Think chicken, rather than Dave Grohl, and it will make sense.
Doh! Thank you for solving that particular ( decades-old ) mystery! I actually groaned when I read that, it seems so obvious now.
One other that occurred to me this morning was 'Mouse' for the AAC Sioux. Though they weren't anything as quiet as mice, clattering overhead...
'Robbo' for anything in the Robinson helicopter brochure. 'That Bloody Robbo Again' after a couple of hours of spotting.
'Belslow' occasionally encountered from ex-service personnel for the Belfast though the Shorts people I know boringly just called it 'Belfast' or 'her'.
'Bag' reportedly for RN Sea King AEW but I never encountered that one personally.
'Tiff' and 'Tiffie' rather unimaginatively for Typhoon.