Aircraft Systems and Structures

Aircraft Structural Components

• 821 is the forward cargo door (right side), 821AR is an access panel on the forward cargo door, and 821AZ is an access panel on the forward cargo door liner.

Reference Datum

• A reference datum or datum is established by the manufacturer for each aircraft model.
• The datum is an imaginary vertical plane or line that sits at a right angle to the aircraft's longitudinal axis.
• The datum is the point from which all horizontal measurements are taken, with the aircraft in a level flight attitude.
• The location of all items, including equipment, tanks, baggage compartments, seats, engines, and propellers, is listed as being so many inches or millimeters from the datum.

Composite Skinning

• Composite skinning involves multiple layers of fiber impregnated and glued together with a resin matrix to form a thick fiber skin.
• Another method used to obtain strength from composite skins is bonding a thinner fiber or metal skin to a honeycomb core.

Aerodynamic Components

• The center wing section, or wing box, is one of the strongest areas in the aeroplane.
• In modern aircraft, the wing box is built of composite materials.
• The upper and lower surface panels and the spars of the wing are made entirely of the same composite material being used on the fuselage.

Cleaning Methods

• Wet washing removes oil, grease, or carbon deposits and most soils, with the exception of corrosion and oxide films.
• Dry washing is used to remove aircraft film, dust, and small accumulations of dirt and soil when the use of liquids is neither desirable nor practical.
• Polishing restores the luster to painted and unpainted surfaces of the aircraft and is usually performed after the surfaces have been cleaned.

Airframe Symmetry

• Checking the relative alignment and adjustment of an aircraft's main structural components is called a rigging check.
• Rigging involves two principal types of operations: aligning the aircraft structure and aligning control surfaces and controls.

Airframe Alignment

• The fuselage is aligned in assembly jigs at the time of manufacture.
• Fixed surfaces, such as wings, stabilizers, and tail booms, are aligned and assembled in jigs and fixtures to ensure correct shape and positioning of attachment fittings.

Pressure Bulkheads

• Pressure bulkheads are designed to withstand pressurization loads during flight.
• Forward and rear pressure bulkheads are used at the front and rear of pressurized aircraft.

Beams and Doublers

• Beams are long structural members in the airframe designed to support/carry heavy loads.
• A doubler is a piece of metal used to strengthen skin structure where a component is attached.

Struts

• A strut is a compression-resistant member made from steel tubing or heavy-walled aluminum alloy tubing.
• Struts keep beams or spars separated and combat compression loads.