There's a soft "ching" as the tow cable releases and then we're free, soaring through the skies at 3,000ft with no engine to keep us aloft, just 70ft of smooth, narrow glider wing built for one thing - catching a lift on thermal air currents rising up from the ground.
Unfortunately, there aren't too many thermals around on this blowy, overcast morning at the London Gliding Club, on the Dunstable Downs near Luton. But not to worry. Behind me, with his hand on the joystick and his feet on the rudder pedals, is John Jeffries, a legendary figure in gliding, with 50 years' experience and an uncanny knack for sniffing out whatever lift is available.
As the little yellow tow-plane disappears into the distance, we turn gently to the left and head for a thin patch of telltale cumulus cloud, the fluffy white variety formed by columns of rising air. With the only sound the light whoosh of air slipping over the cockpit, it's easy enough to chat, relax, gape at the view, and enjoy the peace undisturbed by the buzz of a propeller or the roar of an engine. A cloud contains about 20 tons of water, Jeffries says, as we reach the cumulus, and it's all held up by air, so there's more than enough energy around to help nudge a two-man glider further upwards.
We're flying a K21 Schlikker, a sleek, half-ton, red- and-white craft built, like most gliders, by the Germans. Largely thanks to the Treaty of Versailles after the first world war, Germany now dominates the market: the treaty banned powered flight in the Fatherland but made no mention of the unpowered variety. So gliding boomed. Apparently it enjoyed particular popularity with the Hitler Youth.
The K21 has dual controls and, once we've gained more height, Jeffries lets me take over. The joystick is so sensitive that you don't so much move it as simply apply light pressure and then wait. It couldn't be simpler: left to go left, right to go right, back for up and forward for down. And keep your hands away from the big lever on the top. In the very unlikely case that you are forced to abandon ship, that's the ejector button. Give a yank on that and it's parachute time.
Engineless flight is an awesome feeling. We go digging into the bowels of the Earth for filthy, black, polluting oil when there's billions of horsepower just hanging around up in the air.
But it would be wrong to think gliders are at the mercy of the elements. The planes can hold their own in winds of up to 60 knots and have been known to reach speeds of 200kmph. The world record for staying airborne is 56 hours, which dwarfs anything achieved with fuelled flight, although record attempts have now been banned for safety reasons. Should you nod off with exhaustion at 3,000ft you might never wake up.
But most impressive and surprising of all are the stunts. If you thought you had to be in a Red Arrows jet to loop the loop, think again. Gliders can do it, too, although a glider will go through the manoeuvre like a ballet dancer rather than a bullet. To prove the point, Jeffries pushes the stick forward to dive and build up speed, then pulls it back. One minute we're tearing towards the fields below, the next the sky and the ground have swopped places and the centrifugal force is so powerful I can't raise my hands and I can feel my cheeks being pushed in against my teeth. It makes a ride on a rollercoaster seem like a go on a kids' slide, especially when it's followed up by a stall turn - an almost vertical climb, a 180- degree turn about a wingtip, then a breathtaking dive back down.
Aerobatic tricks cost altitude so Jeffries heads for some nearby downs while I try to compose myself and my internal organs. The K21 corkscrews upwards inside a column of rising air about 400ft in diameter, then we fly over Whipsnade Zoo.
The London Gliding Club has been going since 1929 and, in the early days, it was not unknown for less-experienced gliders to land in the zoo's enclosures. On one occasion, Lawrence Wright pitched down among the bison.
Those were dashing days. No fancy winches or tow planes then. Gliders were launched by elastic ropes stretched manually, catapult fashion, by teams of six or more. But as things grew more advanced, records were set and broken. On April 22, 1939, Geoffrey Stephenson set off from Dunstable Downs in a Gull-1 to perform the first glide across the English Channel. As there are no thermals over the sea, Stephenson had to climb to around 5,500ft before setting off on his journey, which was then downhill all the way.
He only just made it - no mean achievement when you consider how crude the crafts were then. In those days, without the help of thermals or wind, gliders lost about 300ft in altitude for every mile travelled. In modern gliders, the figure is about 100ft, which allows Jeffries to lead convoys of gliders on marathon round-trips to north Wales or Somerset, reading the lift and gently leapfrogging from thermal to thermal across the country.
It's time to land. The air-brakes - little barriers like mini-hurdles set into the wings - spring up and we drift downwards towards the strip. It's all over in seconds: a smooth descent, an almost imperceptible little bump, a short trundle to a standstill, then a slow lean to the right as the glider comes to rest on its wingtip. No snarl of brakes, no squeal of tyres, no whine of engines being thrown into reverse - just flying the way it ought to be.
The practicals
The London Gliding Club is at Dunstable Downs, Tring Road, Bedfordshire, LU6 2JP; 01582 663 419. A 15- to 20-min trial lesson with a qualified instructor costs £50. Yearly membership costs £400 (£320 if you take a trial lesson). Members pay £17 for a plane launch or £5 for a winch launch, plus 42p per minute for use of a glider and equipment. Five day courses begin at £349. Open day: May 7. To find yor nearest gliding school, ring the British Gliding Association on 0116 253 1051 or http://www.gliding.co.uk.
