Investigating Power Benefits for a Helicopter by Variation of the Anti-Torque Device

With the usage of electrically driven devices, the rigid connection between main rotor and tail rotor can be broken up, allowing for a tail section that can possibly be optimized for different operating conditions. This paper presents the results of a study investigating the power benefits of different variations of the electric anti-torque device. The investigations were performed using an engineering model of a main rotor - tail rotor helicopter built up in the Versatile Aeromechanics Simulation Tool (VAST). The studied variations include horizontal and vertical tilting of the tail rotor, changing tail rotor speed and fin angle as well as fin size and geometry. Various flight conditions such as hover, forward flight, quartering flight, climb, and descent have been investigated. The largest power benefits were observed for (1) a combination of reduced tail rotor speed and a fin angle varying between 12 deg for low speed forward flight and 6 deg for high flight speeds and (2) an increased fin area with the tail rotor being shut off for flight speeds above 35 m/s

Application of the Predictor-Based Subspace Identification Method to Rotorcraft System Identification

In this paper, the optimized predictor-based subspace identification (PBSIDopt) method is applied to identify linear models of DLR's research helicopter ACT/FHS and to evaluate its usage to enhance existing physics based models in the future. For this effort, dedicated identification flight test data is used. This paper first describes the well known Maximum Likelihood frequency domain output error method and the applied physical model briefly. Then, the PBSIDopt method is presented and parameters, which influence the identification process, are discussed. Results from both methods using the same flight test data of the ACT/FHS are compared; model accuracy, order and missing dynamics are investigated. Advantages and disadvantages of both methods are evaluated and the applicability of the PBSIDopt method to rotorcraft system identification and its usage to improve the existing physical model structure is discussed

Retrospective and Recent Examples of Aircraft and Rotorcraft System Identification at DLR

Aircraft system identification has a five-decades-long tradition at German Aerospace Center (DLR). Over the last two decades, the research covered various topics related to system identification of fixed- and rotary-wing aircraft, nonconventional applications and atmospheric effects, the development of new flight-test procedures for system identification purposes, and specific aircraft model enhancements and corresponding parameter estimation. Comprehensive tools were developed that support this research and can be applied to a variety of different problems and types of vehicles. The paper starts with a short description of the different system identification methods used at DLR and the corresponding tools. The discussion of flight-test procedures and maneuver design as well as sensor fusion and flight-path reconstruction provides information on how to optimize the flight tests for system identification and to arrive at a consistent flight-test database. The examples for fixed-wing aircraft provide information on identification including abnormal conditions such as icing and interaction with atmospheric disturbances as well as modeling of structural mechanics and loads. The identification of high-order rotorcraft models that account for rotor and engine dynamics and even structural modes is discussed, and the identification of rotor mast moments as well as the identification of non-physics-based models and their integration into physics-based models are also covered. A final section shows that system identification can also be used to derive models for gyroplanes and parachutes as well as to derive control equivalent turbulence input models and to estimate complex wind field geometries. Thus, a broad overview of possible applications of system identification is given

LuFo V-3 CORINNE - Schlussbericht Comfort Of Ride Improved eNgiNEering -Komfortverbesserung im niederfrequenten Bereich für Hubschrauber

Hubschrauberpiloten sind auch in aktuellen Hubschraubermustern einem hohen Vibrationsniveau ausgesetzt. Diese Vibrationen können negative Auswirkungen auf die Gesundheit und die Leistungsfähigkeit der Hubschrauberbesatzung und der Passagiere haben. Insbesondere Schwingungen im niederfrequenten Bereich standen dabei im Fokus des Verbundprojekts CORINNE. Diese Vibrationen werden u.a. durch Turbulenz angeregt und wirken verstärkt durch Flugregelungssysteme und Autopiloten auf die flugmechanischen Moden des Hubschraubers. Im DLR-Beitrag von CORINNE wurde hauptsächlich an drei Teilaspekten zur Reduzierung der niederfrequenten Vibrationen geforscht. Erstens wurde ein Turbulenzmodell für den Forschungshubschrauber ACT/FHS auf Basis von Flugversuchsdaten erstellt und validiert. Dieses sog. CETI-Modell wurde auch auf andere Hubschraubermuster skaliert. Zusätzlich ist es im ACT/FHS und AVES Simulator verfügbar, um Turbulenz zu simulieren. Zweitens wurde das Simulationsverfahren UPM in das Hubschraubersimulationsmodell von Airbus Helicopters integriert und validiert. Mit diesem Simulationsverfahren können flugmechanische Stabilitätseigenschaften wie die der Phygoide und des Dutch Rolls genauer vorhersagt und die Simulationsgüte im Manöverflug gesteigert werden. Drittens wurde ein Beobachter für die longitudinalen und lateralen Rotormastmomente des ACT/FHS auf Basis von Flugversuchsdaten entwickelt. Der Beobachter benötigt dabei lediglich Messgrößen aus dem stehenden Hubschraubersystem, welche auch auf Serienhubschraubern verfügbar sind. Durch die Integration des Beobachters in die Flugregelung soll der Komfort in turbulenter Luft gesteigert werden

Full Electric Helicopter Anti-Torque

On the way to complete electric flight, the electrification of helicopter subsystems is an essential milestone. This paper discusses the design of an electric helicopter anti-torque system, which uses Kopter's AW09 helicopter as a platform and shall be tested in ground tests. Analysis of state of the art anti-torque devices for helicopters has helped to identify concepts, which are suitable to be combined with electric propulsion and actuation. Engineering models are used to estimate the power benefits of varied tail rotor RPM, enlarged and steerable vertical stabilizers and drag reducing devices, which cover the rotor in forward flight. In connection with operational benefits viewed from the OEMs perspective, an architecture is proposed which consists of an electric driven shrouded tail rotor, an electric pitch actuation system and additional aerodynamic surfaces, like a steerable vertical stabilizer and a drag optimized tail rotor cover. The systems were developed according to the results of a safety analysis to meet the requirements of CS-27. The electric tail rotor drive is designed with an internal level of redundancy that allows to compensate for subsystem failures

Vergleich zweier Verfahren zur Frequenzgangerzeugung.

In diesem Bericht wurden zwei Verfahren zur Frequenzgangbestimmung verglichen, das am Institut für Flugsystemtechnik in HHQTools und Fitlab implementierte Verfahren sowie das Verfahren aus CIFER. Dabei wurden zunächst die theoretischen Grundlagen bereit gestellt und dann die beiden Berechnungsverfahren erläutert. Um das in CIFER benutzte Verfahren auch in Fitlab nutzen zu können, musste es in Matlab implementiert werden. Einzelheiten dieser Implementierung wurden ebenfalls erläutert. Die Korrektheit der Implementierung wurde durch Vergleichsrechnungen mit CIFER nachgewiesen. Abschließend wurden die beiden Verfahren an Hand von drei Beispielen verglichen. Dabei ergaben sich nur geringe Unterschiede, die vor allem bei niedrigen Frequenzen und im Bereich geringer Kohärenz liegen. Da das Verfahren aus CIFER neben den Frequenzgängen auch die Auto- und Kreuzspektren der Eingangs- und Ausgangssignale liefert, soll es als Alternative zum bisherigen Verfahren in Fitlab implementiert werden

FitlabGui - A MATLAB Tool for Flight Data Analysis and Parameter Estimation - Version 2.5

FitlabGui is a MATLAB tool for flight data analysis and parameter estimation. The software has developed over the years and this report describes version 2.5. The report first describes how to install and call the software. Then, the different panels and their options are presented. Several utilities that come with FitlabGui and the demonstration examples for the parameter estimation are also described. A separate chapter explains how to use the underlying parameter estimation software FITLAB from the command line instead of starting it via FitlabGui. In the appendix, the mathematical background for the three implemented frequency response generation methods is given. A second appendix explains the parameter estimation methods implemented in FitlabGui

User's Guide FITLAB - Parameter Estimation Using MATLAB - Version 2.3

Der Bericht enthält die Benutzeranleitung für die neueste Version des Software-Pakets FITLA

ACT/FHS System Identification Including Rotor and Engine Dynamics

At the DLR Institute of Flight Systems models of the ACT/FHS, an EC135 with a fly-by-wire/light flight control system, are needed for control law development and simulation. Thus, models are sought that cover the whole flight envelope and are valid over a broad range of frequencies. Furthermore, if the models are to be used in the feedforward loop of the model following control system, they have to be invertible and thus must not have any positive transmission zeros. Maximum likelihood system identification in the frequency domain was used to derive the desired models. For rotor flapping the explicit formulation with flapping angles was modified slightly to avoid positive transmission zeros. For the regressive lead-lag a simple model formulation was found that needs only one dipole with two states. The engine dynamics were first modeled separately and then coupled to the body/rotor model. The final integrated model has seventeen states and yields a good match for frequencies up to 30 rad/s