NAVWEPS 00-8OT-80  BASIC AERODYNAMICS  ure is not too accurate because  of the sharper  variation of parasite drag at high angles of  attack.  In a sense,  the airplane efficiency  fac-  tor would change from the constant value and  decrease.  The deviation of the actual airplane  drag from the approximating curve is quite  noticeable for airplanes with low aspect ratio  and sweepback.  Another factor to consider is  the effect of compressibility.  Since compressi-  bility effects would destroy this relationship,  the greatest  application is for subsonic  perform-  ance analysis.  in with the induced drag coefficient by a con-  stant factor which is defined as the “airplane  e5ciency factor”, c.  By this method of ac-  counting the airplane drag coe5cient is ex-  pressed  as :  where  C  DPmB=  minimum parasite drag  coefficient  CD;= induced drag coe5cient  e = airplane e5ciency factor  The total airplane drag is the sum of the  parasite and induced drags.  where  In this form, the airplane drag coefficient is  expressed  as the sum of drag not due to lift  F%d”  ) and drag due to lift (G).  The air-  plane efficiency  factor is some co&ant (usually  less than unity) which includes parasite drag  due to lift with the drag induced by lift.  C  Dpmr”  is invariant with lift and represents  the  parasite drag at zero lift.  A typical value of  C  r,Pmin  would be 0.020, of which the wing may  account for 50 percent, the fuselage  and nacelles  40 percent, and the tail 10 percent. The term  of  (  0.318 g  >  accounts for all drag due’ to  lift-the  drag induced by lift and the extra  parasite drag due to lift.  Typical values of  the airplane efficiency  factor range from 0.6 to  0.9 depending on the airplane configuration  and its characteristics. While the term of  drag due to lift does include some parasite  drag, it is still generally referred to as induced  drag.  The second graph of figure 1.34 shows that  the sum of CD,  and G can approximate the  -mm  e  actual airplane CD through a large range of lift  coefficients. For airplanes of moderate aspect  ratio, this representation of the airplane total  drag is quite accurate in the ordinary range of  lift coefficients  up to near 70 percent of CL,,.  At high lift coefficients  near CL-, the proced-  In this form, the equivalent parasite area, f,  is the product of CDPml”  and S and relates an  or  R=fq  $^{where }$f = equivalent parasite area, sq. ft.  f = CDPmi,S  q= dynamic pressure,  psf  UP  =-  295  DpEfg  Di= induced drag  =(0.318 $+S  D= D,+D<  D,= parasite drag  and  When expressed  in this form the induced drag,  Di, includes all drags due to lift and is solely  a function of lift.  The parasite drag, D,, is  the parasite drag and is completely independent  of lift-it  could be called the “barn door”  drag of the airplane.  An alternate expression  for the parasite drag  is:  89 