Each main unit may contain one of the wheels the wheels, a pair of wheels on the side or in tandem, or four wheels and more. As aircraft become heavier, increasing the load on each wheel, resulting in a significant increase in damage to the track. By having the weight spread over a large number of wheels, reduces the pressure contact LG. also increase security if the Ban on landing. The Boeing 747 has 18 four-wheeled main units, each with four wheels and dual wheel unit.
Single units outside the main wheels, the most simple type is the twin-wheel arrangement-a-side (or double), used in many of the fighters, but also the means of transport such as the Boeing 727 and turboprop aircraft 737, Fokker F28 and many.
The most common main unit setup for large aircraft is now available-double in tandem, also known by the name of unidentified objects or trucks. It is widely used in commercial aircraft, because it gives a good combination of low pressure in the soil and setting the shrinkage is relatively easy. The Boeing 747, 757, 767 and Airbus series aircraft are a few examples of the many have used this arrangement. He can easily pull back to front or side, and the enemy can be rotated to accommodate in difficultspaces. If necessary, the enemy can be kept parallel with the ground during your depreciation, to allow the use of shallow wells.