R. Bradley

The principles and practical application of helicopter inverse simulation

Inverse simulation is a technique whereby the control actions required for a modelled vehicle to fly a specified manoeuvre can be established. In this paper the general concepts of inverse simulation are introduced, and an algorithm designed specifically to achieve inverse simulation of a single main and tail rotor helicopter is presented. An important element of an inverse simulation is the design of the input functions i.e. manoeuvre definitions, and the methods used are also detailed. A helicopter mathematical model is also discussed along with the validation and verification of the inverse simulation. Finally, the applicability of the method is demonstrated by illustration of its use in two flight dynamics studies.

How Do Helicopter Pilots Know When to Stop, Turn or Pull Up? (Developing Guidelines for Vision Aids)

The title of this paper, posed as a question, reflects the current interest in gaining an improved understanding of visual perception in flight control to inform the development of design guidelines for future pilot vision aids. The paper develops the optical flow theory of visual perception into its most recent incarnation, tau-coupling, where tau is the time to closure to surfaces at current velocity. General tau-theory posits that the closure of any type of gap, using any form of sensory input, is guided by sensing and constantly adjusting the tau of the gap. According to the theory, and contrary to what might be expected, information about the distance to obstacles or the landing surface, for example, and about the speed and deceleration of approach, are not necessary for precise control of landing or stopping. Analysis is presented that supports the importance of tau-coupling in flight control. Results from simulation trials conducted at DERA and at The University of Liverpool demonstrate the considerable power of what we describe as tau-guides, that lead the pilot to adopt a prospective flight control strategy.

Mathematical Definition of Helicopter Maneuvers

Helicopter performance and handling qualities are now routinely assessed in relation to specific maneuvers. The use of inverse simulation is then attractive as it allows a helicopter mathematical model to be driven by a pre‐defined maneuver, and the control histories required to achieve this trajectory to be found. The manner in which maneuver is defined is then of great importance, and this paper aims to outline some appropriate techniques for modelling helicopter maneuvers. The basic principles and requirements for inverse simulation are introduced, and several methods of defining trajectories are described and examples given. Finally, for validation purposes, models of the Rapid Sidestep and Transient Turn Mission Task Elements (MTEs) are compared with flight data.