and a little up the sides as well, enough to give

the rider some control. By moving his weight

to dig the left runner in further than the right,

he would create more friction on the left,

causing it to go more slowly than the runner

on the right, and turning the toboggan in that

direction.

What that all meant to me was that if I was

going to be on ice I would have wanted to use

runners. Even if I was going for straight-line

speed, thin runners would keep me on course,

whereas wider tracks – skis – could tend to

drift sideways, robbing me of straight-line

speed and generally proving difficult to control.

However, I was going to be riding a sled on

snow, and using skis as runners. The snow

would not be deep and powdery; it would be

hard packed on a ski run but would still have

more ‘give’ to it than pure ice.

Compacting the snow beneath them and

causing friction by moving across it, a skiers

skis ride on a temporary film of water. The

power generated by the friction beneath the

skis of a normal skier on an average piste has

been calculated at around 300 watts, more than

enough to melt a bit of snow. To turn, skiers

transfer their weight and tilt the skis so the

edges of the skis bite into the snow, creating the

extra friction that makes the ski grip. The way

that the ski is shaped and the way that it flexes

under the weight of the skier also help it to

turn. Given that I was to be going for straight-

line speed, however, I wasn’t aiming to have to

do much turning.

Nick Hamilton and the lads in Sheffield were
more than happy to use their experience and
technical know-how to help design a record-
breaking supersled. Nick explained that skis
used for speed skiing events, where the piste
is a straight run down the mountainside, were

generally longer and wider than normal skis,

to give them good stability at high speed. The

bases of the skis are not only waxed to repel the

water created by the friction, allowing them

to ride the water as fast as possible, but they

also have a kind of tread pattern that forces the

water out the back of the ski, again to help push

harder and faster down the slope.

But it wasn’t only friction on the snow that I

would have to deal with – our old enemy air

resistance would come into play as well. One

of Nick’s colleagues, John Hart, is a senior

sports Computational Fluid Dynamics (CFD)

engineer with the CSER team and an expert on

aerodynamics. John explained that, just as it

had been a major factor on the Britain’s Fastest

Bike challenge, drag would play a part in the

supersled record as well. I didn’t think it would

be wise to ask Dave Jenkins if he would be

willing to drive his racing truck down a ski run

in front of me – the danger being that he might

just have said yes! – so we had to consider other

possible ways of minimising drag.

Speed skiers use skin-tight lycra costumes

(sometimes with a special plastic coating),

wear streamlined helmets that would make

Darth Vader green with envy and even have

aerodynamic fairings on their ski boots. I hadn’t

given any thought to what I would wear – I

never really do – but our supersled was going

to have to be as aerodynamic as possible. John

had a few ideas about how that might work. In

the meantime, if I was to ride a record-breaking

supersled, I needed a few tips about hurtling

downhill head first.

frost and friction    215