XV-15 litho - NASA's History Office

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16 Research and Engineering), obtained support from C. W. (Bill) Harper, Chief of the Aeronautics Division in the Office of Advanced Research and Technology (OART) at NASA Headquarters, for another entry in the Ames 40- by 80-foot wind tunnel. This test involved configuration variations that were predicted to alter the rotor/pylon/wing aeroelastic stability. The test results were compared with the pre-test predictions to determine if the evolving analytical methodology adequately represented the aircraft’s structural dynamics. Without a speed capability well in excess of the helicopter’s maximum speed, the tilt rotor aircraft did not fulfill the performance requirements of the VTOL mission. Lacking a valid structural stability prediction method, the design of a new tilt rotor aircraft was considered to have a high level of uncertainty and therefore an unacceptable high-risk undertaking. The planned test could have exposed the XV-3 aircraft, as well as the 40- by 80foot wind tunnel, to possible damage due to the potential for an explosively rapid failure caused by instability. Could Ames accept this unusual risk? Showing great confidence in the technical approach, the decision to accept the test was made by Mark Kelly, NASA’s Chief of the Large Scale Aerodynamics Branch, and Woodrow L. (Woody) Cook, Chief of the Advanced Aircraft Programs Office. The Bell test team was led by Kipling (Kip) Edenborough, who served as test director, and included Claude Leibensberger, Flight Test Engineer for the XV-3 project. The test, which ran from October to November 1968, proceeded remarkably well for all of the planned test conditions. The level of damping (i.e. stability) was assessed by disturbing the pylon and measuring the resulting vibrations. Decaying vibration amplitudes indicated a stable structure, constant amplitude vibrations indicated neutral stability, and growing amplitudes revealed a dangerous unstable condition. Test results showed that configurations predicted to be stable were in fact stable, and those predicted to be unstable showed signs of decreasing stability as the stability limit speed was approached. With the aircraft in its most stable condition, a run at maximum wind tunnel speed, recognized as a high risk condition, completed the test activity. When the wind tunnel was taken to its maximum airspeed capability (of nearly 200 knots), the vibratory loads data once again verified the predicted stability. Disaster Strikes Suddenly both pylons separated from the wing and were blown down the tunnel. The XV-3 was extensively damaged in what appeared to be the result of the inability to design an aeroelastically stable tilt rotor aircraft. However, after months of careful examination of the damaged structure and analyses of the incident, the test data revealed this was not the case. The failure was traced to a fatigue crack and rivets working loose in the left wingtip spar. The progressing crack and loose rivets reduced the stiffness of the pylon attachment to the level where a resonance occurred, producing the high oscillatory loads that led to the subsequent massive structural failure. The right rotor, exposed to extremely high
overloads as the aircraft was being shaken during the initial failure, failed under a whirl divergence condition. In the final analysis, the wind tunnel investigation successfully accomplished its goals, but this wind tunnel entry would be the final research activity conducted with the XV-3 experimental aircraft. 8 XV-3 Legacy At first look, an assessment of the results of 13 years of flight, ground, and wind tunnel investigations with the XV-3 did not present a favorable prospect for the future of the tilt rotor aircraft. The severely underpowered XV-3 had limited hover capability and cruise performance. The maximum level flight speed of 115 knots (155 knots in a dive) was not adequate to prove that the tilt rotor had a useful airplane mode capability. However, it was fortunate that the airplane-mode speed was so restricted since the aircraft would likely have been destroyed in flight, due to the rotor/pylon/wing aeroelastic instability. The XV-3 also suffered from handling qualities problems, including lateral and roll instabilities when hovering in ground effect (IGE), and a directional divergent oscillation and poor control responses in the longitudinal and directional axes at low airspeeds. In addition, a complex gear shifting process, required to reduce rotor RPM after converting to the airplane mode (to improve rotor efficiency), produced an unacceptably high pilot workload. On the positive side, the significant achievement of the XV-3 project was clearly the demonstration of the ability of the tilt rotor aircraft to perform in-flight conversion from the helicopter configuration to the fixed-wing (airplane) configuration and back to the helicopter mode in a safe, stable, controllable manner. This was accomplished with sufficient airspeed margins and maneuverability and adequate tolerance to gusts and turbulence throughout the process. A total of 110 full conversions were performed during the 125 flight hours logged by the 10 XV-3 test pilots (three Bell, three Army, two Air Force and two NASA). The proven conversion capability, coupled with the predicted but unproven performance potential in the hover and cruise flight regimes, provided the basis for continued interest in the tilt rotor concept in the military and within the NASA Langley and Ames Research Centers that were focusing on the search for new VTOL vehicle technologies. A description of the XV-3 is provided in Appendix A. Encouraged by the outcome of the flight and wind tunnel tests of the XV-3, Bell 8 After years of storage at Moffett Field, California, Tucson, Arizona, and the Wright-Patterson AFB near Dayton, Ohio, the remains of the XV-3, tail number 4148, were found at the U.S. Army Air Museum at Fort Rucker, Alabama, in 1984. This unexpected discovery occurred when the Bell XV-15 flight test team visited the museum while conducting a demonstration tour with the XV-15 tilt rotor research aircraft. The XV-3 had been stored outside and was in need of extensive repair (including the damage from the wind tunnel accident). Claude Leibensberger, an XV-3 engineer who at the time was retired from Bell, led the restoration accomplished with Army support. The refurbishment was completed by December 1986 but the aircraft was not put on display due to limited museum space. By late 1995, the XV-3 was again seen disassembled in an indoor storage area where it remains as of the time of this writing. 17
Page 1: The History of The XV-15 Tilt Rotor
Page 5: Contents Prologue . . . . . . . . .
Page 9: Dedication The story of the success
Page 13: Foreword The development of tilt ro
Page 17 and 18: List of Figures Figure 1 Leonardo d
Page 19 and 20: Figure 41 Simultaneous static test
Page 21 and 22: Figure A-2 Transcendental Model 2 t
Page 23 and 24: List of Acronyms AARL Army Aeronaut
Page 25: TRENDS Tilt Rotor Engineering Datab
Page 28 and 29: Figure 2. Illustration of vertical
Page 30 and 31: Figure 4. McDonnell XV-1 compound h
Page 32 and 33: Figure 7. Henry Berliner tiltpropel
Page 34 and 35: Top: Figure 9. The Baynes Heliplane
Page 36 and 37: Figure 13. Illustration from the Ha
Page 38 and 39: Figure 17. Bob Lichten, extreme lef
Page 40 and 41: Figure 20. Tiedown tests of the XV-
Page 44 and 45: 18 management continued to show int
Page 46 and 47: 20 Building the Technology Base Aer
Page 48 and 49: Figure 25. Bell 25-ft. diameter pro
Page 50 and 51: Figure 28. Performance tests of 5-f
Page 52 and 53: Figure 31. Bell 25-ft. diameter pro
Page 54 and 55: 28 Tilt Rotor Research Aircraft Pro
Page 56 and 57: 30 During the late 1960s and early
Page 58 and 59: 32 range of loading conditions and
Page 60 and 61: 34 The initial projected cost of $4
Page 62 and 63: Figure 35. Illustration of the Boei
Page 64 and 65: Figure 36. 1/5 scale XV-15 model in
Page 66 and 67: 40 under the contract. To accomplis
Page 68 and 69: 42 Aircraft Development The primary
Page 70 and 71: 44 Test stand angle box Test stand
Page 72 and 73: Figure 40. Proprotor response to co
Page 74 and 75: Figure 41. Simultaneous static test
Page 76 and 77: 50 helicopters. For the conversion
Page 78 and 79: 52 Prior to the start of flight ope
Page 80 and 81: Figure 44. Initial Bell tiedown sho
Page 82 and 83: 56 degrees 25 and a brief assessmen
Page 84 and 85: Figure 45. XV-15 in the Ames Resear
Page 86 and 87: 60 NAVAIR managers as a means of de
Page 88 and 89: Figure 46. Government and Bell pers
Page 90 and 91: Figure 49. Tiedown test facility at
Page 92 and 93:
66 Wheel height Top: Figure 51. Met
Page 94 and 95:
68 Symmetric beam mode Antisymmetri
Page 96 and 97:
Figure 55. XV-15 during short takeo
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Top: Figure 56. Flow visualization
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74 during “degraded” flight con
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Figure 59. Hover acoustics tests du
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78 Nose weight Top: Figure 61. Typi
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80 Following the completion of cont
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82 After the proprotors stopped, th
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84 sudden stoppage of the right eng
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86 A reconversion to the helicopter
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88 Paris Air Show By early 1981, th
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90 enroute from Farnborough to Fran
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Top: Figure 66. Senator Goldwater i
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Figure 69. Shipboard evaluations of
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Figure 71. XV-15 at the New York Po
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98 Crash (October 16 and 17, 1991).
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100 The End of an Era By the mid 19
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Top: Figure 73. XV-15 at the Dallas
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104 management system was very effe
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106 could make use of the same flig
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Figure 76. The Bell tilt rotor eagl
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110 demonstrations two years earlie
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112 Future Tilt Rotor Aircraft By t
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114 tiltrotor aircraft program. Thi
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116 Model 1-G Characteristics Power
Page 144 and 145:
Figure A-3. Transcendental Model 2
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Figure A-4. XV-3 three-view drawing
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Figure A-5. XV-3 inboard drawing, s
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Nacelle angle (degrees) 124 120 90
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Figure A-8. General layout and majo
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Figure A-9. Side view inboard profi
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Figure A-11. XV-15 height-velocity
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132 Weight Design . . . . . . . . .
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134 WBS LEVEL: Bell Army/NASA I II
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136 US Army Air Mobility Research a
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138 Army/NASA (continued) Staff (19
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140 Appendix C—Chronology 1452-15
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142 1968 Boeing Vertol awarded cont
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144 November, Initial piloted simul
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146 24 March 1982 XV-15 demonstrate
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148 30 July 1987 FAA/NASA/DOD Tilt
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150 21 August 1990 V-22 reached 340
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152 14 June 1993 The Department of
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154 Appendix D—Awards and Records
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Figure D-1. Jean Tinsley, first wom
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Figure E-3. XV-15 flying by the Sta
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Figure E-7. Bell test pilots Roy Ho
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Figure E-11. Ken Wernicke, Bell til
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164 Appendix F—Bibliography Tilt
Page 192 and 193:
166 Ball, J. C. “XV-15 Shipboard
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168 Churchill, G. B.; Dugan, D. C.
Page 196 and 197:
170 Edenborough, H. K. “Investiga
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172 Harendra, P. B.; Joglekar, M. J
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174 Kvaternik, Raymond G. “Studie
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176 Magee, J. P.; Pruyn, R. “Pred
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178 Martin, Stanley, Jr.; Erb, Lee
Page 206 and 207:
180 Rutledge, Charles K.; George, A
Page 208 and 209:
182 Tischler, M. B.; Leung, J. G. M
Page 210 and 211:
184 Whitaker, H. L.; Cheng, Yi. “
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186 Daniel C. Dugan Daniel Dugan gr
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188 Carnet, 88 Carpenter, Ron, 91 C
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190 Moffett Airfield, Moffett Field
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Monographs in Aerospace History Lau
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National Aeronautics and Space Admi
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XV-15 litho - NASA's History Office

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