MIKE GERZANICS / WARTON
BAE's latest Hawk advanced jet trainer may not be the final. article, but the demonstrator gained high marks in our test flight
BAE Systems' Hawk New Demonstrator Aircraft (HNDA) is the latest in a long line to bear the Hawk name. Based on the Hawk 127 variant sold to Australia as a lead-in fighter trainer, the HNDA is a work in progress, rather than a final product. The aircraft is being used to develop and test new concepts and components.
The most significant difference between the HNDA and the Royal Australian Air Force's 127 is its Adour 951 engine. The 127 has the 5,800lb-thrust (25.4kN) Adour 871. The 6,500lb-thrust Adour 951, with full-authority digital engine control (FADEC), is under development for the South African Air Force Hawk. The HNDA is powered by a hybrid version incorporating the 951's FADEC, but not its single-crystal turbine blades, and with a thrust output identical to the 871's.
Over its 30-year life the Hawk has undergone several changes. While the HNDA may look like the original Royal Air Force Hawk T1, under the skin it is almost a totally new aircraft. The wing, vertical and horizontal tail and fuselage have been strengthened to improve fatigue life. Engine thrust has been increased from a baseline 5,200lb, while time between overhauls has improved from 1,200h to 4,000h.
The cockpit changes are the most striking. Aside from the locations of the throttle and stick, there is little else in common between the earliest and latest Hawks. The HNDA has a head-up display (HUD) and three multifunction displays (MFDs), quite a change from the original's analogue gauges.
BAE is proposing a 128 version of the Hawk for the advanced jet trainer component of the Royal Air Force's Military Flight Training System (MFTS) programme, and gave Flight International the opportunity to sample what may lie in store for future student pilots with a flight in its demonstrator aircraft.
During the pre-flight inspection, Paul Hopkins, chief test pilot, combat and training aircraft, pointed out some of the features. The extended nose can house a forward-looking infrared sensor and laser designator, as well as other mission avionics. The wing incorporates a slight fixed leading-edge droop to improve turn performance in the Mach 0.4-0.7 speed range.
While the aircraft would be clean for our flight, it is capable of carrying external stores on a centreline and four underwing pylons, as well as wingtip missile rails. Fuel tanks can be carried on the centreline and two inboard wing pylons, increasing unrefuelled range. Beneath the vertical fin is a brake parachute and box to accommodate chaff and flares. There are provisions for a radar warning receiver.
Cockpit access was via an external stand, but integral boarding steps are available. The relatively wide front cockpit made strapping into the Martin Baker Mk10LH zero-zero ejection seat relatively easily. Front cockpit layout mimics that of the RAAF's Boeing F/A-18s. The forward instrument panel is dominated by three 130 x 130mm (5 x 5in) colour liquid-crystal MFDs. The dual-combiner HUD has a total field of view of 25¼.
Below the HUD is a data-entry panel, similar to the upfront controller found in later model Lockheed Martin F-16s. Secondary flight instruments are positioned between the centre MFD and the data-entry panel. As is the case with the F-16 and F/A-18, the primary instrument flight display is the HUD. Side consoles contain numerous switches for systems operation. Cockpit lighting is night-vision compatible, with goggle storage space provided on the rear of the right console.
Dual mission computers and avionics components are integrated via a 1553B databus. The 128 will incorporate an open-systems architecture to facilitate upgrades, BAE says. The rear cockpit, normally the instructor's station, closely duplicates the front, with the capability to override essential controls. The rear seat is notably higher than the front seat, giving the instructor a direct view forward. While there is no HUD in the rear cockpit, a high-mounted centre MFD acts as a repeater. Field of view from both seats is excellent.
After cockpit safety checks were completed, the jet fuel starter was initiated. This acts like an auxiliary power unit, providing power for systems and bleed air for engine start, making the HNDA fairly self-sufficient. The combined inertial navigation/ global positioning system was initialised using current GPS position. Full alignment to 1.5km (0.8nm) accuracy took 3.9min.
Pushing the engine start button caused the onboard oxygen generating system to drop off line as bleed air was routed for starter engagement. The throttle was immediately placed to "idle", with the FADEC controlling the start. Light off occurred at 24% NH (high-pressure spool speed), with idle rpm of 56% NH being reached in 36s.
After pre-taxi checks, air traffic control cleared us to taxi. Unlike first-generation Hawks, the HNDA has nosewheel steering. Hydraulically actuated, this allowed easy tracking of the taxiway centreline en route to runway 26. Flaps were set to half in preparation for take-off. Acceleration on take-off roll was brisk. The rotation speed of 120kt (220km/h) was reached 18s after brake release. Control forces were light and about half aft stick travel was required to attain a 10¼ nose-up attitude. The 6,100kg (13,440lb) aircraft (with 1,225kg of fuel) lifted off after about a 600m (2,000ft) ground roll. Gear and flap retraction caused no discernible stick-force changes as we accelerated to a climb speed of 350kt.
The initial climb to 10,000ft over the Irish Sea took about 2min, for an average climb rate of 5,000ft/min (25m/s). Once level, power was set to 84% NH to simulate a medium-altitude transit to a working area. At 330kt indicated airspeed and M0.59, fuel flow was 408kg/h (900lb/h). Slowing down to 300kt and M0.55 reduced fuel flow to 354kg/h.
Designed to enhance manoeuvrability, the combat flap system is armed by a pushbutton on the throttle. When armed, the wing flaps extend to the quarter, or 12.5¼, position below 350kt. At 330kt and maximum power, without the combat flaps extended, the HNDA was able to sustain around 3.8g. With the flaps armed, the sustained g rose to about 4.5, a marked increase in manoeuvrability. Stick forces in the pitch axis were light, increasing directly as a function of g. With a full-up Adour 951, sustained g capability will no doubt increase.
A series of half-deflection aileron rolls at 330kt gave a roll rate of around 100¼/s. Roll control forces were light, and the aircraft easily stopped at the desired bank angle. Rolls were accomplished with feet on the floor, the yaw damper preventing any discernible sideslip developing.
Next we were joined by a Hawk T1A, which acted as a photography platform. About 10min of close-formation flying followed, a skill I had not exercised in years. But during a series of 20-35¼ banked turns at speeds of 300-330kt, I was easily able to maintain the desired formation position. Control harmony was excellent, while the responsive pitch trim system relieved manoeuvring stick forces. Power response from the FADEC-controlled engine was good, easing the station-keeping task.
After completing the photo shoot, we climbed to 18,000ft to see how the HNDA behaved in the low-speed portion of its flight envelope. With 1,030kg of fuel the aircraft weighed 5,903kg as it slowed in idle power for a clean-configuration stall. Light buffet preceded the onset of moderate buffet and small pitch nodding, while the left wing dropped to 30¼ bank at the 126kt stall speed. Pitch attitude was 16¼ nose high with an angle of attack (AoA) of 15.2¼. Control in all three axes was good, even at this elevated AoA. Moving the control stick forward to break the stall effected recovery.
Stall warning
To improve turning performance, the HNDA has only a single breaker strip on the leading edge of each wing, whereas the T1A has two. Unlike the T1A, the HNDA in the landing configuration, gear down and flaps full, has no reliable aerodynamic stall warning cues. As the aircraft slowed through 115kt there was a small amount of aerodynamic buffet, the stall warning tone sounding at 113kt/9.2¼ AoA. Continuing to hold stick back pressure brought the nose up to a 20¼ pitch attitude. As the speed slowed to 100kt the aircraft briefly pitched up, then dropped to a 10¼ nose-low attitude. Recovery was immediate when the stick was moved forward of the neutral position.
After determining the HNDA had good stall warning cues, we climbed to 26,000ft for a deliberate spin. In a 20¼ nose-high, 30¼ left-bank climb, I retarded the throttle to idle at 200kt. Slowing through 145kt, I abruptly pulled full aft stick while simultaneously putting in full right (opposite) rudder. Initially the nose pitched up as the aircraft rolled over the top to the right. The aircraft settled into a 45¼ nose-low attitude, with a stabilised yaw rate of about 70¼/s.
After three complete turns, I centred the rudder and released the stick passing 21,000ft. In less than a quarter of a turn the yaw rate stopped and the aircraft was flying again in a 70¼ nose-low attitude at 17,500ft. After pulling less than 4gs, the aircraft was in level flight at 15,000ft. Should a student enter a spin while training in the Hawk, simply releasing the controls should result in an expeditious recovery.
Before descending for a low-level flight through England's Lake District, I flew two simulated bombing passes on the Hilpsford Point lighthouse. The stores management system display on the left MFD showed we had four simulated Mk82 225kg bombs. The first pass was shallow dive attack simulating the drop of a low-drag bomb. Weapons symbology in the HUD, designed to reflect that presented in Australian F/A-18s, was logical and easy to interpret.
The second pass was a 20¼ dive on an unplanned target with a low-drag bomb. After visually acquiring the target, I slewed the HUD's target box over it and designated the target with a button on the throttle. Following steering guidance in the HUD, I started a gentle pull, the bomb releasing 2.2km away. Again, specific switch actions mimicked those in the F/A-18.
The two passes showed that the HNDA is a stable bombing platform able to generate combat-representative delivery speeds and g loading for weapon escape manoeuvres. Additionally, five pylons give the HNDA the ability to employ both training and real air-to-ground ordnance. While HUD camera film analysis is a great training aide, actually feeling a bomb come off the wing and seeing it hit the target are an essential part of a fighter pilot's training.
While the threat and corresponding tactics are constantly evolving, the ability to fly at high speed and low altitude is a skill fighter pilots will continue to need. Over a low-level route, I was able to see how the HNDA performed at low altitude. Before coasting in from Morecambe Bay, I levelled the HNDA at 500ft above ground level, as displayed by the radar altimeter readout in the HUD. At a typical speed of 420kt, fuel flow was 844kg/h. Increasing to 520kt, more representative of the final run to a target, upped the fuel flow to 2,040kg/h. Raw speed matters for low-level flying training, and is an area where straight-wing aircraft like Aero Vodochody's L-159 fall short.
With over 1,270kg of internal fuel, the HNDA clearly has the ability to fly an hour-long, low-level training route at tactical speeds, and the excess power to accelerate to realistic weapon-delivery speeds. Flying at 500ft over the rolling terrain showed the HNDA to be a stable low-level training platform. Control in the pitch axis was responsive yet precise enough to accurately follow terrain contours. Roll control was equally as responsive, allowing aggressive turns at low altitudes.
The INS/GPS provided accurate steering guidance for the route in the HUD. Turning to place the heading line under the steering caret tracked the aircraft towards the next waypoint. While the avionics computed the estimated time over the next waypoint, it was only presented head-down on one of the MFDs. I would have preferred to have timing information presented in the HUD, perhaps in the form of a "fly to" airspeed caret.
Bomb target
The last point along the route was a small island in the middle of a reservoir. The weapon system was set up to drop a simulated high-drag Mk82 bomb on the island from level flight at 300ft. The target was hidden from view behind a hill on our approach heading. Only at the last moment, just before weapons release, did the target come into view. The INS/GPS steering was spot on, the target box in the HUD squarely over the island.
After overflying the target, I started a 6g idle power break turn to defeat a notional infrared missile launch. During this aggressive manoeuvre the nose tracked smoothly across the horizon as I rotated the hot exhaust plume away from the incoming missile. An aural "Bingo" sounded in my headset, indicating there was 450kg of fuel left and it was time to return to Warton.
The circuit for runway 26 was entered at 1,000ft and 350kt. A 3.5g break turn was started with the ventral airbrake extended overhead midfield. Flaps were selected to half slowing through 250kt. Abeam the approach end of the runway the gear was lowered, causing the airbrake to retract, and flaps extended to full. A power-on 140kt turn to final was flown, rolling out at 300ft. A 22kt direct right crosswind necessitated a fairly sizeable crab on final. Final approach speed was 135kt, until the power was retarded to idle for the flare.
Co-ordinated application of left rudder and right aileron allowed the aircraft to touch down wings level on centreline with the nose pointed down the runway. Once the nosewheel was lowered to the runway, half flaps were selected in preparation for a touch and go. I advanced the power to the "max" position, and rotated at 130kt. After the gear was retracted we entered a downwind for another visual circuit.
I accomplished several more touch and go patterns, with each one my level of proficiency increasing. While the HNDA has many of the same characteristics as a fighter, it is a trainer at heart requiring no special skills or techniques in the landing pattern.
One safety-enhancing feature of the HNDA is the jet fuel starter. In the unlikely event of an engine failure it can be started and used to motor the engine. With the starter maintaining relight rpm, the pilot can slow the aircraft to maximum-range glide speed, not needing to sacrifice altitude and glide range for a restart attempt.
Before the full stop landing, Hopkins demonstrated a simulated flame-out landing pattern. High key, overhead the landing runway on runway heading, was flown at 3,500ft above ground level. Reaching low key at 190kt, abeam the touchdown point on downwind, the gear was extended and flaps set to half. Flaps were set to full on final when the landing was assured. Touch down was within the first third of the runway, and provided ample room to stop had we not executed another touch and go.
Once rolled out on downwind, I took control for the full stop landing. Final approach, with 227kg of fuel, was flown at 134kt. Main gear touchdown was at 113kt. After lowering the nose gear to the runway, I applied the toe brakes and deployed the 2.64m-diameter brake parachute. Left rudder was needed to keep the aircraft from weather-vaning into the right crosswind during the 670m ground rollout. Taxiback and shutdown after a 1h 7min flight were uneventful.
The Hawk is renowned as a good flying aircraft, and I came away from my HNDA flight impressed by its excellent flying qualities and handling characteristics. The FADEC-controlled Adour 951, at 6,500lb thrust, should increase sustained-g turn performance while allowing some performance margin when aircraft weight inevitably creeps upward.
Missing avionics
While HNDA's cockpit mirrors the F/A-18's, it is representative of many fourth-generation fighters. The digital databus and future open architecture should facilitate the introduction of new systems. Where I did find the HNDA lacking was in its avionics, primarily the absence of a radar. A radar is an expensive piece of equipment, and its cost has to be balanced against the training benefit. BAE feels it can replicate most radar training scenarios using simulation or other synthetic means.
A work in progress it may be, but the HNDA clearly shows the Hawk's potential to remain an excellent advanced jet trainer for future generations of fighter pilots.
Source: Flight International
