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Flutter Free FLight Envelope eXpansion for ecOnomical Performance improvement

Periodic Reporting for period 3 - FLEXOP (Flutter Free FLight Envelope eXpansion for ecOnomical Performance improvement)

Reporting period: 2018-06-01 to 2019-11-30

The FLEXOP project is about developing multidisciplinary design capabilities for Europe that will increase competitiveness in terms of aircraft development costs. A closer coupling of wing aeroelasticity and flight control systems in the design process opens new opportunities to explore previously unviable designs. Results of the project will help certification standards for future EU flexible transport aircraft. Within WP1 the consortium designs the demonstrator applicable for scale-up and designs the different sets of wings and develops the suitable mathematical models of these designs. Within WP2 the flutter prediction and control design methods are addressed including 3 tasks: control oriented modelling, flutter analysis/prediction and flexible aircraft control methodologies. WP3 deals with the demonstrator related design, manufacturing and integration. Predictions and real world implementation meets in WP4 where the demonstrator is flight tested (including implementation of flight control laws and ground testing). The methods and tools are validated against flight test data, which serves as a baseline for scale up studies. WP5 deals with coordination, exploitation & dissemination. The partners have successfully mature their tools and methods in a multidisciplinary collaboration and were able to prove most of the project aims. The demonstrator aircraft was successfully flown and the obtained flight test data proved the performance claims coming from simulation. Also, the technology for aeroelastically tailored wings have been shown to industry and its impact could be substancial. Especially, since the scale-up study showed a fuel efficiency improvement of more than 8% or payload increase of more than 25% w.r.t. the baseline (state-of-art) configuration. Dissemination and exploitation activities were also very successful with large number of scientific publications, popular media appearances and significant attention from industry.
Largely due to the focus of designing and manufacturing the demonstrator a large number of theoretical and practical results have been achieved so far. Several iterations about the wing planform were followed by laying down the draft specifications for the demonstrator aircraft. This was unavoidable since very limited literature and prior experience exists about designing a wing, which will flutter at relatively low airspeed. The investigations were later followed by detailed mathematical modelling and iterative development of the aircraft. WP2 investigated the flutter LFT/LPV modelling choices and effects, model order reduction techniques as well as different control design approaches to damp structural modes leading to flutter. The demonstrator aircraft and its wings, avionics and other custom hw and sw components were developed, integrated and tested within WP3. Extensive ground testing of the aircraft (airworthiness and physical behavior) confirmed the design choices and mathematical models of the partners, whet was followed by the flight test campaign where valuable data was obtained and later its correlation with model predictions were successfully shown to the consortium. In parallel the scale-up study showed a potential of 8% fuel efficiency reduction, or 25% payload increase by using the flutter control and aeroelastic tailoring tools during aircraft design. The results have been presented at numerous conferences, like part of the plenary talk at IFASD and also in two joint sessions at the AIAA Scitech conferences. Moreover the results have featured in German and Hungarian television, radio and newspapers. All the members of the consortium reported significant exploitation potential, by using the tools and methods and moving them towards product development, create further collaborations as well as using the results in University education.
FACC experimented with very thin ply technology to manufacture aircraft structural components (carbon fiber and glass fiber), also gained insight in manufacturing and integration of FBG sensors and experimental testing of wing structural deformations under loads. TUM gained expertise in designing wings for flutter, including tuning masses and joint structural/aerodynamical optimization, improved their knowledge in operating UAS in the common airspace. TUD gained insight in aeroelastic tailoring methods applied to manufacturable aircraft structures, improved their know-how on aircraft overall optimisation to include FEM in preliminary design. AGI-UK gained insight on the properties of aircraft wings using different design criteria (tailored vs. non-tailored). AGI-G gained insight on the characteristics of flutter frequency and modes, caused by tuning masses on the wing, also in 3D printing flight control surface parts. INASCO gained insight on embedded implementation of fibre brag sensing on small-scale instrumentation and also on reverse FEM methodology to recover loads from FBGs. SZTAKI gained insight on model order reduction of large scale LPV systems, and on automatic code generation for HILs testing environment. DLR gained insight in controllability of flexible structures with pre-defined control layout, where large scale FEM and aerodynamic models are included in the design. The control oriented modelling toolchain, developed by DLR and TUM is also beyond SOA. RWTH and AGI-G gained insight in the scale up related abstraction level, the use of standard data sharing protocols across different locations is clearly the way of the future.
The demonstrator aircraft has flown with aeroelastically tailored wings what are designed for passive load alleviation, this is a World's first. Moreover in the wing there are more than 10 distinct design regions, while in the first aeroelastically tailored wing aircraft, the X-29 has only 1 design region, an no other aircraft to date has more than one.
Moreover the simulation, analysis and synthesis tools and methods have been matured via the collaboration of the partners and reached a much higher maturity level, from which the whole European aerospace research community can benefit. These tools and methods have been also validated by ground and flight test data, and the possible mechanisms to update and adapt the methods based on new experimental data have been also developed. The advanced sensing and shape reconstruction methods via novel sensors were also developed for the first time in Europe, after the X-56 have flown with FBG sensors in the US.
The scale-up showed a potential of 8% fuel efficiency improvement, what has a significant potential to help reducing environmental footprint and make aviation greener in the near future. The developed methods and tools also confirmed the applicability of active flutter mitigation techniques, what might be included in the certification of new commercial aircraft by EASA and FAA in the near future.
Direct drive actuator CAD
Demonstrator on display at FACC
Ground control station layout
Fully assembled flight control computer stack
Fatigue testing of 3D printed parts
Simulation view for pilot training
Fligh test area at EDMO airfield
Aircraft conceptional design with payload and control surface layout
CAD drawing of the aircraft including wings and outer skin
Finite element model of the demonstrator
CAD drawing of the aircraft fuselage with avionics components
Velocity tracking during the simulated test of the full N.L. -0 model
Conceptual drawing of the Flexop demonstrator in flight
Mode shape of the flutter mode, with external mass layout
FBW system layout for flutter mitigation