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Proceedings ArticleDOI

Combined Feedback and LIDAR-Based Feedforward Active Load Alleviation

05 Jun 2017-
TL;DR: A combined feedback and feedforward active load alleviation system and its associated design and tuning methodology that remains very easy to use and tune, thanks to a limited number of parameters that can easily be interpreted physically and that exhibit only very little and very predictable couplings.
Abstract: This paper presents a combined feedback and feedforward active load alleviation system and its associated design and tuning methodology The feedback part is strongly structured and its robust performance across the flight envelope is ensured by the use of a multi-model and multi-objective controller design approach The feedforward function is based on a Doppler LIDAR sensor and the processing of the measurements as well as their physical interpretation combines various ideas from the system identification, the signal processing, and the control design domains The proposed solution remains very easy to use and tune, thanks to a limited number of parameters that can easily be interpreted physically and that exhibit only very little and very predictable couplings The performance and behavior of the active load alleviation functions is shown extensively based on a representative flexible long range aircraft model (based on the Airbus XRF1 configuration)

Summary (1 min read)

Feedforward load alleviation commands

  • Reconstructed wind profile ahead of the aircraft.
  • The synthesis of each controller only needs to focus on a smaller problem (simple constraints, simple goal, and few tuning parameters).
  • Advanced tools (e.g. from the linear and robust control theories) can be used for each of these feedforward control design problems.

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Combined LIDAR-Based Feedforward and
Feedback Gust and Turbulence Load Alleviation
Nicolas Fezans, Hans-Dieter Joos
DLR (German Aerospace Center)
AIAA Aviation June 6
th
2017
Denver, CO, USA
Paper: AIAA-2017-3548

Gusts and Turbulence Cause Loads and Passenger Discomfort
DLR.de • Chart 2 > Combined LIDAR-Based Feedforward and Feedback Gust and Turbulence Load Alleviation > Fezans, Joos > AIAA Aviation > Denver, CO, USA > Jun. 2017
Additional loads must be taken into account in the design of the structure
Reducing the loads acting on the aircraft enables weight savings and
thereby also more efficient aircraft
Additionally cause undesired aircraft motions through the change in
aerodynamic forces and moments (+ coupling with the structure)
can become a safety threat (e.g. for passengers or cabin crew
personnel who are not seated or with their seat belts unfastened)
causes discomfort and passenger anxiety
Three main options:
1. Procedure (e.g. fly slower when in turbulence)
2. Passive load alleviation
3. Active load alleviation

Active Load Alleviation: Feedback vs. Feedforward?
Feedback and Feedforward!
> Combined LIDAR-Based Feedforward and Feedback Gust and Turbulence Load Alleviation > Fezans, Joos > AIAA Aviation > Denver, CO, USA > Jun. 2017 DLR.de • Chart 3
Feedback controller can act on the
flexible modes (e.g. to damp them)
Anticipation is possible with
LIDAR-based feedforward
1
2
3
4
Results

LIDAR
What are Doppler LIDAR sensors?
How can they help to detect gust and turbulence ahead of the aircraft?

Doppler LIDAR
Based on the backscattering of light on particle(s)/molecules of the air
Doppler-shift relative line-of-sight velocity between the particle(s)/molecules
that have scattered the light back and the sensor.
What Are Doppler LIDAR Sensors?
DLR.de • Chart 5 > Combined LIDAR-Based Feedforward and Feedback Gust and Turbulence Load Alleviation > Fezans, Joos > AIAA Aviation > Denver, CO, USA > Jun. 2017
V
LoS
V
RelativeWind
Wind
Problem:
Relative wind components perpendicular to LoS are lost!
And the vertical component at a location ahead of the aircraft is the
most interesting wind information for load alleviation

Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, in-flight remote sensing technologies are considered for two applications: active load alleviation of gust and turbulence and wake impact alleviation and the strong commonalities in terms of sensors and measurement post-processing algorithms are outlined.
Abstract: In this paper, in-flight remote sensing technologies are considered for two applications: active load alleviation of gust and turbulence and wake impact alleviation. The paper outlines the strong commonalities in terms of sensors and measurement post-processing algorithms and presents also the few differences and their consequences in terms of post-processing. The way the post-processing is being made is detailed before showing results for both applications based on a complete and coupled simulation (aircraft reaction due to disturbances and control inputs during the simulation is influencing the sensor measurements). The performances in terms of wind reconstruction quality for the gust/turbulence case and in terms of wake impact alleviation performance for the wake vortex case are shown based on simulations and are very promising.

24 citations


Cites background from "Combined Feedback and LIDAR-Based F..."

  • ...14/23 alleviation function presented in [2] and [3] focuses on the exploitation of the anticipation capability provided by the LIDAR and the certifiability aspect rather than on “inverting” the flexible modes of the airplane to get the maximum alleviation performance at the price of a lack of robustness and the need for adaptive control....

    [...]

  • ...The wind reconstruction results based on the LIDAR sensors are very promising and the combined results of [2] and [3] show that they are sufficient to enable the design of such an effective anticipation-capable feedforward load alleviation function....

    [...]

  • ...Results obtained in closed-loop with both the feedforward and feedback load alleviation functions will be published in the near future along with the design of the control functions (see [2] and [3])....

    [...]

  • ...The way the load alleviation itself is performed (based on this reconstructed wind) is not presented here but can be found in [2] and [3]....

    [...]

  • ...Unfortunately, the authors presently do not have such realistic gust/turbulence wind fields at their disposal yet in order to investigate the behavior of the algorithm (including also the associated load alleviation function of [2] and [3]) on these cases....

    [...]

Journal ArticleDOI
TL;DR: An overview of the DLR activities on active load alleviation in the CleanSky Smart Fixed Wing Aircraft project is presented, using a generic long-range benchmark provided by Airbus on the basis of the XRF-1 model.
Abstract: This paper presents an overview of the DLR activities on active load alleviation in the CleanSky Smart Fixed Wing Aircraft project. The investigations followed two main research directions: the multi-objective, multi-model, structured controller design for the feedback load alleviation part and the use of Doppler LIDAR technologies for gust/turbulence anticipation. On this latter topic, the prior work made in the AWIATOR European FP6 project constituted a reference in terms of demonstrations and the objective was not to repeat these previous investigations with a real sensor in flight test but to develop new ideas for the exploitation of the Doppler LIDAR measurements for gust alleviation purposes. Very fruitful exchanges between industry partners and research organizations took place during this project and all the work presented in this paper has been made using a generic long-range benchmark provided by Airbus on the basis of the XRF-1 model.

23 citations

01 Jan 2018
TL;DR: Optimization studies performed on a representative large transport aircraft wing show that using MLC results in a significant weight reduction, and that concurrently optimized GLA controllers effectively reduce gust loads until they are not sizing anymore.
Abstract: Improving the performance of large transport aircraft requires high aspect ratio and lightweight wings, making aeroelasticity an important factor in wing structural design. Active control of aeroelastic loads can be used to improve the aeroelastic behavior of the wing. Two active load control techniques are considered: Maneuver Load Control (MLC) and Gust Load Alleviation (GLA). GLA controllers are normally tuned using optimal control methods, which use objectives that do not directly relate to load control. In this thesis, it is investigate whether it is also possible to optimize MLC and GLA control parameters concurrently with the wing structure, without the need for optimal control methods. Optimization studies performed on a representative large transport aircraft wing show that using MLC results in a significant weight reduction, and that concurrently optimized GLA controllers effectively reduce gust loads until they are not sizing anymore.

10 citations


Cites background from "Combined Feedback and LIDAR-Based F..."

  • ...feedback control if feedforward is also used, is to guarantee a robust response if the actual system dynamics are different than the system dynamics for which the controllers are designed [46, 114, 141]....

    [...]

Journal ArticleDOI
TL;DR: The significant influence of aileron size and position on overall GLA performance is demonstrated and hence a consideration during the preliminary aircraft design process is recommended.
Abstract: Considering active gust load alleviation (GLA) during aircraft design offers great potential for structural weight savings. The effectiveness of a GLA control system strongly depends on the layout of available control surfaces, which is investigated in this article. For the purpose of wing load reduction, a concurrent optimization of controller gains and aileron geometry parameters is carried out. To that end, an efficient update routine for the nonlinear model of a large-scale flexible aircraft with unsteady aerodynamics is presented. Compared to a GLA system using the original aileron configuration, a 9% performance improvement is achieved. Furthermore, a trade-off study is carried out which enables a target-oriented balancing between individual load channels. The significant influence of aileron size and position on overall GLA performance is demonstrated and hence a consideration during the preliminary aircraft design process is recommended.

9 citations

Proceedings ArticleDOI
11 Jan 2021
TL;DR: Two dynamic actuator concepts are studied by means of CFD methods on a generic wing-fuselage aircraft configuration and it is shown that the TEFs are promising in terms of mitigation of gust induced WBM and the LEFs are able to compensate the WTM induced by the deflected TEFs.
Abstract: Gust load analysis plays a substantial role in the certification process of aircraft. Active gust load alleviation techniques exhibit a high potential in significantly reducing the transient gust loads and thus the overall structural weight. In this paper, two dynamic actuator concepts are studied by means of CFD methods on a generic wing-fuselage aircraft configuration. The concepts comprise spanwise segmented trailing edge flaps (TEF) and leading edge flaps (LEF), which are already existent on the research model for high-lift and maneuvering purposes. Simulations based on Euler and RANS equations are utilized to assess the aerodynamic potential of the actuators regarding alleviation of critical idealized "1-cos" type vertical gusts. 2D simulations of a representative wing section are considered in an extended parametric study to derive an initial guess for the required actuation deflections on the aircraft configuration. An iterative analysis of spanwise varying actuator amplitudes is conducted in order to obtain strong control authority over the wing bending moment (WBM) and wing torsional moment (WTM). It is shown that the TEFs are promising in terms of mitigation of gust induced WBM and the LEFs are able to compensate the WTM induced by the deflected TEFs. Unsteady phenomena are identified at large TEF deflections resulting in unfavorable response of the aircraft. The transient behavior of the force coefficients shows significant dependencies on the flap scheduling. Only small improvements are achieved through segmented flap actuation compared to continuous flap actuation for the limited investigated setups.

9 citations

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