The main objective of this project was to explore the possible solutions for cleaning devices capable of clearing out the leading edges of business jets or airliners. Particular attention was carried out in the modification of already existing devices on sailplanes. The cleaning concept was compatible with the surface treatment/coating of the leading edge of commercial aircrafts.
In the first step, the work focused on concept trade-offs. Innovative solutions were compared with the already existing devices used for sailplanes. An evolution of the existing systems was their adaptation for wings with high lift devices, such as slats, and also for the space left inside the wing because of the presence of fuel tanks. Then, the dynamic elements of the already existing systems, which are actuated by hand or compact electrical motors, were redesigned because of the difference in efforts acting on an aircraft and a sailplane; but also, to ensure the level required by civil aviation certification.
The consortium was led by EPFL with a small company in Austria for consultancy on the sailplane devices.
Investigations made for the definition of a wing leading edge cleaning system led to a solution operating after take-off, in-flight conditions. The main system had been divided in three subsystems:
- A movable subsystem: Composed of two modules, this system is located on the wing skin. The cleaning module ensures the cleaning of the zone to clean. Composed of sponges and/or wires the module is placed inside a shuttle whose main functions are to ensure the link between the cleaning system to the wing structure, to allow the displacement of the cleaning module along the wing span and minimize the external aerodynamic loads applied on the cleaning module.
- A driver and guidance subsystem: Its function is to ensure the displacement of the movable subsystem from wing root to wing tip and backwards. It also has the function to absorb some of the loads applied on the movable subsystem and avoid his separation with the aircraft structure. This subsystem is located inside the wing structure.
- A storage subsystem: Defined to ensure a minimal impact of the cleaning system on the aerodynamic performances before and after the cleaning operations, the retained solution consists on the storage of the movable subsystem inside the fuselage structure by the opening of a door located at wing root.
CFD studies demonstrated that the shuttle is exposed to non-negligible aerodynamic forces. As a first approximation, the pressure distribution on the shuttle can be considered the one on the wing at shuttle location in absence of cleaning device. This leads to a strong normal force on the shuttle upper side which tends to generate an opening hinge torque as well as to separate the shuttle from the wing suction side. These effects can be counteracted by adding some passive aerodynamic control surface. The shuttle size has to be minimal to have affordable aerodynamic efforts on the cleaning device; thus, the cleaning module has to be chosen taking into account this extra constraint. Note also that the magnitude of these aerodynamic efforts required to reinforce wing skin at the location where the shuttle upper part roller passes, moreover if aerodynamic forces are used to help clamping the cleaning device on the wing leading edge.
The analysis of the first implemented solution on the Airbus NLF wing showed some limitations regarding the efficiency of the cleaning system after IFAM first experiments. Nevertheless, investigation made so far on the three subsystems allowed the definition of good solutions ensuring the achievement of the technical requirement defined for this project.
If the implementation of the inner rail with a wing skin crack is structurally feasible, a shuttle2 should allow the implementation of a cleaning module. Indeed, investigations for the enhancement of the cleaning module are needed. The design of the shuttle as defined so far should allow the implementation of a large range of solution for the cleaning module. Minor changes should be applied to the presented shuttle keeping in mind that due to the aerodynamic forces acting on the shuttle, its size has to be minimised (shuttle must just fit the cleaning module) and its shape must be optimised.
If the wing skin crack cannot be implemented, a system similar to the one for Dassault NLF wing, can be envisaged.
The solutions defined for the Airbus NLF wing test case are implemented by assuming a wing-skin crack opening allowing a rigid link between the movable subsystem and the driver cart located inside the wing structure. This solution has been mainly motivated for safety issues as the cleaning operation will occur in flight conditions. If implemented after the 1.5 % chord length at the wing pressure side, the crack opening and the joints remaining after the closure of the crack are of no major importance regarding the full efficiency of the Airbus NLF wing. As this solution is acceptable for the Airbus test case, the presence of wing-skin crack opening is not possible for the Dassault NLF wing test case.
Following system analysis, the approach for the Dassault NLF case is:
- Definition of a solution for the driver and guidance subsystem allowing the motion of a cart placed on the wing-skin (thus subjected to aerodynamic forces) without any alteration of the wing skin i.e. without the presence of a wing-skin crack and ensuring all the safety requirements.
- Adapt the solution for the movable subsystem (cleaning module and shuttle).
Note that no investigations have been made on the storage subsystem, no major improvements on the solution presented in the mid-term report have been defined.
In order to allow the cleaning system to move along the wing span in an autonomous way without any alteration of the wing-skin, investigations led to a solution using magnetic forces to ensure the link between the driver cart (located inside the wing structure) and the movable subsystem (located on the wing skin). A study of feasibility conducted at EPFL showed that the size of a magnet able to ensure the safety and the technical requirements has not to be larger than 130 x 65 x 20 mm. This study has been conducted taking into account a wing-skin of 5 mm and with the enhanced shuttle shape i.e. for the highest and worst oriented resulting aerodynamic force on the cleaning device. As the resulting main dimensions of the magnets are quite suitable regarding the place available in the Dassault NLF wing, a solution ensuring all the technical requirements defined to ensure reliability and safety of the cleaning system has been defined.