Larry A. Moody*
The Boeing Company, Seattle, WA, 98124-2207
One of the most useful contributions of the Flight Simulator to the technical development of new aircraft is to provide a tool that can be used to develop and evaluate the aircraft’s control characteristics. Early aircraft were controlled entirely with manual actuation of the control surfaces through cables and push rods. In contrast, some modern aircraft are controlled almost entirely with computer actuation, or at least with computer augmentation. This paper discusses how, from one end of this spectrum to the other, simulation of control techniques has evolved and is paramount to successful aircraft development and usage. The purpose of this paper is to provide a perspective on the evolution of flight control simulation, and with that perspective, how we may ponder new and greater uses for this emerging new technology.
HE science of developing, testing, and refining the control systems that define the handling characteristics of aircraft has seen phenomenal progress in the last half century, due primarily to the advanced capabilities of computer simulation systems. It is now commonplace for completely new aircraft to demonstrate remarkably precise handling and control characteristics on the very first flight, something which was rarely seen before the advancement of control system simulation. Flight test envelope expansion can progress with fewer test flights as confidence in the aircraft is gained through good correlation with simulation data, saving millions of dollars in development costs. Simulation of the aircraft response characteristics has become so accurate that even mission effectiveness studies can be conducted before the first piece of aluminum is cut. This paper attempts to recap some of the major advancements in control system simulation, along with exploring the possibilities of where the future might take us. These advancements typically fall into the categories of modeling the aircraft dynamics, modeling the control system and components, and simulating the pilot vehicle interface. Computational capability is a factor in each of the categories and is discussed as well.
Modeling the Aircraft Dynamics
The foundation of successful control system simulation is accurate modeling of the aircraft dynamics. This requires correct aircraft aerodynamic force and moment data to calculate accelerations, and equations of motion with computational integration methods to obtain velocities and positions from the accelerations. Over time, techniques have been developed to adapt these mathematics concepts to analog computers and then digital computers. The speed of the digital computer has a significant bearing on the update rate and resulting model fidelity. A. Equations of Motion
The first known adequate formulation of the equations of motion occurred around 1755 when Leonhard Euler, a Swiss mathematician, formulated the equations of motion based on Newtonian mechanics and the works of John and Daniel Bernoulli1. Interestingly, Euler was educated in his native town under the direction of John Bernoulli, who also had made significant contributions to hydrodynamics that were later applied to
Figure 1. Leonhard Euler, 17071783. First Known Formulation of Equations of Motion.
Boeing Associate Technical Fellow, Phantom Works Flight Control Research, P.O. Box 3707 / MC 4A-10, AIAA Member.
American Institute of Aeronautics and Astronautics
aerodynamics2. Although Euler was blinded in 1768, he was remarkably still able to recast and improve much of his earlier work. Euler was born in Basel, Switzerland in 1707, spent most of his career in St. Petersburg and Berlin until he died in 1783. Unfortunately, neither Euler nor anyone else in the 18th and early 19th centuries had the ability to solve these equations in a practical way for simulating aircraft...