Ron Wheeldon with Guy Leitch
Flying a Hunter starts hours before actually walking out to the aircraft. This machine is a legend, but it is first of all about the highest performance machine that it is feasible for a civilian to fly. Flying it is not to be taken lightly.
It goes places quickly, between 4 and 10 miles a minute, it has a prodigious thirst, great sensitivity and, in the single seat version at least, it is cramped.
So you plan the fuel, the route and the frequencies even more carefully than you would in a normal flight because it is extremely difficult to revise them once airborne. There is no autopilot, no heads-up display, no GPS. To remain ahead of the aircraft, you need to know where you are going and retain a high level of situational awareness.
If it’s the two-seat aircraft and there’s someone going with you, you need to start preparing them well in advance.
The cockpit of a Hunter is intimidating to those who are not familiar with it, doubly so for non-pilots. It is cluttered and claustrophobic and there are ejection seats and strapping procedures to cope with. Unlike most aircraft, ex-military jets like the Hunter have an escape system which means that, if there is some catastrophic failure and the aircraft is going down, your options are greater than sneaking a cell phone goodbye or reciting your rosary – you can have an enormous kick in the backside and an excellent view of the accident. The trouble is that the seat rewards casual mishandling with death. That may sound melodramatic, but it is the simple truth.
It is absolutely essential that anyone who is going to sit in a live ejection seat understands its potential lethality in chilling detail. With the amazing reliability of the Hunter, the greatest actual threat to all involved is a casual approach to the seat. If the aircraft does go wrong, though, it is comforting to know that 93% of the 197 recorded ejections with the Martin-Baker Mk 3H seat were successful, and 96% of the 54 recorded with Mk 4H seat fitted to the two seat Hunter. In recent years, 3 out of 3 ejections using the Mk 3 seat were successful.
Walk Around
As with all aircraft, the pre-flight inspection or walk around is essential. With the Hunter the pre-flight will have started at least two hours before the first flight of the day. Tyre pressures are crucial and must be correct. The inspection starts in the cockpit. Uppermost in mind must be the seat – check that the safety pins on the ejection seat are “safe for parking” – this means that the face screen and seat pan pins are in place, and the main gun and canopy pins have been removed.
The final walk round starts at the nose, checking in the gun camera aperture that the hole for the cockpit ram air feed is clear.
Next is the nose gear front door and latches for security and freedom of movement, the creep mark on the nosewheel tyre, the condition of the tyre and that it looks about right for inflation (8.0-8.2 bar). When operating without ground crew pre-flights, I check this with a gauge.
Next is the nose gear strut where the shock extension must be a minimum of 100mm. Further aft check that the rear nose gear door is free from cracks, particularly where the struts connect. In the nose gear well the checks are that the oxygen charging cap is on and locked, that the microswitches appear to be in good condition and that the bag for the oxygen fittings is properly zipped up.
Next is the starboard intake – check that the auxiliary air blow in doors operate freely, top and bottom, that the spring tension is correct, that the intake and boundary layer duct are both free of obstructions or debris.
Further aft, check the main wheel well for security of all fittings, ground locks removed, door linkages and locks, absence of leaks and aileron accumulator pressure minimum 900 psi. The oleo is then checked for security and cleanliness and absence of leaks from the walking joints which carry the brake hydraulics down to the callipers. The tyre is checked for cracks and creep and pressure (min 13.0 bar) and the brake discs for free movement and condition of braking faces and pads.
Fuel leaks are most likely to manifest under the wings, as are hydraulic leaks, so the whole underside of the wing is checked carefully. Moving outboard, check the drop tanks for security and for sound, that they sound right for the amount of fuel alleged to be in them. Normally there is just one drop tank under each wing, the inboard “150” which holds 675 lit, but for a ferry flight the outboard “100” of 455 lit capacity will have been fitted and is also checked for security and removal of the safety pin from the jettison apparatus.
On top of the wing, the jettison unit cover is checked for security. Next is the navigation light and cover before moving back to the aileron which is checked for free and full movement and for the absence of lateral movement. Now at the back of the wing the flap is checked along its hinge line and for security of the jack fittings. The hydraulic sight glass is at the rear of the wing and is checked for the filler being wire locked and hydraulic fluid being visible just under the mesh. Although an accurate engine oil reading is not possible pre-start, you check that the oil is visible in the sump sight glass.
Moving under the aircraft, you check the oil levels in the main and auxiliary gearboxes, that the starter bay door is open and locked with the flame shield in place and that there are no oil, fuel or hydraulic leaks. There are six fuel drains, two of which should be dry, all of which are checked before buttoning up the belly panels apart from the starter door.
Moving aft it is just a general inspection for distortion or cracking and that the tailplane indicates neutral trim. Moving to the tail, the check is to see that the rudder lock has been removed, that the jet pipe is free from obstruction, that the EGT probes appear undamaged and that the jet pipe moves, also that the brake parachute doors are closed and latched fore and aft.
Half way there! Coming up the port side, check the elevator accumulator pressure gauge before approaching the rear of the wing with its flap. Flap, aileron, drop tank, navigation light and underwing checks are same as the starboard, but on the port side you check the pitot and in the port wheel well check the filler cap for security and the tank selector switch to see that it tallies with the advertised fuel configuration. Check the port intake, blow in doors and Sabrina and we’re back at the base of the ladder.
Into the Cockpit
Strapping in is quickly accomplished if you are used to it. In the single seater, it involves putting on the parachute and then the seat. You wear leg restraint garters (if you’re a western fan, you adjust them to clink together when you walk) and these are connected to the leg restraint cords – in an ejection these pull your legs back into the seat, which prevents them from flying around or getting nipped off by parts of the structure (which, apparently, hurts a bit).
The drill is to adjust the straps until they seem excessively tight, and then tighten them some more – you need to be very firmly in the seat. Once you are in and strapped, a ground crew member will remove the face screen pin while you will remove the seat pan pin and place both in the block on the cockpit coaming that holds these. The seat is now “live”.
The pre-start scan starts on the left cockpit shelf with the Low pressure valve opened, High pressure valve/throttle moved to the “on” position and cracked open about half an inch, checks that everything in the cockpit is as it should be and ends, in the two seater, with the passenger, to see that he is secure, his oxygen supply is on and working, all the pins are out of his seat, the intercom is working, and there are no visible signs of distress.
This aircraft uses AVPIN to start. This is a monofuel which blasts the starter turbine up to 45,000 rpm in 0.3 sec which spins the main turbine up to 2500 rpm for 30 seconds, more than enough for the Avon to cough into life and settle into its 2500-2750 rpm idle.
It’s a busy time in the cockpit as you monitor the rpm and JPT during the start and check the oil pressure, hydraulic pressure and generators through the process. The after-start mnemonic is TTAAFFIIOOHH – tailplane, trim, airbrake, anti-ice, flaps (set flaps 4, engage hydraulic controls during travel), fuel, inverters, instruments, oil pressure, oxygen, hydraulics (check overall and brake pressure), hatch. The last is normally left open until the holding point because otherwise the cockpit temperature, on a summers’ day, can quickly be extreme.
Taxiing is straightforward if you are used to the British system of differential braking on the main wheels with the brakes controlled by a lever on the joystick, the nosewheel being free castoring. The technique is to go from one full rudder deflection to the other so only the wheel on the side you want to brake is braked, otherwise both are braked and heat build-up is rapid.
The first check after the aircraft starts rolling is to check that the brakes are working and then, on the taxi, another abbreviated TAFFIIO and, if it’s the two seater, take the passenger through the take-off briefing again.
At the holding point the engine is run up to 4500 rpm for the control check, checking full deflection in all directions and that the hydraulic boosters remain engaged. Close the canopy, check that it locks, trim set, flaps set, fuel pressure indicators in line, anti-ice off, oil pressure good, generator lights out, hydraulic pressure min 2800psi and we are “ready”.
Lining up is straightforward allowing the aircraft to run straight a few metres to ensure the nose wheel is straight.
“Clear take-off” and the engine is accelerated to 6800 rpm against the brakes, check brakes holding, check JPT minimum 560 degrees and at between 7000 and 7200, depending on temperature, the aircraft should start to overpower the brakes. Release the brakes, full power, 7850 rpm and 670 degrees JPT, and acceleration is swift, keeping straight on the brakes until about 70 knots when the rudder becomes effective.
At 110 knots you positively lift the nosewheel and then check forward with the stick to about 7-degree AoA and, at about 145 knots she flies off the runway.
Brakes on, gear up (at full throttle the retract button is reached with the finger without taking the hand off the throttle), watching the trim change as it retracts, switching the pressurization on, then as the gear completes its travel, red lights out, select flaps up, trimming forward as they go, throttle back to max continuous 7600 rpm to save the engine and try to rein in the surging acceleration as we climb away.
The Hunter can climb to 45,000 feet within 7 minutes of takeoff, but the highest I am allowed to go is FL 195 and, typically, on a local flight, there’s a TMA to remain below. This means coming back very quickly on the power to about 6800 rpm once the aircraft is cleaned up and even leaving a notch of flap out to keep the speed down, wallowing out of the airspace. Once clear and allowed up to 250 knots, the flap can be retracted, but you have to watch the airspeed like a hawk because she is very slippery and accelerates for nothing.
The Hunter is at its best in the 400 – 480 knot range and, at FL195 at its most economical power setting (6900 rpm) in its draggiest configuration (4 drop tanks). The still air ground speed hovers around 440 knots, or 7.4 nm a minute and about 55lb/min fuel burn (that’s a mere 32.5 litres a minute).
With the powered ailerons and elevator, the controls are very light. The main problem most people have with converting to the Hunter is avoiding over controlling, but you soon get used to it. I find accurate height holding in the cruise a challenge and it has to be watched very carefully. The machine will gain or lose 1000 feet in the blink of an eye.
If you are on your way to an aerobatic “box” for an aerobatic flight with a large chunk of airspace to yourself, it is much more fun – the aircraft seems to come alive as it passes 300 knots and, in keeping with the Swiss SOP, I select the follow up tailplane “on”.
The Hunter has a species of all flying tail where the tailplane and elevator work together. The RAF procedure was to use it only at speeds in excess of Mach 0.9- it is essential for transonic flight – but the Swiss used it all the time. My compromise is to use it for aerobatics, one less thing to think about. The easiest aerobatic manoeuvre in the Hunter is the roll which requires a pitch up of about 12 degrees AoA at the lower speeds and which is accomplished smoothly and easily with little tendency to drop the nose – without outboard drop tanks.
The experience WITH outboard drops is quite spectacularly different – unlike the inboards these do have a significant effect on the performance of the aircraft – speed is restricted to M0.88 and the pilot notes restrict the aircraft to no more than one roll at a time with these fitted. I find it produces quite a serious “scoop”. At first I thought this was just me, but I take comfort from footage of the 1958 SBAC airshow at Farnborough where a Hunter with outboard tanks just about scoops into the ground!
The maximum rate of roll is at 420 knots when full aileron deflection produces a roll rate of around 420 degrees a second – exciting with a tendency to bash the helmet on the side of the canopy. Inverted flight is a breeze too, although very firm forward pressure is necessary to maintain level flight and inverted flight must not exceed 45 seconds as the fuel, when inverted, is supplied by two recuperators with limited capacity. Barrel rolls are effortless and strangely satisfying while a steep turn, with one notch of flap and full power will sustain 4G while any fixed point below remains fixed, it seems, to the wingtip.
There is no audible stall warning as such, but three distinct stages of buffet, only one of which, the first, is ordinarily encountered. This manifests as a slight tremor through the airframe – almost like a rumble strip on the road – and the cure is to release the back pressure ever so slightly. In a turn, if you are continually touching the rumble and releasing it slightly to where you know it is just a whisker away, the aircraft is generating its best rate of turn. It is also a reliable indicator in any manoeuvre that you are on the edge of the most efficient flight, but still far from provoking a departure from controlled flight – I find it exquisite, the aircraft “talking” to me through the tips of my fingers.
The third stage of buffet, by the way, which precedes a stall, is a very violent shudder that you would have to be unconscious to miss. I enjoy looping the Hunter and have been working on entering and exiting the loop at precisely the same height, speed and heading, typically starting at 12,000 feet at 350 knots and using 3G which makes for a thoroughly comfortable manoeuvre with a diameter of around 3000 feet. I fly without a G-suit (cannot get my middle aged spread into the one I was given!) which helps with our self-imposed G limit of +5. The published limit is +7.8, and – 3.5, but that, in flying an historic aircraft for fun, is unnecessary and hard on the structure, consuming fatigue life at a much accelerated pace for no good reason.
Monitoring the fuel position is important because the rates of consumption vary widely depending on height and throttle setting and the fuel in the drop tanks is not gauged (except for the large British 230 gallon tanks where the gauging is not particularly accurate), you either have fuel remaining (doll’s eyes black) or no fuel remaining (doll’s eyes white). When the drop tanks are empty, you have 2700lbs remaining, and that is gauged.
Flying in the Cape, either near Langebaan or Agulhas, I used to head for FACT when indicating 1200 a side, to allow a good margin for a diversion to Langebaanweg or Overberg. Ideally you want to be on downwind when the “bingo” lights come on at 750-800 lbs a side although, in service, that was when the recovery home was initiated.
Flying from when Thunder City operated, we regularly practice flight in “manual” and simulated forced landings, although the latter are not recommended unless an airfield is nearby. The combination of loss of engine power and manual flight, with the latter the inevitable consequence of the former, is about the most challenging thing you can do in a Hunter.
As the power controls are selected off, the sensitive stick becomes the sword in the stone – all but immovable. The rudder, which has a powerful rolling effect, remains fully effective and becomes an important control, although the others, for all their apparent immovability are still effective – one of the qualifying tests for flying a Hunter is being able to produce 3G in manual – doable, but a workout.
To simulate an engine failure, power is reduced to 5500rpm and 2 notches of flap (23 degrees) and this produces a rate of descent of 2000 fpm at the best glide speed of 210 knots. To make a successful dead stick landing you need to be 4000 feet above the selected touchdown point on downwind and fly a curved approach, dropping the undercarriage on final and the flaps only when you are sure the runway is made, without hydraulic power both actions are irreversible as they are blown down on the emergency systems. The brake accumulator holds sufficient hydraulic reserve pressure for a normal full stop landing, but one would stream the brake chute and brake in one continuous application only after the aircraft has slowed to the point of the rudder losing effectiveness.
On a normal return to the circuit, you join downwind with speed around 200 knots (having two or even four notches of flap down helps with this as engine rpm must not drop below 5500 rpm for the sake of reliable hydraulic operation and a speedy engine response if necessary).
Downwind procedure is to lower the undercarriage, check three greens and check the brake pressure with brakes on and off, no more complicated than that. Speed is monitored carefully in the base and final turns. It should be decaying slowly, so that you start final with 160 knots, selecting full flap (8 notches, 80 degrees) once established on final and try to peg the power at about 6600 rpm which should produce a stable approach at about 135-140 knots, depending on weight.
Stall, in this configuration, is at about 125 knots and some of the real exponents would fly much slower than I, but the biggest danger on the landing is exceeding 14 degrees AoA which scrapes the tail (the tail skid provides no protection and seems carefully designed to puncture the jet pipe). Carrying a few extra knots makes that virtually impossible and with 3.4 kilometres of runway to stop on, it seems a silly risk to take.
The weakest part of the Hunter design and where it truly shows its age (75 and counting) is its brakes, which went unchanged from the Mk 1, some 6 tonnes fully loaded, to the late Mks which typically land at about 8.2 tonnes. Replacing them is horribly expensive, so I, who have to pay for them, use them as little as possible. I aim for a gentle touchdown and keep the nose up as long as possible with full nose up trim for a measure of aerodynamic braking. This results in the aircraft running out of energy towards the end of the runway without using the brakes at all.
Landing at Wonderboom or Swartkop AFB, about 1.8 km, where the runway is much shorter, requires getting the weight down as much as possible, using as much tarmac as possible, landing firmly, streaming the brake ‘chute and then – critically – leaving the braking until 90 knots or below. As a Swiss squadron commander explained to me, he had seen plenty of Hunters with burnt out brakes that had then run off the runway, but none where the pilot left the brakes alone until 90 knots! Some of their “war emergency” runways were only 1000m long, which shows what can be done when the taxpayer is paying for the brakes.
After landing procedures are to retract the flaps, turn off the pressurization, turn off the power controls, retract the landing light (only Swiss Hunters had these) and crack the canopy open a bit for fresh air. If you have a passenger aboard, remind them about the dangers inherent in the “bang” seat until made safe and taxi back to the hangar.
On parking, the aircraft should be trimmed back to neutral and, in the two seater with its hydraulic canopy, the canopy opened fully while the engine is driving the hydraulics. There is an accumulator and it should open on that, but it has been known to stick. The engine is allowed to stabilize for a full minute at idle, noting the idle rpm (2500 -2750) and fuel remaining on the gauges. The engine is cut by moving the throttle back through the spring loaded high pressure gate and closing it completely, immediately turning off the electrics and caging the artificial horizons.
The next priority is refitting the pins to the ejection seat or seats to make them “safe for parking”, whereafter the unstrap can begin. The engine rundown is timed and should be a minimum of 70 seconds with a swing back of the turbine as it stops of 1-3 blades as viewed from the port intake through the guide vanes.
Once the turbine is stopped, the LP valve is shut (if you see a Hunter with a puddle of fuel near its port rear wing root, it’s a safe bet the pilot forgot!) and the oil level on the engine is checked ten minutes after shut down when the sight gauge is accurate.
The big problem after this is the grin. It’s an embarrassing aberration of the facial features which is impossible to avoid and fades only slowly, no matter what’s going on around you.
Somehow the mundane becomes strangely dim and distant for a time and there’s that vague feeling of being on a higher plane. Of joy that it happened. Joy tinged with sorrow that it has ended with the encouragement of knowing it could happen again.