Article Source: IMechE
The long car rolled serenely across the tarmac.
There was a brief roar – then before much of the audience realised it had sprung forwards smoothly, effortlessly going beyond 200mph. The car was stabilising at 50mph without the throttle pressed down, said driver Andy Green to Professional Engineering. There seemed to be an inevitability about the success of this ‘low speed’ public test.
Two years later, nothing is so straightforward for the Bloodhound LSR. Flying across the South African desert, crosswinds and low friction mean the giant car sometimes leaves three tyre tracks in the dry flood pan, front-left wheel in front of back-right as driver Andy Green battles the steering wheel. Metal panels are peeled away by abrasive streams of coarse, kicked-up dirt.
Yet the car is hitting its highest ever speeds. On 6 November it hit 501mph, more than halfway to the project’s original goal of 1,000mph. How has the potential land speed record breaker reached this key milestone after travelling from Newquay Airport to the Hakskeen Pan in the Kalahari? Professional Engineering spoke to the project’s engineering director Mark Chapman about some of the challenges overcome on track to the first 500mph.
Challenge One: Where’s the water?
“We have been out here now for over a month, and it is challenging,” says Chapman. Utilities are non-existent in the Kalahari, making otherwise routine alterations and simple engineering tasks much more difficult. Spare parts cannot simply be picked up from suppliers down the road, meaning a new degree of forward planning is required.
“We have literally had to bring our own water with us, so it’s not Silverstone or even Newquay. There is a lot of stuff going on that you have to think quite hard about – when you decide to do some repairs you need to make sure you have got all the stuff with you.”
Challenge Two: Feeling the heat
Not only is the desert dry, it is also very hot – an obvious point, but another hurdle to overcome in a land speed record bid. The daytime temperature ranges from the mid-thirties to low-forties, and it is even hotter in the car. Driver Green described the 35ºC+ breeze as feeling like a “lovely cool rush of air” as he clambered out of the cockpit after a successful run.
More importantly, the heat and 1,000m altitude make starting the engine a challenge. An air start cart imported from Brize Norton and originally intended for providing high-pressure air to start Rolls-Royce Conway 10s struggled in those conditions. To overcome the issue, the team has been turning the car towards the wind to get it started. “With that, we quickly got up to about 350mph,” says Chapman.
Challenge Three: Desert debris
The Hakskeen Pan was carefully selected for the record bid thanks to its size and flatness. The track was finely surveyed and locals meticulously checked and cleared the surface of rocks – more than 16,000 tonnes were reportedly removed. Despite the tireless work, the surface is very different from Newquay Airport.
The wheels, which are designed to spin at 10,500rpm, cut through the ‘crust’ under the weight of the almost six-and-a-half tonne vehicle. During high-speed runs, that has kicked up material into the rest of the car.
“The first surprise we had was the amount of debris striking the deltas,” says Chapman. A narrow strip of incredibly fast dirt was “absolutely hammering into the undersides of the car.” During two runs that debris damaged the car’s rear deltas, the bottom edges of the rear suspension. Bits of the panel were peeled back – at supersonic speeds higher than the current land speed record of 763mph (1,228km/h), that could cause a serious safety issue.
To tackle the issue, Chapman and his team redesigned fasteners to keep the rear deltas secure under the barrage of debris. “We increased the diameter and strength of the fasteners and for the last three runs it’s been fine.”
Challenge Four: High wind
The desert is hot, high and dry. It is also very windy, catching the car’s giant fin.
In an online report, Green says the fin “is too big for the car this year”, without the extra rocket power that could propel it beyond the land speed record he set in Thrust SSC. The large fin makes the car “a bit too stable aerodynamically,” he writes, essentially trying to point it into gusts of wind. The yaw static margin, between the centre of gravity and the aerodynamic centre in yaw, is currently too large.
But the wind is actually welcome for now, says Chapman, as it lets the team test the car to its limits. Compared to Newquay, there is much more room to manoeuvre – the track is 200m wide, with 300m spare either side.
“In Newquay we couldn’t explore the crosswind limits – you ran out of runway. We have run on some deliberately high crosswind days… and revised that, to see what we can do. It’s not really about top speed at the moment, it’s about doing things we couldn’t in the UK.”
Challenge Five: Chuting practice
The current test runs are also the first time the team has been able to try out the vehicle’s parachutes. The engineers tried different designs to find ones that inflate cleanly, as well as trying two at once.
“When we did the twin deployment, the second one that came out hit the other one, but that was kind of expected,” says Chapman. “You would never normally run with two parachutes.”
The chute was also adding too much yaw, pulling the back of the car from side-to-side, so the team removed some rings from its outer edge. Now, says Chapman, “it just hangs there” behind the car.
The first 500mph has not been easy, but the team has tackled issues confidently and decisively, drawing on years of detailed planning. “It would be kind of boring if it just worked,” jokes Chapman. “We were actually surprised about how well it did work.”
Since reaching 500mph, the team has faced new challenges. The chassis was split and the engine removed last week after an internal FireWire cable, which degrades with high temperatures, caused overheat warnings. The team made improvements to engine bay cooling and reviewed operating temperatures during the break from testing.
The latest runs are testing the car’s air brakes. Rather than being deployed after the car has reached top speed, they are fully opened at 60º before the runs start. The team can then analyse vortex frequencies coming off the air brakes, to plan potential alterations.
Elsewhere in the team, aerospace engineer Dr Ben Evans from Swansea University is comparing wheel load data from pressure sensors with dynamic models. “We are looking at wheel load data and the correlation of that and CFD [computational fluid dynamics data],” says Chapman. “When we get back [to the UK] in the early part of next year, we’ll do all that data correlation stuff then use that to tell us how big a rocket we need.”
Each run has given engineers vital data for the record attempt, he says. “We haven’t had a run out where we haven’t learned something new.”
The engineering director praises all the staff who have worked on the project over its sometimes tumultuous 11 years. The successful tests are an achievement for everyone, he says, not just those working on the “new white-and-red Bloodhound”.
The next 500mph?
After a few more tests, the team will return to the UK. Next time in the desert will be the record ‘campaign’, sometime in the next 12-18 months.
The crew will have to make more key tests. The air brakes will be actuated in the record attempt, requiring testing beforehand. The car will be fitted with its new Nammo rocket on top of the current EJ200 Eurofighter Typhoon jet engine. Low-speed runs will test the rocket’s operation, says Chapman, as well as the team’s ability to run, refuel and stop it safely. After that, though, “it’s pretty much into accelerating speed”.
Acceleration – to a point. At the moment, the mission is focused on a new land speed record rather than the original 1,000mph goal. That grander aim is still considered possible, but will involve modifications to parts including wheel fairings.
“The project at the moment is very much on just a land speed record. We have not really thought about what the 1,000 would look like,” says Chapman. “We’ll have to look again at some of the design to get up to the land speed record… the challenge is going to be the forces involved, they are all squared terms. There’s a fair bit more energy to get halfway to 1,000… once we have achieved that one, we’ll see what we have to do to get another one.”