Definition of "Rumpty"

In his initial assignment to Training Squadron No. 4 of the Royal Flying Corps, Field began his flying in the Maurice Farman "Shorthorn" trainer, sometimes called a Rumpty. […]

2007, Jack S. Ballard, War Bird Ace: The Great War Exploits of Capt. Field E. Kindley, page 23

To do him justice, there were a few wires which he did not loosen in climbing into the cockpit, but then the machine, a Henri Farman (or Rumpty as they were commonly known), was at all times hard to get into.

2009, Ira Jones, King of Airfighters: The Biography of Major Mick Mannock, page 42