We are now starting to finalise the design of the parachute braking system. The parachutes weren’t needed during the low speed tests at Newquay, so the development work on these wasn’t completed at the time, but they will be vital during the high speed tests in South Africa.
The deployment of the parachute system is one of the most complex and unpredictable systems on the car. The nature of the parachute unfurling in the turbulent air flow means there is an almost infinite number of ways in which the chute could open: indeed, attempting to model that scenario would make even the biggest supercomputer start to smoke. As a result, this is one system that is designed through calculation, experience, the right amount of over-engineering for the unknowns… and, most importantly, testing!
During the Thrust SSC project, multiple parachute failures occurred, although these were mainly due to excessive heat damaging components that then failed. Many lessons have been learned from this. Not surprisingly, Andy Green is very involved with the detail of the design and deployment of the parachutes. As he likes to remind the team: “Going faster is optional; stopping is not.”
The parachutes will be used extensively during high speed testing, providing the main means of reducing the car’s speed to 200mph. From that speed, the front disc brakes can also be used. However, the parachutes cannot – and in fact MUST not – be deployed over 670mph.
Only one parachute is used to slow the car. The second parachute is there only as a backup in case the first one fails.
Each parachute consists of a small drogue chute, the main canopy and a rope (called the strop) that attaches it to the vehicle. Andy releases the parachute by pulling a lever connected to a cable that runs back through the car, releasing a pin. This, in turn, releases a spring to fire the drogue chute out of the back of the car.
The drogue chute opens, pulling the main chute out of its canister. As this happens, the main chute remains tightly packed and pulls out the strop. The strop pulls tight, giving a jolt at the back of the car. The main chute then unfurls and opens fully, giving a second jolt. The shock loading through both these events is carefully managed by using a strop that has plenty of elasticity, so it stretches to reduce the ‘snatch’ loads.
This is the standard method of deploying a parachute system and is well proven. What isn’t well proven is deploying the system at such high speeds.
At the maximum deployment speed of about 670mph, the chute will produce a drag force of around 9 tonnes force, with an opening ‘shock’ load of up to 12 or 13 tonnes force. It’s a very rapid and violent process, which is why it’s vital to test the whole system this year before we go supersonic next year.
We are working with Survival Equipment Services in Tetbury, which is very experienced in the design and manufacture of specialised systems, including those for parachute deployment. Managing Director Del Hall has a wealth of knowledge of such systems, making the company the ideal choice for supporting us in this vital aspect of the project.
There are many other design considerations related to the parachute braking system. For example, as the deployment occurs, the drogue and strop will be travelling through Bloodhound’s ‘wake’, which is the turbulent air flow behind the car. As a result, the system can move around. If the strop isn’t directly behind the vehicle upon deployment, the initial load won’t be applied centrally, so we’re looking at the implications of that. We’re also making sure the design ensures the snatch/shock loads are distributed through the car framework correctly.
