飞行器系统概论

Whyflight vehicles fly in the air

Today we can see many flight vehicles fly in the air,airplanes,missiles,balloons,airships and so on.They have different uses .For example,airplanes are used to load people while missiles are used to attack the target. But,here we have a question:why can they fly in the air?

First,a flight vehicle has its own flight principles.The flight vehicle need forces to make it fly. The most important of all is aerodynamics.Aerodynamics are produced by the nearby air of a flying vehicle. Aerodynamics can be divided into three forces in three directions. They are lift to overcome the gravity, drag to block the flight vehicle and lateral force to make the flight vehicle slope.And of course, the flight vehicle has thrust itself, and this is the main force to make it forward. All these forces acted on the fight vehicle keep it balance in the air, so the flight vehicle can move smoothly. Another important action to the flight is moment. There are aerodynamic moments and thrust moment. Aerodynamic moments are also divided into three components named rolling moment, yawing moment, and pitching moment. Rolling moment makes the flight vehicle roll around its longitudinal axis. Yawing moment lets the flight vehicle roll around its vertical axis. Pitching moment makes the flight vehicle roll around its lateral axis. Thrust moments are produced by thrust when it does not pass through the mass center. All

these moments also need to be balanced when the flight vehicle flies in the air normally. If the flight vehicle wants to change direction or its velocity, it can change these forces and moments through its control surface such as rudder, elevator, and aileron.

Actually, a flight vehicle is very complex. Just having these principles, a flight vehicle is far to fly. Take a missile for example, to finish the specific tasks, it need a system. A missile system is to be as an overall body. It is mainly composed of the main five parts as follows. They are propulsion system, fuselage, guidance and control system, warhead and fuse system, and missile power supply.

Propulsion system is the device which takes the engine as the core to provide sufficient power for missile. Usually rocket engines such as solid and liquid engine, jet engine,like turbojet engine and ramjet engine and combination engine are used on the missiles.Guidance and control system is the general terms of instruments, devices and equipment which could lead and control the missile to fly to the target.Warhead and fuse on the missile is used to destroy and damage the target directly. For it is always at the head of the missile, we name it warhead customarily. Fuselage is the main body of the missile. It is composed of cabins, segments and aerodynamic surfaces such as wings, control planes and stabilizer. Missile power supply is the device which provides electrical energy to the subsystems on the missile.