Mark B. Tischler

Forward flight trim and frequency response validation of a helicopter simulation model

This article describes a new trim procedure that includes the calculation of the steady-state response of the rotor blades and is applicable to straight flight and steady coordinated turns. This article also describes the results of a validation study for a high-order linearized model of helicopter flight dynamics that includes rotor, inflow, and actuator dynamics. The model is obtained by numerical perturbations of a nonlinear, blade elementtype mathematical model. Predicted responses are compared with flight test data for two values of airspeed. The comparison is carried out in the frequency domain. Numerical simulations and comparisons with flight test data show that the trim algorithm is accurate and preserve the periodicity of the aircraft states. The results also indicate that the predictions of the on-axis frequency response are overall in good agreement with flight test data, especially at medium and high frequencies.

Lateral/Directional Control Law Design and Handling Qualities Optimization for a Business Jet Flight Control System

Design of lateral/directional control laws for a business jet was performed using a two step optimization approach to meet a comprehensive set of stability, handling qualities, and performance specifications. First, a linear-quadratic regulator method was employed for preliminary design as a way to initialize the control law feedback gain values for optimization. Subsequently, a multi-objective parametric optimization approach was used to arrive at feed-forward and feedback gains that concurrently satisfy all specifications. The specifications were divided into two tiers. The first were the key flight control and handling qualities requirements and were used directly for optimization, while the second were used as a check afterwards. This paper describes the control law architecture used as well as the optimization approach, the specifications used, and the design results.

Pre- and post-flight-test models versus measured skyship-500 control responses

The dynamical equations-of-motion (EOM) for cruising airships require nonconventional terms to account for buoyancy and apparent-mass-effects, but systematic validation of these equations against flight data is not available. Using a candidate set of EOM, three comparisons are made with carefully-measured describing functions derived from frequency-sweep flight tests on the Skyship-500 airship. The first compares the pre-flight predictions to the data; the second compares the best-fit equations to data at each of two airspeeds and the third compared the ability to extrapolate from one condition to another via airship-specific scaling laws. Two transient responses are also compared. The generally good results demonstrate that fairly simple, perturbation equation models are adequate for many types of flight-control analysis and flying quality evaluations of cruising airships.

Longitudinal Control Law Design and Handling Qualities Optimization for a Business Jet Flight Control System

A comprehensive set of stability, handling qualities, and performance specifications was used to drive the optimization of commonly used fixed-wing longitudinal control laws applied to a business jet. The specifications were divided into two tiers. The first were the key flight control and handling qualities requirements and were used directly for optimization, while the second were used as a check afterwards. Similarities between the commonly used longitudinal control laws investigated in this study and a model following controller were exploited to explicitly set feed-forward gains to provide good handling qualities. A linear-quadratic regulator method was employed for preliminary design as a way to initialize the control law feedback gain values for optimization. A multi-objective parametric optimization approach was then used to arrive at feedback gains that concurrently satisfy all specifications. Using this optimization approach, the trade-offs of increased crossover frequency were investigated. In addition, a smooth gain schedule was generated by optimizing the control law parameters of different flight conditions to meet the same requirements. This paper describes the control law architecture used as well as the optimization approach, the specifications used, and the design results.

Practical Methods for Aircraft and Rotorcraft Flight Control Design: An Optimization-Based Approach

this time, many textbooks on composite materials have emerged, helping to educate several generations of aircraft designers and aeronautical engineers. Some of these books stood the test of time and are now entering into their third editions. Composite Materials for Aircraft Structures is one of these few. Its first edition was published in 1986, second in 2004 and the third in 2016. Two things make this book remarkable. Firstly, the book is focused on aircraft structures and everything an engineer needs to know about composites and all that they are made of, from fibre and matrix properties, manufacturing, quality control and fundamentals of mechanics of composite materials to joining, damage detection and repair. Secondly, unlike other textbooks, this one is written not by a single author or a pair of co-authors, but by a large team of contributors from many universities and research institutions, predominantly from Australia, but also from Malaysia and USA. It is to the editors’ great credit that the book does not feel like a patchwork of separate chapters but a volume that speaks with one voice and reflects a shared vision underpinned by vast theoretical knowledge and practical expertise of the team. The book is generously illustrated with figures, photographs, diagrams and tables that support discussion and aid understanding of various points in the text. It is great as a reference work, but for a textbook to be used in teaching of university students, it does not have many examples or problems to solve. Although one could argue that they are not really necessary in a volume that is already 600 pages long, since students could be referred to other excellent textbooks around for suitable exercises. Another thing is missing from the book – a chapter on recycling. With composite structures being used so extensively nowadays, a question of what happens to them after they reach the end of their service life should be considered and discussed. Something for the fourth edition, perhaps? Professor Maria Kashtalyan University of Aberdeen

Full Flight-Envelope Simulation and Piloted Fidelity Assessment of a Business Jet Using a Model Stitching Architecture

This paper presents the development and piloted assessment of a full flight-envelope simulation model of a light business jet using a model stitching architecture. Individual state-space models and trim data for discrete flight conditions were combined to produce a continuous simulation model, which was integrated into a fixed-base simulation facility. Back-to-back flight/simulation piloted evaluations of a similar light business jet in flight and the stitched model in simulation were performed to assess the fidelity of the stitched model. Overall pilot impressions were that the stitched simulation model was representative of the actual aircraft. Simulation Fidelity Ratings were given to quantify simulation fidelity for each of the evaluated qualitative tasks, in which mostly Fidelity Level 1 ratings were assigned, suggesting full transfer of training for those tasks. Guidance on flight testing for the development of fixed-wing aircraft stitched models is provided.

Development and Validation of a Flight-Identified Full-Envelope Business Jet Simulation Model Using a Stitching Architecture

A full flight-envelope simulation model of the Calspan Variable Stability Learjet-25 was developed from flight data. The model is based on a stitched model architecture, which falls into the class of quasi-Linear-Parameter-Varying models, and was developed using a series of discrete linear point models and trim data. Point models were identified from flight data at five different flight and loading conditions. A scaling method was used and validated to convert all identified point models to the same loading configuration. The quasi-linear aerodynamics from the models were then combined with trim data and the full nonlinear equations of motion to develop the stitched model. Through validation with flight data, the model was shown to accurately represent the aircraft dynamics within the normal flight envelope and be able to estimate the effects of weight and center of gravity variations. The paper provides a brief background of model stitching, lists the steps required to develop a stitched model from flight data, and then demonstrates how the steps are applied to the Learjet.

Low Cost Flight-Test Platform to Demonstrate Flight Dynamics Concepts using Frequency-Domain System Identification Methods

A low-cost prototype platform for educational use has been developed. The goal of the system is to serve as a hands-on classroom flight dynamics demonstrator. Onboard sensors and data storage devices allow for recording of multiple flight parameters for system identification. The prototype is hosted on the Dynam HawkSky model airplane, an inexpensive foam electric glider equipped with standard 3-axis primary controls. The flight control and data acquisition hardware and software are all open-source, providing an architecture which is readily accessible to university students. The core of the hardware is a commercially available flight controller based on the Arduino Mega micro-controller board. The open-source software can be easily modified by students to evaluate various flight control laws. Modular hardware simplifies the swapping of the system from one airplane to another, allowing for effective and data driven flight testing of student’s design projects at minimal cost. Successful flights have demonstrated the capability for flight parameter identification using frequency response techniques through the CIFER ® software package. This paper presents flight test identification results for the 6DOF stability and control derivatives and compares these with the analytical estimates as based on first principles.

Identification of XV-15 Aeroelastic Modes Using Frequency Sweeps

The XV-15 tilt-rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier-transformed). Modal frequencies and damping were determined by performing curve fits to frequency-response magnitude and phase data. Results are given for the XV-15 with its original metal rotor blades. Frequency and damping values are also compared with predictions by two different programs, CAMRAD and ASAP.

Handling Qualities Flight Test Assessment of a Business Jet N zU P-β Fly-By-Wire Control System

Fly-by-wire control laws for a business jet were developed and a handling qualities assessment flight test was conducted on the Calspan Variable Stability System Learjet-25. The control laws, which provide an nzu-command response type in the longitudinal axis and a p-β-command response type in the lateral/directional axes, were optimized to meet Level 1 requirements for a comprehensive set of stability, handling qualities, and performance specifications. The control laws were evaluated in flight by USAF Test Pilot School and Textron Aviation test pilots using a series of handling qualities demonstration maneuvers. These included pitch and roll capture and tracking tasks and an offset landing task. Quantitative performance metrics were collected, in addition to pilot handling qualities ratings and comments. Several modifications were made to the control laws based on initial pilot comments and ratings. The final results show that the optimized fly-by-wire control laws provided assigned Level 1 handling qualities for discrete tracking and offset landing tasks.