STP Paxton Turbine Special

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The first of a new series in which senior racing car designers nominate a machine they didn’t design, but which they admire either for technical ingenuity, elegant simplicity, or sheer results

Ask me to name a car I’d like to have been involved with, and I’d go for one which was almost before my time — the STP Paxton Gas Turbine car which ran at Indianapolis in 1967. Parnelli Jones would have won in it — it led for most of the race until a few laps from the end when a small bearing failed.

It was a very interesting car which only appeared once, in that race. I believe it was designed by someone called Ken Wallis whom! never heard of again — I don’t know what he did after that Its design was unusual in that it had a central backbone chassis with a cruciform front and rear part going round differentials at the front and at the rear for the Harry Ferguson FF four-wheel-drive system. The gasturbine engine was on the left side of the backbone with the driver in a pod on the other side, and there was a bulky but minimalist body which coveted all the mechanical elements.

I liked it because it didn’t follow convention, it took a different route and they got it right. But for that bearing it would have won. The layout of the car was completely different, yet they managed to make a success of it.

The following year STP commissioned Lotus to do a turbine car, and Chapman produced a much more conventional design, the 56, with the turbine behind the driver in the conventional mid-mounted position. It was revised for Formula One, too, as the 56B which Fittipaldi raced in 1971, though he wasn’t very keen because it was a heavy old beast and wasn’t really that competitive. But! liked the first one because it was the path-finder; it was very bold at that time to choose a turbine, four-wheeldrive and that unusual layout Indy suited it perfectly because gas-turbines are best as constant-speed devices, and Indy is closer to steady-speed racing than anywhere else. Of course you could tie a turbine to a CVT (continuously variable transmission) which would keep the engine at a fairly constant speed and let the transmission deal with the variations.

But I think the other thing which probably helped that car is that at that time there was no real equivalence formula between a turbine and a normal piston engine. I think the following year there was some sort of inlet area restrictor on the turbines, but on the car Pamelli Jones drove there was no restriction. I seem to remember a number like 550 shaft horsepower — not necessarily an outstanding horsepower level compared to the piston engines it was running against.

By the nature of the centre spine layout you’re not going to have a high cross-sectional area, and the longitudinal torsional stiffness depends on that, so it isn’t a structure you would choose if you were going to put everything in line. But Wallis could see that the power unit was pretty long, so the whole package would be too long if he put in in line. Once he’d decided to put the engine on one side and the driver on the other, it was logical to hang them each side of a backbone.

I read an article at the time showing how the backbone chassis was at first made of welded stainless steel, but when they heat-treated it it went like a banana; then they got sensible and made it out of rivetted steel and aluminium.

It had almost identical suspension at all four corners — twin wishbones with outboard springs and dampers, and a steering rack and arms at one end and an equivalent fie-rod at the other to lock the steering. I believe it had common hub carriers, hubs and suspension members at each corner too. I suppose they felt that the performance was going to come from the turbine engine and the 4WD, and they wanted to keep the rest of it as simple as possible.

As to cars my designs competed against, I always used to think that although Gordon Murray was not necessarily that interested in the deeper, inner engineering of the cars, he always used to produce very elegant, logical designs. Given the engine they had at the time, the BT5 3 was a very neat, logical car to benefit from the enormous power of the BMW and the fact that it tended to be rather brutal. It was an unusual design that put much more weight over the rear axle than most — very appropriate for the engine’s characteristics. A very neat, clever, simple little car. There were a few of Gordon’s cars that I used to look at and think they were well thought out.

When I started at Lola, there tended to be a much greater diversity of layouts of racing car, and I was involved in a few which were a bit different in my early days. Mind you, the things that departed most from the standard theme were probably the least successful. Nowadays you have a pretty standard layout so you don’t get the opportunity to do anything different.

Just before my time they were doing 4WD Indy cars, and I remember Al Unser Snr telling me that his 4WD car had about 1000hp for qualifying, and of course it had no wings on it. He went over some oil and all four wheels lit up — he had wheelspin on all four wheels! Which with no downforce is not surprising with all that power — must have been quite interesting to drive.

But the layout of those 4WD systems was pretty interesting: when I went to Lola we were doing CanAm cars and one or two unusual Indy cars, so there was more variety than now, but by the mid-Seventies the classic layout of driver, fuel tank behind him and engine behind that had become totally established. Now designers have much less opportunity to have a go at challenging layouts and dealing with unusual problems.

Patrick Head was talking to Gonion Cruiduhank

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