Adaptive twisting of a fibre reinforced composite aircraft wings

Design team members: Adam Bruecker, Winnie Leung

Supervisors: Prof G. Heppler, Christian Anhalt

Background

Composite materials for aeroplane construction

Composite materials have proven to have very high strength-to-weight and stiffness-to-weight ratios, which is a very desirable property for aircraft design and construction. Due to the remarkable specific properties of composite materials, component weight savings of up to 30% have been achieved. This technology has been progressing in the aircraft construction industry as more and more parts of the aircraft are made from composite materials.

The use of composite materials in aircraft construction offers other possibilities, given that composite materials, unlike metallic materials, have different properties in different directions. For instance, depending on the fibre alignment, the material may be stronger or stiffer in a certain direction. A section of material could also be induced to twist in a certain direction, if forces are applied in the appropriate fashion to the material e.g. coupled extensive trussing. In fact, such exists for all materials, however the ability to influence material properties of composite materials by modifying their construction allows us to tailor their behaviour in a desired, predefined manor. (See Figure 1)

composite material construction
Figure 1 : Composite material construction

Improving flight efficiency through manipulation of aerodynamic loadings

The wings of modern long-range aircraft are characterized by a large wing span and a high aspect ratio. The slimness has the disadvantage of large deformations in bend and torsion, if they are not rigidly built. In addition, the „wash out“ phenomenon occurs as a result of the sweep of the wing which makes the arircraft difficult to control at high velocities. Since the wings of aircraft are currently only passive structures, increases in aerodynamic efficiency can only be achieved by changing the velocity or weight of the aircraft.

With the ability to actively manipulate the coupling between the wing exterior torsion and the angle of incidence, an optimal deformation suited for different phrases of flights can be achieved. An active system can potentially be implemented directly in the load path of the outer part of the wing, thus providing the capability of active deformation, at any time, to achieve an optimal wing configuration.

Due to the large forces required to deform the wings and the rigidity of the wing, it is assumed that this deformation will not be achieved using Piezo-ceramics or SMA wire, but from conventional hydraulics actuators. By a direct twisting of the outer wing, the lift of the wing is shifted, concentrating the force more towards the fuselage. This reduces the bending moment at the point where the wing and fuselage are connected, which substantially decreases chances for the material fatigue in this area.

A large part of the design process will be the determination of the prescribed aerodynamics loadings to design the structural deformation of that structure. Here, the reaction of the wing deformation to the aerodynamic loadings will be examined, as well as the resulting structural deformations. It is hoped that significant improvements can be reached with respect to lift, resistance reduction and weight, which will lead to a more environmental, safer and more economic flight.

Project description - adaptive twisting of wing

This project aims to look at deformation of the outer part of an aeroplane wing, and how this deformation can be used to improve the flight characteristics of the aeroplane. More specifically, the integration a deforming wing tip system into a transsonic aeroplane to optimize the flow, load, and structure control during the phases of flight where lift is most required, with the respective flow and operating conditions taken into consideration. Objectives in examining the use of composite building material and the mechanics of the adaptive twist were set out in the design phase.

The purpose of this project is to integrate a system into a transsonic airplane to optimize the flow, load, and structure control during the phases of flight where lift is most required (takeoff/landing), with the respective flow and operating conditions.

In summary, it is hoped that:
The operating cost will be lowered, as well as a reduction in fuel consumption.
Due to controllable structures with active load control and contour adjustment, planes can be less sensitive to high frequency turbulence, as well as improved gust load reduction.

Problem statement

To achieve maximum overall aerodynamic efficiency of flight mechanics against aeroelastic conditions, the outer portions of aircraft wings, made out of laminated fibre reinforced material aligned in an optimal fashion, will be designed to have the ability to actively twist through active torsion mechanisms.

Design methodology

Objectives breakdown

Study the aeroelastic behaviour of a flat plate built out of laminated CFRP (Carbon Fibre Reinforced Plastic)

  • Determine the patterns between the fibre alignment of the material and the corresponding twist reactions.

  • Aeroelasticity: effects aerodynamic loadings on the flat plate model

Design the wing section (as a flat plate) built out of CFRP

  • Decide on proper construction (fibre alignment, material layering, configuration of ‘plates’) to achieve desired twisting motions.

Model evaluation: Approximation of the aerodynamic benefits of the resulting design

  • Determine if there is a reduction of the bending moments at the junctions between the fuselage and the wings

Devise a way to mechanically twist the wing.

  • How to apply forces to the composite construction? Hydraulics? Piezoelectric actuators?

  • Power supply system considerations

Design process (in accordance to above objectives)

1. Identifying needs (Reduction of Project Scope)

First approximation of the aerodynamic benefits of twisting the outer portion of the wing

Reduction of bending moment at the junction between the fuselage and the wings
Divide project focus into
Flat Plate Modelling of CFRP with aerodynamic considerations (incompressible subsonic inviscid flow)
Structural design of Active Torsion Mechanics for the outer portion of the wing – black box approach: given I/O, without details of model within, design transfer function to achieve desired I/O relationship.

2. Planning and specifications (overall goals, constraints, boundary conditions)
Flat plate modelling

Develop a working understanding of the mechanics of laminated fibre reinforced material (properties, characteristics and reactions to external forces)
MATLAB programming to simulate material behaviour with respect to loadings (bending coupling, twist coupling)
Active Torsion Mechanics
Technical specifications: target twist angle, target time constant and displacement

3. Concept generation
Flat plate modelling

different alignments of material that will achieve the desired twisting motion
Active torsion mechanics
Investigate means of applying forces on the structure – Hydraulic actuators? Electrical Motors?
Placement of these actuators/ motors
Power and bandwidth requirement (effective operation frequency range)

4. Concept selection
Select the optimization scheme - optimization problem: Genetic Algorithm – solution selection
Evaluation matrix/ criteria that defines ‘desired twisting motion’

5. Concept testing
Presentation of the concept through sketches
Mathematical modelling of the concept
Emulation/ simulation of concept’s behaviour under specific loadings

6. Construction and testing
Physical Construction of prototype
Testing of Prototype