Gill Sensors & Controls’ Regional Sales Manager, Simon Peaty, caught up with Bloodhound Systems Engineer Kevin Murray to discuss where Gill level and postion sensors are being used on the Bloodhound Super Sonic Car and how important the data is to make the land speed record a success.
Simon: How many sensors are installed in the Bloodhound car and what do they do?
Kev: At last count we had 501 sensors in the car, the majority of which are pressure and strain so that we can check after every run that the car is doing as we predicted on the CFD Model. 19 of those sensors are Gill sensors. We have various GSposition sensors fitted and we have 7 GSlevel capacitive level sensors.
Simon: Great, so where on the car are the various tanks that the level sensors will be installed?
Kev: Starting in the Cockpit where Andy Green will sit, just behind the bulk head in the cockpit sits the tank for the High-Test Peroxide. There will be two GSlevel sensors installed, which will be used mainly for re-fuelling so that we know exactly how much fuel is in the tank. We will need to have a specific weight in the tanks for each run. For the first years run we have a target speed of 800mph and we will fill the tank to its full capacity (1,000 kilogram) and so we need accurate level measurement for that.
Simon: The HTP fuel, (High- Test Peroxide) is being used to run the main jet engines?
Kev: The main jet engine will use JET A1 fuel, tthe High-Test Peroxide will be pumped using a 500 weight horse power car engine to the rocket system and through to the rocket, through catalysts where it will decompose and come out of the catalysts as super-heated steam. There will then be effectively a rubber fuel grain in that rocket tube.
Simon: …and that’s a solid fuel?
Kev: That’s right, this will combust combined with the super-heated steam and oxygen to give us our thrust to get us up to the top speeds we are aiming for.
Simon: …and this is the difference from going from 500mph to 1000mph…
Kev: Yes, it provides the extra thrust to reach the top speeds.
Simon: OK, just to cover some of the other applications, we’ve got some GSposition sensors on the winglets as well?
Kev: Yes that’s right. We also have some 360 Rotary Sensors on the air brake doors. When Andy gets down to 800mph he’ll be able to deploy the air brake doors. These will open gradually as obviously opening them straight out into the wind at 800mph would not be the best idea! We need to know exactly when we’re there and the feedback from the 360 Rotary Sensors will give us that information.
Simon: You’re also using our 25mm Position Sensors for front and rear suspension defection measurement, but for me I think one of the most interesting applications is the 20mm Position Sensor which is actually installed to the brake and accelerator pedals isn’t it?
Kev: Yes that’s right. These sensors are obviously extremely important as the actual disc brakes won’t be used until Andy gets down to 200mph. If Andy presses the pedals too much at that point there is still a chance that the brakes could overheat, so we need a good indication of where the pedal is positioned so the sensors need to be extremely accurate for that.
Simon: …and am I correct in saying it is a fly-by-wire system, so the 20mm Position Sensor is actually making the link between the input from Andy and the rocket going?
Kev: That’s right, the signal will go from the sensor up to the computer which controls the jet and that computer will send the signal to the jet.
For more information on the significance of the sensors watch the Second Part of the Interview with Bloodhound.
Simon Peaty, GSC Regional Sales Manager discusses how vital the level and position sensors installed in the Bloodhound SSC are throughout testing and in the final land speed record attempt.
Simon: What made the Gill capacitive level sensors suitable for tanks on the car?
Kev: The capacitive aspect of the sensor design was very attractive to us; it means that they are fully sealed sensors and operating on a dried lake bed, things will get very dusty. Having all the sensors as sealed units means they are going to be more reliable. The moving part aspect means we can fit the sensors without worrying about dust ingress and getting into moving parts, so should be very good for that side of things.
Where we have the HTP sensors mounted into bulk head of the car, to get access to these we actually have to split the car at the bulk head and open it up to get into the HTP tank.
Simon: So you need sensors that will be super reliable that you can just fit?
Kev: It’s major, major maintenance getting into there and it will effectively mean packing everything up and coming back to the UK and into the workshop. Because of the dusty environment out there we just wouldn’t be able to do that kind of work.
Simon: …so these sensors can’t be accessed on location?
Kevin: That’s right, we would have to pack everything up and come back to the UK. It would mean delaying the project by another year, so it’s massively important that these are reliable level sensors.
Simon: Absolutely. So how important are sensors to the performance of the car?
Kevin: One of the main points of a land speed record has obviously got to be safety, so we’ve got to know that the data we’re receiving from the sensors is accurate. We compare the data after each and every run and if there are any areas of concern then we stop the run and we find the route of the problem. So every time we see an anomalous or mysterious reading we will stop the run for the day and analyse the data to find the reason why. We need to be confident that the sensors are going to be reliable.
Simon: Right, so the sensors give you a vision into what is happening throughout the whole car. Why is measuring the suspension deflection important?
Kevin: Well as I mentioned the surface of the desert is an alkali plate so it will have almost like a crust on top of the mud. The wheels have been designed to sit in the crust to give us some lateral traction. If we have too much downforce on the car we will be putting too much pressure on that crust and may break through it and end up on the softer mud underneath…
Simon: …which will cause extra drag and slow you down…
Kevin: …exactly, so we need to monitor the amount that the suspension is moving and how much the car is pushing down on those wheels, which is where the 25mm Position sensors play a key part.
Simon: So we are still working through the exact specification and design but we are also looking at a brake stand-off sensor application as well to make sure that the brake disc isn’t engaged with the pad in any way. How is that going to affect the performance of the car?
Kevin: We need to be 100% certain that there is no contact between the brake pad and the disc as the car increases in speed over 200mph. When it gets over 800mph, if there’s any contact at all the brakes will overheat and Andy will lose those brakes when it comes to slowing back down and stopping before the end of the 12 mile straight…
Simon: …and Andy has a mile overrun, how many miles is it to brake?
Kevin: It’s a 12 mile strip; we are using the centre 11 miles, so he has 5 miles to get up to speed, do the measured mile and then 5 miles to stop so we have about half a mile overrun at the end. We have to have the measured mile done in the centre because he’s got to turn around and do another run in the opposite direction within an hour. So he will have the same amount of overrun at each end. So if those brakes overheat then he’s got to rely on the parachutes and the air brakes to stop…
Simon: …and those are going to be less effective below the 200mph speeds, so the sensors are pretty key ensure that 200mph to 0mph is achieved.
Kevin: Yes exactly.