Investigating the Coupling of Helicopter Aerodynamics with SIMPACK for Articulated and Hingeless Rotors

In this paper the results of a tight coupling of rotor aerodynamics with a rotor model built up in the multibody software SIMPACK are presented. The aerodynamics are calculated by S4, which is a simulation tool developed at the Institute of Flight Systems of the German Aerospace Center. In a first step, the coupling approach was verified via cross code comparison for simple load cases such as hover flight for a hingeless blade with a straight elastic axis. The conclusions drawn for the verification methodology will be pointed out in the beginning of this paper. Investigations of a four bladed rotor in trimmed forward flight condition were conducted, leading to the discovery of a drawback in the representation of flexible beam-like structures in SIMPACK for helicopter applications. Additionally, a model of the articulated 7A rotor has been created. With this rotor a high speed flight condition test case was performed in the S1 wind tunnel and the results of the simulations are compared to the test results. In an attempt to eliminate the modeling deficiencies of the one-dimensional beam, a three-dimensional finite element model of the 7A rotor blade has been built at the Institute of Aeroelasticity as well. A comparison of the eigenmodes and eigenfrequencies of the one- and three-dimensional model will be shown

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

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

Merging an Analytical Aerodynamic Model for Helicopter Applications with a State-Space Formulation for Unsteady Airfoil Behavior

A new comprehensive simulation tool for computation of the whole helicopter is currently being developed at the Institute of Flight Systems of DLR. A main requirement of such a tool is the calculation of the aerodynamic forces acting at the blades, including all effects that are typical for helicopter rotor operational conditions, while maintaining small calculation times. Therefore, for the calculation of the rotor blade element aerodynamics, a semi-empirical analytical model is used. A formulation in state-space description was chosen to represent the unsteady circulation lag and the modeling of the noncirculatory force response was also added. The analytical models' formulation of the unsteady viscous effects, i.e. stall delay, was transferred to state-space form as well. The resulting combined model is used for the calculation of steady airfoil data as well as unsteady hysteresis curves for a harmonically oscillating airfoil. The results are compared to CFD data

Validierung von Mehrkörpersimulationen für Hubschrauber (VaMeSH) : Abschlussbericht

Das Projekt VaMeSH hatte zum Ziel, in Vorarbeiten gefundene Unzulänglichkeiten in der Beschreibung der Dynamik von Rotorblättern in Mehrkörpersimulationen (MKS) auszuräumen und eine Anbindung von Hubschrauberaerodynamik an eine MKS aufzubauen und zu verifizieren. Die in diesem Bericht dargestellten Aktivitäten konzentrieren sich auf den Aufbau der Kopplung und die Erstellung von Modulen für die Beschreibung der Aerodynamik der verschiedenen Komponenten eines Hubschraubers. Die Entwicklungen bezüglich der Blattmodellierung sind dem gleichnamigen Bericht des Projektpartners zu entnehmen. Im Rahmen des Projektes konnte eine neue Balkenbeschreibung zur Abbildung des elastischen Verhaltens von Rotorblättern im MKS Programm Simpack validiert werden und die Kopplung von MKS mit Aerodynamik für den gesamten Hubschrauber verifiziert werden

Merging an Analytical Aerodynamic Model for Helicopter Applications with a State-Space Formulation for Unsteady Airfoil Behavior

A new comprehensive simulation tool for computation of the whole helicopter is currently being developed at the Institute of Flight Systems of DLR. A main requirement of such a tool is the calculation of the aerodynamic forces acting at the blades, including all effects that are typical for helicopter rotor operational conditions, while maintaining small calculation times. Therefore, for the calculation of the rotor blade element aerodynamics, a semi-empirical analytical model is used. A formulation in state-space description was chosen to represent the unsteady circulation lag and the modeling of the noncirculatory force response was also added. The analytical models' formulation of the unsteady viscous effects, i.e. stall delay, was transferred to state-space form as well. The resulting combined model is used for the calculation of steady airfoil data as well as unsteady hysteresis curves for a harmonically oscillating airfoil. The results are compared to CFD data

Rotor Simulation and Multi Body Systems: Coupling of Helicopter Aerodynamics with SIMPACK

The Institute of Flight Systems of the German Aerospace Center uses and develops a high resolution comprehensive simulation tool called S4 for the computation of isolated helicopter rotors. The aerodynamic calculation is based on blade element theory and employs advanced models for the sectional air loads. S4 uses a modal synthesis approach for a one-dimensional, pre-twisted beam to calculate the blade motion. New and advanced blade designs cannot be represented by simple linear beam approaches with sufficient accuracy especially when large deformations occur. Modern multibody systems offer the potential to remedy that deficit by incorporating high-fidelity finite state models of rotor blades and provide implicit facilities to simulate moved reference frames and complex kinematics of entire rotor systems including the hub and control system. This paper describes the work to establish and verify a tight coupling between the rotor simulation S4 and the multibody system SIMPACK. The structural dynamics model of S4 is replaced by a SIMPACK model supplied with NASTRAN solutions for the flexible properties of the blade. The coupling architecture is explained in detail and differences between both approaches are discussed. The NASTRAN model and the Houbold-Brooks beam are compared in terms of eigenmodes and eigenfrequencies. Simple load cases are used during verification and the tight coupling is demonstrated with trimmed calculations for the hover case

AERODYNAMIC AND STRUCTURAL MODELING IN THE ROTORCRAFT MULTI-PHYSICS SIMULATION VAST

Comprehensive aeromechanics simulation for rotorcraft is a complex field involving models from different disciplines with very different structure and complexity. VAST (Versatile Aeromechanics Simulation Tool) addresses this field with a new approach involving a generic coupling of state-space models. The paper describes the approach and focuses on aerodynamic and structural methods used in the framework. The implemented models for aerodynamics include unsteady aerodynamics based on a semi-empirical analytical model for the blade sectional airloads and a vortex-lattice model for the computation of the rotor wake. The structural modeling is based on a generic multi-body approach

eTail - Variationsrechnungen mit konventionellem Heckrotor

Im Rahmen des Projekts eTail wurden mit dem Simulationstool VAST Untersuchungen zu verschiedenen Konfigurationsvarianten für einen AW09 Hubschrauber durchgeführt: - Schubvektorisierung in Längsrichtung (Pusher) und in vertikaler Richtung. - Variation der Heckrotordrehzahl. - Einstellbares Seitenleitwerk, simuliert durch ein Anstellen der gesamten Finne, auch in Kombination mit einer Reduktion der Heckrotordrehzahl. - Vergrößerung der Leitwerksfläche um den Heckrotor im schnellen Vorwärtsflug vollständig zu entlasten. - Trimmung über über die Heckrotordrehzahl als Alternative zur Trimmung über den Kollektivwinkel am Heckroto

A New Approach to Comprehensive Rotorcraft Aeromechanics Simulation

A new comprehensive aeromechanics code for rotary wing aircraft is being developed at the German Aerospace Center. It follows a new and very general approach in modeling all physical subsystems and numerical methods in one common interface description. The structure of the code makes no assumptions about the system to be modeled and builds the global system strictly from the logical connections of the sub-models. It relies heavily on modern language features and programming techniques like algorithmic differentiation. This paper describes the novel approach and currently implemented features. While verification and validation are a part of the paper it is not the sole purpose. The calculations serve rather as a means of verifying the general approach and its fitness for the long-term vision of the code. The description of the architectural concept is the main purpose of this paper. The description and evaluation is being underlined with a set of verification and preliminary validation cases