McDonnell's take on the Rotodyne concept
McDonnell's take on the Rotodyne concept
I found the attached concept drawing in a McDonnell light VTOL transport study dated February 1960. It is hardly necessary to point out the obvious Rotodyne influence; the only relics of the McDonnell XV-1 compound and Model 120 helicopter are the McDonnell rotor system and the vestigial tail rotor, which isn't actually needed for yaw control in a rotodyne! Imitation really IS the sincerest compliment.
The link to the full document is
www.dtic.mil/dtic/tr/fulltext/u2/232716.pdf.
To me, this is the perfect solution:
- a rigid rotor system which allows a low pylon while retaining adequate vertical tail clearance and has very high speed potential compared with the conventional, articulated rotor of the original Rotodyne
- the rigid rotor also makes it possible to unload the rotor almost completely in cruise; this proved impossible in the Rotodyne - its wing incidence had to be reduced to keep the rotor loaded, or excessive flapping would occur
- a pressure-jet system for helicopter operation with the lowest possible weight penalty and life-cycle cost
The problem that the Rotodyne was designed to solve - basically, intermodal transfer delays - is worse today than back then. There is also a new problem - that of increasing centralization, with carriers operating out of central "hubs" and forcing travelers to travel hundreds, sometimes thousands of miles out of their way by traveling from their point of origin to a hub, and from there possibly to another hub, and from there to destination, instead of making the trip directly. Making the trip directly goes a long way toward reducing not only delays but fuel consumption, even factoring in the cost of operating the pressure jet system at takeoff and landing.
ADDENDUM: The rotor system of the XV-1 is
not rigid. It is semi-rigid, since there is no lead-lag hinge, but there are still flapping hinges. What makes it so much more stable at speed than a conventional articulated rotor is not the mere removal of one degree of freedom, but the rotor head system designed by Hohenemser which couples flapping and feathering, and has independent delta-three angles for collective and for cyclic flapping/feathering. Brilliant! Though it does have problems at low rotors speeds and when starting in a high wind, which a later patent by Hohenemser, taken out while he was at McDonnell, attempts to fix.