Military


T-45 Goshawk

The T-45A aircraft, the Navy version of the British Aerospace Hawk aircraft, is used for intermediate and advanced portions of the Navy pilot training program for jet carrier aviation and tactical strike missions. The latest version of the aircraft, known as the T-45C, includes a digital cockpit. The T-45 replaces the T-2 Buckeye trainer and the TA-4 trainer with an integrated training system that includes the T-45 Goshawk aircraft, operations and instrument fighter simulators, academics, and training integration system. The T-45 Goshawk replaced the TA-4J Skyhawk in the Advanced Jet Training Program and replaces the T-2 Buckeye in the Intermediate Jet Pilot Training Program. The Goshawk Training System combines academic, simulation, and flight phases into an integrated computer-based training approach that greatly improves training efficiency and safety.

The primary mission of the T-45 is to provide Navy strike flight training. The aircraft provides the capability to train student naval aviators for high performance jet aircraft and to qualify students for a standard instrument rating and initial carrier qualification. In addition, the aircraft supports training in fundamental tactical skills, emphasizing the development of habit patterns, self confidence, and judgment required for safe and efficient transition to fleet aircraft with advanced technology weapon systems.

The T-45 Training System (T-45TS) is the first totally integrated undergraduate jet pilot training system. It consists of five elements: instructional programs using computer-assisted techniques; advanced flight simulators; the T-45 aircraft; a Training Integration System (TIS); and contractor logistics support package. The training system elements build upon each other to teach pilot skills progressively and logically.

All required flight training knowledge and basic aviation skills are taught in electronic classrooms and with computer-assisted instruction using sophisticated animation techniques. These skills are then refined in high fidelity simulators where students practice T-45 cockpit procedures, and instrument and visual flight techniques. Validation of these skills then occurs rapidly and safely in the T-45A aircraft. The TIS coordinates and tracks all training activities, including the scheduling of instructors, equipment and students. It tracks students' progress and maintains their records while analyzing the training activities. Contractor logistics support is an integral part of the T45TS, with Boeing Aircraft Company providing the maintenance of all system elements (air and ground) as well as all logistic support.

The T-45A Goshawk is powered by a single Rolls-Royce/Turbomeca Adour turbofan engine, producing a sea level static thrust of 5527 pounds. The wing is low mounted and moderately swept, with full span leading edge slats and double slotted trailing edge flaps. The single vertical stabilizer and horizontal stabilator are both of swept design, with the vertical stabilizer integrating a mechanically powered rudder and control augmentation system for all speed flight. Speed brakes are mounted on the aft fuselage just forward of the stabilator. All control surfaces, with the exception of the rudder, are hydraulically powered.

Two wing pylons permit carriage and delivery of a variety of training weapons, including Mk-76 practice bombs. Five external stores stations accommodate a wide variety of weapons, including a 30mm gun pod as one of the alternates on the fuselage centerline station. The cockpit is air conditioned and pressurized, accommodating two aircrew in a tandem seating arrangement. The instructor is in a raised position behind the student, both under a large single-piece, sideway-opening canopy, providing excellent visibility. Each cockpit is fitted with the Martin-Baker Navy Aircrew Common Ejection Seat (NACES) affording safe escape from zero airspeed and zero altitude. Maximum weight for the T-45A is approximately 15,000 pounds. The aircraft is capable of achieving an airspeed of 0.85 Mach at 30,000 feet in level flight.

While construction was fairly conventional, every effort was devoted to improving the reliability and maintainability of the new trainer through appropriate selection of operating system design and components and their installation.

History

Selected as the basis for the airplane portion of the Navy's VTXTS jet training system, the British Aerospace Hawk is well established as the Royal Air Force's (RAF) principal jet trainer, and has also found a similar niche with other countries' air forces. One of several multipurpose trainer/light ground attack aircraft developed in various European countries during the seventies, it was found adaptable to the U.S. Navy's training role, including carrier operations, with a minimum of aerodynamic modification -- a tribute to the excellent characteristics of the basic design.

The Hawk's beginnings go back to the late sixties when Hawker Siddeley (one of the predecessor companies of today's British Aerospace) began design studies for a prospective new RAF jet trainer suitable for basic/advanced training and also for strike/weapon delivery mission type training. The RAF settled on its final requirements in 1970 and Hawker Siddeley's final HS-1182 design proposal was the winner of the subsequent competition. In the spring of 1972, development and a total of 176 airplanes were ordered.

The first Hawk made its initial flight on 21 August 1974, flying at that year's Farnborough show in early September. Subsequent aircraft joined the flight development program which resulted in minor modifications--enlargement of the ventral fins being one of the more obvious changes -- by the time the Hawk T.1s went into RAF training squadron service in late 1976. Assignment to the tactical weapons unit followed in 1978.

Meanwhile, one extra Hawk had been registered for company use as G-Hawk, while the Mk 50 series export Hawk found customers in various parts of the world. Finland was the first foreign purchaser, with plans for production there. Active NavAir interest in the Hawk as one candidate for possible replacement of T-2s and TA-4s in the Training Command began in 1977 as part of a general study of what could be accomplished through various alternatives, including new development as well as derivatives of the newly-developed European advanced jet trainers.

In 1978, the US Navy initiated the VTXTS Advanced Trainer program 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. With this proposal selected as the winner, another British Aerospace design has found its place in Naval Aviation alongside the already well-known Harrier.

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.

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. 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.

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. Flight tests of the T-45 subsequently verified that 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).

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.

Upgrades

The T-45C is known as Cockpit-21 because its cockpit has been reconfigured with multifunctional displays. Its head-up displays have also been upgraded. The digitally modified T-45C is a step up in technology from the analog cockpit associated with the T-45A jet trainer, first flown in 1988. This change to Cockpit-21 is more like the configurations of present tactical fighter aircraft. In contrast to the dated analog system, Cockpit-21 has two multi-function displays providing navigation, weapon delivery, aircraft performance and communications data. Not only will the T-45C upgrade enhance the Navy's ability to train future F/A-18 Hornet, AV-8B Harrier and other aircraft carrier pilots, but it will also shorten training time.

Procurement of the T-45C (digital configuration) is scheduled for 15 aircraft per year with associated ground training systems and support until 2003, for a total of 187 aircraft and 17 simulators. Eighty-two T-45As and 16 T-45Cs had been accepted by the Navy through calendar year 1998. The T-45Cs, which began delivery in December 1997, are based at NAS Meridian, Mississippi, and training in the T-45C began in August 1998. All T-45As will be retrofitted to the digital configuration starting in FY 2004. In the long run, the Navy projects savings of more than $400 million by completing the acquisition and delivery of new T-45's by the year 2002 instead of 2005.

Logistics support is provided by Contractor Logistics Support Package (CLSP) with the Boeing Company, with Boeing providing the maintenance of all system elements, as well as all other logistic support. Principal subcontractors are British Aerospace for the airframe, Rolls-Royce for the engine and Hughes Training Inc. for the simulators.

The three major deficiencies of concern to aircrew that remain from the T-45 Full Scale Development (FSD) days ('89-'94) are probably ground handling, engine surge, and environmental control system fogging and icing. Blown tires on the catapult came to light once the aircraft began flying students operationally in '94. Not surprisingly, these fall into the number one, two, three and eight most desired items to be fixed from the Operator's Advisory Group (OAG) '99 list.

T-45 students have suffered at least 16 incidents of blown tires on the catapult that have ultimately resulted in two Class A mishaps, including one fatality. Preceding an August '98 mishap, TRACOM experienced a blown tire incident roughly once every other Carrier Qualification (CQ) detachment. The T-45 project office tested a toe-bar modification (a small metal bar across the rudder pedal used as a proper position toe guide) in September '98, which has been partially responsible for significantly reducing the incidents of blown tires on the catapult. Since the toe-bar modification was installed, the T-45 experienced one more blown tire incident on the catapult. The toe-bar modification was helpful in reducing the incidents of blown tires, but due to its ergonomic shortcomings, is certainly not the long term solution.

The T-45 has been plagued with poor ground handling characteristics since its inception. Five of the ten Goshawk Class-A mishaps occurred during ground handling operations. While all of the mishaps had other complicating factors, the basic ground handling characteristics are the underlying cause that make incidents such as blown tires into a major emergency, vice the minor emergency it would be in any tactical fleet aircraft. Under normal, benign landing conditions the aircraft has a tendency to cause Pilot Induced Oscillations (PIO) on landing rollout, particularly when the jet is light. Numerous factors, identified by a joint Navy-McDonnell Douglas team formed in 1994, contribute to the undesirable characteristics.

The T-45 fleet is experiencing a growing looseness or freeplay in the stabilator due to wear in the various linkages of the longitudinal flight control system. The stabilator is free to rotate as much as 0.25o independent of commands from the pilot's longitudinal stick input. Engineers predict that with sufficiently large freeplay, the stabilator will encounter destructive flutter at high dynamic pressures within the NATOPS envelope. NAVAIR flutter engineers have however, through analysis, cleared the T-45 to fly the entire NATOPS envelope up to 0.25o of freeplay and to the limits of 350 KIAS, 0.7 IMN and 4 g's up to 0.30o freeplay. For freeplay values greater than 0.30o, the jet is not cleared to fly.

An excessive amount of water enters the Goshawk cockpit through the ECS system in the forms of liquid, fog, snow and ice. Ice chunks frequently navigate the defog ducts and impact the pilot's visor. Water also falls from the eye vents onto the consoles, potentially promoting corrosion. A multiphase program to identify the cause(s) and develop solutions began in the fall of 98. Phase I testing discovered that a pressure relief valve opened unexpectedly following a pressure build up in the water separator and coalescer sock. This phenomenon was associated with throttle transients or ECS controller changes, which resulted in a mild burst of airflow, ice and fog through the eye-vents/defog ducts, but the cause of the pressure build up was not understood. Additionally, temperature and flow oscillations were observed that appeared unrelated to any pilot activity. Phase II ground testing (June '99) identified a low frequency rumble in the ECS system that had not been seen previously. Some of the proposed solutions include; modified temperature selector to permit more precise control of the temperature, a coalescer ice screen to prevent ice from forming in the coalescer, and a modified vent demist valve to reduce the moisture in the system. These and other potential modifications will produce a long-term solution to ECS fog and ice in the T-45.

NGS (Navigation Guidance System) the Standard Heading Attitude Reference System (SAHRS) used in the T-45A as the primary attitude source has had an unacceptably high failure rate, and the vendor has ceased support for it. BAE/Marconi has developed NGS as a form, fit and function replacement.

In 1997 the project office conducted extensive tests with the baseline engine and a modified higher-bypass engine to see if the bypass ratio would improve the engine stall margin. The result was that the bypass did not improve the engine stall resistance sufficiently to go forward with production. PMA-273 continued the effort to reduce the engine's susceptibility to surges an 18 month flight test program, beginning fall 2000 that initially modified the way the Fuel Control Unit (FCU) schedules fuel to the engine, then follows up with tests of a modified engine inlet. T-45 test pilots and engineers evaluated the modifications for their efficacy at reducing engine surges and their effect on general engine handling qualities.



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