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Adaptive Landing Gears for Improved Impact Absorption (ADLAND)

Final Report Summary - ADLAND (Adaptive Landing Gears for Improved Impact Absorption)

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 objectives of project were:
- to develop a concept of adaptive shock-absorbers;
- to develop new numerical tools for design of adaptive vehicles and for simulation of the adaptive structural response to an impact scenario;
- to develop technology for actively controlled shock-absorbers applicable in landing gears (two options: MR fluid-based and piezo-valve-based will be take into consideration);
- to design, model and perform repetitive impact tests of the adaptive landing gear model with high impact energy dissipation effect;
- to design, produce and test in flight the chosen full-scale model of the adaptive landing gear.

In contrast to the passive systems, the conducted 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 guaranteed optimal dissipation of impact energy.

Up to now, landing gears have been designed as structures with passive oleo-pneumatic shock absorbers or with spring beams as a energy dissipaters. The former has higher efficiency - up to 90 % - and is used in most of airplanes. The latter is used in airplanes with take-off masses not higher than 5 000 kg (2 268 lb), because of low efficiency and low weight. Landing gear (LG) must be designed to meet standards such as JAR 23, JAR 25 or other requirements (civil, military, etc.).

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:
1. 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).
2. to develop MR fluid in accordance to the requirements defined by the consortium representatives from aeronautic industry.
3. 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.
4. 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.
5. 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).
6. 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 high 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;
- development, design, and test of corresponding control equipment.
Meaningful is fact of conducting of 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 could strongly extend 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 profound 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.