NAVWEPS 00-801-80  BASIC AERODYNAMICS  approximates that of the elliptical  wing.  Hence, the stall pattern is much the same as the  elliptical wing.  (D) The highly  tapered wing  of taper  ratio=0.25 shows the stall tendency inherent  with high taper. The lift distribution of such  a wing has distinct peaks just inboard from the  tip.  Since the wing stall is started in the  vicinity of the highest local lift coefficient,  this planform has a strong “tip stall” tendency.  The initial stall is not started at the exact tip  but at the station inboard from the tip where  highest local lift c,oefficients  prevail. If an  actual wing were allowed to stall in this  fashion the occurrence  of stall would be typi-  fied by aileron buffet and wing drop.  There  would be no buffet of the empennage or aft  fuselage, no strong nose down moment, and  very little-if  any-aileron  effectiveness. In  order to prevent such undesirable happenings,  the wing must be tailored to favor the stall  pattern. The wing may be given a geometric.  twist or “washout”  to decrease the local  angles of attack at the tip.  In addition, the  airfoil section may be varied throughout the  span such that sections with greater thickness  and camber are located in the areas of highest  local lift coefhcients. The higher ct-  of  such sections  can then develop the higher local  C~S  and be less likely to stall.  The addition  of leading edge slots or slats toward the tip  increase  the local c  t- and stall angle of attack  and are useful in allaying tip stall and loss of  aileron effectiveness. Another device for im-  proving the stall pattern would be the forcing  of stall in the desired location by decrctising  the  section ctmar  in this vicinity.  The use of sharp  leading edges or “stall  strips” is a powerful  device to control the stall pattern.  .(E) The pointed tip wing of taper ratio  equal to zero develops extremely high local  lift coefficients at the tip.  For all practical  purposes,  the pointed tip will be stalled at any  condition of lift unless extensive tailoring is  applied to the wing.  Such a planform has no  An additional effect on sweepback is the re-  duction in the slope of the lift curve and maxi-  mum lift coeflicient. When the sweepback is  large and combined with low aspect ratio the  lift curve is very shallow and maximum lift  coefficient can occur at tremendous angles.of  attack. The lift curve of one typical low  aspect ratio, highly tapered, swept wing air-  plane depicts a maximum lift coefficient at  approximately 43’ angle of attack.  Such dras-  tic angles of attack are impractical in many  respects.  If the airplane is operated at such  high angles of attack an extreme landing gear  configuration is required, induced drag is ex-  tremely high, and the stability of the airplane  may seriously deteriorate.  Thus, the modern  conhguration of airplane may have “minimum  When sweepback and taper are combined in  a planform, the inherent tip stall tendency is  considerable. If tip stall of any significance is  allowed to occur on the swept wing, an addi-  tional complication results: the forward shift  in the wing center of pressure creates an un-  stable nose up pitching moment.  The stall  sequence  of a swept, tapered wing is indicated  by the tuft-grid photographs of figure 1.33.  (F) Sweepback  applied to a wing planform  alters the lift distribution similar to decreasing  taper ratio.  Also, a predominating influence  of the swept planform is the tendency for a  strong crossflow of the boundary layer at high  lift coefficients. Since the outboard sections  of the wing trail the inboard sections, the out-  board suction pressures tend to draw the  boundary layer toward the tip.  The result is  a thickened low energy boundary layer at the  tips which is easily separated. The develop  ment of the spanwise flow in the boundary  layer is illustrated by the photographs of  figure 1.33. Note that the dye streamers  on  the upper surface of the~swept wing develop a  strong spanwise crossflow at high angles of  attack. Slots, slats, and flow fences help to  allay the strong tendency for spanwise flow.  practical application to an airplane which is  definitely subsonic in performance. 