RAAF Lead-in Fighter Programme – BAe Hawk Part 2

The Hawk 100 no longer strikes the eye as a mere trainer. Its nose houses a FLIR and a laser rangefinder, and it features chaff/flare dispensers, 26 degree swept leading edge, wingtip missile rails and five underside ordnance pylons, combining to make it a competent lightweight. Indeed, the Hawk is offered in single seat, digital cockpit Hawk 200 form, a dedicated light fighter with an APG-66 radar (as on the F-16) with multirole air defence and ground attack capabilities.

The Aircraft

The Hawk 100’s sturdy wing has two degrees dihedral and carries area increasing double slotted flaps with settings up to 1/2, 3/4 or full. Combat flap (1/4 or 12.5 degrees) is selected by pressing the airbrake rocker switch. The all moving tailplane has 34 degrees sweep and 10 degrees of anhedral. An underbelly airbrake below it is automatically retracted when the wheels are extended to prevent ground contact.

The wingtip missile rails are wired for either AIM-9L or AIM-9P Sidewinder AAMs, and could be adapted to accept other AAMs. They can quickly be replaced by curved tips, and have no limitations. Although the wingtip rails required slight cropping of the outer ailerons, the launchers’ endplate effect restores both lift and roll rate, causing no noticeable difference in handling. Additionally, five underwing pylons each carry up to 515 kg, allowing the Hawk 100 to take a bigger warload over a greater distance than either the MB-339FD or the Goshawk, which only has three hardpoints and is not configured for weapons carriage.

Standard BAe figures state that two 590 litre fuel tanks on its inboard pylons will boost sortie length from around 70 minutes to an hour and three quarters, or ferry duration to 3.5 hours, for a 1,360 nm (2,520 km) range. A two hour combat air patrol is possible at over 100 nm (185 km) from base, or a 345 nm (640 km) radius of action with 1,000 kg of ordnance. The centreline hardpoint will take a 30 mm Aden cannon, a TAXAN towed target or a Vinten reconnaissance pod, and could be adapted for an Apollo ECM pod. The aircraft will lift a mix of 48 81 mm rockets, 16 100 mm rockets or up to five 270 kg cluster bombs, five 500 kg bombs, nine 250 kg bombs or 36 40 kg practice bombs. Two fixed chaff/flare dispensers behind the fin may be made detachable. Each holds 36 flares or chaff cartridges which can be fired manually or integrated with the radar warning receiver (RWR) to automatically dispense a pre-programmed decoy pattern.

The Rolls-Royce Adour Mk 871 turbofan has an increased 5,845 lb (26.2 kN) thrust to restore the earlier, lighter models’ performance. Optimised for 35°C, it retains power at high Mach and elevated outside temperatures, giving a good maximum Mach number, better takeoff performance and increased low level speed with low fuel consumption. Its high intakes help prevent FOD damage and it is reliable, with a 1,200 hour TBO. Its gas turbine starter can be run either by the onboard batteries or external power.

The simple fuel system’s fuselage bag tank and integral wing tanks hold 1,645 litres (1,300 kg). Inboard pylon drop tanks will increase this to 2,827 litres (2,234 kg). The Hawk 200’s refuelling probe might be incorporated if required, but this would require some airframe reworking.

The acrylic windscreen will withstand a 0.9 kg birdstrike at 454 kt (841 km/h), and the rear seat has an additional internal flat-plate screen inside the single canopy frame. The long one-piece canopy hinges to the right and is zig-zagged with miniature detonating cord to shatter during ejection. The crew sits on Martin Baker Mk 10LH zero/zero ejection seats.

The Cockpit

The aircraft is flown solo from the front cockpit, which has the sole controls for the pressurisation, air conditioning and some radio aids, although the rear seater can monitor and override or veto most important systems. The cockpits are compact without being cramped, the forward pilot’s view being dominated by his HUD and its data entry panel (DEP).

Takeoff for an AGM-65 Maverick and fuel tank equipped Hawk 100 demonstrator. The RAAF’s lead-in fighter requirement does not specify a ground attack capability. The Hawk’s improved cockpit and weapon control systems are properly representative of modern frontline aircraft, making it a competent ground attack, navigator and weapons system operator trainer. The INU sends navigation data to the main computer for weapons aiming and release through dual 1553 digital databuses.

British Aerospace is developing a new glass cockpit for the Hawk 100 to meet the digital cockpit requirements of the lead-in fighter program. Australian LIF aircraft would have their INUs continuously updated by GPS, while the current single CRT screen would be replaced by two or three compact, lightweight, low power colour LCD displays, while the HUD would use F/A-18 symbology.

The cartridge programmed HUD holds up to 30 waypoints and offsets along one 10 turn-point route, recording alterations, systems failures, weapons release and mark points. General Navigation, the basic mode, displays attitude, heading (true or magnetic), airspeed, Mach number, barometric or radar height, course to the next waypoint, angle of attack (AOA), vertical speed and distance to the next waypoint. G is displayed when it exceeds 2g, and a declutter button removes the last four parameters. Seventy seconds from each waypoint the HUD transitions to Close Navigation mode, overlaying a diagonal cross on the waypoint’s computed position and surrounding the central aircraft symbol with an unwinding countdown ring. The Approach Display gives flight director steering commands for an ILS.

The WAC supplies the HUD with four air-to-ground and two air-to-air attack modes: The Continuously Computed Release Point for bombing pre-planned targets; the Computed Impact Point for automatic bomb release against unplanned targets; the Continuously Computed Impact Point for rocket or gun attacks and the Depressed Sightline mode, a back-up mode, allowing manual bombing. The Continuously Computed Impact Line displays a weaving green string of pearls predicting the path and range of your cannon shells, while Air-to-Air Missile mode displays a boresight cross or scan circle showing the missile’s field of view.

The HUD will also present hostile radar signals detected by the RWR, either on the central screen or the sensor display. A miniature video camera monitors both the view ahead and the front seater’s HUD and the view ahead for the instructor’s screen, which occupies no more of the scene ahead than the front pilot’s ejector seat head-box. This image is also recorded onto cassette; an incredibly useful training aid which can extract three or four hours’ worth of learning from each 50 minute detail.

The central MPD (multipurpose display) screen of the standard Hawk 100 shows: a track-up or North-up Route Map, with all waypoints, total distance and fuel required at current flow. Map displays the present leg in greater detail. HSI gives inertial or navaid steering information to the next waypoint. ADI shows attitude and compass information. These options all display IAS, Mach, course, groundspeed, altitude and range, bearing and time to waypoint, with a wind velocity in the lower right corner. Engine and fuel information can also be summoned.

Either side of the MPD are standby instruments. On the left are the weapons control panel (WCP), chaff/flare dispenser controls and VHF/UHF radio head. The WCP selects and arms ordnance. It can be pre-programmed for a set sequence of releases prior to flight, and will automatically prevent gross asymmetry or invalid weapon selections, greatly reducing pilot workload at a critical time, and making munitions management much less prone to finger trouble. The WCP can also depict and deploy a simulated weapon load for training.

To the right is the FLIR screen and, outboard, the parking brake handle and central warning system panel (CWP) with 27 coloured lights, red flashing attention getters and audible chime and lyrebird tones. Later Hawks also have voice alerts, immediately directing the pilot’s attention to the appropriate system. A male voice has replaced its female forerunner since, although feminine tones apparently command a quicker response from some pilots, others tend to react rather less willingly to female directives.

The left console carries flap and undercarriage selectors, throttle, hydraulic and brake controls and indicators, trim position indicators, nosewheel steering, anti-skid and yaw damper switches and starting panel. The right console holds lighting, INU, VCR and other avionics controls plus the towed target controls in front.

The laser rangefinder is slewed by a throttle-top knob through a 20 degree cone from 300 to 9,900 metres, sending accurate ranges to the HUD/WAC for nav updating, HUD mark entry, bomb release and armament impact points. The FLIR has a slightly bigger field of view. Its images can be portrayed either on the sensor display or the HUD.

Flying the Hawk

Recently I sampled the Hawk’s capabilities with the patient Paul Hopkins, one of Warton’s staff test pilots, who had the courage to put me in the front seat of ZJ100, BAe’s development Hawk 100.

Engine starting was quick and simple, the Adour lighting with a whoomph within 10 seconds of moving the throttle to idle and, after briefly increasing rpm to 65% to close the bleed valve, it soon settled at 55% with a TGT of 272°C. Alignment of the INU’s laser ring gyros takes eight minutes (or less if it was fully aligned before the previous shutdown). Setup simply requires entry of present position and altitude (plus heading for fast alignment) via the DEP. Once powered, the flying controls exhibit very little friction or inertia and a low break-out force.

Releasing the parking brake and applying a puff of power got us moving. Rudder pedal steering is optional (operating through 45 degrees, with reduced gearing in the first two thirds travel) but this pre-production prototype relies on differential toe brakes. Equipped with anti-skid, these are heavier than expected, but work well, holding the aeroplane against full power provided you press hard enough. The nosewheel castors to 235 degrees and has little tendency to self-centre, so the brakes have to be used both to enter and to exit turns. The only limitation is that the sum of taxi speed and wind strength must not exceed 40 kt (75 km/h). The system seemed easier to use once we were moving relatively quickly.

Half flap is selected for takeoff on a clean aircraft, or when carrying stores in some hot-and-high circumstances, 3/4 flap is more normally used with stores at sea level. Stopping on Warton’s Runway 26, in accordance with SOPs, I slammed open the throttle to check proper operation of the engine limiters at 600°C and 97 to 104% rpm. Acceleration from idle to full power (101% rpm) took six seconds. Checking for no CWP lights, I released the brakes, holding a little into wind aileron. The Hawk’s crosswind limit is 30 kt (55 km/h) wet or dry, with or without nosewheel steering or external stores. Although I needed a teeny dab of brake to keep straight initially, the rudder was fully effective within four seconds, passing 50 kt (93 km/h).

A single rotation (up to 10 degrees when heavy) is made at Vr (in our case 128 kt / 237 km/h), achieved 18 seconds after brake release, just 1,100 metres along the runway. Our takeoff weight, (two up and with full internal fuel but no stores) was 6,120 kg so our power loading was 2.32. With a maximum power loading of 3.43 on a top weight takeoff, performance would obviously be degraded, but this Adour 871 is less prone to power loss at high density altitudes than earlier marks. At sea level, with a 30°C OAT the Hawk uses 1,820 metres of runway at maximum weight, while at 5,000 feet altitude and 30°C it needs less than 3,000 metres.

Tapping the brakes on and off before the gear came up, I reduced AOA to five degrees while Paul retracted the flaps. Neither caused any discernible trim change. Increasing speed to the normal 350 kt (650 km/h) for climb, we reached this passing 1,500 feet 50 seconds after takeoff. There was only a small trim change with the increased speed, and none noticeable with power reduction. A straight full power climb to 6,000 feet then took a little under two minutes. Climbing later from 10,000 to 20,000 feet took two further minutes, and to FL300 at 0.74 Mach three more. BAe quotes 7.5 minutes from MSL to 30,000 feet.

The Hawk’s vision is superb, perhaps the best I have ever experienced, with excellent transparencies. The tiny wings (way back aft) and the fuselage itself being the only obstructions in an otherwise unhindered panorama. The seats’ significant height differential makes the rear occupant’s view very nearly as good as from the front.

The Hawk’s +8 to -4 g-limits make this compact aircraft highly agile. Although it has only a 21 degree quarter chord sweep, the Hawk 100’s buffet band better resembles a swept wing combat aircraft’s than the RAF’s Hawk T.1s. This is because the 100’s ‘Toblerone’ leading edge breaker strips give it a very on/off buffet margin, rather more like a straight winged aircraft. Nevertheless, being unaccustomed to the technique, I found it hard to fly precisely on the ‘nibble’, even at lower speeds where the band is wider, often finding myself pulling through it into heavier buffet and killing the turn rate. Of course a good trainer demands precise and sympathetic handling to give its best.

Despite its comparatively limited power, the Hawk 100 has a 15 degree per second low level sustained turn rate, a steady 5.5g max rate turn being possible in light buffet at about 375 kt (695 km/h) and medium altitude. This is increased by half a g or so using combat flap, which is available at any speed below 350 kt (650 km/h), automatically retracting when this is exceeded. When extended, the positive g-limit remains +8, but the negative limit drops from -4 to -2.

The Hawk not only has a remarkable roll rate, but near instantaneous roll acceleration, enabling a full 360 degree roll to be initiated and completed in well under two seconds. Slow rolls require just a little forward stick while inverted, and the 30 second inverted flight limit allows really slow rolls.

For a loop I accelerated with full power to 350 kt (650 km/h) at 8,500 feet. Pulling initially to 4g, as speed decreased I held the light buffet, watching the speed drop to 130 kt (240 km/h) inverted at 13,850 feet, nearly 5,500 feet higher than entry. Reducing rpm to 90% as we started down, I felt for the light buffet, occasionally pulling through it and arresting our pitch rate. Miraculously my loop finished back at 8,500 feet, but our speed had scrubbed to 310 kt (575 km/h).

Closing the throttle and zooming to 10,000 feet, I selected speedbrake to kill the speed, inducing light buffet and a very slight pitch down. Paul warned that the Hawk 100’s higher wing loading diminished pre-stall buffet over earlier marks, but there was still good warning. With the stick well back, light buffet set in at 133 kt (246 km/h) and 14° AOA, immediately followed by controllable wandering in roll and heading. At 22° AOA and 125 kt (232 km/h), with the stick fully aft, the descent rate became increasingly rapid, quickly hitting the VSI’s 6,000 ft/min stop, while first the left wing, then the right dropped and the nose pitched down to 25° below the horizon, the HUD’s velocity vector shooting off the bottom of the display. Each wing was easily raised with aileron, and recovery was instantaneous once I released back pressure and applied full power. We lost 1,500 feet during the stall and recovery.

Full flap further masks the buffet, and an audio stall warning system operates with the gear extended, when deceleration is quicker, even with 75% rpm. The two-tone chime started sounding at 10 degrees AOA, increasing in rapidity as the nose rose. At 15 degrees the aircraft pitched down and rolled, first 20 degrees right, then 70 left as our speed dropped to 106 kt (196 km/h). Again a small pitch down and full throttle quickly got us flying again, although we still lost nearly 1,500 ft. This time the recovery was accompanied by the aural warning “Oil, Oil” because of slight negative g.

The Hawk 100 is quoted as capable of Mach 1.2, at which the Mach number is self-limiting, but it was suggested that the most I might be able to coax from it would be Mach 1.1. In the event the engine controller developed a rare flight test instrumentation problem, restricting full power. So, having staggered up to 40,000 feet and accelerated to maximum speed, and despite gently rolling inverted, pulling into a 45 degree dive, quickly rolling level, and then forcing the nose down to 55 degrees through FL300, the best I could achieve was Mach 0.99. However, having heard of lateral control quirks in the Hawk’s transonic phase, I encountered no such symptoms, just the expected pitch changes during entry and recovery.

Like most modern combat aircraft, the Hawk is inherently spin resistant and, having once been forced to autorotate, it has the good manners to recover promptly. Inverted spinning is prohibited and erect spins are limited to four turns. I am told the Hawk 100 can be a little less predictable than earlier marks, but I had no trouble either inducing or stopping one. My standard entry was made from 27,000 feet off a 45 degree banked left turn with the throttle closed. As recommended, at the onset of buffet as the speed decayed through 155 kt (287 km/h), taking two seconds, I gently applied full left rudder and pulled the stick to the aft stop.

Like a playful dolphin, the little aeroplane lazily rolled its belly to the heavens, nosed slowly earthwards and gently started rotating, only settling into a recognisable spin after a full turn. Initial rotation was slow, but gently built to around five seconds per turn in a varying 40 to 60 degree nose down attitude, the speed increasing from a 135 kt (250 km/h) minimum to 170 kt (315 km/h) as we lost around 1,000 feet per turn. Full in-spin control has to be held to keep the autorotation going, and relaxation gave immediate recovery within less than a quarter turn. Our three turn spin used 4,000 feet, and the recovery took another 3,500.

Upper air work complete, we descended to sample the nav/attack system and simulate weapons delivery, before going low level around the Lake District. Running in from the Irish Sea to Hilpsford Point lighthouse, Paul showed me how the FLIR can help identify a landmark, particularly on a hot, hazy day, when he uses it rather than the video from his rear seat because of its superior penetration.

The Hawk’s weapons system permits attacks without seeing the target, the HUD’s steering chevron indicating direct to the next point. Deviations from the planned route require but a glance at the MPD map display for re-orientation, and a couple of button pushes for a steer direct to the next target, while the laser rangefinder can be used to update the nav system on any known landmark, increasing its accuracy. Unfortunately reducing fuel limited us to 350 kt (650 km/h), at which, with 250 feet indicated on the radar altimeter, handling, turn radius and ride were all excellent. One could expect both ride and turning g to be harsher at 450 kt (835 km/h).

Returning to Warton, Paul set up the flight director. Appearing automatically when an ILS is selected, it merely requires insertion of QDM and an intermediate approach height. First holding height and heading, the director then gives a 35 degree intercept to the localiser. Rather than a civilian system’s command bars or chevron, this one uses a target dot over two unequal length horizontal lines. As the dot moves left or right, the lines move laterally in proportion to its displacement, appearing to define an ‘elastic triangle’, its sides delineated by the lines’ ends, with your aiming point at its apex. You simply centre the aircraft symbol on the dot and pin it there. Established on the glideslope a pair of short supplementary pitch lines define a three degree descent path, and the raw ILS data can be monitored on the MPD.

Passing 1000 feet on final two odd things happened. First the aural warning ‘Bingo, Bingo’ warned we were down to our last 500 kg of fuel; and secondly my fevered brow was chilled by a welcome shower of ice pellets from the over enthusiastic air conditioning vent beyond the HUD. Once visual I was able to place the diamond-shaped lateral velocity vector over the threshold to take us there. Approach speed is around 130 kt (240 km/h), the guiding parameter being 5.5 degrees AOA. At the threshold, after a brief hold-off and momentary warble from the stall warner, the Hawk settled gently to the runway with its stick against the aft stop. The wide track trailing link main undercarriage legs will absorb a high descent rate, but I found this unnecessary, easily making soft touchdowns from each of three approaches. Visual circuits proved quick and simple, thanks to the superb visibility, being the ideal way to use up the fuel. Paul finished with a demonstration short landing, streaming the braking parachute (normally only needed when still carrying munitions) to halt us in under 600 metres.

In summary the Hawk 100 is as easy to fly and operate as a single pilot entry level business jet. But, like the ideal trainer it is, it needs pilot skill, concentration and ability to extract the very best of its agility and combat potential.

The Hawk and Australia

British Aerospace has been actively marketing the Hawk to the RAAF for many years. The aircraft has been well established in RAF and overseas service for nearly two decades and it is well proven, does not have a history of fatigue problems and the Adour turbofan is reliable and relatively economical.

According to BAe, the major advantage of the Hawk for the RAAF is its greater all round capability “which enables it to be effective over a wider range of training tasks.” BAe says that the Hawk provides an environment more representative of front line aircraft and that for weapons/tactical training and ADF support roles the Hawk can fly flight profiles and speeds with external stores closely simulating front line fighters.

BAe is also likely to produce a very strong Australian Industry Involvement (AII) package, although details were not available at presstime. British Aerospace Australia would have overall management of Australian Hawk work, while BAe says agreements are in place with Australian companies for a number of work packages.