C-Wing: Application to Large Aircraft

The first application of this concept to an aircraft design study was in connection with recent interest in very large civil transports. Many difficulties remain to be resolved for a successful large conventional design. Airport and manufacturing constraints limit the span of a new large aircraft. The location of the outboard engine is a problem, and the height of the vertical tail becomes excessive. The C-Wing design was proposed as one way of addressing these issues and perhaps improving the performance of such large aircraft. Additional sections of this paper describe the evolution of the C-wing concept and include the following:

Large Aircraft Design

Basic C-Wing Configuration Development

Optimization and Initial Results

Continuing Work

C-Wing Summary

The advantages of the C-wing configuration for a large capacity subsonic transport are listed below. They include those directly associated with the nonplanar wing geometry and those that arise indirectly from the overall configuration shown on previous pages.

Nonplanar Wing:
1. Reduced span or reduced vortex drag at fixed span
2. Efficient trim with short fuselage
3. Improved lateral handling (lower effective dihedral, reduced adverse yaw)
4. Potential for aeroelastic control: prevent aileron reversal, active flutter control
5. Reduced tendency for pitch-up, control at high alpha
6. Reduced vertical tail height
7. Possible reduction in wake vortex strength

Configuration:
1. Improved aero/structural performance through span loading, potential for reduced wetted area
2. Effective use of redistributed wetted area reduces high lift system cost or TO thrust / noise, potential for laminarization.
3. Some advantages of all-wing design with reduced risks: egress, windows, growth, structure, acceptability
4. 2 wing-mounted engines reduce obstacle problem with outer engine / engine out yaw
5. Single deck in wing facilitates loading, emergency egress

Disadvantages:
1. Details of emergency egress remain uncertain
2. Aerodynamics of thick inboard sections still an issue
3. Aeroelastics may be controllable but may need to be controlled

Ilan Kroo (kroo@leland.stanford.edu)