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The Bell-Boeing V-22 Osprey

TiltrotorFrom Wikipedia, the free encyclopedia

A tiltrotor is an aircraft which generates lift andpropulsion by way of one or more powered rotors(sometimes called proprotors) mounted on rotatingengine pods or nacelles usually at the ends of a fixedwing or an engine mounted in the fuselage withdrive shafts transferring power to rotor assembliesmounted on the wingtips. It combines the vertical liftcapability of a helicopter with the speed and range ofa conventional fixed-wing aircraft. For verticalflight, the rotors are angled so the plane of rotation ishorizontal, lifting the way a helicopter rotor does. Asthe aircraft gains speed, the rotors are progressivelytilted forward, with the plane of rotation eventuallybecoming vertical. In this mode the wing providesthe lift, and the rotor provides thrust as a propeller.Since the rotors can be configured to be more efficient for propulsion (e.g. with root-tip twist) and itavoids a helicopter's issues of retreating blade stall, the tiltrotor can achieve higher speeds thanhelicopters.

A tiltrotor aircraft differs from a tiltwing in that only the rotor pivots rather than the entire wing. Thismethod TRADES off efficiency in vertical flight for efficiency in STOL/STOVL operations.

Contents

1 History2 Technical considerations

2.1 Controls2.2 Speed and payload issues

3 Mono tiltrotor4 List of tiltrotor aircraft5 See also6 References7 External links

History

The idea of constructing Vertical Take-Off and Landing aircraft using helicopter-like rotors at thewingtips originated in the 1930s. The first design resembling modern tiltrotors was patented by GeorgeLehberger in May 1930, but he did not further develop the concept. In World War II, a Germanprototype, called the Focke-Achgelis FA-269, was developed starting in 1942, but never flew.[1][2][3]

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Bell X-22

A Bell XV-15 prepares to land

Two prototypes which made it to flight were the one-seat Transcendental Model 1-G and two seatTranscendental Model 2, both powered by single reciprocating engines. Development started on theModel 1-G in 1947, though it did not fly until 1954. The Model 1-G flew for about a year until a crash inChesapeake Bay 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 infavor of the Bell XV-3 and it did not fly much beyond hovertests. The Transcendental 1-G is the first tiltrotor aircraft to haveflown and accomplished most of a helicopter to aircraft transitionin flight (to within 10 degrees of true horizontal aircraft flight).

Built in 1953, the experimental Bell XV-3 flew until 1966,proving the fundamental soundness of the tiltrotor concept andgathering data about technical improvements needed for futuredesigns.

A related technology development is the tiltwing. Although twodesigns, the Canadair CL-84 Dynavert and the LTV XC-142,were technical successes, neither entered production due to otherissues. Tiltrotors generally have better hover efficiency thantiltwings, but less than helicopters.[4]

In 1968, Westland Aircraft displayed their own designs—a smallexperimental craft (We 01C) and a 68-seater transport We 028—at the SBAC Farnborough Airshow.[5]

In 1972, with funding from NASA and the U.S. Army, BellHelicopter Textron started development of the XV-15, a twin-engine tiltrotor research aircraft. Two aircraft were built to provethe tiltrotor design and explore the operational flight envelope formilitary and civil applications.[6][7]

In 1981, using experience gained from the XV-3and XV-15, Bell and Boeing Helicopters begandeveloping the V-22 Osprey, a twin-turboshaftmilitary tiltrotor aircraft for the U.S. Air Force andthe U.S. Marine Corps.[6]

Bell teamed with Boeing in developing acommercial tiltrotor, but Boeing went out in 1998and Agusta came in for the Bell/AgustaBA609.[7][8] This aircraft was redesignated as theAW609 following the transfer of full ownership toAgustaWestland in 2011.[9] Bell has alsodeveloped a tiltrotor unmanned aerial vehicle(UAV), the TR918 Eagle Eye.

Around 2005[10]-2010,[11] Bell and Boeing teamedup again to perform a conceptual study of a larger Quad TiltRotor (QTR) for the US Army's Joint HeavyLift (JHL) program. The QTR is a larger, four rotor version of the V-22 with two tandem wings sets offixed wings and four tilting rotors.

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In January 2013, the FAA defined US tiltrotor noise rules to comply with ICAO rules. A noisecertification will cost $588,000, same as for a large helicopter.[12][13]

AgustaWestland says they have free-flown a manned electric tiltrotor in 2013, with its rotors inside thewingspan.[14][15]

In 2013, Bell Helicopter CEO John Garrison responded to Boeing's taking a different airframe partnerfor the US Army's future lift requirements by indicating that Bell would take the lead itself in developingthe Bell V-280 Valor,[16] with Lockheed Martin.

In 2014, the Clean Sky 2 program (by the European Union and industry) awarded AgustaWestland andits partners $328 million to develop a "next-generation civil tiltrotor" design for the offshore market,with Critical Design Review near the end of 2016. The goals are tilting wing sections, 11 tonnesMaximum takeoff weight, seating for 19 to 22 passengers, a ceiling of 25,000 feet, a range of 500nautical miles and a top speed of 330 knots.[17][18][8]

Technical considerations

Controls

In vertical flight, the tiltrotor uses controls very similar to a twin or tandem-rotor helicopter. Yaw iscontrolled by tilting its rotors in opposite directions. Roll is provided through differential power orthrust. Pitch is provided through rotor cyclic or nacelle tilt. Vertical motion is controlled withconventional rotor blade pitch and either a conventional helicopter collective control lever (as in theBell/Agusta BA609) or a unique control similar to a fixed-wing engine control called a thrust controllever (TCL) (as in the Bell-Boeing V-22 Osprey).[19]

Speed and payload issues

The tiltrotor's advantage is significantly greater speed than a helicopter. In a helicopter the maximumforward speed is defined by the turn speed of the rotor; at some point the helicopter will be movingforward at the same speed as the spinning of the backwards-moving side of the rotor, so that side of therotor sees zero or negative airspeed, and begins to stall. This limits modern helicopters to cruise speedsof about 150 knots / 277 km/h. However, with the tiltrotor this problem is avoided, because theproprotors are perpendicular to the motion in the high-speed portions of the flight regime (and thus neversuffering 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 cruisespeeds of 250 knots / 460 km/h are achieved.[19]

This speed is achieved somewhat at the expense of payload. As a result of this reduced payload, someestimate that a tiltrotor does not exceed the transport efficiency (speed times payload) of a helicopter,[20]

while others conclude the opposite.[8] Additionally, the tiltrotor propulsion system is more complex thana conventional helicopter due to the large, articulated nacelles and the added wing; however, theimproved cruise efficiency and speed improvement over helicopters is significant in certain uses. Speedand, more importantly, the benefit to overall response time is the principal virtue sought by the militaryforces 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 inpopulated areas for commercial uses and reduce the threat of detection for military uses. Tiltrotors,

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Curtiss-Wright X-19 experimentalVTOL plane in flight

however, are typically as loud as equally sized helicopters in hovering flight. Noise simulations for a 90-passenger tiltrotor indicate lower cruise noise inside the cabin than a Bombardier Dash 8 airplane,although low-frequency vibrations may be higher.[21]

Tiltrotors also provide substantially greater cruise altitude capability than helicopters. Tiltrotors caneasily reach 6,000 m / 20,000 ft or more whereas helicopters typically do not exceed 3,000 m / 10,000 ftaltitude. This feature will mean that some uses that have been commonly considered only for fixed-wingaircraft can now be supported with tiltrotors without need of a runway. A drawback however is that atiltrotor suffers considerably reduced payload when taking off from high altitude.

Mono tiltrotor

A mono tiltrotor aircraft uses a tiltable rotating propeller, or coaxial proprotor, for lift and propulsion.For vertical flight the proprotor is angled to direct its thrust downwards, providing lift. In this mode ofoperation the craft is essentially identical to a helicopter. As the craft gains speed, the coaxial proprotoris slowly tilted forward, with the blades eventually becoming perpendicular to the ground. In this modethe wing provides the lift, and the wing's greater efficiency helps the tiltrotor achieve its high speed. Inthis mode, the craft is essentially a turboprop aircraft.

A mono tiltrotor aircraft is different from a conventional tiltrotor in which the proprotors are mounted tothe wing tips, in that the coaxial proprotor is mounted to the aircraft's fuselage. As a result of thisstructural efficiency, a mono tiltrotor exceeds the transport efficiency (speed times payload) of both ahelicopter and a conventional tiltrotor. One design study concluded that if the mono tiltrotor could betechnically realized, it would be half the size, one-third the weight, and nearly twice as fast as ahelicopter.[22]

In vertical flight, the mono tiltrotor uses controls very similar to a coaxial helicopter, such as the KamovKa-50. Yaw is controlled for instance by increasing the lift on the upper proprotor while decreasing thelift on the lower proprotor. Roll and pitch are provided through rotor cyclic. Vertical motion iscontrolled with conventional rotor blade blade pitch.[23]

List of tiltrotor aircraft

AgustaWestland AW609AgustaWestland Project ZeroAmerican Dynamics AD-150Bell XV-3Bell XV-15Bell Eagle EyeBell-Boeing V-22 OspreyCurtiss-Wright X-19Focke-Achgelis Fa 269IAI PantherBell V-280 Valor

See also

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A BA609 (now AW609) in airplanemode at Paris Air Show 2007

Pitch drop-backTiltjetTiltwingTailsitterVTOLThrust vectoring

References

1. ^ Springmann, Enno; Gottfried Hilscher (1997). Focke:Flugzeuge und Hubschrauber von Heinrich Focke 1912-1961.Aviatic-Verlag GmbH. ISBN 3-925505-36-9.

2. ^ Nowarra, Heinz (1985–1988). Die Deutsche Luftrüstung 1933-1945. Bernard & Graefe. ISBN 3-7637-5464-4.

3. ^ Maisel, M.D (2000). The History of the XV-15 Tilt RotorResearch Aircraft: From Concept to Flight(http://history.nasa.gov/monograph17.pdf). National Aeronautics and Space Administration, Office of Policyand Plans, NASA History Division.

4. ^ Warwick, Graham. "Tilting at targets (http://www.flightglobal.com/pdfarchive/view/1992/1992%20-%200262.html)" page 44 Flight International, February 1992. Accessed: 4 January 2014.

5. ^ "twenty Sixth SBAC Show" (http://www.flightglobal.com/pdfarchive/view/1968/1968%20-%202034.html)FLIGHT International, 19 September 1968 p446

6. ^ a b "History of tiltrotor technology", NASA Ames Research Center(http://www.simlabs.arc.nasa.gov/library/tiltrotor/ctr20th.html#History)

7. ^ a b Maisel, Martin D.; Giulianetti, Demo J.; Dugan, Daniel C. (2000). The History of the XV-15 Tilt RotorResearch Aircraft (http://history.nasa.gov/monograph17.pdf). Monographs in Aerospace History No. 17.NASA. ISBN 0-16-050276-4. NASA SP-2000-4517.

8. ^ a b c "8.6 Next Generation Civil Tiltrotor (NextGenCTR) Project – WP1(http://ec.europa.eu/research/participants/data/ref/h2020/other/guide-appl/jti/h2020-guide-techprog-cleansky-ju_en.pdf)" pages 254-301. Size: 747 pages, 23 MB. Clean Sky 2, 27 June 2014. Accessed: 7 October 2014.

9. ^ Wynbrandt, James (11 February 2012). "AW609 Finally Ready for its Close-up"(http://www.ainonline.com/aviation-news/hai-convention-news/2012-02-11/aw609-finally-ready-its-close).AINonline.com. Retrieved 14 February 2012.

10. ^ "Bell-Boeing's QTR selected for Heavy Lift study"(http://boeing.com/news/releases/2005/photorelease/q3/pr_050923p-1.html). Boeing, 22 September 2005.

11. ^ Brannen, Kate. "Pentagon Sheds Some Light on JFTL Effort" (http://www.defensenews.com/story.php?i=4710186&c=AME&s=LAN). Defense News, 15 July 2010.

12. ^ "Noise Certification Standards for Tiltrotors" (https://www.federalregister.gov/articles/2013/01/08/2013-00111/noise-certification-standards-for-tiltrotors). Federal Aviation Administration. 8 January 2013.Retrieved 13 January 2013.

13. ^ "FAA Publishes Modified Noise Rules For Tiltrotors" (http://www.aero-news.net/subscribe.cfm?do=main.textpost&id=98a33b6f-df48-4348-88bd-c66db2d8a24a). Aero-News. 11 January 2013. Retrieved13 January 2013.

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14. ^ Paur, Jason (6 March 2013). "Meet Project Zero, the World's First Electric Tilt-Rotor Aircraft"(http://www.wired.com/autopia/2013/03/agustawestland-electric-tilt-rotor/). Wired (website). Retrieved6 March 2013.

15. ^ "AgustaWestland Unveils Revolutionary Project Zero Tilt Rotor Technology Demonstrator"(http://www.asdnews.com/mobile/news/47974/AgustaWestland_Unveils_Revolutionary___Project_Zero___Tilt_Rotor_Technology_Demonstrator.htm). ASDNews. Retrieved 6 March 2013.

16. ^ "Bell to Take V-22 Development Forward Alone Without Boeing?"(http://www.aviationtoday.com/rw/products/airframes/Bell-to-Take-V-22-Development-Forward-Alone-Without-Boeing_78676.html)

17. ^ Huber, Mark. "AgustaWestland Pushes Ahead with Larger Tiltrotor (http://www.ainonline.com/aviation-news/aviation-international-news/2014-10-05/agustawestland-pushes-ahead-larger-tiltrotor)" AINonline, 5October 2014. Accessed: 7 October 2014. Archived(http://web.archive.org/web/20141007180847/http://www.ainonline.com/aviation-news/aviation-international-news/2014-10-05/agustawestland-pushes-ahead-larger-tiltrotor) on 7 October 2014

18. ^ "AgustaWestland civil tiltrotor (http://www.cleansky.eu/sites/default/files/documents/events/20141609/6b-_frc_tiltrotor.pdf)" AgustaWestland

19. ^ a b Norton, Bill. Bell Boeing V-22 Osprey, Tiltrotor Tactical Transport. Midland Publishing, 2004. ISBN1-85780-165-2.

20. ^ Tiltrotor/Helicopter Payload comparison and transport efficiency shown at "Naval Expeditionary Logistics:Enabling Operational Maneuver from the Sea", Commission on Physical Sciences, Mathematics, andApplications, figs D.3 and D.4, Page 82(http://www.nap.edu/books/0309064295/html/82.html#p0200064b99960082001)

21. ^ Grosveld, Ferdinand W. et al. "Interior Noise Predictions in the Preliminary Design of the Large CivilTiltrotor (LCTR2) (http://ntrs.nasa.gov/search.jsp?R=20130013992)" 20130013992 NASA, 21 May 2013.Accessed: 9 June 2014.

22. ^ http://handle.dtic.mil/100.2/ADA428702 Leishman, J. G., Preator, R., Baldwin, G. D.,Conceptual DesignStudies of a Mono Tiltrotor (MTR) Architecture, U.S. Navy Contract Number: N00014-03-C-0531, 2004.

23. ^ http://www.baldwintechnology.com/MTR_AHS_Jan07.pdf Baldwin, G. D., 'Preliminary Design Studies ofa Mono Tiltrotor (MTR) with Demonstrations of Aerodynamic Wing Deployment', AHS InternationalSpecialists Meeting, Chandler, Arizona, January 23–25, 2007.

External links

First motorized Tiltrotor (1909) (http://www.pionnair-ge.com/spip1/article.php3?id_article=162)Tiltrotor and The Future - Independent 60 minute documentary video on technologicaldevelopment of tiltrotor technology (free on YouTube) (http://www.youtube.com/watch?v=Ud66wf47DX0&list=PLgA_7RbhBCLDy3SXfdRCyRNKhUXKlrBJD)

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Categories: Tiltrotor aircraft Aircraft configurations

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