Bloodhound Diary: Coping with volcano conditions
- 4 April 2014
- From the section Science & Environment
A British team is developing a car that will be capable of reaching 1,000mph (1,610km/h). Powered by a rocket bolted to a Eurofighter-Typhoon jet engine, the vehicle will mount an assault on the world land speed record. Bloodhound will be run on Hakskeen Pan in Northern Cape, South Africa, in 2015 and 2016.
Wing Commander Andy Green, the current world land-speed record holder, is writing a diary for BBC News about his experiences working on the Bloodhound project and the team's efforts to inspire national interest in science and engineering.
The build programme for our 1,000mph car marches on.
Bloodhound SSC is the ultimate kit car, with around 3,500 bespoke components, plus fasteners (including 15,000+ rivets in the rear chassis alone).
Of course, that doesn't stop me greeting the team with a helpful "Hi guys - have you finished it yet?" each time I go down there. "Not just yet", is the answer, but we're still on track to run in South Africa next year.
Great news for the project, with the recent announcement of Castrol joining as a major sponsor.
They have been part of an amazing total of 21 World Land Speed Records, going back to 1924.
In an era when milk was still being delivered on horse-drawn floats, the company was supporting Malcolm Campbell in setting his first world record, at an astonishing 146mph.
Most recently, Castrol supported Thrust SSC in 1997, when we hit 763mph and became the only supersonic record car in history. Now, the company is up for an even bigger Engineering Adventure. Well done them. Check out the video here.
A key part of running a World Land Speed Record car is being able to stop it, as discussed in last month's update.
Bloodhound will have a truly huge amount of energy at 1,000mph - about 660 mega-joules. To put that in perspective, a 70-tonne High Speed Train, blasting along at 125mph, has about 560 mega-joules of energy - 100 less than our car. It's enough energy to boil over 300,000 kettles, so it's a safe bet that we can't stop Bloodhound with wheel brakes alone.
Our brilliant aerodynamicist and performance expert, Ron Ayers, has calculated that about 52% of Bloodhound's energy will be absorbed by aerodynamic drag, 36% will be absorbed by the airbrakes (and/or drag chutes) and 11% will be dissipated by the vehicle's rolling resistance. That makes 99%. The remaining 1% will be absorbed by the car's wheel brakes.
If the wheel brakes are only going to absorb a measly 1% of the energy, then why are we even bothering to fit them? Well, partly because we need them for the UK runway tests next year, at the Newquay Aero Hub, where the brakes will have to do most of the work. Want to come and watch? Join our Supporters Club Gold Members and we'll send you an invitation.
For the runway runs, Bloodhound will have brakes on all four wheels, with dual circuits, to give us lots of stopping power and redundancy.
The runway at Newquay is 2,700m (9,000 ft) long, which is huge until you're doing 200+mph in a six-tonne car, when it's not quite so huge anymore.
We'll be using carbon-carbon brakes, the same as those used by aircraft and high-performance race cars, to give us the best braking performance on the runway.
When we get to the desert, the brakes are less important, as they are only doing 1% of the work. It's an important last bit though.
There's no point in getting 99% of the braking done and then trundling off the end of Hakskeen Pan at 50mph. That would just be embarrassing. The wheel brakes will shorten the stopping distance by about half a mile and they will also let me slow the car down to walking speed, turn it through 180 degrees and stop right next to the turn-round crew.
The FIA Land Speed Record regulations require two runs in opposite directions, within one hour, so turning round and stopping in exactly the right place is a key part of it.
There is a problem with wheel brakes on the desert, though. We won't need to use them at 1,000 mph, but they will still be along for the ride, at over 10,000rpm (that's 170 revolutions per second). We tested a carbon fibre brake disc at 10% above this spin speed, to give us a safety margin. The disc exploded.
This carbon disc was one of the best in the world, the same specification as the RAF's new Typhoon jet uses. We already knew that no jet fighter has ever flown at 1,000mph at ground level, and now we know their brakes won't survive it either. We need another solution.
The proposed alternative is an unusual one, using steel discs. No-one uses steel for brake discs in extreme applications. Steel doesn't absorb as much energy as carbon and it can be damaged by the extreme heat that race car brakes experience.
Steel does have one key advantage for us, though - it's stronger than a carbon disc. Steel will survive the extreme loads at 1,000-mph, but the question is, will it survive exposure to 1% of Bloodhound's huge amount of energy?
To test the steel brake discs, we went to AP Racing, where the rest of Bloodhound's brake assembly has been made.
We cranked their rig up as fast as it could go, which equates to around 160mph for Bloodhound. The test team did 10 full stops from maximum speed on the same steel disc. Maximum temperature on the disc was around 1,100C, roughly the same temperature as the inside of a volcano. Harsh conditions for a brake disc - have a look at this video to see just how tough.
The good news is that the aluminium brake calliper (the fixed bit that holds the pads and brake mechanism) only hit 150C, so no problems there. The final bits of the test are to conduct a metallurgical analysis of our super-heated steel disc, to check it's still OK, and then spin it up to over 10,000rpm (simulating 1000+ mph) to make sure it can still cope.
Once it survives all of that, then we've found our desert wheel-braking solution. It's only 1%, but it's an important 1%.
Travelling at 1,000mph brings some other interesting challenges. To get into the cockpit, I will climb down through an oval canopy hatch positioned on the top of the cockpit.
This area is subject to a very low pressure at supersonic speeds, as the air accelerates over the cockpit, and this low pressure will try to tear the cockpit hatch off the car. At supersonic speeds, that will make my 1,000mph office more than a little windy. If it got ripped off, the hatch would immediately be eaten by the EJ200 jet engine, and both would be destroyed in the process.
To make sure that the hatch stays on, our stress expert Roland has put a lot of work into making sure that the canopy latches are strong enough. The finished result has just been delivered and looks great. The latch doesn't look much, but it's stressed to a normal working load of 2,5kN (quarter of a tonne) - that's three large guys hanging off this little handle all at the same time.
Just behind the "office", the HTP tank (containing one tonne of rocket oxidiser) needs to slot into the carbon fibre monocoque. The rocket will burn off the whole one tonne load of HTP in a little over 20 seconds.
It is located close to the centre of the car to make sure that the vehicle's centre of gravity doesn't move too much with this considerable change in weight. Therefore the HTP tank sits directly behind my seat. I have, though, been promised that there are lots of bulkheads and seals to prevent the HTP joining me in the cockpit at any stage of the journey.
Meanwhile, the tank has now had its first test-fit inside the monocoque. It's snug, but it all fits nicely, and we can reach all the key points to install the plumbing and to service it.
The front suspension is also coming along well, with AMRC completing the upper section and now working on the lower parts. They look simply stunning and I can't wait to see them all on the car.
Each upper section was machined from a forged block of aerospace-grade aluminium, provided by Thyssen Krup, measuring the size of a coffee table and weighing 300kg. After 180 hours of machining, we're left with an upper suspension piece now weighing just 18kg, with over 280kg of material to be recycled for next time.
This phase of Bloodhound's engineering is all about details. Any mistakes we make now will cost us dear when we get to the desert in South Africa next year and things don't work as they should. If we're going to have a world-class Engineering Adventure, and push the boundaries of physics at 1,000mph, and do it all safely, then we need to get the details right first time.
It's a fascinating process to watch, as it all starts to come together.