Final Project's Outcomes

Objectives
The main goals of GLAMOUR projects are the following:

• Validate the Load Alleviation techniques based on control architectures defined by ITD member
• Develop of alternative control schemes
• Design and manufacturing of a wind tunnel model representing half GRA aircraft
• Perform wind tunnel test under gust excitation
• Draw a final assessment on the global benefits achievable using technologies in both design and off‐design flight conditions

The GLAMOUR project appears as especially challenging for two main reasons. At first for the complexity of the model to be tested, i.e. a complete aeroelastic model, fully instrumented so to measure the relevant aeroelastic responses (accelerations, displacements, section loads, actuation forces) by means of embedded sensors as well as external optical measurement systems, and equipped with different control surfaces. On the other hand, for the test conditions to be investigated, allowing for a deep validation of proposed GLA concepts in a very realistic flight environment.

Description of work
The activity carried out during GLAMOUR project has been distributed along two different time periods, for a total of 34 months of activity. During the first period the activity has been focused on the following intermediate goals:

• To develop new Gust Load Alleviation control strategies to be applied to the reference Green Regional Aircraft (GRA) and to compare the obtained results with ones available using the original LA strategies proposed by the ITD.
• To define the architecture of the wind tunnel model with a special attention to the geometric scale of the model and to the dynamic scaling strategies.
• To identify the most suitable configuration for the wind tunnel model. Indeed, the half aircraft model is tested in an unusual configuration with the fuselage connected to the floor of the wind tunnel testing room and the wing in vertical position.
• To identify a possible design and manufacturing technology able to match the requirements related to the dynamic scaling.
• To design the servo controllers able to match the main testing requirements as well as the space constraints available to install them inside the model's wing and tailplane.

The research activity carried out during this first research period has delivered the following main results:

• The control laws proposed by partners POLIMI, UNIVBRIS and IIT were able to reach a wing root bending moment reduction ranging from 10% to 35%, where the highest values are obtained by the control architectures using the Angle of Attack sensor. Indeed, it was shown that an early warning of the upcoming gust may allow an aircraft response that reduces the gust loads dramatically using information from the aircraft nose sensor to pre-empt the incoming gust, and move the control surfaces in advance. The effectiveness of the different control laws has been demonstrated on gust family of different wavelengths.
• For what concerns the wind tunnel model, the geometrical scale has been frozen at 1:6 while the scaling strategy selected is the so-called iso-frequency, with respect the real aircraft. The main reason was to keep the bandwidth requested for the actuators limited and compatible with the maximum space available to embed them inside the model wing.
• The wind tunnel model, is connected to the wind tunnel floor with an ad hoc system, called Weight Augmentation System (WAS) able to guarantee the free plunge and pitch motion, but configured so to be able to reproduce an artificial gravity, necessary to trim the model due to the vertical position of the wing.
• A preliminary configuration in terms of hardware and software for the actuation systems to be used for ailerons and elevator has been selected and designed, based on a high performance brushless motor connected to the control surfaces by means of belts.
• Finally, a structural configuration for the wind tunnel model has been identified, based on a flexible wing obtained using a single carbon fiber spar and several aerodynamic sectors. The section of the spar has been obtained through an optimization process so to match the stiffness properties requested by the dynamic scaling strategy adopted. For what concerns the fuselage and tailplanes, they have to be considered rigid. To allow best possible adaptation of the model inertia, the fuselage structure need to be as light as possible. The structural configuration is a light polymer fuselage skin structure supported and stiffened by an internal carbon fiber, from wing to horizontal tail plane.

Once finalised the main choices and design strategies, the activity performed during the second research period aimed at the following targets:

• Finalize the design and manufacturing of the wind tunnel model and of the Gust Generator.
• Complete the ground test activity for model validation, including static test and GVT in different configurations.
• Finalize the measurement and control system to be used during the wind tunnel test campaign.
• Perform the wind tunnel test campaign to validate the different gust load alleviation strategies developed and implemented during the project activity.
• Assess the obtained results and the possible future implementation of such as techniques on future aircraft.

Results
During the project, a range of control laws have been developed and compared with previous laws, developed for the ITD, for the gust loads alleviation of a GRA simulated aeroelastic model. It was shown that all of the approaches were capable of achieving good loads reduction based upon the wing root bending moment. A range of different weight cases, flight conditions and gust lengths were considered. In some cases the loads alleviation was significant. No one control law could be considered to be better than the others.
A scaled wind tunnel model was designed, and the control laws applied to a simulated version of this model. Similar loads alleviation to the full scale model was achieved by all of the control laws. A unique half-aircraft model was designed and manufactured, in combination with heave and pitch motions and also gust generation vanes. A sophisticated sensor set-up was implemented in order to be able to simultaneously measure a wide range of displacement, accelerations, loads and control surface rotations. Apart from a minor issue with friction, and the inability to be able to put representative fuel weight into the model, the wind tunnel model is a great achievement and is a valuable resource that should be used in future research programmes in this technical area.

Figure 3: The wind tunnel model fuselage (left) and wing (right) finalization.

The experimental test campaign validated all of the findings from the simulations.

a) Timeline & main milestones
The GLAMOUR project started in February 2014 and finished end of November 2016. During more than two years of research activity many relevant mail-stones have been reached, among the others:

1. Selection of LC&A CL concepts
2. WT Gust Generator Critical Design Review
3. WT Laboratory Critical Design Review
4. Test Plans: Static Check, GVT, WTT
5. Static check and GVT
6. WT Tests and Results
7. Overall assessment of project results

b) Environmental benefits
GLAMOUR addressed the validation of Load Alleviation technologies by means a dedicated design activity coupled to an extensive experimental activity. The project objective is directly related to aircraft performances in terms of load alleviation, reductions of maximum stress with and a potential weight saving and consequently fuel saving, so impacting the quality of future aircraft design and the global impact on the environmental.
The impact of GLAMOUR will be felt through a comprehensive design and evaluation of the proposed LA concepts by means of numerical tools and analysis together with dedicated experimental validation.
The potential of new control strategies proposed into GLAMOUR will has been assessed by comparing the obtained performances with ones achieved adopting the already available approaches proposed by ITD member and to other related design requirements.
GLAMOUR is oriented towards the objective of the industrial development of the European regional green aircraft. This kind of transport system would directly derive benefit from the LA solutions offered by the project in terms of new technologies for active aeroelastic control, response alleviation, sizing loads mitigation and hence contributes to reduced emissions towards the challenging target set up by ACARE.
Furthermore, GLAMOUR combines advanced control, aero-servo-elastic and structural design and optimization which is, up to now, rarely seen in the European research programs. Hence, GLAMOUR will influence and encourage future research programs to focus more on multiple disciplines not only in the analysis of the performance but also in the design of new innovative concepts. GLAMOUR will thus provide an impact on the European aerospace research and industry.

c) Maturity of works performed
GLAMOUR project investigated different concepts and technologies. For what concerns the active control architectures for gust load alleviation on full aircraft they can be considered more than mature, and immediately applicable to the real aircraft. The main issues concern the integration with the flight control systems and certification requirements impacting safety, maintenance and costs.
For what concerns the technologies specifically developed for wind tunnel testing, they appear as very reliable and ready to be used for future applications. The installation of half model on a dedicated Weight Augmentation System opens new possibilities in terms of applicable gust or turbulence profiles together with the possibility to almost eliminate the effect of the friction that always affected the wind tunnel tests on half models with free-free degrees of freedom.
The 3D printing technology adopted for the aerodynamic sectors of the wing, combined with new, more performing materials, could represent in the future a very reliable and efficient technology for the manufacturing of wind tunnel models with reduced costs and time.
The optical measurement system, already used since many years in different field of the industrial engineering, could represent a new significant approach for ground testing due the very large bandwidth and the almost noise-free capability to measure the structural displacements remotely without wiring.

Figure 4: The optical measurement system (left) and the GLAMOUR model ready for testing (right).