The motivation for this research was to respond to requirements for high impact energy absorption in aircraft landing gears.
Typically, shock absorbers are designed as passive devices with characteristics adjusted either to the most frequently expected impact loads or to ultimate load conditions. However, in many cases the variation of real working conditions is so high that the optimally designed passive shock absorber does not perform well enough.
In contrast to the passive systems, this research focused on active adaptation of energy absorbing structural elements, where a system of sensors recognises the type of impact loading and activates energy absorbing components in a fashion that guarantees optimal dissipation of impact energy.
The ADLAND project dealt with evaluating the options for adaptive shock absorbers to be applied in aircraft landing gears. Analytical design procedures were developed to simulate different potential design options and the best practical solution was determined. The different hardware components regarding adaptive shock absorbers were developed and tested with regard to an adaptive landing gear model.
The project objectives were:
- to develop a concept of adaptive shock-absorbers;
- to develop new numerical tools for the design of adaptive vehicles and for the simulation of the adaptive structural response to an impact scenario;
- to develop technology for actively controlled shock-absorbers applicable in landing gears (there are two options: Magneto-Rheological Fluid-based (MRF) and Piezoelectric Valve-based);
- to design, model and perform repetitive impact tests of the adaptive landing gear model with high impact energy dissipation effects; and
- to design, produce and test in flight the chosen full-scale model of the adaptive landing gear.
The approach of the project focused on active adaptation of the energy absorbing system (equipped with sensors identifying impact in advance and controllable semi-active dissipaters) with the ability to adapt to extreme overloading during landing. The term active adaptation refers to the particular case of actively controlled energy dissipater, where the need for external sources of energy is minimised and the task for actuators is reduced to modify local mechanical properties rather than to apply externally generated forces. These applications of active control concept are usually more reliable, stable and cost-effective. Therefore, adaptive systems are more appropriate in the impact dissipation task than their fully active counterparts.
The main tasks defined for the project participants were:
- to develop an efficient methodology and strategy of control for the adaptive landing gears during landing impact (with assessment of its applicability and feasibility study);
- to develop MR fluid in accordance to the requirements defined by the consortium representatives from aeronautic industry;
- to develop, design and fabricate an adaptive landing gear utilising the MRF technology. The task in this problem did cover the following issues: design of the device in accordance to the aeronautic requirements, to develop the control unit, which withstand the timing requirements occurring in the case of the landing impact, laboratory validation of the developed and fabricated devices;
- to develop, design and fabricate a piezo-actuated adaptive landing gear, with controllability of the internal hydraulic fluid flow by means of a piezo-valve. The task in this problem did cover the following issues: design of the device in accordance to the aeronautic requirements, to design an appropriated fluidic duct and the piezo-valve head, to develop the control unit, which withstand the timing requirements occurring in the case of the landing impact, laboratory validation of the developed and fabricated devices;
- to validate experimentally in the laboratory conditions, the landing gears with the active systems for small passenger aircraft (1.1 t) and for small cargo aircraft (8 t), and the final task was
- to perform the field testing of the developed device on the small cargo aircraft.
In the frame of the project development, a large effort was put into fundamental research of effects and techniques of active shock absorber control for landing gear application. The most significant achievements were:
- development of a series of types of MR fluids;
- MRF behaviour analysis and prediction;
- design of MRF damping device;
- lab and full scale tests of MRF damper;
- development of piezo actuated damping valve shock absorber; and
- development, design, and test of corresponding control equipment.
An important milestone in the project was the the first flight test of a piezo-actuated adaptive aircraft shock absorber prototype in EU and worldwide.
In the ADLAND project, FhG-ISC developed various new magnetorheological (MR) fluids for the potential application in the shock absorber of a landing gear as well as two damping devices, a drop test facility with a modularly designed shock absorber and a vibration damper with fail-safe characteristics.
FhG-ISC strongly extended its know-how concerning formulations of MR fluids aimed at special profiles of application-relevant properties. Several new compositions based on different material components were elaborated and evaluated in testing devices. It is expected that this knowledge will also be exploited for other applications in future research and development (R&D) projects.
Further expertise with a high potential could be gained in the magnetic circuit design for magnetorheological dampers. A new damper which shows an excellent performance in terms of controllability was developed. This device offers a very good base for the development of new MR technology in the field of impact absorption and vibration damping.
The results achieved in the project were planned to be exploited in a patent application and disseminated in several publications.