Thrust SSC - Mach 1 Club

ThrustSSC Mach 1 Club


by Richard Noble

If you’ve read the earlier articles by Harvey Shapiro about Art Arfons LSR exploits, then you will know that sitting in his workshop, he has Green Monster No27, a tiny lightweight jetcar built to take Richard Noble’s existing record. If you believe what you hear, sometimes from Art himself when things aren’t going right, then he has retired more times than Frank Sinatra! In a visit to the UK in 1995 he revealed that once again, he would head for Bonneville with his car ‘just to see what it would do’. A couple of years earlier, he’d invited Richard Noble to Bonneville to witness his first serious runs in the car. Here’s Richard’s account of those runs.

"Well, Richard, I reckon that we ought to reach 600mph in six runs."

If it had been anyone other than the legendary Art Arfons making that statement, I would have decided to make the trip a year later to allow time for development. But Arfons is a real charger - renowned for blowing away Breedlove's hard-won 1965 555.127mph record in just two passes, raising that record to 576.553mph without any testing or time-wasting preliminaries. So I had to go - besides I had never witnessed a full-blown LSR run before; I had always been behind Thrust 2's wheel!

Mention land speed records, and your audience response is Bonneville. Everyone seems to have heard of that legendary place. In fact, the Salt Flats are remains of the 3000mÝ Lake Bonneville which started drying 10000 years ago. Rainwater falling on the surrounding Utah mountains picks up mineral salt, flows into the lake and then, since there is no outlet, evaporates, leaving the salt behind. Vast quantities of salt have amassed and each year the flats are dry for some three months. The track is unbelievable smooth and hard with a better grip for your tyres than tarmac. In a good year 12 miles are available but, even more important, the very hardness ensures that, should your car take a high speed tumble, it is unlikely to dig in, but rather dissipate the energy in a long and often relatively survivable high velocity slide. So it's safe, long, grippy and very fast.

As the Land Speed Record began to creep up through the 500mph range, the cars became, by definition, transonic - which in principle means that local airflows go supersonic over parts of the bodywork. For instance, on Thrust 2, at around 550mph, I could see the shockwave establish on the nose and around that speed the airflow under the car also exceeded the speed of sound. The flow over the cockpit eventually reached Mach 1.4 (1.4 times the speed of sound) and at around 615mph two huge shockwaves established on the wheel arches. All these shockwaves create an additional increment on aerodynamic drag over and above the conventional subsonic drag which increases as the square of the speed of sound. The speed of sound varies with temperature - the higher the temperature, the faster the speed of sound, and hence the faster the car can run before the transonic drag starts building. Thus, these transonic cars are Mach number limited - the trick being to devise a car shape which builds transonic drag gently once the shockwaves establish. Having achieved that, it is often beneficial to run in the hottest part of the day, thus achieving the fastest ground speed before the transonic drag builds to the point where total drag equals the thrust from the jet engine - and the car goes no faster.

Since the track length is limited, a very rapidly accelerating (and decelerating) car is needed and a key factor here is the power-to-weight ratio of the engine. Thrust 2's 1960s technology Rolls-Royce Avon 302 weights 3700lbs for a thrust of 16800, or 4.54 lbs of thrust for every point of engine.

Art Arfons' plan was to build a small, lightweight and rapidly accelerating transonic car. He would reduce the crossectional area of the car to the absolute minimum, resulting in minimal drag which would enable him to use the smallest, lightest, highest power/weight ratio gas turbine he could obtain. His J-85 engine weighs 800 lbs for 4500 lbs of thrust, or 5.6 lbs of thrust for each pound of engine. Thus, as a direct comparison, Thrust 2 weighs 8000 lbs for 16800 lbs thrust, whilst Green Monster no. 27 weighs 1800 lbs for 4500 lbs thrust. In theoretical acceleration terms, Thrust 2 can achieve 2.1G, Green Monster 2.5G (0-55mph in 1 second, 0-110 in 2 seconds). But there are other considerations, like high speed stability, the strength of the structure and its ability to resist the huge aerodynamic and mechanical loads, the overall operational reliability and consistency, Many of these necessities affect car weight and the trick is to achieve consistent high performance with minimum weight increase. It's not for nothing that the FIA Land Speed Record requirements demand two passes over the measured mile within 60 minutes. (It is no good having a car that, on paper, can lick the opposition, but is operationally unreliable.) The question that fascinated LSR addicts was whether Arfons could achieve both speed and sufficient consistency of performance with such a light-weight car to achieve a new World Speed Record.

The Southern California Timing Association were holding the first late season Bonneville meet, and had agreed to accommodate Art and the Monster, which saved him considerable expense. Around 50 racers booked in with a dedicated core attempting to beat the 25 year-old Goldenrod world wheel-driven record of 409.277mph. Art was after my 633.468 record, which meant that he had to raise it to at least 639.80 to make it official - that would mean a peak speed in excess of 655mph. The only time the Thrust Team had run at Bonneville was in 1981. Then, the salt had been almost transparently thin, revealing a brown muddy underbase. Thrust 2's alloy wheels broke through continuously, and the weather eventually broke on 11 October, terminating the record attempt before we could get past 500mph. But, this time, the salt was 4 inches deep and the track smooth and level, and the midday temperature was in the mid 70s. The Bonneville racers had never seen conditions like it so late in the season.

The Green Monster was easy to find in the Pits, since there was a large crowd of admirers, but difficult to see as it is only 40 inches high. I joined the crowd but, before I could focus the Olympus IS-1000 wonder camera, I was grabbed at the elbow by a grinning Arfons: "You don't hide that easy, Richard.". Arfons, three times holder of the World Land Speed Record, the owner of 100 jet engines (mostly collected for the pleasure of owning and rebuilding them), was out to prove his concept of the new light-weight Mini-LSR car in the only way with which he felt comfortable - by driving the car to the fastest speed ever achieved on land, and at an age when most people are looking forward to retirement. In order to achieve the Green Monster's 1800 lbs overall weight target, the frame was built from 1 inch tube and the panels are Kevlar, thus Art's exposed driving position ahead of the front wheels gives him almost no accident protection. Other Bonneville racers, whose rules demanded heavy roll bars and protective structures, were surprised that Art was allowed to run such a lightweight car. Originally, the car had been conceived as a two-wheeler, but had flown at 300mph - Art somehow surviving a steep climb, roll and the inevitable plunge to the salt. However, this was chicken-feed compared with his 610mph 1965 accident, which scattered the most famous Green Monster of all over a four mile area, which one wheel flying between the rotor blades of the airborne Press helicopter. Amazingly, Art - ever the survivor - was on his feet the next day. It was the fastest ever recorded auto accident. So, losing faith in two wheels, Art had replaced the rear wheel with two unsprung stabiliser solid wheels, but so small that, at 650mph, they would revolve at nearly 14000rpm. Steering is also unusual, being with two side levers, rather than conventional wheels or yoke.

By midday, we were ready to roll and, with a two mile run-in, the Monster was started smartly and efficiently by Tim Arfons with a neat gas turbine APU with unusual hydraulic drive. Art had decided to run initially without afterburner. This have him little thrust to play with, sinc the fixed jet nozzle was designed with a wide orifice for the afterburner. The car accelerated cleanly but, seen from behind, it snaked up the course clearly lacking directional stability. Targetting a 200mph opening speed, Art achieved an average of 178mph for the mile. When we caught up with him later he was worried; "It won't find centre, Richard". I explained that, when we first ran Thrust 2 at Bonneville on solid wheels, our problems were similar but more dire, for we left the Bonneville course altogether - twice, at 245 and 275 mph. We finally got to grips with the situation by driving only with full power or parachute brake - thus eliminating unstable cruising. Arfons wanted to think it over, and the Monster stayed in its trailer that afternoon.

That evening, the Salt Flats Films crew, making a 1˝ hour feature film on Art's incredible career, hosted a filmed discussion in the nearby Bonneville Museum of Speed, and Craig Breedlove joined us, fresh from purchasing two J-79 series 8 engines for the next Spirit of America. Amazingly, we found we all had a common inspiration - John Cobb. I had seen his jet boat, Crusader, on Loch Ness in 1952, Art had started salt racing with the Anteater - his V-12 Allison-powered design based on the Railton Mobil Special, and Craig, searching for a worthwhile career, had come across a photo of Cobb with the Railton in a textbook and, like the rest of us, was instantly hooked. Sadly, that evening session lacked the highly articulate and motivated Gary Gabelich, who held the record at 622.407mph between 1970 and 1983 and was killed in a motorcycle accident in 1984. On the salt the next morning, I met Slick Gardener, who had bought Arfons' early 70s Green Monster and had run it unofficially on Bonneville. He had a wide grin, for, at an auction the previous week, he had been offered $1.3 million for the car, which he promptly turned down.

By midday, Art was lined up and ready for the second run. This time, as he accelerated away there was a huge bang as the afterburner lit and the Green Monster raced away, hurtling salt at the start team. The stability appeared fine, and the blip of afterburner electrified the onlookers. Shortly after, his parachute was out and the timekeepers were announcing 301mph. To us on the start line, the challenge was really on, for clearly Art was gaining confidence and the stability problem was a thing of the past. 301mph was an early milestone which demonstrated low speed stability - the next mark would be 450 or 500 mph. However, at the other end of the track Art was unhappy. He told me that the cockpit had filled with salt dust and that vibration from the solid wheels on the hard salt was so severe that he could not even see the speedometer and was having difficulty following the course. Nevertheless, he was on for the next run which took place at 3.40pm. Together with Gregg Morgan of the Bureau of Land Management who manage the Bonneville site, we took up position near the start of the measured mile. Arfons appeared travelling like a dingbat, the afterburner blipping in and out and then finally stabilising with a huge roar. A trackside summary would suggest a fuel flow problem with the afterburner, otherwise a good 400mph+ run. The timekeepers announced the run at 328mph for the mile. "Show him the cockpit video" Art directed. The Sony 8 video was rewound, and I watched the run again. The car held a good, steady position to the left of the track but the cockpit vibration was intense, appearing to increase with speed. This was similar to the rough ride we had with Thrust 2 at Bonneville, though John Ackroyd had positioned the cockpit at around 50% of the wheelbase, while the Green Monster's cockpit was ahead of the front wheels, thus amplifying the vertical accelerations.

"It's no good, I can't see the speedometer or even the track for the vibrations. I thought that was a good 450mph run". "I was surprised it was only 328," I replied, "It looked very much faster". Tim Arfons was also worried. "We've got a serious howl problem with the afterburner; it's a destructive resonance and could destroy the engine". As I was thinking this one through, Art suddenly announced his retirement, the Monster went back into its truck and the record attempt was over.

"Are you mad at me?" he asked David Finn of Salt Flat Films, conscious of having thrown a wrench into the film crew's carefully-planned production which had been following him since March. "No, it was the right thing to do", David replied.

It might have been the end of an era, had it not been for Breedlove's decision to buy those J-79s, which means that we can expect the new Spirit of America in around 2 years.

© Richard Noble, OBE
The latest in a long line of Green Monsters Technical Summary follows...............


Type 650mph transonic Land Speed Record Car
- Length26 feet
- Fuselage width30 inches
- Front Track6 inches
- Rear Track70 inches
Weight loaded1800 lbs
PowerJ-85 (Learjet) gas turbine
- Dry3200 lbs
- With afterburner4500 lbs
- Front2 x 26.5 inch diameter (3 inch tread width)
- RPM range to 8500
- Rear2 x 16 inch diameter (2 inch tread width)
- RPM range to 14000
Construction1 inch tube steel 4130 spaceframe with composite panels
- FrontKawasaki motorcycle discs
- Parachute
- High speed3 foot diameter ribbon type
- Medium speed6 foot diameter ribbon type
- Low speed14 foot cruciform type
SteeringBy cable from front motorcycle suspension type arrangement with double acting levers on each side of cockpit
- FrontAir over oil pneumatic
- RearNil
Fuel22 US Gallons Jet A-1
Electrics24V DC
StartingHydraulic drive from external gas turbine APU
Aerodynamic Pitch ControlTwin variable incidence Canard unifoils listed mechanically to suspension

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