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58-594: The Percival Prince is a British light transport of the early postwar period. It was a twin-engine, high-wing, cantilever monoplane of all-metal stressed-skin construction; the undercarriage was of retractable , tricycle type. The design of the Prince continued from the solitary Merganser . Further development of the type led to the Survey Prince survey aircraft and the Sea Prince . An improved version of

116-501: A ski-jump on take-off is subjected to loads of 0.5g which also last for much longer than a landing impact. Helicopters may have a deck-lock harpoon to anchor them to the deck. Some aircraft have a requirement to use the landing-gear as a speed brake. Flexible mounting of the stowed main landing-gear bogies on the Tupolev Tu-22 R raised the aircraft flutter speed to 550 kn (1,020 km/h). The bogies oscillated within

174-414: A "boat" hull/floats and retractable wheels, which allow it to operate from land or water. Beaching gear is detachable wheeled landing gear that allows a non-amphibious floatplane or flying boat to be maneuvered on land. It is used for aircraft maintenance and storage and is either carried in the aircraft or kept at a slipway. Beaching gear may consist of individual detachable wheels or a cradle that supports

232-442: A 10 in (25 cm) thick flexible asphalt pavement . The 210,000 lb (95 t) Boeing 727 -200 with four tires on two legs main landing gears required a 20 in (51 cm) thick pavement. The thickness rose to 25 in (64 cm) for a McDonnell Douglas DC-10 -10 with 443,000 lb (201 t) supported on eight wheels on two legs. The heavier, 558,000 lb (253 t), DC-10-30/40 were able to operate from

290-474: A 90° angle during the rearwards-retraction sequence to allow the main wheel to rest "flat" above the lower end of the main gear strut, or flush within the wing or engine nacelles, when fully retracted. Examples are the Curtiss P-40 , Vought F4U Corsair , Grumman F6F Hellcat , Messerschmitt Me 210 and Junkers Ju 88 . The Aero Commander family of twin-engined business aircraft also shares this feature on

348-476: A forward and aft position. The forward position was used for take-off to give a longer lever-arm for pitch control and greater nose-up attitude. The aft position was used to reduce landing bounce and reduce risk of tip-back during ground handling. The tandem or bicycle layout is used on the Hawker Siddeley Harrier, which has two main-wheels behind a single nose-wheel under the fuselage and

406-511: A ground loop, the pilot must respond to any turning tendency quickly, while sufficient control authority is available to counteract it. Once the aircraft rotates beyond this point, there is nothing the pilot can do to stop it from rotating further. Ground loops occur when the aircraft is moving on the ground—either taxiing , landing , or during takeoff . Ground loops can damage the undercarriage and wingtips of an aircraft. Several extreme incidents of ground loop have resulted in fatalities. In

464-585: A higher sink-rate requirement because the aircraft are flown onto the deck with no landing flare . Other features are related to catapult take-off requirements for specific aircraft. For example, the Blackburn Buccaneer was pulled down onto its tail-skid to set the required nose-up attitude. The naval McDonnell Douglas F-4 Phantom II in UK service needed an extending nosewheel leg to set the wing attitude at launch. The landing gear for an aircraft using

522-474: A higher sink-rate requirement if a carrier-type, no-flare landing technique has to be adopted to reduce touchdown scatter. For example, the Saab 37 Viggen , with landing gear designed for a 5m/sec impact, could use a carrier-type landing and HUD to reduce its scatter from 300 m to 100m. The de Havilland Canada DHC-4 Caribou used long-stroke legs to land from a steep approach with no float. A flying boat has

580-489: A light aircraft, an emergency extension system is always available. This may be a manually operated crank or pump, or a mechanical free-fall mechanism which disengages the uplocks and allows the landing gear to fall under gravity. Aircraft landing gear includes wheels equipped with solid shock absorbers on light planes, and air/oil oleo struts on larger aircraft. As aircraft weights have increased more wheels have been added and runway thickness has increased to keep within

638-403: A lower fuselage with the shape of a boat hull giving it buoyancy. Wing-mounted floats or stubby wing-like sponsons are added for stability. Sponsons are attached to the lower sides of the fuselage. A floatplane has two or three streamlined floats. Amphibious floats have retractable wheels for land operation. An amphibious aircraft or amphibian usually has two distinct landing gears, namely

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696-586: A navigation and anti-submarine trainer; the C.Mks. 1 and 2 were flown in the transport role. However, these were land planes and not COD (carrier on board delivery) aircraft. Sea Princes operated in both roles from 1954 to 1972 and as a navigation trainer until 1978, when it was replaced by the Handley Page Jetstream Data from British Naval Aircraft since 1912 General characteristics Performance Related development Undercarriage (aeronautics) Landing gear

754-537: A nosewheel) chassis. Landing is done on skids or similar simple devices (fixed or retractable). The SNCASE Baroudeur used this arrangement. Historical examples include the "dolly"-using Messerschmitt Me 163 Komet rocket fighter, the Messerschmitt Me 321 Gigant troop glider, and the first eight "trolley"-using prototypes of the Arado Ar 234 jet reconnaissance bomber. The main disadvantage to using

812-407: A paved surface: for example, after an engine failure in multi-engine airplanes produces asymmetric thrust. Another common cause is failure of a tire or wheel brake, causing a loss of directional control. A controlled ground loop may also be used as a rudimentary form of emergency braking while landing, "in case one is still rolling too fast to stop." According to Robinet, "The pilot would merely hold

870-457: A similar arrangement, except that the fore and aft gears each have two twin-wheel units side by side. Quadricycle gear is similar to bicycle but with two sets of wheels displaced laterally in the fore and aft positions. Raymer classifies the B-52 gear as quadricycle. The experimental Fairchild XC-120 Packplane had quadricycle gear located in the engine nacelles to allow unrestricted access beneath

928-520: A smaller wheel near the tip of each wing. On second generation Harriers, the wing is extended past the outrigger wheels to allow greater wing-mounted munition loads to be carried, or to permit wing-tip extensions to be bolted on for ferry flights. A tandem layout was evaluated by Martin using a specially-modified Martin B-26 Marauder (the XB-26H) to evaluate its use on Martin's first jet bomber,

986-557: A tricycle undercarriage to prevent damage to the underside of the fuselage if over-rotation occurs on take-off leading to a tail strike . Aircraft with tail-strike protection include the B-29 Superfortress , Boeing 727 trijet and Concorde . Some aircraft with retractable conventional landing gear have a fixed tailwheel. Hoerner estimated the drag of the Bf 109 fixed tailwheel and compared it with that of other protrusions such as

1044-412: Is also unique in that all four pairs of main wheels can be steered. This allows the landing gear to line up with the runway and thus makes crosswind landings easier (using a technique called crab landing ). Since tandem aircraft cannot rotate for takeoff, the forward gear must be long enough to give the wings the correct angle of attack during takeoff. During landing, the forward gear must not touch

1102-409: Is applied to the nosewheel, a condition known as wheel-barrowing . If the aircraft heading is different from the aircraft's direction of motion, a sideways force is exerted on the wheels. If this force is in front of the centre of gravity, the resulting moment rotates the aircraft's heading even further from its direction of motion. This increases the force and the process reinforces itself. To avoid

1160-465: Is required to reduce the impact with the surface of the water. A vee bottom parts the water and chines deflect the spray to prevent it damaging vulnerable parts of the aircraft. Additional spray control may be needed using spray strips or inverted gutters. A step is added to the hull, just behind the center of gravity, to stop water clinging to the afterbody so the aircraft can accelerate to flying speed. The step allows air, known as ventilation air, to break

1218-527: Is the undercarriage of an aircraft or spacecraft that is used for taxiing , takeoff or landing . For aircraft, it is generally needed for all three of these. It was also formerly called alighting gear by some manufacturers, such as the Glenn L. Martin Company . For aircraft, Stinton makes the terminology distinction undercarriage (British) = landing gear (US) . For aircraft, the landing gear supports

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1276-705: The Beriev A-40 Hydro flaps were used on the Martin Marlin and Martin SeaMaster . Hydroflaps, submerged at the rear of the afterbody, act as a speed brake or differentially as a rudder. A fixed fin, known as a skeg , has been used for directional stability. A skeg, was added to the second step on the Kawanishi H8K flying boat hull. High speed impacts in rough water between the hull and wave flanks may be reduced using hydro-skis which hold

1334-561: The Martin Marlin , the Martin M-270, was tested with a new hull with a greater length/beam ratio of 15 obtained by adding 6 feet to both the nose and tail. Rough-sea capability can be improved with lower take-off and landing speeds because impacts with waves are reduced. The Shin Meiwa US-1A is a STOL amphibian with blown flaps and all control surfaces. The ability to land and take-off at relatively low speeds of about 45 knots and

1392-702: The Martin XB-48 . This configuration proved so manoeuvrable that it was also selected for the B-47 Stratojet . It was also used on the U-2, Myasishchev M-4 , Yakovlev Yak-25 , Yak-28 and Sud Aviation Vautour . A variation of the multi tandem layout is also used on the B-52 Stratofortress which has four main wheel bogies (two forward and two aft) underneath the fuselage and a small outrigger wheel supporting each wing-tip. The B-52's landing gear

1450-470: The maximum takeoff weight (MTOW) and 1.5 to 1.75% of the aircraft cost, but 20% of the airframe direct maintenance cost. A suitably-designed wheel can support 30 t (66,000 lb), tolerate a ground speed of 300 km/h and roll a distance of 500,000 km (310,000 mi) ; it has a 20,000 hours time between overhaul and a 60,000 hours or 20 year life time. Wheeled undercarriages normally come in two types: The taildragger arrangement

1508-676: The Prince 3 with an increased wingspan and engine and undercarriage modifications was developed for the Royal Air Force as the Percival Pembroke . The Prince was produced in six versions for the civil market. Several examples were operated as executive aircraft including Standard Motors and Shell Oil . Three aircraft were used by the UK Ministry of Civil Aviation as airport facilities checking aircraft. The Sea Prince operated in two roles: in T.Mk.1 form it served as

1566-416: The aircraft can be landed in a satisfactory manner in a range of failure scenarios. The Boeing 747 was given four separate and independent hydraulic systems (when previous airliners had two) and four main landing gear posts (when previous airliners had two). Safe landing would be possible if two main gear legs were torn off provided they were on opposite sides of the fuselage. In the case of power failure in

1624-470: The airstream, it is called a semi-retractable gear. Most retractable gear is hydraulically operated, though some is electrically operated or even manually operated on very light aircraft. The landing gear is stowed in a compartment called a wheel well. Pilots confirming that their landing gear is down and locked refer to "three greens" or "three in the green.", a reference to the electrical indicator lights (or painted panels of mechanical indicator units) from

1682-533: The case of the 1947 crash of Pan Am Flight 121 , Captain Michael Graham, one of the surviving passengers, said that the landing would have been successful had an engine on the port wing not dug into the ground, dragging the plane in that direction in a ground loop and breaking it in two. Ground loops may occur when landing on muddy ground, wet pavement, or frozen surfaces, especially if there are puddles or patches. They may also occur when an aircraft departs

1740-422: The craft when it is not flying, allowing it to take off, land, and taxi without damage. Wheeled landing gear is the most common, with skis or floats needed to operate from snow/ice/water and skids for vertical operation on land. Retractable undercarriages fold away during flight, which reduces drag , allowing for faster airspeeds . Landing gear must be strong enough to support the aircraft and its design affects

1798-440: The downwind wing of the glider than on the upwind wing. If the flight controls are unable to overcome the rolling tendency at this low speed, the upwind wingtip will contact the ground and initiate a ground loop; the glider pilot must release the tow rope to abandon the takeoff. Gliders with a large main wheel and a tail wheel or tail skid are particularly susceptible to this form of ground looping during cross-wind takeoffs because of

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1856-410: The entire aircraft. In the former case, the beaching gear is manually attached or detached with the aircraft in the water; in the latter case, the aircraft is maneuvered onto the cradle. Helicopters are able to land on water using floats or a hull and floats. For take-off a step and planing bottom are required to lift from the floating position to planing on the surface. For landing a cleaving action

1914-418: The fuselage for attaching a large freight container. Helicopters use skids, pontoons or wheels depending on their size and role. To decrease drag in flight, undercarriages retract into the wings and/or fuselage with wheels flush with the surrounding surface, or concealed behind flush-mounted doors; this is called retractable gear. If the wheels do not retract completely but protrude partially exposed to

1972-424: The fuselage lower sides as retractable main gear units on modern designs—were first seen during World War II, on the experimental German Arado Ar 232 cargo aircraft, which used a row of eleven "twinned" fixed wheel sets directly under the fuselage centerline to handle heavier loads while on the ground. Many of today's large cargo aircraft use this arrangement for their retractable main gear setups, usually mounted on

2030-438: The fuselage. The 640 t (1,410,000 lb) Antonov An-225 , the largest cargo aircraft, had 4 wheels on the twin-strut nose gear units like the smaller Antonov An-124 , and 28 main gear wheels. The 97 t (214,000 lb) A321neo has a twin-wheel main gear inflated to 15.7 bar (228 psi), while the 280 t (620,000 lb) A350 -900 has a four-wheel main gear inflated to 17.1 bar (248 psi). STOL aircraft have

2088-603: The hull out of the water at higher speeds. Hydro skis replace the need for a boat hull and only require a plain fuselage which planes at the rear. Alternatively skis with wheels can be used for land-based aircraft which start and end their flight from a beach or floating barge. Hydro-skis with wheels were demonstrated as an all-purpose landing gear conversion of the Fairchild C-123 , known as the Panto-base Stroukoff YC-134 . A seaplane designed from

2146-471: The hydrodynamic features of the hull, long length/beam ratio and inverted spray gutter for example, allow operation in wave heights of 15 feet. The inverted gutters channel spray to the rear of the propeller discs. Low speed maneuvring is necessary between slipways and buoys and take-off and landing areas. Water rudders are used on seaplanes ranging in size from the Republic RC-3 Seabee to

2204-402: The landing gear usually consists of skis or a combination of wheels and skis. Some aircraft use wheels for takeoff and jettison them when airborne for improved streamlining without the complexity, weight and space requirements of a retraction mechanism. The wheels are sometimes mounted onto axles that are part of a separate "dolly" (for main wheels only) or "trolley" (for a three-wheel set with

2262-405: The landing gear usually only supports the vehicle on landing and during subsequent surface movement, and is not used for takeoff. Given their varied designs and applications, there exist dozens of specialized landing gear manufacturers. The three largest are Safran Landing Systems , Collins Aerospace (part of Raytheon Technologies ) and Héroux-Devtek . The landing gear represents 2.5 to 5% of

2320-432: The large angle of attack on the wing. Gliders with a nose wheel or nose skid cause the wing to present a lower angle of attack at the commencement of the take off roll and are much less susceptible to this form of ground looping. Tow plane pilots are taught to delay applying full power until the glider is moving fast enough that its tail is off the ground, reducing the angle of attack on the wing. Pilots may decide to execute

2378-417: The lower corners of the central fuselage structure. The prototype Convair XB-36 had most of its weight on two main wheels, which needed runways at least 22 in (56 cm) thick. Production aircraft used two four-wheel bogies, allowing the aircraft to use any airfield suitable for a B-29. A relatively light Lockheed JetStar business jet, with four wheels supporting 44,000 lb (20 t), needed

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2436-504: The main gear struts lengthened as they were extended to give sufficient ground clearance for their large four-bladed propellers. One exception to the need for this complexity in many WW II fighter aircraft was Japan's famous Zero fighter, whose main gear stayed at a perpendicular angle to the centerline of the aircraft when extended, as seen from the side. The main wheels on the Vought F7U Cutlass could move 20 inches between

2494-489: The main gears, which retract aft into the ends of the engine nacelles . The rearward-retracting nosewheel strut on the Heinkel He 219 and the forward-retracting nose gear strut on the later Cessna Skymaster similarly rotated 90 degrees as they retracted. On most World War II single-engined fighter aircraft (and even one German heavy bomber design ) with sideways retracting main gear, the main gear that retracted into

2552-611: The nacelle under the control of dampers and springs as an anti-flutter device. Some experimental aircraft have used gear from existing aircraft to reduce program costs. The Martin-Marietta X-24 lifting body used the nose/main gear from the North American T-39 / Northrop T-38 and the Grumman X-29 from the Northrop F-5 / General Dynamics F-16 . When an airplane needs to land on surfaces covered by snow,

2610-444: The nosewheel/tailwheel and the two main gears. Blinking green lights or red lights indicate the gear is in transit and neither up and locked or down and locked. When the gear is fully stowed up with the up-locks secure, the lights often extinguish to follow the dark cockpit philosophy; some airplanes have gear up indicator lights. Redundant systems are used to operate the landing gear and redundant main gear legs may also be provided so

2668-722: The outset with hydro-skis was the Convair F2Y Sea Dart prototype fighter. The skis incorporated small wheels, with a third wheel on the fuselage, for ground handling. In the 1950s hydro-skis were envisaged as a ditching aid for large piston-engined aircraft. Water-tank tests done using models of the Lockheed Constellation , Douglas DC-4 and Lockheed Neptune concluded that chances of survival and rescue would be greatly enhanced by preventing critical damage associated with ditching. The landing gear on fixed-wing aircraft that land on aircraft carriers have

2726-556: The pilot's canopy. A third arrangement (known as tandem or bicycle) has the main and nose gear located fore and aft of the center of gravity (CG) under the fuselage with outriggers on the wings. This is used when there is no convenient location on either side of the fuselage to attach the main undercarriage or to store it when retracted. Examples include the Lockheed U-2 spy plane and the Harrier jump jet . The Boeing B-52 uses

2784-409: The right brake (in this case...no place on the left) harder than the left and wishes the airplane around in a tight turn on the ground. Another way of putting it, the airplane swaps ends. This is a ground loop." Gliders commencing a takeoff behind a tow plane are vulnerable to ground looping during cross-wind conditions because the slipstream from the propeller of the tow plane generates more lift on

2842-513: The runway loading limit . The Zeppelin-Staaken R.VI , a large German World War I long-range bomber of 1916, used eighteen wheels for its undercarriage, split between two wheels on its nose gear struts, and sixteen wheels on its main gear units—split into four side-by-side quartets each, two quartets of wheels per side—under each tandem engine nacelle, to support its loaded weight of almost 12 t (26,000 lb). Multiple "tandem wheels" on an aircraft—particularly for cargo aircraft , mounted to

2900-423: The runway first, otherwise the rear gear will slam down and may cause the aircraft to bounce and become airborne again. Ground loop (aviation) In powered aeroplanes, the ground loop phenomenon is predominantly associated with aircraft that have conventional landing gear , due to the centre of gravity being positioned behind the main wheels. It may also occur with tricycle landing gear if excessive load

2958-538: The same thickness pavements with a third main leg for ten wheels, like the first Boeing 747 -100, weighing 700,000 lb (320 t) on four legs and 16 wheels. The similar-weight Lockheed C-5 , with 24 wheels, needs an 18 in (46 cm) pavement. The twin-wheel unit on the fuselage centerline of the McDonnell Douglas DC-10 -30/40 was retained on the MD-11 airliner and the same configuration

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3016-508: The takeoff dolly/trolley and landing skid(s) system on German World War II aircraft—intended for a sizable number of late-war German jet and rocket-powered military aircraft designs—was that aircraft would likely be scattered all over a military airfield after they had landed from a mission, and would be unable to taxi on their own to an appropriately hidden "dispersal" location, which could easily leave them vulnerable to being shot up by attacking Allied fighters. A related contemporary example are

3074-685: The water suction on the afterbody. Two steps were used on the Kawanishi H8K . A step increases the drag in flight. The drag contribution from the step can be reduced with a fairing. A faired step was introduced on the Short Sunderland III. One goal of seaplane designers was the development of an open ocean seaplane capable of routine operation from very rough water. This led to changes in seaplane hull configuration. High length/beam ratio hulls and extended afterbodies improved rough water capabilities. A hull much longer than its width also reduced drag in flight. An experimental development of

3132-482: The weight, balance and performance. It often comprises three wheels, or wheel-sets, giving a tripod effect. Some unusual landing gear have been evaluated experimentally. These include: no landing gear (to save weight), made possible by operating from a catapult cradle and flexible landing deck: air cushion (to enable operation over a wide range of ground obstacles and water/snow/ice); tracked (to reduce runway loading). For launch vehicles and spacecraft landers ,

3190-499: The wings was raked forward in the "down" position for better ground handling, with a retracted position that placed the main wheels at some distance aft of their position when downairframe—this led to a complex angular geometry for setting up the "pintle" angles at the top ends of the struts for the retraction mechanism's axis of rotation. with some aircraft, like the P-47 Thunderbolt and Grumman Bearcat , even mandating that

3248-424: The wingtip support wheels ("pogos") on the Lockheed U-2 reconnaissance aircraft, which fall away after take-off and drop to earth; the aircraft then relies on titanium skids on the wingtips for landing. Some main landing gear struts on World War II aircraft, in order to allow a single-leg main gear to more efficiently store the wheel within either the wing or an engine nacelle, rotated the single gear strut through

3306-445: Was common during the early propeller era, as it allows more room for propeller clearance. Most modern aircraft have tricycle undercarriages. Taildraggers are considered harder to land and take off (because the arrangement is usually unstable , that is, a small deviation from straight-line travel will tend to increase rather than correct itself), and usually require special pilot training. A small tail wheel or skid/bumper may be added to

3364-467: Was used on the initial 275 t (606,000 lb) Airbus A340 -200/300, which evolved in a complete four-wheel undercarriage bogie for the heavier 380 t (840,000 lb) Airbus A340-500/-600. The up to 775,000 lb (352 t) Boeing 777 has twelve main wheels on two three-axles bogies, like the later Airbus A350 . The 575 t (1,268,000 lb) Airbus A380 has a four-wheel bogie under each wing with two sets of six-wheel bogies under

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