The Tilt Wing Design For A Family Of High Speed VSTOL Aircraft

The tilt wing is emerging as the most efficient, most cost effective, safest and easiest to operate powered lift concept for high speed VSTOL aircraft. It is shown that the tilt wing design has many operational and cost advantages over the tilt rotor. Tilt wing development started with the Boeing Vertol VZ-2 in the mid 1950’s. This was followed by the Hiller X-18 in the early 60’s and the LTV/ Hiller/Ryan XC-142A in the mid 60’s. In the late 60’s and early 70’s the Canadair CL-84 tilt wing was successfully tested and demonstrated. This paper discusses the unique U.S. Patent (3,029,043) by Gary B. Churchill for a tilt wing “geared flap” that simplifies the flight control system of the tilt wing in hover and in transition to and from aerodynamic flight. Recent simulation evaluations conducted by NASA Ames in their Vertical Motion Simulator (VMS) demonstrates the progress being made to adopt this control design to future tilt wing aircraft. It is shown that future tilt wing aircraft will benefit from the rapidly advancing state of the art in structures (composites where appropriate), advanced propulsion systems and power trains, advanced computerized flight control systems, advanced glass cockpits and avionics. A clearer understanding of the major differences between the tilt wing, tilt rotor, helicopter and other vertical lift concepts is bringing to the surface the true operational and cost advantages of the tilt wing for high speed VSTOL aircraft. The paper singles out several major advantages of the tilt wing design over the tilt rotor. In tilt rotor aircraft the rotor wake impinging on the upper surface of the wing, fuselage and sponsons in hover creates a vertical down force, called download. This download seriously reduces the tilt rotor aircraft’s useful load and thus reduces valuable payload and/or range. it also cancels out what lifting advantage the rotors lower disc loading would have over the higher disc loading propeller used on tilt wing aircraft. The tilt wing aircraft has no download in hover. A weights comparison between the CL-84 tilt wing and the XV-15 tilt rotor, and a similar weights comparison between the XC-142A tilt wing and the V-22 tilt rotor, each pair with matching power, reveals interesting results which clearly favor the tilt wing. The much higher propulsive efficiency in level cruising flight for tilt wing propellers compared to tilt rotor rotors is reviewed. These reviews and other technology comparisons, as they relate to the design process, are invaluable as we move forward with a family of high speed VSTOL tilt wing aircraft to meet future global markets. The authors suggest a family of civil VSTOL tilt wing aircraft that are sized to carry 4, 9, 19, and 30 passengers or 4 LD-3 cargo containers. The authors predict that larger size vertical lift aircraft, tilt wing or tilt rotor, due to limited acceptable hovering downflow, will be more appropriate to STOL operations using maximum 500 foot long runways. 100 to 150 passenger tilt wing STOL aircraft using partial tilting of the wing are practical and feasible. A 9-passenger, 11 seat, tilt wing vehicle about the size of the Canadair CL-84 is considered the most feasible first generation high speed VSTOL aircraft for civil roles including search and rescue (SAR) missions. The history of military aircraft that have evolved from civil aircraft development is reviewed. A prediction is made that future civil tilt wing aircraft will lead to several military tilt wing derivatives. In keeping with the AHS forum theme “Pursuing Global Partnerships”, the struggle to find innovative financial partners from inside or outside the United States is covered.