Partners in Freedom

		Boeing T-45 Goshawk


Specifications Manufacturer Boeing Date in service January 1992 Type Trainer Crew Two Engine Rolls Royce F405-RR-401 Users U.S. Navy Dimensions Wingspan . . . . . . . . . . . .30.1 ft Length . . . . . . . . . . . . . . 39.3 ft Height . . . . . . . . . . . . . . 14.0 ft Wing area . . . . . . . . . . 180 sq ft Weight Empty . . . . . . . . . . .. . 9,394 lb Gross . . . . . . . . . . . . .13,636 lb Performance Max speed . . . . . Mach number of 1.04

		Highlights of Research by Langley for the T-45 At the request of the Navy, Langley participated in an independent assessment team review of technical progress during early development. Langley conducted exploratory research to define potential wing leading-edge modifications to cure severe low-speed wing drop on the original configuration. Tests were conducted at Langley to determine the spin and spin recovery characteristics of the aircraft and its potential utility as a spin trainer. Langley provided critical tire characterization data that dramatically improved the modeling and analysis of pilot-induced oscillations during landing. Tests were conducted in the Langley 16-Foot Transonic Tunnel to identify potential candidates for a revised engine inlet configuration. The Boeing (formerly McDonnell Douglas) T-45 Training System is the first totally integrated training system developed for and used by the U.S. Navy. It includes the T-45 Goshawk aircraft built by Boeing, advanced flight simulators, computer-assisted instructional programs, a computerized training integration system, and a contractor logistics support package. The integration of all five elements produced a superior pilot in less time and at lower cost than previous training systems. The two-seat, single-engine T-45 Goshawk is the heart of the training system. The T-45 replaces the T-2 and TA-4 aircraft formerly used for Navy advanced jet trainers. The Goshawk’s design is based on the British Aerospace Hawk land-based aircraft; however, design modifications have been made to the Goshawk that make the aircraft more suitable for carrier-based operations. The modifications include strengthened landing gear, the addition of an arresting hook, and catapult launch fittings. The latest version of the aircraft, known as the T-45C, includes a digital cockpit. Langley’s involvement in the T-45 began with an independent assessment team review of technical progress during the initial development program in 1988. Subsequent activities included spin tunnel tests, wind-tunnel research on wing leading-edge modifications, characterization of landing gear tires for improved handling characteristics during ground rollouts on landing, and wind-tunnel assessments of new engine inlet designs. Langley facilities involved in support of the T-45 Program included the 16-Foot Transonic Tunnel, the 12-Foot Low-Speed Tunnel, the 20-Foot Vertical Spin Tunnel, and the Landing Loads Facility.

		Langley Contributions to the F/A-18

Early Configuration Development		The U.S. Navy initiated the Advanced Trainer (VTX) Program in the early 1980’s to replace the existing T-2 Buckeye and TA-4 Skyhawk advanced jet trainers. Industry responses to the Navy request for proposals (RFP) included several existing and new aircraft configurations. A team from McDonnell Douglas and British Aerospace proposed both a modification of the existing British Hawk land-based configuration and a new trainer. The VTX contract was awarded to the McDonnell Douglas and British Aerospace team in November 1981. The Boeing (formerly McDonnell Douglas) T-45 Goshawk evolved from the Hawk design. Conversion of the Hawk land-based aircraft to a naval trainer with carrier capabilities involved considerable research and development. In addition to the necessary strengthening of landing gear components and the inclusion of arresting gear, development work was required in numerous areas that were critical for carrier-based operations. Some areas of concern included the handling qualities, engine response characteristics, and stall characteristics of the T-45. In 1988, following extensive preliminary flight-test evaluations by the Navy at the Patuxent River Naval Air Station in Maryland, the Navy cited several major deficiencies in the T-45. The deficiencies included high approach speed, slow engine thrust response, and longitudinal and lateral stability deficiencies. McDonnell Douglas and British Aerospace developed candidate solutions and recommended approaches to resolve these issues. In 1989 the Navy convened a blue ribbon independent assessment team to review the technical status and plans for the program. In response to a request from the Navy for Langley representation, Joseph R. Chambers served on the team.
Stall Characteristics		The stall characteristics of the initial T-45 configuration were judged to be unacceptable by the Navy on the basis of a severe wing-drop behavior at the stall and high approach speeds (aggravated by the increased weight required to strengthen the airframe for carrier operations). During the Navy’s flight evaluations, the wing drop was so severe that uncommanded roll motions often exceeded 90 deg. Langley researchers Long P. Yip and Holly M. Ross examine a T-45 model with a discontinuous leading-edge modification in the Langley 12-Foot Low-Speed Tunnel in 1989. While McDonnell Douglas and British Aerospace explored various candidate solutions to the wing-drop issue, Langley proposed a joint research project to assess the effectiveness of a Langley concept for enhanced stall characteristics. As part of research to improve stall and spin characteristics of general aviation aircraft, Langley had conceived a wing leading-edge modification that significantly improved the lateral stability and spin resistance of several general aviation research aircraft during stall-spin research flight tests. The leading-edge modification consisted of a discontinuous “snag” at about the 75-percent span location that acted similar to an aerodynamic fence and maintained attached flow on the outer wing panel to very high angles of attack (beyond stall). Although the wing leading-edge radius of the T-45 was much smaller than those of general aviation aircraft, it was hoped that the modification would also be effective for the advanced trainer. Led by Langley’s Long P. Yip, tests were conducted on a 0.15-scale T-45 model in the Langley 12-Foot Low-Speed Tunnel. The test techniques included conventional static force tests as well as single-degree-of-freedom free-to-roll tests to determine wing-drop tendencies. The results of the investigation indicated that the wing modification was effective in minimizing wing-drop tendencies for the cruise configuration; however, the modification was not effective for the landing configuration with the wing trailing-edge flaps deflected. The T-45 Program subsequently adopted a wing redesign, which incorporated wing leading-edge slats. The slats virtually eliminated the wing-drop tendency and lowered the carrier-approach speed to a more acceptable value.
Spin Characteristics		Flight-test experience with the British Hawk aircraft had indicated that the aircraft was very reluctant to spin and that attempts to intentionally spin the aircraft usually resulted in a spiral with rapidly increasing airspeed. The Hawk recovers from the high-speed spiral when controls are neutralized. Spin tests of the T-45 in the Langley 20-Foot Vertical Spin Tunnel by Langley researcher Raymond D. Whipple indicated that the Goshawk would exhibit similar characteristics. In fact, it was virtually impossible to obtain spins for the T-45 model in the normal upright attitude because, after being hand launched with prerotation into the vertical airstream, the model would immediately nose over and rapidly increase airspeed beyond the test capability of the Spin Tunnel. T-45 model undergoing test in the Langley Spin Tunnel. Full-scale flight tests of the T-45 subsequently verified the predictions of the Langley Spin Tunnel tests. During spin attempts, airspeed rapidly increased, and stabilized spins could not be obtained. As a result of this spin resistant behavior, the T-45 is not used for spin training. (The T-2 and TA-4 had been used for spin training.)
Ground Handling		In 1999, the Navy requested that Langley provide data, analysis, and recommendations to eliminate a severe pilot-induced oscillation (PIO) resulting in erratic yaw behavior of the T-45 during runway rollout in land-based landing operations. The Navy also requested assistance in determining the cause of uncontrollable aircraft yaw when tires failed. In response to the Navy requests, Langley researcher Robert H. Daugherty led a Langley effort that conducted over 160 aircraft main and nose tire tests to define cornering and braking behavior in the T-45. The Langley team conducted on-site tests at Patuxent River with a special truck apparatus in a program that included evaluations of various tire states, including normal and blown tires. The tests determined the effect of aircraft roll attitude on uncommanded tire cornering force, identified the drag behavior of failed main gear tires and the reason for lack of yaw control, and provided models of physical tire behavior for analysis. A particularly valuable output of this effort was a dramatic improvement in the modeling capability of T-45 landing operations and the inclusion of the data generated by Langley in the T-45 rollout and training simulators. After the Langley data had been incorporated in the simulator, the landing dynamics of the simulated aircraft were significantly more realistic. The T-45 Program was especially complementary in recognizing this effort as a timely, critical, and valuable NASA contribution to the program. The T-45 tire characteristics during landing rollout were studied by Langley.
Inlet Performance		Flight-test experience with the T-45 has demonstrated that the aircraft sometimes experiences undesirable propulsion system characteristics during certain maneuvers. In particular, the aircraft engine has experienced self-clearing “pop” stalls, pop surges, and occasional locked-in surges during simulated air-combat maneuvers and recovery maneuvers from aircraft (wing) stalls. As a result of concern over these characteristics, the Navy requested that Langley provide support to, and participate in, wind-tunnel tests of the engine inlet behavior of the T-45. In support of this request, a Langley, Navy, and Boeing Team conducted two separate T-45 test entries (May 1998 and July 1999) in the Langley 16-Foot Transonic Tunnel. Langley researcher E. Ann Bare led the test operations. The 0.26-scale inlet distortion model used in the tests consisted of the T-45 forebody, fuselage contour to the wing trailing edge, and wings. The model was powered with an aft-mounted ejector and included extensive instrumentation to measure steady state and dynamic pressure distortion characteristics. The scope of the test program included evaluations of minor and moderate inlet changes for the cruise and power approach configurations of the T-45. T-45 inlet performance model in the Langley 16-Foot Transonic Tunnel.