Back in January this year I covered a bit on the history of the Land Speed Record, and listed the current contenders looking to break the existing record:
I recently had the opportunity to attend a presentation given by Major Oli Morgan, the Team Leader of the Royal Electrical and Mechanical Engineers (REME) team from the British Army supporting the Bloodhound project. REME supplies a small team of engineers to the project to work alongside the rest of the team in developing the car. As a large part of the aim of Bloodhound is to inspire a future generation of engineers, having a number of young REME engineers working for them (each for about six months) helps the individuals themselves develop and also gives them the opportunity to inspire others to take up engineering as a career.
The Bloodhound projects aims are:
- Inspire the next generation about science, technology, engineering and mathematics.
- Share an iconic research and development programme with a global audience.
- Set a new World Land Speed Record of 1000mph.
So with programmes in place to inspire the next generation, and details about the programme available about the team’s research and development on their website and updated regularly on twitter, they now just have to worry about the third objective. The current land speed record holder (Thrust SSC) was produced by the team currently building Bloodhound, and as the only supersonic car to date, they do have some valuable lessons that have been learnt from the previous car. When Thrust SSC was designed, the design team used Computational Fluid Dynamics for the first time, and the performance data was checked against a rocket sledge test at Pendine and it correlated so well that for this car they have relied totally of CFD for the design. It did take 13 iterations of the shape of the car before they arrived at an aerodynamically neutral (no lift, no downforce) car from standstill all the way to 1000 mph.
One of the effects that the CFD or rocket sledge testing didn’t predict was the shockwave loading on the rear wheels as the car approached supersonic speeds. Thrust SSC has rear wheel steering, with one wheel ahead of the other. This was done for aerodynamic reasons, with the wheels close to the centreline. The shockwave loading required the driver (Andy Green) to turn the steering wheel over 90° to keep the car on the course. Lesson learned, in future runs Andy can be seen applying the opposite lock in advance of the shockwave, so that he doesn’t have to apply quite so much steering lock. This is one reason why Andy Green considers himself a test driver, and follows the run plan set by the head of engineering. So that as the speed builds up in increments, the lessons can be learned about how to successfully drive a car this fast.
While Thrust SSC was powered by two jet engines, to break the record another form of propulsion is required. The EJ200 engine while capable of powering a Typhoon aircraft supersonic, will not do so at sea level. Additional thrust is required, and this is delivered in the form of a hybrid rocket motor. The jet engine is used to get the car up to about 600 mph, and then the rocket is fired and collectively they accelerate the car up to 1000 mph. However the front fan of the jet engine is only rated to 800 mph, so the air intake is designed to cause a shockwave that slows the air down to below 800 mph even when the car is travelling faster.
Originally the layout of the car had the rocket motor on top of the jet. This meant that when the rocket was fired the car would be pushed down into the ground, so the small front wings would need to be angled up to give a compensating amount of lift. One of the young engineers then asked the question about what would happen if the rocket failed, and the resulting backflip of the car was not considered to be the safest option. So the design was changed, with the jet engine above the rocket. Now when the rocket fires the front wings have to generate compensating downforce, and if the rocket fails the car is pushed into the ground, which is considered to be the safer option.
The hybrid rocket uses concentrated hydrogen peroxide (known as High Test Peroxide HTP) as its liquid fuel. This is H₂O₂ (basically water with added oxygen), and when passed through a catalyst (in this cased a silver mesh) breaks down into its component parts (water and oxygen). It does this at high temperature (about 600°C), so the water turns instantly into steam. This fuel is fed into the front of the rocket motor, which is a hollow tube lined with rubber. The steam at high pressure rushes out the back of the tube creating thrust, while the high temperature and oxygen rich environment causes the solid rubber fuel to ignite and contribute to the thrust. The liquid fuel needs to be pumped in at the rate of 800 litres (about one tonne) at 75 Bar (1100 psi) in just 20 seconds. For this the team uses a 5 litre supercharged Jaguar V8 from the F-Type. They did have a Cosworth V10 F1 engine, but experimentation with the rocket motor showed that they didn’t need the 800 bhp fuel pump, and could make do with a 550 bhp one instead. The reduced servicing requirements of the standard production Jaguar unit will bring benefits when the car is undergoing its record runs. Overall the car has the equivalent of 135,000 bhp so over seven times the power of the F1 grid (and for those who think F1 is quiet, you still won’t hear this coming).
It will take about six miles to accelerate the car from standstill to 1000 mph, then there is the measured mile (which all land speed record cars must pass once in each direction within an hour) and at 1000 mph this will take 3.6 seconds. Then the car has to be slowed down. As the rocket is a hybrid rocket, it can be turned off by stopping the fuel, then the jet engine can be throttled back. The aerodynamic drag of the car will slow the car to 600 mph, before air brakes are deployed which will slow the car down to 200 mph. At this point disc brakes are used to bring the car to a stop where the crew can start the process of refuelling the car and turning it around to get back through the measured mile within the one hour time limit. Parachutes are there as a back-up, they were considered as the primary method of slowing the car but after they failed once on Thrust SSC Andy Green asked for an alternative method.
The car is just about complete it is due to do its ‘low speed’ runs in the spring of 2016. These will be up to about 200 mph conducted in South Wales before being shipped to South Africa in late 2016 for the first season’s runs, which target getting up to 800 mph. The car will then return to the UK for a rebuild before returning in late 2017 with the intention of getting to 1000 mph. For the low speed runs in the UK the car will use rubber tyres (as it will be running on a runway) and carbon carbon brakes. However for the high speed runs in the dessert, the car will run on aluminium wheels and use steel brakes. The carbon brakes were found to shatter when they rotated at the equivalent of 800 mph, and rubber tyres would disintegrate well below that speed. The wheels instead have a V profile, at low speed they dig into the dessert surface to give some lateral grip, at higher speed the profile acts like the hull of a speed boat, and they plane along the surface. At this point the steering will have very little effect on the cars direction, until at a high enough speed the wheels will act as a rudder through the air. This will make directional stability of the car challenging as it accelerates and decelerates, as differing amounts of steering lock will be needed to achieve the same effect.
Of the competitors, the North American Eagle has run at above 400 mph currently, but Oli Morgan didn’t think the car was capable of challenging for the record. The closest competition was considered to be the Aussie Invader, but being an entirely rocket powered car; it will accelerate much faster than Bloodhound, but still take the same time to stop. This means that a lot of the one hour turnaround time will be needed to move the car back towards the measured mile so that it can start its second run.
It will be an interesting few years as these challengers start to run in anger. You can follow the progress of the teams on their websites linked above, or follow Major Oli Morgan on Twitter @Oli_Morgan
The Bloodhound programme started in 2008, and its total cost is currently estimated at £41 Million. That has to be exceptional value when you consider the amount spent by F1 teams.
All photos Courtesy Flock and Siemens