Landing gear

The landing gear forms the principal support of the airplane on the surface. The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations, or skis for landing on snow.

Figure 5: The landing gear supports the airplane during the takeoff run, landing, taxiing, and when parked.

The landing gear on small airplanes consists of three wheels - two main wheels, one located on each side of the fuselage, and a third wheel, positioned either at the front or rear of the airplane. Landing gear employing a rear-mounted wheel is called a conventional landing gear. Airplanes with conventional landing gear are often referred to as tailwheel airplanes. When the third wheel is located on the nose, it is called a nosewheel, and the design is referred to as a tricycle gear. A steerable nosewheel or tailwheel permits the airplane to be controlled throughout all operations while on the ground.

Tricycle landing gear airplanes

A tricycle gear airplane has three main advantages:

1. It allows more forceful application of the brakes during landings at high speeds without resulting in the airplane nosing over.
2. It permits better forward visibility for the pilot during takeoff, landing, and taxiing.
3. It tends to prevent ground looping (swerving) by providing more directional stability during ground operation since the airplane´s center of gravity (CG) is forward of the main wheels. The forward CG, therefore, tends to keep the airplane moving forward in a straight line rather than ground looping.

Nosewheels are either steerable or castering. Steerable nosewheels are linked to the rudders by cables or rods, while castering nosewheels are free to swivel. In both cases, you steer the airplane using the rudder pedals.

However, airplanes with a castering nosewheel may require you to combine the use of the rudder pedals with independent use of the brakes.

Tailwheel landing gear airplanes

On tailwheel airplanes, two main wheels, which are attached to the airframe ahead of its center of gravity, support most of the weight of the structure, while a tailwheel at the very back of the fuselage provides a third point of support. This arrangement allows adequate ground clearance for a larger propeller and is more desirable for operations on unimproved fields.

Figure 6: Tailwheel landing gear.

The main drawback with the tailwheel landing gear is that the center of gravity is behind the main gear. This makes directional control more difficult while on the ground. If you allow the airplane to swerve while rolling on the ground at a speed below that at which the rudder has sufficient control, the center of gravity will attempt to get ahead of the main gear. This may cause the airplane to ground loop.

Another disadvantage for tailwheel airplanes is the lack of good forward visibility when the tailwheel is on or near the surface. Because of the associated hazards, specific training is required in tailwheel airplanes.

Fixed and retractable landing gear

Landing gear can also be classified as either fixed or retractable. A fixed gear always remains extended and has the advantage of simplicity combined with low maintenance. A retractable gear is designed to streamline the airplane by allowing the landing gear to be stowed inside the structure during cruising flight.

Figure 7: Fixed and retractable gear airplanes.

Brakes

Airplane brakes are located on the main wheels and are applied by either a hand control or by foot pedals (toe or heel). Foot pedals operate independently and allow for differential braking. During ground operations, differential braking can supplement nosewheel/tailwheel steering.