SP-3300 Flight Research at Ames, 1940-1997

 

Rotorcraft Research

 

[67] Rotorcraft flight research began in earnest at Ames in the early 1970s in conjunction with the newly established program between NASA and the U.S. Army in rotorcraft technology and further to support NASA's emphasis on civil rotorcraft. This work accelerated in the late 1970s with the arrival of several aircraft from NASA Langley when rotorcraft research was consolidated at Ames. The flight research activity initially concentrated on control and handling issues for terminal-area operations under adverse weather conditions and was pursued along with an extensive ground-based simulator program to develop the control systems for flight. Later on, rotor aerodynamics, acoustics, vibration, loads, advanced concepts, and human factors research would be included as important elements in the joint program activity. 46 The various rotorcraft in operation at Ames are noted in table 9.

After its arrival at Ames, the UH-1H (fig. 129) was flown extensively in a series of experiments to develop and evaluate control systems for fully automatic flight for helicopters. This work was driven by the need to develop a database for navigation and guidance concepts for instrument flight operations. A fully automatic digital flight and guidance system known as V/STOLAND that had conventional autopilot capabilities including autoland was developed for the program under the leadership of Fred Baker. The system used Kalman filtering for extracting aircraft position and inertial velocities from multiple ground-based and on-board sensors based on the earlier navigation system research. 47 Complex approach profiles consisting of helical descending flightpaths were investigated as a means of confining the operational airspace for the helicopter and segregating it from conventional transport operations at crowded airports (ref. 158). A variety of approach profiles and procedures were also examined for manual operations to provide the FAA background on the aircraft system requirements and limitations for these operations (ref. 159). Principal engineers for these experiments were George Xenakis, John D. Foster, and Harry Swenson.

 

TABLE 9. AIRCRAFT USED FOR ROTORCRAFT RESEARCH

.

Aircraft Name

Arrival or First Flight Date

Departure Date

.

H-23C (USA 56-2288)

November 3, 1958

April 28, 1959

UH-1B (USA 62-1908 NASA 732)

October 14, 1970

February 10, 1980

UH-1H (USA 69-15231 NASA 733)

May 4, 1974

April 20, 1988

YO-3A (USA 69-18010 NASA 718)

April 27, 1977

June 27, 1997

SH-3G (Bu. No. 149723 NASA 735)

November 9, 1977

July 27, 1993

UH-1H (USA 64-13628 NASA 734)

March 1, 1978

September 29, 1993

AH-1G (USA 66-15248 NASA 736)

March 1, 1978

May 23, 1985

RSRA (72-002 NASA 741)

February 12, 1979

October 10, 1991

CH-47B (USA 66-19138 NASA 737)

August 14, 1979

September 20, 1989

RSRA (72-001 NASA 740)

September 29, 1979

October 10, 1991

JAH-1S (USA 77-22768 NASA 730)

May 8, 1985

July 5, 1988

NAH-1S (USA 70-15979 NASA 736)

November 10, 1987

.

UH-60 (USA 82-23748 NASA 748)

September 22, 1988

.

JUH-60 (USA 78-23012 NASA 750)

September 23, 1989

.

 

Figure 129. Bell UH-1H V/STOLAND helicopter.

Figure 129. Bell UH-1H V/STOLAND helicopter.

 

[68]

Figure 130. Bell AH-1G Huey Cobra.

Figure 130. Bell AH-1G Huey Cobra.

 

Figure 131. Sikorsky Rotor Systems Research Aircraft (RSRA) helicopter confifuration.

Figure 131. Sikorsky Rotor Systems Research Aircraft (RSRA) helicopter confifuration.

 

Figure 132. Sikorsky Rotor Systems Research Aircraft (RSRA) compound confifuration.

Figure 132. Sikorsky Rotor Systems Research Aircraft (RSRA) compound confifuration.

 

 

The aircraft was also used in a series of flights to investigate flying qualities criteria for nap-of-the-Earth operation and certification criteria for civil helicopter operations (refs. 160 and 161). Lloyd Corliss and Victor Lebacqz led these respective programs. Results identified the important features of the helicopter's response for low-altitude maneuvering and the longitudinal stability, control augmentation, and guidance and control displays necessary for civil instrument flight operations. Subsequently, the first demonstration on a helicopter of automatic control laws that used the nonlinear inverse method of George Meyer was conducted on the UH-1H. With these automatic controls the aircraft was flown from takeoff to cruise flight, then through the helical descent back to hover and landing, a first for this approach. Dan Dugan and Ron Gerdes were the project pilots for the UH-1H research.

The AH-1G White Cobra, the original NASA 736 (fig. 130), had originally been flight tested at Langley Research Center to examine the effects of different aerodynamic blade designs on rotor performance and loads. On its arrival at Ames, the Tip Aerodynamics and Acoustics Test was initiated to obtain extensive aerodynamic and load measurements to provide a better understanding of prediction methods and of the underlying physical phenomena for this rotor. 48 The highly instrumented rotor blades and instrumentation package used by the U.S. Army for the previous Operational Loads Survey tests were obtained. Additional absolute pressure instrumentation was added to the rotor tip to increase the number of radial stations measured from five to eight. This resulted in a total of 188 pressure transducer measurements on one rotor blade and an additional 126 measurements on the other blade and rotor hub. Detailed aerodynamic and performance measurements were made (refs. 162 and 163) and acoustic measurements were also obtained in flight with the YO-3A and with a ground array. Gerald Shockey was the project leader; Jeff Cross and Michael Watts were the engineers responsible for the tests, and Army LTC Robert (Bob) Merrill served as the project pilot.

Helicopter test beds for investigating new rotor concepts in flight were developed under a NASA/Army program at Langley Research Center and later transferred to Ames to be used as flight research facilities. Two vehicles, built by Sikorsky Aircraft, were known as the Rotor Systems Research Aircraft (RSRA), one in a helicopter configuration (fig. 131), the other a compound helicopter (fig. 132). They were designed to be fully capable of flight in three different modes: helicopter, compound (with or without wings), and fixed wing with no rotor. 49 These aircraft were powered by two T-58-GE-5 turboshaft engines through an S-61 main transmission. The compound configuration added two TF-34-GE-400A turbofans as auxiliary engines and a large wing including fixed-wing control surfaces. During the first several years at Ames, the aircraft flight envelopes were expanded to the design limits. These aircraft were intended to test new rotor concepts at full scale in the flight environment at conditions that could not be achieved in a wind tunnel. The compound aircraft was equipped with 14 load cells to measure main-rotor thrust, torque, and drag, wing lift and drag, tail-rotor thrust, and auxiliary engine thrust; the helicopter ....

 

[69]

Figure 133. Boeing CH-47 Chinook in-flight simulator.

Figure 133. Boeing CH-47 Chinook in-flight simulator.

 

.....version was instrumented to measure main-rotor thrust, torque, drag, and tail-rotor thrust. Both aircraft were equipped to measure over 500 other aircraft and rotor state, structural, and acceleration parameters. Representative results from the flight-test program with the two aircraft are noted in references 164-167. The helicopter version was diverted as the base airframe for the X-Wing concept development.

The compound configuration continued in flight research and provided critical support to the X-Wing project. One contribution came in a flight test by the Ames team at Dryden, where the aircraft was flown without the rotor system. This flight mode was required for the aircraft to test high-risk rotor configurations, which might have to be separated from the aircraft as a result of system failure or instability. The pyrotechnic blade-separation system was used for both the RSRA and X-Wing. Gregory Condon led the program at the outset, followed at a later date by William (Bill) Snyder. John Burks, Ruben Erickson, and Ed Seto served as test directors for the two aircraft. Warren Hall was the project pilot throughout the program; LTC Bob Merrill also participated as a program pilot during the early stages. The RSRA compound configuration was placed in flyable storage in 1986 after an extensive internal assessment determined that the most cost-effective way to meet industry's needs for modern rotor air-load data was through tests with a UH-60 airframe.

Boeing's CH-47B Chinook was further developed by the Army and NASA as a variable stability helicopter at the NASA Langley Research Center. It was transferred to Ames in 1979 in support of Ames' newly assigned lead role for NASA rotorcraft research. Full-authority electrohydraulic actuators were driven originally by signals from a large on-board TR-48 analog computer. At Ames, the aircraft (fig. 133) was modified to include two digital flight computers, a programmable force-feel system, and a programmable color cathode-ray tube display. This in-flight simulation capability was the catalyst for a variety of flight experiments that ranged from investigations in support of a new flying qualities specification for military rotorcraft that was developed primarily at Ames, to the evaluation of advanced multi-input, multi-output control laws. In all cases, exploratory development of the criteria and advanced control laws was performed on the Vertical Motion Simulator before moving into flight. Experiments to further explore control during flight near the terrain showed the significance of control and response cross-coupling on flying qualities (ref. 168). Height-control requirements during bob-up maneuvers were established in the experiment reported in reference 169.

As a basis for developing advanced control laws, fundamental work was carried out on the modeling of the rotorcraft, to include the effects of high-order influences of the rotor system and to determine the sophistication of models required for control design (ref. 170). Representative of the advanced control activities were the efforts carried out on model-following systems and the effect of high-order system dynamics on the ability to tightly control the aircraft's dynamic response (refs. 171 and 172). Some of the advanced controls research was also performed in close association with [70] Stanford University (ref. 173). Advanced displays were evaluated to determine the information required and the symbol dynamics necessary to precisely hover and land the aircraft (refs. 174 and 175).

A number of individuals led the various experiments, including Robert Chen, Bill Hindson, Kathryn Hilbert, Douglas Watson, Michelle Eshow and Jeffery Schroeder. Hindson and George Tucker performed the bulk of the evaluation flying. Figure 134 shows the aircraft's research team. The aircraft was returned to the Army in 1989 for remanufacture to a CH-47D model. As a consequence of the expertise Ames had acquired from these wide-ranging flight and simulation activities, a team led by Mark Tischler took part in an extensive investigation of the flying qualities of Boeing's Advanced Digital Optical Control System demonstrator, a highly modified UH-60A helicopter. Their work pointed out areas of agreement between flight results and the original design guidelines for these advanced systems, as well as those aspects needing improvement (ref. 176).

The in-flight and ground-based simulation research on flying qualities for nap-of-the-Earth maneuvering conducted by the Army and NASA team led to a collaborative activity with counterparts in the German aeronautical research establishment, the....

 

Figure 134. Boeing CH-47 research team. From left to right: Greg Condon, Emmett Fry, George Tucker, Gale Kaplan, Katie Hilbert, Jphn Wilson, Grady Wilson, Dave Nishikawa, Bill Hindson, Al Parker, Bob Chen, Vic Lebacqz.

Figure 134. Boeing CH-47 research team. From left to right: Greg Condon, Emmett Fry, George Tucker, Gale Kaplan, Katie Hilbert, Jphn Wilson, Grady Wilson, Dave Nishikawa, Bill Hindson, Al Parker, Bob Chen, Vic Lebacqz.

 

[71]

 Figure 135. Sikorsky UH-60 Air-Loads Research Aircraft.

Figure 135. Sikorsky UH-60 Air-Loads Research Aircraft.

 

....DFVLR. As part of the Army's memorandum of understanding with the Germans, Ames engineers and pilots took part in flight programs carried out by the Germans at their military flight test center at Manching in Bavaria. 50 From 1981 through 1984, Ron Gerdes went to Germany to fly their UH-1D and BO-105C helicopters over slalom courses set up to enable assessment of flying qualities in aggressive maneuvers near the terrain. Edwin Aiken was the Army's principal investigator for those tests. Later, LTC Grady Wilson and LTC Rick Simmons, along with Chris Blanken, now the program's technical leader, took part in flights on the BO-105C and, starting in 1989, with the German's new variable stability BO-105, to pursue investigations in more detail. This phase of the program continued until 1993.

A UH-60A Black Hawk (NASA 748, fig. 135) with conventional structural instrumentation installed on the blades was tested in 1987 at Edwards AFB under Ames' sponsorship as part of the Modern Rotor Aerodynamic Limits Survey. This effort was led by Jeff Cross; a summary is reported in reference 177. Sikorsky Aircraft was contracted to build a set of highly instrumented blades for the Black Hawk test aircraft: a pressure blade with 242 absolute pressure transducers and a strain-gauge blade with an extensive suite of strain gauges and accelerometers. This aircraft was transferred to Ames in 1988 and integration of a data system for the highly instrumented blades was started. The required high-bandwidth data of the blade pressure measurements resulted in a 7.5 megabit data stream from the rotor, a capability that was beyond the state of the art at that time. A number of approaches to obtaining the high data rate were attempted and success was finally achieved. Approximately 30 gigabytes of data were obtained in 1993-94 and installed in an electronic database that was immediately accessible to the domestic rotorcraft industry. 51 A number of results are documented in references 178-180. Ed Seto was the project manager at the outset, and William (Bill) Bousman and Robert Kufeld led a large research team that carried out this complex project (fig. 136). The project pilots were Rick Simmons and Munro Dearing. In 1995, the air-loads project team was honored with the Grover E. Bell Award by the American Helicopter Society in recognition of its contribution to the understanding of this complex technical area.

This Black Hawk was also used in a test program to develop and demonstrate a method for identifying system stability and flying qualities for slung-load operations. 52 The slung load consisted of an instrumented 8- by 6- by 6-foot cargo container. Tests focused on the characteristics of longitudinal and lateral axes with results computed as the flight tests progressed. Mark Tischler's system-identification software was used to compute flying qualities parameters, control system stability margins, and characteristic roots for the load pendulum (ref. 181). Results were also used to validate a slung-load simulation model. Tischler and George Tucker developed the program as part of a U.S./Israeli collaborative effort on rotorcraft aeromechanics and man-machine integration. Luigi Cicolani conducted the research with Rick Simmons and LTC Chris Sullivan as the project pilots.

 

[72]

Figure 136. Sikorsky UH-60 air-loads research team. Front row: Franck Pichay, Jim Phillips, Karen Studebaker, Stan Uyeda Munro Dearing, Rick Simmons, Mario Garcia, Anna Almaraz, Allen Au, Frank pressbury, Bob Kufeld, Marianne Kidder, Nancy Bachford, Jack Brilla, Dwight balough, Chico Rijfkogel, Paul Aristo. Back row: Tom English, Dick Dennan, Patrick Brunn, Tom Reynolds, Bud Billings, Paul Espinosa, Bill Bjorkman, Chee Tung, Leonard Hee, Bill Bousma, Tom Maier, Ron Fong, Steve Timmons, Jeff Cross, Colin Coleman, Paul Loschke, John Lewis, Jim Lesko, Alex Macalma.

Figure 136. Sikorsky UH-60 air-loads research team. Front row: Franck Pichay, Jim Phillips, Karen Studebaker, Stan Uyeda Munro Dearing, Rick Simmons, Mario Garcia, Anna Almaraz, Allen Au, Frank pressbury, Bob Kufeld, Marianne Kidder, Nancy Bachford, Jack Brilla, Dwight balough, Chico Rijfkogel, Paul Aristo. Back row: Tom English, Dick Dennan, Patrick Brunn, Tom Reynolds, Bud Billings, Paul Espinosa, Bill Bjorkman, Chee Tung, Leonard Hee, Bill Bousma, Tom Maier, Ron Fong, Steve Timmons, Jeff Cross, Colin Coleman, Paul Loschke, John Lewis, Jim Lesko, Alex Macalma.

 

Figure 137. Sikorsky JUH-60 Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL).

Figure 137. Sikorsky JUH-60 Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL).

 

A second Black Hawk, originally the Boeing Advanced Digital Optical Control System demonstrator, arrived in 1989 as the replacement vehicle for its predecessor, the CH-47B, to carry on the variable stability and control and guidance system research of the Center. This JUH-60A (NASA 750), now known as the Rotorcraft Aircrew Systems Concepts Airborne Laboratory (fig. 137) and dubbed RASCAL for short, is the most sophisticated in the long line of variable stability helicopters to be developed by NASA and the Army. The RASCAL was developed incrementally in a four-phase program led initially by Edwin Aiken, then by Bob Jacobsen, and Nick Rediess. While the advanced 32-bit Research Flight Control System (RFCS) was being produced under contract by Boeing for installation in phase 4, extensive vehicle and rotor-system instrumentation, a real-time stereo-video passive ranging system, and a sophisticated on-board image generation system (ref. 182) were developed in-house and used to conduct productive flight research. During this time Rediess and Ernie Moralez carried the responsibility for the RFCS-associated development, and Phil Smith developed the passive ranging system; Jay Fletcher and Eric Strassilla developed the hybrid laser/accelerometer-based blade-motion measurement system.

[73] A principal focus of the work with the RASCAL helicopter is the development and evaluation of advanced flight control concepts to improve the agility of military rotorcraft, while also providing the pilot with carefree maneuvering within an automatically protected flight envelope. Other research applications include the development of active sensors (such as millimeter-wave radar), passive sensors (such as infrared), and symbologies for advanced displays. These are technologies needed to....

 

Figure 138. RASCAL research team. Front row: Zsolt Halmos, Jim Ahlman, Sonya Mahal, Paul Aristo, Bob Brunelle, Brad Curelop, Chima Njaka. Second row: Jack Brilla, Shirley Worden-Burek, Paul Espinosa, Seth Kurasaki, Benny Cheung, Alla Silverman, Adel Delous, Sharon Cioffi, Larry Hintz, Trudy Schlaich, Ursula Hawkins, Janice Bachkoksky, Amara Dekeczer, Ed Aiken, Tony Gudino. Third row: Zoltan Szoboszlay, Tom Kaiserstatt, Bob Burney, Cas Lesiak, Ernie Moralez, Hossein Mansur, Jim Jeske, Gary Villere, Paul Everhart, John Foster, Bob Jacobsen, Luigi Cicolani, Vern Merrick, Rick Zelenka, Rich Coppenbarger, Bill Handson. Fourth row: Court Bivens, Bill Decker, Mark Tischler, Stewart Anderson, Nick Rediess, Brian DeSilva, Mark Takahashi, Laura Iseler. Fifth row: Lee Mountz, Jack Trapp, Gary Leong, Roy Williams, K.C. Shih. Back row: Eric Strasilla, Amir Arani, Eric Weihauser, Thad Frazier.

Figure 138. RASCAL research team. Front row: Zsolt Halmos, Jim Ahlman, Sonya Mahal, Paul Aristo, Bob Brunelle, Brad Curelop, Chima Njaka. Second row: Jack Brilla, Shirley Worden-Burek, Paul Espinosa, Seth Kurasaki, Benny Cheung, Alla Silverman, Adel Delous, Sharon Cioffi, Larry Hintz, Trudy Schlaich, Ursula Hawkins, Janice Bachkoksky, Amara Dekeczer, Ed Aiken, Tony Gudino. Third row: Zoltan Szoboszlay, Tom Kaiserstatt, Bob Burney, Cas Lesiak, Ernie Moralez, Hossein Mansur, Jim Jeske, Gary Villere, Paul Everhart, John Foster, Bob Jacobsen, Luigi Cicolani, Vern Merrick, Rick Zelenka, Rich Coppenbarger, Bill Handson. Fourth row: Court Bivens, Bill Decker, Mark Tischler, Stewart Anderson, Nick Rediess, Brian DeSilva, Mark Takahashi, Laura Iseler. Fifth row: Lee Mountz, Jack Trapp, Gary Leong, Roy Williams, K.C. Shih. Back row: Eric Strasilla, Amir Arani, Eric Weihauser, Thad Frazier.

 

[74]

Figure 139. Bell JAH-1S FLITE Cobra.

Figure 139. Bell JAH-1S FLITE Cobra.

 

Figure 140. Bell NAH-1S FLITE Cobra.

Figure 140. Bell NAH-1S FLITE Cobra.

 

....assist the military pilot in conducting nap-of-the-Earth flight at night and in adverse weather conditions; they can also improve the safety of civilian operations such as emergency medical services, fire fighting, or oil-rig support. The research team, which is carrying out a wide range of investigations, is shown in figure 138. As a part of the research into helicopter flight mechanics modeling, Jay Fletcher performed a thorough parameter identification for the aircraft in hover and at speeds of 40 and 80 knots in forward flight to define its characteristics for use in control law design (ref. 183). Bill Hindson conducted experiments to explore noise abatement approaches using differential global positioning system guidance (ref. 184). Richard Zelenka and Richard Coppenbarger carried out research on sensors and displays for low-altitude terrain flight (ref. 185). Hindson and George Tucker served as the principal pilots at the outset of the program. Currently, Rick Simmons and Army LTC Chris Sullivan perform that role. Based on Ames experience with nap-of-the-Earth guidance and control, Harry Swenson led an Ames team that carried out a flight program on the Army's STAR Black Hawk at Ft. Monmouth, New Jersey, to evaluate the use of a stored digital terrain base and flightpath-centered pursuit guidance for near terrain flight (ref. 186). Ames pilots on this program were Gordon Hardy and Munro Dearing.

From the start of Ames crew station and human factors flight research, experiments were carried out on the JAH-1S Cobra (fig. 139). This helicopter, called the Flying Laboratory for Integrated Test and Evaluation (FLITE), arrived at Ames in 1985. It was the first Cobra on which the prototype AH-64 visually coupled night vision system helmet mounted display (HMD) was installed. The aircraft took part in the Army's first use of visually coupled HMD systems and was later involved in a study of a modified communication system. 53 This system, designed by Zoltan Szoboszlay, allowed pilots to switch between three radios and internal communications with the co-pilot, without removing either hand from the flight control sticks (ref. 187). Loran Haworth was the principal investigator and project pilot. The aircraft was returned to the Army in 1985 for overhaul.

The NAH-1S (fig. 140), the successor to the original FLITE Cobra, has been used extensively in joint NASA/Army human factors research in the areas of night vision displays and voice communications since its arrival at Ames in 1987. It was originally modified for use as a surrogate trainer for pilots of the McDonnell Douglas AH-64 Apache helicopter through the installation of a pilot night vision system (PNVS). Haworth and Szoboszlay coordinated the test projects on the aircraft. In night-vision research, the aircraft was used for a study in which the pilot's performance was measured on a low-altitude course while the pilot's field-of-view was restricted to simulate that of night-vision devices. Human performance curves were generated as a function of field-of-view; the results were published in reference 188. In that same vein, the FLITE Cobra was also employed in two studies in which performance with 40-degree field-of-view night-vision goggles was compared with daytime performance with a 40-degree field-of-view restriction, and also with daytime performance without [75] this restriction (ref. 189). In another test, the effects of depth perception when using night-vision goggles and the PNVS FLIR (ref. 190) were examined. Visual estimation of altitude in near-terrain flight was performed and reported in reference 191. Concerning voice communications, pilots evaluated active noise-reduction technologies for better audio communications while piloting this helicopter (refs. 192 and 193). The aircraft was also used in tests of computer voice recognizers and synthesizers. In a different area of human factors research, the FLITE Cobra was used simultaneously with a fixed-base crew station simulator to conduct a simulation sickness study (ref. 194). Principal investigators for the various flight tests were Haworth and Szoboszlay, along with Army flight surgeon LTC John Crowley, .....

 

Figure 141. FLITE Cobra research team. Front row: Tom Reynolds, Nick Proett, Sean Hogan, Loran Haworth, John Browning. Second row: Mary Kaiser, John Spooner, Richard Lee, Munro Dearing, Sue Laurie, Paul Aristo, Alan Lee, Zsolt Halmos, Zoltan Szoboszlay, Dick Denman, Lee Mountz. Back row: David Foyle, Millard Edgerton, Ron Fong, Trudy Schlaich, Gary Leong, Linda Blyskal, Brian Hookland, Steve Timmons, Fran Kaster, Wendell Stephens, Alex Macalma, Dana Marcell.

Figure 141. FLITE Cobra research team. Front row: Tom Reynolds, Nick Proett, Sean Hogan, Loran Haworth, John Browning. Second row: Mary Kaiser, John Spooner, Richard Lee, Munro Dearing, Sue Laurie, Paul Aristo, Alan Lee, Zsolt Halmos, Zoltan Szoboszlay, Dick Denman, Lee Mountz. Back row: David Foyle, Millard Edgerton, Ron Fong, Trudy Schlaich, Gary Leong, Linda Blyskal, Brian Hookland, Steve Timmons, Fran Kaster, Wendell Stephens, Alex Macalma, Dana Marcell.

 

[76] ....David Foyle, Daniel Hart, Robert Hennessy, Thomas Sharkey, and Carol Simpson. Pilots who participated throughout were Haworth, Munro Dearing, Bill Hindson, George Tucker, and Army pilots LTC Thomas Reynolds, MAJ Ronald Seery, and LTC Rick Simmons. The FLITE team is shown in figure 141.

In addition to human factors studies, the FLITE Cobra was used to validate the military rotorcraft flying qualities specification maneuvers, visual cues, and test methods in a degraded visual environment. In support of the Army's RAH-66 Comanche Program, the aircraft was used as a radar target while hovering in front of a directed imaging radar, used for testing the F117 radar signature on the ground. This was the first use of the radar against a rotorcraft in hover flight. The tests proved that this type of technology radar is useful for measuring the radar signature of a rotorcraft through 360 degrees of rotation to test for radar-signature conformity. Also in support of the Comanche program, the aircraft flew prototype fiber-optic connectors to gather long-term fiber-optic attenuation data. In another test, a color video camera was installed and boresighted to the PNVS. Several hours of infrared and color video imagery were collected over various types of terrain for use in a part-task infrared trainer in a collaborative program with the Israeli Ministry of Defense. The aircraft is being modified to test an image fusion sensor for night vision, a programmable helmet-mounted display system, and an automated gearbox health-monitoring system.

A novel method of measuring rotorcraft impulsive noise in which a quiet aircraft is used as a microphone platform was developed by Fred Schmitz and his Army/NASA team in the mid-1970s. The aircraft was instrumented with a tail microphone and flown in formation with the test helicopter at selected airspeeds and rates of sink at which the helicopter was known to radiate large amounts of impulsive noise. The distance between the aircraft and the helicopter was held within 1-meter accuracy using a visual range finder. The concept was first proven by using a Grumman OV-1C Mohawk aircraft that was borrowed from the Army Engineering Flight Activity at Edwards Air Force Base. 54 The test team, led by Fred Schmitz and Donald Boxwell of the Army and supported by Army and NASA personnel, was the first to document and record true free-field measurements of helicopter impulsive noise. The results led to a new appreciation for and understanding of the major sources of these very complicated rotorcraft acoustic phenomena (ref. 195).

The success of this new measurement technique prompted a search for a better measurement platform, one that was quieter and better suited to the flight conditions in which rotorcraft impulsive noise was likely. The search led to a YO-3A that was originally built by Lockheed for the Army as a surveillance aircraft and operated by the Federal Bureau of Investigation. It was modified to accept on-board recording and monitoring equipment that included wing-tip microphones which, together with a tail microphone, helped assess the directivity of the radiated noise. The initial YO-3A team is shown in figure 142. Special emphasis was placed on quantitatively measuring....

 

[77]

Figure 142. Lockheed YO-3A acoustics research team: From left to right: Don Boxwell, Fred Schmitz, Bob Williams, Lee Jones, Bob George, Vance Duffy.

Figure 142. Lockheed YO-3A acoustics research team: From left to right: Don Boxwell, Fred Schmitz, Bob Williams, Lee Jones, Bob George, Vance Duffy.

 

Figure 143. Lockheed YO-3A.

Figure 143. Lockheed YO-3A.

 

.....the impulsive noise during the landing approach of a series of Army helicopters (fig. 143); the results are reported in references 196 and 197. The aircraft was also used to evaluate the noise characteristics of the contending designs for the Army's Utility Tactical Transport Aircraft System and the Advanced Attack Helicopter, with results reported directly to the source selection board. The resulting external noise data proved invaluable and helped in selecting the eventual winners of both large Army contracts. This series of experiments also provided a unique database to the technical acoustic community that helped focus the research efforts of the next 20 years. These very successful in-flight acoustic test programs made it clear that this new research tool was an important asset to acoustic research.

In mid-1977, Ames acquired its own YO-3A and took up the role of providing in-flight acoustic measurements for future rotorcraft research programs. Upgraded equipment and instrumentation were added to the NASA YO-3A aircraft, but the basic measurement procedures remained similar to those of the earlier test programs. Use of the YO-3A by NASA for far-field measurement of rotorcraft noise is described in references 198 and 199. Several major research programs were undertaken by [78] NASA, with the Army as a major partner. Tests were carried out on the AH-1, XV-15, UH-60, S-76, BO-105, and MD-900 aircraft. Typical results from the flight research effort, including comparisons with data from tests in the 40- by 80-foot wind tunnel are presented in references 200 and 201.

The Ames flight operations staff of 1991 is shown in figure 144.

 

Figure 144. Flight operations personnel circa 1991. From left to right: Loran Haworth, Rick Simmons, Tom Reynolds, Goli Davidson, Jack McLaughlin, Trudy Schlaich, Jim Martin, Mike Storz, Gordon Hardy, Patti Bergin, Nancy Lowe, Ron Seery, Larry Hintz, Mike Landis, Munro Dearing, George Tucker.

Figure 144. Flight operations personnel circa 1991. From left to right: Loran Haworth, Rick Simmons, Tom Reynolds, Goli Davidson, Jack McLaughlin, Trudy Schlaich, Jim Martin, Mike Storz, Gordon Hardy, Patti Bergin, Nancy Lowe, Ron Seery, Larry Hintz, Mike Landis, Munro Dearing, George Tucker.

 


46. Bill Snyder 1998: personal communication.

47. John D. Foster 1998: personal communication.
48. William (Bill) Bousman 1998: personal communication.
49. Bill Snyder and Gregory Condon 1998: personal communication.
50. Ron Gerdes and Chris Blanken 1998: personal communication.
51. Bill Bousman 1998: personal communication.
52. Luigi Cicolani 1998: personal communication.
53. Loran Haworth 1998: personal communication.
54. Fred Schmitz 1998: personal communication.

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