“The Development of a Mechanism for the Actuation of a Morphing Winglet”
This project follows the design and development of a mechanism for the actuation of a morphing winglet for use during a typical civil aviation flight mission. The advantages of such a system are described below and the results within this project focused on displaying the system and structures ability to cope with the expected forces encountered throughout the flight mission and an analysis of the final designs performance.
This page provides a snap shot over view of the project conducted as part of a bachelors dissertation in Mechanical Engineering with Aeronautics.
Current Winglet Technology
Aircraft winglets are a bio-inspired concept in which a wing has vertical sections towards its tip. These winglets are inspired by bird wings in which the primary flight feathers at the tips of the wing can curl up to an almost vertical angle. This adaptation allows for increased lift without an increase in wing length, which would reduce the turning circle of these birds making it difficult to manoeuvre effectively. This function of the bird wing can be seen clearly on the left wing in the picture below.
Notice the wing tip primary feathers curl upward. Credit: AlaskaStock/Corbis ©
The aerodynamics of a wing are such that the pressure difference between the top and bottom surface create vortex’s at the wing tips, these vortices cause drag for the aircraft. “The drag breakdown of a typical transport aircraft shows that the lift-induced drag can amount to as much as 40% of the total drag at cruise conditions and 80–90% of the total drag in take-off configuration”. [1] The winglets therefore allow for a reduction in these vortices and so a reduction in lift induced drag [2] and an increase in top cruise speed. This therefore increases the wings lift to drag ratio, which allows for more efficient aerodynamics.
Morphing Winglets (Morphlet)
Morphing winglets are a relatively new concept of aerodynamic systems currently being developed for a variety of aircraft from civil to military. With promises of fuel saving, efficiency and manoeuvrability benefits a morphing winglet looks to be a feature of future aircraft wings. Especially with the priorities of many civil aviation companies being a focus on increased fuel and aerodynamic efficiency throughout the flight mission with motivation from both financial and environmental pressures.
Why Morphing Winglets ?
Many civilian aircraft now sport fixed winglets, such as some of the most recent Airbus and Boeing aircraft the A350 and 737 Max respectively; with winglet technology first introduced in the 1970’s these aircraft represent the current operational state of the art in winglet design. Even so all current winglet designs share a common difficulty in that they are fixed, therefore there aerodynamic shape can only be optimised in one state. Therefore winglets, are most commonly configured by optimising the winglet for the whole flight mission and not individual stages. This therefore means that during the take-off, climb, initial cruise, final cruise and landing the aerodynamics of the aircraft are not optimised and therefore have efficiency losses through its drag.
The advantage of morphing winglets is that throughout the flight mission the aerodynamics of the wing can be optimised for each stage (Take-off, Climb, Cruise, decent and landing). When referring to a morphlet that can adjust to all flight mission stages and compared to a fixed winglet “It has been determined that a significant 4.2–6.6% specific air range gain can be accomplished across all cruise phases for a maximum-range mission profile, in addition to achieving a 3.1% lift to drag ratio improvement in climb.”[3]
The above picture shows the required movement of the 737 winglet throughout the flight mission.
Modelling the Expected Aerodynamic Forces using Tornado
Tornado is a computer program used to model conceptual aircraft and solve for various aerodynamic derivatives using a wide range of aircraft geometries. It uses vortex lattice method and models all lifting surfaces as thin plates. Tornado uses MATLAB to run its code and uses a text based interface which allows for the geometry associated with the project to be easily imported and adjusted for its varying cant, twist and rudder angles. Tornado is still in the development phase and is being developed in cooperation between Royal Institute of Technology (KTH), University of Bristol, Linköping University and Redhammer Consulting Ldt.
The above graphs display a section of data taken from the results given by Tornado. Cp distribution top, spanload across wing bottom.
Final Design
The final design concept shows a simple hinged mechanism design and the incorporation of a conventional flap into the winglet which allows for futher refinement of the winglets aerodynamic profile during the flight mission, but also allows for the winglet to use the aerodynamic forces to assist the movement of the winglet between different cant angle positions. It also features two electro-mechanical acuators (EMA's) to drive and assist the motion of the winglet. This design uses conventional aircraft materials and acuators to achieve its motion and so could be approved for use in a much sorted time scale than other efforts using unconventional methods and materials.
Top down view of the exposed internal mechanism showing 2 EMA's.
Rear view of winglip showing winglet in full cant extention and flap deployed.
Rendered view of winglet at around 80 degrees cant angle.
Renderd view of exposed internal mechanism.
Finite Element Analysis (FEA)
FEA was conducted to validate and iterate the design using ANSYS. This therefore then allowed for the definition and selection of appropriate material use.
Principle stress of winglet box section hinge. Under maximum loading.
Deformation of wing box section. Under maximum loading.
Conclusion
The process of conducting this study produced results clearly defining the major aerodynamic loads experienced by morphlets during a standard flight mission and manoeuvres undertaken by a Boeing 737. Showing the proposed design can withstand such forces whilst using conventional methods of actuation of the aircraft control surfaces and standard aerospace grade materials. This study also showed the potential for using those aerodynamic forces as part of the winglet actuation to be developed in further research.
Further Work
Aero elastic study of the effects of using the aerodynamic loads to actuate the winglet.
The possibility of using the aerodynamic loads to actively actuate the winglets requires a full aero elastic study to discern the effects of the winglets moving in such a way that it would not adversely effect the aircrafts stability or performance.
Development of a morphing skin at the winglet hinge point.
737 Above the Clouds.
Featured in the "MADE IN BRUNEL" show 2013.
All content (Graphics & CAD) created by Adam Pinkstone ©
Unless otherwise stated.
Programs Used: Adobe Photoshop, Solidworks, Photoview 360, ANSYS (FEA), MATLAB, Tornado.
References:
[1] Joel E. Guerrero∗, Dario Maestro, Alessandro Bottaro “Biomimetic spiroid winglets for lift and drag control” C. R. Mecanique 340 (2012) 67–80
[2] R. T. Whitcomb, NASA technical note, “A design approach and selected wind tunnel results at high sub-sonic speeds for wingtip mounted winglets”, July 1976, Report number: NASA TN D-8260
[3] D. D. Smith; R. M. Ajaj; A. T. Isikveren; M. I. Friswell "Multi-Objective Optimization for the Multiphase Design of Active Polymorphing Wings", Journal of Aircraft, Vol. 49, No. 4 (2012), pp. 1153-1160.
[4] N. M. Ursarche, T. Melin, A. T. Isikveren, M. I. Friswell, “Technology Integration for Active Poly-Morphing Winglets Development”, Proceedings of SMASIS08, October 28-30, 2008
