This retired engineer built his grandkids their very own rollercoaster in the back garden

A retired engineer has taken the award for Best Grandparent Ever after building three working rollercoasters in his garden for his grandkids.

Paul Gregg, who was an aerospace engineer at Boeing for 34 years, designed and built the rides after he retired.

The video above shows two of his grandchildren road-testing the coasters in his Seattle garden.

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It’s an unpowered rollercoaster, so Paul himself pushes the carts up to the top of the drop – the momentum then carries them round the rest of the track.

The ride in the video is known as Little Rocket, as it’s the smallest of the three Paul has made for his six grandchildren.

The biggest ride has been dubbed Smaug The Terrible after the dragon in the Hobbit, while the third is known as Negative G.

But Paul isn’t keeping all that good grandad karma to himself – he’s written a book on how to build back-yard coasters, and is helping parents who like the idea of building their own.

“For me, the most difficult task in developing a backyard roller coaster is the body of the cart,” he said of the Red Racer shown in the video above. “The Red Racer has a foot-powered car body, and the Little Rocket is made from a 15 gallon water barrel.”