NAVWEPS m-60T-30  BASIC AERODYNAMICS  It is derived from the relative pressure and  velocity distribution.  (2) Influenced only by the shape of the  surface  and angle of attack since these factors  determine the pressure  distribution.  existing on the surface. Of course, the ve-  locity distribution, and resulting pressure dis-  tribution, is determmed by the.shape or pro-  file of the surface and the angle of a ’ track.  Thus, any aerodynamic force can be repre-  sented as the product df three major factors:  the surface  area of the objects  the dynamic pressure  of the airstream  the coefficient  or index of force determined  by the relative pressure  distribution  This relationship is expressed  by the following  equation :  (3) An index which allows evaluation of  the effects of compressibility and viscosity.  Since the effects  of area, density, and velocity  are obviated by the coefficient form, com-  pressibility and viscosity effects can be  separated  for study.  THE BASIC LIFT EQUATION.  Lift has  been dehned as the net force developed per-  pendicular to the relative wind.  The aero-  dynamic force of lift on an airplane results  from the generation of a pressure  distribution  on the wing.  This lift force is described by  the following equation:  F= C,qS  where  F = aerodynamic force, lbs.  C,=coeflicient of aerodynamic force  ,iay;mic  pressure,  psf  S=surface area, sq. ft.  In order to fully appreciate the importance  of the aerodynamic force coe&cient, C,, the  ,  above equation is rearranged to alternate  forms :  L=C&  where  L=lift,  lbs.  C, = lift coefficient.  q= dy;:mic pressure,  psf  +p  S= wing surface area, sq. ft.  The lift coefhcient  used in this equation is the  ratio of the lift pressure  and dynamic pressure  and is a function of the shape of the wing and  angle of attack. If the lift coefficient of a  conventional airplane wing planfoi-m were  plotted versus  angle of attack, the result would  be typical of the graph of figure 1.11. Since  the effects  of speed, density, area, weight, alti-  tude, etc., are eliminated by the coefficient  form,  an indication of the true lift capability is ob-  tained.  Each angle of attack produces a par-  ticular lift coefficient since the angle of attack  is the controlling factor in the pressure dis-  tribution.  Lift coeflicient increases  with angle  of attack up to the maximum lift coefficient,  c  L,,,~., and, as angle of attack is increased be-  yond the maximum lift angle, the airflow is  unable to adhere to the upper surface. The  airflow then separates  from the upper surface  and stall occurs.  In this form, the aerodynamic force coefficient  Js appreciared as the aerodynamic force per  surface area and dynamic pressure. In other  words, the force coefficient is a dimensionless  ratio between the average aerodynamic pres-  sure (aerodynamic force.per  ‘ area) and the air-  stream dynamic pressure. All the aerodynamic  forces  of lift and drag are studied on this basis-  the common denominator in each case being  surface  area and dynamic  pressure.  By such a  definition, a “lift  coefficient” would .be the  ratio between lift pressure and dynamic pres-  sure; a  “drag coefficient” would be the ratio  between drag pressure and.:d.ynamic pressure.  The use of the coefficient form of an aero-  dynamic force is necessary since the force  coellicient is:  (1) An index 04 the aerodynamic force  independent of area, density, and velocity.  JNTERPRETATION OF THE LIFT EQUA-  TION.  Several important relationships are  23 