A Question for you Chaps

Evening all
Just got a book on the history of the Douglas Propliners DC-1 to 7, excellent book by the way. I came across a bit of a poser when Donald Douglas built several models one of which was and I quote from the book. "Powered by a Whiling Wheel filled with Gun Powder"
I've had a look on Google and can't find anything so can someone tell me what a Whiling Wheel is.
Cheers
A very perplexed Rich
Just got a book on the history of the Douglas Propliners DC-1 to 7, excellent book by the way. I came across a bit of a poser when Donald Douglas built several models one of which was and I quote from the book. "Powered by a Whiling Wheel filled with Gun Powder"

Cheers
A very perplexed Rich
