Tiltrotor
Overview
 
A tiltrotor is an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 which uses a pair or more of powered rotors (sometimes called proprotors) mounted on rotating shafts or nacelles at the end of a fixed wing for lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 and propulsion
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

, and combines the vertical lift capability of a helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

 with the speed and range
Range (aircraft)
The maximal total range is the distance an aircraft can fly between takeoff and landing, as limited by fuel capacity in powered aircraft, or cross-country speed and environmental conditions in unpowered aircraft....

 of a conventional fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...

. For vertical flight, the rotors are angled so the plane of rotation
Plane of rotation
In geometry, a plane of rotation is an abstract object used to describe or visualise rotations in space. In three dimensions it is an alternative to the axis of rotation, but unlike the axis of rotation it can be used in other dimensions, such as two, four or more dimensions.Mathematically such...

 is horizontal, lifting the way a helicopter rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...

 does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical.
Encyclopedia
A tiltrotor is an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 which uses a pair or more of powered rotors (sometimes called proprotors) mounted on rotating shafts or nacelles at the end of a fixed wing for lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 and propulsion
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

, and combines the vertical lift capability of a helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

 with the speed and range
Range (aircraft)
The maximal total range is the distance an aircraft can fly between takeoff and landing, as limited by fuel capacity in powered aircraft, or cross-country speed and environmental conditions in unpowered aircraft....

 of a conventional fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...

. For vertical flight, the rotors are angled so the plane of rotation
Plane of rotation
In geometry, a plane of rotation is an abstract object used to describe or visualise rotations in space. In three dimensions it is an alternative to the axis of rotation, but unlike the axis of rotation it can be used in other dimensions, such as two, four or more dimensions.Mathematically such...

 is horizontal, lifting the way a helicopter rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...

 does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical. In this mode the wing provides the lift, and the rotor provides thrust as a propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

. Since the rotors can be configured to be more efficient for propulsion (eg. with root-tip twist) & it avoids a helicopter's issues of Retreating blade stall
Retreating blade stall
Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the rotor blade rotating away from the direction of flight stalls. The stall is due to low relative airspeed and/or excessive angle of attack...

, the tiltrotor can achieve higher speeds than helicopters.

A tiltrotor aircraft differs from a tiltwing
Tiltwing
A tiltwing aircraft features a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. It is similar to the tiltrotor design where only the propeller and engine rotate. Tiltwing aircraft are typically fully capable of VTOL operations.The tiltwing...

 in that only the rotor pivots rather than the entire wing. This method trades off efficiency in vertical flight for efficiency in STOL
STOL
STOL is an acronym for short take-off and landing, a term used to describe aircraft with very short runway requirements.-Definitions:There is no one accepted definition of STOL and many different definitions have been used by different authorities and nations at various times and for a myriad of...

/STOVL
STOVL
STOVL is an acronym for short take off and vertical landing.This is the ability of some aircraft to take off from a short runway or take off vertically if it does not have a very heavy payload and land vertically...

 operations.

History

The idea of constructing Vertical Take-Off and Landing
VTOL
A vertical take-off and landing aircraft is one that can hover, take off and land vertically. This classification includes fixed-wing aircraft as well as helicopters and other aircraft with powered rotors, such as cyclogyros/cyclocopters and tiltrotors...

 aircraft using helicopter-like rotors at the wingtips originated in the 1930s. The first design resembling modern tiltrotors was patented by George Lehberger in May 1930, but he did not further develop the concept. In World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, a German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

, called the Focke-Achgelis
Focke-Achgelis
Focke-Achgelis & Co. G.m.b.H. was a German helicopter company founded in 1937 by Henrich Focke and Gerd Achgelis.-History:In 1936 Focke had been ousted from the Focke-Wulf company he had cofounded in 1924 by shareholder pressure...

 FA-269 was developed starting in 1942, but never flew.

Two prototypes which made it to flight were the one-seat Transcendental Model 1-G and two seat Transcendental Model 2, both powered by single reciprocating engines. Development started on the Model 1-G in 1947, though it did not fly until 1954. The Model 1-G flew for about a year until a crash in Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

 on July 20, 1955, destroying the prototype aircraft but not seriously injuring the pilot. The Model 2 was developed and flew shortly afterwards, but the US Air Force withdrew funding in favor of the Bell XV-3 and it did not fly much beyond hover tests. The Transcendental 1-G is the first tiltrotor aircraft to have flown and accomplished most of a helicopter to aircraft transition in flight (to within 10 degrees of true horizontal aircraft flight).

Built in 1953, the experimental Bell XV-3
Bell XV-3
|-See also:- References :NotesBibliography*Markman, Steve, and William G. Holder. Straight Up: A History of Vertical Flight. Schiffer military/aviation history. Atglen, PA: Schiffer Pub, 2000....

 flew until 1966, proving the fundamental soundness of the tiltrotor concept and gathering data about technical improvements needed for future designs.

A related technology development is the tiltwing
Tiltwing
A tiltwing aircraft features a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. It is similar to the tiltrotor design where only the propeller and engine rotate. Tiltwing aircraft are typically fully capable of VTOL operations.The tiltwing...

. Although two designs, the Canadair CL-84 Dynavert
Canadair CL-84
The Canadair CL-84 "Dynavert", designated by the Canadian Forces as the CX-131, was a V/STOL turbine tilt-wing monoplane designed and manufactured by Canadair between 1964 and 1972. Only four of these experimental aircraft were built with three entering flight testing...

 and the LTV XC-142, were technical successes, neither entered production due to other issues.

In 1972, with funding from NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 and the U.S. Army, Bell Helicopter Textron
Bell Helicopter Textron
Bell Helicopter is an American rotorcraft manufacturer headquartered in Hurst, Texas, near Fort Worth. A division of Textron, Bell manufactures military helicopter and tiltrotor products in and around Fort Worth, as well as in Amarillo, Texas, and commercial rotorcraft products in Mirabel, Quebec,...

 started development of the XV-15, a twin-engine tiltrotor research aircraft. Two aircraft were built to prove the tiltrotor design and explore the operational flight envelope for military and civil applications.

In 1981, using experience gained from the XV-3 and XV-15, Bell and Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...

 Helicopters began developing the V-22 Osprey
V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, military, tiltrotor aircraft with both a vertical takeoff and landing , and short takeoff and landing capability...

, a twin-turboshaft military tiltrotor aircraft for the U.S. Air Force and the U.S. Marine Corps.

Bell, teamed with AgustaWestland
AgustaWestland
AgustaWestland is an Anglo-Italian helicopter design and manufacturing company. It was formed in July 2000 when Finmeccanica S.p.A. and GKN plc agreed to merge their respective helicopter subsidiaries to form AgustaWestland with Finmeccanica and GKN each holding a 50% share.AgustaWestland is now a...

, is developing the commercial BA609
Bell/Agusta BA609
The AgustaWestland AW609, formerly the Bell/Agusta BA609, is a civil twin-engined tiltrotor VTOL aircraft with a configuration similar to the Bell-Boeing V-22 Osprey.-Design and development:...

, and the firm has also developed a tiltrotor unmanned aerial vehicle
Unmanned aerial vehicle
An unmanned aerial vehicle , also known as a unmanned aircraft system , remotely piloted aircraft or unmanned aircraft, is a machine which functions either by the remote control of a navigator or pilot or autonomously, that is, as a self-directing entity...

 (UAV), the TR918 Eagle Eye
Bell Eagle Eye
-References:* This article contains material that originally came from the web article by Greg Goebel, which exists in the Public Domain.-External links:** * ....

.

Bell and Boeing have teamed up again to perform a conceptual study of a larger Quad TiltRotor
Bell Boeing Quad TiltRotor
The Bell Boeing Quad TiltRotor is a proposed four-rotor derivative of the V-22 Osprey tiltrotor developed jointly by Bell Helicopter and Boeing. The concept is a contender in the U.S. Army's Joint Heavy Lift program...

 (QTR) for the US Army's Joint Heavy Lift (JHL) program. The QTR is a larger, four rotor version of the V-22 with two tandem wing
Tandem wing
thumb|right|QAC Quickie Q2A tandem wing aircraft usually involves two full-sized wings, both of which are full airfoils. Sometimes an aircraft of this configuration can look like a variation on the biplane, but is in fact very different. The forward wing is often technically a canard, fitted with...

s sets of fixed wings and four tilting rotors.

Controls

In vertical flight, the tiltrotor uses controls very similar to a twin or tandem-rotor helicopter. Yaw is controlled by tilting its rotors in opposite directions. Roll is provided through differential power or thrust. Pitch is provided through rotor cyclic or nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...

 tilt. Vertical motion is controlled with conventional rotor blade pitch
Blade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...

 and either a conventional helicopter collective control lever (as in the Bell/Agusta BA609
Bell/Agusta BA609
The AgustaWestland AW609, formerly the Bell/Agusta BA609, is a civil twin-engined tiltrotor VTOL aircraft with a configuration similar to the Bell-Boeing V-22 Osprey.-Design and development:...

) or a unique control similar to a fixed wing engine control called a thrust control lever (TCL) (as in the Bell-Boeing V-22 Osprey
V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, military, tiltrotor aircraft with both a vertical takeoff and landing , and short takeoff and landing capability...

).

Speed and payload issues

The tiltrotor's advantage is significantly greater speed than a helicopter. In a helicopter the maximum forward speed is defined by the turn speed of the rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...

; at some point the helicopter will be moving forward at the same speed as the spinning of the backwards-moving side of the rotor, so that side of the rotor sees zero or negative airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....

, and begins to stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...

. This limits modern helicopters to cruise speeds of about 150 knots / 277 km/h. However, with the tiltrotor this problem is avoided, because the proprotors are perpendicular to the motion in the high-speed portions of the flight regime (and thus never suffering this reverse flow condition), meaning that the tiltrotor has relatively high maximum speed - over 300 knots / 560 km/h has been demonstrated in the two types of tiltrotors flown so far, and cruise speeds of 250 knots / 460 km/h are achieved.

This speed is achieved somewhat at the expense of payload. As a result of this reduced payload, a tiltrotor does not exceed the transport efficiency (speed times payload) of a helicopter. Additionally, the tiltrotor propulsion system is more complex than a conventional helicopter due to the large, articulated nacelles and the added wing; however, the improved cruise efficiency and speed improvement over helicopters is significant in certain uses. Speed and, more importantly, the benefit to overall response time is the principal virtue sought by the military forces that are using the tiltrotor. Tiltrotors are inherently less noisy in forward flight (airplane mode) than helicopters. This, combined with their increased speed, is expected to improve their utility in populated areas for commercial uses and reduce the threat of detection for military uses. Tiltrotors, however, are typically as loud as equally sized helicopters in hovering flight.

Tiltrotors also provide substantially greater cruise altitude capability than helicopters. Tiltrotors can easily reach 6000 m / 20,000 ft or more whereas helicopters typically do not exceed 3000 m / 10,000 ft altitude. This feature will mean that some uses that have been commonly considered only for fixed-wing aircraft can now be supported with tiltrotors without need of a runway. A drawback however is that a tiltrotor suffers considerably reduced payload when taking off from high altitude.

Mono tiltrotor

A mono tiltrotor aircraft uses a tiltable rotating propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

, or coaxial proprotor, for lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 and propulsion
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

. For vertical flight the proprotor is angled to direct its thrust downwards, providing lift. In this mode of operation the craft is essentially identical to a helicopter. As the craft gains speed, the coaxial proprotor is slowly tilted forward, with the blades eventually becoming perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

 to the ground. In this mode the wing provides the lift, and the wing's greater efficiency helps the tiltrotor achieve its high speed. In this mode, the craft is essentially a turboprop aircraft.

A mono tiltrotor aircraft is different from a conventional tiltrotor, in which the proprotors are mounted to the wing tip
Wing tip
A wing tip is the part of the wing that is most distant from the fuselage of a fixed-wing aircraft.Because the wing tip shape influences the size and drag of the wingtip vortices, tip design has produced a diversity of shapes, including:* Squared-off...

s, rather than being mounted to the aircraft's fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

. As a result of this structural efficiency, a mono tiltrotor exceeds the transport efficiency (speed times payload) of both a helicopter and a conventional tiltrotor. One design study concluded that if the mono tiltrotor could be technically realized, it would be half the size, one-third the weight, and nearly twice as fast as a helicopter.

In vertical flight, the mono tiltrotor uses controls very similar to a coaxial helicopter, such as the Kamov Ka-50
Kamov Ka-50
The Kamov Ka-50 "Black Shark" is a single-seat Russian attack helicopter with the distinctive coaxial rotor system of the Kamov design bureau. It was designed in the 1980s and adopted for service in the Russian army in 1995...

. Yaw is controlled for instance by increasing the lift on the upper proprotor while decreasing the lift on the lower proprotor. Roll and pitch are provided through rotor cyclic. Vertical motion is controlled with conventional rotor blade blade pitch
Blade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...

.

List of tiltrotor aircraft

  • 194_ - Focke-Achgelis Fa 269
  • 1955 - Bell XV-3
    Bell XV-3
    |-See also:- References :NotesBibliography*Markman, Steve, and William G. Holder. Straight Up: A History of Vertical Flight. Schiffer military/aviation history. Atglen, PA: Schiffer Pub, 2000....

  • 1957 - Doak VZ-4
    Doak VZ-4
    |-References:NotesBibliography* The Illustrated Encyclopedia of Aircraft . London: Orbis Publishing, 1985.* Swanborough, F.G. and Peter M. Bowers. United States Military Aircraft since 1909. London: Putnam, 1963....

  • 1963 - Curtiss-Wright X-19
    Curtiss-Wright X-19
    |-See also:-External links:*...

  • 1966 - Bell X-22
    Bell X-22
    -References:NotesBibliography* Markman, Steve and Bill Holder. Straight Up: A History of Vertical Flight. Atglen, PA: Schiffer Publishing, 2000. ISBN 0-7643-1204-9....

  • 1967 - Aérospatiale N 500
    Aérospatiale N 500
    The Aérospatiale N 500 Cadet was a single-seat VTOL research aircraft built by Nord in 1967.-Design and development:A model kit presenting the concept was first shown at the Paris Air Show at Le Bourget in 1965...

  • 1977 - Bell XV-15
    Bell XV-15
    The Bell XV-15 was an American tiltrotor VTOL aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.-Early VTOL rotor aircraft:...

  • 1989 - Bell-Boeing V-22 Osprey
  • 1998 - Bell Eagle Eye
    Bell Eagle Eye
    -References:* This article contains material that originally came from the web article by Greg Goebel, which exists in the Public Domain.-External links:** * ....

  • 2003 - AgustaWestland AW609
  • 2010 - IAI Panther
    IAI Panther
    The Israel Aerospace Industries Panther is a tilt-rotor unmanned aerial vehicle produced by Israel Aircraft Industries in Israel.The Panther employs a tilt-rotor propulsion system patented by IAI and designed for tactical use, allowing runway-free takeoffs and landings on unprepared locations...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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