North American Eagle bids to become the fastest land vehicle
4 mins read
For a brief period in 1964, when the rules governing land speed records were transitioning from wheel powered to jet propelled vehicles, the official land speed record was held by Donald Campbell in his Bluebird – and this was set in Australia. That apart, the record has been set for the past 80 years in America, principally at the Bonneville Salt Flats or, more recently, at the Black Rock Desert.
For some reason, this appears to give the Americans a feeling of ownership over the record, even though it has been in British hands since 1983, when Richard Noble drove Thrust2 at 633mph – a mark beaten only by Andy Green in the next generation ThrustSSC in 1993, who set the current record of 763mph.
"When the British or any other country can transport their vehicle to the US, use US resources and take the record and research information back to England without so much as a 'by your leave', there is something dreadfully wrong," claims the North American Eagle (NAE) website. But the tongue is firmly in cheek. The respect which the NAE team has for its British counterparts is immediately apparent – but it doesn't stop them wanting to bring the record 'back' to the US.
Steve Wallace, the team's system engineer, has an unusual set of challenges. The most obvious when looking at the NAE is that, rather than being a purpose built vehicle like ThrustSSC, it had a previous life as a jet aircraft - a F104 Starfighter, produced by the Lockheed 'Skunk Works' in the 1950s. Rather unfortunately, it earned the nickname of the Widowmaker on account of the number that crashed. However, some 2500 were made and they remained in service for nearly a decade after their introduction in 1958.
Wallace commented on the choice: "We could have built something from scratch like the Brits, but when we thought what it would look like, Ed and Keith thought it would look like an F104 – so why not get an F104 and start there?" Ed Shadle and Keith Zanghi, the cofounders of NAE, found the hulk of an old F104 at a scrap yard in Maine.
Transforming it into a land speed record breaking car was the next step. According to Wallace, this was simply a case of: "Taking the wings off and modifying it so that it could taxi at 800mph!" This has involved extensive structural modification, but Wallace has also had his work cut out.
With the jet engine creating 45,000hp and with the unknown effects of shock waves generated as the vehicle goes transonic (speeds round the sound barrier), there is a 'delicate aerodynamic situation'. Referring to the forthcoming trials this autumn Wallace commented: "We are very anxious to get information about the vehicle when it is generating shock waves and that is more than 600mph – that is when we will know if we have a lot of work ahead of us or no work ahead of us when it comes to going for the record. We are very interested to see what sort of stability we have in that transonic region because that is the dangerous part – we are not too concerned about what happens above or below.
"Everything needs to be balanced correctly to avoid harming the driver or vehicle. So this is where the electronics and data acquisition come in. My focus has been on getting data that proves in the field what we have predicted using computational fluid dynamics. We have models that show exactly what the pressures are about the vehicle, so we know how it is moving aerodynamically from a computer modelling standpoint.
Now we need to go out in the field, do some test rounds, measure pressures about the vehicle and compare those with our model to make sure that what we predicted is what we see. Other data collection tasks include: monitoring the control stick position; wheel position. to check what the response is to the steering system; and monitoring vibration with accelerometers in some critical areas – we have strain gauges for the parachute coupling, for example."
Having shaken his previous data collection system to bits, Wallace partnered with National Instruments for his new system. He has installed a cDAQ-9188XT, a ruggedised eight slot Ethernet chassis that is linked to an on board computer on which he has created his test programs in LabVIEW. All the information is held on board because Wallace has an aversion to telemetry. "It is prone to transmission problems, in which case you are likely to lose your data – I like to have it on board. I don't need the information straight away, just to have it in a secure location on a solid state hard drive and then download it for later analysis."
Data acquisition is probably the most sophisticated part of the electronics. Rules state there cannot be any aerodynamic or automatic controls – it has to be all 'driver authority'. The main problem in creating the NAE, from an electronics perspective, was therefore obsolescence.
Wallace explained: "The basic engine control power systems are based on the original F104 Starfighter, but duplicated with components that we have had to scrounge from various sources. Some things are very hard to get – voltage regulators for generators are hard to come by. The 28V power supply had selenium rectifiers in it and they have a limited shelf life. So I had to remove the rectifiers and replace them with some sort of equivalent solid state devices so I could get rectified 28V dc to run my systems."
The challenge involved in testing the system – even with the new rugged data acquisition system – is complicated by its nature. "We have a unique situation where we have a vehicle with a turbine that is generating a lot of static. Not just static because of the air flow, but also from spark generators that are igniting things like afterburners, so it is an extremely noisy rf environment. I can't have amplifiers very far away from the sensors or I will not get good analogue signals going back to my data collection system. So I have had to build amplifiers and embed them behind body panels to get air pressure data where I need it. Also, the ground inside this vehicle is awful, so I have had to install my own copper bus to provide a solid ground for all of my instruments.
"It's a very noisy vehicle electronically and I don't want to pick up that noise on my data. It has been a bit of a struggle, but it is working now."
There are still potential problems arising from the F104's age. "One of those old components could decide it doesn't want to be more than 60 years old," observed Wallace. "We had a transformer fail a couple of months ago during a test session and I had to replace a lot of smoking wires!"
However, Wallace is confident of the team's success, but admits: "There is always the great equaliser – Mother Nature. It doesn't matter how rich or poor you are, Mother Nature can rain on your parade and ruin everything. And when you fail, you fail big."
