Flying the Cheetah

My eyes snapped open, my heart beating wildly. I’d hardly slept. I shot a glance at the bedside table clock for the tenth time in the last hour. 0330. Okay – Time to get moving.
Einstein once said, ‘Time is nothing but an illusion.’ Now, finally I understood what he was talking about. How else could I explain being this psyched before a flight? After all – I’d logged more than 18000 hours on 85 types over the past 30 years.

Surely flying aeroplanes should’ve become mundane by now! Well the kid in me couldn’t agree. He booted his wife out of bed. Bredasdorp was a three hour drive from George – if you stuck to the speed limit. A short while later the austere beauty of the Agulhas landscape was lost to at least one of the occupants of the low flying VW Polo.

Jannie was waiting for us at the gates of TFDC’s (Test Flight Development Centre) base at AFB Overberg with the security clearances. Formalities and briefings behind us, we suited up in the gym-like locker room and strode out to our waiting steed. On the hallowed walls down the corridor to the flight-line hung portraits of previous TFDC test pilots – three of whom were now my colleagues and friends at SAA.

Jannie busied himself with the pre-flight while the ground crew strapped me in. No place for overweight pilots here. It’s a tight fit by anyone’s standards. Much over 95 kilos or 1.85 meters and they’ll need a shoehorn to get you in. A little like getting a cork back into a champagne bottle. In fact 95 kilos (excluding flying equipment) is the maximum weight for the ejection seat to do a decent job of popping you out in a hurry.

The strap-in procedure is time consuming and intricate with lanyards attached to clips on the knees, ankles and arms. These prevent you from splaying out like a spatchcock chicken and save you from certain dislocation or dismemberment should the airflow or canopy sever them during a high-speed bale-out. The G-suit is connected via a hose on your midriff to the aircraft, along with the oxygen hose to your mask and communications portals to your helmet. A five point harness holds everything tightly in place, with a quick release tab below the left knee should you feel the need to unbuckle in a hurry. Unexpectedly the Mae-West is the most uncomfortable, limiting head movement and constricting your upper body as much as the G-suit does your lower.

“Ready to close the canopy?“
“Affirm,” I replied in a nasal twang, sucking the air from the oxygen mask strapped to my face. The checklist and start sequence was faster than I expected and at 7 percent turbine speed the fuel and ignition were introduced and a light-up quickly ensued. Engine parameters were stable within the minute. As part of the after-start checklist, I unclipped the ejection seat safety pin and with a quick gesture to the ground crew confirmed the zero/zero seat was now ‘live.’ If need be, we could now dispatch ourselves from the aircraft on the rocket powered ejection seats at zero forward speed and zero height. On the older seats you needed a combination of forward speed or height to bale out safely. Even ejecting simultaneously is no longer a problem as the seats fire at different angles, averting a chance collision on the way out.

A quick punch of the throttle and she was rolling. Turns are performed with asymmetric stabs on the toe brakes. A short taxi out to runway 18 at Bredasdorp and we’re ready to go. No messing about with long-winded airliner checklists here.
This was a jet fighter. The very aircraft that decided my career path – at the magical age of six! The Mirage III. The variant we were flying today had once been the III D2Z – upgraded with the Israeli canards, new avionics and a 15300lbs thrust motor – to be renamed the Cheetah D.

I had first seen the original from my grandparent’s ancient Mercedes. It was 1966 and we had camped on the airfield perimeter in preparation for my first airshow at Waterkloof Air force base. There were rumours that the SAAF were going to demonstrate their new jet fighter. The rumours were true.

It was love at first sight. She wore burnished silver with red lightening flashes on her waist and a sharpened spear protruded her jet-black nose. Her wings and tail were raked back at an exquisite angle. She roared and crackled when she smote the sky and trailed a white drag-chute like a surrender flag when she returned to appease it. She was the most beautiful aircraft I’d ever seen. She still is.

The Mirage IIICZ.

That was the moment I decided to fly. But not just anything… I had to fly her! As we lined up on the threshold Jannie stood on the brakes while he wound up the Atar9K50 engine. Then shoving the throttle through the gate he lit the afterburner and released the brakes. Acceleration was comparable to the Lear 24. Impressive – but mild compared to what would shortly follow.

From the backseat I followed through on the controls. At 150 knots we raised the nose and she lifted into the air at 190. A quick flick of the gear lever and the aircraft was clean. Like Concorde there are no leading or trailing edge flaps on a delta wing, requiring very high takeoff and landing speeds.

Staying low the speed accelerates sharply and the first turn was back over the field at 450 knots and 300 feet before streaking south between the hills to the coastline. A quick 90 degree roll and grunt on the stick had us pointing eastwards over the ocean towards Cape Infanta. Then we lit the afterburner for the second time…! The best way to describe this acceleration is to compare it to a galloping horse that suddenly bolts! At 450 knots the ram effect into a jet engine makes it super efficient and pumping raw fuel into the afterburner produces astonishing results! Within seconds we were passing 620 knots and I saw the condensation flashes of the shock wave pulsing off the intakes outside my elbows. We were about to go supersonic at low level!

I had seen this speed in an Airbus 340. But that was with a 140 knot tailwind at 41000 feet off the coast of Bermuda. At 300 feet off the coast of Africa you know you’re moving it! Your peripheral vision is a blur!

As briefed, Jannie started a 6 G pull at Mach .95 but at that speed it’s not as quick to get to the vertical as my Pitts doing a leisurely 180 knots and I became acutely aware of the G-suit strangling my legs and midriff. Initial rate of climb was 60,000 feet/minute! (No, it’s not a typo error.)

With a thrust to weight ratio less than 1, the Cheetah gradually loses energy in the vertical but within the time it took to write this sentence, we’d rolled over and leveled off at 20,000 feet. We were now ready for a more polite assault of the sound barrier.

TFDC restrict this old bird to Mach 1.6 – though in her heyday she was capable of more than twice the speed of sound. By Mach 1.1 we’d proved the point and throttled back for some high level aeros. At that height the air is dry so there are no visible shock waves to indicate your transit through the sound barrier. No significant Mach Tuck. Nor any control reversal – as the veterans sometimes found in the early days of supersonic flight. Only the Machmeter suggesting you were now flying faster than a rifle bullet and a little aft stick to compensate for the loss of lift in the supersonic band. Very different from a Boeing 737-200 where you feel the distant rumble of the shock wave eroding the lift – then the slight nose down tuck – quickly compensated by the Mach Trimmer, when you venture a little too close to Critical Mach speed. (This is the speed where the localized airflow becomes transonic even though the airflow over most of the aircraft is still subsonic. In the 737 this speed is only Mach .76! – still well below the actual speed of sound.)

This sharp-nosed baby however was designed for swifter things. In fact, if you didn’t know where to look you’d never even realize you were supersonic! We began with loops, then a series of rolls. The numbers are impressive. With a 5 G pull – 5000 feet from the bottom of the loop to the top! 500 degrees/second roll rate! The Pitts is nowhere near that. The Sukhoi 29 comes close in roll but I’m not making a fair comparison here. They’re just numbers I’m more familiar with.
After awhile an audible tone heralded “Bingo Fuel,” and it was time to head back to the field for a couple of touch and goes from the back seat.

Circuit height is 1500’ and allowing the speed to decay below 300 knots hauls the delta wing onto the back of the drag curve. This instigates a very pronounced sink rate that’s repelled only by a copious application of thrust, which is held on all the way to the flare. (The angle and force of the thrust vector is essentially what controls for your sink rate.)

The Cheetah is very light and responsive in the rolling plane, while a tad heavy in pitching. She also has some fascinating idiosyncrasies. The canards for example, increase the initial pitch rate but also cause her to lose energy faster than the Mirage at high angles of attack (i.e. she can attain higher AoA due to the canards but the result is higher drag at these higher AoA’s) – especially if it’s sustained for any length of time. A progressive audio tone grabs your attention as the angle of attack creeps towards the high side. The canard of course prevents the wing from stalling in the conventional sense but I’m told causes a violent pitch down when its lift vector lets go in a high angle of attack scenario. (the wing actually has a much flatter lift curve than a straight wing, therefore no ‘classic’ stall, due to a gradual reduction in lift past CLmax. The canard provides positive pitch authority up to very high AoA. In fact at about 45º – 46º indicated AoA [about 27 true] the airflow over the rudder gets blanked out enough for the aircraft to completely lose directional stability. The result is a violent departure from controlled flight, normally characterized by a slicing of the nose even past 150º of flight direction! If the departure is not arrested immediately by unloading – decreasing AoA – a spin will result, which takes a LOT of altitude to recover from.

(Several years ago an SAA colleague, Captain Louis Du Plessis survived just such an experience – but by the time he ejected the aircraft was diving earthwards at more than 500 knots! The instructor was killed trying to recover the aircraft while Louis was badly mauled by the slipstream! His battered ejection seat now hangs on a wall in High Flyers pub in Boksburg.)

Interestingly, sustained high-rate roll maneuvers can cause a roll-couple that’s potentially catastrophic if the CG position is discordant with the lift vector. (Something akin to an unbalanced spinning top in the lateral plane.) And unexpectedly, very low speed maneuvering (i.e. sub 140 KCAS) works better holding the stick neutral and simply ruddering her through the turn. Delta wings don’t have separate elevators and ailerons. Rather they’re combined as elevons and applying lateral stick into an already low-speed, low-altitude turn causes the upgoing elevon to dump lift when you need it most. So inducing the roll with rudder works better while bringing the stick back into your gut and pouring thrust on to stop the sink.

In the old days final approach speed used to be 210 knots. But that was before the canard modification. Now it’s 190 with a nose high attitude that has the same forward visibility as the Pitts Special. ie Nil! (If you can’t see the runway to the left or right – it must be in front of you!) This however is only a problem for the rear seat guy (normally the instructor! Front seat visibility is good enough.) Craning your neck to one side does allow enough forward vision to aim at the touchdown point. Closing the throttle with a quick flare kisses the mains to the runway with the nosewheel held off as long as possible for aerodynamic braking.

Opening thrust for the touch and go is virtually instantaneous compared with the slow spool-up of a big fan jet and I’ve seen circuits performed without the nosewheel even touching the ground!

We popped the drag-chute on the second landing and the head-nodding deceleration commits you to a full stop – unless it malfunctions and you need to be caught on the next try by an articulated net at the end of the runway. Energy absorption by the brakes make a drag-chute an absolute necessity.

Taxing in, Jannie warned of a little tradition awaiting me after shutdown. “Hope your watch is waterproof,” he hinted. A quick strip of the helmet, G-suit and Mae West and I was ceremoniously dumped into a bath of cold water beside the hangar. Ahh, the supersonic baptism! Heavenly after the greenhouse bake of the cockpit. Lingering in the water I couldn’t help reflecting on how generous this career and its ractitioners had been to me over the years. Dodgy eyesight had indeed forced a career change from fighters to airliners, but still – here I was, finally flying the aircraft I’d always dreamed of – the one that first started this whole fantastic love affair with flight so many years ago.

And as I lay in the blissful coolness I marveled at the way events had unfolded in my life. Would I change anything – given the chance? Nahh… Funny how things always turn out for the best in the long run. To Lieutenant Colonel Jannie Scott and all the guys at TFDC – thanks for making a six year old kids dream come true.

The author is a Senior A340 Captain with SAA and CEO of Flight Training College in George.

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