Conventional landing gear

A Cessna 150 converted to taildragger configuration by installation of an after-market modification kit.

Conventional landing gear, or tailwheel-type landing gear, is an aircraft undercarriage consisting of two main wheels forward of the center of gravity and a small wheel or skid to support the tail.^[1]^[2] The term conventional persists for historical reasons, but nowadays most aircraft—including all jet aircraft—are configured with tricycle gear.

The term taildragger is aviation jargon for an aircraft with a conventional undercarriage, although some writers have argued that the term should refer only to an aircraft with a tailskid and not a tailwheel.^[2]^[3]

History

Tailwheel detail on a Tiger Moth biplane

Unusually for a helicopter, the AgustaWestland Apache has a tailwheel configuration in order to leave room for the front-facing 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 is steered by the pilot through a connection to the rudder pedals, allowing the rudder and tailwheel to move together.^[2]^[3]

Before aircraft commonly used tailwheels, many aircraft (like a number of the Sopwith single-seat fighters from later in World War I, especially the Camel and Dolphin fighters) were equipped with steerable tailskids, which operate exactly like 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 did give 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 selectively to the main wheels in order to turn in that direction. This is also used on some tricycle gear aircraft, with the nose wheel 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

Douglas DC-3, a taildragger airliner

The tailwheel configuration offers several advantages over the tricycle landing gear arrangement.^[2]

Due to its position well behind the center of gravity, a tailwheel only supports a small part of the aircraft's weight and can be made much smaller and weaker than a nosewheel. This makes tailwheels less expensive to manufacture and maintain. A smaller wheel also experiences less parasitic drag, allowing a tailwheel aircraft without retractable gear to cruise at a higher speed than if it had a nosewheel.^[2]

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. ^[2]

Tailwheel aircraft are easier to fit into some hangars.^[2]^[4]

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.^[2]

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.^[2]

Tailwheel aircraft are more suitable for operation on skis.^[2]

Disadvantages

A replica World War 1 F.E.2 fighter. This aircraft uses a tail-skid. The small wheel at the front is a safety device intended to prevent nose-over accidents

The conventional landing gear arrangement does have some disadvantages, compared to nose wheel equipped aircraft.^[2]

Tailwheel aircraft are much more subject to "nose-over" accidents due to injudicious application of brakes by the pilot.^[2]

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, wingtips, propeller and engine. Ground-looping occurs because, whereas a nosewheel aircraft is steered from ahead of the center of gravity, 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. Avoiding ground loops requires increased pilot training and skill.^[1]^[2]

A Vought F4U Corsair. If this aircraft was taxiing, the pilot would be unable to see the photographer.

Tailwheel aircraft generally suffer from poorer forward visibility on the ground, compared to nose wheel aircraft. In some cases this necessitates "S" turning on the ground to allow the pilot to see while taxiing.^[2]

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.^[2]

Due to the nose high attitude on the ground, propeller powered taildraggers are more adversely affected by P-factor - 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 up than when going down due to the difference in angle the blade experiences when passing through the air. The aircraft will then pull to the side of the downward 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 yaw unless the pilot is prepared for it.

Jet-powered tailwheel aircraft

A Royal Navy Supermarine Attacker of 1831 Squadron RNVR, during a final approach for landing (1956)

The only surviving Yak-15 in a Moscow museum (2012)

Jet aircraft generally cannot use conventional landing gear, as this orients the engines at a high angle, causing their jet blast to bounce off the ground and back into the air, preventing the elevators from functioning properly. This problem occurred with the third, or "V3" prototype of the German Messerschmitt Me 262 jet fighter.^[5] 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 world's first jet, the Heinkel He 178, and a single Vickers VC.1 Viking, which was fitted with Rolls Royce Nene engines and so became 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 and the Soviet Yakovlev Yak-15. Both aircraft first flew in 1946 and both owed their configuration to the fact that elements of their design were borrowed from earlier, propeller aircraft.

The Attacker was a naval fighter which served with British forces until 1957 and with Pakistani forces until 1967. Its tail-wheel configuration was chosen to allow the Attacker to make use of the wing design of the Supermarine Spiteful propeller aircraft, without expensive design modification or retooling.

The Yak-15 was a Soviet jet fighter that was largely based on the Yakovlev Yak-3 propeller fighter. Its engine, based on the German Junkers Jumo 004, was mounted under the forward fuselage and a steel heat shield was fitted under the rear fuselage to protect it from the jet-blast. Despite its unusual configuration, the Yak-15 was an easy aircraft to fly. Although nominally a fighter, it was mainly used to give Soviet pilots jet experience, to prepare them for flying more advanced types.

Monowheel undercarriage

A Schleicher Ka 6e 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. Both monowheel gliders and 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 illustrated Schleicher 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 PPL pilots now learn to fly in tricycle gear aircraft (e.g. Cessna 172 or Piper Cherokee) and only later transition to taildraggers.^[2]

Techniques

Landing a conventional geared aircraft can be accomplished in two ways.^[6]

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,^[6] 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 main wheels while maintaining the tailwheel in the air with elevator to keep the angle of attack low. Once the aircraft has slowed to a speed that can ensure control will not be lost, but above the speed at which rudder effectiveness is lost, then the tailwheel is lowered to the ground.^[6]

Examples

Examples of tailwheel aircraft include:

Modifications of tricycle gear aircraft

Several after-market modification companies offer kits to convert many popular nose-wheel equipped aircraft to conventional landing gear. Aircraft for which kits are available include:

References

Citations

1 2 Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 133. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Aviation Publishers Co. Limited, From the Ground Up, page 11 (27th revised edition) ISBN 0-9690054-9-0
1 2 Brandon, John. "Recreational Aircraft Australia - Groundschool". Archived from the original on 2008-07-19. Retrieved 2008-12-05.
↑ Scott, Jeff. "Aerospace Web - Aircraft Landing Gear Layouts". Retrieved 2008-12-05.
↑ Boyne 2008, p. 60.
1 2 3 Transport Canada, Aeroplane Flight Training Manual, page 111 (4th revised edition) ISBN 0-7715-5115-0

Bibliography

Boyne, Walter J. "Goering's Big Bungle". Air Force Magazine, Vol. 91, No. 11, November 2008.

Aircraft components and systems

Airframe structure	Aft pressure bulkhead Cabane strut Canopy Cruciform tail Dope Empennage Fabric covering Fairing Flying wires Former Fuselage Hardpoint Interplane strut Jury strut Leading edge Lift strut Longeron Nacelle Rib Spar Stabilizer Stressed skin Strut T-tail Tailplane Trailing edge Twin tail Vertical stabilizer V-tail Wing root Wing tip Wingbox

Flight controls	Aileron Airbrake Artificial feel Autopilot Canard Centre stick Deceleron Dive brake Electro-hydraulic actuator Elevator Elevon Flaperon Flight control modes Fly-by-wire Gust lock Rudder Servo tab Side-stick Spoiler Spoileron Stabilator Stick pusher Stick shaker Trim tab Wing warping Yaw damper Yoke

Aerodynamic and high-lift devices	Active Aeroelastic Wing Adaptive compliant wing Blown flap Channel wing Dog-tooth Droop Flap Gouge flap Gurney flap Krueger flap Leading edge cuff LEX Slats Slot Stall strips Strake Variable-sweep wing Vortex generator Vortilon Wing fence Winglet

Avionic and flight instrument systems	ACAS Air data computer Airspeed indicator Altimeter Annunciator panel Attitude indicator Compass Course deviation indicator EFIS EICAS Flight data recorder Flight management system Glass cockpit GPS Heading indicator Horizontal situation indicator INS Pitot-static system Radar altimeter TCAS Transponder Turn and slip indicator Vertical Speed Indicator Yaw string

Propulsion controls, devices and fuel systems	Autothrottle Drop tank FADEC Fuel tank Gascolator Inlet cone Intake ramp NACA cowling Self-sealing fuel tank Splitter plate Throttle Thrust lever Thrust reversal Townend ring Wet wing

Landing and arresting gear	Arrestor hook Autobrake Conventional landing gear Drogue parachute Landing gear Landing gear extender Oleo strut Tricycle landing gear Tundra tire

Escape systems	Ejection seat Escape crew capsule

Other systems	Aircraft lavatory Auxiliary power unit Bleed air system Deicing boot Emergency oxygen system Entertainment system Environmental control system Hydraulic system Ice protection system Landing lights Navigation light Passenger service unit Ram air turbine Weeping wing

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