fuselage station – buttock line -water line – aerodynamic balance – high lift device – large trans a/c wing

 Fuselage Station

Distances along the fuselage are known as stations and their number represent the distance in the units of the designers choice, ( usually Inches or Centimetres), from a fixed datum. The datum is usually at or about the nose of the aircraft and in some cases it may be a point in space in front of the aircraft ( measured forward from a specific position ).

Station numbers aft of the datum have positive values and station number forward of the datum have negative values.

Fuselage frames only require one station number, but small items or position have also to be located vrtically.

 

Buttock Lines or Butt Lines

Body buttock lines ( BL ) are measurements left or right vertical plane runing through the aircraft’s longitudinal axis. Expressed as LBL or RBL the may tu be used for fuselage locations, particularly in wide bodied aircraft and also wing location on smaller aircraft.

On large aircraft wings are also divided into reference planes to provide a means of identifying wing components the methods vary according to manufacturer and can either be measured in inches from the root rib datum and each rib being numbered from the root outwards or as wing station number and wing buttock lines.

W.STA Wing Station. A plane perpendicular to the wing set at 90° to leading edge WBL wing Buttock Line. A plane perpendicular to the wing and parallel to the body buttock line.

Stabilisers and even large control surfaces are treated in much the same way.

Most manufacturers will paint or stencil the location numbers on various structural elements. This assists in the determination of locations without the need to take measurements from the datums.

 

Water Line

Water Line is the vertical distance from the longitudinal Datum. This datum may be some convenient part of the fuselage, such as passenger cabin floor, or it may be the ground with the aircraft on it’s wheels. Water line measurements above the datum have positive values and those below have negative values.

Aerodynamic Balance

aerodynamics balance is provided to assist the pilot in moving the control surfaces. In general terms, aerodynamic balance is provided on control surfaces which are operated manually. An aircraft which has power operated controls with manual reversion will usually have some from of aerodynamic balance to assist the pilot when flying the aircraft manually.

Aerodynamic balance may take the form of a horn tip, balance tab or spring tab. These are dealt with in the ‘Basic Aerodynamics’ module.

 

High Lift Device 

Aileron And Spoiler Attachments

Flying control such as ailerons and spoilers are connected to the wing rear spar by multiple hinge fittings. The hinge fittings may be mounted on the spar itself, or on special ribs which transfer the loads to the spar, depending on the size of the wing. Actuators are attached to strenghened structural members.

Flap Attachments

The attachment of trailling edge flaps will depend on the type and size of the surface used. Most large aircraft use extension flaps which move rearward as well as down. They generally travel on flap tracks. These are large forged steel or titanium beams suspended from the wing auxiliary spar, rear spar and mid spar or underwing fitting depending on the design.

Leading edge flaps and slats and their actuators are attached to the front spar either directly or through the leading edge ribs and structure.

 

Large Transport Aircraft Wings

The main frame of a modern transport wing consist of spars, ribs, bulkheads, and skin panels with spanwise stiffening members and uses failsafe construction technique.

The wing structure may include non-metallic composite components, adhesive bonding of metal structures as well as conventional metal alloys and fasteners. The wing must be strong enough to carry its own weight togrther with the weight of the fuel in the wings, the weight of engines attached to the wings and the forces imposed by the flight controls. These forces vary a great deal both in direction and in mangnitude as the aircraft’s operations change from moving on the ground, flying then returning to the ground.

Large transport aircraft wings consist of two or more main spars, with intermediate spars used between the main spars in some designs. The intermediate spars assist the main spars in carrying the operational loads. The front and rear spars provide the main supporting structure for fittings attaching the fuselage, engine pylons, main landing gear, and flight surface to the wing. Located between the spars are ribs, which, depending upon their design, may be used for purposes such as fuel bulkheads and the support of control surfaces as well  as providing the airfoil shape of the wing. The auxiliary structure of the wing include the wing tips, leading edge, and trailing edge. The leading edge of the wing incorporates leading-edge ribs, structural reinforcement members, and attachment points for components such as slats and leading-edge flaps.