Steven G. Hagerott

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.

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.

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.

Piloted Simulation Handling Qualities Assessment of a Business Jet Fly-By-Wire Flight Control System

A pilot-in-the-loop handling qualities assessment of fly-by-wire control laws for a business jet with a sidestick was conducted in a simulation environment. The control laws were optimized to meet Level 1 requirements for a comprehensive set of stability, handling qualities, and performance specifications. This piloted fixed-based simulation experiment evaluated the control laws using a series of handling qualities demonstration maneuvers, including pitch and roll capture and tracking tasks, as well as an offset landing task. Quantitative performance metrics were collected, in addition to pilot handling qualities ratings and comments. The results show Level 1 handling qualities for the roll tracking and landing tasks, and borderline Level 1 handling qualities for the pitch tracking task. In addition, the fly-by-wire control laws were rated as very predictable and pilots could be more aggressive with a higher level of precision than with the bare-airframe.

A Coupled Lateral/Directional Flight Dynamics and Structural Model for Flight Control Design

A lateral/directional flight dynamics model which includes airframe flexibility is developed in the frequency domain using system-identification methods. At low frequency, the identified model tracks a rigid-body (static-elastic) model. At higher frequencies, the model tracks a finite-element NASTRAN structural model. The identification technique is implemented on a mid-sized business jet to obtain a state-space representation of the aircraft equations of motion including two structural modes. Low frequency structural modes and their associated notch filters impact the flight control frequency range of interest. For a high bandwidth control system, this frequency range may extend up to 30 rad/sec. These modes must be accounted for by the control system designer to ensure aircraft stability is retained when a control system is implemented to help avoid aeroservoelastic coupling. A control system is developed and notch filters are selected for the developed coupled aircraft model to demonstrate the importance of including the structural modes in the design process.