NAVWEPS 00-ROT-80  AIRPLANE PER,FORMANCE  REQUIRED  THRUST AND  POWER  DEFINITIONS  knots requires one horsepower of propulsive  power.  However, each pound of drag at 650  knots requires two horsepower while each  pound of drag at 162.5 knots requires one-half  horsepower. The term “power”  implies work  rate and, as such, will be a function of the speed  at which a particular force is developed.  All of the principal items of flight perform-  ance involve steady state flight conditions and  equilibrium of the airplane.  For the airplane  to remain in steady level flight, equilibrium  must be obtained by a lift equal to the air-  plane weight and a powerplant thrust equal to  the airplane drag. Thus, the airplane drag  defines the thrust required to maintain steady  level flight.  Distinction  between thrust required and  pawcr  required is necessary  for several reasons.  For the items of performance  such as range and  endurance, it is necessary  to relate powerplant  fuel flow with the propulsive requirement for  steady IeveI flight.  Some powerplants incur  fuel flow rate according to output thrust while  other powerplants incur fuel flow rate depend-  ing on output power. For example, the turbo-  jet engine is principally. a thrust producing  machine and fuel flow is most directly related  to thrust output. The reciprocating engine is  principally a power producing machine and  fuei flow is most directiy reiated to power  output.  For these reasons the variation of  thrust required wil1 be of greatest interest in  the performance of the turbojet powered air-  plane while the variation of power required  will be of greatest interest in the performance  of the propeller powered airplane. Also, dis-  tinction between power and thrust required is  necessary  in the study of climb performance.  During a steady climb, the rate of climb will  depend on excess power while the angle of  climb is a function of excess  thrust.  The total drag of the airplane is the sum of  the parasite and induced drags: Parasite drag  is the sum of pressure  and friction drag which  is due to the basic configuration and, as de-  fined, is independent of lift.  Induced drag is  the undesirable but unavoidable consequence  of the development of lift.  In the process  of  creating lift by the deflection of an airstream,  the actuai iift is inclined and a coimponcn: of  lift is incurred parallel to the flight path direc-  tion.  This component of lift combines with  any change in pressure and friction drag due  to change in lift to form the induced drag.  While the parasite drag predominates at high  speed, induced drag predominates at low speed.  Figure 2.1 illustrates the variation with speed  of the induced, parasite, and total drag for a  specific airplane configuration in steady level  flight.  The total power required for flight can be  considered as the sum of induced and parasite  effects  similar to the total drag of the airplane.  The induced power required is a function of the  induced drag and velocity.  The power required for flight depends on the  thrust required and the flight velocity.  By  definition, the propulsive horsepower required  is related to thrust required and flight velocity  by the following equation:  pr= Trv  3%  p,,,!g  Pri= induced power required, h.p.  D<=induced drag, lbs.  V= true airspeed, knots  Pr=power required, h.p.  Tr= thrust required (total  drag), Ibs.  V= true airspeed, knots  where  where  By inspection of this relationship, it is appar-  ent that each ’ pound of drag incurred at 325  96 