A FORMER U.S. aerospace engineer is keeping himself busy in retirement by constructing roller coasters in his back garden for his grandchildren to enjoy.

    Paul Gregg, a retired aerospace engineer from Utah, wanted to thrill his six grandchildren and keep his skills sharp when he set out to design and build a simple backyard roller coaster at his Seattle home in July 2014.

    He had only retired from his job at aerospace company Boeing, where he’d worked on space and military aerospace programs, in February of that year.

    Searching online, Gregg found some existing backyard roller coasters, even a few he decided were “pretty well done.”

    “But I thought I could make a few improvements in design, analysis, and fabrication methods,” Gregg says in his book, which he has written on the topic of backyard roller coasters and made for sale on his website.

    He found most of the coasters he saw online had been built by energetic teenagers and looked pretty poorly made and “of questionable safety.”

    “I also felt I could add to the safety aspects, and employ the more rigorous engineering certification testing methodology similar to what I had learned in the aerospace industry,” he says.

    The backyard coaster has strict safety rules: no one is allowed near the track when it’s running, seat belts are used and the carts are stored safely away from the tracks when not in use.

    “Is this more dangerous than sitting on the couch? Yes. But due to the controlled nature of the ride, extensive testing and safety precautions; I feel that it’s at least as safe as swimming pools, trampolines, skateboards, or any number of other things we let our kids do just because we’re more used to them,” he says.

    Gregg now owns and operates three backyard roller coasters — with the help of his grandchildren.

    And now he has uploaded a video of two of his six grandchildren testing out one of the timber and metal contraptions.

    He has to push the cars up the first hill himself, but once they have picked up momentum they take themselves around the track with no need for further human intervention. (SD-Agencies)