The information about Bell Helicopter Model 47, NC-3H described on this website was obtained from the following sources:
Bell Helicopter Textron Story by Brown
Bell Aircraft Since 1935 by Pelletier
Interviews of Ed Unwin and Harry Gilliand of Bell Helicopter
Roy Coleman letter to the CAA dated 04-08-46
Letters between Bell Aircraft and the CAA dated January and March 1951
Bell Aircraft and CAA Documents dated 05-15-46 and 06-14-51
Up with Bell Helicopters by G.J. Butterbaugh
Research conducted by Harry Gilliand, Bell Helicopter Test Pilot and Historian
Research conducted by Paul D. Faltyn, Niagara Aerospace Museum