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68-655: Lockheed began developing its rigid rotor concept with the CL-475 helicopter design in 1959. The choice of a rigid rotor meant that the helicopter was more agile than it would have been with a flapping rotor. The performance of the CL-475 encouraged Lockheed to seek further development. Lockheed submitted the CL-475 to the Army as a candidate to replace the Bell OH-13 Sioux and Hiller OH-23 Raven observation helicopters. Lockheed also tested

136-497: A fantail ), and MD Helicopters ' NOTAR . The number of rotors is also important, many helicopters have two rotors in a single line, and another configuration is 4 rotors. An example of two-blade rotor is the Bell 212 , and four blade version of this helicopter is the Bell 412 . An example of the effect of rotor blade number is the UH-72 ( EC145 variant ); the A model had four blades, but

204-409: A common flapping or teetering hinge at the rotor shaft. This allows the blades to flap together in opposite motions like a seesaw . This underslinging of the blades below the teetering hinge, combined with an adequate dihedral or coning angle on the blades, minimizes variations in the radius of each blade's center of mass from the axis of rotation as the rotor turns, which in turn reduces the stress on

272-400: A composite yoke. This yoke is attached to the mast and runs through the blade grips between the blades and the shear bearing inside the grip. This yoke does transfer some movement of one blade to another, usually opposing blades. While this is not fully articulated, the flight characteristics are very similar and maintenance time and cost are reduced. The term rigid rotor usually refers to

340-468: A conventional design the rotor blades' angle of attack is reduced via a collective pitch control. Slowing the rotor instead can reduce drag during this phase of flight and thus improve fuel economy. Most helicopters have a single main rotor but require a separate rotor to overcome torque. This is accomplished through a variable-pitch antitorque rotor or tail rotor. This is the design that Igor Sikorsky settled on for his VS-300 helicopter, and it has become

408-447: A direction opposite that of the main rotor's rotation, thereby countering the torque effect created by the main rotor. Tail rotors are simpler than main rotors since they require only collective changes in pitch to vary thrust. The pitch of the tail rotor blades is adjustable by the pilot via the anti-torque pedals, which also provide directional control by allowing the pilot to rotate the helicopter around its vertical axis, thereby changing

476-494: A ducted fan can have a smaller size than a conventional tail rotor. The Fenestron was used for the first time at the end of the 1960s on the second experimental model of Sud Aviation's SA 340 and produced on the later model Aérospatiale SA 341 Gazelle . Besides Eurocopter and its predecessors, a ducted fan tail rotor was also used on the canceled military helicopter project, the United States Army 's RAH-66 Comanche , as

544-408: A fixed RPM (within a narrow range of a few percent), but a few experimental aircraft used variable speed rotors . Unlike the small diameter fans used in turbofan jet engines, the main rotor on a helicopter has a large diameter that lets it accelerate a large volume of air. This permits a lower downwash velocity for a given amount of thrust. As it is more efficient at low speeds to accelerate

612-593: A flexible hub, which allows for blade bending (flexing) without the need for bearings or hinges. These systems, called flexures , are usually constructed from composite material. Elastomeric bearings may also be used in place of conventional roller bearings . Elastomeric bearings are constructed from a rubber type material and provide limited movement that is perfectly suited for helicopter applications. Flexures and elastomeric bearings require no lubrication and, therefore, require less maintenance. They also absorb vibration, which means less fatigue and longer service life for

680-480: A helicopter are long, narrow airfoils with a high aspect ratio , a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure, and steel or titanium , with abrasion shields along

748-409: A helicopter. Twin rotors turn in opposite directions to counteract the torque effect on the aircraft without relying on an antitorque tail rotor. This lets the aircraft apply the power that would have driven a tail rotor to the main rotors, increasing lifting capacity. Primarily, three common configurations use the counterrotating effect on rotorcraft. Tandem rotors are two rotors—one mounted behind

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816-548: A hingeless rotor system with blades flexibly attached to the hub. Irv Culver of Lockheed developed one of the first rigid rotors, which was tested and developed on a series of helicopters in the 1960s and 1970s. In a rigid rotor system, each blade flaps and drags about flexible sections of the root. A rigid rotor system is mechanically simpler than a fully articulated rotor system. The aerodynamic and mechanical loads from flapping and lead/lag forces are accommodated through rotor blades flexing, rather than through hinges. By flexing,

884-441: A large amount of air by a small degree than a small amount of air by a large degree, a low disk loading (thrust per disc area) greatly increases the aircraft's energy efficiency, and this reduces the fuel use and permits reasonable range. The hover efficiency ("figure of merit") of a typical helicopter is around 60%. The inner third length of a rotor blade contributes very little to lift due to its low airspeed. The blades of

952-417: A minimum. This stability is achieved by keeping the center of pressure virtually unchanged as the angle of attack changes. Center of pressure is the imaginary point on the chord line where the resultant of all aerodynamic forces are considered to be concentrated. Today, designers use thinner airfoils and obtain the required rigidity by using composite materials. Some airfoils are asymmetrical in design, meaning

1020-577: A rigid rotor compound helicopter with a pusher tail-mounted propeller which was ordered into production as the Lockheed AH-56 Cheyenne attack helicopter. However technical problems led first to delays then to a suspension of production. Compounded by inter-service rivalry and political issues the Cheyenne was cancelled completely in 1972 and it was Lockheed's last helicopter. The two XH-51A examples (Serial Numbers 61-51262 and 61-51263) are stored at

1088-544: A speed of 263 knots (302.6 mph, 486.9 km/h) in a shallow descent. The highest level flight speed was 223 kn (413 km/h; 257 mph). In June 1964, NASA ordered a five-seat, three-bladed variant, the XH-51N (NASA 531) as a helicopter test vehicle. Lockheed built two demonstrator aircraft, designated the Lockheed Model 286, to market to the public (registration numbers N286L and N265LC ). These aircraft had

1156-474: A tandem configuration. An advantage of quad rotors on small aircraft such as drones is the opportunity for mechanical simplicity. A quadcopter using electric motors and fixed-pitch rotors has only four moving parts. Pitch, yaw and roll can be controlled by changing the relative lift of different rotor pairs without changing total lift. The two families of airfoils are Symmetrical blades are very stable, which helps keep blade twisting and flight control loads to

1224-504: Is an increased mechanical complexity of the rotor system because it requires linkages and swashplates for two rotor systems. Also, because the rotors must rotate in opposite directions, the mast is more complex, and control linkages for pitch changes to the upper rotor system must pass through the lower rotor system. An example of coaxial design in a compound helicopter was the Sikorsky Skyraider X , which also had pusher prop at

1292-492: Is derived from the Greek words helix , helik-, meaning spiral; and pteron meaning wing. The helicopter rotor is powered by the engine, through the transmission, to the rotating mast. The mast is a cylindrical metal shaft that extends upward from—and is driven by—the transmission. At the top of the mast is the attachment point (colloquially called a Jesus nut ) for the rotor blades called the hub. The rotor blades are then attached to

1360-401: Is gradual and visible. The metal-to-metal contact of older bearings and the need for lubrication is eliminated in this design. The third hinge in the fully articulated system is called the feathering hinge about the feathering axis. This hinge is responsible for the change in pitch of rotor blades excited via pilot input to the collective or cyclic. A variation of the fully articulated system is

1428-470: Is simple and eliminates torque reaction, prototypes that have been built are less fuel efficient than conventional helicopters. Except for tip jets driven by unburnt compressed air, very high noise levels is the single most important reason why tip jet powered rotors have not gained wide acceptance. However, research into noise suppression is ongoing and may help make this system viable. There are several examples of tip jet powered rotorcraft. The Percival P.74

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1496-452: Is that the center of pressure changes with changes in angle of attack. When the center of pressure lifting force is behind the pivot point on a rotor blade, it tends to cause the rotor disc to pitch up. As the angle of attack increases, the center of pressure moves forward. If it moves ahead of the pivot point, the pitch of the rotor disc decreases. Since the angle of attack of the rotor blades is constantly changing during each cycle of rotation,

1564-483: Is the most common tandem rotor helicopter. Coaxial rotors are a pair of rotors mounted one above the other on the same shaft and turning in opposite directions. The advantage of the coaxial rotor is that, in forward flight, the lift provided by the advancing halves of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift: retreating blade stall . However, other design considerations plague coaxial rotors. There

1632-649: The Focke-Achgelis Fa 223 , as well as the world's largest helicopter ever built, the Mil Mi-12 . It is also the configuration found on tiltrotors such as the Bell-Boeing V-22 Osprey and the AgustaWestland AW609 . A quad rotor or quadrotor comprises four rotors in an "X" configuration. Rotors to the left and right are in a transverse configuration while those in the front and to the rear are in

1700-516: The United States Army Aviation Museum at Fort Novosel . Data from Janes's All The World's Aircraft 1969-70 General characteristics Performance Related development Related lists Helicopter rotor#Rigid On a helicopter , the main rotor or rotor system is the combination of several rotary wings ( rotor blades ) with a control system, that generates the aerodynamic lift force that supports

1768-548: The lead-lag hinge or drag hinge , allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for acceleration and deceleration caused by the difference in drag experienced by the advancing and retreating blades. Later models have switched from using traditional bearings to elastomeric bearings. Elastomeric bearings are naturally fail-safe and their wear

1836-476: The soft-in-plane rotor system. This type of rotor can be found on several aircraft produced by Bell Helicopter, such as the OH-58D Kiowa Warrior . This system is similar to the fully articulated type in that each blade has the ability to lead/lag and hunt independently of the other blades. The difference between a fully articulated system and soft-in-plane system is that the soft-in-plane system utilises

1904-555: The FANTAIL. NOTAR, an acronym for no ta il r otor , is a helicopter anti-torque system that eliminates the use of the tail rotor on a helicopter. Although the concept took some time to refine, the NOTAR system is simple in theory and provides antitorque the same way a wing develops lift by using the Coandă effect . A variable pitch fan is enclosed in the aft fuselage section immediately forward of

1972-516: The U.S. and radio-control aeromodeler Dieter Schlüter in Germany, found that flight stability for helicopters could be achieved with a stabilizer bar, or flybar. The flybar has a weight or paddle (or both for added stability on smaller helicopters) at each end to maintain a constant plane of rotation. Through mechanical linkages, the stable rotation of the bar mixes with the swashplate movement to damp internal (steering) as well as external (wind) forces on

2040-546: The UH-72B was changed to five blades which reduced vibration. Other blade numbers are possible, for example, the CH-53K , a large military transport helicopter has a seven blade main rotor. The tail rotor is a smaller rotor mounted so that it rotates vertically or near-vertically at the end of the tail of a traditional single-rotor helicopter. The tail rotor's position and distance from the center of gravity allow it to develop thrust in

2108-504: The United States. Examples of hazards faced by Helicopters, includes ones common to aircraft such as bird-strikes , but also a number of others depending on the design of the helicopter and conditions. This includes but its not limited to: Dynamic rollover , Ground resonance , Loss of tail-rotor effectiveness , Retreating blade stall , Dynamic stall , Vortex ring state , Servo transparency , Mast bumping, and Tailstrike . Because

Lockheed XH-51 - Misplaced Pages Continue

2176-424: The advantage of easy reconfiguration and fewer mechanical parts. Most helicopter rotors spin at constant speed. However slowing the rotor in some situations can bring benefits. As forward speed increases, the advancing rotor tip speed soon approaches the speed of sound . To reduce the problem, the speed of rotation may be slowed, allowing the helicopter to fly faster. To adjust the rotor lift at slower speeds, in

2244-426: The amount of airflow from the rotorwash. This is augmented by a direct jet thruster which also provides directional yaw control, with the presence of a fixed-surface empennage near the end of the tail, incorporating vertical stabilizers. Development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began concept development work. In December 1981, Hughes flew an OH-6A fitted with NOTAR for

2312-462: The blades from lead and lag forces caused by the Coriolis effect . Secondary flapping hinges may also be used to provide sufficient flexibility to minimize bouncing. Feathering is accomplished by the feathering hinge at the blade root, which allows changes to the pitch angle of the blade. Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some rotor hubs incorporate

2380-456: The blades tend to flap, feather, lead, and lag to a greater degree. Hexacopter is a popular configuration for unmanned drone helicopters, and ways to manage and improve the control of multirotor drones has been studied. The octocopter configuration is used notably in NASA's planned Dragonfly probe , designed to fly in the atmosphere of Saturn 's Moon Titan . A manned multirotor helicopter that

2448-451: The blades themselves compensate for the forces that previously required rugged hinges. The result is a rotor system that has less lag in control response because of the large hub moment typically generated. The rigid rotor system thus eliminates the danger of mast bumping inherent in semirigid rotors. The semirigid rotor can also be referred to as a teetering or seesaw rotor. This system is normally composed of two blades that meet just under

2516-578: The commercial market waters without success. However, in February 1962, Lockheed's Model 186, a new design based on the CL-475 rigid rotor, was selected as the winner for a joint Army-Navy program to evaluate the rigid rotor for high-speed flight capability. Two four-seat, three-bladed XH-51As were ordered and built for the program. Powered by the 550 shp (410 kW) Pratt & Whitney Canada PT6B-9 turboshaft engine, XH-51A (serial number 61-51262) first flew on 2 November 1962. As flight testing progressed,

2584-465: The designs has not fully settled, with eVTOL being a popular name, also manned drone, or even flying car being used, or in certain cases Air Taxi. As an aircraft, the FAA has worked to refine the regulations surrounding eVTOL designs, which is oriented towards traditional Helicopters and airplanes, but in 2024 finalized airworthiness criteria as it resolves how to classify and certify these types of aircraft in

2652-423: The direction the craft is pointed. Fenestron and FANTAIL are trademarks for a ducted fan mounted at the end of the tail boom of the helicopter and used in place of a tail rotor. Ducted fans have between eight and eighteen blades arranged with irregular spacing so that the noise is distributed over different frequencies. The housing is integral with the aircraft skin and allows a high rotational speed; therefore,

2720-459: The end of wings or outriggers perpendicular to the body of the aircraft. Similar to tandem rotors and intermeshing rotors, the transverse rotor also uses differential collective pitch. But like the intermeshing rotors, the transverse rotors use the concept for changes in the roll attitude of the rotorcraft. This configuration is found on two of the first viable helicopters, the Focke-Wulf Fw 61 and

2788-429: The engine turns the rotor creates a torque effect that causes the body of the helicopter to turn in the opposite direction of the rotor. To eliminate this effect, some sort of antitorque control must be used with a sufficient margin of power available to allow the helicopter to maintain its heading and provide yaw control. The three most common controls used today are the tail rotor, Eurocopter's Fenestron (also called

Lockheed XH-51 - Misplaced Pages Continue

2856-482: The first time. A more heavily modified prototype demonstrator first flew in March 1986 and successfully completed an advanced flight-test program, validating the system for future application in helicopter design. There are currently three production helicopters that incorporate the NOTAR design, all produced by MD Helicopters. This antitorque design also improves safety by eliminating the possibility of personnel walking into

2924-625: The five-seat configuration of the XH-51N with the four-bladed rotor system of the XH-51A. The Model 286 was certificated for civil operation by the FAA on 30 June 1966, but Lockheed never sold any aircraft. Lockheed used the aircraft for several years as executive transports. The aircraft were eventually sold to a collector and later destroyed by fire in 1988. To meet the US Army's "Advanced Aerial Fire Support System" program for an attack helicopter, Lockheed designed

2992-402: The front rotor tilts right and the rear rotor tilts left. To pivot left, the front rotor tilts left and the rear rotor tilts right. All rotor power contributes to lift, and it is simpler to handle changes in the center of gravity fore-aft. However, it requires the expense of two large rotors rather than the more common one large main rotor and a much smaller tail rotor. The Boeing CH-47 Chinook

3060-470: The helicopter components. Controls vary the pitch of the main rotor blades cyclically throughout rotation. The pilot uses this to control the direction of the rotor thrust vector , which defines the part of the rotor disc where the maximum thrust develops. Collective pitch varies the magnitude of rotor thrust by increasing or decreasing thrust over the whole rotor disc at the same time. These blade pitch variations are controlled by tilting, raising, or lowering

3128-506: The hub, and the hub can have 10-20 times the drag of the blade. Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: rigid, semirigid, and fully articulated, although some modern rotor systems use a combination of these classifications. A rotor is a finely tuned rotating mass, and different subtle adjustments reduce vibrations at different airspeeds. The rotors are designed to operate at

3196-429: The individual blades through pitch links and pitch horns. The non-rotating plate is connected to links that are manipulated by pilot controls—specifically, the collective and cyclic controls. The swash plate can shift vertically and tilt. Through shifting and tilting, the non-rotating plate controls the rotating plate, which in turn controls the individual blade pitch. A number of engineers, among them Arthur M. Young in

3264-586: The leading edge. Rotorcraft blades are traditionally passive; however, some helicopters include active components on their blades. The Kaman K-MAX uses trailing edge flaps for blade pitch control and the Hiller YH-32 Hornet was powered by ramjets mounted on the blade ends. As of 2010 , research into active blade control through trailing edge flaps is underway. Tips of some helicopter blades can be specially designed to reduce turbulence and noise and to provide more efficient flying. An example of such tips are

3332-482: The main rotor is vital to keeping a helicopter in the air, any damage to can have disastrous consequences. Because the tip is usually the farthest extremity helicopters flying in formation have be careful to keep their distance and not touch tips or tail rotors, or with surroundings. Blade pitch Too Many Requests If you report this error to the Wikimedia System Administrators, please include

3400-485: The most unusual design of this type was the Rotary Rocket Roton ATV , which was originally envisioned to take off using a rocket-tipped rotor. The French Sud-Ouest Djinn used unburnt compressed air to drive the rotor, which minimized noise and helped it become the only tip jet driven rotor helicopter to enter production. The Hughes XH-17 had a tip jet-driven rotor, which remains the largest rotor ever fitted to

3468-449: The original three-bladed, rigid rotor system demonstrated instability at higher speed ranges. Lockheed engineers solved the problem by modifying the aircraft with a four-bladed rotor system. In 1963, the Army's Technology Research and Evaluation Command (TRECOM) contracted with Lockheed to modify one of the XH-51 aircraft into a compound helicopter . The second XH-51A (serial number 61-51263)

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3536-495: The other. Coaxial rotors are two rotors mounted one above the other on the same axis. Intermeshing rotors are two rotors mounted close to each other at a sufficient angle to let the rotors intermesh over the top of the aircraft. Another configuration—found on tiltrotors and some early helicopters—is called transverse rotors, where a pair of rotors are mounted at each end of a wing-type structure or outrigger. Tandem rotors are two horizontal main rotor assemblies mounted one behind

3604-480: The other. Tandem rotors achieve pitch attitude changes to accelerate and decelerate the helicopter through a process called cyclic pitch. To pitch forward and accelerate, both rotors increase the pitch at the rear and reduce the pitch at the front (cyclic) keeping torque the same on both rotors, flying sideways is achieved by increasing the pitch on one side and reducing pitch on the other. Yaw control develops through opposing cyclic pitch in each rotor. To pivot right,

3672-471: The others. These rotor systems usually have three or more blades. The blades are allowed to flap, feather, and lead or lag independently of each other. The horizontal hinge, called the flapping hinge , allows the blade to move up and down. This movement is called flapping and is designed to compensate for dissymmetry of lift . The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one hinge. The vertical hinge, called

3740-579: The rear. Intermeshing rotors on a helicopter are a set of two rotors turning in opposite directions with each rotor mast mounted on the helicopter with a slight angle to the other so that the blades intermesh without colliding. This configuration is sometimes referred to as a synchropter. Intermeshing rotors have high stability and powerful lifting capability. The arrangement was pioneered in Nazi Germany in 1939 with Anton Flettner 's successful Flettner Fl 265 design, and later placed in limited production as

3808-406: The recognized convention for helicopter design, although designs do vary. When viewed from above, most American helicopter rotors turn counter-clockwise; French and Russian helicopters turn clockwise. Another type of rotorcraft is the tiltrotor , which has many similarities to helicopter main rotors when in mode of powered lift . With a single main rotor helicopter, the creation of torque as

3876-451: The rotor. The Lockheed rotor system used a control gyro, similar in principle to that of the Bell stabilizer bar, but designed for both hands-off stability and rapid control response of the hingeless rotor system. In fly-by-wire helicopters or Remote Control (RC) models, a microcontroller with gyroscope sensors and a Venturi sensor can replace the stabilizer. This flybar-less design has

3944-417: The rotor. This makes it easier for the pilot to maintain control of the aircraft. Stanley Hiller arrived at a similar method to improve stability by adding short stubby airfoils, or paddles, at each end. However, Hiller's "Rotormatic" system also delivered cyclic control inputs to the main rotor as a sort of control rotor, and the paddles provided the added stability by damping the effects of external forces on

4012-647: The successful Flettner Fl 282 Kolibri , used by the German Kriegsmarine in small numbers (24 airframes produced) as an experimental light anti-submarine warfare helicopter. During the Cold War , an American company, Kaman Aircraft , produced the HH-43 Huskie for USAF firefighting and rescue missions. The latest Kaman model, the Kaman K-MAX , is a dedicated sky crane design. Transverse rotors are mounted on

4080-410: The swash plate with the flight controls. The vast majority of helicopters maintain a constant rotor speed (RPM) during flight, leaving the angle of attack of the blades as the sole means of adjusting thrust from the rotor. The swash plate is two concentric disks or plates. One plate rotates with the mast, connected by idle links, while the other does not rotate. The rotating plate is also connected to

4148-438: The tail boom and is driven by the main rotor transmission. To provide the sideways force to counteract the clockwise torque produced by a counterclockwise-spinning main rotor (as seen from above the main rotor), the variable-pitch fan forces low pressure air through two slots on the right side of the tailboom, causing the downwash from the main rotor to hug the tailboom, producing lift and thus a measure of antitorque proportional to

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4216-498: The tail rotor. A predecessor (of sorts) to this system existed in the form of Great Britain's Cierva W.9 helicopter, a late 1940s aircraft using the cooling fan from its piston engine to push air through a nozzle built into the tailboom to counteract rotor-torque. The main rotor may be driven by tip jets. Such a system may be powered by high pressure air provided by a compressor. The air may or may not be mixed with fuel and burnt in ram-jets, pulse-jets, or rockets. Though this method

4284-545: The tips of the BERP rotors created during the British Experimental Rotor Programme. Description of a simple rotor: Juan de la Cierva developed the fully articulating rotor for the autogyro . The basis of his design permitted successful helicopter development. In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges that let the blade move independently of

4352-405: The upper and lower surfaces do not have the same camber. Normally these airfoils would not be as stable, but this can be corrected by bending the trailing edge to produce the same characteristics as symmetrical airfoils. This is called "reflexing." Using this type of rotor blade allows the rotor system to operate at higher forward speeds. One of the reasons an asymmetrical rotor blade is not as stable

4420-487: The weight of the helicopter, and the thrust that counteracts aerodynamic drag in forward flight. Each main rotor is mounted on a vertical mast over the top of the helicopter, as opposed to a helicopter tail rotor , which connects through a combination of drive shaft (s) and gearboxes along the tail boom. The blade pitch is typically controlled by the pilot using the helicopter flight controls . Helicopters are one example of rotary-wing aircraft ( rotorcraft ). The name

4488-433: Was flying in the 2010s had 18 electrically powered rotors; the single seat aircraft is powered by batteries. The first aerobatic manned drone, as this type of electrically powered multi-rotor helicopter is known, had 12 rotors and could carry 1-2 people. Manned drones or eVTOL as they are called typically multirotor designs powered by batteries gained increasing popularity and designs in the 2020s. The naming of some of

4556-475: Was subsequently converted by adding wings with a span of 16.1 ft (4.9 m), and a 2,900 lbf (12.9 kN) Pratt & Whitney J60-2 turbojet engine mounted on the left wing to increase performance. The XH-51A Compound first flew without powering up the turbojet on 21 September 1964, while tests were conducted for balance and handling. The aircraft's first flight as a true compound helicopter took place on 10 April 1965. and on 29 November 1967 achieved

4624-418: Was under-powered and could not fly. The Hiller YH-32 Hornet had good lifting capability but performed poorly otherwise. Other aircraft used auxiliary thrust for translational flight so that the tip jets could be shut down while the rotor autorotated. The experimental Fairey Jet Gyrodyne , 48-seat Fairey Rotodyne passenger prototypes and McDonnell XV-1 compound gyroplanes flew well using this method. Perhaps

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