[ News
| Homes
| Life
| Entertainment
| History
| Science
| Community
| Shop ]
| Sport
| Culture
| Cars
| Money
| Broadband
| Learning
| Health
| Dating
| Games ]
[ Text Only: Homepage ]
[ Graphical: Channel4 Homepage ]
[ Graphical page ] [ Home | Challenges | About Scrapheap | Forum | Links ] [ Credits | Apply for Scrapheap 2005 ]
[ The challenge and teams | Result | Irn Cru's diary | Maximus' diary | Science | Related links ]
Bouncing bombs
The designs
General science
Pros and cons
Potential catastrophes
History
During the Napoleonic wars, naval gunners extended the range of their ordnance by bouncing the cannon balls across the surface of the sea. Engineer and aircraft designer Barnes Wallis was aware of this and experimented with the principle using a toy catapult, marbles and a tank of water in his back garden. He was researching his scheme to destroy the German Möhne, Sorpe and Eder dams during World War II and found that if he spun a cylindrical bomb backwards as fast as possible while keeping the projectile trajectory low and the speed high, he would be able to skip bombs over the torpedo nets that protected the dams. Not only that but when the projectile hit the dam, the bomb would sink while the backspin would cause the projectile to hug the wall. With a depth charge set to the lower reaches of the dam wall the bomb would explode with the heavy pressure of the deep water actively focusing the bomb's power at the concrete.
How they work
The direct drive on the Irn Cru's bomb-carrying 2CV chassis provided the backspin that characterised Barnes Wallis' bombs. This backspin creates a number of factors for the barrel; stabilisation, which guarantees a straighter path and lift, like a plane's wing. This curious phenomenon is known as the Magnus Effect. There are two other critical factors to take into account to get objects to bounce on water; velocity and angle. Think of velocity as rather like a water skier – if velocity is of a certain speed, the flow resistance against the skis (or any object) is high enough not to sink! The angle is critical – too steep and it will plop into the water like a … bomb. If it is shallow enough, it'll skip along like a lamb in springtime!
Maximus
Maximus' design was a scaled-up clay-pigeon firer. A scaffold pole acting as an arm was pulled back and as it swung around, the clay was thrown up the arm. The power came from the springs – at 86lb per square inch, a couple of the springs at maximum extension could take the power up to about 3,000lb – the weight of an adult rhinoceros!
Irn Cru
The Irn Cru's design consisted of three components which together would launch a steel beer barrel. The components were a winch, a trolley and a buffer. The trolley was accelerated by the winch via a cable and through a system of pulleys sourced from a conveyor system on the heap.
Maximus
The power house of Maximus' design was a massive tension spring (also called an expansion spring). These springs were used on the doors of horse trailers and lorries as a damper.
When the arm was released, the potential energy stored in the spring was converted to kinetic energy and the arm of the machine flew forward. Some of the kinetic energy caused the arm to move, some caused the projectile to move. In order that most of the kinetic energy was used by the projectile, the arm needed to be made of a light material.
Centrifugal force pushed the projectile from its rest position by the pivot, outwards along the arm and off the end.
The whole machine was attached to a trailer. This would either be fabricated from a steel frame and wheels or, if a suitable horse trailer could be found, from the chassis of the trailer. This would allow Maximus' expert Mike and the team to aim the projectiles.
The projectiles were be fabricated by the team and were made from two sections of compressor tanks welded together into a flying saucer shape.
Irn Cru
Irn Cru's winch was made from a Jag engine, an axle and a winch drum which was twice the size of the wheel. This took in the winch rope at twice the rate and therefore accelerated the trolley at twice the speed.
The trolley was made from a stripped-down 2CV chassis. Newton's second law states that force = mass x acceleration. In other words, the lighter the trolley, the greater the acceleration. The advantage of using the stripped 2CV rather than a box frame was the inbuilt suspension which would steady the trolley on its run to the lake. The smoother the ride the better as friction would sap the trolley's (and therefore the barrel's) kinetic energy and slow it down.
Inside of the trolley was a mechanism to rotate the barrel backwards so that it would enter the water with backspin. Backspin would stabilise the barrel and increase its chance of bouncing. The rotator was made of four mini metro wheels and two lengths of scaffold poles. The mini wheels were linked to the 2CV's wheels via a sprocket and chain so all the wheels were rotating anticlockwise. The barrel was set on top of these wheels and would be pushed around in the opposite direction.
Over the run up of 50m, it was predicted the trolley should be able to get up to a speed of around 60mph. A system of buffers would need to be fabricated to stop the trolley.
The weight of the trolley, the friction of the trolley on the ground and the friction of the rope against the pulleys would all be acting against the winch and were variables which would affect the speed the trolley would get up to.
Maximus
Pros:
Maximus