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. 
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. 
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. 
STALL PATTERNS 
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 
NAVWEPS OD-ROT-RO 
RASIC AERODYNAM!CS 
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 : 
(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