optimized, stability and control coefficients calculated, open-loop plant model created, flight controller designed, and closed-loop simulation run, all in a rapid …

This paper uses a combination of free and commercial off-the-shelf (COTS) modeling and simulation software to simplify and accelerate the flight vehicle design process. Using an example of a new light-weight aircraft the paper shows how a vehicle’s geometry can be optimized, stability and control coefficients calculated, open-loop plant model created, flight controller designed, and closed-loop simulation run, all in a rapid iterative fashion, to confirm that system level requirements are satisfied.

CREATING a new or modifying an existing flight vehicle is a complex and time-consuming process. Engineers have to make decisions about vehicle configuration and flight control design that will ensure that system-level specifications are met. Any changes to hardware are very expensive and time consuming. Therefore it is important to finalize and verify the design as much as possible before any hardware is built. Model-Based Design enables engineers to test and verify their ideas in the early stages of the design process when making changes to the design is still relatively easy and inexpensive.
In this paper we use an example of a design of a new light aircraft to present a method for rapid iteration over vehicle geometric configuration and flight control design. The paper describes the steps that stability and control engineers typically go through in the early stages of the design process. These steps include: definition of the vehicle’s geometry, determination of the vehicle’s aerodynamic characteristics, creation of a simulation to verify the performance, and design of flight control laws.
Each of these steps can be a time-consuming task. In this paper we present tools and techniques for streamlining these steps and ensuring rapid iteration over the design. We first talk about a method for determining the vehicle’s aerodynamic characteristics based on its geometry. We discuss US Air Force Digital Data Compendium (Datcom) software and present results of Digital Datcom analysis of our particular vehicle configuration. We then demonstrate how to rapidly and easily import results obtained from Digital Datcom into MATLAB® for further analysis. We illustrate what preliminary analysis of aerodynamic stability and control coefficients and derivatives can reveal about the vehicle’s performance and stability.
We then show how to quickly create a simulation of a flight vehicle. We discuss modeling equations of motion, calculating forces and moments acting on the aircraft, modeling vehicle components such as sensors and actuators, and modeling environmental effects such as atmosphere, gravity, and wind gusts. We demonstrate how aerodynamic coefficients from Digital Datcom can be used in the simulation to rapidly calculate aerodynamic forces and moments acting on the vehicle.
Next, flight control design techniques are discussed. Using the example of longitudinal control design for our aircraft we show how the simulation model can be easily linearized and how a controller can be designed that meets both time domain and frequency domain specifications. We also show how, for our specific example of longitudinal light control, we design the inner- and outer-loop controller effectively.
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Download Model-Based Design of a New Light-weight Aircraft.pdf