Bell 412 System Identification and Model Fidelity Assessment for Hover and Forward Flight

Aeroelastic stability of complete rotors with application to a teetering rotor in forward flight

In this work, optimization methodologies of the kinematics of flapping wings in forward and hover flights are considered. Particularly, local and global optimization algorithms are combined with the unsteady vortex lattice method (UVLM) to determine the most efficient kinematics. In the first problem, the kinematic optimization of a three-dimensional flapping wing in forward flight with active shape morphing is aimed at maximizing the propulsive efficiency under lift and thrust constraints. Results show that due to the quasi-concavity of the objective function associated with the flapping kinematics employed in forward flight, local gradient-based optimizers perform very well in terms of accuracy and computational cost. In the second problem, the objective is to identify the optimized kinematics of a twodimensional hovering wing that minimize the aerodynamic power under lift constraint. The results show that using a hybrid optimization algorithm (combination of local and global schemes) accelerates the convergence to optimal points and avoids being trapped at local minimum points. While the efficiency of using a local optimizer, a global optimizer, or a hybrid of the two depends on the nature of the problem and associated design space, it is determined that hybrid optimization is best suited for determining local minima.

Systematic design methodology for development and flight testing of a variable pitch quadrotor biplane VTOL UAV for payload delivery

The design of new helicopter rotor blades is a challenging task. The individual blade sections undergo very different flow conditions during the various flight regimes of the helicopter. In forward flight, the advancing side operates in a transonic regime where potentially shock waves can occur, while on the retreating side little flow velocities at high angle of attacks are seen up to reverse flow. In hover, the oncoming tip vortex of the previous blade drastically influences the inflow on the rotor. This paper joins the classical blade shape design with numerical optimization techniques. Opposing to the direct solution process of directly modifying the blade shape, the rotor blade is conventionally considered as a set of airfoils, a planform and a twist distribution. First, rotor airfoils are found through numerical optimization and then placed on the reference rotor. The planform and twist of this rotor are then also numerical optimized. The obtained trade-off blade for hover and forward flight drastically improved the performance over the reference HART-II blade (11% in forward flight, 5% in hover flight). In order to arrive at industrial relevant blades, further work including more disciplines becomes necessary.

In this paper, an optimal controller is investigate d based on the Linear Quadratic Control method. The controller simulation is execut ed based on a small-scale autonomous model helicopter, Yamaha R-50. Genetic algorithms are employed to generate weighting matrices by optimizing the performance index of the control system. As a result, this method produces optimal weighting matrices which further improve the Linear Quadratic Controller. A full state feedback approach is used in the control design process. A Kalman observer is integrated into the controller to predi ct full state variables, since only a limited number of state variables are measured. Finally, th e performance of the controller is evaluated in the time domain with and without disturbances when the model helicopter is in hovering flight and forward flight. I. Introduction utonomous helicopters offer special advantages for major operations in both civilian and military sect ors, particularly in cases that are considered either in accessible or dangerous for human beings, due to th eir vertical take-off and landing (VTOL) capabilities. The contr ol system of autonomous helicopters plays a key rol e in its ability to carry out the assigned task effectively. This has lead to a growing interest in the design and analysis of the control system of autonomous helicopters. In 1990s, classic control theory was widely used for autonom ous helicopter control systems, which is mainly a succe ssive loop closure approach. The control gains are selected separately using tools such as Root locus, Bode and Nyquist plots. The controller parameters are usual ly tuned based on the controller performance measured either in ti me domain or in frequency domain. This design procedure becomes increasingly difficult as more and more loo ps are added, specifically, when the dynamics invol ve multiple inputs, multiple outputs, or multiple feedback loop s with complex performance criteria. To control an autonomous helicopter modeled as a complex Multiple Input Multiple Output (MIMO) system, the performance criteria can not be easily met by the approach based on classis cont rol theory. Several researchers have developed a number of diff erent ways for the control system design of autonom ous helicopters in the literature. Shim et al 1 presented three different control methods using li near robust, fuzzy logic, and nonlinear tracking controls, for an autonomous helicopter in hover and low speed flight. Johnson a nd Kannan 2

The paper describes a methodology to extract linearized state-space dynamic inflow model from a generic and high fidelity aerodynamic analysis for single and coaxial helicopter rotor systems. Both hover and forward flight are studied including maneuvering and the results are demonstrated by a free-wake analysis. The proposed methodology which is founded on a Single Frequency Analysis is computationally efficient and provide the entire frequency-domain behavior of the wake inflow states. Besides being able to incorporate any advanced computational tool, the present methodology takes advantage of exact wake states and thus adequately encompasses high frequency responses. The paper also extends the methodology to the case where states of higher harmonics are required and to the case of heaving, rolling and pitching rotor disc. For a single rotor system the results resemble the well known classical dynamic inflow model. For coaxial rotor system in hover, the high mutual couplings between the rotors are clearly demonstrated and affect the resulting system matrices. An important feature of the present methodology lays in the fact that the entire formulation is non-dimensional and the in-flow analysis is completely separated from the loads analysis, which enables a consistent generalization of the results.

Results from a neural network validation study with full-scale XV-15 tilt-rotor experimental hover and forward flight data are presented. Two test data bases, acquired during separate tests conducted at NASA Ames, were used. These two isolated XV-15 rotor test data bases were: the 80by 120-Foot Wind Tunnel hover and forward flight test data base, and secondly, an outdoor hover test data base. For this neural-network-based data validation study, the objective associated with the wind tunnel test data was: obtain neural network representations, conduct data quality checks, and demonstrate sensitivity to test conditions. Neural networks were successfully used to represent and assess the quality of full-scale tilt-rotor hover and forward flight performance test data. The neural networks accurately captured tilt-rotor performance at steady operating conditions and it was shown that the wind tunnel forward flight performance test data were generally of very high quality. The second objective, using outdoor hover test data, was to formulate and implement a neural-network-based wind correction procedure. Compared to existing, momentum-theorymethod based wiad corrections to outdoor hover performance, the present neural-network-procedure-based corrections were better. The present wind corrections procedure, based on a well-trained neural network, captured physical trends present in the outdoor hover test data that had been missed by the existing, momentum-theory-based method. Copyright © 1998 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. A a

A linear theory for soft ferromagnetic elastic solids

For the last few decades, Canada's National Research Council (NRC) has been at the forefront in analyzing dynamic systems and developing tools to construct aircraft models based on flight test data. With a fixed and rotary-wing aircraft fleet available, NRC has the capability to perform leading edge R&D System Identification (SI); this worldleading SI technology has been developed and has assisted industry partners, Department of National Defense (DND), and various universities in aircraft simulation and development. As a result, NRC has gained extensive experience in modeling aircraft using SI techniques. In collaboration with CAE, this paper demonstrates the acceleration of the NRC's current flight modeling techniques, highlighting recent advances in Artificial Intelligence (AI) and Machine Learning (ML). A new Bayesian ML software is being developed to identify a 6 degrees of freedom (6-DoF) quasisteady model using simulated flight test data. To achieve this, data from the CAE Sample electric Vertical Take-Off and Landing (eVTOL) simulation platform vehicle during hover maneuvers is utilized. Additionally, this paper presents results on extending the model to include rotor dynamics using the classical SI approach for comparison purposes. In summary, all methods provide a high-fidelity model; with the higher model structure, the vertical acceleration match was noticeably better.

This study examines hexacopter performance in hover and forward flight with single rotor failure. A classical configuration (adjacent rotors spinning in opposite directions) and an alternate configuration are considered. The simulation model uses calculates rotor forces and moments by using blade element theory coupled with a finite-state dynamic inflow model. For the alternate hexacopter, if one of four rotors (out of six) fails, trim is possible in hover and forward flight, and the aircraft remains fully controllable. Recovery from the failure of one of the other two rotors is impossible. For the classical hexacopter, if any of the forward-facing rotors fail, the aircraft can be trimmed in forward flight and is fully controllable. If an aft rotor fails, trim is not possible but the aircraft could be turned around to orient the failed rotor forward. Although the classical hexacopter can be trimmed in hover by turning off the rotor diametrically opposite to the failed rotor, the aircraft is not independently controllable about all axes. In the event of a rotor failure, the classical hexacopter could cruise and land, but it cannot maintain a sustained hover. Power penalties of up to 23% are observed in the event of failure due to increased drag on the operational rotors.

This paper deals with some recent developments of a boundary element methodology for the unified aerodynamic/aeroacoustic analysis of subsonic and transonic potential flows past helicopter rotors in hover and forward flight. In this methodology, first the potential solution is derived on the rotor-blade surfaces. Then, the boundary integral representation gives the potential everywhere in the field, and the Bernoulli theorem yields the acoustic pressure. Numerical results are presented for helicopter rotors in hover and forward flight at both subsonic and transonic rotor speeds. Comparisons with existing numerical results and experimental data are included.

Design and experimental study of a new flapping wing rotor micro aerial vehicle

In the present study, the parametric study was performed to analyze the effect of the tab on the aerodynamic performance and characteristics of rotor blades. Also, the tab shape was designed to improve the aerodynamic performance of rotor blades. A computational fluid dynamics solver based on three-dimensional Reynolds averaged Navier–Stokes equation using an unstructured mesh was used for the parametric study and the tab design. For airfoils, the effect of length and angle of a tab was studied on the aerodynamic characteristics of airfoils. In addition, including those parameters, the effect of a span of a tab was studied for rotor blades in hovering flight. The results of the parametric study were analyzed in terms of change of the aerodynamic performance and characteristics to understand the effect of a tab. Considering the analysis, the design of tab shape was conducted to improve the aerodynamic performance of rotor blades. The simply attached tab to trailing edge of the rotor blades increases the thrust of the rotor blades without significant changing of aerodynamic characteristics of the rotor blades in hovering and forward flight.

This paper presents the implementation and validation of a state-space free-vortex wake model with a vortex lattice near-wake formulation, developed for rotorcraft applications. The model is expressed in state-variable form as a nonlinear time-periodic (NLTP) system in first-order structure, enabling linearization and simplification through time-invariant systems theory and model-order reduction techniques. It is applied to a UH-60-like rotor and evaluated in hover, forward flight, and vortex ring state (VRS) conditions. Two configurations are considered: one with tip vortex dynamics only, and another incorporating both tip vortex dynamics and a near-wake vortex lattice model. A parametric study is conducted to determine optimal parameters for solution accuracy. Validation in hover and forward flight is performed against high-fidelity computational fluid dynamics (CFD) results and available experimental data. Validation in VRS includes comparisons with experimental measurements and momentum theory. Overall, the state-space free-vortex wake model accurately predicts blade loads and induced velocities across all three validation cases, with the exception of a slight underprediction observed in fully developed VRS conditions. The inclusion of the near-wake model is essential for accurate blade load prediction in hover and contributes to improved predictions in forward flight.

Development and preliminary assessment of the open-source CFD toolkit SU2 for rotorcraft flows