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Scottish Cartie Association Championship

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Reckon you're quick? Taking part in more than one event in Scotland this year? Why not register for the SCA Championship and find out how good you really are! 

The SCA Championship is a competition run across the main soap box events in Scotland with the aim of encouraging participation in the various events and to create friendly rivalry between teams.

Teams can register for free and are awarded points for their final position in the participating events, and the team with the greatest number of points after the last event will be crowned as the SCA Champion. There are separate classes for Soapbox Cartie and Gravity Sidecar.

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The UK's Fastest Soapbox Racer Returns to Scotland

C12 : The UK's Fastest Soapbox

This is the only view most racers ever have of C12.

Steve Thomas has been winning races the length and breadth of the UK for several years now with his sleek carbon fibre creation. It is a genuine all round champion, and has won at high speed gravity races and sub 20mph grass track events alike.  He is also the undisputed King of the Mountain at the now defunct Cairngorm Soapbox Extreme, having won convincingly there from 2010 to the last race held there in 2012, and was clocked on radar speed gun travelling at 70mph.

Steve's success is not only due to his technical expertise in creating his carbon fibre masterpiece. He is also a very skilful driver, as can be seen from this gutsy overtaking move in the final at CSEx 2011.

He has started 2014 with yet another win at the Tetbury Wacky Races, and will be travelling up to Scotland to defend his title at the Border Bogie Challenge later this month and, barring accidents or an uncharacteristic driving mistake, it looks like that Steve will be travelling home with more silverware to add to his collection.

 

Soapbox Speed Calculator

Gradient %
Total Mass kg
Mass of Wheels kg
CdA m2
Crr  
Air Density Kg/m3
Top Speedmph
 kmh
Distancem

Terminal velocity of a gravity racer is the theoretical maximum speed at which the drag forces exactly equal the force due to gravity. It is theoretical because it is an asymptotic limiting value that cannot ever be reached, although you can get very very very close.

The table on the right will allow you to calculate the approximate top speed of a cartie on a given slope, and the distance needed to reach that speed. Just use the "up" and "down" arrows to adjust the parameters and see how the top speed changes.

Because terminal velocity is is never achieved, the figure quoted is the distance needed to reach 99.9% of the terminal velocity.

For a more accurate estimation of speeds on any given course, grab yourself a copy of SCA Cartie Sim.

"Power to Weight" for Soapbox Racers

One of the key indicators of a car's performance is its power to weight ratio. The better ratio is, the faster the car will accelerate.

Obviously this can't work for a gravity powered soapbox racer as it has no engine, but there is an equivalent figure.

Aerodynamics of Soapbox Racers

soapbox racer drag v. speed Aerodynamic drag is by far the largest factor affecting a carties top speed, but how big an effect is it? I've been doing some maths and have come up with some interesting typical figures. The three sources of drag on a cartie are;

  • Aerodynamic drag
  • Rolling resistance
  • Wheel inertia

soapbox drag versus speed Rolling resistance is almost constant at all speeds, and wheel inertia actually decreases as speed increases (or - more correctly - as acceleration decreases), but aerodynamic drag increases as the square of the speed. It starts off very low, but soon becomes the dominant factor.

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