McLaren Advanced Vehicles’ contender to go through the Sound Barrier on land
will break all sorts of new ground in the technological war of distance against time
What is the Sound Barrier? Well, it’s one of those intangibles that may or may not exist, a hypothetical barrier of shockwaves that surrounds an object travelling near the speed of sound. The real question is: What is the speed of sound? That’s tougher to define.
Traditionally it is evaluated by Mach number after Ernest Mach, the Austrian scientist who first measured it. The Mach number is the vehicle’s speed divided by the speed of sound at the vehicle’s altitude. Popularly it is 750mph, but in truth it varies according to temperature and sea level. To give examples, NASA calculates it at 728.1mph at 15 degrees Fahrenheit, ranging through 740.2 at 31 degrees to 754.4 at 50 degrees, but even that can differ according to altitude. At sea level, for example, it might be 761mph, at 3657ft, only 621mph.
Aeroplanes have regularly crashed the Sound Barrier since Chuck Yeager stretched the envelope with the Bell X-1 back in 1947, but the problem for a land-bound vehicle is the potentially destabilising effect of the sonic shockwaves on the car as they are reflected from the ground. What will happen then? Plenty of people have ideas, just like Dr Johnson once suggested that man couldn’t travel above 20mph and continue to draw breath. But in truth nobody knows. Wind tunnel and computer simulations can offer close predictions, but the only way anyone will know for sure is to go out and do it . . .
The technological problems posed by an 800 to 900mph car present designers with a fearsome challenge.
“Maverick must be capable of being safely operated at that sort of speed,” stresses Dr Bob Bell, the former head of aerodynamics at McLaren who is in charge of the project. “That’s the point. Whether or not a flat enough piece of land exists to allow that or the car has the performance capability is another question. The maximum depends on the size of available flat earth and the performance of the vehicle itself. We at this stage do not have enough information about things such as track surface conditions, which tremendously influences the rolling resistance of the vehicle, to be able to give a terribly accurate top speed to it. But we are optimising the vehicle to operate between 800 and 900 miles per hour.”
Bell estimates acceleration from standstill to 850 in 40s, at 4.5g, which may not seem too fantastic when compared with something like Sammy Miller’s 6000Ibt rocket dragster Vanishing Point, which would hit 250 in less than two seconds at 6g. That, however, is like comparing apples with oranges because the two are built for different purposes, the latter for quarter mile drags, the former for maximum speed down a much longer course.
“We have set ourselves a design criteria of a 13 mile stretch,” says Bell. “because the way the regulations are written we by and large have to have the measured mile in the middle of that.” Offset it, and you hurt yourself on one of the two runs (within an hour of one another) that are mandatory to set a record.
Maverick is being designed to run on either clay playas such as the Black Rock Desert where Richard Noble set the current record of 633.468mph in 1983, or salt beds such as Bonneville. There are other sites in the world: such as Australia’s Lake Gairdner, Lake Deborah and Lake Eyre, and America’s Alvord Dry Lake and Roach Dry Lake. There are salt flats in Iran and Russia too, although political and geographical influences have always militated against detailed investigation in the past. McLaren boss Ron Dennis has an open mind, and says, “We’ve looked at them all.” The real nitty gritty of venue choice will come later.
By its very nature the Maverick project will break new ground, and Bell admits that he has drawn more on aerospace data than from previous lsr cars. His reasons are entirely practical: “We have studied the published information, such as it is, but that is minimal!” he says dryly. “We’ve looked to the best degree that we can. You can draw conclusions from looking at the shapes employed on past record breakers, but a philosophy that we have with this is trying not too much to follow what people have done before, because primarily with the exception of Stan Barrett with his unofficial run at those sorts of speeds, where the distances were measured over feet rather than a measured mile, no-one yet has operated a ground effect vehicle at those speeds. So the difference in aerodynamic characteristics at those speeds between just subsonic and transonic speeds is enormous and really the design database that exists from previous vehicles is not really of a great deal of benefit. It’s more aeronautical than automotive.”
The Blue Flame, which held the record for 13 years before Noble’s Thrust 2 took over, was actually designed to go supersonic even though it ultimately achieved ‘only’ 622.407 for the mile and 630.388 for the kilo. A one-twentyfifth scale model was wind tunnel tested at speeds in excess of Mach 1.10 (around 920 corrected mph) in Ohio State University’s facility, with air flow at such speeds simulated by Schlieren (or shadow) photography. However, this was not a moving ground tunnel.
“One of the biggest problems we have with the design of this vehicle is the ground plane effect,” Bell continues. “There is a huge database of knowledge about aerodynamics of vehicles at these speeds away from the ground, but in ground effect it’s a totally different situation. Obviously we have quite a database of information about low-speed vehicles operating in ground effect, and one of the key pieces of technology for that is the moving ground plane or classic rolling road which all racing teams now have access to. But you’d probably be hard pressed to find one in the world that does in excess of one hundred miles an hour. And Formula One cars do two hundred. But because of that low-speed range they can extrapolate quite happily. For us, we would have to do wind tunnel testing at the actual vehicle Mach number. That’s the critical thing. So obviously, the first thing we need is a rolling road which is capable of doing those speeds, and that is one of the most technologically challenging problems within the project. How do we simulate the ground plane?
“Now we have experimental solutions to that. There are ways of doing it. There are rocket sled facilities which exist in the world, which basically allow you to power a model down a track. That’s one solution. Another solution is to do wind tunnel testing with a non-moving ground plane, and then do subsidiary tests to verify the boundary effect of the ground plane. And the final way of doing it is to rely heavily on using the Computational Fluid Dynamics method.”
CFD is an electronic version of a wind tunnel using high-speed computers to generate mathematically the flow of fluid over a computer-designed model. The computer analyses the aerodynamic forces on the vehicle’s surfaces and sorts through a number of possible design modifications to present the optimum solution. Effectively it provides aerodynamicists with a time-saving testing tool using a three-dimensional image.
“These techniques have been developed continually for some time, and computer capacity today has now reached the point where full vehicles of the highly three dimensional nature such as we have, can be tackled,” Bell enthuses. “Companies such as British Aerospace and the Aircraft Research Association have a lot of experience in this field and are now capable of applying these techniques to the design of an aircraft with amazing accuracy of prediction. For instance, something like an Airbus; when that thing first flies they are able to predict within a quarter of a percent what the drag of it will be. And a lot of that is based around CFD techniques. Unfortunately, the downside is that you need an enormous amount of computing capacity in terms of the size of the computer. The Cray which we use is obviously a new breed of super computer which people like British Aerospace have access to, which allow you to do the sums. And that is a technology which we will rely very heavily on to do the final design of the vehicle, in conjunction with experimental testing such as I’ve mentioned. But we will use the two in unison.
“If you like, one of the things that McLaren can bring to bear on this problem, that gives us a technological edge that people perhaps haven’t been fortunate enough to have access to, is that to harness what you have to harness you have to have an active vehicle. That is the technology that McLaren is very, very comfortable with. It’s a marriage of aerospace aircraft technology and our own technology.
“Depending on what the design of the vehicle was, one of two things would probably happen if the car was passive. If you were very lucky the forces acting on it, the aerodynamic forces, would tend to push it into the ground slightly. Enough that the ground was perfectly capable of supporting it and the suspension system strong enough to react. If you were very unfortunate and got it wrong, the forces could go the other way and try and lift the vehicle off the ground, pitch it nose up or nose down. The forces acting on a vehicle that size at those speeds are capable of producing forces many times in excess of the vehicle’s own weight. The whole key to the success of this project is not one of trying to design a vehicle with the performance necessarily to do the job, but with the stability and control characteristics at all Mach numbers to obtain what we deem to be the optimal ground loading and aerodynamic state of trim.”
The Budweiser Rocket, which some mistakenly believe penetrated the Sound Barrier at Edwards Air Force Base in December 1979, actually ran for a distance like a wheelbarrow, with only its front wheel in contact with the ground.
“The problem gets up until just sonic,” Bell continues, “the problem is relatively straightforward in that the conditions are linear; you can extrapolate from one speed to the next using classical aerodynamics. Once you go transonic everything starts to go out the window in terms of classical theory, and becomes highly non-linear. Once you get properly through the Sound Barrier and the upper limit of this vehicle is just touching that region then things quieten down and become more linear again, and very predictable.
“The other key issue is that to analyse our structure dynamically, in other words analyse its behaviour when it’s flexing under motion, again the calculations to do that require that sort of technology.
“if people ask will this project affect me driving round in my normal road car, well, a lot of the technology is more relevant to the aerospace industry. There will be a spin-off for them, which perhaps in some ways is more obvious, more immediate. It’s a very nice proving ground for some of their current computer technologies but because of the lead time it takes to design an aircraft, such as the European fighter aircraft, it has only been applied retrospectively. That’s a wonderfully sophisticated vehicle but because of the timescale it was originally designed quite a few years ago these technologies weren’t around then. So now this is a very good opportunity for them to actually demonstrate the power of some of those computers.”
Structurally the car will also move record breaking into new territory, away from the traditional spaceframe and stressed aluminium skin methods employed because of their suitability for one-off prototype manufacture. Again, it’s another indication what you can do when the project is front-loaded, with sufficient budget in place to facilitate serious research and development.
“We will use a fully-stressed carbon composite shell structure, which allows us to get down to these sort of weights,” Bell explains. “Using traditional metal techniques you would struggle to get down to them. You also have to bear in mind that something like 1000kg of that is the weight of the engine itself. The mass of the vehicle is important; it doesn’t normally affect top speed, but it does when you are distance-limited. It affects the acceleration you have and therefore the speed you reach in the given distance that you’ve got. It’s an area to which we are paying great attention because of the performance ramifications, but also because the heavier it is the more highly stressed it has to be, and the more energy and inertia there is is the event of an accident. There are many reasons for making the vehicle as light as you possibly can.”
Safety has been a watchword right from the start, precisely as it was with Thrust designer John Ackroyd. There’s the primary consideration: trying to eliminate the potential for an accident in the first place. And the secondary: protecting the pilot in the event of one. On this there have long been two schools of thought with record cars and boats: do you keep the pilot with the vehicle, or try to eject him? At present Maverick clearly has an ejector seat, but Bell admits he is ambivalent on that subject.
“You have to establish the categories of potential accident, and you then have to say to yourself these are the potential accidents and these are the potential result from them, what is the best way of protecting the driver in those circumstances? Now if you were travelling along quite happily and you came to deploy your parachutes and you couldn’t.” – as happened to Breedlove over 500mph back in 1964, when Spirit of America ended nose-down in a brine lake “nothing would give you more confidence than the ability to eject. However, if the vehicle suddenly lost a wheel or whatever, then the last thing on earth you would want is an ejector seat. Now we have to go through a formal process to establish what those risk categories are, and therefore make a judgement.” That’s why the cockpit canopy on the mock-up is so high and all clear Perspex currently. Bell admits it is a structural compromise to include an ejector seat.
“If you talk of safety in terms of the vehicle specifically, the crashworthiness of carbon composite construction is well proven. Obviously we are in a totally different speed regime, potentially, but nonetheless the same principles do apply, and that is partially why we will use composite materials. We will go to great lengths to design the structure such that a) it will resist having accidents in the first place, and b) in the event of an accident, it will give maximum safety. We can do lots of things. We can design the structure to be frangible so that in the event of an accident the engine breaks clear, the horizontal stabilisers break clear, perhaps even the fuel tank drags out with the engine. All to minimise the amount of energy that’s going into the driver. And with carbon composite too you can tailor the structure to absorb energy in specific ways. Even the choice of the intake system, which really you would design with no other compromises in mind purely on the basis of engine performance; part of the reason we’ve chosen that layout is that it puts a lot of energy-absorbing structure around the driver who sits in the middle of the intake system.
“All that goes for the vehicle itself, but safety goes way beyond that. From the moment Ron and I first talked about this project and right the way through to the day the guy steps out of the car, it involves all people from the cleaners in your facility right the way up to the people operating the vehicle. Safety is a presence of mind, it’s a philosophy that people must understand and apply to their individual jobs exactly like Formula One.”
Though newly-formed McLaren Advanced Vehicles clearly has the commitment and resources to push ahead with the initial stages of the project, Dennis and Bell stress that sponsorship is needed and that the budget is far from unlimited. Ron won’t quantify the financial nature of the undertaking – estimates suggest that more than £250,000 has already been invested to get to the current mock-up stage – but Bell says: “With a project like this – any modern project – there are no unlimited budgets any more. We will be working to a budget, to a timescale, and it will be properly planned, formally planned and executed to achieve those goals. Nobody in the past with the Land Speed Record has been in a luxurious financial position and we are not any different. We have a lot more resources, but we still have to meet realistic budget constraints.”
Both men are keen not to sound as if they are denigrating the efforts of previous Isr contenders and achievers. “There is no way one should detract from Richard Noble’s achievements,” stresses Dennis. “His achievements with what he had, how he approached it, the technology that was contributed to it, were significant. His car was a flying brick, which may be a bit harsh,” and it should be stressed it was the most stable flying brick in history “but it is a completely different challenge, a different approach that is required, in order to take that technological step through the Sound Barrier.”
“I have absolutely no axe to grind with anybody who has been before,” says Bell. “I have enormous respect for what Richard did and what John Ackroyd designed, and all the guys who went before. Because of the budget/time restraints that they had. Lack of funds. And the fact that they, by and large a lot of them, went out, designed the thing themselves, got into and drove it, found the funding, did the whole thing . . . Enormous respect for them.
“This is a totally different operation. This is McLaren Advanced Vehicles doing it. There is only one way for us to do it. It’s exactly the same as if British Aerospace themselves were doing it. All the ts have got to be crossed, all the is have got to be dotted, and we have to be able to stand up, hand-on-heart, and believe in the product that we produce, because we are asking somebody else to drive it. Now that person may be perfectly prepared to accept any risk, but at the end of the day we are asking somebody else to do that job, and we are carrying an enormous burden of responsibility to get it right.”
Some of the foregoing sounds like it’s bordering dangerously on arrogance, but what both men mean is that as well as the personal responsibility that there always is for anyone involved with a record attempt, there is also a corporate responsibility sometimes lacking in other ventures.
There is already ample evidence just how serious the Maverick project is. Dennis insists that a decision will be taken around June whether to continue with it, but a couple of things suggest that much of the die is already cast. For a start, he unveiled the car to visiting journalists in December, “as a Christmas present.” It’s not his style to inflate a corporate McLaren balloon just to see it burst by taking a subsequent decision not to proceed.
And he also allowed: “I will be bitterly disappointed to fail or to see one of these vehicles destroyed . . .” One of these vehicles . . . When you pick him up on that little point, he expands: “We set for ourselves a target. The objective is to beat the target. And if we don’t reach it with one vehicle, we could well make another. If we don’t reach it with that, we’ll do it with another. This is a goal we’ve set ourselves, and that’s the way we’ll tackle it.” Don’t be fooled. This is not a man who lets anything slip unintentionally.
But who will drive Maverick? It’s entirely within keeping with the perceived Dennis philosophy that he is looking for a test pilot figure, a landbound Yeager, rather than a racing driver.
“I don’t think that we’ll have to do much asking. I think when you meet pilots that fly military aircraft you very quickly understand these are guys whose characters are such that I think there will be more than one who will want to drive it. And I don’t think we will want anyone to drive it who is paid to drive it.
“There is the necessity for competence, there is the necessity for a person to be familiar with the environment he will find himself in. So, for example, a pilot of a commercial aircraft would not have experienced the imaging that is experienced when an aircraft flies at low level at high speed. We have no interest in training or familiarising the individual to accept the sensation of everything coming towards you quickly, etc, etc. So obviously you are talking about someone that’s flown military high-speed aircraft. That said, we will never detract from the competence or the courage that an individual needs to have to drive this vehicle. But, equally, the ultimate accolade that comes with success has got to be correctly proportioned between that individual, the company that produced the vehicle, and the people who provided us with technical contribution and guidance.” Perhaps that’s another reason for a pilot rather than a racing driver, a backroom boy rather than a prima donna, a Yeager rather than a Goodlin.
“I honestly feel at this stage that there will be individuals who will want to do it, first, and they will want to feel safe, they will want to feel part of the programme and there will be other things on the list, and somewhere down at the bottom of the list there will be some monetary issue. But I don’t think in any shape or form that that will be at the top of the list. I should think you would be absolutely amazed – we would all be amazed – at the salaries earned by space crew.”
“We want that type of person, because we want to draw on their technical expertise, relevant to modern high-speed aircraft technology. Right from the start. Involve them technically right from the start,” Bell adds. Take heart, lest all this sounds like it’s leading up to emasculation of the pilot’s role. There will be a man in the missile, and he will guide it.
“The main thing is that the driver must be in control of the steering and power function. Probably we won’t have a steering wheel. Probably it will be a sidestick control, like a fighter aircraft.”
“Probably it will be something that the individual is totally familiar with,” Ron interjects. “And very consistent with the training that he’s received in whatever model we choose to model the control functions on.”
And so proceeds the thinking for the first true corporate attack on the Land Speed Record – where an established company is the prime mover as opposed to a visionary individual or group of individuals who create a project specifically – since Louis Coatalen brought Sunbeam so successfully into the arena in the Twenties. Its 1000hp car was a brilliant success that burst through the 200mph barrier for the first time; the subsequent Silver Bullet an unhappy flop. I’d put my money on Maverick emulating the former rather than the latter. D J T
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