Two nine-year-old English schoolgirls have become the world's youngest formation wingwalkers.

Reaching speeds of up to 160 km/h and flying only metres apart, Rose Powell and Flame Brewer took to the skies on two of their grandfather's vintage biplanes over Gloucestershire.

They became the third generation of their family to wingwalk on the Boeing Stearman aircraft when they took off near Cirencester.

The cousins, both from London, were inspired to undertake the feat by the plight of their six-year-old friend Eli Crossley, who suffers from Duchenne Muscular Dystrophy.

His parents have set up the Duchenne Children's Trust to raise money to research a treatment or cure in time to save Eli's life.

The girls' grandfather, Vic Norman, was at the controls of Rose's plane while Martyn Carrington, director of flying at Aerosuperbatics Ltd, piloted Flame's aircraft.

Speaking minutes after getting down from the plane, Rose said: "That was amazing. It's really hard to explain what it's like.

"It just felt like we were birds soaring over the neighbourhood - it was really cool. When we were up in the air the houses were like Lego blocks.”

"I was a little bit frightened but once I was in the air and having fun I got over it, it was really fun. It's quite scary when you take off but if you like mega funfair rides I think you'll find the take-off really cool.”

"The best bit was probably taking off or doing the Superwoman pose."

"It feels really nice to have done something to help Eli and hopefully get lots of people to know about the Duchenne Children's Trust."

"It is dreadful that the older children like Eli get, the less able they become to do things that I take for granted."

Mr Norman, who has had a pilot's licence since he was 17, said he was not nervous about the flight because it was in perfect weather conditions.

"It was a double responsibility for me because it was my grandchildren," he said.

"I was more worried about whether they were going to enjoy it because although they have wanted to do it every year from the age of three, I've always said no.”

"What I'm most proud about on this occasion, when they asked again, I said no but they said 'Hang on, grandad, there's this friend of ours with this terrible disease and we want to raise awareness because no one knows about it'.”

"They gave me the whole story and I said OK, on this occasion I'll give in and we'll do it once.”

Emily Crossley, Eli's mother and founder of the Duchenne Children's Trust, said: "We are very honoured that Rose and Flame are wingwalking to break a world record to help raise awareness of our charity.”

Duchenne Muscular Dystrophy is the most common genetic killer of children worldwide.

The disease is caused by a mistake on the genetic code in a gene called dystrophin which is found on the X chromosome.

Although girls may carry the mistake, they have two X chromosomes, so the healthy one cancels out the faulty one.

But boys have only one X chromosome so they are more likely to be affected.

The effect is that children suffering from the disease cannot produce dystrophin, a protein necessary for muscle survival. As a result, every skeletal muscle in the body deteriorates.

It is 100% fatal and there is no cure. Most boys die in their early 20s from heart or respiratory failure.

The Duchenne Children's Trust is working to find a cure for the disease in 10 years.