Definition
A small wheel mounted at the rear of an airplane's fuselage that supports the tail when the aircraft is on the ground. It is the third point of contact in a conventional landing gear arrangement, where the two main wheels sit forward of the center of gravity and the tail wheel sits aft. The tail wheel is usually steerable through the rudder pedals and often includes a mechanism that allows it to swivel freely (caster) when needed for tight ground maneuvering.
Plain English
A small wheel under the back of the airplane that holds the tail up off the ground when the airplane is parked, taxiing, taking off, or landing. On airplanes built this way, the tail sits low and the nose points up while on the ground.
Context Anchor
You will encounter this term when reading about conventional landing gear, ground handling, taxiing, takeoff, and landing in tailwheel airplanes.
Why Pilots Care
An airplane with a tail wheel handles very differently on the ground than one with a nose wheel. The center of gravity sits behind the main wheels, which makes the airplane prone to swinging sideways during takeoff and landing (a ground loop) if the pilot is not actively flying it with rudder. Tail wheel airplanes require specific training and an endorsement to fly solo as pilot in command.
Grounding Statement
Picture a small airplane sitting slightly nose-up on the ramp, with two main wheels under the front part of the airplane and a small wheel holding up the tail.
Intuition Check
Do not think of a tail wheel as just a small rear support wheel with no effect on handling. In a tailwheel airplane, that rear wheel is part of why the airplane behaves differently on the ground than a nosewheel airplane.
Example Sentence 1
Before flying the Piper Cub solo, she had to log several hours of dual instruction and receive a tail wheel endorsement from her instructor.
Example Sentence 2
Before flight the mechanic inspected the tail wheel tire for proper pressure and signs of wear.