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Geissler W.,Institute of Aerodynamics | Wall B.G.V.D.,Institute of Flight Systems
Annual Forum Proceedings - AHS International | Year: 2010

As early as 1934, Prof. Dr. Hans-Georg Küssner from the Aerodynamische Versuchsanstalt Göttingen (AVA) in Germany was thinking about an alternative to helicopter rotor torque compensation, that was tried experimentally already in 1921 by Passat in England. Based on the theoretical work about two-dimensional unsteady airfoil aerodynamics, especially combined plunge and pitch of an airfoil that revealed a propulsive force as is used by bird flight, he was tempted to try this concept on driving a helicopter rotor via forced flapping of its rotor blades. Experiments have been carried out in the mid-30ies and patents applied for the concept which were granted a long time later after an intense and controversy dispute with the responsible officials. This paper describes Küssner's efforts regarding the forced flapping concept and experimental results he obtained in the AVA wind tunnel in hovering condition. © 2010 by the American Helicopter Society International, Inc.

Rudinger I.,Institute of Flight Systems
DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte | Year: 2014

This thesis covers the topic of pilot gain in flight test based on simulator tests in Germany and flight tests with the NF-16D "VISTA" at the USAF test pilot school. Potential pilot gain measures are introduced and validated based on a dedicated approach which can be easily adapted to different types of tasks. In a second section, a potential root cause for differences in natural pilot gain is evaluated and discussed. Based on the cortical arousal theory, a correlation between the pilot's personality trait of "extraversion" and pilot gain was assumed and supported by simulator and personality tests. Finally, the workload buildup flight test technique is investigated as a potential means to increase pilot gain in flight test. The results of this thesis confirm that this technique is able to gradually increase pilot gain; however, the resulting pilot gain is often not higher than for an intentional pilot gain increase on command.

Rosic B.V.,TU Braunschweig | Rosic B.V.,Institute of Scientific Computing | Diekmann J.H.,German Aerospace Center | Diekmann J.H.,Institute of Flight Systems
Journal of Aircraft | Year: 2015

The paper deals with the propagation of uncertainty in input parameters through the aircraft model in clean cruise configuration triggered by the elevator pulse. Assuming aerodynamic coefficients as random variables and processes, the evolution of uncertainties in the aircraft state is estimated with the help of efficient nonintrusive procedures-stochastic collocation and the nonintrusive Galerkin approaches, here contrasted to the slow convergent Monte Carlo integration. These numerical methods are implemented by using the flight simulator in a black-box manner. In this way, the set of samples of aircraft states is simply obtained by solving the corresponding systems of deterministic ordinary differential equations. Additionally, the paper provides the variance-based sensitivity analysis of a flight model carried out with the help of the polynomial-chaos approach. © 2014 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.

Vicroy D.D.,NASA | Huber K.C.,German Aerospace Center | Rohlf D.,German Aerospace Center | Rohlf D.,Institute of Flight Systems | Loser T.,DNW
32nd AIAA Applied Aerodynamics Conference | Year: 2014

Several static and dynamic forced-motion wind tunnel tests have been conducted on a generic unmanned combat air vehicle (UCAV) configuration with a 53° swept leading edge. These tests are part of an international research effort to assess and advance the state-of-art of computational fluid dynamics (CFD) methods to predict the static and dynamic stability and control characteristics for this type of configuration. This paper describes the dynamic forced motion data collected from two different models of this UCAV configuration as well as analysis of the control surface deflections on the dynamic forces and moments.

Rohlf D.,German Aerospace Center | Rohlf D.,Institute of Flight Systems | Schmidt S.,Defence Science and Technology Organisation, Australia | Irving J.,BAE Systems
Journal of Aircraft | Year: 2012

Different methods are described to determine dynamic derivatives of an unmanned combat air vehicle configuration called SACCON (for "stability and control configuration"). These methods can be applied to both experimental and computationally obtained data sets. The first method assumes a linear derivative model and is based on a least-square curve-fitting technique and a subsequent evaluation step to actually compute the derivatives themselves. Based on the unsteady simulation obtained by computational fluid dynamics, the routine is able to recover the major trends of vehicle performance with reasonable agreement for pitching stiffness and damping. Lift-related quantities do show a discrepancy, particularly at high angle of attack. The second approach also assumes a linear derivative model. In this case, however, the static pitching stiffness terms are defined explicitly from the static test results and then subtracted from the dynamic results to give the residual effect of the damping terms. A leastsquares fit of these is used to determine the damping derivatives. Using this approach, it is demonstrated that the linear-derivative assumption falls down at higher angle of attack, and a more-generalized modeling paradigm is required. The final approach enables the use of nonlinear model equations and is therefore applicable to the entire tested angle-of-attack and angle-of-sideslip regime, generating a single set of nonlinear derivatives. Thus, the hysteresis loops of the coefficients derived from dynamic wind-tunnel tests can be reproduced satisfactorily with most of their inherent significant changes depending on angle of attack and forced oscillation frequency.

Nonnenmacher D.,Institute of Flight Systems | Mullhauser M.,Institute of Flight Systems
CEAS Aeronautical Journal | Year: 2011

Active side sticks offer the possibility to adjust the force-feel characteristics to account for various piloting tasks and flight conditions. This promises a decrease in pilot workload and an increase in handling qualities. However, the optimum force-feel characteristics are not well understood and modeled; therefore, their tuning still rely on experimental methods. Experimental pilot-in-theloop methods are time-consuming, expensive and have to be repeated with every change in control law dynamics. If a purely mathematical method for force characteristics optimization could be developed based on a better understanding of the principles underlying good force-feel systems, then the optimization could be done more efficiently and offline. This paper presents our current developments and achievements towards this new understanding to assess if and how a purely mathematical method could be derived from selected experiments. Even if this final goal could not be derived yet, the paper presents the selected approach and the lessons learned so far. More precisely, a simulatorbased experiment was developed to provide the data for the later analyses and the identification of mathematical models suitable for that purpose. For this experiment, a roll tracking task is considered whose evaluation is based on both a qualitative (Cooper–Harper rating) and a quantitative criterion. The very encouraging results obtained so far on this scenario are detailed. © Deutsches Zentrum für Luft-und Raumfahrt e.V. 2011.

Bertram O.,Institute of Flight Systems
10th Annual International Systems Conference, SysCon 2016 - Proceedings | Year: 2016

There is a strong need to investigate future aircraft high-lift systems in virtual as well as real test rigs. An investigation of innovative high-lift systems is only possible with integrated approaches of different disciplines involved in the aircraft design process. For this reason, an interdisciplinary design method for determination of actuator loads will be presented. Involved disciplines are aerodynamics and systems. The method will be applied to a future test rig for high-lift systems. Two different kinematic mechanisms will be modeled with the so-called "module method" for analyzing flap deployment and determination of actuation loads. Aerodynamic calculations of the pressure distributions, which are used for the air load calculations, are carried out with the panel method in the VSAERO software tool. The air loads will be the input for the calculation of the actuation loads, which constitute the basis for the dimensioning of the test rig components. A comparative study for flap movement and actuation loads is finally carried out for different mechanisms. © 2016 IEEE.

Jann T.,German Aerospace Center | Jann T.,Institute of Flight Systems | Geisbauer S.,German Aerospace Center | Geisbauer S.,German Institute of Aerodynamics and Flow Technology
AIAA Aerodynamic Decelerator Systems (ADS) Conference 2013 | Year: 2013

The paper presents the approach and the results from the CFD analysis and the further evaluation of the aerodynamics characteristics of three different bluff body shapes used in an airdrop and parachute simulation. In a joint effort between the Institute of Aerodynamics and Flow Technology and the Institute of Flight Systems within the internal DLR-project MiTraPor II, aerodynamic coefficients for two cuboids and a hemispherical shell representing scaled models of payloads and parachute were evaluated. The evaluation of the aerodynamic coefficients is based on a CFD analysis of a first cuboid with an aspect ratio of 11 × 9 × 5, a second cuboid (or semi-cube) with 11 × 9 × 9 and a hemispherical shell. The analysis covers the full 360° angle of attack range with a side-slip angle of zero, and additional points at β ≠ 0. For being used within the airdrop and parachute simulation, the CFD results were post-processed to obtain analytical approximations for the steady aerodynamic coefficients. © 2013 by Thomas Jann and Sven Geisbauer. Published by the American Institute of Aeronautics and Astronautics, Inc.

Adolf F.-M.,Institute of Flight Systems
AIAA Infotech at Aerospace Conference and Exhibit 2012 | Year: 2012

This paper presents an online multi-query path planner for exploration tasks planned onboard an unmanned helicopter. While the desirable properties of roadmaps can be exploited in offine path planning, the dynamic nature of exploration scenarios hinders to utilize conventional roadmap planners. Hence, the presented path planning approach utilizes a deterministically sampled roadmap which is dynamically indexed in real time. To address situations of partial terrain knowledge, the roadmap can be extended from its a priori dimensions towards locations of unknown terrain that are outside its original, a priori boundaries. The multi-query property of the planning system allows for combinatorial optimization such that a rapidly acting decisional autonomy is achievable during exploration flights. D*-Lite is used as dynamic heuristic path searcher in order to re-plan effIciently. Inspired by the original work on this path search algorithm, the roadmap graph is augmented with an exploration vertex which steers the exploration behavior of the vehicle. As a result, the presented roadmap guides an unmanned rotorcraft through a priori unknown urban terrain in real time. © 2012 by Florian-M. Adolf, German Aerospace Center (DLR).

De Almeida F.A.,German Aerospace Center | De Almeida F.A.,Institute of Flight Systems | De Almeida F.A.,Campus Do Centro Tecnico Aeroespacial CTA | Leissling D.,German Aerospace Center | Leissling D.,Institute of Flight Systems
Journal of Guidance, Control, and Dynamics | Year: 2010

This work presents a novel method of fault-tolerant model predictive control where the response of a reference closed-loop model is followed even in the presence of an actuator fault. This architecture is capable of redistributing the control efforts among healthy actuators in a stable manner, respecting their limitations. Also, a constrained guidance system that works in conjunction with the inner-loop fault-tolerant controller is proposed. The guidance law considers the calculated limitations of the inner-loop control system as input constraints in order to smooth the transition between two consecutive navigation legs defined by waypoints. A trajectory-tracking system composed of the constrained guidance and the fault-tolerant model predictive controller is demonstrated through numerical simulations and experimental results on an experimental midsize transport aircraft, showing adequate performance.

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