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Jasmine: I’d say so. His calculations for the total distance for acceleration and deceleration
seem about right. The problem l have is with the length of the track. I think his ten-kilometre
figure is OK for an ideal world scenario, but it doesn't leave much margin for error.
Andrew: No. Because at full speed, you’re going to be covering, what, a kilometre every three
seconds. So if there’s some kind of problem, you’re going to be eating up the kilometres at a
pretty frightening rate.
Jasmine: You can say that again. I think he'll need every kilometre of track length he can get on
that site. Plus some sort of emergency stopping facility at the end of the line, just in case.
Andrew: Definitely, yeah.
Jasmine: Then I don't know what you think about using wheels, instead of skids.
Andrew: Well, technically, it’s feasible to build wheels capable of spinning at that sort of speed,
because it's been done on land speed record cars. The only problem is, if you get a wheel failure
at the kind of speeds we’re talking about, the consequences are going to be unthinkable.
Jasmine: Yeah. I haven’t calculated exactly what centrifugal forces they’d have to cope with, but
for wheels of about 500 mil diameter, at full speed, I worked out they’d be spinning at over
13.000 rpm.
Andrew: Yeah, that’s a lot. Plus, of course, skids should give better frictional resistance under
braking.
Jasmine: Possibly.
Andrew: Maybe not?
Jasmine: Well, the friction from wheel bearings spinning at that sort of speed might be higher.
And the skids wouldn't be in permanent contact with the rails, don't forget. But, anyway, I think
skids are the only safe option.
Andrew: I’d go for skids. Definitely.
Jasmine: And then for the brakes, I think the first point is that, for the initial deceleration, even
without applying any brakes, the aerodynamic resistance is going to be huge. In fact, that alone
might even exceed 2 G, for a short time.
Andrew: Possibly, it'd depend how much drag there was, which obviously depends on the
bodywork design, doesn’t it?
Jasmine: Yeah.
Andrew: I don't like the idea of a friction system, against the rails. It would have to withstand a
tremendous amount of heat.
Jasmine: Yeah. I think that’s a non-starter, at these kinds of speeds. Aerodynamic braking has
got to be the best option. Possibly, you could deploy flaps initially, at top speed, then maybe
release a parachute as a second stage. Maybe deploy the parachute at, l don’t know, what sort of
speeds do dragsters reach? They use parachutes, don't they? What do they do? 400 Ks?
Andrew: A bit more, I think. 450, something like that. There’s also the option of reverse engine
thrust, like they use on aircraft.
Jasmine: in that case, though, you’d still need another system, in case you get an engine failure.
But it’s a possibility. I think the bottom line is that it needs a combination of systems to make it
absolutely fail-safe.

d In pairs, discuss the points raised in their conversation and make notes summarising
your thoughts in preparation for a meeting with the entrepreneur.

e Prepare a short presentation for the entrepreneur using your notes from Exercise 9d.
Student A, you are the consultant engineer. Give the presentation. Student B, you are the
entrepreneur. Listen and ask questions about specific details. Swap roles and practise
again.

To: Jasmine Murray

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