NAVWEPS 00-805-80  AIRPLANE PERFORMANCE  combined effects would be approximated  for the case of the airplane with high in-  trinsic acceleration by the following:  The effect of density altitude on powerplant  thrust depends much on the type of power-  plant.  An increase  in altitude above standard  sea level will bring an immediate decrease  in  power output for the unsupercharged  or ground  boosted reciprocating engine or the turbojet  and turboprop engines.  However, an increase  in altitude above standard sea level will not  cause a decrease  in power output for the super-  charged reciprocating engine until the altitude  exceeds  the critical altitude.  For those power-  plants which experience  a decay in thrust with  an increase in altitude, the effect on the net  accelerating force and acceleration can be ap-  proximated by assuming a direct variation  with density. Actually, this assumed vari-  ation would closely approximate the effect on  airplanes with high thrust-to-weight ratios.  This relationship would be as follows:  where  S,= standard sea level takeoff distance  Ja= takeoff distance at altitude  o=altitude density ratio  g=(gyx(~)  g=(i)x(;)  s2  12  -=  -  0  J-1  a  a2  Fm  P  -=-=-En  al  Frill PO  As a result of these relationships, it should.  be appreciated that density altitude will affect  takeoff performance in a fashion depending  much on the powerplant type. The effect of  density altitude on takeoff distance can be  appreciated by the following comparison:  where  ai, Fn, = acceleration and net accelerating  force corresponding to sea level  aa, Fn, = acceleration and net accelerating  force corresponding to altitude  ~=altitude density ratio  In order to evaluate the effect of these items on  takeoff distance, the following relationships  are used  :  if an increase  in altitude does not alter ac-  celeration, the principal effect would be  due to the greater TAS  where  if an increase in altitude reduces accelera-  tion in addition to the increase  in TAS, the  From the previous table, some approximate  rules of thumb may be derived to illustrated  the differences between the various airplane  types.  A 1,ooo-ft. increase  in density altitude  Si=standard sea level takeoff distance  St= takeoff distance at altitude  o-altitude  density ratio  ;=(g,yxe)  f2 1  -=-  $1 (T  sealevel....  I.cmft.....  Z,cmfC.....  ,,mfi.....  4.@JJfc.....  5.Ccnft.....  6.-xafC.....  --  1  1  I  I  1  I  ..om  .0?.98  ..c605  L. wls  L. 126  L. 1605  1.1965 $^{L.cca }$ L.oa5  1.125  1.191  1.264  1.347  1.431  P  --  drirude  --  0  0  2.98 6.05  6.05 12.5  9.28 19.5  12.6 26.4  16.05 34.7  19.65 0.1  0  9.8  19.9  30.1  40.6  52.3  65.8  191 