SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 13 - JULY 5, 2006

08 AIRCRAFT STABILITY AND CONTROL
Includes flight dynamics, aircraft handling qualities, piloting, flight controls, and autopilots.

For related information see also 05 Aircraft Design, Testing and Performance; and 06 Avionics and Aircraft Instrumentation.

20060019397 Surrey Univ., Guildford, UK

Combined Singularity Avoidance for Variable Speed Control Moment Gyroscope Clusters

Richie, David J; Lappas, Vaios J; Asghar, Sajjad; Richie, David J; Palmer, Phil L; Apr 18, 2006; 16 pp.; In English Report No.(s): AD-A446272; CI04-1769; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA446272; Avail.: CASI: A03, Hardcopy

Variable Speed Control Moment Gyroscopes (VSCMGs), defined by Schaub in [1], effectively applied to combined energy storage and attitude control in [2,3], and further studied by Yoon and Tsiotras in [4,5], can avoid attitude singularities by varying wheel speed.

However, this device's key advantage lies in torque amplification via gimballing (i.e. operating in its CMG mode). The primary limitation of this CMG mode, though, is the existence of gimbal-lock singularity states.Avoiding escapable singularity states, studied extensively byWie for CMGs [6] and Schaub for VSCMGs [7], is exacerbated in the case of simultaneous attitude and power tracking requirements [5]. Although [5] gives an algorithm for combined energy storage and attitude control with VSCMG singularity avoidance, it does not directly evaluate this algorithm with respect to other robust CMG singularity avoidance methods from the literature. For this reason, two practical steering laws were adapted from previous results for this challenging case and compared to the results given in [5]. First,Wie's Generalized Singularity Robust (GSR) steering law, originally developed for attitude tracking with CMGs [8] was modified to use VSCMGs.

Although the GSR effectively perturbs gimbals through locked configurations when compared to classical CMG methods (see [6,9, 10]), it also imparts small altitude torque errors which can linger for a few minutes after a CMG singularity. This problem can be disruptive to some space missions that use satellite off-pointing (e.g. precision earth imaging) where accurate trajectory tracking during operations is paramount. DTIC

Algorithms; Attitude Control; Control Moment Gyroscopes; Gimbals; Space Missions; Speed Control

20060019804 Air Force Research Lab., Wright-Patterson AFB, OH USA

Vision-Based UAV Flight Control and Obstacle Avoidance

He, Zhihai; Jan 2006; 12 pp.; In English Report No.(s): AD-A446852; AFRL-VA-WP-TP-2006-313; No Copyright; Avail.: CASI: A03, Hardcopy

In this work, we explore various ideas and approaches to deal with the inherent uncertainty and image noise in motion analysis, and develop a low-complexity, accurate and reliable scheme to estimate the motion fields from UAV navigation videos.

The motion field information allows us to accurately estimate ego-motion parameters of the UAV and refine (or correct) the motion measurements from other sensors.

Based on the motion field information, we also compute the range map for objects in the scene.

Once we have accurate knowledge about the vehicle motion and its navigation environment (range map), control and guidance laws can be designed to navigate the UAV between way points and avoid obstacles. DTIC

Drone Vehicles; Flight Control; Obstacle Avoidance; Pilotless Aircraft; Vision

20060020159 NASA Langley Research Center, Hampton, VA, USA

Switching LPV Control of an F-16 Aircraft via Controller State Reset

Lu, Bei; Wu, Fen; Kim, SungWan; [2004]; 24 pp.; In EnglishContract(s)/Grant(s): NAG1-01119; 23-762-65-AG; Copyright; Avail.: CASI: A03, Hardcopy

In flight control, the design objective and the aircraft dynamics may be different in low and high angle of attack regions.This paper presents a systematic switching Linear Parameter-varying LPV method to determine if it is practical to use f or flight control designs over a wide angle of attack region. The approach is based on multiple parameter-dependent Lyapunov functions a family of LPV controllers are designed, and each of them is suitable for a specific parameter subspace. The state of the controller is reset to guarantee the stability requirement of the Lyapunov function when the switching event occurs. Two parameter-dependent switching logics, hysteresis switching and switching with average dwell times are examined. The proposed switching LPV control scheme is applied to an F-16 aircraft model with different design objectives and aircraft dynamics in low and high angle of attack regions. The nonlinear simulating results using both switching logics are compared. Author

Controllers; Flight Control; Liapunov Functions; Linear Parameter-Varying Control; Switching; Control Systems Design; Aircraft Control

Source: NASA