UFO sound

Does anyone out there know exactly how they produced the sound for the
UFO's? I've always liked that whirring echoey sound, but I've never been
able to pinpoint exactly what it is. I know most of the time, especially
in older TV and movie productions the "sounds" for flying saucers and space
ships were often something you'd never imagine. To me the UFO's sound like
some kind of weird vacuum cleaner with something being done to it, but
processed through a delay unit of some kind...probably an old analog tape
echo unit. I'm also curious how the sound of a damaged UFO is
produced...such as when Sky One hits one but doesn't blow it up, and it
spins wildly to the earth's surface while billowing out the red smoke. If
anyone knows, how about posting a reply here in the SHADO list. Thanks.