Guest Blogger
British Army Mechanical Engineer - Bloodhound SSC
Corporal Lisah Brooking is a Vehicle Mechanic supervisor in the British Army’s Royal Electrical and Mechanical Engineers(REME). She is currently attached to the Bloodhound Supersonic Car project in Bristol, supporting the development and testing of the car’s custom gearbox.
I joined the Army in Sept 2002 when I was just 16 years old. Without any previous engineering experience, I decided to join the Royal Electrical Mechanical Engineers as a Vehicle Mechanic because it offered me a good trade. In 2003 after completing basic training (learning soldiering skills) I went to the Army School of Electrical and Mechanical Engineering (SEME) to train as a Mechanic.
After graduating I completed all the necessary requirements to qualify as an apprentice (plus I was getting a decent wage!) and soon after, I deployed to Afghanistan and later Iraq – a challenging experience but an amazing opportunity to test my technical skills under extreme pressure.
In 2009 I was selected to return back to SEME to complete my Vehicle Mechanic Supervisors course gaining NVQ level 3 in Mechanical Engineering where I learned advanced vehicle systems technology. As part of the course, all supervisors are required to complete a rigorous leadership assessment to identify individuals to go on senior managers fast track system to become “Artificers” – I completed the assessment and was really chuffed to be selected for the scheme which I hope to start soon.
After completing the course and 6 months in Camp Bastion leading a team repairing vehicles damaged by IEDs, I answered an advert in an Army magazine for soldiers from the Royal Electrical and Mechanical Engineers (REME) to be attached to the Bloodhound Supersonic Car team in Bristol.
I had not heard of the project up to that point and did a bit of research and was exicted to find out about the 1000mph Land Speed Record attempt. A few weeks later I was in Bristol being interviewed by a joint panel of Army and Bloodhound Engineers to assess my competence to be a team member – I was over the moon when the Army Team Leader called me that night to let me know I was going to be part of the team.
Since starting on Bloodhound team in February 2013, I have been working alongside Lee Giles, building and testing the gearbox that steps down the output of the Formula 1 Cosworth engine to Bloodhound’s rocket pump. I arrived just in time as the final components arrived in the workshop for the gearbox to be built and then tested at Xtrac on the western side of Reading
As we are using a Cosworth F1 engine to drive the rocket oxidiser pump, we needed a reduction gearbox. Since this has never been done before, there wasn’t one readily available and a custom solution had to be found.
James Painter, the engineer responsible for the gearbox, designed it so that it would reduce the Cosworth’s 18,000rpm output and step it down to a cool 11,000rpm to meet the requirements of the rocket pump. In addition, the gearbox had to have a clutch system to allow engagement of the rocket pump at exactly the right time to allow driver, Wing Commander Andy Green, to throttle the rocket.
Before assembling the gearbox we had to measure the gears and clutch plates, not only to record any significant wear, but to set the clutch stack so that we could achieve correct clutch preload to achieve the target friction co-efficiency. During assembly of the one off gearbox we realised we didn’t have a clutch alignment tool and with testing at Xtrac soon to start, we decided to do things the old-fashioned way and use a DTI gauge.
It’s not a fast process but we managed to align the clutch to within 40 microns. With the clutch plate aligned and the dog clutch in we used a test rig to ensure that the clutch engaged and disengaged correctly.
Gearbox testing at Xtrac was immensely valuable - it showed us what worked, what needed fine tuning and what needed rethinking.
I must point out that our gearbox testing at Xtrac was the first of its kind. We had to tilt the gearbox at 64° (not as easy as it sounds) to simulate the 2g+ acceleration that it would experience in the car as it goes through its record runs up to 1000mph.
We successfully completed 35 simulated runs over the test including running the gearbox at 18,000rpm for 60 sec, which proved it was more than capable of coping with the output of the Cosworth engine. During the testing we did relocate one spray bar due to minimal drive train lubrication; its new positioning solved this problem.
The oil system proved to be a bit more tricky. During initial tests we noticed that we were getting back-flow and aeration at high shaft speeds due to low oil pressure. Originally we were running on a single-pump, wet sump system and then converted this to a two-pump dry sump system with one pump to scavenge and one pump for pressure. We also put a restriction in the oil line to help with the airation, although this did help we were still seeing low oil pressure.
We then added a small external oil tank and modified the breather system to cope with the unexpected higher gear case pressure with the breather returning to the external tank. These modifications improved the oil flow, but ultimately we concluded that the external oil pump we were using was struggling with the oil’s viscosity.
The solution is either a pump capable of handling the oil’s viscosity or perhaps some other adjustments to the oil system to deliver higher oil pressure - this has gone back to the design team to assess the most effective solution. Despite seeing lower than desired oil pressure we still successfully completed the full programme of gearbox test work at Xtrac.
After the test at Xtrac we dismantled the gearbox to check for any damage that had occurred, inspect plates for wear, gears for mesh, pitting and any bearing surface issues. We measured all the plates to calculate the theoretical clutch stack compared to the actual clutch and compared this to our first measurements before testing to calculate actual wear – all of which proved to be minimal and no damage was reported.
So what’s it like working on the Bloodhound SSC team? It’s incredible – I am having the time of my life using the skills the Army has taught me and taking them to a new level being mentored by the best in the business. As for what I’m going to do when I return back into the field force, I want to get on my Artificer course – watch this space!
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