Originally Posted by
Porky Speedpig
Solves a mystery - it sounded like a brace of Vanguards over here!
Actually in powerplant terms it's exactly half a Vanguard.
Used to live in The Wirral as a kid, Vanguards on LHR-Belfast were certainly audible from the ground there in the cruise, probably at 20-25,000 ft. Likewise one running up for departure from Edinburgh's old runway 31 could be heard on quiet winter evenings from up at Edinburgh Castle. I don't know why they were so noisy when their close competitor for size and power, the Bristol Britannia, was the opposite, the "Whispering Giant". I suspect the props rather than the powerplant, I believe De Havillands for the Vanguard and Dowtys for the Britannia.