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38-477: The XH-17 was a heavy-lift rotorcraft that was designed to lift loads in excess of 15 metric tons. To speed construction, parts of the XH-17 were scavenged from other aircraft. The front wheels came from a North American B-25 Mitchell and the rear wheels from a Douglas C-54 Skymaster . The fuel tank was a bomb bay-mounted unit from a Boeing B-29 Superfortress . The cockpit was from a Waco CG-15 military glider and

76-411: A jet engine , and there is no need for a tail rotor . In high-speed flight the airfoil is stopped in a spanwise position, as the main wing of a three-surface aircraft , and the engine exhausts through an ordinary jet nozzle. Two Boeing X-50 Dragonfly prototypes with a two-bladed rotor were flown from 2003 but the program ended after both had crashed, having failed to transition successfully. In 2013

114-444: A helicopter – with anti-torque and propulsion for forward flight provided by one or more propellers mounted on short or stub wings. As power is increased to the propeller, less power is required by the rotor to provide forward thrust resulting in reduced pitch angles and rotor blade flapping. At cruise speeds with most or all of the thrust being provided by the propellers, the rotor receives power only sufficient to overcome

152-414: A helicopter, autogyros and rotor kites do not have an engine powering their rotors, but while an autogyro has an engine providing forward thrust that keeps the rotor turning, a rotor kite has no engine at all, and relies on either being carried aloft and dropped from another aircraft, or by being towed into the air behind a car or boat. A rotary wing is characterised by the number of blades . Typically this

190-408: A specific airspeed at which a power-off glide is most efficient. The best airspeed is the one that combines the greatest glide range with the slowest rate of descent. The specific airspeed is different for each type of helicopter, yet certain factors (density altitude, wind) affect all configurations in the same manner. The specific airspeed for autorotations is established for each type of helicopter on

228-412: A state of autorotation to develop lift, and an engine-powered propeller , similar to that of a fixed-wing aircraft , to provide thrust. While similar to a helicopter rotor in appearance, the autogyro's rotor must have air flowing up and through the rotor disk in order to generate rotation. Early autogyros resembled the fixed-wing aircraft of the day, with wings and a front-mounted engine and propeller in

266-436: A three-year period beginning in 1952. The XH-17 flew in 1953 at a gross weight in excess of 50,000 pounds (23,000 kg). It still holds the record for flying with the world's largest rotor system. Only one unit was built, since the aircraft was too cumbersome and inefficient to warrant further development. The propulsion system was unusual. Two General Electric J35 turbojet engines were used, sending bleed air up through

304-429: A tractor configuration to pull the aircraft through the air. Late-model autogyros feature a rear-mounted engine and propeller in a pusher configuration. The autogyro was invented in 1920 by Juan de la Cierva . The autogyro with pusher propeller was first tested by Etienne Dormoy with his Buhl A-1 Autogyro . The rotor of a gyrodyne is normally driven by its engine for takeoff and landing – hovering like

342-402: A −63 °C (−81.4 °F) temperature at that altitude, as soon as he reduced power, the engine flamed out and could not be restarted. By using autorotation he was able to land the aircraft safely. Autorotation is the normal operating mode of autogyros ; the distance record is 1653 km. For helicopter, "autorotation" refers to the descending maneuver in which the engine is disengaged from

380-439: Is a heavier-than-air aircraft with rotary wings that spin around a vertical mast to generate lift . The assembly of several rotor blades mounted on a single mast is referred to as a rotor . The International Civil Aviation Organization (ICAO) defines a rotorcraft as "supported in flight by the reactions of the air on one or more rotors". Rotorcraft generally include aircraft where one or more rotors provide lift throughout

418-625: Is a powered rotorcraft with rotors driven by the engine(s) throughout the flight, allowing it to take off and land vertically, hover, and fly forward, backward, or laterally. Helicopters have several different configurations of one or more main rotors. Helicopters with a single shaft-driven main lift rotor require some sort of antitorque device such as a tail rotor , fantail , or NOTAR , except some rare examples of helicopters using tip jet propulsion, which generates almost no torque. An autogyro (sometimes called gyrocopter, gyroplane, or rotaplane) uses an unpowered rotor, driven by aerodynamic forces in

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456-399: Is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro , rather than engine power driving the rotor. The term autorotation dates to a period of early helicopter development between 1915 and 1920, and refers to the rotors turning without the engine. It is analogous to

494-415: Is an engine malfunction or failure, but autorotation can also be performed in the event of a complete tail rotor failure, or following loss of tail-rotor effectiveness , since there is virtually no torque produced in an autorotation. If altitude permits, autorotations may also be used to recover from a vortex ring state , also known as settling with power . In all cases, a successful landing depends on

532-412: Is between two and six per driveshaft. A rotorcraft may have one or more rotors. Various rotor configurations have been used: Some rotary wing aircraft are designed to stop the rotor for forward flight so that it then acts as a fixed wing. For vertical flight and hovering it spins to act as a rotary wing or rotor, and for forward flight at speed it stops to act as a fixed wing providing some or all of

570-399: Is drawn into the main rotor system from above and forced downward, but during autorotation, air moves into the rotor system from below as the helicopter descends. Autorotation is permitted mechanically because of both a freewheeling unit , which allows the main rotor to continue turning even if the engine is not running, as well as aerodynamic forces of relative wind maintaining rotor speed. It

608-443: Is required to stop a helicopter that is descending more slowly. Therefore, autorotative descents at very low or very high airspeeds are more critical than those performed at the minimum rate of descent airspeed. An optimum landing manoeuvre stops all of vertical movement, horizontal movement and rotational movement within the craft to a perfect standstill. In practice a perfect landing is rarely achievable. Each type of helicopter has

646-404: Is the means by which a helicopter can land safely in the event of complete engine failure. Consequently, all single-engine helicopters must demonstrate this capability to obtain a type certificate . The longest helicopter autorotation in history was performed by Jean Boulet in 1972 when he reached a record altitude of 12,440 m (40,814 ft) in an Aérospatiale SA 315B Lama . Because of

684-517: The gliding flight of a fixed-wing aircraft. Some trees (for example maple trees) have seeds that have wing-like structures that enable the seed to spin to the ground in autorotation, which helps the seeds to disseminate over a wider area. The most common use of autorotation in helicopters is to safely land the aircraft in the event of an engine failure or tail-rotor failure. It is a common emergency procedure taught to helicopter pilots as part of their training. In normal powered helicopter flight, air

722-570: The US Naval Research Laboratory (NRL) published a vertical-to-horizontal flight transition method and associated technology, patented December 6, 2011, which they call the Stop-Rotor Rotary Wing Aircraft. The Australian company StopRotor Technology Pty Ltd has developed a prototype Hybrid RotorWing (HRW) craft. The design uses high alpha airflow to provide a symmetrical airflow across all

760-607: The XH-17 had a very small tail rotor compared to its main rotor. This drive system was inefficient, limiting the test aircraft to a range of only 40 miles (64 km). The XH-28 was a derivative, with a maximum weight of 104,000 pounds (47,000 kg). Though a wooden mockup of the design was made, the program was canceled and none were built. Data from McDonnell Douglas aircraft since 1920 Vol.2 General characteristics Performance Aircraft of comparable role, configuration, and era Rotorcraft A rotary-wing aircraft , rotorwing aircraft or rotorcraft

798-432: The basis of average weather and wind conditions and normal loading. A helicopter operated with heavy loads in high density altitude or gusty wind conditions can achieve best performance from a slightly increased airspeed in the descent. At low density altitude and light loading, best performance is achieved from a slight decrease in normal airspeed. Following this general procedure of fitting airspeed to existing conditions,

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836-443: The blade radius, which produces the forces needed to turn the blades during autorotation. Total aerodynamic force in the driving region is inclined slightly forward of the axis of rotation, producing a continual acceleration force. This inclination supplies thrust, which tends to accelerate the rotation of the blade. Driving region size varies with blade pitch setting, rate of descent, and rotor rotational speed. The inner 25 percent of

874-414: The driving region, the pilot can adjust autorotative rotational speed. For example, if the collective pitch is raised, the pitch angle increases in all regions. This causes the point of equilibrium to move inboard along the blade's span, thereby increasing the size of the driven region. The stall region also becomes larger while the driving region becomes smaller. Reducing the size of the driving region causes

912-432: The entire flight, such as helicopters , autogyros , and gyrodynes . Compound rotorcraft augment the rotor with additional thrust engines, propellers, or static lifting surfaces. Some types, such as helicopters, are capable of vertical takeoff and landing . An aircraft which uses rotor lift for vertical flight but changes to solely fixed-wing lift in horizontal flight is not a rotorcraft but a convertiplane . A helicopter

950-457: The helicopter's height and velocity at the commencement of autorotation (see height-velocity diagram ). At the instant of engine failure, the main rotor blades are producing lift and thrust from their angle of attack and velocity . By immediately lowering collective pitch , which must be done in case of an engine failure, the pilot reduces lift and drag and the helicopter begins an immediate descent, producing an upward flow of air through

988-609: The lift required. Additional fixed wings may also be provided to help with stability and control and to provide auxiliary lift. An early American proposal was the conversion of the Lockheed F-104 Starfighter with a triangular rotor wing. The idea was later revisited by Hughes. The Sikorsky S-72 research aircraft underwent extensive flight testing. In 1986 the Sikorsky S-72 Rotor Systems Research Aircraft (RSRA)

1026-437: The main rotor system and the rotor blades are driven solely by the upward flow of air through the rotor. The freewheeling unit is a special clutch mechanism that disengages any time the engine rotational speed is less than the rotor rotational speed. If the engine fails, the freewheeling unit automatically disengages the engine from the main rotor, allowing the main rotor to rotate freely. The most common reason for autorotation

1064-487: The pilot can achieve approximately the same glide angle in any set of circumstances and estimate the touchdown point. This optimum glide angle is usually 17–20 degrees. During vertical autorotation, the rotor disc is divided into three regions—the driven region, the driving region, and the stall region. The sizes of these regions vary with the blade pitch, rate of descent, and rotor rotational speed. When changing autorotative rotational speed, blade pitch, or rate of descent,

1102-431: The profile drag and maintain lift. The effect is a rotorcraft operating in a more efficient manner than the freewheeling rotor of an autogyro in autorotation, minimizing the adverse effects of retreating blade stall of helicopters at higher airspeeds. A rotor kite or gyroglider is an unpowered rotary-wing aircraft. Like an autogyro or helicopter, it relies on lift created by one or more sets of rotors in order to fly. Unlike

1140-448: The rate of descent is airspeed. Higher or lower airspeeds are obtained with the cyclic pitch control just as in normal flight. Rate of descent is high at zero airspeed and decreases to a minimum at approximately 50 to 90 knots, depending upon the particular helicopter and the factors previously mentioned. As the airspeed increases beyond the speed that gives minimum rate of descent, the rate of descent increases again. Even at zero airspeed,

1178-399: The rotor blade is referred to as the stall region and operates above its maximum angle of attack (stall angle) causing drag, which slows rotation of the blade. A constant rotor rotational speed is achieved by adjusting the collective pitch so blade acceleration forces from the driving region are balanced with the deceleration forces from the driven and stall regions. By controlling the size of

Hughes XH-17 - Misplaced Pages Continue

1216-469: The rotor blades, requiring it to drop almost vertically during transition. Inflight transition from fixed to rotary mode was demonstrated in August 2013. Another approach proposes a tailsitter configuration in which the lifting surfaces act as a rotors during takeoff, the craft tilts over for horizontal flight and the rotor stops to act as a fixed wing. Autorotation (helicopter) Autorotation

1254-416: The rotor hub. The blades were hollow, and the hot compressed air traveled through the blades to tip jets where fuel was injected. In flight, the main rotor spun at a sedate 88 revolutions per minute, less than half the speed of typical helicopter rotors. Since the rotor was driven at the tips rather than the hub, little torque compensation was required, mostly due to friction in the main rotor bearing. Thus,

1292-408: The rotor is quite effective, as it has nearly the drag coefficient of a parachute despite consisting of blades. When landing from an autorotation, the kinetic energy stored in the rotating blades and the forward movement of the aircraft are used to decrease the rate of descent and make a soft landing. A greater amount of rotor energy is required to stop a helicopter with a high rate of descent than

1330-456: The rotor system. This upward flow of air through the rotor provides sufficient thrust to maintain rotor rotational speed throughout the descent. Since the tail rotor is driven by the main rotor transmission during autorotation, heading control is maintained as in normal flight. Several factors affect the rate of descent in autorotation: density altitude , gross weight , rotor rotational speed, and forward airspeed . The pilot's primary control of

1368-419: The sizes of the regions change in relation to each other. The driven region, also called the propeller region, is the region at the end of the blades. Normally, it consists of about 30 percent of the radius. It is the driven region that produces the most drag. The overall result is a deceleration in the rotation of the blade. The driving region, or autorotative region, normally lies between 25 and 70 percent of

1406-558: The tail rotor from a Sikorsky H-19 Chickasaw was used for yaw control. In the late 1940s, Hughes developed an interest in helicopters. In August 1947, helicopter manufacturer Kellett sold his design for the giant XH-17 Sky Crane to Hughes, who commissioned the development of the XH-17 Flying Crane research vehicle. In 1948, the XH-17 began to take shape. The giant helicopter was tested in Culver City, California over

1444-480: Was fitted with a four-bladed stopped rotor, known as the X-wing. The programme was cancelled two years later, before the rotor had flown. The later canard rotor/wing (CRW) concept added a "canard" foreplane as well as a conventional tailplane, offloading the rotor wing and providing control during forward flight. For vertical and low-speed flight, the main airfoil is tip-driven as a helicopter's rotor by exhaust from

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