AIRCRAFT STRUCTURE IN THE EMPENNAGE

STRUCTURE IN THE EMPENNAGE

The stabilizers and the control surfaces of an airplane are constructed in a manner similar to the wings but wings but on a much smaller scale. They usually include one or more main longitudinal members (spare) and ribs attached the fuselage or may be a separate member which is both adjustable and removable.

The horizontal stabilizers often appear as the forward part of a wing, with the elevator serving as the rear part. Usually the airfoil section is that is, it has the same degree of chamber for both top and bottom.

STABILIZERS STRUCTURE

The internal structure consists of two main spars which extend the full length of the span. At the rear is an auxiliary spar to which four hinges are riveted to provide for installation of the elevators.

The principal structural members of the unit are rear spars and the ribs. The outside of the unit is covered with sheet-aluminum alloy, which adds considerably to the strength/the center section, which is within the fuselage. See Figure 2.9

 

Figure 2.9: Structures in empennage 

CONTROL SURFACE CONSTRUCTION

Control surfaces are:

a)                 Ailerons

b)                 Elevators

c)                  Rudders

d)                 Flaps & Slats

e)                 Spoilers

Construction structures of the control surfaces are basically same as the wings having attachment fittings to the main planes or tail planes or fins as applicable.

2.9   DOOR CONSTRUCTION

The doors for aircraft are usually constructed of the same materials used for the other major components.

Typically, the main framework of a door consists of:

a)                 A doorframe which is a strong and rigid sheet-metal structure

b)                 A sheet-metal outer skin which is riveted to the doorframe

The doors for a pressurized airliner must be much stronger and much more complex than the door for a light airplane. Typical of a door for the main cabin of a jet airliner is that the door consists of a strong framework of aluminum alloy to which is riveted a heavy outer skin formed to the contour of the fuselage. At the top and the bottom edges of the door are hinged gates that make it possible, in effect, to decrease the height of the door so it can be swung outward through the door opening.

The hinging and controlling mechanism of the door is rather complex in order to provide for the necessary maneuvering to move the door outside the airplane when loading and unloading passengers. For safety in a pressurized airplane, the door is designed to act as a plug fir the door opening and the pressure in the cabin seats the door firmly in place. To accomplish this, the door must be larger than its opening and must be inside the airplane with pressure pushing outward. This prevents the rapid decompression of the cabin that could occur if the door should be closed from the outside and the securing mechanism should become unlatched.

The doors and special exits for passenger carrying aircraft must conform to certain regulations designed to provide for the safety and well being of passengers. The FAA establishes these regulations, and they must be followed in the design and manufacture of all certificated aircraft for passengers.

The requirements for emergency exits for transport category airplanes are classified according to size and arrangement. The classifications are as follows:

Type 1 : A rectangular opening not less than 24 in wide by 48 in high with corner radii not less that one third the width of the exit. On each side of the fuselage must be located in the aft portion of passenger compartment unless the configuration of the airplane is such that some other location could afford a more effective means of passenger evacuation. All type-1 exits are floor level exits.

Type II :  A rectangular opening not less than 20 in (50.8 cm) wide by 44 in (112 cm) high with corner radii not greater than one-third the width of the exit. Unless type-I exits are required. one type-II exit on each side of the fuselage must be located in the aft portion of the passenger compartment except where the configuration of the airplane  is such that some other location would afford a more effective means of passenger evacuation. Type-II exit must be floor-level exits unless located over the wing, in which case they must have a step-up  inside the airplane of not more than 10 in (25.4 cm) and a step-down outside the airplane of not more than 17 in (42.18 cm).

Type-III : A rectangular opening not less than 20 in (50.8 cm) wide by 36 in (91.44 cm) high, with corner radii not greater than one-third the width of the exit, located over the wing a step-up inside the airplane of not more than 20 in (50.8 cm) and  a step-down outside the airplane of not more than 27 in (68.58 cm).

Type-IV : A rectangular opening not less than 19 in (48.26 cm) wide by 26 in (66.04 cm)high with corner radii not greater than one-third the width of the exit, located over the wing with a step up inside the airplane of not more than 29 in (72.66 cm) and a step-down outside the airplane of not more than 36 in (91.44 cm).