text: A change in altitude can produce signifi- 
  cant changes in the curves of thrust and power 
  required. The effects of altitude on these 
  curves providea great part of the explanation of 
  the effect of altitude on range and endurance. 
  Figure 2.4 illustrates the effect of a change in 
  altitude on the curves of thrust and power re- 
  quired for a specific airplane configuration and 
  long as compressibility 
  gross weight. As 
  effects are negligible, 
  the principal effect of 
  increased altitude on the curve of thrust re- 
  quired is that specific aerodynamic conditions 
  occur at higher true airspeeds. For example, 
  the subject airplane at sea level has a minimum 
  drag of 1,250 lbs. at 160 knots. The same 
  airplane would incur the same drag at altitude 
  if operated at the same cqthdcnt airsprcd of 160 
  knots. However, the equivalent airspeed of 
  160 knots at 22,000 ft. altitude would produce 
  a true airspeed of 227 knots. Thus, an in- 
  crease in altitude will cause the curve of thrust 
  required to flatten out and move to the direc- 
  tion of higher velocity. Note that altitude 
  alone will not alter the value of minimum drag. 
  The effect of altitude on the curve of power 
  required can best be considered from the effect 
  on true airspeed to achieve a specific aero- 
  dynamic condition. The sea level power re- 
  indicates that 
  quired curve of 
  CW>mz occurs at 160 knots and requires 615 
  h.p. 
  is operated at 
  WD)ma at an altitude of 22,000 ft., the same 
  drag is incurred at a higher velocity and re- 
  quires a higher power. The increase in ve- 
  locity 
  to 227 knots accounts for the increase 
  the 
  in power required to 872 hp. Actually, 
  various points on the curve of power required 
  can be considered affected in this same fashion. 
  At specific lift coefficients and angles of attack, 
  a change in altitude will alter the true airspeed 
  particular to these points and cause a change 
  in power required because of the change in 
  true airspeed. An increase in altitude will 