Lofting coordinates are used for aircraft body measurements. The system derives from the one that was used in the

shipbuilding Shipbuilding is the construction of ships and other Watercraft, floating vessels. In modern times, it normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation th ...

lofting Lofting is a Technical drawing, drafting technique to generate curved lines. It is used in plans for streamlined objects such as aircraft and boats. The lines may be drawn on wood and the wood then cut for advanced woodworking. The technique can be ...

process, with longitudinal axis labeled as "stations" (usually fuselage stations, frame stations, FS), transverse axis as "buttocks lines" (or butt lines, BL), and vertical axis as "

waterline The waterline is the line where the hull of a ship meets the surface of the water. A waterline can also refer to any line on a ship's hull that is parallel to the water's surface when the ship is afloat in a level trimmed position. Hence, wate ...

s" (WL). The lofting coordinate frame is similar, but not the same as

aircraft principal axes An aircraft in flight is free to rotate in three dimensions: '' yaw'', nose left or right about an axis running up and down; ''pitch'', nose up or down about an axis running from wing to wing; and ''roll'', rotation about an axis running from nos ...

used to describe the aircraft flight. For the US-manufactured aircraft the ticks on the axes are labeled in

inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...

es, (for example, WL 100 is 100 inches above the base waterline).

Fuselage station

Fuselage stations are traditionally nonnegative, thus the origin is located at the

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

of the plane or, sometimes, ahead of it. When compared to the coordinates used for

aeromechanics Aeromechanics is the science about mechanics that deals with the motion of air and other gases, involving aerodynamics, thermophysics and aerostatics. It is the branch of mechanics that deals with the motion of gases (especially air) and their ef ...

, the fuselage stations are measured in the opposite direction than the ticks on the x-axis (and might not be aligned at all, if the wind-aligned coordinate system is used to describe the flight). Some manufacturers use the designation "body stations", with the corresponding abbreviation BS.

Waterline

Per the

US Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...

Airframe Maintenance and Repair Manual (1960), a horizontal waterline extends from the

nose cone A nose cone is the conically shaped forwardmost section of a rocket, guided missile or aircraft, designed to modulate oncoming fluid dynamics, airflow behaviors and minimize aerodynamic drag. Nose cones are also designed for submerged wat ...

of the aircraft to the

exhaust cone Exhaust, exhaustive, or exhaustion may refer to: Law *Exhaustion of intellectual property rights, limits to intellectual property rights in patent and copyright law **Exhaustion doctrine, in patent law ** Exhaustion doctrine under U.S. law, in ...

. The base line of the aircraft is designated as waterline 0 (zero). The location of this base line varies on different types of aircraft. However. the planes of all waterlines above and below the zero waterline are parallel. The waterline number (WL or W.L.) in the US is expressed in

es, values increase upwards. Two typical alignments for the base line are the tip of the nose (negative WL are possible) or the "nominal ground plane" (measurements will be nonnegative).

Butt line

Butt line ticks increase to the right of the pilot with the origin at the centerline. When compared to the (

right-handed In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to and causing it to be stronger, faster or more Fine motor skill, dextrous. The other hand, comparatively often the weaker, less dext ...

) aeromechanics coordinate systems, the direction of the butt line is opposite to the y-axis.

Other

Many other reference points are used, especially on a large aircraft: *

Aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement aroun ...

station (AS), distance from the inboard edge of an aileron; * Flap station (KS), distance from the edge of the flap; *

Nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

station (NS); *

Elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

station (ES); * Vertical stabilizer station (VSS).

References

Sources

* * * {{cite book , last=FAA , title=Aviation Maintenance Technician Handbook-Airframe , publisher=Aviation Supplies & Academics, Incorporated , year=2012 , isbn=978-1-56027-950-1 , url=https://books.google.com/books?id=nXSvVRQtumsC&pg=SA1-PA39 , access-date=2024-07-02 Aerospace engineering