Before he helped conceive the world’s first supersonic car, this month’s ‘victim’ designed missiles. So it is perhaps no surprise that his choice is this stunning piston—engined ‘Exocet’
Ron Ayers Thrust SSC Aerodynamicist
Goldenrod is perhaps the most beautiful of all LSR cars, being functional and elegant. Sadly, its record did not get the accolades it deserved, as the jet-car era had just started, achieving much higher speeds by simpler means and reaping the publicity.
To push a car through the air at record speeds, a designer has to pack the maximum possible amount of power behind the smallest possible frontal area. The solution adopted by the Summers brothers in 1965 was breathtakingly simple — put four high-powered engines in line in a long, slender tube. In this way they achieved a ratio of bhp per square foot of frontal area which was about three times greater than that achieved on Donald Campbell’s Bluebird CN7, the highest to that date.
The solution was not without its problems: the drive mechanism — two engines driving the front wheels, two driving the rear — was complicated, and many teething problems were encountered. But the real challenge was packaging the driver, four engines, transmissions, fuel and ignition systems into a frontal area of only 8.5sq ft.
It’s a masterpiece of engineering. You’ve got to see it to believe it. The body is only 28in high to the top of the engine hood— you could trip over it The main thing you notice when you take the skin off is that there is practically no space for air in there — it’s just solid metal. I — met Bill Summers, the car’s engineer, at last year’s Goodwood Festival of Speed. He was very modest about their achievement. People have gone faster since, but only one-way or less than one percent faster, so I believe Bill’s brother, Bob, still holds the overall FIA-approved wheel-driven record.
The Goldenrod team did some sophisti-cated wind-tunnel testing with models at CalTech, so they were pretty confident With a drag coefficient of only 0.1165, they had reason to be. I have a copy of the report, which says the data was analysed by Chrysler, on a computer, a rare claim in those days. The report also claims that they were trying to minimise drag and generate aerodynamic downforce to increase traction. Although they did brilliantly with the drag, I do not think they will have been very successful with the downforce, as such slender drapes are very inefficient at creating lift, either upwards or downwards. After all, a jet fighter would not get much lift without its wings. You can get some downforce at the front by tilting the nose down, but this increases drag. Also, you’d have to find a way to get matching download at the rear wheels to give balanced traction. I expect they ended up aiming for traction balance and didn’t worry too much about overall downforce.
With Thrust SSC, our problem was different. Its wider shape was quite efficient for lifting so, at sonic speeds, the car only had to lift its nose by 0.5 degree to do a backflip. That was why Jerry Bliss, our systems designer, in-corporated an active suspension to control the lift force throughout the mach number range.
On the other hand, yaw stability, ‘weathercock’ stability, from the fin is crucial; the car could conceivably roll if it got into a sideslip. But when you see Goldenrod you realise it is so low to the ground that the chances of it rolling are very small indeed. I’ve not done the sum to see what angle of friction would be required to cause the car to roll over, but I suspect it could actually skid without rolling.
Goldenrod’s structure is a steel frame with aluminium panels on it. You need plenty of access panels with any record car because you have only one hour of turn-round time between record runs,and a lot of engineering to check. On Thrust SSC Glynne Bowsher, our designer, chose a spaceframe and panel construction rather than a monocoque for this reason, despite the weight penalty:are tight turn-round time is a good engineering discipline. It stops vehicles being too special, and it is the level playing field we all work to.
If I had to design a wheel-driven record contender, I could not improve on Goldenrod using piston engines. To get more power per frontal area I’d have to use a turbine. There are several trying this route, using the turboshaft engine from a Chinook helicopter, to aim for 450-500mph. But the limit, I feel sure, is wheel adhesion, not power.
You get to the point where overcoming aerodynamic drag takes all of the available adhesion, so you can’t accelerate any more. What you find on a wheel-driven car, as opposed to a jet-car, is that you eat up the ground but only gain 10-20mph at each mile marker. So minimising the aerodynamic drag is not only important as regards to the power required but also for wheel adhesion. Rolling resistance is also crucially important, particularly as the salt or mud record tracks are much more draggy than concrete or Tarmac. And this is where Goldenrod was at a disadvantage: its four engines and drive mechanism made it extremely heavy, and the wheels were very small — only 24in in diameter. This caused high rolling resistance, substantially greater than the aerodynamic drag by my estimate, and greater than Bluebird CN7 at the same speed. This suggests that the performance could have been increased by using larger wheels, as the reduction in rolling resistance would have more than compensated for the increase in aerodynamic drag.
Walter Korff, the aerodynamicist, used rolling resistance data which was only valid at much lower speeds. Consequently, at 400mph, he underestimated rolling resistance by a factor of three, so he would not have seen it as a great problem. He no doubt thought he had got the optimum shape.
My observations are made with the advantage of hindsight and more recent data. Frankly, I am pleased he did not use bigger wheels, as that would have required putting humps in the shell to accommodate them, and a perfect shape would have been spoiled. Sacrilege!
Ron Ayers was talking to Gordon Cruickshank