What a pleasant summer evening, nice temperature, dinner in the garden, for once clear skies, then a slowly rising gentle Zuuuuumzuuuuumzuuuuum of distant but slightly unsynchronised propellers. Not a Q400 out of London City, but I scan skywards, and there it is, heading slowly due westwards directly overhead at altitude. There's only one thing that sounds like that, it's a Ukrainian 4-prop Antonov 12 at 21,000 feet. Built 1971, 48 years young. It left Plovdiv in Bulgaria this afternoon, stopped at Frankfurt Hahn, and passed overhead on its way to Shannon, which quite likely means it will be heading out across the Atlantic.
https://www.flightradar24.com/data/aircraft/ur-cjn
** EDIT **
And amazingly, an hour later, a second An-12, just as noisy, on quite a different track, Vitoria in Spain to Paris then Birmingham, heading northwards crosses the route of the first one right overhead here
https://www.flightradar24.com/data/aircraft/ur-cnn