design is necessary to obtain the best results from these two  conflicting conditions.  In comparison, the rectangular wing has a tendency to stall  first at the wing root and provides adequate stall warning,  adequate aileron effectiveness, and is usually quite stable.  It is, therefore, favored in the design of low cost, low speed  airplanes.  The second means of changing the planform is by tapering  (decreasing the length of chord from the root to the tip of the  wing). In general, tapering causes a decrease in drag (most  effective at high speeds) and an increase in lift. There is also  a structural benefit due to a saving in weight of the wing.  If an aircraft were viewed in straight-and-level flight from the  front  [Figure 5-34],  and if the forces acting on the aircraft  could be seen, lift and weight would be apparent: two forces.  If the aircraft were in a bank it would be apparent that lift  did not act directly opposite to the weight, rather it now acts  in the direction of the bank. A basic truth about turns is that  when the aircraft banks, lift acts inward toward the center of  the turn, perpendicular to the lateral axis as well as upward.  Most training and general aviation type airplanes are operated  at high coefficients of lift, and therefore require comparatively  high aspect ratios. Airplanes that are developed to operate at  very high speeds demand greater aerodynamic cleanness and  greater strength, which require low aspect ratios. Very low  aspect ratios result in high wing loadings and high stall speeds.  When sweepback is combined with low aspect ratio, it results  in flying qualities very different from a more conventional  high aspect ratio airplane configuration. Such airplanes  require very precise and professional flying techniques,  especially at slow speeds, while airplanes with a high aspect  ratio are usually more forgiving of improper pilot techniques.  The elliptical wing is the ideal subsonic planform since it  provides for a minimum of induced drag for a given aspect  ratio, though as we shall see, its stall characteristics in  some respects are inferior to the rectangular wing. It is also  comparatively difficult to construct. The tapered airfoil is  desirable from the standpoint of weight and stiffness, but  again is not as efficient aerodynamically as the elliptical  wing. In order to preserve the aerodynamic efficiency of the  elliptical wing, rectangular and tapered wings are sometimes  tailored through use of wing twist and variation in airfoil  sections until they provide as nearly as possible the elliptical  wing’s lift distribution. While it is true that the elliptical  wing provides the best coefficients of lift before reaching an  incipient stall, it gives little advance warning of a complete  stall, and lateral control may be difficult because of poor  aileron effectiveness.  Newton’s First Law of Motion, the Law of Inertia, states that  an object at rest or moving in a straight line remains at rest  or continues to move in a straight line until acted on by some  other force. An aircraft, like any moving object, requires a  sideward force to make it turn. In a normal turn, this force  is supplied by banking the aircraft so that lift is exerted  inward, as well as upward. The force of lift during a turn is  separated into two components at right angles to each other.  One component, which acts vertically and opposite to the  weight (gravity), is called the “vertical component of lift.”  The other, which acts horizontally toward the center of the  turn, is called the “horizontal component of lift” or centripetal  force. The horizontal component of lift is the force that  pulls the aircraft from a straight flight path to make it turn.  Centrifugal force is the “equal and opposite reaction” of the  aircraft to the change in direction and acts equal and opposite  to the horizontal component of lift. This explains why, in a  correctly executed turn, the force that turns the aircraft is  not supplied by the rudder. The rudder is used to correct any  deviation between the straight track of the nose and tail of the  aircraft into the relative wind. A good turn is one in which the  Figure 5-34.  Forces during normal, coordinated turn at constant altitude.  5-22  Level flight  Medium banked turn  Steeply banked turn  Centrifugal force  Horizontal  component  Vertical component  Resultant load Centrifugal force  Horizontal  component  Vertical component  Resultant load  Lift Total lift Total lift  Weight Weight Weight  Aerodynamic Forces in Flight Maneuvers  Forces in Turns 