Conventional Undercarriage
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Conventional landing gear, or tailwheel-type landing gear, is an
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
undercarriage consisting of two main wheels forward of the
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
and a small wheel or skid to support the tail.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 133. Aviation Supplies & Academics, 1997. From the Ground Up, 27th edition, page 11 The term taildragger is also used, although some argue it should apply only to those aircraft with a tailskid rather than a wheel. The term "conventional" persists for historical reasons, but all modern
jet aircraft A jet aircraft (or simply jet) is an aircraft (nearly always a fixed-wing aircraft) propelled by jet engines. Whereas the engines in propeller-powered aircraft generally achieve their maximum efficiency at much lower speeds and altitudes, je ...
and most modern propeller aircraft use
tricycle gear Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle g ...
.


History

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 The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system. Airframe design is a field of aerospa ...
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 A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. C ...
fighter) were equipped with steerable tailskids, which operate similar 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 Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...
", in which the tailwheel is a simple, freely
caster A caster (or castor) is an undriven wheel that is designed to be attached to the bottom of a larger object (the "vehicle") to enable that object to be moved. Casters are used in numerous applications, including shopping carts, office chairs, t ...
ing mechanism, and the aircraft is steered by applying brakes to one of the mainwheels in order 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

The tailwheel configuration offers several advantages over the
tricycle landing gear Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle g ...
arrangement, which make tailwheel aircraft less expensive to manufacture and maintain. * Due to its position much further from the
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
, a tailwheel supports a smaller part of the aircraft's weight allowing it to be made much smaller and lighter than a nosewheel. As a result, the smaller wheel weighs less and causes less
parasitic drag Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of ...
. * Because of the way airframe loads are distributed while operating on rough ground, tailwheel aircraft are better able to sustain this type of use over a long period of time, without cumulative airframe damage occurring. * If a tailwheel fails on landing, the damage to the aircraft will be minimal. This is not the case in the event of a nosewheel failure, which usually results in a
prop strike In aviation, a propeller strike, or prop strike, also called a sudden stoppage, is an accident in which an aircraft's propeller contacts any object and is forcibly stopped or slowed. Propeller strikes can be the result of the propeller contacting ...
. * Due to the increased propeller clearance on tailwheel aircraft less stone chip damage will result from operating a conventional geared aircraft on rough or gravel airstrips, making them well suited to
bush flying Bush flying refers to aircraft operations carried out in the bush. Bush flying involves operations in rough terrain where there are often no prepared landing strips or runways, frequently necessitating that bush planes be equipped with abnormally ...
. * Tailwheel aircraft are more suitable for operation on skis. * Tailwheel aircraft are easier to fit into and maneuver inside some hangars.


Disadvantages

The conventional landing gear arrangement has disadvantages compared to nosewheel aircraft. *Tailwheel aircraft are more subject to "nose-over" accidents due to incorrect application of brakes by the pilot. *Conventional geared aircraft are much more susceptible to ground looping. A ground loop occurs when directional control is lost on the ground and the tail of the aircraft passes the nose, swapping ends, in some cases completing a full circle. This event can result in damage to the aircraft's undercarriage, tires,
wingtip A wing tip (or wingtip) is the part of the wing that is most distant from the fuselage of a fixed-wing aircraft. Because the wing tip shape influences the size and drag of the wingtip vortices, tip design has produced a diversity of sha ...
s, propeller and engine. Ground-looping occurs because, whereas a nosewheel aircraft is steered from ahead of the
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
, a taildragger is steered from behind (much like driving a car backwards at high speed), so that on the ground a taildragger is inherently unstable, whereas a nosewheel aircraft will self-center if it swerves on landing. In addition, some tailwheel aircraft must transition from using the rudder to steer to using the tailwheel while passing through a speed range when neither is wholly effective due to the nose high angle of the aircraft and lack of airflow over the rudder. Avoiding ground loops requires more pilot training and skill. *Tailwheel aircraft generally suffer from poorer forward visibility on the ground, compared to nose wheel aircraft. Often this requires continuous "S" turns on the ground to allow the pilot to see where they are taxiing. *Tailwheel aircraft are more difficult to taxi during high wind conditions, due to the higher angle of attack on the wings which can then develop more lift on one side, making control difficult or impossible. They also suffer from lower crosswind capability and in some wind conditions may be unable to use crosswind runways or single-runway airports. *Due to the nose-high attitude on the ground, propeller-powered taildraggers are more adversely affected by
P-factor P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller,) where the propeller's center of thrust moves off-center when the aircraft is at a high angle of attac ...
– asymmetrical thrust caused by the propeller's disk being angled to the direction of travel, which causes the blades to produce more lift when going down than when going up due to the difference in
angle In Euclidean geometry, an angle is the figure formed by two Ray (geometry), rays, called the ''Side (plane geometry), sides'' of the angle, sharing a common endpoint, called the ''vertex (geometry), vertex'' of the angle. Angles formed by two ...
the blade experiences when passing through the air. The aircraft will then pull to the side of the upward blade. Some aircraft lack sufficient rudder authority in some flight regimes (particularly at higher power settings on takeoff) and the pilot must compensate before the aircraft starts to yaw. Some aircraft, particularly older, higher powered aircraft such as the P-51 Mustang, cannot use full power on takeoff and still safely control their direction of travel. On landing this is less of a factor, however opening the throttle to abort a landing can induce severe uncontrollable yaw unless the pilot is prepared for it.


Jet-powered tailwheel aircraft

Jet aircraft generally cannot use conventional landing gear, as this orients the engines at a high angle, causing their
jet blast Jet blast is the phenomenon of rapid air movement produced by the jet engines of aircraft, particularly on or before takeoff. A large jet-engined aircraft can produce winds of up to as far away as behind it at 40% maximum rated power. Jet b ...
to bounce off the ground and back into the air, preventing the
elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...
s from functioning properly. This problem occurred with the third, or "V3" prototype of the German
Messerschmitt Me 262 The Messerschmitt Me 262, nicknamed ''Schwalbe'' (German: "Swallow") in fighter versions, or ''Sturmvogel'' (German: "Storm Bird") in fighter-bomber versions, is a fighter aircraft and fighter-bomber that was designed and produced by the Germa ...
jet fighter.Boyne 2008, p. 60. 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 Heinkel He 178 was an experimental aircraft designed and produced by the German aircraft manufacturer Heinkel. It was the world's first aircraft to fly using the thrust from a turbojet engine. The He 178 was developed to test the jet propu ...
, the
Ball-Bartoe Jetwing __NOTOC__ The Ball-Bartoe JW-1 Jetwing was a US research aircraft flown in the 1970s to investigate blown wing technology. Design and development The Jetwing was a small, mid-wing design powered by a turbofan and fitted with tail-wheel unde ...
research aircraft, and a single
Vickers VC.1 Viking The Vickers VC.1 Viking is a British twin-engine short-range airliner derived from the Vickers Wellington bomber and built by Vickers-Armstrongs Limited at Brooklands near Weybridge in Surrey. After the Second World War, the Viking was a ...
, which was modified with
Rolls-Royce Nene The Rolls-Royce RB.41 Nene is a 1940s British centrifugal compressor turbojet engine. The Nene was a complete redesign, rather than a scaled-up Rolls-Royce Derwent"Rolls-Royce Aero Engines" Bill Gunston, Patrick Stephens Limited 1989, , p.111 w ...
engines to become the world's first jet airliner. Rare examples of jet-powered tailwheel aircraft that went into production and saw service include the British
Supermarine Attacker The Supermarine Attacker is a British single-seat naval jet fighter designed and produced by aircraft manufacturer Supermarine for the Royal Navy's Fleet Air Arm (FAA). The type has the distinction of being the first jet fighter to enter oper ...
naval fighter and the Soviet
Yakovlev Yak-15 The Yakovlev Yak-15 (russian: Яковлев Як-15; NATO reporting name: Feather, USAF/ DOD designation Type 2) was a first-generation Soviet turbojet fighter developed by the Yakovlev design bureau (OKB) immediately after World War II. The ...
. 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 The Yakovlev Yak-3 (Russian: Яковлев Як-3) was a single-engine, single-seat World War II Soviet fighter. Robust and easy to maintain, it was much liked by both pilots and ground crew.Glancey 2006, p. 180. One of the smallest and lighte ...
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 to prepare Soviet pilots for flying more advanced jet fighters.


Monowheel undercarriage

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 Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliffs ...
. 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 The Schleicher ASK 23 is a single-seat Club Class sailplane that was built by the German manufacturer Alexander Schleicher GmbH & Co. Design The ASK 23 was the last glider to be designed by Rudolf Kaiser. It is an early-solo sailplane with doc ...
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 The Cessna 172 Skyhawk is an American four-seat, single-engine, high wing, fixed-wing aircraft made by the Cessna Aircraft Company.
or
Piper Cherokee The Piper PA-28 Cherokee is a family of two-seat or four-seat light aircraft built by Piper Aircraft and designed for flight training, air taxi and personal use.Plane and Pilot: ''1978 Aircraft Directory'', pages 62–64. Werner & Werner Corp, ...
) and only later transition to taildraggers.


Techniques

Landing a conventional geared aircraft can be accomplished in two ways.
Transport Canada Transport Canada (french: Transports Canada) is the department within the Government of Canada responsible for developing regulations, policies and services of road, rail, marine and air transportation in Canada. It is part of the Transportati ...
, ''Aeroplane Flight Training Manual'', page 111 (4th revised edition)
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, as rudder control may be reduced severely before the tailwheel can become effective. The alternative is the ''wheel landing''. This requires the pilot to land the aircraft on the mainwheels while maintaining the tailwheel in the air with
elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...
to keep the
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
low. Once the aircraft has slowed to a speed that can ensure control will not be lost, but above the speed at which
rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
effectiveness is lost, then the tailwheel is lowered to the ground.


Examples

Examples of tailwheel aircraft include:


Airplanes

*
de Havilland Canada DHC-2 Beaver The de Havilland Canada DHC-2 Beaver is a single-engined high-wing propeller-driven short takeoff and landing (STOL) aircraft developed and manufactured by de Havilland Canada. It has been primarily operated as a bush plane and has been used ...
*
Douglas DC-3 The Douglas DC-3 is a propeller-driven airliner manufactured by Douglas Aircraft Company, which had a lasting effect on the airline industry in the 1930s to 1940s and World War II. It was developed as a larger, improved 14-bed sleeper version ...
*
Maule M-7 The Maule M-7 is a family of single-engine light aircraft that has been manufactured in the United States since the mid-1980s. Design and development Based on the Maule M-4, it is a high-wing, strut-braced monoplane of conventional configu ...
*
Messerschmitt Bf 109 The Messerschmitt Bf 109 is a German World War II fighter aircraft that was, along with the Focke-Wulf Fw 190, the backbone of the Luftwaffe's fighter force. The Bf 109 first saw operational service in 1937 during the Spanish Civil War an ...
*
Piper J-3 Cub The Piper J-3 Cub is an American light aircraft that was built between 1938 and 1947 by Piper Aircraft. The aircraft has a simple, lightweight design which gives it good low-speed handling properties and short-field performance. The Cub is Pi ...
*
Supermarine Spitfire The Supermarine Spitfire is a British single-seat fighter aircraft used by the Royal Air Force and other Allied countries before, during, and after World War II. Many variants of the Spitfire were built, from the Mk 1 to the Rolls-Royce Grif ...


Helicopters

*
Boeing AH-64 Apache The Boeing AH-64 Apache () is an American twin-turboshaft attack helicopter with a tailwheel-type landing gear arrangement and a tandem cockpit for a crew of two. It features a nose-mounted sensor suite for target acquisition and night visi ...
- Attack helicopter *
Sikorsky SH-3 Sea King The Sikorsky SH-3 Sea King (company designation S-61) is an American twin-engined anti-submarine warfare (ASW) helicopter designed and built by Sikorsky Aircraft. A landmark design, it was one of the first ASW rotorcraft to use turboshaft engi ...
- Anti-submarine helicopter


Modifications of tricycle gear aircraft

Several aftermarket modification companies offer kits to convert many popular nose-wheel equipped aircraft to conventional landing gear. Aircraft for which kits are available include: *
Cessna 150 The Cessna 150 is a two-seat tricycle gear general aviation airplane that was designed for flight training, touring and personal use.Plane and Pilot: ''1978 Aircraft Directory'', pages 22-23. Werner & Werner Corp, Santa Monica CA, 1977. In 19 ...
*
Cessna 152 The Cessna 152 is an American two-seat, fixed- tricycle-gear, general aviation airplane, used primarily for flight training and personal use. It was based on the earlier Cessna 150 incorporating a number of minor design changes and a slightly ...
*
Cessna 172 The Cessna 172 Skyhawk is an American four-seat, single-engine, high wing, fixed-wing aircraft made by the Cessna Aircraft Company.
*
Cessna 175 The Cessna 175 Skylark is a four-seat, single-engine, high-wing airplane produced by Cessna between 1958 and 1962. Production history The 175 was designed to fill a niche between the Cessna 172 and the faster Cessna 182. The engine of the 17 ...
*
Cessna 182 The Cessna 182 Skylane is an American four-seat, single-engined light airplane built by Cessna of Wichita, Kansas. It has the option of adding two child seats in the baggage area. Introduced in 1956, the 182 has been produced in a ...
* Piper PA-22 Tri-Pacer


References


Citations


Bibliography

*Boyne, Walter J. "Goering's Big Bungle". Air Force Magazine, Vol. 91, No. 11, November 2008. *Aviation Publishers Co. Limited, ''From the Ground Up'', page 11 (27th revised edition) {{Aircraft components Aircraft undercarriage Aircraft configurations