NAVWEPS 00-8OT-80  BASIC AERODYNAMICS  EFFECT OF HIGH LIET DEVICES.  The  primary purpose of high lift devices (flaps,  slots, slats, etc.) is to increase the CLn, of the  airplane and reduce the stall speed. The take-  off and landing speeds are consequently re-  duced. The effect of a typical high lift device  is shown by the airplane lift curves of figure  1.15 and is summarized here:  weight of the airplane and the horizontal com-  ponent of lift be equal to the centrifugal force.  Thus, the aircraft in a steady turn develops a  lift greater than weight and experiences in-  creased  stall speeds.  Trigonometric ‘relationships allow  deter-  mination of the effect of bank angle on stall  speed and load factor. The load factor, B, is  the proportion between lift and weight and is  determined by:  n=load factor (or “G”)  cos 6 = cosine of the bank angle, + (phi)  where  Typical values of load factor determined by  this relationship are:  The stall speed in a turn can be determined by:  where  v,+= stall speed at some bank angle +  V,= stall speed  for wing level, lift-equal-  weight flight  n=load  factor corresponding to the  bank angle  The percent increase in stall speed in a turn is  shown on figure l.i6.  Since this chart is predi-  cated on a steady turn and constant CL,, the  figures a!e valid for any airplane. The chart  shows that no appreciable change in load fac-  tor or stall speed  occurs  at bank angles less than  30“.  Above 4S” of bank the increase in load  factor and stall speed is quite rapid.  This fact  emphasizes  the need for avoiding steep turns at  low airspeeds-a flight condition common to  stall-spin accidents.  For example, assume  the airplane described by  the lift curves of figure 1.15 has a stall speed of  100 knots at the landing weight in the clean  configuration.  If the flaps are lowered the  reduced stall speed is reduced to:  where  V,,= stall speed with flaps down  v,=stall  speed without flaps  C,= maximum lift coefficient of  the clean configuration  C&,= maximum lift coefficient  with flaps down  .+.- 00  130  300  450  600  759  n-l.00  1.035 1.154 1.414 z.ooo 4.ooo  -  v,=v,  z%  J  Ch,  The principal effect of the extension of flaps is  to increase the C,,  and reduce the angle of  attack for any given lift coefficient. The in-  crease in CL,, afforded by flap deflection re-  duces the stall speed in a certain proportion,  the effect described by the equation:  L  fizz--  W  1  n=-  cos I$  c.mip~tion  L.  (II far C ‘ ,  clun(tla~Up)  . . . . .  . . . . . . . .  1.5  200  Php down.  2.0  IS.9  37 