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TEXT ONLY | CREDITS | APPLY FOR SCRAPHEAP 2005 | |||||||||||||
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| DON'T MISS SCRAPHEAP ON CHANNEL 4 EVERY SUNDAY, 6.30PM |  |
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Flying Cars | |
Result | |
Fireblades' diary | |
Knights' diary | |
Science | |
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All challenges | |
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The Thirsty Knights' diary
The brief Each team had to build a vehicle to complete a slalom-style manoeuvring course and a straight-line speed dash. The vehicles could not have any control, braking or drive through their wheels. They were to be propelled and controlled only by aerodynamic forces. The design After a brief discussion, we quickly decided on a tricycle with a short wheelbase and castoring front wheel. Thrust was to be supplied by a rear-mounted fan or propeller. We decided to steer the vehicle by rotating the entire fan/propeller about the vertical axis. Primary design features were prioritised as low mass and low load on the castoring wheel and the fan/propeller was mounted to give a long lever about the vehicle's centre of rotation. The Fireblade's design was broadly similar to our own. Key differences were a long wheelbase, rudders instead of a steerable propeller and a propeller mounted closer to the vehicle's centre of rotation. The build We recovered a virtually intact Reliant three-wheel car from the heap. This was brought into our build area and the engine started within minutes. It was probably not entirely necessary to start the engine at this stage, but it did serve to intimidate the opposition! The Reliant was soon stripped of all bodywork aft of the bulkhead, revealing a surprisingly good chassis. To shorten the wheelbase, we removed the rear axle, discarded the springs and dampers and re-attached the axle directly to the chassis rails. The new axle position was directly below the front seats. One of the effects of moving the axle was to angle the whole vehicle nose-down. This had the unfortunate result of destroying the front castor/trail geometry. To correct this, we cut the front spring to allow the front suspension to be lowered and the geometry tuned to improve castoring. With the original steering linkage removed, we pushed the vehicle around the build area to confirm it would behave as expected – and it did. Moving on to the matter of propulsion, we decided to use the suspension strut from a front-wheel-drive car to locate our propeller. The strut provided us with a thrust bearing (wheel bearing), a CV joint, steering pivots and a steering arm with a tie-rod end attached. We removed the brake disc and calliper to save weight. The strut was mounted upside down on a short triangular frame about 18 inches aft of the rear of the chassis. What had been the lower ball joint of the strut was braced with a fabricated frame in the form of a 'slanted pyramid' mounted on the rear chassis. We found an industrial ventilation fan, four feet in diameter with 12 removable blades which could be adjusted for pitch. The fan was fitted to the drive flange on our strut, using the wheel studs and nuts. To couple our engine to the fan, we created a propshaft consisting of the front end of the original Reliant shaft, the end of the driveshaft that came with the strut and a nice straight length of thin wall steel tube. We spent some time ensuring our propshaft, which was six feet long, was straight and ran true. The prospect of an unstable shaft running at 2,400rpm next to our ears was not attractive. Steering control was achieved by the addition of a bicycle handlebar assembly in place of the steering wheel, coupled by a long pushrod to the tie-rod end and steering arm of the strut. The Fireblades' vehicle was based on a trailer, with a Suzuki 4x4 engine mounted high, carrying a propeller on the gearbox output shaft. Two large rudders were mounted behind the prop. A scooter wheel was mounted in a fabricated fork at the front. The tests Before the tests began, we were allowed some time to titivate our creations. For us, that meant pushing it along the runway and setting front-wheel castor geometry, followed by a tasteful paint job. The Fireblades took the opportunity to alter their castor geometry (by cutting and re-welding), add a handbrake and paint their creation in lurid orange. A coin was tossed to establish which team would run first. I won the toss and nominated The Fireblades for first go. Slalom The Fireblades took some time to start their engine, amid much jeering and sarcasm. Once started, the flag dropped and the vehicle started to move, veering off to the right. The driver (pilot, passenger, victim etc … make up your own description) was able to bring it back straight but it was clear it needed most of the available left steering just to stay straight. The first part of the slalom was a right turn, which the orange wonder negotiated easily. The following left turn was a struggle, with the vehicle narrowly missing the marker. The next right turn was once more easily accomplished, but the vehicle continued to turn right. By the time the driver regained control, he had run out of runway and was in the weeds. Our vehicle was pushed to the start line and the engine promptly started. As the flag dropped, I released the handbrake and … it moved. This was the first time the contraption had moved under its own power. Picking up speed quickly, I tried a couple of gentle turns to confirm that things worked as predicted. With only the fan for steering, the vehicle would only turn when under power, so the procedure was to steer, then blip the throttle to swing round to the desired heading. Our short wheelbase paid off immediately, making short work of the tight slalom course. Speed trial Our advantage after the slalom was such that we were ahead on points and really only needed only to complete the run to win. With this in mind, I set off from the start line with a short burst of power and quickly eased off to confirm that I still had the vehicle under control during the over-run. A few more bursts of power and I crossed the finish line at 21mph. This may not sound fast but if you try to imagine sharing a supermarket trolley with a 40bhp bacon slicer, you may begin to appreciate my position. The Fireblades put in a respectable run, but the penalty for not finishing the slalom cost them the contest. And so it was that The Thirsty Knights went through to the semi finals … |
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