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 
practical application to an airplane which is 
definitely subsonic in performance. 
(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. 
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. 
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