NAVWEPS 004OT-80  BASIC AERODYNAMICS  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).  (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 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.  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  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  the effect of area distribution and taper along  the span. If the elliptical lift distribution is  EFFECT OF TAPER AND SWEEPBACK  74 