NAVWEPS OD-ROT-RO  RASIC AERODYNAM!CS  1.32. As with the rectangular wing, the non-  uniformity of downwash and lift distribution  result in inefficiency of rhis planform.  For  example, a pointed wing of AR=6 would have  17 percent higher induced angle of attack for  the wing and 13 percent higher induced drag  than an elliptical wing of thesame aspect  ratio.  advantages of root stall first are that ailerons  remain effective at high angles of attack,  favorable stall warning results from the buffet  on the empennage and aft portion of the fuse-  lage, and the loss of downwash behind the root  usually ptovides a stable nose down moment  to the airplane. Such a stall pattern is favored  but may be difficult to obtain with certain wing  configurations. The types of stall patterns in-  herent with various planforms are illustrated  in figure 1.33. The various planform effects  are separated  as follows :  Between the two extremes of taper will  exist planforms of more tolerable efficiency.  The variations of 2 for a wing of taper ratio  =0.5 closely approxtmates  the lift distribution  of the elliptical wing and the drag due to lift  characteristics are nearly identical.  A wing  of AR=6 and taper ratio=0.5  has only 3  percent  higher ai and 1 percent greater CD: than  an elliptical wing of the same aspect ratio.  ,A separate effect on the spanwise lift dis-  tribution is contributed by wing sweepback.  Sweepback  of the planform tends to alter the  lift distribution similar to decreasing  the taper  ratio. Also, large sweepback  tends to increase  induced drag.  (A) The elliptical planform has constant  local lift coefficients  throughout the span from  root to tip.  Such a lift distribution means that  all sections will reach stall at essentially the  same wing angle of attack and stall will begin  and progress uniformly throughout the span.  While the elliptical wing would reach high  lift coefficients before incipient stall, there  would be little advance warning of complete  stall.  Also, the ailerons may lack effectiveness  when the wing operates near the stall and lat-  eral control may be difficult.  (B) The lift distribution of the rectangular  wing exhibits low local lift coefficients  at the  tip and high local lift coe5cients at the root.  Since the wing will initiate stall in the area of  highest local lift coefficients, the rectangular  wing is characterized by a strong root stall  tendency. Of course, this stall pattern is fav-  orable since there is adequate stall warning  buffet, adequate aileron effectiveness,  and usu-  ally strong stable moment changes on the ait-  plane.  Because  of the great aerodynamic and  structural ine&ciency of this planform, the  rectangular wing finds limited application only  to low cost, low speed light planes.  The sim-  plicity  of construction and favorable stall  characteristics  are predominating requirements  of such an airplane. The stall sequence  fot a  rectangular wing is shown by the tuft-grid  pictures.  The progressive flow separation il-  lustrates the strong root stall tendency.  The elliptical wing is the ideal of the sub-  sonic aerodynamic planform since it provides  a minimum of induced drag for a given aspect  ratio.  However, the major objection to the  elliptical planform is the extreme difficulty of  mechanical layout and construction.  A highly  tapered planform is desirable from the stand-  point of structural weight and stiffness and  the usual wing planform may have a taper  ratio from 0.45 to 0.20. Since structural con-  siderations are quite important in the develop-  ment of an airplane configuration, the tapered  planform is a necessity for an efficient configu-  ration. In order to preserve the aerodynamic  efficiency, the resulting planform is tailored  by wing twist and section variation to obtain  as near as possible the elliptic lift distribution.  An additional effect of the planfotm area  distribution is on stall pattern of wing.  The  desirable stall pattern of any wing is a stall  which begins on the root sections first. The  (C) The wing of moderate taper (taper  ratio=0.5) has a lift distribution which closely  STALL PATTERNS 