1956 - project
A cargo helicopter of twin side-by-side rotor scheme. The D-218 would have been powered by two R-1820-34 engines.
David A. Brown "The Bell Helicopter Textron Story", 1995
This undated, unnumbered project consists of a kind of harmonica-shaped helicopter or flying wing, with a large rotor at each end intended to give the rotorcraft fast forward speed. The planned engines, Wright R 1820 or Pratt and Whitney R 280, are to be so geared that the rotors may be driven by one engine alone should the other fail. They may also perhaps be replaced by gas turbines. In either event, the rotors will have differential lift to even out any uneven loading.
The planned size of this project is approximately that of a Convair 340, and it is built to carry forty passengers over a distance of 480km. It is likely that experience acquired with the XV-3 convertiplane will be embodied in this flying wing.
P.Lambermont "Helicopters and Autogyros of the World", 1958