The tail group

A. In order to provide the necessary stability airplanes are fit­ted with a tail unit (a tail group, empennage) which usually consists of the horisontal tail surfaces — stabiliser and elevators and the verti­cal surfaces — fin and rudder. The stabilizer and the fin are fix­ed portions, the elevator and the rudder are movable.

B. A movable control surface called an elevator is hinged to the rear of the tail plane. It is intended to control the altitude of the aircraft in flight. It can be deflected upwards or downwards. Moving up the elevator reduces its angle of attack and creates a down load on the tail which raises the nose of the aircraft.

C. In order to secure directional stability the fin is used which is the vertical fixed control surface at the rear of the fuselage. The action of the vertical surface is quite clear. Since it has agreat lever arm from the airplane's centre of gravity the vertical surface is able to stabilize the directional motion of the plane. Directional control of the airplane is achieved by means of the rudder, which is a movable vertical surface hinged to the rear of the fin. It can be moved to right or left or retained in the neutral position in line with the fin.

D. When the pilot needs to change his flight direction towards the right (or starboard) he moves the rudder to the right. The reaction of the stream on the surface produces a couple about the centre of gravity and the nose of the aircraft is turned to star­board. If it is necessary for the pilot to control the altitude of the aircraft and cause the nose to rise or fall this is done by means of the elevator.

E. In addition to the principal control surfaces there are some auxiliary ones such as trimming tabs (trimmers) which represent small adjustable areas arranged near the trailing edges of the movable surfaces. They are used to produce constant control de­flections to hold the airplane in a certain attitude of flight. They are adjustable from the cockpit.

F. There is also a dorsal fin placed along the upper side of the aft portion of the fuselage body.

G. On large fast airplanes it is usually necessary to provide the movable surfaces with some area called balance area. It re­duces the hinge moment needed to deflect the surface. This is often required because the hinge moment increases with size and speed. This dynamic balancing is one of the precautions taken to avoid flutter, a violent vibration of a wing or control surface.

H. The structure of the tail plane as well as that of a wing consists of longitudinal and transverse structural elements called spars and ribs.

Comprehension Check

1. Match the given titles with the corresponding paragraphs. Watch out! There is an extra title.

1. balance area

2. tail unit arrangement

3. tail unit function

4. tail plane structure

5. elevator

6. dorsal fin

7. rudder

8. lifting force

9. trimmers

2. Guess what it is:

1) This component of the aircraft provides the necessary stability.

2) The structure of the tail plane consists of these members.

3) It is used in the tail group to avoid flutter and violent vibration.

4) They are arranged near the trailing edges of the movable surfaces.

5) When the pilot needs to change the flight direction he moves it to the right or left.

6) It is a vertical fixed surface of the tail unit.

7) It is used to produce constant control deflections.

8) This part is to stabilize the directional motion of the airplane.

9) It is a horizontal movable plane. It can be deflected upwards and downwards.

10) This part of the tail group is placed along the upper side of the aft portion of the fuselage body.

11) These portions are used when the pilot is to cause the nose to rise or to fall.

12) This is used to reduce the hinge moment which increases with size and speed.

3. In the text find the definition of flutter.

Дата добавления: 2015-07-11