How It Works: Trailing-Link Landing Gear

A deeper look into how landing gear does its job.

landing gear
A shock absorber connected to the flex joint at an angle creates the gear's give. The flexible L-shaped joint is the heart of a trailing-link gear system.Bryan Christie Design

Landing gear gets as little respect as that old comedian Rodney Dangerfield — not much, really, which is surprising when you consider that almost everyone seems to measure the quality of the flight by the smoothness of the touchdown. That final transition that turns a flying airplane into a taxiing one, even when the distance to the surface is just a few feet, can impose huge impact loads on an airplane if it’s not handled well, something that poses a challenge to ­designers. That’s why the landing gear is ­always so beefy. But even the sturdiest traditional landing gear design can’t cover up a botched flare that’s been known to smash passengers’ teeth together.

Smoothing Out the Bumps

An airplane built with a trailing-link landing gear system, where the gear itself functions like an extra shock absorber, smooths even the hardest arrivals into minor vibrations to the passengers.

A traditional landing gear is built around a single vertical strut with the wheels at the bottom, a setup that guarantees a solid arrival is transmitted directly to the cabin floor. The rather unique L-shaped trailing-link gear, however, functions like a lever that uses an angular shock absorber to squelch the hardest knocks long before they reach the passenger compartment. Think about this kind of gear as the difference between settling down on a regular living room couch versus one with coil-spring cushions — it has some give to it.

A typical trailing-link landing gear consists of an L-shaped, flexible arm ahead of the wheel that is connected to an oleo strut — an air-oil shock absorber that cushions the landing impact and damps vertical oscillations. As the strut compresses, so too does the air, but the viscosity of the oil damps the rebounding tendency. Besides being stronger than straight oleo struts, trailing-link gear systems are also more forgiving of botched landings.

There’s enough of a difference between traditional and trailing-link landing gear that anyone might wonder why trailing link hasn’t simply become the default on all airplanes, especially when you realize trailing-link gear is easier to repair. Changing a shock absorber on this kind of gear is easier than on a straight-leg gear because the mechanic doesn’t need to remove the entire wheel assembly to do the job.

Some manufacturers still choose the gear system cautiously, however, because it tends to be heavier than its counterpart. Trailing-link gear also means more moving parts to lubricate. Most importantly, the way the wheels hang on a trailing-link system often complicates the gear retraction process.