Propeller Car

This week: propeller-powered and steered cars. There's the usual sprint and slalom to test the teams.

Barfy (Chris Barfe), Big George (Wise), and Smarty (Steve Martindale) make up the Fireblades. They play in orange, and can call on the assistance of regular Scrapheap expert John Gifford.

Roo (Carl Verlander), Pete Twissell, and Frog Twissell are the Thirsty Knights. The team are in navy, and their expert is another regular, Billy Brooks.

The constructions need to be light - both teams will use a three-wheel car, with the Fireblades adding a larger engine and rudders. Lisa reckons this'll be great in a straight line. The Knights will connect the existing smaller engine to a fan, and will steer by swivelling the entire unit. This will steer better, but won't be so fast down the straights.

Now, all this assumes that there are two three-wheeled vehicles on the heap. There's only the one, and it's the Knights who get to bag it first. Back to the old drawing board for the Fireblades, who find a two-wheel trailer frame that's just the ticket. They now need a large engine, just as they did before. The Knights rip off the lid of their car, and now all they need is a large fan, then a prop shaft to steer it.

Both front wheels will need to castor, like the wheels on a shopping trolley. If it's not positioned in the exact centre of gravity, it will wobble badly. The Knights simply cut their existing front wheel free. The Fireblades are using the front wheel and forks from a rather mangled small moped.

But they'll both need a prop. This is not a trivial task, but there are heating ducts to go round. The Fireblades are using an aeroprop, in the shape of an I; the Knights have a large heating fan with five blades.

The Fireblades will need to use some gearing, as the propeller can't turn at the same speed as the engine - and the two turn in the reverse direction! They can either mount the engine behind the propeller, or run the engine in reverse
gear all the time. They go for the latter option. The Knights need to make their shaft exactly the right length, otherwise they'll have problems steering.

The Knights have the basic construction done before nightfall, which is very good progress. They still need to get the thing fully ship-shape and Bristol fashion, but it works, it provably works. The Fireblades don't have this luxury, and have to complete during the hour's tinkering time. The Knights get to use this hour to set their front castor just so.

First up is the slalom - round the course and into the home target. 20 seconds of penalty for missing a gate, 30 seconds bonus for stopping on the painted target. The judge spots that the Knights have come down to three blades in their fan; the Fireblades have a wobbly nosewheel.

In practice, the Fireblades start well, but struggle with the steering. So badly that he completely misses the roundabout, and doesn't cross the finish line. The Knights take the corners very wide, but the steering is spot on. One
of the team reckons it's like a mad bumble bee. No steering problems here, and he comes within a whisker of stopping on the target.

The sprint is - well, a pedal to the metal sprint. The Knights complete the course in 21 seconds; the Fireblades start slowly, and finish in 27 seconds and one piece. That's all they need to win, by two challenges to one. The Knights
will meet the Hairy Hogs in the first semi-final.