undercarriages

Undercarriage is the assembly of parts that support and propel a vehicle from below. The term is used across transportation domains, including aircraft, trains, and road vehicles, as well as some industrial machinery. In general, it includes the structural elements and mechanical systems located beneath the main body that bear weight, enable movement, and protect critical components from ground contact.

In aviation, undercarriage refers to the landing gear, which supports the aircraft on the ground and during takeoff and landing. The gear typically comprises a strut or oleo-pneumatic shock absorber, wheels with brakes, and a retraction mechanism on many airplanes. It may be fixed or retractable to reduce drag; most modern airliners use a tricycle arrangement with a nose gear, while some smaller aircraft or historical designs use tail or tandem configurations.

In rail transportation, the undercarriage denotes the bogies or trucks that carry the car body and provide the running gear. Each bogie houses wheels and axles, and incorporates suspension, braking equipment, and attachments for couplers. The undercarriage is designed to smooth out track irregularities, distribute heavy loads, and allow safe braking and acceleration.

For road vehicles, the undercarriage is the bottom portion of the vehicle, including the chassis or frame, suspension, drivetrain components, exhaust system, fuel lines, and protective underbody shields. It is designed to withstand road hazards, support weight distribution, and minimize aerodynamic drag.

Because it bears structural loads and supports safety-critical systems, the undercarriage requires regular inspection for wear, corrosion, leaks, and damage. Maintenance may involve lubrication, brake servicing, alignment checks, and protection of exposed components.