84
P. Liu
Fig. 2.8 Aerodynamic classification
study of flight speed lower than sound speed is called subsonic aerodynamics,
the study of flight speed higher than sound speed is called supersonic aerodynamics, and the study of flight speed around sound speed is called transonic
aerodynamics. When intercontinental missiles and spacecraft return to the
atmosphere, their speed will be more than ten times of the sound speed in
a short time at first. This kind of flight is called hypersonic flight. Generally speaking, the hypersonic flight is defined as a flight with a speed greater
than five times the sound speed, and the one dealing with this problem is
called hypersonic aerodynamics. In addition, we also study the rarefied gas
mechanics in the outer atmosphere, magnetohydrodynamics of ionization in
the outer atmosphere, etc.
2.2 Low-Speed Airfoil Flow
First of all, humans have realized the dream of flying by air buoyancy based
on balloons, but it is not enough to fly only by balloons. Birds and many
aircraft do not fly by air buoyancy, but by the relative motion of air around
them. So people gradually realize that when the air around the wing has
relative motion, it can produce lift, and the lift is much greater than the
buoyancy. The second is that the object moving in the air must overcome
air resistance, so the concept of aircraft dynamics is introduced. The third is
that the concept of force multiplying distance, i.e., the concept of moment,
is introduced when the aircraft is able to maintain stable flight in the air. So
these three concepts lay the foundation for us to realize real flight (as shown
in Fig. 2.9).
Aircraft research starts from imitating birds, which is called imitation birds.
Later, people separated the power from the lift, and then there appeared fixedwing aircraft. The so-called fixed wing is that the lift surface is fixed, so the
earliest fixed wing is the glider. A glider is an unpowered aircraft, which generates lift through its wings. In addition, when the aircraft is equipped with an
P. Liu
Fig. 2.8 Aerodynamic classification
study of flight speed lower than sound speed is called subsonic aerodynamics,
the study of flight speed higher than sound speed is called supersonic aerodynamics, and the study of flight speed around sound speed is called transonic
aerodynamics. When intercontinental missiles and spacecraft return to the
atmosphere, their speed will be more than ten times of the sound speed in
a short time at first. This kind of flight is called hypersonic flight. Generally speaking, the hypersonic flight is defined as a flight with a speed greater
than five times the sound speed, and the one dealing with this problem is
called hypersonic aerodynamics. In addition, we also study the rarefied gas
mechanics in the outer atmosphere, magnetohydrodynamics of ionization in
the outer atmosphere, etc.
2.2 Low-Speed Airfoil Flow
First of all, humans have realized the dream of flying by air buoyancy based
on balloons, but it is not enough to fly only by balloons. Birds and many
aircraft do not fly by air buoyancy, but by the relative motion of air around
them. So people gradually realize that when the air around the wing has
relative motion, it can produce lift, and the lift is much greater than the
buoyancy. The second is that the object moving in the air must overcome
air resistance, so the concept of aircraft dynamics is introduced. The third is
that the concept of force multiplying distance, i.e., the concept of moment,
is introduced when the aircraft is able to maintain stable flight in the air. So
these three concepts lay the foundation for us to realize real flight (as shown
in Fig. 2.9).
Aircraft research starts from imitating birds, which is called imitation birds.
Later, people separated the power from the lift, and then there appeared fixedwing aircraft. The so-called fixed wing is that the lift surface is fixed, so the
earliest fixed wing is the glider. A glider is an unpowered aircraft, which generates lift through its wings. In addition, when the aircraft is equipped with an