown by certain optical techniques. Schlieren  photographs and shadowgraphs can define the  various wave patterns and their effect on the  airflow.  The Schlieren photographs presented  in figure 3.11 define the flow conditions on an  aircraft in supersonic flight.  While many of the particular effects of super-  sonic flight will be presented in the detail of  later discussion, many general effects may be  anticipated. The airplane configuration must  have aerodynamic shapes  which will have low  drag in compressible  flow.  Generally, this will  require airfoil sections of low thickness ratio  and sharp leading edges and body shapes of  high fineness  ratio to minimize the supersonic  wave drag.  Because  of the aft movement of the  aerodynamic center with supersonic flow, the  increase in static longitudinal stability will  demand effective, powerful control surfaces  to  achieve adequate controllability  for super-  sonic maneuvering.  Aircraft configurations developed for high  speed flight will have significant differences  in  shape and planform when compared with air-  craft designed for low speed flight.  One of  the outstanding differences will  be in the  selection of airfoil profiles for transonic or  supersonic flight.  AIRFOIL  SECTIONS. It should be ob-  vious that airfoils for high speed subsonic  flight should have high critical Mach num-  bers since critical Mach number defines the  lower limit  for shock wave formation and  subsequent force divergence. An additional  complication to  airfoil  selection in  this  speed range is that the airfoil should have  a high maximum lift coefficient and sufficient  thickness to allow application of high lift  devices. Otherwise an excessive wing area  would be required to provide maneuverability  and reasonable takeoff and landing speeds.  TRANSONIC AND SUPERSONIC CONFIGU-  RATIONS  PHENOMENA OF SUPERSONIC FLIGHT.  As a corollary of supersonic  flight the shock  wave formation on the airplane may create  special problems outside the immediate vicinity  of the airplane surfaces. While the shock  waves a great distance away from the airplane  no 