SP-3300 Flight Research at Ames, 1940-1997

 

Boundary Layer Control, STOL, V/STOL Aircraft Research

 

[47] BOUNDARY LAYER CONTROL RESEARCH

Motivated by the military's interest in reducing landing speeds for their jet fighter aircraft, Ames aerodynamicists began to explore practical ways of controlling the boundary layer of free-stream air on wings, high-lift devices, and control surfaces in the 1950s. Blowing directly over an airfoil increases the circulation of the air over the airfoil, thereby increasing lift and, by energizing the boundary layer, preventing separation of the airflow from the surface. Extensive testing was done in the 40- by 80-foot wind tunnel to explore different approaches for boundary-layer control.29 This led to flight investigations of a variety of boundary-layer control concepts on the F-86F over the period 1954-57, including suction at the leading edge of the wing, suction at the leading edge of the flap, and blowing over the flap to energize the boundary layer. The blown flap, which eventually saw application on operational aircraft, proved to be more effective than suction at the leading edge of the wing or flap for increasing lift since it increased circulation at the wing whereas suction just enabled the wing to approach its theoretical maximum lift. Results of tests of the three different schemes were reported in references 102-104. Ames continued its flight investigation of boundary-layer control lift augmentation in tests of the FJ-3, F9F-4, and F9F-6 aircraft. The F9F-6 was also used to obtain low-speed lift and drag data during approach.

The F-100A aircraft was used in a test of blown leading-edge and trailing-edge flaps. The system exhibited improved longitudinal stability and reduced the onset of buffet to airspeeds about 35 knots lower than for the conventional aircraft. Contributions to this reduction in speed could be attributed to the addition of short-span trailing-edge flaps (15 knots), blowing on the leading-edge flaps (13 knots), and blowing on the trailing-edge flaps (7 knots).30 However, control problems began to appear that were not evident at the higher approach speeds (ref. 105). Hervey Quigley led this program with Bob Innis as the principal pilot. The experience gained from all this testing was utilized in designing the blown flap systems used on the F-104 Starfighter and the F-4 Phantom II and in designing the short takeoff and landing (STOL) transport aircraft to come.

Innis teamed with Stew Rolls in another boundary-layer control (BLC) application, this time to a large four-engine jet transport, the Boeing 707 prototype 367-80. Using a system developed through tests with a 30 percent scale model of the aircraft in the 40- by 80-foot wind tunnel, the aircraft was routinely flown at approach speeds 20 to 35 knots below those used in normal operations. Lift and drag data were obtained in flight as a function of engine thrust coefficient. The lift coefficients achieved were not as high as those obtained in the tunnel, a result that was attributed to the effects of model scale on flow as influenced by the leading-edge devices (ref. 106).The various BLC, as well as STOL and vertical and short takeoff and landing (V/STOL) aircraft, are noted in table 8. The collection of BLC aircraft appears in figures 98-102.

 

Figure 98. F-86F Sabre.

Figure 98. F-86F Sabre.

 

Figure 99. North American FJ-3 Fury.

Figure 99. North American FJ-3 Fury.

 

Figure 100. Grumman F9F-4 Panther.

 

[48]

Figure 101. Grumman F9F-6 Cougar.

Figure 101. Grumman F9F-6 Cougar.

 

Figure 102. North American F-100A Super Sabre.

Figure 102. North American F-100A Super Sabre.

 

Figure 103. Stroukoff YC-134A.

Figure 103. Stroukoff YC-134A.

 

TABLE 8. AIRCRAFT USED FOR BOUNDARY LAYER CONTROL, STOL, AND V/STOL RESEARCH

.

Aircraft Name

Arrival or First Flight Date

Departure Date

.

F-86F (AF 52-4535 NASA 228)

October 10, 1953

September 13, 1965

FJ-3 (Bu. No. 135800)

September 3, 1954

April 30, 1956

F9F-4 (Bu. No. 125156)

October 21, 1954

August 10, 1955

F9F-6 (Bu. No. 128138)

May 9, 1955

August 3, 1955

F-100A (AF 53-1585A NACA 200)

October 2, 1956

February 15, 1960

VZ-3RY (AF 56-6941 NASA 235, NASA 705)

May 20, 1958,

February 24, 1959

August 24, 1959

June 20, 1966

YC-134A (AF 54-556 NASA 222)

March 6, 1959

May 31, 1961

XV-3 (AF 54-148)

August 12, 1959

June 9, 1965

X-14 (AF 56-4022)

October 2, 1959

.

X-14A (NASA 234)

1960

.

X-14B (NASA 704)

1971

May 29, 1981

NC-130B (AF 58-712)

June 30, 1961

December 20, 1961

.

February 27, 1963

May 23, 1963

.

November 16, 1963

November 5, 1967

YROE-1(4020, 4021, 4024)

November 16, 1961

1961

CV-340 (NASA 707)

May 21, 1963

September 3, 1976

XV-5B (USA 62-4505 NASA 705)

March 17, 1964

January 30, 1974

B367-80 (N70700)

April 1967

July 1967

.

May 1968

August 1968

C-8A (USA 63-13686)

June 10, 1967

Delivered to Boeing for modification to AWJSRA

OV-10A (Bu. No. 152881 NASA 718)

April 8, 1968

October 7, 1976

C-8A (AWJSRA NASA 716)

May 1, 1972

September 22, 1981

DHC-6 (NASA 720)

August 7, 1973

September 19, 1979

XV-15 (NASA 702)

March 23, 1978

April 5, 1990

C-8A (USA 63-13687 QSRA NASA 715)

August 3, 1978

November 22, 1993

XV-15 (NASA 703)

October 30, 1980

April 28, 1994

YAV-8B (Bu. No. 158394 NASA 704)

April 11, 1984

November 30, 1995

AV-8C (Bu. No. 158387 NASA 719)

January 21, 1986

February 17, 1995

 

STOL RESEARCH

Short takeoff and landing flight research was motivated by the desire of military and civil operators for transport aircraft with short-field operational capability and jet cruise speeds. For Ames, it was a natural extension of the earlier boundary-layer control activity undertaken to achieve low-speed performance. The first STOL flight research at the Center involved two transports that had been developed for the Air Force, the YC-134A and NC-130B (figs. 103 and 104). Both aircraft used boundary-layer control over the flaps to augment lift. For the NC-130B, extensive tests in the 40- by 80-foot wind tunnel had shown the capability of BLC flaps to enable operation at low airspeeds. However, uncertainties still existed about the ability to control [49] the aircraft in this flight regime. To provide the control power required at speeds as low as 60 knots, the NC-130B also used blowing over drooped ailerons, elevator, and rudder. Two engine pods were attached to the wing of the aircraft for the sole purpose of providing bleed air for the entire boundary-layer control system. Results of the NC-130B tests are reported in reference 107. Both aircraft, as modified, proved the low-speed performance anticipated, but they were found by the pilots to suffer from poor lateral-directional control characteristics during the low-speed approach and landing. Control augmentation systems were devised for the NC-130B on a ground-based simulator and then demonstrated in the airplane to improve lateral-directional control at these conditions (ref. 108). Special procedures were developed during the flight tests to reduce the time spent in the low-speed configuration during takeoff and landing to reduce the overall pilot workload.

Ames research with these aircraft brought the team into contact with comparable activities under way in France and Japan. Joint flight programs were undertaken with both countries in order to improve the understanding of a wide variety of STOL configurations and their operations.31 Two major tests were carried out in France on the Breguet 941 (fig. 105), a four-engine, deflected-propeller slipstream transport, to determine the aircraft's performance and flying qualities (ref. 109), and to explore its operation in low-visibility instrument flight conditions (ref. 110). The program with the Japanese involved tests of their Shin-Meiwa STOL seaplane. This aircraft was also a propeller-driven four-engine deflected slipstream design that was evaluated to determine its flying qualities with and without stability and control augmentation at low speed (ref. 111). Curt Holzhauser and Hervey Quigley were the research leaders for these programs, and Bob Innis served as project pilot. Innis received the Octave Chanute Award in 1964 for his contributions to the evaluation of the performance and handling of this variety of aircraft. The team of Innis, Holzhauser, and Quigley was recognized by Ames Research Center for pioneering research in STOL aircraft performance and flying qualities with the H. Julian Allen Award for an outstanding research paper in 1972. That paper (ref. 112) still stands as the authoritative document on STOL flying qualities and operating characteristics.

Several preliminary STOL designs were investigated by NASA analytically and in wind tunnels in the late 1960s, and a few of these were eventually developed for flight evaluation under the auspices of a research aircraft project office, established within the Aeronautics Directorate at Ames in the late 1960s. During his stint at headquarters as head of NASA aeronautics, Bill Harper had been successful in convincing NASA upper management of the desirability of building proof-of-concept aircraft to validate ground-based technology in a full-scale vehicle in the flight environment. His idea was that these aircraft would provide a focus for the integration of the technologies required in the development of operational vehicles of the type and then could serve the NASA research community as a flight facility for more broad ranging research for that class of aircraft.32 From the outset at Ames, the Center director, H. Julian Allen, and the director of Aeronautics, Russell (Russ) Robinson, provided....

 

Figure 104. Lockheed NC-130B.

Figure 104. Lockheed NC-130B.

 

Figure 105. Breguet 941 (French military transport).

Figure 105. Breguet 941 (French military transport).

 

[50]

Figure 106. North American OV-10A Bronco rotating-cylinder flap research aircraft.

Figure 106. North American OV-10A Bronco rotating-cylinder flap research aircraft.

 

Figure 107. Boeing/deHavilland Augmentor Wing Jet STOL Research Aircraft.

Figure 107. Boeing/deHavilland Augmentor Wing Jet STOL Research Aircraft.

 

....strong leadership and advocacy for this idea. Harvey Allen's successor as director, Hans Mark, along with Leonard Roberts, who followed Russ Robinson as director of Aeronautics, and Brad Wick, chief of Flight Systems and Simulation, later were stalwarts in program advocacy and in securing approval and sustained support for several projects. 33 Woody Cook led the advanced aircraft project office from the start. Reference 113 by Dave Few provides insight into the workings of the project office, including a description of each aircraft program and its significance.

The OV-10A Bronco (fig. 106), which was the first of the several flight projects flown at Ames, served as the test bed for the rotating-cylinder-flap concept. The wing of the aircraft was modified to incorporate a two-segment flap located aft of the hydraulically driven rotating cylinder. The Bronco is a twin-propeller aircraft powered by two T-53 turbine engines, interconnected through a cross-shaft. The rotating cylinder in this case energized the boundary layer, thus keeping the airflow from separating from the wing flaps. At the same time, the cylinder also deflected the propeller thrust to provide a powered-lift component to the wing lift. The aircraft was tested in both the 40- by 80-foot wind tunnel and in flight, starting in mid-1971. Flight testing showed the anticipated improvement in low-speed performance, but also revealed adverse stability and control characteristics that prohibited the aircraft from being flown routinely to its full performance potential (ref. 114). In this case, the airplane became increasingly unstable longitudinally as speed decreased, a result of increased downwash on the horizontal stabilizer at the higher flap angles. Increasing the deflection of the trailing segment on the inboard flap improved longitudinal stability sufficiently to achieve a reduction in approach speed to 57 knots. James (Jim) Weiberg led the program and Bob Innis served as the project pilot.

A modified deHavilland C-8A Buffalo, the Augmentor Wing Jet STOL Research Aircraft (AWJSRA), was the research aircraft used in evaluating the augmentor wing concept and was the world's first jet STOL transport demonstrator (fig. 107). The aircraft was the first major aircraft development program of the new project office and was the focus of a joint NASA/Canadian Department of Industry, Trade and Commerce project to demonstrate the concept in the low-speed regime and in terminal-area operations. Woody Cook, Curt Holzhauser, and Hervey Quigley led the program definition and advocacy effort. 34 Once under way, the project was headed by Dave Few, with technical direction by Quigley. Bob Innis was the project pilot and was joined by Seth Grossmith, a pilot from the Canadian Ministry of Transport. The wing of the C-8 was replaced with one of reduced span that incorporated augmentor flaps, spoilers, blown ailerons, and fixed leading-edge slats. In this design, ejecting fan air between the upper and lower segments of the augmentor flaps enhanced lift. The fan flow was cross-ducted from each engine to the augmentor flaps so that the system would provide balanced lift with one engine inoperative. The engines' jet exhaust could be vectored from 6 degrees to 104 degrees below the horizontal. Extensive tests were carried out in the 40- by 80-foot wind tunnel and on the Flight Simulator for Advanced Aircraft to develop the augmentor flap and the....

 

[51]

Figure 108. deHavilland DHC-6 Twin Otter.

Figure 108. deHavilland DHC-6 Twin Otter.

 

....control system design. The flight program began in mid-1972. Nominal approach speeds of 60 knots were routine, and speeds as low as 50 knots were demonstrated. Takeoff and landing distances of less than 1000 feet over a 50-foot-high obstacle were easily achieved, as were ground rolls of 350 feet. Quigley, Dick Vomaske, and Jack Stephenson documented the aerodynamics of the augmentor flap along with the airplane's performance and stability and control characteristics in references 115-117.

After flight tests proved the powered-lift design, a digital guidance, control, and display system (STOLAND) was installed in the Augmentor Wing to provide a capability for advanced control, as well as guidance and navigation research for STOL operations. This system provided computer control of pitch, roll, and yaw, as well as thrust and thrust deflection along with electronic head down displays for precision guidance. All had been developed in the course of several experiments in the Flight Simulator for Advanced Aircraft and in precursor flight experiments with the Convair 340 and a DHC-6 Twin Otter aircraft (fig. 108), the latter lent to Ames for this purpose by the FAA. 35 The modified Augmentor Wing was then used to evaluate flying-qualities criteria, augmented controls, and flight director concepts under the leadership of Jack Franklin and Bill Hindson, the latter representing the Canadian National Aeronautical Establishment.

Flying qualities design criteria for flightpath and speed control during landing approach and in the flare to touchdown resulted from these tests (ref. 118). The criteria were used in the Air Force's development of specifications for STOL transports and were ultimately applied to the C-17 military transport design. The data were also used by the FAA in defining airworthiness criteria for this category of civil transports. Experience with attitude, flightpath, and speed-control augmentation designs, flight director guidance, and operating procedures are documented in reference 119.

An automatic approach and landing system for STOL terminal-area operations was also developed and flown extensively. Donald Smith and DeLamar (Del) Watson headed up this effort (ref. 120) and demonstrated, for the first time, fully automatic flight for a powered-lift STOL aircraft. Gordon Hardy served as project pilot for this phase of the program with support from Bill Hindson. Later on, Luigi Cicolani and George Meyer used the aircraft for the flight demonstration of Meyer's nonlinear inverse control concept to a full flight envelope autopilot for a powered-lift aircraft (ref. 121). The initial effort with nonlinear inverse control had been carried out on the DHC-6 to prove the concept would work in flight. These efforts were the precursor of research by Meyer and several of his colleagues in which this control scheme was applied to a variety of powered-lift vehicles. The nonlinear inverse concept eventually joined classical control design methods as a contending approach for control augmentation design in the U.S. industry.

 

[52]

Figure 109. Crows Landing Naval Auxiliary Landing Field and flight research facility, Crows Landing, Calif.

Figure 109. Crows Landing Naval Auxiliary Landing Field and flight research facility, Crows Landing, Calif.

 

Figure 110. Boeing Quiet Short Haul Research Aircraft (QRSA).

Figure 110. Boeing Quiet Short Haul Research Aircraft (QRSA).

 

It is appropriate to note that an important contribution to the success of these flight research programs came from the development of the Crows Landing remote test facility (fig. 109). Ames had used this airfield, long a U.S. Navy auxiliary landing field, for several tests over the years, most notably for the carrier approach speed and steep descent experiments cited earlier. However, the addition of a precision tracking radar and laser system, an experimental microwave landing system, and a digital data acquisition and processing system proved to be crucial to the successful accomplishment of these STOL research projects, as well as those for V/STOL and rotorcraft and occasional other civil and military experiments. The leadership of Henry Lessing, along with key contributions by Michio Aoyagi, Michael Bondi, and the NASA and contractor team of the Avionics Research Branch, in the development and operation of this facility are to be commended.

The Quiet Short-Haul Research Aircraft (QSRA) was the last of the STOL transport designs to be carried to flight evaluations by the Ames project office (fig. 110). A major objective of this development was to achieve STOL performance at the lowest noise levels possible. Wally Deckert, Curt Holzhauser, David Hickey, and Anthony Cook were instrumental in defining the program and in having it approved. 36 This aircraft used upper surface blowing (USB) and attained short-field takeoff and landing performance that ultimately exceeded that of all the competing designs. Modified by Boeing from a deHavilland C-8A Buffalo aircraft, the QSRA featured four jet engines whose exhaust was directed over the upper surface of the wing and curved flaps. Through the Coanda effect, a portion of the propulsive force was deflected into propulsive lift while lift was further augmented by increased circulation associated with the high-velocity exhaust air flowing over the wing. Once again, this design was thoroughly developed during tests in the 40- by 80-foot wind tunnel and the Flight Simulator for Advanced Aircraft.

The first flight took place in mid-1978. John Cochrane led the project and, along with his team (shown in fig. 111 next to the original C-8A), completed the proof-of-concept phase ahead of schedule and under budget. Jim Martin was the project pilot. Dennis Riddle assumed responsibility for the first phase of the flight research program during which he, Victor Stevens, and Michael Shovlin served as principal investigators. During the initial performance and stability and control test phase, the aircraft achieved stable flight at lift levels three times those generated on conventional aircraft, although the levels of lift obtained were somewhat less than those achieved in the wind tunnel tests (ref. 122).

Noise levels of 90 EPNdB (equivalent perceived noise) at a sideline of 500 feet were obtained, the lowest achieved for any jet STOL transport design. The aircraft's noise footprint was substantially smaller than that of a comparable conventional jet transport. The QSRA further demonstrated its STOL performance by operating aboard the aircraft carrier U.S.S. Kitty Hawk without a need for catapult launch or landing arresting gear (ref. 123). A series of reduced-thrust takeoffs was performed to....

 

[53]

Figure 111. QRSA project team. From left to right: John Cochrane, Robert Price, Howard Turner, Mike Shovlin, Dennis Ridlin, Al Boissevain, Dennis Brown, Patty Beck, John Weyers, Bob McCracken, Peter Patterakis, Jack Ratcliff, Al Kass, Bob Innis, Tom Twiggs (Boeing).

Figure 111. QRSA project team. From left to right: John Cochrane, Robert Price, Howard Turner, Mike Shovlin, Dennis Ridlin, Al Boissevain, Dennis Brown, Patty Beck, John Weyers, Bob McCracken, Peter Patterakis, Jack Ratcliff, Al Kass, Bob Innis, Tom Twiggs (Boeing).

 

....demonstrate the applicability of this high-lift USB technology to future powered-lift transport aircraft with more conventional thrust-to-weight ratios. Results of those tests showed substantial increases in payload or reductions in field length at the lower thrust-to-weight ratio compared to current wing/flap designs (ref. 124). Stability and control characteristics extracted in flight were analyzed and documented by Jack Stephenson in references 125 and 126. In the interest of technology transfer to potential users, an extensive flight demonstration program was carried out to introduce U.S. military and civilian pilots and operators to high-performance, quiet STOL operations with the aircraft. Later, as part of a technical exchange program with the Japanese National Aerospace Laboratory, Japanese pilots had the opportunity to fly the QSRA, and Jim Martin and Gordon Hardy in turn flew the new Japanese STOL transport, the ASKA, a four-engine, upper-surface-blown flap design.

The QSRA was later equipped with a digital, fly-by-wire control system and head-up and head-down electronic displays that used the flightpath-centered pursuit-tracking idea pioneered earlier by Dick Bray. George Meyer's nonlinear inverse control method [54] was employed in the design of the powered-lift controls. Del Watson led the system development effort. Then the aircraft was flown in a program to evaluate integrated flightpath/airspeed controls and displays for making precision instrument approaches and landings; Gordon Hardy was the project pilot. Jack Franklin, Charlie Hynes, and Del Watson led the research team (fig. 112) through several experiments. Flying instrument approaches, the pilots were able to achieve precise control to the desired approach path and assessed the flightpath and speed command controls and HUD to produce fully satisfactory flying qualities (refs. 127 and 128). Further experiments included instrument approaches to touchdown, flown using the HUD with modifications to the control system to compensate for ground effect. These tests produced touchdown accuracies comparable to those for non-flared carrier landings (ref. 129). Influences of control augmentation and wind conditions on the precision landing capability were documented in reference 130. The Air Force developed flying qualities specifications for the C-17 transport based on the results of the earlier Ames Augmentor Wing and QSRA research flights. Pilots on the C-17 joint test team from the Air Force and McDonnell Douglas flew the QSRA in a program run by Hynes and Hardy to evaluate flightpath control augmentation and the head-up display. Results of these tests were eventually incorporated into the C-17 design. Hynes and Hardy also used their experience with display design for STOL aircraft to assist Lockheed with a display application to the MC-130E.

 

Figure 112. QRSA research team. Front row: Jim Ahlman, Bob Innis, Del Watson, Jim Lesko, Lee Mountz, Mike Herschel, Tom Kaisersatt, Jack Stephenson. Back row: Dennis Riddle, Nels Watz, Jack Franklin, Gordon Hardy, Bob Hinds, Charlie Hynes, Richard Young, Jim Martin, Joe Eppel, John White, Bob America, Hien Tran, Bill Bjorkman.

Figure 112. QRSA research team. Front row: Jim Ahlman, Bob Innis, Del Watson, Jim Lesko, Lee Mountz, Mike Herschel, Tom Kaisersatt, Jack Stephenson. Back row: Dennis Riddle, Nels Watz, Jack Franklin, Gordon Hardy, Bob Hinds, Charlie Hynes, Richard Young, Jim Martin, Joe Eppel, John White, Bob America, Hien Tran, Bill Bjorkman.

 

[55] The last research flights with the QSRA were jump-strut tests, conducted by Joseph Eppel and flown by Martin and Hardy. In these flights, the nose landing gear hydraulic system was used to initiate the nose-up rotation of the aircraft during takeoff roll, permitting a further reduction of takeoff distance. In addition to research, the QSRA demonstrated the capability of USB powered lift at the 1983 Paris International Air Show and the 1986 Expo '86/Abbotsford Air Show. The flight from Moffett Field to Paris Le Bourget and return, carried out at about 200 knots over several legs along a nearly great circle route, was an accomplishment in itself. A chronology of the QSRA program and its accomplishments has been documented by Cochrane and Riddle and their team in references 131 and 132.

As a footnote to the guidance and control research carried out on these aircraft, Sperry Flight Systems made particular use of the experience gained from flying these digital systems in state-of-the-art flight computers. Evolutions of those computers found their way on to the space shuttle trainer aircraft, the AV-8B, the DC-10 refueling system, and the MD-80. 37

V/STOL RESEARCH

As was mentioned in the Introduction, Ames became the center for V/STOL research when the NACA was absorbed into NASA. This decision was a consequence of Ames' experience with low-speed aircraft flying qualities and of the availability of the 40- by 80-foot wind tunnel for low-speed, full-scale aircraft testing. 38 The technical issues associated with V/STOL concerned the means by which an aircraft could be configured to achieve acceptable hover and cruise flight performance and be able to transition between the two flight regimes with ease. Controllability was always a concern at low speed, because conventional aerodynamic surfaces were no longer effective and the propulsion system then became the only source of control. Many different aircraft arrangements were explored in the wind tunnel and a few eventually made their way into flight. The V/STOL program also led to the development of two new flight simulators that were used extensively in conjunction with Ames V/STOL flight research. From his position as division chief, Bill Harper encouraged the development of the Six-Degree-of-Freedom hover flight simulator (fig. 113), the first large motion device at Ames. Built in the mid-1960s, it was an open cockpit arrangement that operated within an 18-foot cube. In the mid-1970s, the design of a much larger motion platform, the Vertical Motion Simulator (fig. 114), was initiated to support the Center's powered-lift and rotorcraft programs. This facility, which is still the world's largest motion simulator, combined 60 feet of vertical travel and 40 feet of either longitudinal or lateral travel with high-response rotational freedom to produce cockpit motion with the closest resemblance to flight of any ground-based facility. It has been used in the development of a number of aircraft configurations and flight control systems, and has been tightly linked to all of Ames' recent flight research programs.

 

Figure 113. Six-degree-of-Freedom Simulator.

Figure 113. Six-degree-of-Freedom Simulator.

 

Figure 114. Vertical Motion Simulator.

Figure 114. Vertical Motion Simulator.

 

[56]

Figure 115. Ryan VZ-3RY Vertiplane.

Figure 115. Ryan VZ-3RY Vertiplane.

 

Figure 116. Bell X-14A (VTOL experimental aircraft).

Figure 116. Bell X-14A (VTOL experimental aircraft).

 

Ames' experience with V/STOL configurations in the late 1950s came from flying the VZ-3, X-14, and XV-3, along with the VZ-2 and VZ-4, and formed the basis for early attempts to define flying qualities criteria and to gain an understanding of operational techniques for these aircraft (refs. 133 and 134). The VZ-3RY (fig. 115) used deflected propeller slipstream to augment wing lift, and a form of engine exhaust gas reaction control for low-speed pitch and yaw control. Ames added full-span slats to the wing to increase its lift. Tests were carried out in the 40- by 80-foot wind tunnel to define its performance, stability and control, and handling characteristics. With any wind, the aircraft could nearly hover out of ground effect, but it was ungainly and difficult to control in the presence of gusts. Its flying qualities and control characteristics were explored and are documented in reference 135. Howard Turner led the project and Glen Stinnett and Fred Drinkwater did most of the flying. The aircraft was lost when Stinnett ran out of nose-down control at low power and the aircraft pitched inverted and crashed into San Francisco Bay. He was able to eject and survived to continue his career in Ames flight test. The aircraft was subsequently rebuilt to complete the test program.

The first jet VTOL aircraft to be flown at Ames was the X-14, a configuration developed by Bell Aerospace for the Air Force from a Beech T-34 wing and tail. It was initially powered by two Bristol-Siddeley Viper engines exhausting through cascade thrust deflectors. Ames developed an analog variable stability system for the aircraft for use in conducting flying qualities investigations in hover. Frank Pauli was in charge of the variable stability system design, which is described in reference 136. The aircraft was also fitted with General Electric J-85 turbojet engines at that time to increase thrust margins for hover. It was then redesignated as the X-14A (fig. 116). Extensive flight testing was led by Stew Rolls to investigate a range of flying qualities in hover; those flight tests resulted in criteria for longitudinal, lateral, and directional control power, sensitivity and damping (refs. 137 and 138). Height-control requirements were developed from X-14 flight data and from simulator results by Ron Gerdes (ref. 139). Tests of lateral thrust vectoring control, as a means of achieving lateral translation without banking the aircraft, were carried out by Terrell Feistel and Emmett Fry (ref. 140). Drinkwater and Gerdes were the principal pilots throughout this program. Research with this aircraft, in conjunction with a number of related experiments on the new Six-Degree-of-Freedom hover simulator, contributed to the military flying qualities specification for V/STOL aircraft and played an important role in the control system development of the Hawker P.1127, a British V/STOL tactical fighter that was developed into the Harrier, the western world's only operational fixed-wing V/STOL strike fighter. Additionally, in 1965 the X-14 was flown by Neil Armstrong to evaluate control characteristics in vertical flight that would be representative of the Apollo lunar lander during final descent to landing on the Moon. Drinkwater's contributions in flight testing these V/STOL aircraft were recognized when he received the Octave Chanute Award in 1964.

[57] The aircraft was again modified, under the direction of Richard (Dick) Greif and Terry Gossett, to install a digital variable stability system and uprated GE J-85 engines; it then became known as the X-14B (fig. 117). Ron Gerdes then assumed sole responsibility as the project pilot. Flight and simulation experiments during that period were conducted by Lloyd Corliss and Dick Greif to establish criteria for pitch and roll attitude command concepts, which had become the control augmentation of choice for precision hover (ref. 141). During a later experiment phase in 1981, the aircraft made a hard landing as a consequence of a lateral control software design flaw that led to a pilot-induced oscillation. It was never flown again. The test team, assembled for the aircraft's twentieth anniversary in 1977, appears in figure 118.

As in the case of STOL research, Ames V/STOL expertise led to interaction with aeronautical establishments in other countries that were pursuing this technology. Contacts overseas came through the North Atlantic Treaty Organization's Advisory Group for Aeronautical Research and Development (AGARD), often as a .....

 

 

Figure 117. Bell X-14B (VTOL experimental aircraft).

Figure 117. Bell X-14B (VTOL experimental aircraft).

 

Figure 118. X-14 team. Front row: Fred Drinkwater, Jim Meeks, Lonnie Phillips, Jim Kozalski, Vic Bravo. Second row: Bill Carpenter, Sid Selan, Dick Gallant, Terry Stoeffler. Third row: Ron Gerdes, Lloyd Corliss. Fourth row: Cy Sewell, Dick Greif, Ed Vernon, Lee Jones. Fifth row: Dan Dugan, Jim Rogers, Dave Walton, Terry Feistel. Back row: Frank Pauli, Seth Anderson. Not pictured: Terry Gossett, Bob Innis, Stew Rolls, Lawson Williamson.

Figure 118. X-14 team. Front row: Fred Drinkwater, Jim Meeks, Lonnie Phillips, Jim Kozalski, Vic Bravo. Second row: Bill Carpenter, Sid Selan, Dick Gallant, Terry Stoeffler. Third row: Ron Gerdes, Lloyd Corliss. Fourth row: Cy Sewell, Dick Greif, Ed Vernon, Lee Jones. Fifth row: Dan Dugan, Jim Rogers, Dave Walton, Terry Feistel. Back row: Frank Pauli, Seth Anderson. Not pictured: Terry Gossett, Bob Innis, Stew Rolls, Lawson Williamson.

 

[58]

Figure 119. Hawker P. 1127 (U.K. experimental V/STOL fighter).

Figure 119. Hawker P. 1127 (U.K. experimental V/STOL fighter).

 

Figure 120. Dornier DO-31 (German experimental VTOL transport).

Figure 120. Dornier DO-31 (German experimental VTOL transport).

 

Figure 121. Bell XV-3 (experimental tilt rotor).

Figure 121. Bell XV-3 (experimental tilt rotor).

 

....consequence of Seth Anderson's membership on the V/STOL panel. Thus, Ames became involved in flight research and evaluations with two noteworthy jet-lift developments in England and Germany, the P.1127 and the Dornier DO-31. Before the first flight of the P.1127 in England, the Hawker test pilots, Bill Bedford and Hugh Merewether, came to Ames to fly the X-14 in order to acquaint themselves with handling a jet V/STOL aircraft in hover. The two went away with an appreciation of the skill required to hover an unstabilized vehicle and of the control sensitivities necessary to do so. After the P.1127 program was under way, Fred Drinkwater had an opportunity to fly that aircraft to explore its flying qualities in transition and hover (fig. 119). The DO-31 program was established by Woody Cook, Paul Yaggy from the Army organization at Ames, and Jack Brewer from NASA Headquarters. It provided for simulation evaluations of the aircraft at Ames, and flight tests by a NASA Ames and Langley team at the Dornier facility outside of Munich. Curt Holzhauser and Bob Innis were assigned as the Ames representatives to evaluate this jet VTOL transport.39 The aircraft had a mixed-propulsion arrangement, including eight wing-tip mounted lift engines, and two wing-pod-mounted lift-cruise engines whose thrust could be deflected for transition and hover (fig. 120). The flight program was aimed at acquiring experience with this class of V/STOL aircraft to prepare for their then-anticipated development for commercial service. Flight tests generated data on the performance, flying qualities, and operating characteristics of the DO-31 in transition and during approach and vertical landing, including simulated instrument flight. The aircraft exhibited a broad transition performance envelope and good attitude-control characteristics with the attitude-command augmentation system. A primary deficiency concerned the multiplicity of controls the pilot was required to manipulate for flightpath and airspeed control during the deceleration to hover, particularly under instrument meteorological conditions (ref. 142).

One concept among many envisioned by the Army in its efforts to combine the hover performance of the helicopter with the cruise flight capability of propeller-driven aircraft was the tilt rotor. The tilt-rotor configuration uses large-diameter rotors mounted on wing-tip nacelles to hover with a significant payload. For cruise flight, the rotors tilt forward so that they operate as propellers to generate the thrust necessary for high speeds. The first successful tilt-rotor aircraft, the XV-3 (fig. 121), was produced by Bell Helicopter for the Air Force and Army and went through extensive development testing in the 40- by 80-foot wind tunnel before being flown by the Air Force at Edwards Air Force Base and subsequently at Ames. The Air Force tests were led by Wally Deckert, who, prior to joining Ames, was a member of the Air Force team.40 These tests, along with an earlier series at Bell, identified a rotor/nacelle/wing whirl mode instability that limited the flight envelope to 130 knots, severely restricting the aircraft's desired performance envelope. When the aircraft arrived at Ames, Hervey Quigley carried out the research and Don Heinle and Fred Drinkwater conducted much of the test flying. In the Ames tests, flapping of the teetering rotors during maneuvers introduced moments that reduced damping of the longitudinal ....

 

[59]

Figure 122. Bell XV-15 Tilt Rotor Research Aircraft.

Figure 122. Bell XV-15 Tilt Rotor Research Aircraft.

 

....and lateral-directional oscillations to near zero at speeds approaching 140 knots (ref. 143). Despite these problems and despite being under-powered and limited in payload, the XV-3 proved the capability of the tilt rotor to perform in-flight conversions between the helicopter and the airplane modes. Analytical studies and test data showed that the XV-3 design had a substantial transition flight envelope. However, the rotor dynamics and flight control issues needed to be resolved for the promising attributes of the tilt-rotor concept to be achieved. These problems were attacked by Bell through extensive analytical studies and scale model experiments leading to another round of 40- by 80-foot wind tunnel tests. Results produced an understanding of the physics of rotor-pylon dynamics and validated methods for assuring stability. 41

The demonstration of fundamental tilt-rotor capabilities with the XV-3 flight tests resulted in the formation of a NASA/Army joint project at Ames to further develop tilt-rotor technology through contracted and in-house analytical and experimental efforts. This work culminated in the most significant demonstrator aircraft program that Ames has pursued, the design and construction of two XV-15 Tilt Rotor Research Aircraft (fig. 122). The XV-15 was the first proof-of-concept aircraft built as an entirely new airframe to Ames' specifications. Leadership during the program definition came from Wally Deckert, who had moved to Ames by then, along with Mark Kelly and Demo Giulianetti, and from Paul Yaggy, Dean Borgman, and Kipling (Kip) Edenborough of the Army Laboratory at Ames. 42 Again, Bell Helicopter produced the flight vehicle. Once the program was under way, Dave Few served as the project manager followed by Army LTC James Brown and later by John Magee.

The aeronautical facilities at Ames played an important part in the design and test of these aircraft, including wheel-pod drag tests in the 7- by 10-foot wind tunnel, rotor performance and dynamics tests in the 40- by 80-foot wind tunnel, and a number of control systems development piloted simulations in the Flight Simulator for Advanced Aircraft. Prior to flight envelope expansion, the first XV-15 (NASA 702) was tested in the 40- by 80-foot wind tunnel in mid-1978 for a preliminary evaluation of the aircraft's aerodynamic and aeroelastic characteristics.

At the completion of envelope expansion flight tests at the Dryden Flight Research Center by the Ames project team, the second aircraft (NASA 703) was delivered to Ames in mid-1981. It became the subject of a series of technology development activities over the next two decades. Laurel Schroers led the flight research program, and he, Gary Churchill, Marty Maisel, and Jim Weiberg served as principal investigators. Daniel (Dan) Dugan, Ron Gerdes, George Tucker, LTC Grady Wilson, and LTC Rick Simmons were program pilots at various stages. The project team is pictured in figure 123. The flight activity included flying qualities and stability and control evaluations, control law development, side-stick controller tests, performance evaluations in all flight modes, acoustics tests, flow surveys, and documentation of its loads, structural dynamics, and aeroelastic stability characteristics (refs. 144-146). [60] Speeds in cruise flight exceeding 300 knots were achieved and these tests showed that the wing-pylon whirl-mode instability had been eliminated within the flight envelope (ref. 147). Comparisons of wind tunnel and flight results are presented in reference 148. A large digital database from the program was maintained on Ames' computer facilities and made available on-line for use by U.S. industry and the military services. Advanced Technology Blades, developed by Boeing under the leadership of Marty Maisel, were flown on the aircraft to advance the technology for rotor-blade design.

The aircraft's large transition envelope and good flying qualities were found to make it easy for pilots to operate in any flight regime from cruise to hover. Operational demonstrations were performed for over 100 military and industry pilots, and included nap-of-the-Earth flight, air-to-air combat, aerial refueling, and launch and recovery aboard an aircraft carrier. The aircraft also performed flight displays and was ....

 

Figure 123. XV-15 project team. From row: Mike Bondi, Dan Dugan, Shorty Schroers, Wally Deckert, Marty Maisel, Violet Lamica, Robby Robinson, Demo Giulianetti. Back row: Jerry Bree, Gary Churchill, Dave Few, Jerry Barrack, Kip Edenborough, Jim Lane, Mike Carness, Dave Chappel, Duane Allen. Not pictured: Woody Cook, Jim Weiberg, Dean Borgman, Jim Brown, John Hemiup, Al Gahler, Ron Gerdes, Cliff McKiethan, Bill Snyder, Rick Simmons.

Figure 123. XV-15 project team. From row: Mike Bondi, Dan Dugan, Shorty Schroers, Wally Deckert, Marty Maisel, Violet Lamica, Robby Robinson, Demo Giulianetti. Back row: Jerry Bree, Gary Churchill, Dave Few, Jerry Barrack, Kip Edenborough, Jim Lane, Mike Carness, Dave Chappel, Duane Allen. Not pictured: Woody Cook, Jim Weiberg, Dean Borgman, Jim Brown, John Hemiup, Al Gahler, Ron Gerdes, Cliff McKiethan, Bill Snyder, Rick Simmons.

 

[61]

Figure 124. Ryan XV-5B (<<fan-in-wing>> VTOL research aircraft)

Figure 124. Ryan XV-5B ("fan-in-wing" VTOL research aircraft)

 

....exhibited at the Paris Air Show in 1981. In recognition of the significant contributions of the XV-15 program, the project team received the American Helicopter Society's Grover E. Bell award in 1980. The validation of tilt-rotor analytical methods resulting from the XV-15 flight program provided sufficient confidence in the technology for the initiation of the JVX program, which led to the Bell-Boeing V-22 Osprey program by the U.S. Marines. The Ames flight program was terminated following the Advanced Technology Blade Project when, during subsequent acoustic tests, the aircraft was subjected to severe vibratory loads in conjunction with a blade-root cuff failure. NASA 703 was bailed to Bell to continue tilt-rotor technology development and demonstration flying. In addition, it provided direct support to the NASA Short Haul Civil Tilt Rotor Project at Ames. The Bell model 609 civil tilt rotor, designed to carry six to nine passengers, directly evolved from the 15,000-pound XV-15.

Lift fans were another powered-lift generating device that received thorough scrutiny by V/STOL configuration developers and by Ames aerodynamicists in the 40- by 80-foot wind tunnel. Tests in and out of ground effect of various wing and inlet configurations, exit-vane designs, nose fans, and control devices were carried out. David Hickey led these investigations at Ames. A flight vehicle came out of this work in the form of the Army-sponsored Ryan XV-5A, which used two J-85 engines either for cruise thrust or, with its exhaust flow diverted, to drive tip turbines on two wing-mounted lift fans and a nose-mounted pitch fan. 43 Movable vanes in the exit plane of the wing fans could either deflect or spoil fan thrust. Army flight tests in the mid-1960s were sufficiently encouraging, despite a marginal transition corridor and lack of short takeoff capability, that the XV-5A was rebuilt following a fatal crash.44 Research at Ames began after the reconstruction of the damaged airframe into the XV-5B (fig. 124). The program included aerodynamic, acoustics, and flying qualities evaluations of the lift-fan configuration and an investigation of the transition-to-hover using different configurations and control techniques. Correlation of the flight-measured aerodynamics and acoustics characteristics with the earlier wind tunnel test results were reported in reference 149. Flightpath control procedures were complex, and it was difficult to find a compromise control procedure for flying a precision approach (refs. 150 and 151). Charlie Hynes was the technical leader of these flight tests, which were flown extensively by Ron Gerdes.

The last of the V/STOL research aircraft flown at Ames was the YAV-8B Harrier. It was lent to Ames by the U.S. Marines in 1984 so that Ames could carry out a program of advanced controls and displays research that the Marines anticipated would be applied to the next generation of V/STOL fighter aircraft. The flight research effort was based on results of an extensive program carried out by Vern Merrick on the Vertical Motion Simulator to screen and develop promising control and display concepts. This research followed from that conducted earlier on the X-14 and in simulation experiments conducted by Lloyd Corliss on translational rate command systems. It was motivated by the desire of the Navy and Marines to operate aboard assault carriers and even destroyers in adverse weather and sea conditions.

 

[62]

Figure 125. McDonnell Douglas YAV-8B V/STOL Systems Research Aircraft (VSRA).

Figure 125. McDonnell Douglas YAV-8B V/STOL Systems Research Aircraft (VSRA).

 

The aircraft, the remaining prototype for the AV-8B, incorporated the AV-8B wing, a modified engine inlet and cold exhaust nozzles, and under-fuselage lift-improvement devices in an otherwise stock AV-8A fuselage and empennage. The aircraft was powered by a single Rolls-Royce Pegasus turbofan engine. It was modified into the V/STOL Systems Research Aircraft (VSRA, fig. 125) with the installation of digital fly-by-wire controls for pitch, roll, yaw, thrust magnitude and thrust deflection, and programmable electronic head-up displays. Del Watson and John D. Foster led the team that developed this highly complex system, with the frequent consultation of Merrick. Charlie Hynes and Ernesto (Ernie) Moralez carried out the software development, K. C. Shih specified the servo requirements, and Nicholas (Nick) Rediess completed the hardware implementation. This system development and aircraft modification was performed almost entirely by Watson's team, which did the design, system integration, and installation. Alan Page served as the aircraft manager and as the contact with the Marines and Navy on all aspects of Harrier operation and maintenance. Foster provides background for the program and an overview of the system in reference 152.

An extensive flight program was then carried out on the VSRA through transition-to-hover and vertical landing to evaluate the candidate control schemes. These experiments identified the flying qualities trade-offs for the range of control augmentation concepts, and demonstrated that fully satisfactory flying qualities could be achieved with decoupled flightpath and longitudinal command controls during a continuously decelerating approach to hover. Further, a three-axis translational rate command system proved satisfactory for precision hover and vertical landing. In addition, the control authority used by each of the designs was documented for the designers' use. Jack Franklin led this phase of the research and reported the results in reference 153. Advanced guidance and navigation displays based on the flightpath-centered pursuit-tracking idea pioneered by Dick Bray were also evaluated on the aircraft. They were found to offer excellent guidance for a complex approach path and to give the pilot the ability to achieve precise hover positioning for the vertical landing (ref. 154). Daniel Dorr, Ernie Moralez, and Vern Merrick were responsible for this work. Ron Gerdes, Michael Stortz, and Gordon Hardy served as project pilots over the course of the research program. The project team is shown in figure 126. Outside pilot participation came from the U.S. Marines, the U.K. Royal Air Force, McDonnell Douglas, and Rolls-Royce.

Results of the flight tests, in combination with simulation experiments on the Vertical Motion Simulator, were used by Franklin to develop flying qualities criteria and control system and display designs for future short takeoff and vertical landing (STOVL) fighter aircraft as part of the Joint Strike Fighter program. The displays are also being installed in the AV-8B Harrier to improve precision and reduce the pilot's workload during recovery aboard ship at night. Flight tests were also conducted with the basic YAV-8B to establish reaction control bleed flow in low-speed flight to measure jet-induced ground effects, and to conduct infrared measurements of hot gas....

 

[63]

Figure 126. VSRA team. Front row: Dave walton, Seth Kurasaki, Bill Laurie, Jim Ahlman, Nels Watz, Del Watson, Terry Stoeffler, Linda Blyskal, Ed Hess, Manny Irrizarry, Mike Stortz, Bruce Gallmeyer. Second row: Dave Nishikawa, Stan Uyeda, Trudy Schlaich, Tom Kaiserstatt, John Foster, Nick Rediess, Kent Shiffer, Paul Borchers, Mike Casey, Sterling Smith, Charlie Hynes, Vern Merrick, Jack Franklin. Back row: Thad Frazier, Eric Weirshauser, Steve Timmons, Brian Hookland, Joe Paz, Ken Christensen, Jack Trapp, Bill Bjorkman, Ernie Moralez, Joe Konecni.

Figure 126. VSRA team. Front row: Dave walton, Seth Kurasaki, Bill Laurie, Jim Ahlman, Nels Watz, Del Watson, Terry Stoeffler, Linda Blyskal, Ed Hess, Manny Irrizarry, Mike Stortz, Bruce Gallmeyer. Second row: Dave Nishikawa, Stan Uyeda, Trudy Schlaich, Tom Kaiserstatt, John Foster, Nick Rediess, Kent Shiffer, Paul Borchers, Mike Casey, Sterling Smith, Charlie Hynes, Vern Merrick, Jack Franklin. Back row: Thad Frazier, Eric Weirshauser, Steve Timmons, Brian Hookland, Joe Paz, Ken Christensen, Jack Trapp, Bill Bjorkman, Ernie Moralez, Joe Konecni.

 

.....flow fields near the ground for correlation with computational fluid dynamics predictions. The bleed-flow tests provided a detailed look at the attitude-control power used by the pilot during maneuvers in all the phases of jet-borne flight. Results of some of these efforts are presented in references 155-157. Flight research was completed with this aircraft in late 1997.

 

[64]

Figure 127. Boeing X-36 (tailless, unmanned research vehicle).

Figure 127. Boeing X-36 (tailless, unmanned research vehicle).

 

The last of Ames' project aircraft was the X-36, an unmanned, tailless, scale model of an advanced, highly agile, fighter configuration. Even though it is not a V/STOL aircraft, it is included here to complete the picture of the efforts of the Ames aircraft project office. The objective of the X-36 program was to demonstrate that a tailless aircraft could achieve the maneuverability and agility of current-class fighters at angles of attack up to stall without the directional stabilization and control power provided by vertical tails. 45 The aircraft, at 28 percent scale, was developed for Ames by Boeing's Phantom Works. As can be seen in figure 127, it is a wing-canard configuration without vertical stabilizers. It is 18 feet long with a 10-foot wing span, weighs 1245 pounds, and is powered by a Williams Research F112 turbofan engine that produces 700 pounds of thrust and includes thrust-vectoring control. Under normal operation, the aircraft was flown remotely by a pilot sitting in a ground station using a head-up display. It could also be flown through an autopilot and was also capable of autonomous operation. Flight tests were carried out at the Dryden Flight Research Center. The aircraft was flown to angles of attack up to 40 degrees, and it demonstrated excellent stability and maneuverability up to those conditions. Rodney (Rod) Bailey was the program manager, and Mark Sumich led the project team. The NASA and Boeing team won the American Institute of Aeronautics and Astronautics Aerospace Design Engineering Award in recognition of the program's contributions.

Ames flight operations personnel as they appeared in 1984 can be seen in figure 128.

 

[65]

Figure 128. Flight operations personnel circa 1984. Front row: Wally Stahl, Ron Gerdes, Pat Morris, Dick Gallant Warren Hall, Glen Stinnett, Frank Kosik. Second row: Jack McLaughlin, Marc Betters, Fred Drinkwater, Nancy Lowe, Kathleen Burns, Vicki Rodriguez, Nancy Bouchet. Back row: Dan Dugan, Gordon Hardy, Bob Innis, Grady Wilson, Casey Call, Tex Ritter, Jim Martin, Mike Landis, George Tucker.

Figure 128. Flight operations personnel circa 1984. Front row: Wally Stahl, Ron Gerdes, Pat Morris, Dick Gallant Warren Hall, Glen Stinnett, Frank Kosik. Second row: Jack McLaughlin, Marc Betters, Fred Drinkwater, Nancy Lowe, Kathleen Burns, Vicki Rodriguez, Nancy Bouchet. Back row: Dan Dugan, Gordon Hardy, Bob Innis, Grady Wilson, Casey Call, Tex Ritter, Jim Martin, Mike Landis, George Tucker.

 


29. Bill Harper 1998: personal communication
30. Woody Cook 1998: personal communication.
31. Brad Wick 1998: personal communication.
32. Bill Harper 1998: personal communication.
33. Woody Cook 1998: personal communication.
34. Woody Cook 1998: personal communication.
35. Del Watson 1998: personal communication.
36. Woody Cook 1998: personal communication.
37. Del Watson 1998: personal communication.
38. Bill Harper 1998: personal communication.
39. Woody Cook 1998: personal communication.
40. Woody Cook 1998: personal communication.
41. Kip Edenborough 1998: personal communication.
42. Woody Cook 1998 personal communication; Bill Snyder and Marty Maisel 1998: personal communication.
43. Woody Cook 1998: personal communication.
44. Ron Gerdes 1998: personal communication.
45. Rod Bailey and Lloyd Corliss 1998: personal communication.
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