The glider pilots surfing the skies over Scotland

Loch Tay Image copyright Sant Cervantes
Image caption Surfing clouds above Loch Tay on Wednesday's flight

Two glider pilots have each soared more than 600 miles across Scotland, powered only by the "exceptional" weather conditions.

When glider pilots look at the sky and see lenticular clouds, they know the flying will be good.

The stationary, lens-shaped clouds - often mistaken for UFOs - tend to provide very smooth and strong lift, enabling gliders to fly vast distances.

Skilled pilots can surf these "waves" in the sky for hours - until the lift or the light runs out.

On Wednesday, strong north-westerly winds set up a series of giant "ripples" across the skies of Scotland and two pilots managed to break through the 1,000km (621 miles) barrier.

John Williams, who lives near Scotlandwell in Perth and Kinross, said it was an "exceptionally good wave day" - the sort of day that only comes along every few years.

He took off from the Scottish Gliding Centre's Portmoak airfield in his Antares glider at 06:50 and remained in the air for 11 hours and 38 minutes.

He flew 1,684km - "which nicely puts it just over a thousand miles" - harnessing the power of the atmosphere alone.

Image copyright Wendy MacPhedran
Image caption John Williams lands after 11 hours and 38 minutes in the air

"When you get a wind from the north-west blowing across the mountains of Scotland, you get big ripples in the air set up. That's when you see these long, white lenticular clouds," he told the BBC.

"You can fly right along the edge of these clouds, just like a surfer on a beach. It's great fun."

The 63-year-old flew up to Killin, by Loch Tay, and then on to Aberdeenshire. He repeated the Killin to Aberdeenshire leg three times before flipping around and returning to his home airfield.

"My first leg was a bit slower than I was hoping for, so I thought, I could do better than that, so I tried it again," he said.

"And then I tried it again which is a bit unusual."

His average speed on the middle run, which was the fastest, was 184km/h (114mph).

To an untrained eye, it might appear that glider pilots are randomly floating around, but they're actually engaged in a constant search for lift and the best line to take them further and faster.

It's something that becomes even more critical at the speeds Mr Williams was travelling.

Image copyright John Williams
Image caption John Williams' flight on Wednesday marked in red

The pilot said he finds it an "endlessly fascinating" mental challenge, and one which enables him to concentrate hard for long periods of time.

Mr Williams already holds the UK gliding distance record - 1,108km (688 miles) - which he set almost exactly 10 years ago.

He said Wednesday's feat will not count as an official UK record, as the rules state you cannot repeat legs during the flight.

But his achievement has still been noted as a "significant achievement" by members of the UK gliding community.

"John is an exceptional pilot," says Sant Cervantes, who holds four UK gliding records.

"He's set the bar for people like myself to follow."

Image copyright Wendy MacPhedran
Image caption A "tired but happy" Sant Cervantes after landing

Mr Cervantes, 66, set off from Portmoak in a much smaller glider on Wednesday. He spent less time in the air, but still managed to fly 1,009km (627 miles) and reached an altitude of 13,000ft (3,962m).

He followed a similar route to Mr Williams, who said it was the first time anyone had achieved such a distance in a glider that size.

Mr Cervantes, a retired airline pilot, said there were only a handful of days each year which delivered really good wave days.

But Scotland has more days like this than many countries and is generally recognised as having some of the best gliding conditions in Europe - which is why many committed gliders end up moving here.

Mr Cervantes came to Scotland in 1972 and Mr Williams in 1997. Both of them now live conveniently close to the Portmoak airfield and devote much of their time to the world of gliding.

'On a knife edge'

"Your glider is extension of your personality," Mr Cervantes told the BBC.

"What you've got out there is an ocean of air and each day is different. It's a voyage of discovery - of the sky and yourself."

Each flight might be different, but days like Wednesday can live in a pilot's memory for a long time, the 66-year-old said.

"If you're competent then you get in the zone like an athlete. You've got the conditions, you've got the glider and you've got yourself.

"When you get it right you feel like you're in harmony with the environment. You're on a knife edge and you just shoot along. It's fantastic."

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