T&E 4105 FW Modern Flight Control Systems

Course Description

The course is designed to provide a “top-level” introduction to Modern Flight Control Systems (FCS’s). Basic elements of modern FCS’s are reviewed along with typical basic structures and system elements for modern fly-by-wire FCS’s. Classic linear control tools (Root Locus, Bode Plots, Block Diagram Algebra) and their practical application are discussed. Modern software analysis tools are introduced and demonstrated during the course. Handling qualities criteria and special issues related to modern complex FCS’s such as Pilot Induced Oscillations (PIO’s) are reviewed. The need for systematic closed-loop handling qualities evaluations is emphasized. Different control strategies are presented (pre-filters, response feedback, g-command and q-command systems, and model following). The effects of common control system feedback implementations are presented using software and the dedicated Navion and FastJet Variable Stability Ground Simulators (VSGS) and Variable Stability Instructors. Command path shaping and the effects of time delay and rate limiting are also discussed. Course learning objectives are reinforced when students go through a hands-on guided demonstration on the VSGS. The objective of the course is to provide a high level of understanding of the Principles, Issues, and Test Methods related to modern FCSs to enable the student to conduct a professional engineering evaluation. Daily review, tutorials and a final written exam are part of the course.

The following topics will be covered:

  • Dynamics Review
  • S-Plane and Bode Plots
  • Block Diagrams
  • FCS Overview
  • FCS Strategies and Design Criteria
  • Pre-Filters
  • Response Feedback
  • Command Systems
  • Augmentation Effect of Various Feedback Parameters
  • Fixed Wing Example
  • Bode Plots Stability Analysis
  • Fixed Wing and Rotary Wing Performance Specifications
  • FCS Issues and Testing

Anticipated Course Learning Outcomes

Be familiar with

  • Block diagram representation of a system and block diagram Algebra.
  • Generic structure of flight control systems.
  • The Poles and zeros formalism of a system
  • Application of Pre-filters in modern flight controls systems.
  • Response feedback technique used by modern flight control systems in order to augment stability of an aircraft.
  • Effects of common parameters feedback on aircraft stability.
  • Basic concepts of systems command and dynamic inversion.
  • General design criteria used for modern flight controls.
  • General design criteria used for modern flight controls.

Understand

  • The relationship between poles location on the S-Plane and dynamic modes of the system.
  • The relationship between transfer functions and frequency response of a system
  • The meaning of Gain and Phase margins and how to extract those from the Bode plots.
  • The meaning of bandwidth and phase delay and how to extract those from Bode plots.
  • The basic approach in flight testing of a highly augmented aircraft. This includes angle of attack, pitch rate command / pitch attitude hold, NzU, Nz, C*U, C*, roll rate command / roll attitude hold, and P-Beta. This also includes envelope protection features.

Know

  • How to construct Bode plots and how to interpret the frequency response information they retain.
  • How to implement the Root Locus analysis in order to assess the closed loop stability of a system.
  • How to use software to solve for basic stability augmentation problems.
  • How to use the Cooper Harper rating scale, PIO rating scale, and comment cards for the evaluation of modern flight control systems
  • How to use and set up synthetic tracking tasks.
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