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General science
The designs
Pros and cons
In order to build a flame flinger, our challengers need to take a few things into account.
Stored energy
Catapults, trebuchets, spring-loaded cannons etc, all work by storing energy as potential energy and converting it into kinetic energy which is released at one time to propel the projectile with a sudden force.
In the spring-loaded machine, the spring is compressed and becomes loaded with potential energy. Hooke's Law of Elasticity says the greater the distance the spring is compressed, the greater the amount of energy stored.
Aiming
Angle, speed and weight of projectile will determine how far our flame flingers fling. A projectile fired at high speed at a low angle will go far (horizontal motion) and hit the target quicker. A projectile fired at a steep angle will go higher in the air and take longer to hit the target. An angle of 45 degrees will propel the projectile the furthest!
Winching
A winch will be needed to compress the spring or pull back the ruler. This is a system of gears which increase the number of revolutions the handle has to turn, to wrap a length of cable around the winch drum. Therefore each turn of the handle requires less work for that revolution.
Flammability
To burn, fires need heat, fuel and oxygen. If the projectiles do not contain enough fuel or are not burning fiercely enough at launch, they will go out before they reach the target. If you fling a projectile too fast, the cooling air lowers the ignition temperature of the fuel to such a level that it goes out.
Centripetal and Centrifugal Force
Centripetal force is a centre-seeking force. It pushes on a spinning body, pushing it towards the centre of the circular path.
Newton's Third Law says that for every action, there is an equal and opposite reaction, i.e. push right, you go left. So centrifugal force is the opposite balancing force to centripetal force, i.e. is centre-fleeing, it acts on the centre of the circular path pushing outwards.
In short, our brave builders need to design a high-speed, low-radius flame flinger that will project our flames with the biggest force.
The Anoraks went for a machine that relied on centripetal force. Paul Denney mounted a rotating arm on a tower and drove it with a car engine. The projectile was clamped to the end of the arm and released via an automatic, spring-loaded trigger mechanism to bowl the projectile, cricket ball-like, towards the target.
The design for the motorised spinner machine was based on giant Punkin' Chunkin' machines which are used in a bizarre vegetable-throwing contest held in Delaware, USA. The current record for throwing a pumpkin by machine lies at over 3km.
They used an engine from an old London black cab to rotate the heavy arm. A flaming projectile was then flung towards the target when the trigger mechanism was released.
Up 'n Atoms
Essentially, the Atoms' Partickle Axelirator MKI is an outsized tennis-ball launcher. By taking a Volvo estate, the machine involves two pairs of wheels rotating in opposite directions.
The wheels were positioned fairly close together, if not actually touching, so that when a ball is introduced to the tyres by means of an old airport conveyor, it was flung forward. A notched barrel kept the ball on track.
The Anoraks
Pros