(Des Barker – In an extract from his book, Recollections From a Test Pilot’s Logbooks, Des Barker describes the flight test clearance of the V3C on the Mirage F1).
Under the international arms embargo the South African defence industry was forced to design and develop its own weapons for the SAAF’s fighter force.
These locally developed weapons had to be extensively flight test before they could be released for service into the SAAF’s operational fighter squadrons. The weapons clearance programmes were the ‘bread and butter’ of the South African Air Force’s Test Flight and Development Centre (TFDC) during the UN embargo years in the 1970s.
A key weapon in the SAAF arsenal was the much improved V3C air to air missile developed locally by Kentron. This required extensive testing before it could be cleared for the Mirage F1.
INTRODUCTION
During the V3C missile launch envelope clearance programme on the Mirage F1AZ in August 1986, TFDC had successfully fired eleven missiles from the F1AZ. All that still remained from this particular phase of the flight test programme was the final launch at maximum Mach number.
PRE-FLIGHT
The military control and safety oversight of an aircraft is very strictly regulated and before any flight, the aircraft is required to be signed off by a number of senior technicians before the aircraft can be accepted for flight by the test pilot. This is not only because the aircraft is a State asset and that the State stands guarantor for its serviceability and insurance, but because of the complexity and the hazardous nature of some of the systems. The matrix of systems includes: ejection seats, armament, radar and avionics, engine and airframe. All of these have their own unique ground and air system checks before the pilot can accept the aircraft for flight.
With the aircraft signed off by the various technical specialists, and accepted and signed for by the test pilot, the pre-flight commences with the walk-out to the aircraft where technical specialists await the pilot. But before the normal aircraft pre-flight inspection can commence, the pilot must first check the basic safety of the aircraft; there is equipment on the fighter that can cause significant harm if incorrectly handled.
Besides the air-to-air missile, the ejection seat presents a potential ‘loaded gun’ hazard so it is imperative to check that all five of the ejection seat pins are in place and that the Armament Master is off, the gun trigger is folded and the normal and emergency oxygen, hydraulics and fuel systems are checked to confirm replenishment. Only after ticking off all the sub-system elements as safe, can the walk-around commence.
With the aircraft accelerating to 650+ KIAS/M2.0 up to an altitude of 50,000 feet for the missile launch, it is obviously imperative that all panels, flaps, slats and spoilers and canopy seals are serviceable and secure.
On a sophisticated fighter with many complex systems, besides the standard airframe checks and inspections on wheels and wings, the pilot will check the angle of attack and temperature sensor probes; check the air intake shock cones (mice), that the static and dynamic pressure vents on the balanced nose probe are unobstructed and that the air intake auxiliary doors are free to open during certain high power settings to prevent intake choking.
Climbing into the cockpit via the external ladder, the Martin Baker Mk.04 leg garters to retract the legs during ejection are fastened, seat straps, negative-g and lap straps, survival pack and shoulder harnesses are ‘tight and locked’. With the quick-release box locked, the anti-g suit plugged in and the helmet donned, the first series of cockpit checks can continue. This includes the normal and emergency oxygen system and the anti-g suit inflation system and if the pilot is satisfied that all the systems check out serviceable, the ejection seat pins are removed by the marshaller.
ENGINE START
Starting the Atar 09K50 is a relatively simple task with most of the starting cycle functions, automated; Low Pressure main cock open, switch on both right- and left-hand fuel pumps as well as the Starting Fuel Pump, which lifts the safety guard, exposing the Start pushbutton. With the fuel low pressure warning light out, simultaneously depressing the stopwatch and the starter for approximately one second, the starting sequence is initiated.
With a sharp audible whine, the starter motor accelerates the compressor and at between 300 and 600 RPM, the throttle is moved to the Idle position. The pilot’s focus now is to monitor the engine starting procedure by checking that several warning lights extinguish as the various engine and auxiliary services come on line. Importantly, the compressor Blow Off Valve warning light extinguishes timeously, fuel and oil pressure warning lights flicker and extinguish and the engine spools up to at least 2000 RPM within 15 secs. HYD 1, HYD 2 and EMG Hyd warning lights extinguish in turn while simultaneously the pilot monitors that the Jet Pipe Temperature (JPT) does not exceed 850°C. Now with both Alternators having come on line between 2600 and 2800 RPM, the engine idles at approximately 2900 RPM, allowing the pilot to continue with the after-start cabin, airframe, avionics and weapons systems checks.
Starting on the right-hand console and moving across to the left-hand console, the pilot follows a flow through for each system’s checks. First, the Air Conditioning is switched on and the temperature settings made, Identification Friend or Foe (IFF – military jargon for the Transponder) is switched on STBY and the navigation computer’s heading modes selected, A/A/ missile plunger on the weapons control panel is off, VOR/ILS on, standby artificial horizon on and uncaged, Radar Warning Receiver on, Moving Map Display on and importantly, the shock cone (mice) plunger and nosewheel steering plunger is engaged in the High Sensitivity position. Flying supersonically at Mach 2.0 on this sortie, if the ‘mice’ don’t move out at M1.27, the risk exists that a compressor stall will occur or even worse, the engine could cut. At a cost of approximately R100,000 for this sortie, nothing ‘can go wrong’ – we have to get it right first time. V/UHF radio’s on, it is now time for the final airframe checks.
Using the neumonic TAFFIOHC, Trims are set at zero for the takeoff, Airbrakes are opened and closed on command of the marshaller and the high lift devices tested; the flaps, slats and combat flaps tested through the various combinations of high lift device options. While the pilot continues with the various fuel checks, the fuel Detote (contents) and Cross Feed Cock off, the particular fuel transfer sequence for this air-to-air configuration is selected. Due to the criticality of mass distribution and aeroelastic considerations, the pilot is required to select one of two fuel transfer options – one for the air-to-ground bombing role to deal with the mass distribution of bombs and external fuel tanks hanging on the wings and fuselage weapons stations, and one for non-bomb or fuel tanks carriage roles.
The Integrated Flight Control Test (IFCT) is run while the built-in test equipment runs through the 35 different mode tests. After Auto-Pilot is selected, it runs through to mode 88, satisfying the pilot that the flight control systems are functional and will be able to operate satisfactorily out to the maximum Mach Number.
With the canopy now closed, the marshaller signals the pilot to test the elevator and aileron flight controls for full and free movement and the nosewheel steering through the rudder pedals. All the various control selections are confirmed externally by the marshaller who appears to be performing some weird double-jointed arm flailing and hand signals that to an outsider, look strange.
With the sight set, hydraulic pressures normal and ‘nothing to consider’ on the failure warning panel, final checks are carried out on the oxygen system, the ejection seat connections, particularly the maritime survival pack, and harnesses are tight and locked in the event of having to eject. Since the missile will be launched in the air-to-air missile range off the Cape west coast at Jacobs Bay, the maritime survival equipment is of critical importance. The SA Navy’s crash rescue boats stationed at nearby Langebaan are on standby in the event of an emergency requiring ejection.
Checks complete, taxi instructions received from ATC, the engine power is opened against the wheel brakes to 6000 RPM. Brakes released the aircraft is allowed to taxi forward to check the brakes which requires a sharp application on the brake pedals to enable the marshaller to confirm that the pitch dampers responded to the deceleration forces and the subsequent nose-down pitch force. The F1 is provided with both pitch and yaw dampers which are essentially an active feedback control system generated through an air data computer/gyro control of the aircraft in pitch and yaw to damp any oscillations, modifying the aircraft’s response to perturbations and preventing pilot induced oscillations – critical elements of the flight control system required for stability and control, particularly in supersonic flight.
But we’re not yet ready. ‘Last chance’ checks are done by another marshaller to verify that there are no loose panels, or fuel or oil leaks, a final salute from the marshaller is acknowledged and the aircraft taxied to the holding point of runway 02 at Langebaanweg.
TAKE-OFF AND CLIMB TO 48,000 FT
The planned heading after take-off is northwards, and the fuel is so critical that fuel cannot afford to be wasted by first completing a 180° turn if the reciprocal runway 20 was used. Fortunately, the northerly wind favours runway 02. With no time to spend on the runway, the aim is a non-standard take-off procedure by completing the pre- take-off vital actions: CHAFL during taxying and only stopping at the holding point to have the missile safety pins removed by the armourers. Then take-off is with full afterburner.
Canopy is closed and the CAB P warning light is out, Harnesses are tight and locked, Airbrakes are in and Auto Arthur, which manages the sensitivity of the control stick as a function of airspeed, is selected, Flaps and Slats are extended and all failure warning lights are extinguished as the F1 enters the runway.
Mini-afterburner (A/B) (French terminology ‘PC’ for ‘Post Combustion’) is selected for take-off, the pilot monitoring JPT and AB light-up sequence. Once a jet pipe temperature (JPT) of 750°C is reached, Max AB is selected. Several lights in the cockpit illuminate, the SRL light and then the red coloured INJ (injection) light indicating that the afterburner hot streak injector fuel is feeding fuel into the afterburner section. A steady green light replaces the red INJ light indicating that the A/B activation has been successful and it’s a ‘go’ for take-off.
With only a single 96 kg missile on the wingtip, the aircraft mass at take-off is 11,350 kgs and with the maximum afterburner producing 15,355 lbs of static thrust, the F1 in this relatively light weight configuration (thrust to weight ratio of approximately 0.62), accelerates at 10 kts/second at sea-level.
Fuel is so critical that it cannot afford to be wasted by doing a 180° turn if the reciprocal runway is used
Nosewheel steering is used via the rudder pedals to maintain centreline and after a very rapid 12 seconds acceleration, rotation at 120 KIAS allows the F1 to fly off at 150 KIAS and with the acceleration rate increasing, the undercarriage must be selected up and nearly simultaneously, the flaps must be retracted to half-flap before 225 KIAS. By 300 KIAS the flaps are fully retracted and the afterburner is cut to MIL power for the dry climb to 30,000 ft. The take-off from standstill to 300 KIAS was completed within 25 seconds and the F1 accelerated in the climb to 470 KIAS/M0.92 in a 10° pitch attitude.
We had never launched a V3C missile at that Mach number or height before but knew that to achieve the test point of maximum Mach number of at least M2.0, we would have to fly the most fuel/energy efficient profile possible. We had to have the Rutowski energy profile flown accurately. This implied that we would only carry one missile, but it could actually increase the trim drag due to the asymmetric carriage. How much? We didn’t know.
The F1AZ internal fuel load is only 4,300 litres. It may sound like lots of fuel, but for the intended flight profile, is barely sufficient. We knew that we would have to accelerate to a point in the airspace from which we could Bingo (minimum fuel state to terminate the mission) and land safely. Fuel consumption graphs indicated that the start, taxy, take-off, climb and acceleration to M2.0 would require at least 2,500 litres, leaving us with 1,800 litres, 600 of which were mandated to be the minimum fuel state to enter the landing pattern. Despite 1,200 litres contingency fuel, this was insufficient to reposition for another pass should we not achieve launch parameters at the designated launch point. To this end, ATC provided flight clearance with no restrictions and under radar control, moved all other traffic out of the flight path. No safety/chase plane was included in the plan that could hinder achievement of the Rutowski energy climb schedule. (In 1953 E.S. Rutowski published a seminal paper: Energy Approach to the General Aircraft Performance Problem.)
The profile options were a subsonic max A/B climb at 500 KIAS/M0.95 to 50,000 ft in 2 min 40 secs and then accelerate to M2.0, but a level acceleration to M2.0 at 50,000 ft from M0.95 would use significantly more fuel than using the Rutowski optimum specific excess energy climb schedule. The specific energy climb profile selected was flown at MIL power at M0.9 to 30,000 ft, and then level off, select max A/B and accelerate to 610 KIAS before entering a cruise climb at 610 KIAS/M1.8 through the Tropopause which in the late winter of August, was at 37,000 feet.
Before accelerating supersonically, the shock cone plunger was confirmed depressed and the High Lift Device switch, OFF. The last thing that any pilot would want is for the high lift devices to activate during supersonic flight – the ensuing structural chaos would be too dastardly to consider.
An engine failure at 50,000 ft. would immediately cut the cabin pressurisation
At top of climb, the F1 was overhead Van Rhynsdorp, 80 nautical miles to the north of Langebaanweg and in a very shallow left hand turn, max A/B was selected and the F1 accelerated south-westwards off the Cape west coast to 610 KIAS cruise climbing to 37,000 ft and further accelerating to M1.8, thereafter cruise climbing at M1.8 to 48,000 ft where M2.0 was achieved. Levelling off to accelerate further, the plan was obviously a one chance, single pass, there would not be fuel for a second pass – if a minimum Mach number of M2.0 was not achieved at the designated missile launch point, the sortie would be terminated.
We were unsure how Mach effects would affect the trajectory. The trajectories of all the missiles launched during the missile development testing programme cleared the aircraft safely and satisfactorily although a concern was a tendency for the missile to cut in front of the nose immediately after launch, particularly in the unknown region of M2.0+.
After launch, the acrid smell of the solid fuels from the missile motor was often ingested into the cockpit which was an indication of how close the missile cut across the nose of the F1 and that missile motor gasses were ingested by the engine.
The aero modelling and simulation tools and numerical methods available at that time were not accurate enough to provide useful trajectory predictions. The only way to validate the launch envelope was through actual flight testing. Was there a possibility of the missile cutting in sufficiently to impact the nose of the aircraft? Highly improbable, but not impossible! Was it possible for the missile exhaust plume to be ingested by the engine and the engine suffer a compressor stall – which we had encountered during an earlier missile launch? We did not know.
Although the F1 was fitted with a fuel dipper which effectively reduced fuel flow to the engine to prevent a rich mixture combustion chamber flame-out when the missile was launched, the test plan called for the fuel dipper to be left off so as to test the missile launch under ‘worst case’ conditions.
An engine failure at 50,000 ft would immediately cut the cabin pressurisation and without a pressure suit, there would not be much time to resolve the impending catastrophe which would place the pilot at major risk – but this was, and will always be, the role of the test pilot – go out there and after engineering analyses, prove the safe missile launch envelope. Of course this question passed through the test pilot’s mind and he would be in his full rights to wonder “what the hell am I doing up here?”
During the inbound run for the missile launch, engine performance was continually monitored, particularly the mice movement starting at M1.27 and the automatic activation of the engine overspeed indicated by the engine RPM suddenly increasing to 8,900 RPM on passing M1.4 (and JPT drop to 735°C). It was important for the pilot to monitor the mice moving out in synchronisation with the Machmeter, only 0.01 Mach difference between the mice Mach meter and aircraft’s Mach meter was permitted; any greater deviation would result in termination of the sortie.
With the launch area rapidly approaching and the fuel Detote winding down at four litres/second as the Atar 09k50 guzzled the fuel, the weapons checklist was completed, AIR-AIR guns selected on the throttle, the A/A MISS pushbutton on the weapons panel depressed to arm the missile firing circuit, the flight test onboard cameras selected to standby, the missile safety cover on the control column lifted to enable depressing the missile launch pushbutton on the stick and finally, the Armament Master is selected ON. All that remained was activating the onboard cameras (running at 1000 frames per second) one second before launch and then depressing the missile launch ‘pickle’, providing of course that the launch parameters have been achieved. There is no room for failure. Get it right first time – or else.
The F1 is accelerating at M0.1 every few seconds while covering the ground at up to 20 nms per minute (1,157 KTAS) by the time we reach M2.0. The cockpit walls, canopy and airframe heating from the adiabatic temperature increase due to ram pressure rise is such that by Mach 2.1, the impact temperature on the airframe would be approximately 135°C.
The F1s acceleration coincides well with the desired track and distance to go as M2.0 is reached at the northern border of the air-to-air range; there are still a few seconds to go before reaching the planned launch point.
MISSILE LAUNCH
What maximum Mach number will be achieved by launch time? As the speed reaches M2.02, the aircraft is adjacent to Langebaanweg which from 48,000 feet, appears as if the runway is directly below. Following a countdown from three seconds to the ground engineers, at 1 second, the on-board high-speed cameras are activated, and at the count of zero, the missile ‘pickle’ is depressed.
To the engineering staff on the ground at Langebaanweg watching the launch, they witness the contrail of Mirage F1AZ No. 216 against a perfectly blue sky background and at t=0, the V3C launches from the wingtip of the F1 and rapidly accelerates to an effective speed of close to M4.0.
In the cockpit, there is a moderate lateral ‘bump’ as the missile leaves the rails and the missile initially drops two or three feet before cutting in ahead of the F1, last seen heading into the Atlantic Ocean leaving behind a white plume and a few seconds later, a slight smell of missile motor exhaust gasses in the cockpit. According to engineering calculations, the missile will decelerate rapidly after rocket motor burn-out and then adopt a ballistic trajectory to impact at the southern end of the air-to-air range. In test pilot terms, “the missile launch was safe and satisfactory”.
RECOVERY AND LANDING
At 48,000 feet/M2.02, Cape Town and Table Mountain lie below the F1s nose, only three minutes away at the current speed – the last thing the pilot needs is for the supersonic shockwave to hit the city of Cape Town. The drama and pandemonium in the city would cause chaos and reputational damage to the SAAF which would surely earn the pilot a personal interview with the Chief of the Air Force. It is possible for the shockwave to sweep across the city from the north and then for certain portions of the pressure wave to reflect backwards off Table Mountain – this apparently happened many years ago.
The last thing the pilot needs is for the supersonic shockwave to hit the city of Cape Town
With the missile gone, while still at Mach numbers greater than M1.4, power reduction below MIL is prohibited and as such the throttle is reduced to mini A/B, then MIL while simultaneously applying airbrakes. The deceleration forces at 650+ KIAS are significant, the restrained pilot’s body bearing the brunt of the deceleration forces and emphasising the importance of being strapped in tightly to the ejection seat. The pitch dampers are working overtime to prevent pilot induced oscillations by damping any short period oscillations generated by pitch and yaw perturbations during and after the missile launch.
With the airbrakes extended and power reduced to MIL, the F1 decelerates rapidly to subsonic flight and a spiralling descent at 6,500RPM/M0.92/450 KIAS. Radar vectors to final approach on runway 02 at Langebaanweg relieves some of the pilot workload in managing the energy levels prior to entering the circuit.
Allowing the airspeed to decrease to below 250 KIAS, the standard jet pneumonic of BAUFF is carried out, Brake and Hydraulic pressures checked, High Lift device switch back to NORMAL and now, with the airspeed down to 200 KIAS, Airbrakes in, U/C down and locked, Flaps selected fully down. Fuel contents are down to 800 litres, sight set to approach mode, anti-skid system tested, brakes tested, nosewheel steering light out, Nose-wheel Steering plunger out, and landing light selected on.
The F1 is a delight to fly, particularly the final approach and landing and with fuel contents down to 700 litres, at a landing mass of 8,600 kgs, the aircraft is stable in the landing configuration with a good, unobstructed view of the runway. The pilot’s primary task is to fly a 10° angle of incidence approach, equivalent to approximately 150 KIAS with a Vref of 135 KIAS/ incidence of 13°. The throttle is retarded a few feet above the runway and the pitch attitude maintained as the main wheels touchdown.
The drag chute is deployed holding a nose high pitch attitude for aerodynamic braking until 120 KIAS, the nose is then lowered to the runway. The decelerating tug of the drag chute opening is always welcome on a short runway – failure of the drag chute could require a go-around followed by a drag chute out landing. The rapid deceleration enables the pilot to reduce the landing run considerably and jettison the drag chute alongside the runway where it will be collected by the ground crew.
The engine was shut down with approximately 500 litres remaining.
CONCLUSION
It’s been thirty minutes from engine start to engine shut down and we have successfully and safely demonstrated the launch envelope clearance of the V3C air-to-air missile on the Mirage F1AZ. Thanks to detailed, accurate engineering planning and flying, the V3C missile was launched at M2.02 and cleared the aircraft flow field satisfactorily. The V3C air-to-air missile was cleared for operational test and evaluation on the Mirage F1AZ and likewise for the Mirage F1CZ.
