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词条 Slowed rotor
释义

  1. Background

  2. Theory

  3. Aircraft

  4. List of slowed rotor aircraft

  5. See also

  6. References

     Notes  Citations  Bibliography 

  7. External links

Slowed rotor is a concept in designing and flying certain rotorcraft. Reducing the rotational speed of the rotor reduces the drag, enabling the aircraft to go faster and/or fly more economically.

Background

Rotors of conventional helicopters are designed to operate at a fixed RPM[1][2][3] (within just a few percent),[4][5][6] causing suboptimal operation in large parts of the flight envelope.[6]

Two main issues restrict the speed of rotorcraft:[7][8][9][11]

{{main|Bölkow_Bo_46#Performance_limits|l1=Performance limits}}
  • Retreating blade stall. As forward speed of the helicopter increases, the airflow over the retreating blade becomes relatively slower, while the airflow over the advancing blade is relatively faster, creating more lift. If not counteracted by flapping,[10] this would cause dissymmetry of lift and eventually retreating blade stall,[11][12][13][14][17] and blade stability suffers as the blade reaches its limits for flapping.[11][15]
  • Transonic drag near the rotor blade tip. The faster-moving advancing blade tip may begin to approach the speed of sound, where transonic drag begins to rise steeply, and severe buffeting and vibration effects can occur. This effect prevents any further increase in speed, even if the helicopter has surplus power remaining, and even if it features a highly streamlined fuselage. A similar effect prevents propeller-driven aircraft from achieving supersonic speeds, although they can achieve higher speeds than a helicopter, since the propeller blade isn't advancing in the direction of travel.{{r|rob31}}{{r|silva}}[17][16][17][23]

These (and other)[18][19] problems limit the practical speed of helicopters to around {{convert|160|-|200|kn|km/h}}.[17][23][20][21][22] At the extreme, the theoretical top speed for a rotary winged aircraft is about {{convert|225|kn|mph km/h}},[19] just above the current official speed record for a conventional helicopter held by a Westland Lynx, which flew at {{convert|400|km/h|abbr=on}} in 1986[32] where its blade tips were nearly Mach 1.[23]

Theory

For rotorcraft, advance ratio (or Mu, symbol ) is defined as the aircraft forward speed V divided by its relative blade tip speed.[24][25][26] Upper mu limit is a critical design factor for rotorcraft,[15] and the optimum for traditional helicopters is around 0.4.[8][27]

The "relative blade tip speed" u is the tip speed relative to the aircraft (not the airspeed of the tip). Thus the formula for Advance ratio is

where Omega (Ω) is the rotor's angular velocity, and R is the rotor radius (about the length of one rotor blade)[28][15][42]

When the rotor blade is perpendicular to the aircraft and advancing, its tip airspeed Vt is the aircraft speed plus relative blade tip speed, or Vt=V+u.[11][29] At mu=1, V is equal to u and the tip airspeed is twice the aircraft speed.

At the same position on the opposite side (retreating blade), the tip airspeed is the aircraft speed minus relative blade tip speed, or Vt=V-u. At mu=1, the tip airspeed is zero.[22][30] At a mu between 0.7 and 1.0, most of the retreating side has reverse airflow.[42]

Although rotor characteristics are fundamental to rotorcraft performance,[31] little public analytical and experimental knowledge exists between advance ratios of 0.45 to 1.0,[42][32] and none is known above 1.0 for full-size rotors.[33][34] Computer simulations are not capable of adequate predictions at high mu.[35][36] The region of reverse flow on the retreating blade is not well understood,[37][38] however some research have been conducted,[39][40] particularly for scaled rotors.[41][42] The US Army Aviation Applied Technology Directorate runs a supporting program in 2016 aiming at developing transmissions with a 50% rotor speed reduction.[43]

The profile drag of a rotor corresponds to the cube of its rotational speed.[44][45]

Reducing the rotational speed is therefore a significant reduction of rotor drag, allowing higher aircraft speed[42] or lower power consumption.{{r|khos1}} A conventional rotor such as the UH-60A has lowest consumption around 75% rpm, but higher aircraft speed (and weight) requires higher rpm.[46]

A rotor disk with variable radius is a different way of reducing tip speed to avoid compressibility, but blade loading theory suggests that a fixed radius with varying rpm performs better than a fixed rpm with varying radius.[47]

Aircraft

Traditional helicopters get both their propulsion and lift from the main rotor, and by using a dedicated propulsion device such as a propeller or jet engine, the rotor burden is lessened.[48]

If wings are also used to lift the aircraft, the rotor can be unloaded (partially or fully) and its rotational speed further reduced, enabling higher aircraft speed. Compound helicopters use these methods,{{r|rob31}}{{r|silva}}{{r|cs12-44}}[8] but the Boeing A160 Hummingbird shows that rotor-slowing is possible without wings or propellers, and regular helicopters may reduce turbine RPM (and thus rotor speed) to 85% using 19% less power.{{r|khos1}} Alternatively, research suggests that twin-engine helicopters may decrease consumption by 25%-40% when running only one engine, given adequate height and velocity well inside the safe areas of the height–velocity diagram.[49][50][51]

As of 2012, no compound or hybrid wing/rotor (manned) aircraft has been produced in quantity, and only a few have been flown as experimental aircraft,[52] mainly because the increased complexities have not been justified by military or civilian markets.[53] Varying the rotor speed may induce severe vibrations at specific resonance frequencies.[7]

Contra-rotating rotors like on Sikorsky X2 solve the problem of lift dissymmetry by having both left and right sides provide near equal lift with less flapping.[11][48] The X2 deals with the compressibility issue by reducing its rotor speed[48] from 446 to 360 RPM[42][79] to keep the advancing blade tip below the sound barrier when going above 200 knots.[54]

List of slowed rotor aircraft

Sorted by year. Click <> to sort by other parameters.

Year Aircraft Type Speed Mu Rotor RPM Rotorlift is the lift provided by the rotor as a percentage of total lift, at full speed.|group=NL/D is Lift-to-drag ratio; a measure of flight efficiency.|group=N
1932 Pitcairn PCA-2 Winged autogyro 102|kn|mph km/h}}[55] 0.7[56] 4.8[57]
1955 McDonnell XV-1 Tip-jet autogyro 170|kn|mph km/h}} 0.95[58] 180-410[59] (50%[60]) 85% \\ 15% [61] Wind tunnel tests at 180 RPM with no propeller.[62]|group=N}}
1959 Fairey Rotodyne Tip-jet gyrodyne 166|kn|mph km/h}}[63][64] 0.6[65] 120 to 140[66] 60% \\ 40% [67]
1969 Lockheed AH-56 Cheyenne Compound helicopter 212|kn|mph km/h}}[68][69] 0.8[58] .. \\ 20% [70]
1969 Bell 533 Compound jet helicopter 275|kn|mph km/h}}[71][72]
2005 CarterCopter Winged autogyro 150|kn|mph km/h}}[73] 1 50%[42]
2007 Boeing A160 Hummingbird Unmanned helicopter 140|kn|mph km/h}} 140 to 350[74] No wings or propeller
2010 Sikorsky X2 Helicopter with coaxial rotors 250|kn|mph km/h}}[75][76] 0.8[42] 360 to 446[77][78] No wings [79]
2013 Eurocopter X3[80] Compound helicopter 255|kn|mph km/h}}[81][82] 310 minus 15%[83] 40[83][48]-80% \\ .[84][85]
2013 Carter PAV Winged autogyro 175|kn|mph km/h}} 1.13 105[86] to 350[87]
For comparison :
1986 Westland Lynx Helicopter 216|kn|mph km/h}}[88] 318[89] 2[90]
20xx Bell Boeing V-22 Osprey Tiltrotor 275[91]-305 knots[92] [93]{{#tag:ref>Like the V-22, the AgustaWestland AW609 tiltrotor also reduces its proprotor RPM from 100% to 84% after converting from hover to cruise.[94]|group=N}}
or 333 to 412 RPM[77]		v22fly}}
1. ^Croucher 2008, page 2-12. Quote: [Rotor speed] "is constant in a helicopter".
2. ^Seddon 2011, p216. Quote: The rotor is best served by rotating at a constant rotor speed
3. ^Robert Beckhusen. "[https://www.wired.com/2012/06/hummingbird/#more-84749 Army Dumps All-Seeing Chopper Drone]" Wired June 25, 2012. Accessed: 12 October 2013. Quote: for standard choppers .. the number of revolutions per minute is also set at a fixed rate
4. ^The UH-60 permits 95–101% rotor RPM UH-60 limits US Army Aviation. Retrieved 2 January 2010
5. ^{{cite news |last=Trimble |first=Stephen |title=DARPA's Hummingbird unmanned helicopter comes of age |url=http://www.flightglobal.com/news/articles/darpa39s-hummingbird-unmanned-helicopter-comes-of-225070/ |work=FlightGlobal |date=3 July 2008 |accessdate=14 May 2014|quote="The rotor speed on a typical helicopter can be varied around 95-102%"|archiveurl=https://web.archive.org/web/20140514181119/http://www.flightglobal.com/news/articles/darpa39s-hummingbird-unmanned-helicopter-comes-of-225070/|archivedate=14 May 2014 |deadurl=no}}
6. ^Khoshlahjeh
7. ^1 2 Lombardi, Frank. "Optimizing the Rotor" Rotor&Wing, June 2014. Accessed: 15 June 2014. [https://web.archive.org/web/20140615210037/http://www.aviationtoday.com/rw/commercial/technology/Optimizing-the-Rotor_82267.html Archived on 15 June 2014]
8. ^1 2 Harris 2003, page 7
9. ^Chiles, James R. "Hot-Rod Helicopters" Page 2 Page 3 Air & Space/Smithsonian, September 2009. Accessed: 18 May 2014.
10. ^"Blade flapping" Dynamic Flight
11. ^Robb 2006, page 31
12. ^Silva 2010, page 1.
13. ^"Helicopter Limitations" Challis Heliplane
14. ^"Retreating blade stall" Dynamic Flight
15. ^1 2 Johnson HT, p. 323
16. ^Prouty, Ray. "Ask Ray Prouty" Rotor&Wing, 1 May 2005. Accessed: 18 May 2014.
17. ^"Nomenclature: Transonic drag rise" NASA
18. ^Beare, Glenn. "Why can't a Helicopter fly faster than it does ?" helis.com . Accessed: 9 May 2014.
19. ^1 Krasner, Helen. "Why Can’t Helicopters Fly Fast?" Decoded Science, 10 December 2012. Accessed: 9 May 2014.
20. ^Clean Sky 2012, page 44
21. ^Majumdar, Dave. "DARPA Awards Contracts in Search of a 460 MPH Helicopter" United States Naval Institute, 19 March 2014. Accessed: 9 May 2014.
22. ^1 Wise, Jeff. "The Rise of Radical New Rotorcraft" Popular Mechanics, 3 June 2014. Accessed: 19 June 2014. [https://web.archive.org/web/20140619194953/http://www.popularmechanics.com/technology/aviation/news/the-rise-of-radical-new-rotorcraft-16850989-2 Archive] Quote: "This aerodynamic principle limits conventional helicopters to about 200 mph."
23. ^{{citation |last=Hopkins |first=Harry |url=http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203544.html |title=Fastest blades in the world |journal=Flight International |date=27 December 1986 |accessdate=28 April 2014 |pages=24–27 |format=pdf |quote=[https://web.archive.org/web/20140429045740/http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203544.html Archive page 24] [https://web.archive.org/web/20140429120402/http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203545.html Archive page 25] [https://web.archive.org/web/20140516103440/http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203546.html Archive page 26] [https://web.archive.org/web/20140516103533/http://www.flightglobal.com/pdfarchive/view/1986/1986%20-%203547.html Archive page 27] }}
24. ^"Nomenclature: Mu" NASA
25. ^Definition of Advance ratio
26. ^"Flapping Hinges" Aerospaceweb.org. Accessed: 8 May 2014.
27. ^1 2 Filippone, Antonio (2000). "Data and performances of selected aircraft and rotorcraft" pages 643-646. Department of Energy Engineering, Technical University of Denmark / Progress in Aerospace Sciences, Volume 36, Issue 8. Accessed: 21 May 2014. {{DOI|10.1016/S0376-0421(00)00011-7}} Abstract
28. ^Jackson, Dave. "Tip Speed Ratio (Advance Ratio)" Unicopter, 6 September 2013. Retrieved: 22 May 2015. [https://web.archive.org/web/20141021201634/http://www.unicopter.com/B263.html Archived] on 21 October 2014.
29. ^"Helicopter Flying Handbook", Chapter 02: Aerodynamics of Flight (PDF, 9.01 MB), Figure 2-33 page 2-18. FAA-H-8083-21A, 2012. Accessed: 21 May 2014.
30. ^Berry, page 3-4
31. ^Harris 2008, page 13
32. ^Berry, page 25
33. ^Harris 2008, page 25
34. ^Kottapalli, page 1
35. ^Harris 2008, page 8
36. ^Bowen-Davies, page 189-190
37. ^Harris 2008, page 14
38. ^Bowen-Davies, page 198
39. ^DuBois 2013
40. ^{{cite journal |url=http://www.ingentaconnect.com/content/ahs/jahs/pre-prints/content-JAHS1684 |title=Computational Investigation and Fundamental Understanding of a Slowed UH-60A Rotor at High Advance Ratios |journal=Journal of the American Helicopter Society |volume=61 |issue=2 |pages=1–17 |author1=Potsdam, Mark |author2=Datta, Anubhav |author3=Jayaraman, Buvana |date=18 March 2016 |accessdate=27 March 2016 |doi=10.4050/JAHS.61.022002 |archiveurl=https://web.archive.org/web/20160327150828/http://www.ingentaconnect.com/content/ahs/jahs/pre-prints/content-JAHS1684# |archivedate=2016-03-27 |deadurl=yes |df= }}
41. ^Bowen-Davies, page 216
42. ^{{cite journal|title=Streamwise oscillation of airfoils into reverse-flow |journal = AIAA Journal|volume = 54|issue = 5|pages = 1628–1636|author1=Granlund, Kenneth |author2=Ol, Michael |author3=Jones, Anya |doi=10.2514/1.J054674|year = 2016}}
43. ^{{cite web|url=https://govtribe.com/project/next-generation-rotorcraft-transmission-ngrt/activity |title=Contract Activity: Next Generation Rotorcraft Transmission (NGRT)|author1=Renata Y. Ellington |author2=Laurie Pierce |lastauthoramp=yes |work=Aviation Applied Technology Directorate |publisher=GovTribe |date=21 March 2016|accessdate=27 March 2016|archiveurl=https://web.archive.org/web/20160327124043/https://govtribe.com/project/next-generation-rotorcraft-transmission-ngrt/activity |archivedate=27 March 2016|deadurl=no}}
44. ^Gustafson, page 12
45. ^Johnson RA, page 251.
46. ^Bowen-Davies, page 97-99
47. ^Bowen-Davies, page 101
48. ^1 2 3 4 5 6 Chandler, Jay. "Advanced rotor designs break conventional helicopter speed restrictions (page 1) {{webarchive|url=https://web.archive.org/web/20130718171642/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p1.html |date=2013-07-18 }}" Page 2 {{webarchive|url=https://web.archive.org/web/20130718141528/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p2.html |date=2013-07-18 }} Page 3 {{webarchive|url=https://web.archive.org/web/20130718141548/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p3.html |date=2013-07-18 }}. ProPilotMag, September 2012. Accessed: 10 May 2014. [https://web.archive.org/web/20130718171642/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p1.html Archive 1] [https://web.archive.org/web/20130718141528/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p2.html Archive 2] [https://web.archive.org/web/20130718141548/http://www.propilotmag.com/archives/2012/September%2012/A3_Rotor_p3.html Archive 3]
49. ^Dubois, Thierry. "Researchers Look at Single-engine Cruise Ops on Twins" AINonline, 14 February 2015. Accessed: 19 February 2015.
50. ^Perry, Dominic. "Airbus Helicopters promises safe single-engine operations with Bluecopter demonstrator" Flight Global, 8 July 2015. [https://web.archive.org/web/20150802141742/http://www.flightglobal.com/news/articles/airbus-helicopters-promises-safe-single-engine-operations-with-bluecopter-414417/ Archive]
51. ^Perry, Dominic. "[https://www.flightglobal.com/news/articles/turbomeca-eyes-flight-tests-of-engine-sleep-mode-417150/ Turbomeca eyes flight tests of 'engine sleep mode']" Flight Global, 25 September 2015. [https://web.archive.org/web/20150929212740/https://www.flightglobal.com/news/articles/turbomeca-eyes-flight-tests-of-engine-sleep-mode-417150/ Archive]
52. ^Rigsby, page 3
53. ^Johnson HT, p. 325
54. ^Walsh 2011, page 3
55. ^Harris 2003, page A-40
56. ^Harris 2008, page 19
57. ^{{cite web|last=Duda|first=Holger|title=Flight performance of lightweight gyroplanes|url=http://www.icas-proceedings.net/ICAS2012/PAPERS/434.PDF|publisher=German Aerospace Center|accessdate=April 2014|author2=Insa Pruter|page=5|year=2012}}{{dead link|date=May 2018 |bot=InternetArchiveBot |fix-attempted=yes }}
58. ^1 Anderson, Rod. "The CarterCopter and its legacy" Issue 83, Contact Magazine, 30 March 2006. Accessed: 11 December 2010. Mirror
59. ^Harris 2003, page 14
60. ^Watkinson, page 355
61. ^Robb 2006, page 41
62. ^Harris 2003, page 18. Lift forces at page A-101
63. ^"FAI Record ID #13216 - Rotodyne, Speed over a closed circuit of 100 km without payload {{webarchive|url=https://web.archive.org/web/20150217223109/http://www.fai.org/fai-record-file/?recordId=13216 |date=2015-02-17 }}" Fédération Aéronautique Internationale. Record date 5 January 1959. Accessed: April 2014.
64. ^Anders, Frank. (1988) "The Fairey Rotodyne" (excerpt) Gyrodyne Technology (Groen Brothers Aviation). Retrieved: 17 January 2011. [https://web.archive.org/web/20140226074803/http://www.groenbros.com/FaireyRotodyne.php Archived] 26 February 2014
65. ^Rigsby, page 4
66. ^"Requiem for the Rotodyne." Flight International, 9 August 1962, pp. 200–202.
67. ^Braas, Nico. "Fairey Rotodyne" Let Let Let Warplanes, 15 June 2008. Accessed: April 2014. [https://web.archive.org/web/20130930215301/http://www.letletlet-warplanes.com/2008/06/15/the-fairey-rotodyne/ Archived] on 30 September 2013
68. ^Landis and Jenkins 2000, pp. 41–48.
69. ^"AH-56A Cheyenne" Globalsecurity.org. Accessed: April 2014.
70. ^Harris? not 2008, not Vol1+2, page 119
71. ^Robb 2006, page 43
72. ^Spenser, Jay P. "Bell Helicopter". Whirlybirds, A History of the U.S. Helicopter Pioneers, p. 274. University of Washington Press, 1998. {{ISBN|0-295-98058-3}}.
73. ^Wise, Jeff. "Jay Carter, Jr." Popular Science, 2005. [https://books.google.com/books?id=wgKpEb86UPIC&pg=PA63 Magazine]
74. ^Hambling, David. "The Rise of the Drone Helicopter - A160T Hummingbird" Popular Mechanics. Accessed: April 2014.
75. ^{{cite web|url= http://www.flightglobal.com/articles/2010/09/15/347379/sikorsky-x2-hits-250kt-goal.html |title= Sikorsky X2 hits 250kt goal |author= Croft, John |publisher= Flight International |date= 15 September 2010 |accessdate= 15 September 2010 |archiveurl=https://web.archive.org/web/20110117235150/http://www.flightglobal.com/articles/2010/09/15/347379/sikorsky-x2-hits-250kt-goal.html |archivedate=17 January 2011 |deadurl=no }}
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77. ^1 2 3 4 5 6 7 8 Datta, page 2.
78. ^1 Jackson, Dave. "Coaxial - Sikorsky ~ X2 TD" Unicopter. Accessed: April 2014.
79. ^D. Walsh, S. Weiner, K. Arifian, T. Lawrence, M. Wilson, T. Millott and R. Blackwell. "[https://vtol.org/EB393010-E91A-11E0-8A940050568D0042 High Airspeed Testing of the Sikorsky X2 Technology Demonstrator]" Sikorsky, May 4, 2011. Accessed: October 5, 2013.
80. ^The X3 concept {{Webarchive|url=https://web.archive.org/web/20140512221644/http://www.airbushelicopters.com/site/en/ref/X3-Demonstrator_1099.html# |date=2014-05-12 }} [https://www.youtube.com/watch?v=LxhogYKwV7Y Video1] [https://www.youtube.com/watch?v=eA7oqWXxGz0 Video2], at 2m50s Airbus Helicopters. Accessed: 9 May 2014.
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84. ^Norris, Guy. "[https://www.aviationweek.com/aw/generic/story_channel.jsp?channel=busav&id=news/awst/2012/02/27/AW_02_27_2012_p34-428686.xml&headline=Eurocopter%20X-3%20Targets%20U.S.%20Market Eurocopter X-3 Targets U.S. Market]{{dead link|date=May 2018 |bot=InternetArchiveBot |fix-attempted=yes }}" Aviation Week, 28 February 2012. Accessed: 1 March 2012. Mirror
85. ^Tarantola, Andrew. "Monster Machines: The New Fastest Helicopter On Earth Can Fly At An Insane 480km/h" Gizmodo, 19 June 2013. Accessed: April 2014.
86. ^Warwick, Graham. "Carter Hopes To Demo SR/C Rotorcraft To Military" Aviation Week, 5 February 2014. Accessed: 19 May 2014. [https://web.archive.org/web/20140519054955/http://aviationweek.com/defense/carter-hopes-demo-src-rotorcraft-military-0 Archived on 19 May 2014]
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88. ^1 "Rotorcraft Absolute: Speed over a straight 15/25 km course {{webarchive|url=https://web.archive.org/web/20131203033038/http://www.fai.org/fai-record-file/?recordId=11659 |date=2013-12-03 }}". Fédération Aéronautique Internationale (FAI). Note search under E-1 Helicopters and "Speed over a straight 15/25 km course". Accessed: 26 April 2014.
89. ^Watkinson 2004, page 108
90. ^Harris 2008, page 20
91. ^Wall, Robert. "U.S. Marines See MV-22 Improvements."{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }} Aviation Week, 24 June 2010.
92. ^Norton, Bill. Bell Boeing V-22 Osprey, Tiltrotor Tactical Transport, page 111. Earl Shilton, Leicester, UK: Midland Publishing, 2004. {{ISBN|1-85780-165-2}}.
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94. ^{{cite news |url=http://www.verticalmag.com/news/article/Flying-the-AW609:-a-preview |title=Flying the AW609: A Preview |work=Vertical |first=Elan |last=Head |date=20 January 2014 |accessdate=20 January 2014|archiveurl=https://web.archive.org/web/20140425030900/http://www.verticalmag.com/news/article/Flying-the-AW609:-a-preview|archivedate=25 April 2014 |deadurl=no}}

See also

  • Gyrodyne
  • Convertiplane

References

Notes

Citations

{{Reflist|25em}}

Bibliography

{{Refbegin}}
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{{Refend}}

External links

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4 : Aerospace engineering|Helicopter aerodynamics|Rotorcraft|Slowed rotor
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