thumb|upright=1.14|A [[Cessna 150 converted to taildragger configuration by installation of an aftermarket modification kit]]
Conventional landing gear, also known as tailwheel-type landing gear or taildragger,
Taildraggers are the default undercarriage arrangements of almost all early aircraft up to the first half of the 20th century and the term "conventional" persists for this historical reason, but all modern jet aircraft and most modern propeller fixed-wing aircraft use tricycle landing gears instead, which have a single front gear (nose gear) and two aft main gears.
History
thumb|Tailwheel detail on a [[de Havilland Tiger Moth|Tiger Moth biplane]]
thumb|Like many attack helicopters, the [[AgustaWestland Apache has a tailwheel to allow an unobstructed arc of fire for the gun.]]
In early aircraft, a tailskid made of metal or wood was used to support the tail on the ground. In most modern aircraft with conventional landing gear, a small articulated wheel assembly is attached to the rearmost part of the airframe in place of the skid. This wheel may be steered by the pilot through a connection to the rudder pedals, allowing the rudder and tailwheel to move together.
Before aircraft commonly used tailwheels, many aircraft (like a number of First World War Sopwith aircraft, such as the Camel fighter) were equipped with steerable tailskids, which operate similarly to a tailwheel. When the pilot pressed the right rudder pedal—or the right footrest of a "rudder bar" in World War I—the skid pivoted to the right, creating more drag on that side of the plane and causing it to turn to the right. While less effective than a steerable wheel, it gave the pilot some control of the direction the craft was moving while taxiing or beginning the takeoff run, before there was enough airflow over the rudder for it to become effective.
Another form of control, which is less common now than it once was, is to steer using "differential braking", in which the tailwheel is a simple, freely castering mechanism, and the aircraft is steered by applying brakes to one of the mainwheels to turn in that direction. This is also used on some tricycle gear aircraft, with the nosewheel being the freely castering wheel instead. Like the steerable tailwheel/skid, it is usually integrated with the rudder pedals on the craft to allow an easy transition between wheeled and aerodynamic control.
Advantages
thumb|right|[[Douglas DC-3, a taildragger airliner]]
The tailwheel configuration offers several advantages over the tricycle landing gear arrangement, which make tailwheel aircraft less expensive to manufacture and maintain.
Disadvantages
thumb|A nose-over accident with [[Polikarpov I-15 bis]]
thumb|A replica World War 1 [[Royal Aircraft Factory F.E.2|F.E.2 fighter. This aircraft uses a tailskid. The small wheel at the front is a safety device intended to prevent nose-over accidents.]]
The conventional landing gear arrangement has disadvantages compared to nosewheel aircraft. After the first four prototype Me 262 V-series airframes were built with retracting tailwheel gear, the fifth prototype was fitted with fixed tricycle landing gear for trials, with the sixth prototype onwards getting fully retracting tricycle gear. A number of other experimental and prototype jet aircraft had conventional landing gear, including the first successful jet, the Heinkel He 178, the Ball-Bartoe Jetwing research aircraft, and a single Vickers VC.1 Viking, which was modified with Rolls-Royce Nene engines to become the world's first jet airliner.
thumb|The sole surviving Yak-15. Vadim Zadorozhny Technical Museum, Moscow, 2012
Rare examples of jet-powered tailwheel aircraft that went into production and saw service include the British Supermarine Attacker naval fighter and the Soviet Yakovlev Yak-15. Both first flew in 1946 and owed their configurations to being developments of earlier propeller powered aircraft. The Attacker's tailwheel configuration was a result of it using the Supermarine Spiteful's wing, avoiding expensive design modification or retooling. The engine exhaust was behind the elevator and tailwheel, reducing problems. The Yak-15 was based on the Yakovlev Yak-3 propeller fighter. Its engine was mounted under the forward fuselage. Despite its unusual configuration, the Yak-15 was easy to fly. Although a fighter, it was mainly used as a trainer aircraft to prepare Soviet pilots for flying more advanced jet fighters.
Monowheel undercarriage
right|thumb|A Schleicher ASG 29 glider shows its monowheel landing gear
A variation of the taildragger layout is the monowheel landing gear.
To minimize drag, many modern gliders have a single wheel, retractable or fixed, centered under the fuselage, which is referred to as monowheel gear or monowheel landing gear. Monowheel gear is also used on some powered aircraft, where drag reduction is a priority, such as the Europa XS. Monowheel power aircraft use retractable wingtip legs (with small castor wheels attached) to prevent the wingtips from striking the ground. A monowheel aircraft may have a tailwheel (like the Europa) or a nosewheel (like the Schleicher ASK 23 glider).
Training
Taildragger aircraft require more training time for student pilots to master. This was a large factor in the 1950s switch by most manufacturers to nosewheel-equipped trainers, and for many years nosewheel aircraft have been more popular than taildraggers. As a result, most Private Pilot Licence (PPL) pilots now learn to fly in tricycle gear aircraft (e.g. Cessna 172 or Piper Cherokee) and only later transition to taildraggers.
Normal landings are done by touching all three wheels down at the same time in a three-point landing. This method does allow the shortest landing distance but can be difficult to carry out in crosswinds,