Topic
Static margin
About: Static margin is a research topic. Over the lifetime, 187 publications have been published within this topic receiving 1630 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this article, a moving mass trim controller (MMTC) is proposed to increase the accuracy of axisymmetric, ballistic vehicles, which is based on the deconing device test (DOT) described by White and Robinett.
Abstract: A moving mass trim controller is proposed to increase the accuracy of axisymmetric, ballistic vehicles. The moving mass trim controller differs from other moving mass schemes because it generates an angle of attack directly from the mass motion. The nonlinear equations of motion for a ballistic vehicle with one moving point mass are derived and provide the basis for a detailed simulation model. The nonlinear equations are linearized to produce a set of linear, time-varying autopilot equations. These autopilot equations are analyzed and used to develop theoretical design tools for the creation of moving mass trim controllers for both fast and slow spinning vehicles. A fast spinning moving mass trim controller is designed for a generic artillery rocket that uses principal axis misalignment to generate a trim angle of attack. A slow spinning moving mass trim controller is designed for a generic re-entry vehicle that generates a trim angle of attack with a center of mass offset and aerodynamic drag. The performance of both moving mass trim controllers are evaluated with the detailed simulation. VER the years, techniques for controlling the flight character- istics of missiles and re-entry vehicles (RV) have gravitated to systems that deliver relatively large amounts of control authority. For certain missions, such as an air-to-air missile or an RV designed to evade defenses, a large lateral acceleration capability was required. The technologies used to perform these missions ranged from ac- tuated canards, elevons, and flaps to jet interaction, thrust vector control, and a variety of other techniques.1 Because of the mission requirements for large maneuvers, systems that provided modest amounts of control capability were of little or no value. However, a new mission for accurate artillery rockets and RVs that utilize existing assets has prompted a renewed interest in simpler control techniques that produce small maneuvers. One such control technology is moving mass control. This tech- nique has previously been evaluated in conjunction with other con- trol methods such as the moving mass roll control of an aerodynam- ically asymmetric RV.2'3 A more direct application of moving mass control technology is the moving mass trim controller (MMTC). The MMTC generates a trim angle of attack (AOA) on an axisym- metric, ballistic vehicle directly from the motion of the mass. It is a novel, lightweight, low-cost retrofit to spinning ballistic vehi- cles that require modest flight-path corrections to obtain increased accuracy. Over 10 years ago, initial studies of the MMTC were performed by Regan and Kavetsky4 at the U.S. Naval Systems Warfare Cen- ter. Regan and his co-workers devised a single-shot MMTC that would provide modest range corrections near the target. At Sandia National Laboratories (SNL), the MMTC was an outgrowth of the deconing device test (DOT) described by White and Robinett.5 The DDT provided an initial glimpse of the effects of principal axis mis- alignment (PAM), roll rate, and center of mass offset. The MMTCs developed at SNL address the issue of roll rate, static margin (SM), PAM, and center of mass offset. The trim AOA for a fast spinning vehicle is generated by a PAM, whereas a slow spinning vehicle with a small SM relies on a center of mass offset to create a trim AOA resulting from aerodynamic drag. This paper derives the gen- eral nonlinear equations of motion for a one-moving mass system,
101 citations
TL;DR: In this article, a control law for the inner loop is derived for the independent control of the angular velocity components of the aircraft along roll, pitch, and yaw axes using aileron, elevator, and rudder.
Abstract: This paper presents an application of the inversion theory to the design of nonlinear control systems for simultaneous lateral and longitudinal maneuvers of aircraft. First, a control law for the inner loop is derived for the independent control of the angular velocity components of the aircraft along roll, pitch, and yaw axes using aileron, elevator, and rudder. Then by a judicious choice of angular velocity command signals, independent trajectory control of the sets of output variables (angle of attack, roll, and sideslip angles), (roll rate, angle of attack, and yaw angle), or (pitch, roll, and yaw angles) is accomplished. These angular velocity command signals are generated in the outer loops using state feedback and the reference angle of attack, pitch, yaw, and roll angle trajectories. Simulation results are presented to show that in the closed-loop system, various lateral and longitudinal maneuvers can be performed in spite of the presence of uncertainty in the stability derivatives.
100 citations
18 Apr 2005
TL;DR: Results indicate that BFF is an issue over lower altitude portions of the flight envelope and that active flutter suppression systems should be explored for future work.
Abstract: The paper presents results of aeroelastic analysis on a swept flying wing aircraft developed under contract for the Air Force Research Laboratory (AFRL) SensorCraft program. This configuration is characterized by a high aspect ratio, very flexible wing with 30 sweep. This configuration, like other examples of flexible flying wings, is prone to body freedom flutter (BFF) that results from coupling of the rigid body short period mode with wing bending. A NASTRAN finite element model (FEM) is used for an initial aeroelastic flutter analysis. Stiffness and mass properties are derived from the FEM to construct an approximate beam model of the wing for ASWING aero-structural analysis. Flutter analysis for the open loop aircraft explores trades in wing stiffness, altitude and center-ofgravity (CG) location to determine whether passive means can increase flutter speed to acceptable levels. A similar flutter analysis is performed with the addition of a closed loop pitch axis autopilot to stabilize the aircraft over a wider range of static margin. Initial results indicate that BFF is an issue over lower altitude portions of the flight envelope and that active flutter suppression systems should be explored for future work.
96 citations
TL;DR: In this paper, the effects of a steady angle of attack on nonlinear flutter and LCO of a delta wing-plate model in low subsonic flow have been investigated, and the results provide new insights into nonlinear aeroelastic phenomena not previously widely appreciated, i.e., LCOs for low aspect ratio wings that have a platelike nonlinear structural behavior.
Abstract: Limit cycle oscillations (LCOs) have been observed in flight for certain modern high-performance aircraft. The nonlinear physical mechanism responsible for the LCOs is still in doubt, even to the point of it not yet being determined whether the nonlinearity is principally in the flexible elastic structure of the aircraft or due to the fluid behavior in the surrounding aerodynamic flowfield. One observation from flight tests is that by changing the angle of attack of aircraft, the flight velocity at which LCOs begin may be raised or lowered and that the amplitude of the LCOs may be reduced. It has been suggested that this sensitivity to angle of attack indicates the nonlinearity is in the fluid rather than in the structure. We show that such effects of an angle of attack change can be the result of a structural nonlinearity. Specifically, an investigation to determine the effects of a steady angle of attack on nonlinear flutter and LCO of a delta wing-plate model in low subsonic flow has been made. A three-dimensional time domain vortex lattice aerodynamic model and a reduced order aerodynamic technique were used, and the structure is modeled using von Karman plate theory that allows for geometric strain-displacement nonlinearities in the delta wing structure. The results provide new insights into nonlinear aeroelastic phenomena not previously widely appreciated, i.e., LCOs for low aspect ratio wings that have a platelike nonlinear structural behavior. The effects of a steady angle of attack on both the flutter boundary and the LCOs are found to be significant. For a small steady angle of attack, α 0 ≤ 0.1 deg, the flutter onset velocity increases, whereas for larger α 0 , it decreases. Moreover, as α 0 increases, the maximum LCO amplitude decreases substantially. Such effects have been observed by Bunton and Denegri in flight flutter experiments. It is noted that the present theoretical results do not prove that the LCOs phenomena observed in flight are due to structural nonlinearities; however, the results of the present analysis are consistent with those observed in flight and do show that a structural nonlinearity can give rise to the observed effects of angle of attack on the LCOs.
52 citations
1 Jan 2003
TL;DR: Staelens et al. as discussed by the authors presented three modifications for an improved performance in terms of increased power output of a straight-bladed VAWT by varying its pitch, which can achieve a significant increase in the power output for higher wind speeds but requires abrupt changes in the local angle of attack making it physically and mechanically impossible to realize.
Abstract: The paper presents three modifications for an improved performance in terms of increased power output of a straight-bladed VAWT by varying its pitch. Modification I examines the performance of a VAWT when the local angle of attack is kept just below the stall value throughout its rotation cycle. Although this modification results in a very significant increase in the power output for higher wind speeds, it requires abrupt changes in the local angle of attack making it physically and mechanically impossible to realize. Modification II improves upon the first by replacing the local angle of attack by the blade static-stall angle only when the former exceeds the latter. This step eliminates the two jumps in the local effective angle of attack curve but at the cost of a slight decrease in the power output. Moreover, it requires a discontinuous angle of attack correction function which may still be practically difficult to implement and also result in an early fatigue. Modification III overcomes the limitation of the second by ensuring a continuous variation in the local angle of attack correction during the rotation cycle through the use of a sinusoidal function. Although the power output obtained by using this modification is less than the two preceding ones, it has the inherent advantage of being practically feasible.Copyright © 2003 by Yann Staelens, F. Saeed, and I. Paraschivoiu
50 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 1 |
| 2020 | 3 |
| 2019 | 5 |
| 2018 | 5 |
| 2017 | 6 |
| 2016 | 8 |