### 1. Wheeled landing gear
* * Common situations * *:
* * * Aircraft with flat ground and need to start * *: Wheeled landing gear has become the standard configuration of most fixed-wing aircraft (such as civil passenger aircraft, military fighters, transport aircraft, etc.) because of its ability to provide stable support and good maneuverability on the ground. These aircraft need to take off and land on the ground runway, and the wheeled landing gear can ensure the stability and safety of the aircraft in these processes.
* * * Various runway conditions * *: The wheeled landing gear has been carefully designed to adapt to various runway conditions, including dry runway, wet runway and icy runway. Equipped with different tires and braking systems, the wheeled landing gear can ensure the normal operation of the aircraft under different conditions.
### 2. Buoy landing gear
* * Common situations * *:
* * * Seaplane * *: The pontoon landing gear is specially designed for seaplanes, enabling them to take off, land and glide on the water. This landing gear is usually composed of pontoons, connectors and retraction mechanisms, which can provide enough buoyancy and stability to ensure the safe operation of the aircraft on the water. Seaplanes are widely used in marine monitoring, rescue, fishery patrol and other fields.
### 3. Rotor type (a special type of sled landing gear)
* * Common situation * * (Although the rotor type is not a direct landing gear type, here we take the application of sled landing gear in helicopters as an example):
* * * Helicopter * *: Helicopters are usually equipped with sled landing gear, which has low ground pressure and good terrain adaptability. The sled landing gear enables the helicopter to land and take off on uneven ground, snow and even swamp and other complex terrain. In addition, the sled landing gear also has a certain shock absorption function, which can protect the helicopter from impact when landing.
* * * Aircraft that do not need to start and fly * *: In addition to helicopters, some small or special-purpose fixed-wing aircraft may also use sled landing gear. These aircraft usually do not need a long runway to take off and land, and the sled landing gear can provide enough support and stability to meet their operational needs.
To sum up, different types of landing gear will be more common under certain circumstances. Wheeled landing gear is suitable for fixed-wing aircraft with flat ground and need to start; Buoy landing gear is specially designed for seaplanes; The rotor-type (or the application of sled landing gear in helicopters) is common in helicopters and other aircraft that do not need long runways to fly. The design and application of these landing gear types fully consider the operating environment and design requirements of the aircraft to ensure the safety and stability of the aircraft.
