Air International 1999-11
B.Walters - Happy landings /Technology/
Although the F-16 is one of the world's most potent combat aircraft and was one of, if not the, first combat aircraft to feature a side-stick controller, it has a reputation for being easy to fly. Its Achilles’ heel is the narrow undercarriage which makes it something of a handful to land, particularly in crosswinds.
Some indication of the punishment taken by an undercarriage may be appreciated by this photograph of an Airbus A340 at touch-down. Nor is this particularly severe, there are far harsher landings - higher weight aircraft, higher landing speeds, cross-winds and greater rates of descent (eg carrier-borne aircraft).
An Airbus A340 main undercarriage undergoing retraction tests. The presence of a figure in the photograph gives an indication of the size of the gear.
Russian airliners have traditionally been designed to operate from semi-prepared airstrips. One of their distinguishing features has been a low footprint pressure, achieved by a large number of wheels. Even by Russian standards, the An-225 has an impressive undercarriage, the main assembly having no less than 28 wheels.
Undercarriages are subjected to a number of structural and environmental tests during development, including drop tests. Rubber is burned off the tyre as this A320 main gear is slammed onto the simulated runway.
One of the more unusual solutions proposed for aircraft operating from unprepared airstrips was the Bonmartini Track Gear. Invented by Count G Bonmartini, it was tested on a Piper Cub but, perhaps not surprisingly, never went into production.
Messier-Dowty's first undercarriage was fitted to the Farman 190 in 1927.
Unquestionably the most demanding environment for an undercarriage is that imposed by carrier operations. Not only does the gear have to conform to the 'usual' weight, geometry and reliability constraints; it also has the additional high shock loads imposed during both take-off (nose wheel) and landing (main gear). Note the sturdiness of the Rafale nose undercarriage.