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Conventional landing gear
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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 taildragger is also used.[2]
The term "conventional" persists for historical reasons, but all modern jet aircraft and most modern propeller aircraft use tricycle gear, such as a Boeing 737 MAX or an Airbus A380.
History
[edit]
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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.[2][3]
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 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.[citation needed]
Advantages
[edit]
The tailwheel configuration offers several advantages over the tricycle landing gear arrangement, which make tailwheel aircraft less expensive to manufacture and maintain.[2]
- Due to its position much further from the center of gravity, a tailwheel supports a smaller part of the aircraft's weight allowing it to be made much smaller and lighter than a nosewheel.[2] As a result, the smaller wheel weighs less and causes less parasitic drag.[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]
- 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]
- Due to the increased propeller clearance on tailwheel aircraft, less stone chip damage will result from operating a conventionally geared aircraft on rough or gravel airstrips, making them well suited to bush flying.[2]
- Tailwheel aircraft are more suitable for operation on skis.[2]
- Tailwheel aircraft are easier to fit into and maneuver inside some hangars.[2][4]
Disadvantages
[edit]_nosed_on_the_MAKS-2009_(01).jpg)
The conventional landing gear arrangement has disadvantages compared to nosewheel aircraft.[2]
- Tailwheel aircraft are more subject to "nose-over" accidents due to incorrect 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 and lack of airflow over the rudder. Avoiding ground loops requires more pilot training and skill.[1][2]
- 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.[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 down than when going up due to the difference in angle 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.[citation needed]
Jet-powered tailwheel aircraft
[edit]
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 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.
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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
[edit]
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
[edit]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.[2]
Techniques
[edit]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.[citation needed]
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 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
[edit]Examples of tailwheel aircraft include:
Airplanes
[edit]- de Havilland Canada DHC-2 Beaver
- Douglas DC-3
- Maule M-7
- Messerschmitt Bf 109
- Piper J-3 Cub
- Supermarine Spitfire
Helicopters
[edit]- Boeing AH-64 Apache - Attack helicopter
- Sikorsky SH-3 Sea King - Anti-submarine helicopter
Modifications of tricycle gear aircraft
[edit]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:
References
[edit]Citations
[edit]- ^ a b Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 133. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
- ^ a b c d e f g h i j k l m n o p q From the Ground Up, 27th edition, page 11
- ^ Brandon, John. "Recreational Aircraft Australia - Groundschool". Archived from the original on 19 July 2008. Retrieved 5 December 2008.
- ^ Scott, Jeff. "Aerospace Web - Aircraft Landing Gear Layouts". Retrieved 19 February 2016.
- ^ Boyne 2008, p. 60.
- ^ a b c Transport Canada, Aeroplane Flight Training Manual, page 111 (4th revised edition) ISBN 0-7715-5115-0
Bibliography
[edit]- 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) ISBN 0-9690054-9-0
Conventional landing gear
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Definition and Design
Core Components
The main landing gear in conventional landing gear systems consists of two primary struts positioned forward of the aircraft's center of gravity, supporting the bulk of the airframe's weight during ground operations. These struts typically incorporate wheels fitted with tires designed to handle high-impact loads and provide traction on various surfaces. Shock absorption is achieved through mechanisms such as oleo-pneumatic struts, which utilize a combination of compressed air or nitrogen and hydraulic fluid to dissipate landing forces, or spring-steel struts, which rely on the elastic deformation of high-tensile steel tubes for energy absorption in lighter aircraft.[5][3] The tailwheel assembly serves as the rear support element, featuring a smaller wheel or alternative skid mounted on a swivel fork connected to the fuselage. Castering mechanisms allow the tailwheel to pivot freely up to approximately 30 degrees on either side of center for enhanced maneuverability during taxiing, with some designs incorporating a locking feature to fix the wheel in a straight-ahead position for takeoff and landing stability. In rough-terrain applications, particularly in antique or experimental aircraft, a tailskid made of durable materials may replace the wheel to prevent damage from uneven surfaces.[6][7] Integration of these components occurs through robust attachment points, with the main struts typically bolted or pinned to the lower fuselage or wing structures to distribute loads effectively, while the tailwheel mounts directly to the aft fuselage. This setup results in a load distribution where typically 80 to 90 percent of the aircraft's weight rests on the main gear and 10 to 20 percent on the tailwheel during static conditions. Materials emphasize durability and weight efficiency, including high-strength steels such as 300M or AerMet 100 for struts and forks to withstand repeated impacts, alongside emerging use of carbon fiber composites in lighter applications for reduced mass without compromising integrity. Aluminum alloys are commonly employed for wheel assemblies to balance strength and corrosion resistance.[6][8][9]Configuration Variants
The conventional landing gear, also known as the taildragger configuration, consists of two main wheels positioned forward of the aircraft's center of gravity and a smaller tailwheel at the rear.[1] This arrangement supports the aircraft's weight primarily on the main wheels while the tailwheel provides directional stability during ground rolls.[6] Within this framework, configurations vary between fixed and retractable systems. Fixed variants maintain extended gear at all times, offering simplicity, lower weight, and reduced maintenance, which suits light aircraft operating from rough fields. Retractable variants incorporate mechanisms to fold the main wheels and tailwheel into the fuselage or wings during flight, minimizing aerodynamic drag for improved cruise performance in higher-speed applications.[1] To accommodate propeller clearance, the design often incorporates adjustments to the wing's angle of incidence relative to the fuselage, ensuring the propeller maintains adequate ground separation when the aircraft is in a level flight attitude.[10] Federal regulations mandate a minimum propeller tip clearance of 9 inches for tailwheel-equipped airplanes under static conditions with the landing gear extended as designed for takeoff.[11] Practical designs commonly achieve 10 to 12 inches for enhanced safety margins during operations on uneven surfaces. This clearance requirement influences the tail-down angle on the ground, typically set between 12 and 15 degrees to position the fuselage optimally without excessive drag in flight.[12] Suspension variations in light aircraft conventional gear include bungee-cord systems and leaf-spring mains. Bungee-cord suspension employs elastic rubber cords stretched between the fuselage and main gear legs to absorb landing impacts through controlled rebound, providing lightweight shock mitigation suitable for low-speed operations.[5] Leaf-spring mains, constructed from layered steel or composite struts, flex to dissipate energy upon touchdown, offering durability and ease of attachment directly to the airframe in taildragger setups.[10] The tailwheel's positioning aft of the center of gravity is critical for ground handling stability, as it creates a pivot point that requires active pilot input to counteract inherent directional instability during taxi and takeoff rolls.[6] The center of gravity is typically positioned such that the tailwheel supports approximately 10 to 20 percent of the aircraft's weight, corresponding to the CG being 10 to 20 percent of the wheelbase aft of the main gear, while enabling the tailwheel to steer via rudder linkage for precise control.[1][13]Historical Development
Early Origins
The conventional landing gear configuration, characterized by two main wheels forward of the center of gravity and a rear support, traces its origins to the pioneering efforts of early aviators in the 1900s and 1910s. The Wright brothers played a pivotal role in its development, adding wheels to the skid undercarriage of their early designs, such as the 1904 Wright Flyer II and 1905 Wright Flyer III, which improved mobility over the full skids used on the original 1903 Wright Flyer. These initial skids, often constructed from wood and fabric, provided basic support on soft terrain but limited mobility; the addition of wheels created a tail-supported arrangement, enhancing taxiing and takeoff on unprepared surfaces.[14] By the 1910s, this tail-supported arrangement gained traction in military applications, with the first widespread adoption occurring during World War I. The British Sopwith Camel fighter, introduced in 1917, exemplified the configuration's early emphasis on agility, featuring fixed main wheels and a tail skid that allowed for compact design and maneuverability in combat, contrasting with rare tricycle gear experiments that prioritized stability over lightness. Over 5,400 Camels were produced, making it one of the most prolific fighters of the war and solidifying the tail-type gear as standard for single-seat biplanes.[15][16] The 1920s saw a key transition from full-skid systems to more advanced wheeled setups, enhancing ground handling on increasingly varied airstrips, with tail skids evolving into tailwheels around the mid-1920s for better directional control. Post-war surplus aircraft retained the basic tail skid but incorporated rubber-cord shock absorption on main wheels, reducing damage during rough landings; by mid-decade, partial wheel integrations at the tail began appearing to facilitate easier maneuvering without towing. This shift addressed the limitations of skid-only designs, which dragged on pavement and complicated positioning.[17] The barnstorming era of the 1920s further influenced the standardization of tail-supported gear for operations on short, improvised fields typical of rural America. Pilots flying surplus World War I biplanes, such as the Curtiss JN-4 Jenny with its tail skid, performed stunts and passenger rides from cow pastures and farm strips, necessitating durable, low-profile undercarriages that minimized prop strikes during steep approaches. This period's demands for versatility in unprepared terrain helped entrench the configuration as a reliable choice for civilian aviation before paved runways proliferated.[18][19]Key Milestones and Evolution
During World War II, conventional landing gear dominated fighter aircraft designs, exemplified by the North American P-51 Mustang, which featured a retractable tailwheel configuration that contributed to its aerodynamic efficiency and maneuverability in combat roles across Europe and the Pacific theaters.[20] This setup allowed for a low propeller clearance and compact structure, enabling over 15,000 Mustangs to be produced and play a pivotal role in achieving air superiority by escorting bombers deep into enemy territory.[20] Following the war, conventional landing gear experienced a significant decline in the 1950s as the aviation industry shifted toward tricycle configurations, particularly for jet aircraft, due to improved stability during high-speed takeoffs, landings, and ground handling.[17] Airlines and military operators favored the nosewheel design for its reduced risk of propeller strikes and better visibility for pilots, leading to widespread adoption in commercial and transport planes, which marginalized tailwheel systems in mainstream production.[17] A resurgence occurred from the 1950s through the 1970s, driven by the needs of bush flying and aerobatic applications, where the Piper PA-18 Super Cub's taildragger setup proved ideal for short takeoffs and landings on unprepared terrain in remote areas.[21] Modifications to the Super Cub, including larger tires and reinforced struts, enhanced its versatility for backcountry operations, solidifying its popularity among pilots in Alaska and other rugged environments.[21] Similarly, aerobatic aircraft like the Pitts Special, with its fixed tailwheel, gained prominence in competitions during this era, offering superior propeller clearance and agility for inverted maneuvers and tight turns.[22] In the 2000s, advancements in composite materials revolutionized conventional landing gear by enabling lighter-weight struts made from carbon fiber, which reduced landing gear component weight by up to 40% while maintaining structural integrity under impact loads, as demonstrated in applications like the F-16 drag brace (39% reduction).[23] Concurrent hydraulic improvements, such as active control systems using electro-hydraulic actuators, enhanced shock absorption by dynamically adjusting damping in response to runway conditions, minimizing vibrations and extending component life.[24] In the 2020s, conventional landing gear has seen renewed applications in unmanned aerial vehicles (UAVs) for operations on rough, remote terrains, where tailwheel designs provide better stability and prop clearance compared to tricycle setups.[25] This configuration supports short-field performance in surveillance and logistics missions, often paired with lightweight composites for endurance.[26]Advantages and Disadvantages
Operational Advantages
Conventional landing gear provides superior propeller clearance due to the aircraft's inherent nose-high attitude on the ground, allowing for larger propellers without risk of strikes during takeoff or landing. This configuration is particularly advantageous for short takeoff and landing (STOL) operations, as the elevated propeller position minimizes ground contact hazards on rough or unimproved terrain, thereby reducing the likelihood of stalls during initial climb-out on uneven surfaces.[27] The design also offers better weight distribution for aircraft with the center of gravity positioned aft of the main wheels, promoting ground stability, though it requires precise control to prevent swerves or ground loops, especially in crosswind conditions where tailwheel aircraft demand more skill than tricycle configurations. The tailwheel's role aids in maintaining directional control and resisting weathervaning on the ground.[28] Manufacturing costs for conventional landing gear are lower than those for tricycle gear, owing to the simpler rear attachment mechanism that eliminates the need for complex nosewheel steering systems. This simplicity extends to maintenance, contributing to overall operational efficiency in general aviation applications. Additionally, tailwheel aircraft are generally lighter with less aerodynamic drag in flight, enhancing performance.[28][29] In aerobatic performance, the higher angle of attack achievable on the ground with conventional gear facilitates sharper initial climbs, as the nose-up posture aligns the wings more optimally for lift generation without excessive speed requirements. This trait made it prevalent in World War II fighter aircraft, where such advantages supported agile maneuvers.[27]Structural and Performance Drawbacks
One significant structural drawback of conventional landing gear is the nose-high attitude it imposes on the aircraft when on the ground, which substantially reduces the pilot's forward visibility during taxiing and takeoff rolls. This attitude positions the fuselage at an elevated angle to ensure adequate propeller clearance, thereby obstructing the direct line of sight ahead.[2][30] The castering nature of the tailwheel further exacerbates performance challenges by increasing the susceptibility to ground loops, particularly during landing or low-speed maneuvers, where the aircraft can abruptly yaw due to uneven thrust or crosswinds, demanding precise and skilled rudder input to counteract.[31] This instability arises from the center of gravity being positioned behind the main gear, making directional control more demanding compared to tricycle configurations.[2] The tail components of conventional gear may experience wear from repeated impacts and stresses, though the overall design is simpler and more rugged than tricycle nose gear. While insurance costs are higher due to the risk of ground incidents, maintenance is generally less complex. These drawbacks contrast with operational advantages such as superior short takeoff and landing (STOL) performance on rough terrain, necessitating careful design considerations to mitigate reliability issues.[33][30] Additionally, the tilted fuselage in small aircraft with conventional landing gear complicates passenger entry and exit, as the cabin floor is inclined, requiring passengers to climb awkwardly over the high nose or step down from the rear, while baggage loading is constrained by limited level access points.[34] This ergonomic limitation is particularly pronounced in compact designs, where door placement and cabin layout amplify the inconvenience.[35]Specialized Variations
Jet-Powered Tailwheel Designs
Jet-powered tailwheel designs represent a brief and niche chapter in aviation history, primarily confined to the pioneering era of jet propulsion in the 1940s and early 1950s. These configurations adapted conventional landing gear to accommodate the high thrust and performance demands of early turbojet engines, often retaining taildraggers for simplicity and compatibility with existing airframes. However, the inherent limitations of the tail-up attitude—such as reduced forward visibility and potential instability at high speeds—led to a rapid shift toward tricycle gear as jet aircraft evolved for faster operations.[17] Notable examples include the Heinkel He 178, the world's first aircraft to fly under pure jet power in 1939, which featured a fixed tailwheel undercarriage with main gear intended for retraction but left extended during initial tests. The prototype Messerschmitt Me 262, which conducted its first jet-powered flight in 1942, also employed a taildragger setup to leverage the existing landing gear design from piston-engine predecessors, though production models transitioned to tricycle gear for improved high-speed handling. Other early jets, such as the Soviet Yakovlev Yak-15 of 1946—essentially a modified Yak-3 fighter with a reverse-engineered German Jumo 004 engine—and the British Supermarine Attacker, which entered service in 1951, utilized tailwheel configurations to facilitate quick development from propeller aircraft roots. These designs were particularly suited for transitional roles in military applications, including fighter and trainer duties, but their use declined sharply after the 1950s as jet speeds exceeded 500 mph, favoring nosegear for better propeller-free airflow and pilot visibility.[36][37][38] Adapting tailwheel gear to jet propulsion introduced several engineering challenges. The main landing gear struts required significant reinforcement to withstand the increased dynamic loads from higher approach and touchdown speeds, often approaching or exceeding 100 knots, compared to slower piston aircraft. For instance, early jets like the Yak-15 demanded robust oleo-pneumatic shock absorbers capable of absorbing impacts at velocities that stressed the gear beyond traditional limits. Additionally, the intense heat from jet exhaust—reaching temperatures over 1,000°C—posed risks to the tailwheel assembly, necessitating materials like heat-resistant alloys or protective shielding to prevent melting or structural degradation, as seen in the Attacker where exhaust deflection was critical to avoid runway and gear damage.[39][38] Aerodynamic and stability considerations further complicated these designs. The elevated thrust line of rear-mounted jet engines in a taildragger layout could exacerbate pitch-up tendencies during takeoff, requiring precise alignment of the engine thrust vector with the aircraft's center of gravity to avert nose-over at rotation speeds above 100 knots. This was particularly evident in prototypes like the Me 262, where turbulence from the exhaust interacting with the raised tail disrupted airflow and demanded careful propeller pitch and thrust management during transitions to jet-only power. Overall, while these adaptations enabled rapid entry into the jet age, the operational drawbacks— including ground handling difficulties and exhaust-related wear—contributed to their obsolescence in favor of more stable tricycle arrangements for subsequent generations of jet aircraft.[36]Monowheel and Hybrid Configurations
Monowheel landing gear consists of a single centrally located main wheel positioned beneath the aircraft's center of gravity, typically augmented by auxiliary supports such as a tail skid and nose skid for ground handling and balance. This configuration, distinct from conventional tailwheel arrangements, eliminates the need for multiple wheels, reducing structural complexity and weight while enhancing aerodynamic efficiency. In gliders, the setup often includes small wingtip wheels or skids to prevent lateral tipping during taxiing or low-speed maneuvers on the ground. A historical example is the DFS Olympia Meise sailplane of 1939, where later variants (Mark 2) featured a fixed main wheel to support operations from unprepared fields. Stability in monowheel systems relies on the precise alignment of the main wheel under the center of gravity, which allows the aircraft to balance upright without additional props. The gyroscopic precession generated by the rotating wheel contributes to directional stability during rollout, helping resist yaw deviations, though this effect is secondary to pilot inputs via rudder and weight shift. To further enhance ground stability and prevent wingtip contact, many designs incorporate lightweight wingtip wheels or added ballast at the wing ends, distributing lateral loads effectively. The DFS Meise sailplane of 1939 exemplified this approach with its fixed main wheel and auxiliary skids in later variants, achieving a best glide ratio of 25 at 70 km/h (43 mph).[40] Applications of monowheel gear extend to experimental and ultralight aircraft, where the reduced number of components yields substantial drag savings compared to traditional multi-wheel arrangements—often cited as a key factor in achieving higher glide ratios and cruise efficiencies in low-speed regimes. For instance, modern ultralight motor gliders like variants of the Europa XS employ retractable monowheels to optimize performance, saving weight and parasitic drag while supporting operations from short, rough strips. These configurations remain niche but influential in designs prioritizing minimalism and versatility.[41]Operational Procedures
Pilot Training Requirements
Pilots seeking to operate aircraft equipped with conventional landing gear, also known as tailwheel gear, must obtain a specific endorsement from an authorized flight instructor under Federal Aviation Administration (FAA) regulations. According to 14 CFR § 61.31(i), no person may act as pilot in command of a tailwheel airplane without first receiving and logging ground and flight training from an authorized instructor, followed by an endorsement certifying proficiency in the required maneuvers and procedures, including normal and crosswind takeoffs and landings, three-point landings, and wheel landings.[4] This endorsement is proficiency-based and has no prescribed minimum flight hours, though it typically requires 10 to 15 hours of dual instruction for private pilots transitioning from tricycle gear aircraft.[42] International standards under the International Civil Aviation Organization (ICAO) align with similar proficiency requirements, emphasizing competency in tailwheel operations without specifying hour minima, often implemented through national aviation authorities. Training emphasizes rudder proficiency to maintain directional control, particularly during the critical phases of takeoff and landing where torque effects and propeller forces can induce swings. Instructors focus on immediate and decisive rudder inputs to counteract these forces and prevent ground loops, a common hazard in tailwheel aircraft due to their rearward center of gravity.[6] Initial ground instruction covers these dynamics, often using diagrams or mockups to illustrate torque and P-factor influences, before progressing to flight training in calm wind conditions. The progression from simulator to real-aircraft training varies but prioritizes hands-on experience in actual tailwheel airplanes for endorsement purposes, as simulators may lack the precise ground-handling feedback needed for proficiency. Flight training typically begins with straight-in approaches and advances to crosswind handling, building up to demonstrated aircraft limits—often 15 knots for light tailwheel types—to ensure pilots can manage drift and maintain alignment.[6] Unlike tricycle gear training, which relies on inherent stability from the forward nose wheel, tailwheel instruction places additional emphasis on mastering three-point landings (all three wheels touching simultaneously for minimum speed and control) versus wheel landings (mains first, tail lowered gradually for better visibility and crosswind utility), adapting pilots to the heightened demand for active control inputs.[42] This specialized focus addresses challenges like reduced forward visibility during rollout, necessitating extra vigilance and technique refinement.[43]Takeoff and Landing Techniques
Conventional landing gear, also known as tailwheel gear, requires specific techniques for safe and effective takeoff and landing operations due to the aircraft's rearward center of gravity and the positioning of the tailwheel behind the main landing gear. These procedures emphasize precise control inputs to maintain directional stability and prevent issues like ground loops or unwanted oscillations. Pilots must adapt to the higher angle of attack on the ground compared to tricycle gear aircraft, which influences visibility and control dynamics.[6] For landings, two primary techniques are employed: the three-point landing and the wheel landing. In a three-point landing, the pilot holds the aircraft off the runway until the main wheels and tailwheel make simultaneous contact at the minimum safe speed, typically around 40-50 knots for light aircraft, ensuring a full stall just above the surface. This method provides the shortest ground roll and is ideal for short or soft fields, as it minimizes forward speed at touchdown and enhances braking effectiveness; however, it demands accurate judgment to avoid bouncing or tail-first contact, which could lead to instability.[6][44] The pilot maintains full aft elevator during the rollout to keep the tail down and uses rudder for steering, transitioning to differential braking only if necessary.[6] The wheel landing, conversely, involves touching down on the main wheels first while keeping the tail raised, allowing for a smoother deceleration on paved surfaces through a tail-low attitude at a slightly higher speed than the three-point method. This technique offers better visibility during approach and greater directional control via the mains, particularly in crosswinds, as the higher touchdown speed—often 5-10 knots above stall—facilitates rudder authority before the tail settles.[6][45] After mains contact, the pilot gradually applies full aft elevator to lower the tail as speed decreases, avoiding abrupt inputs that could cause porpoising or loss of control.[45] Wheel landings are preferred on hard runways to reduce tailwheel wear but require a longer rollout due to the elevated initial speed.[6] Takeoff procedures for conventional gear begin with a tail-low attitude to maximize propeller clearance and directional control. The pilot aligns the aircraft on the runway, applies full power smoothly, and uses forward elevator to raise the tail progressively as airspeed builds, typically reaching rotation or liftoff at 55-65 knots for light aircraft, depending on weight and conditions.[6] Rudder inputs are critical to counter torque and P-factor effects that may cause a leftward swing, especially in the initial tail-low phase; the tail is held at a neutral or slightly raised position until flying speed is attained, allowing natural liftoff without forced rotation.[6] For short- or soft-field takeoffs, flaps may be used per manufacturer specifications, with the tail kept low longer to accelerate efficiently before climbing at the best angle of climb speed.[6] Emergency procedures focus on maintaining precise angle of attack control to avoid propeller strikes, which can occur if the tail is not properly managed during acceleration or deceleration on uneven surfaces. During takeoff, pilots raise the tail early on rough terrain to increase prop clearance, preventing strikes from ground contact; in landings, avoiding excessive forward stick in wheel landings or holding off too long in three-point attitudes mitigates risks by ensuring the fuselage remains at the designed incidence angle.[6] Ground loop prevention involves immediate, firm rudder corrections to any yaw without overcorrecting, supplemented by brakes sparingly to preserve directional stability post-touchdown.[6] These techniques, honed through targeted pilot training, are essential for mitigating the inherent challenges of tailwheel operations.[6]Practical Applications
Fixed-Wing Aircraft Examples
The Piper J-3 Cub, introduced in the 1930s, exemplifies a classic fixed-wing aircraft employing conventional landing gear, featuring fixed main wheels positioned ahead of the center of gravity and a steerable tailwheel for enhanced propeller clearance and short takeoff and landing (STOL) performance. This configuration contributed to its status as an icon for bush flying and training, with over 19,000 units produced by 1947, enabling operations on unprepared surfaces due to the gear's simple, rugged design using steel tube construction.[46] The de Havilland Tiger Moth, a 1930s biplane primary trainer, utilized a conventional taildragger landing gear arrangement with raked-forward main legs to mitigate nose-over risks during braking, paired with a fixed tail skid or wheel for ground handling. Over 8,800 examples were built, serving extensively in military roles across the British Commonwealth during World War II, where the gear's wire-braced, split-axle setup supported operations from grass fields and facilitated aerobatic training.[47] In the modern utility category, the Cessna 185 Skywagon, first flown in the 1950s, incorporates non-retractable conventional landing gear with high-strut main legs and a tailwheel, optimized for rugged off-airport operations in bush environments. This six-seat, high-wing design features large tires and a reinforced spring-steel gear system, allowing it to handle loads up to 3,350 pounds gross weight while maintaining stability on uneven terrain, with production spanning from 1960 to 1985 yielding around 4,000 aircraft.[48] For experimental homebuilt applications, the Rutan Quickie from the late 1970s and 1980s represents an innovative use of conventional landing gear in composite construction, with main wheels mounted at the forward wingtips and a steerable tailwheel for compact ground attitude and lightweight efficiency. This single-seat, pusher-propeller canard achieved a maximum speed of 126 mph and cruise speed of 121 mph on 18-35 hp engines, emphasizing the gear's role in enabling short-field capabilities for amateur builders, with approximately 350 kits sold.[49][50]Rotary-Wing Adaptations
In rotary-wing aircraft, conventional landing gear concepts are adapted primarily through elongated skid systems that parallel the main wheel and tailwheel arrangement of fixed-wing designs, providing fore-and-aft support to manage weight distribution and ground contact under rotor-induced loads. These adaptations emphasize simplicity, reduced weight, and compatibility with vertical operations, where skids replace wheels to absorb impacts from hovers and autorotations without the complexity of retraction mechanisms.[51] Light helicopters like the Robinson R22, entering service in the late 1970s and widely used through the 1980s, employ skid-type landing gear with tubular steel skids and replaceable skid shoes made of hardened steel for enhanced ground handling durability. The rear skid sections function similarly to a tailwheel, offering pivotal support during ground maneuvers and preventing forward skids from digging into soft surfaces, which aids in taxiing and positioning without additional equipment. Frequent inspections of skid shoes are recommended after operations involving ground contact, such as power recovery autorotations, to mitigate wear from friction.[52] Military rotary-wing platforms, including variants of the Bell UH-1 Huey introduced in the 1960s, utilize arched tubular skid gear connected by cross tubes for structural integrity under combat loads. To achieve hybrid wheeled functionality, these skids are fitted with removable hydraulic ground handling wheels that elevate the fuselage, enabling rolling movement across paved or hangar surfaces while preserving the skid's advantages for field operations; two such wheel sets are typically required per aircraft. This combination supports logistical efficiency in forward basing without permanent wheel installations that could increase drag or weight.[53] Tail-supported skid configurations provide stability for hover-taxiing over uneven or sloped terrain, where extended rear contact points help distribute the center of gravity and reduce tip-over risks. This is crucial in austere environments like rough fields or ship decks. Skids also absorb energy effectively during vertical descents on non-prepared surfaces by conforming to contours and reducing shock to the airframe.Retrofitting and Modifications
Conversion from Tricycle Gear
Converting an aircraft from tricycle to conventional landing gear is a major retrofit aimed at enhancing short takeoff and landing (STOL) performance, particularly for operations on unprepared surfaces where the original tricycle configuration's limitations, such as restricted propeller clearance and longer required runway lengths, can be disadvantageous. The process begins with structural modifications to the airframe. The main landing gear legs are relocated forward along the fuselage to position the axles properly under the wings for optimal propeller ground clearance and center of gravity balance. A tailwheel assembly is then installed at the rear fuselage, involving the addition of a mounting bracket, spring, and steering linkage, often with reinforcements to adjacent bulkheads and skin panels to handle the new load paths.[54] Regulatory approval is mandatory for certified aircraft, typically obtained through an FAA Supplemental Type Certificate (STC). For instance, 1970s-era kits, such as the Ron Fravel STC for early Cessna 172 models, enable the use of Cessna 170-derived gear components and specify detailed installation procedures to maintain structural integrity and flight characteristics.[55] Other approved STCs, like SA02376AK for Cessna 172 and 175 series, include provisions for upgraded tires and further reinforcements.[56] Post-conversion performance shifts toward better STOL capabilities, with reduced takeoff and landing distances on rough terrain due to improved propeller clearance and a lower angle of attack on the ground, though the added structural elements may increase empty weight. Costs for such conversions on light aircraft can be significant, often ranging from $10,000 to $20,000 as of the early 2000s (adjusted for inflation), encompassing parts, STC fees, and labor for disassembly, modification, and reassembly, followed by updated weight and balance calculations and flight testing.[57] Conversions may alter aircraft handling, requiring thorough flight testing and potential pilot endorsement updates.Maintenance and Upgrade Considerations
Routine maintenance of conventional landing gear emphasizes regular inspections to ensure structural integrity and operational safety, as outlined in FAA Advisory Circular 43.13-1B. Annual or 100-hour inspections require visual examination of struts, wheels, attaching hardware, and shock absorption components for wear, cracks, corrosion, and abnormal play, with the aircraft often jacked to facilitate checks on alignment and movement. For bungee cord systems common in main gear, technicians inspect cords for fraying, stretching, or degradation, replacing them if showing signs of wear to maintain proper shock absorption. Bungee cords typically require replacement every three years or 500 flight hours, whichever occurs first.[58][59] Tire pressures must be verified per manufacturer specifications; for example, on the Cessna 170, mains are typically 24 psi and the tailwheel 34 psi, to prevent uneven wear and ensure stability.[60] Common upgrades focus on enhancing shock absorption and reducing vibrations, particularly in the tailwheel assembly. Hydraulic shimmy dampers, such as the STC-approved 3200 series, can replace traditional mechanical or bungee-based systems, providing hydraulic damping to counteract oscillations and improve ground handling stability during taxi, takeoff, and landing.[61] These upgrades are lightweight and compact, addressing issues like tailwheel shimmy without requiring major structural changes, and are suitable for various caster angles and operating conditions.[62] For main gear, replacing aged bungee cords with modern equivalents or supplementary dampers extends component life and enhances ride quality over rough surfaces. Corrosion prevention is critical, especially for tailwheels exposed to environmental hazards. In saltwater or coastal operations, aircraft must be rinsed with fresh water after exposure to remove salt deposits, followed by application of corrosion-preventive compounds like MIL-C-16173 Grade 4 to protect steel and aluminum components.[58] Regular inspections of wheel wells, axles, and fittings for pitting or oxidation, using methods like magnetic particle testing for steel parts, help identify early degradation.[58] Priming corroded areas with zinc chromate and applying protective coatings further mitigates risks in humid or marine environments.[58] Lifecycle costs for conventional landing gear involve periodic component overhauls and replacements to sustain airworthiness. Tailwheel assemblies and related hardware undergo overhaul every 1,000 to 2,000 hours, depending on usage and manufacturer guidelines, with costs influenced by labor for disassembly, cleaning, and lubrication.[63] Overall, adherence to FAA-mandated annual inspections minimizes downtime and extends gear longevity, though operations in harsh conditions may accelerate wear and increase expenses.[58]References
- https://www.boldmethod.com/learn-to-fly/aerodynamics/[tricycle](/page/Tricycle)-gear-aircraft-instability/