2 Aerodynamics
109
Fig. 2.40 B-spline parametric modeling of supercritical wing
Fig. 2.41 Grid near critical wing
The later designed wing shape can produce lift–drag ratio of more than 20,
for example, the lift–drag ratio of a pure wing of a large passenger plane can
reach about 30. Due to the influence of wingtip, the lift–drag ratio of a threedimensional wing is smaller than that of a two-dimensional airfoil. Because
the fuselage mainly produces drag, the lift–drag ratio of the whole aircraft
will be smaller when the fuselage and other drag components are added. For
example, Boeing 747, when cruising, the lift–drag ratio of the aircraft is about
17 to 18, which is equivalent to lifting 1 kg of gravity only needs to overcome
55 g of drag.
In 1918, the German scientist Prandtl studied the aerodynamic problems
of airfoils with chamber and put forward the thin wing theory. On this basis,
the theory of lift line of a straight wing with a large aspect ratio is put forward.
This work makes people realize the importance of the wingtip effect to the
overall performance of the wing for a finite wingspan wing, and points out
the essential relationship between wingtip vortex and induced drag, which
has not been paid attention to for a long time. On the trailing edge of
a straight wing with a large aspect ratio, a row of silk threads are evenly
pasted along its aspect, and a small cotton ball is tied at the end of the silk
threads. Then the wing is placed in a low-speed wind tunnel for the wind
blowing test. The results show that for a finite span wing, due to the tip
effect, the flow with high pressure on the lower surface of the wing will turn
109
Fig. 2.40 B-spline parametric modeling of supercritical wing
Fig. 2.41 Grid near critical wing
The later designed wing shape can produce lift–drag ratio of more than 20,
for example, the lift–drag ratio of a pure wing of a large passenger plane can
reach about 30. Due to the influence of wingtip, the lift–drag ratio of a threedimensional wing is smaller than that of a two-dimensional airfoil. Because
the fuselage mainly produces drag, the lift–drag ratio of the whole aircraft
will be smaller when the fuselage and other drag components are added. For
example, Boeing 747, when cruising, the lift–drag ratio of the aircraft is about
17 to 18, which is equivalent to lifting 1 kg of gravity only needs to overcome
55 g of drag.
In 1918, the German scientist Prandtl studied the aerodynamic problems
of airfoils with chamber and put forward the thin wing theory. On this basis,
the theory of lift line of a straight wing with a large aspect ratio is put forward.
This work makes people realize the importance of the wingtip effect to the
overall performance of the wing for a finite wingspan wing, and points out
the essential relationship between wingtip vortex and induced drag, which
has not been paid attention to for a long time. On the trailing edge of
a straight wing with a large aspect ratio, a row of silk threads are evenly
pasted along its aspect, and a small cotton ball is tied at the end of the silk
threads. Then the wing is placed in a low-speed wind tunnel for the wind
blowing test. The results show that for a finite span wing, due to the tip
effect, the flow with high pressure on the lower surface of the wing will turn