Slowed rotor

Last updated
The McDonnell XV-1 could slow its rotor from 410 to 180 RPM McDonnell XV-1 in flight.jpg
The McDonnell XV-1 could slow its rotor from 410 to 180 RPM

The slowed rotor principle is used in the design of some helicopters. On a conventional helicopter the rotational speed of the rotor is constant; reducing it at lower flight speeds can reduce fuel consumption and enable the aircraft to fly more economically. In the compound helicopter and related aircraft configurations such as the gyrodyne and winged autogyro, reducing the rotational speed of the rotor and offloading part of its lift to a fixed wing reduces drag, enabling the aircraft to fly faster.

Contents

Introduction

Traditional helicopters get both their propulsion and lift from the main rotor; by using a dedicated propulsion device such as a propeller or jet engine, the rotor burden is lessened. [1] 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, [2] [3] [4] 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. [5] Alternatively, research suggests that twin-engine helicopters may decrease fuel consumption by 25%-40% when running only one engine, given adequate height and velocity well inside the safe areas of the height–velocity diagram. [6] [7] [8]

As of 2012, no compound or hybrid wing/rotor (manned) aircraft had been produced in quantity, and only a few had been flown as experimental aircraft, [9] mainly because the increased complexities have not been justified by military or civilian markets. [10] Varying the rotor speed may induce severe vibrations at specific resonance frequencies. [11]

Contra-rotating rotors (as on the Sikorsky X2) solve the problem of lift dissymmetry by having both left and right sides provide near equal lift with less flapping. [12] [1] The X2 deals with the compressibility issue by reducing its rotor speed [1] from 446 to 360 RPM [13] [14] to keep the advancing blade tip below the sound barrier when going above 200 knots. [15]

Design principles

Speed limits of aircraft rotors

Effect of blade airspeed on lift on advancing and retreating side, when aircraft speed is 100 knots. FAA heli-manual Dissymmetry of lift.PNG
Effect of blade airspeed on lift on advancing and retreating side, when aircraft speed is 100 knots.

The rotors of conventional helicopters are designed to operate at a fixed speed of rotation, to within a few percent. [16] [17] [18] [11] This introduces limitations in areas of the flight envelope where the optimal speed differs. [5]

In particular, it limits the maximum forward speed of the aircraft. Two main issues restrict the speed of rotorcraft: [11] [4] [19] [12]

These (and other) [27] [28] problems limit the practical speed of a conventional helicopter to around 160–200 knots (300–370 km/h). [1] [26] [29] [30] At the extreme, the theoretical top speed for a rotary winged aircraft is about 225 knots (259 mph; 417 km/h), [28] just above the current official speed record for a conventional helicopter held by a Westland Lynx, which flew at 400 km/h (250 mph) in 1986 [31] where its blade tips were nearly Mach  1. [32]

Slowed rotors and aircraft speed

Rotorcraft Aspect ratio (mu) diagram Rotorcraft Aspect ratio (mu) diagram.PNG
Rotorcraft Aspect ratio (mu) diagram
Drag type curves as a function of airspeed (simulated) Simulated drag curve for compound helicopter.jpg
Drag type curves as a function of airspeed (simulated)
Cruise combinations for rotor power, propeller and wings. Venn diagram of slowed rotor aircraft in high speed mode.svg
Cruise combinations for rotor power, propeller and wings.

For rotorcraft, advance ratio (or Mu, symbol ) is defined as the aircraft forward speed V divided by its relative blade tip speed. [33] [34] [35] Upper mu limit is a critical design factor for rotorcraft, [23] and the optimum for traditional helicopters is around 0.4. [4] [26]

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) [36] [23] [13]

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. [12] [37] 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. [30] [38] At a mu between 0.7 and 1.0, most of the retreating side has reverse airflow. [13]

Although rotor characteristics are fundamental to rotorcraft performance, [39] little public analytical and experimental knowledge exists between advance ratios of 0.45 to 1.0, [13] [40] and none is known above 1.0 for full-size rotors. [41] [42] Computer simulations are not capable of adequate predictions at high mu. [43] [44] The region of reverse flow on the retreating blade is not well understood, [45] [46] however some research has been conducted, [47] [48] particularly for scaled rotors. [49] [50] The US Army Aviation Applied Technology Directorate runs a supporting program in 2016 aiming at developing transmissions with a 50% rotor speed reduction. [51]

The profile drag of a rotor corresponds to the cube of its rotational speed. [52] [53] Reducing the rotational speed is therefore a significant reduction of rotor drag, allowing higher aircraft speed [13] A conventional rotor such as the UH-60A has lowest consumption around 75% rpm, but higher aircraft speed (and weight) requires higher rpm. [54]

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. [55]

Fuel economy of slowed rotors

Conventional helicopters have constant-speed rotors and adjust lift by varying the blade angle of attack or collective pitch. The rotors are optimised for high-lift or high-speed flight modes and in less demanding situations are not as efficient.

The profile drag of a rotor corresponds to the cube of its rotational speed. [52] [53] Reducing the rotational speed and increasing the angle of attack can therefore give a significant reduction in rotor drag, allowing lower fuel consumption. [5]

History

Pitcairn PCA-2 autogyro. Unpowered rotor, tractor propeller, wings. Pitcairn Autogiro NASA GPN-2000-001990.jpg
Pitcairn PCA-2 autogyro. Unpowered rotor, tractor propeller, wings.

Technical parameters given for each type listed:

Early development

When Juan de la Cierva developed the autogyro through the 1920s and 1930s, it was found that the tip speeds of the advancing rotor blade could become excessive. Designers such as he and Harold F. Pitcairn developed the idea of adding a conventional wing to offload the rotor during high-speed flight, allowing it to rotate at slower speeds.[ citation needed ]

The 1932 Pitcairn PCA-2 autogyro had a maximum speed of 20-102 knots (117 mph; 189 km/h), [56] μ of 0.7, [57] and L/D pf 4.8 [58]

NACA engineer John Wheatley examined the effect of varying advance ratios up to about 0.7 in a wind tunnel in 1933 and published a landmark study in 1934. Although lift could be predicted with some accuracy, by 1939 the state of the art theory still gave unrealistically low values for rotor drag. [59]

Postwar projects

Fairey Aviation in the UK worked on gyrodynes in the late 1940s and 1950s developing tip-jet propulsion which eliminated the need for countertorque. They culminated in the Fairey Rotodyne, the prototype for a VTOL passenger aircraft, which could combine the vertical landing of a helicopter with the speed of a fixed wing aircraft. The Rotodyne had a single 90 ft diameter main rotor supplemented by a 46 ft wide wing with forward thrust provided by twin turboprop engines. In forward flight the power to the rotor was reduced to about 10%.[ citation needed ] Its maximum speed was 166 knots (191 mph; 307 km/h) a record set in 1959. [60] [61] 0.6. [62] Rotor speed was 120 (high speed cruising flight as an autogyro) to 140 (flare out while landing as a helicopter) rpm [63] During forward flight 60% of the lift came from the wings and 40% from the rotor. [64]

At the same time, the US Air Force was investigating fast VTOL aircraft. McDonnell developed what became the McDonnell XV-1, the first of the V-designated types, which flew in 1955. It was a tip-jet driven gyrodyne, which turned off rotor thrust at high airspeeds and relied on a pusher propeller to maintain forward flight and rotor autorotation. Lift was shared between the rotor and stub wings. It established a rotorcraft speed record of 170 knots (200 mph; 310 km/h). 0.95. [65] 180-410 [66] (50% [67] ). 85% \ 15%. [68] 6.5 (Wind tunnel tests at 180 RPM with no propeller. [69] )

The Lockheed AH-56 Cheyenne military attack helicopter for the US Army arose out of Lockheed's ongoing research programme into rigid rotors, which began with the CL-475 in 1959. Stub wings and a thrust turbojet to offload the rotor were first added to an XH-51A and in 1965 this allowed the craft to achieve a world speed record of 272 miles per hour (438 km/h). The Cheyenne flew just two years later, obtaining its forward thrust from a pusher propeller. Although pre-production prototypes were ordered the program met problems and was cancelled. [70] 212 knots (244 mph; 393 km/h). [71] [72] 0.8. [65] .. \ 20%. [73]

The Piasecki 16H Pathfinder project similarly evolved an initially conventional design into a compound helicopter through the 1960s, culminating in the 16H-1A Pathfinder II which flew successfully in 1965. Thrust was obtained via a ducted fan at the tail. [74]

The Bell 533 of 1969 was a compound jet helicopter. 275 knots (316 mph; 509 km/h). [75] [76]

Modern developments

The compound helicopter has continued to be studied and flown experimentally. In 2010 the Sikorsky X2 flew with coaxial rotors. 250 knots (290 mph; 460 km/h). [77] [78] 0.8. [13] 360 to 446. [13] [14] No wings. [79] In 2013 the Eurocopter X3 flew. [80] 255 knots (293 mph; 472 km/h). [81] [82] 310 minus 15%. [12] 40 [12] [1] -80% \. [83] [84]

The compound autogyro, in which the rotor is supplemented by wings and thrust engine but is not itself powered, has also undergone further refinement by Jay Carter Jr. He flew his CarterCopter in 2005. 150 knots (170 mph; 280 km/h). [85] 1. 50%. [13] By 2013 he had developed its design into a personal air vehicle, the Carter PAV. 175 knots (201 mph; 324 km/h). 1.13. 105 [86] to 350. [87]

The potential of the slowed rotor in enhancing fuel economy has also been studied in the Boeing A160 Hummingbird UAV, a conventional helicopter. 140 knots (160 mph; 260 km/h). 140 to 350. [88]

See also

Related Research Articles

The CarterCopter is an experimental compound autogyro developed by Carter Aviation Technologies in the United States to demonstrate slowed rotor technology. On 17 June 2005, the CarterCopter became the first rotorcraft to achieve mu-1 (μ=1), an equal ratio of airspeed to rotor tip speed, but crashed on the next flight and has been inoperable since. It is being replaced by the Carter Personal Air Vehicle.

<span class="mw-page-title-main">Fairey Rotodyne</span> 1950s British compound gyroplane

The Fairey Rotodyne was a 1950s British compound gyroplane designed and built by Fairey Aviation and intended for commercial and military uses. A development of the earlier Fairey Jet Gyrodyne, which had established a world helicopter speed record, the Rotodyne featured a tip-jet-powered rotor that burned a mixture of fuel and compressed air bled from two wing-mounted Napier Eland turboprops. The rotor was driven for vertical takeoffs, landings and hovering, as well as low-speed translational flight, but autorotated during cruise flight with all engine power applied to two propellers.

<span class="mw-page-title-main">Piasecki X-49 SpeedHawk</span> Type of aircraft

The Piasecki X-49 "SpeedHawk" is an American four-bladed, twin-engined experimental high-speed compound helicopter developed by Piasecki Aircraft. The X-49A is based on the airframe of a Sikorsky YSH-60F Seahawk, but utilizes Piasecki's proprietary vectored thrust ducted propeller (VTDP) design and includes the addition of lifting wings. The concept of the experimental program was to apply the VTDP technology to a production military helicopter to determine any benefit gained through increases in performance or useful load.

<span class="mw-page-title-main">Tail rotor</span> Rotor mounted on the tail of a helicopter

The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. The tail rotor's position and distance from the helicopter's center of mass allow it to develop enough thrust leverage to counter the reactional torque exerted on the fuselage by the spinning of the main rotor. Without the tail rotor or other anti-torque mechanisms, the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.

<span class="mw-page-title-main">Lockheed AH-56 Cheyenne</span> Canceled US helicopter program

The Lockheed AH-56 Cheyenne is an attack helicopter developed by Lockheed for the United States Army. It rose from the Army's Advanced Aerial Fire Support System (AAFSS) program to field the service's first dedicated attack helicopter. Lockheed designed the Cheyenne using a four-blade rigid-rotor system and configured the aircraft as a compound helicopter with low-mounted wings and a tail-mounted thrusting propeller driven by a General Electric T64 turboshaft engine. The Cheyenne was to have a high-speed dash capability to provide armed escort for the Army's transport helicopters, such as the Bell UH-1 Iroquois.

<span class="mw-page-title-main">Tip jet</span> Jet nozzle at the tip of some helicopter rotor blades

A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not requiring the presence of a tail rotor. Some simple monocopters are composed of nothing but a single blade with a tip rocket.

<span class="mw-page-title-main">Gyrodyne</span> Type of VTOL aircraft

A gyrodyne is a type of VTOL aircraft with a helicopter rotor-like system that is driven by its engine for takeoff and landing only, and includes one or more conventional propeller or jet engines to provide forward thrust during cruising flight. During forward flight the rotor is unpowered and free-spinning, like an autogyro, and lift is provided by a combination of the rotor and conventional wings. The gyrodyne is one of a number of similar concepts which attempt to combine helicopter-like low-speed performance with conventional fixed-wing high-speeds, including tiltrotors and tiltwings.

<span class="mw-page-title-main">Rotorcraft</span> Heavier-than-air aircraft which generates lift over rotating wings

A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are 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".

<span class="mw-page-title-main">Bell 533</span> Research helicopter built by Bell Helicopter

The Bell 533 was a research helicopter built by Bell Helicopter under contract with the United States Army during the 1960s, to explore the limits and conditions experienced by helicopter rotors at high airspeeds. The helicopter was a YH-40—a preproduction version of the UH-1 Iroquois—modified and tested in several helicopter and compound helicopter configurations. The Bell 533 was referred to as the High Performance Helicopter (HPH) by the Army, and reached a top speed of 274.6 knots in 1969, before being retired.

<span class="mw-page-title-main">Fairey Jet Gyrodyne</span> Type of aircraft

The Fairey Jet Gyrodyne is a British experimental compound gyroplane built by the Fairey Aviation Company that incorporated helicopter, gyrodyne and autogyro characteristics. The Jet Gyrodyne was the subject of a Ministry of Supply (MoS) research contract to gather data for the follow-up design, the Rotodyne.

<span class="mw-page-title-main">Sikorsky S-69</span> US experimental co-axial compound helicopter

The Sikorsky S-69 is an American experimental compound helicopter developed by Sikorsky Aircraft as the demonstrator of the co-axial Advancing Blade Concept (ABC) with United States Army and NASA funding.

<span class="mw-page-title-main">Helicopter</span> Type of rotorcraft in which lift and thrust are supplied by horizontally-spinning rotors

A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of short take-off and landing (STOL) or short take-off and vertical landing (STOVL) aircraft cannot perform without a runway.

<span class="mw-page-title-main">Sikorsky X2</span> Experimental high-speed compound helicopter

The Sikorsky X2 is an experimental high-speed compound helicopter with coaxial rotors, developed by Sikorsky Aircraft, that made its first flight in 2008 and was officially retired in 2011.

<span class="mw-page-title-main">Fairey FB-1 Gyrodyne</span> Type of aircraft

The Fairey FB-1 Gyrodyne is an experimental British rotorcraft that used single lifting rotor and a tractor propeller mounted on the tip of the starboard stub wing to provide both propulsion and anti-torque reaction.

<span class="mw-page-title-main">Bölkow Bo 46</span> Experimental high-speed helicopter

The Bölkow Bo 46 was a West German experimental helicopter built to test the Derschmidt rotor system that aimed to allow much higher speeds than traditional helicopter designs. Wind tunnel testing showed promise, but the Bo 46 demonstrated a number of problems and added complexity that led to the concept being abandoned. The Bo 46 was one of a number of new designs exploring high-speed helicopter flight that were built in the early 1960s.

<span class="mw-page-title-main">McDonnell XV-1</span> American experimental gyrodyne

The McDonnell XV-1 is an experimental Convertiplane developed by McDonnell Aircraft for a joint research program between the United States Air Force and the United States Army to explore technologies to develop an aircraft that could take off and land like a helicopter but fly at faster airspeeds, similar to a conventional airplane. The XV-1 would reach a speed of 200 mph, faster than any previous rotorcraft, but the program was terminated due to the tip-jet noise and complexity of the technology which gave only a modest gain in performance.

<span class="mw-page-title-main">Carter PAV</span> Two-bladed compound autogyro

The Carter PAV is a two-bladed, compound autogyro developed by Carter Aviation Technologies to demonstrate slowed rotor technology. The design has an unpowered rotor mounted on top of the fuselage, wings like a conventional fixed-wing aircraft mounted underneath, and a controllable pitch pusher propeller at the rear of the fuselage. Heavy weights are placed in the rotor tips to enhance rotational energy and to reduce flapping.

<span class="mw-page-title-main">Eurocopter X³</span> Type of aircraft

The Eurocopter X³(X-Cubed) is a retired experimental high-speed compound helicopter developed by Airbus Helicopters. A technology demonstration platform for "high-speed, long-range hybrid helicopter" or H³ concept, the X³ achieved 255 knots in level flight on 7 June 2013, setting an unofficial helicopter speed record. In June 2014, it was placed in a French air museum in the village of Saint-Victoret.

<span class="mw-page-title-main">Sikorsky S-97 Raider</span> American high-speed scout and attack compound helicopter

The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter based on the Advancing Blade Concept (ABC) with a coaxial rotor system under development by Sikorsky Aircraft. Sikorsky planned to offer it for the United States Army's Armed Aerial Scout program, along with other possible uses. The S-97 made its maiden flight on 22 May 2015.

<span class="mw-page-title-main">Future Vertical Lift</span> Planned family of US military helicopters

Future Vertical Lift (FVL) is a plan to develop a family of military helicopters for the United States Armed Forces. Five different sizes of aircraft are to be developed, sharing common hardware such as sensors, avionics, engines, and countermeasures. The U.S. Army has been considering the program since 2004. FVL is meant to develop replacements for the Army's UH-60 Black Hawk, AH-64 Apache, CH-47 Chinook, and OH-58 Kiowa helicopters. The precursor for FVL is the Joint Multi-Role (JMR) helicopter program.

References

Citations

  1. 1 2 3 4 5 6 7 Chandler, Jay. "Advanced rotor designs break conventional helicopter speed restrictions (page 1) Archived 2013-07-18 at the Wayback Machine " Page 2 Archived 2013-07-18 at the Wayback Machine Page 3 Archived 2013-07-18 at the Wayback Machine . ProPilotMag, September 2012. Accessed: 10 May 2014. Archive 1 Archive 2 Archive 3
  2. 1 2 3 Robb 2006, page 31
  3. 1 2 3 Silva 2010, page 1.
  4. 1 2 3 Harris 2003, page 7
  5. 1 2 3 Khoshlahjeh
  6. ↑ Dubois, Thierry. "Researchers Look at Single-engine Cruise Ops on Twins" AINonline, 14 February 2015. Accessed: 19 February 2015.
  7. ↑ Perry, Dominic. "Airbus Helicopters promises safe single-engine operations with Bluecopter demonstrator" Flight Global , 8 July 2015. Archive
  8. ↑ Perry, Dominic. "Turbomeca eyes flight tests of 'engine sleep mode'" Flight Global , 25 September 2015. Archive
  9. ↑ Rigsby, page 3
  10. ↑ Johnson HT, p. 325
  11. 1 2 3 Lombardi, Frank. "Optimizing the Rotor" Rotor&Wing, June 2014. Accessed: 15 June 2014. Archived on 15 June 2014
  12. 1 2 3 4 5 6 Nelms, Douglas. "Aviation Week Flies Eurocopter’s X3" Aviation Week & Space Technology , 9 July 2012. Accessed: 10 May 2014. Alternate link Archived 2012-10-11 at the Wayback Machine Archived on 12 May 2014
  13. 1 2 3 4 5 6 7 8 Datta, page 2.
  14. 1 2 Jackson, Dave. "Coaxial - Sikorsky ~ X2 TD" Unicopter. Accessed: April 2014.
  15. ↑ Walsh 2011, page 3
  16. ↑ Robert Beckhusen. "Army Dumps All-Seeing Chopper Drone" Wired June 25, 2012. Accessed: 12 October 2013. "for standard choppers ... the number of revolutions per minute is also set at a fixed rate"
  17. ↑ The UH-60 permits 95–101% rotor RPM UH-60 limits US Army Aviation . Retrieved 2 January 2010
  18. ↑ Trimble, Stephen (3 July 2008). "DARPA's Hummingbird unmanned helicopter comes of age". FlightGlobal. Archived from the original on 14 May 2014. Retrieved 14 May 2014. The rotor speed on a typical helicopter can be varied around 95-102%
  19. ↑ Chiles, James R. "Hot-Rod Helicopters" Page 2 Page 3 Air & Space/Smithsonian , September 2009. Accessed: 18 May 2014.
  20. ↑ "Blade flapping" Dynamic Flight
  21. ↑ "Helicopter Limitations Archived 2014-05-17 at the Wayback Machine " Challis Heliplane
  22. ↑ "Retreating blade stall" Dynamic Flight
  23. 1 2 3 Johnson HT, p. 323
  24. ↑ Prouty, Ray. "Ask Ray Prouty: Compound Helicopters, Compressibility (archived)" Rotor&Wing, 1 May 2005. Accessed: 11 Dec 2019.
  25. ↑ "Nomenclature: Transonic drag rise Archived 2016-12-03 at the Wayback Machine " NASA
  26. 1 2 3 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
  27. ↑ Beare, Glenn. "Why can't a Helicopter fly faster than it does ?" helis.com . Accessed: 9 May 2014.
  28. 1 2 Krasner, Helen. "Why Can’t Helicopters Fly Fast?" Decoded Science, 10 December 2012. Accessed: 9 May 2014.
  29. ↑ Majumdar, Dave. "DARPA Awards Contracts in Search of a 460 MPH Helicopter" United States Naval Institute , 19 March 2014. Accessed: 9 May 2014.
  30. 1 2 Wise, Jeff. "The Rise of Radical New Rotorcraft" Popular Mechanics , 3 June 2014. Accessed: 19 June 2014. Archive Quote: "This aerodynamic principle limits conventional helicopters to about 200 mph."
  31. ↑ "Rotorcraft Absolute: Speed over a straight 15/25 km course Archived 2013-12-03 at the Wayback Machine ". Fédération Aéronautique Internationale (FAI). Note search under E-1 Helicopters and "Speed over a straight 15/25 km course". Accessed: 26 April 2014.
  32. ↑ Hopkins, Harry (27 December 1986), "Fastest blades in the world" (pdf), Flight International : 24–27, retrieved 28 April 2014, Archive page 24 Archive page 25 Archive page 26 Archive page 27 {{citation}}: External link in |quote= (help)
  33. ↑ "Nomenclature: Mu Archived 2016-12-03 at the Wayback Machine " NASA
  34. ↑ Definition of Advance ratio
  35. ↑ "Flapping Hinges" Aerospaceweb.org. Accessed: 8 May 2014.
  36. ↑ Jackson, Dave. "Tip Speed Ratio (Advance Ratio)" Unicopter, 6 September 2013. Retrieved: 22 May 2015. Archived on 21 October 2014.
  37. ↑ "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.
  38. ↑ Berry, page 3-4
  39. ↑ Harris 2008, page 13
  40. ↑ Berry, page 25
  41. ↑ Harris 2008, page 25
  42. ↑ Kottapalli, page 1
  43. ↑ Harris 2008, page 8
  44. ↑ Bowen-Davies, page 189-190
  45. ↑ Harris 2008, page 14
  46. ↑ Bowen-Davies, page 198
  47. ↑ DuBois 2013
  48. ↑ Potsdam, Mark; Datta, Anubhav; Jayaraman, Buvana (18 March 2016). "Computational Investigation and Fundamental Understanding of a Slowed UH-60A Rotor at High Advance Ratios". Journal of the American Helicopter Society. 61 (2): 1–17. doi:10.4050/JAHS.61.022002.
  49. ↑ Bowen-Davies, page 216
  50. ↑ Granlund, Kenneth; Ol, Michael; Jones, Anya (2016). "Streamwise oscillation of airfoils into reverse-flow". AIAA Journal. 54 (5): 1628–1636. Bibcode:2016AIAAJ..54.1628G. doi:10.2514/1.J054674.
  51. ↑ Renata Y. Ellington & Laurie Pierce (21 March 2016). "Contract Activity: Next Generation Rotorcraft Transmission (NGRT)". Aviation Applied Technology Directorate . GovTribe. Archived from the original on 27 March 2016. Retrieved 27 March 2016.
  52. 1 2 Gustafson, page 12
  53. 1 2 Johnson RA, page 251.
  54. ↑ Bowen-Davies, page 97-99
  55. ↑ Bowen-Davies, page 101
  56. ↑ Harris 2003, page A-40
  57. ↑ Harris 2008, page 19
  58. ↑ Duda, Holger; Insa Pruter (2012). "Flight performance of lightweight gyroplanes" (PDF). German Aerospace Center. p. 5. Retrieved 5 April 2020.
  59. ↑ Harris (2008) pp.35-40.
  60. ↑ "FAI Record ID #13216 - Rotodyne, Speed over a closed circuit of 100 km without payload Archived 2015-02-17 at the Wayback Machine " Fédération Aéronautique Internationale . Record date 5 January 1959. Accessed: April 2014.
  61. ↑ Anders, Frank. (1988) "The Fairey Rotodyne" (excerpt) Gyrodyne Technology (Groen Brothers Aviation). Retrieved: 17 January 2011. Archived 26 February 2014
  62. ↑ Rigsby, page 4
  63. ↑ "Requiem for the Rotodyne". Flight International. 9 August 1962. pp. 200–202. Archived from the original on 6 March 2016.
  64. ↑ Braas, Nico. "Fairey Rotodyne" Let Let Let Warplanes, 15 June 2008. Accessed: April 2014. Archived on 30 September 2013
  65. 1 2 Anderson, Rod. "The CarterCopter and its legacy" Issue 83, Contact Magazine , 30 March 2006. Accessed: 11 December 2010. Mirror
  66. ↑ Harris 2003, page 14
  67. ↑ Watkinson, page 355
  68. ↑ Robb 2006, page 41
  69. ↑ Harris 2003, page 18. Lift forces at page A-101
  70. ↑ Munson 1973. pp.55,144-5.
  71. ↑ Landis and Jenkins 2000, pp. 41–48.
  72. ↑ "AH-56A Cheyenne" Globalsecurity.org. Accessed: April 2014.
  73. ↑ Harris? not 2008, not Vol1+2, page 119
  74. ↑ Munson 1973. pp.96,187-8.
  75. ↑ Robb 2006, page 43
  76. ↑ 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.
  77. ↑ Croft, John (15 September 2010). "Sikorsky X2 hits 250kt goal". Flight International. Archived from the original on 17 January 2011. Retrieved 15 September 2010.
  78. ↑ Goodier, Rob (September 20, 2010). "Inside Sikorsky's Speed-Record-Breaking Helicopter Technology". Popular Mechanics . Retrieved 22 September 2010.
  79. ↑ D. Walsh, S. Weiner, K. Arifian, T. Lawrence, M. Wilson, T. Millott and R. Blackwell. "High Airspeed Testing of the Sikorsky X2 Technology Demonstrator [ permanent dead link ]" Sikorsky , May 4, 2011. Accessed: October 5, 2013.
  80. ↑ The X3 concept Archived 2014-05-12 at the Wayback Machine Video1 Video2, at 2m50s Airbus Helicopters . Accessed: 9 May 2014.
  81. ↑ Thivent, Viviane. "Le X3, un hélico à 472 km/h" Le Monde , 11 June 2013. Accessed: 10 May 2014. Possible mirror
  82. ↑ X3 Helicopter Sets Speed Record At Nearly 300 MPH Wired
  83. ↑ Norris, Guy. "Eurocopter X-3 Targets U.S. Market [ permanent dead link ]" Aviation Week , 28 February 2012. Accessed: 1 March 2012. Mirror Archived 2014-04-13 at the Wayback Machine
  84. ↑ Tarantola, Andrew. "Monster Machines: The New Fastest Helicopter On Earth Can Fly At An Insane 480km/h" Gizmodo, 19 June 2013. Accessed: April 2014.
  85. ↑ Wise, Jeff. "Jay Carter, Jr." Popular Science , 2005. Magazine
  86. ↑ Warwick, Graham. "Carter Hopes To Demo SR/C Rotorcraft To Military" Aviation Week, 5 February 2014. Accessed: 19 May 2014. Archived on 19 May 2014
  87. ↑ Moore, Jim. "Carter seeks factory" Aircraft Owners and Pilots Association , 21 May 2015. Accessed: 28 May 2014. Archived on 22 May 2015.
  88. ↑ Hambling, David. "The Rise of the Drone Helicopter - A160T Hummingbird" Popular Mechanics . Accessed: April 2014.

Bibliography

External image
Searchtool.svg Some previous attempts at high-speed VTOL only works in Microsoft Internet Explorer
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.