NAVWEPS 004OT-80 
BASIC AERODYNAMICS 
(3) During the landing phase where an 
excessive angle of attack (or excessively low 
airspeed) would create high induced drag 
and a high power setting to control rate of 
descent. A common error in the technique 
of landing modern conbgurations is a steep, 
low power approach to landing. The steep 
flight path requires considerable maneuver 
to flare the airplane for touchdown and 
necessitates a definite increase in angle of 
attack. Since the maneuver of the flare is a 
transient condition, the variation of both 
lift and drag with angle of attack must be 
considered. The lift and drag curves for a 
high aspect ratio wing (fig. 1.31) show con- 
tinued strong increase in C, with 01 up to stall 
and large changes in Co only at the point of 
stall. These characteristics imply that the 
high aspect ratio airplane is usually capable 
of flare without unusual results. The in- 
__^_“^ :- ---I.. -c _&-__ 1. .-* n.-. -..- : 1 C,LaLDC 111 a,l5~~ VI ~LL~CL do *we p~ovmes the 
increase in lift to change the flight path 
direction without large changes in drag to 
decelerate the airplane. 
The lift and drag curves for a low aspect 
ratio wing (fig. 1.31) show that at high angles 
of attack the lift curve is shallow, i.e., small 
changes in C, with increased a. This implies 
a large rotation needed to provide the lift to 
flare the airplane from a steep approach. The 
drag curve for the low aspect ratio wing shows 
large, powerful increases in C, with Cr. well 
below the stall. These lift and drag charac- 
teristics of the low aspect ratio wing create 
a distinct change in the flare characteristics. 
If a flare is attempted from a steep approach at 
low airspeed, the increased angle of attack 
may provide such increased induced drag and 
rapid loss of airspeed that the airplane does not 
actually flare. A possible result is that an 
even higher sink rate may be incurred. This 
is one factor favoring the use of the “no-flare” 
or “minimum flare” type landing technique 
for certain modern configurations. These same 
aerodynamic properties set the best glide 
speeds of low aspect ratio airplanes above the 
speed for (L/D)-. The additional speed pro- 
vides a more favorable margin of flare capabil- 
ity for flameout landing from a steep glide path 
(low aspect ratio, low (L/D)-, low glide 
ratio). 
The landing technique must emphasize 
proper control of angle of attack and rate of 
descent to prevent high sink rates and hard 
landings. As before, to be sure that it will 
not go unsaid, excessive airspeed at landing 
creates its own problems-excessive wear and 
tear on tires and brakes, excessive landing 
distance, etc. 
The effect of the low aspect ratio planform 
of modern airplanes emphasizes the need for 
proper flying techniques at low airspeeds. 
Excessive angles of attack create enormous 
induced drag which can hinder takeoff per- 
formance and incur high sink rates at landing. 
Since such aircraft have intrinsic high mini- 
mum flying speeds, an excessively low angle of 
attack at takeoff or landing creates its own 
problems. These facts underscore the im- 
portance of a “thread-the-needle,” professional 
flying technique. 
EFFECT OF TAPER AND SWEEPBACK 
The aspect ratio of a wing is the primary 
factor in determining the three-dimensional 
characteristics of the ordinary wing and its 
drag due to lift. However, certain local effects 
take place throughout the span of the wing and 
these effects are due to the distribution of area 
throughout the span. The distribution of lift 
along the span of a wing cannot have sharp 
discontinuities. (Nature just doesn’t arrange 
natural forces with sharp discontinuities.) 
The typical lift distribution is arranged in 
some elliptical fashion. A representative dis- 
tribution of the lift per foot of span along the 
scan of a wing is shown in figure 1.32. 
The natural distribution of lift along the 
span of a wing provides a basis for appreciating