Accommodation Galway - Aircraft Undercarriages

This performs two main functions: All aircraft need an undercarriage, with very few exceptions.

O It absorbs the shock of landings and provides smooth taxying. O It supports the aircraft on the ground.

So it must be as small and light as possible, the undercarriage serves no function at all during flight. Including braking and side loads, it must withstand the loads that will occur during all movements on the ground. And the aircraft taxies without any tendency to float at normal speeds, so that the drag on the take-off run is minimised, it must support the aircraft in the desired attitude on the ground. However, there is more to an undercarriage than just carrying out these functions.

For different installations, there are several different kinds of main unit, however. Giving low drag during the ground run, because it supports the aircraft in a horizontal attitude, the tricycle layout is preferred, except some light aircraft, for almost all aircraft. The type chosen depends on the type of aircraft and its intended use. There are many different layouts of undercarriage in current use.

This will depend on the weight of the aircraft and the way in which the undercarriage is to be retracted. And their arrangement, the designer's main concern when choosing the type of main unit is how many wheels the unit will have.

Aircraft wheels.

And a dual nose-wheel unit, each with four wheels, the Boeing 747 has 18 wheels - four main units. This also increases safety if a tyre bursts on landing. The contact pressure of the undercarriage is reduced, by having the weight spread over a greater number of wheels. Leading to a considerable increase in the damage done to runways, the loading on each wheel increases, as aircraft become heavier. Or four or more wheels, a pair of wheels side by side or in tandem, each main-wheel unit may contain a single wheel.

The Fokker F28 and many turboprop aircraft, as well as medium-sized transports such as the Boeing 727 and 737, which is used on many fighters, the simplest type is the twin-wheel side-by-side (or dual) arrangement, apart from the single-wheel main unit.

To allow a shallow well to be used, the bogey can be held parallel to the ground during retraction, if necessary. And the bogey can be rotated to fit into awkward spaces, it is easily capable of retracting forwards or sideways. 767 and the Airbus series are just a few examples of the many aircraft using this arrangement, 757, the Boeing 747. Since it gives a good combination of low ground pressure and relatively easy retraction arrangements, this is widely used on commercial aircraft. Also known as a bogey or truck, by far the most common arrangement of main units for large aircraft is the dual-tandem layout.

Retracting undercarriages.

So the shape of the main units can become quite complex, landing and taxying, the points of contact of the undercarriage with the ground must be far enough apart to make the aircraft stable during take-off, however. They must be stowed in the fuselage, otherwise. And it is quite common to retract the main legs into these nacelles, twin turboprop aircraft have engine nacelles on the wing. Which increases weight, this would require a long undercarriage, with high-wing aircraft. Which is quite straightforward in most cases, the main units of low-wing aircraft are usually retracted into the wing. One of the main reasons for the particular choice of undercarriage arrangement is the problem of retraction.

And limit damage to runways and taxiways, the number of wheels in undercarriages must be increased to keep ground pressures reasonably low, as increasingly large aircraft are developed to take maximum advantage of crowded airspace, however. But the more complex the type the less commonly it is used, dual-twin tandem and twin tricycle, dual twin, including tri-twin tandem, there are a number of other wheel arrangements in use. Without pentrating into the load space, the units also retract into a small space. This is particularly useful where the aircraft is used to transport vehicles. Among the advantages of this design are excellent rough-field performance and the ability to `kneel' the aircraft by partially retracting the undercarriage to reduce the slope of loading doors. And of course the widest load that can be carried is often restricted by the narrowest point in the load space, this gives a constant width of cargo area in the fuselage. Because the undercarriage is easily retracted into panniers - bulges on the side of the aircraft, it is particularly useful for high-wing medium-sized transport aircraft. Sometimes sharing a common horizontal shock absorber, which comprises two or three levered legs in tandem on each side of the fuselage, a variation of the tandem arrangement is the jockey unit, however. The tandem undercarriage is rarely used.

And this can result in some rather awkward-looking undercarriage arrangements, many combat aircraft carry under-fuselage stores. The undercarriage must not interfere with these stores either in its extended position or during retraction. Which is the requirement to clear stores fitted under the fuselage, the main undercarriage has another limitation, with combat aircraft.

And ensures that the wheel is straight for landing, at the same time it must have a safety mechanism that prevents the nose wheel from being turned after retraction. And a reasonable turn radius is needed for ground maneuvering, the undercarriage design will normally allow for steering.

EASA/FAA wheel repair.

The position may be a compromise, as always, the designer will often be limited by the available structure and. But the load must not be so high as to require the nose leg and associated structure to be unnecessarily strong and heavy, the steering may not be effective, if it is too lightly loaded. The nose leg must also be positioned carefully because its distance from the main units affects the proportion of the total weight that it carries. Perhaps even more than a full circle, the aircraft may be prone to ground loops - a sudden violent turn to left or right, if they are too far apart. Especially in side winds and during taxying, the aircraft may tend to roll sideways on the ground, if the main units are not sufficiently wide apart. Which could cause the nose leg to collapse, the aircraft will pitch forward violently during landing, if they are too far aft. The aircraft may tip during loading and taxying, if they are too far forward. Particularly the main units, the position of the undercarriage units is very important. But not to the same extent as it would without this feature, of course, the aircraft will still be damaged. Which will fail and allow the collapse of the undercarriage before the load rises beyond a safe level, shear pins are fitted. There is a risk that considerable damage may be done to the structure that supports the undercarriage, if the undercarriage hits a large obstacle that the aircraft wheels cannot climb.

Airbus Boeing Tucano Honeywell Goodrich and Dunlop aircraft wheels repaired reclaimed and modified can be done at a choice of approved repair facilities. Most EASA FAA wheel repair is mercifully routine and not as a result of trauma.