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  • 1
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    Generation and Calibration of Linear Models of Aircraft with Highly Coupled Aeroelastic and Flight Dynamics (2020)
    In:  CASI
    Details
    Publication Date: 2020-01-23
    Description: This presentation is a refinement of an earlier presentation describing the methods of generating models used for designing control laws for use in vehicles with significant structural effects.
    Keywords: Aircraft Stability and Control
    Type: AFRC-E-DAA-TN76537 , AIAA SciTech Forum 2020; Jan 06, 2020 - Jan 10, 2020; Orlando, FL; United States
    Format: application/pdf
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  • 2
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    Generation and Calibration of Linear Models of Aircraft with Highly Coupled Aeroelastic and Flight Dynamics (2020)
    In:  CASI
    Details
    Publication Date: 2020-01-22
    Description: The lightweight structures and unconventional configurations being considered for the next generation of aircraft mean that any effort to predict or control the flight dynamics is impacted by the structural dynamics. One of the most severe forms of coupling between aeroelasticity and flight dynamics is an instability called body freedom flutter. The existing tools often assume a relatively weak effect of structural dynamics on the flight dynamics, and are therefore incapable of modeling strong interactions like body freedom flutter. A method of combining different sources of data traditionally used for aeroelasticity and flight dynamics is described by reconciling many of the differences between these models. By building upon past modeling efforts, a level of familiarity in the approach is achieved. Generally the differences from the traditional approaches are subtle but significant. The traditional frequency domain flutter model in a modal coordinate system is converted to a form consistent with a time domain flight dynamics model. The time domain rational function approximation about a non-inertial coordinate system and the unique constraints for the conversion between the inertial and non-inertial coordinate systems are discussed. A consistent transformation of the states of aeroelastic models to flight dynamics models is derived, which enables the integration of data from higher fidelity computational fluid dynamics models or wind-tunnel testing. The present method of integrating multidisciplinary data was used to create models that compare well with X-56A flight-test data, including conditions past the flutter speed.
    Keywords: Aircraft Stability and Control
    Type: AFRC-E-DAA-TN75452 , AIAA SciTech Forum 2020; Jan 06, 2020 - Jan 10, 2020; Orlando, FL; United States
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  • 3
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    NASA Armstrong Flight Research Center Dynamics and Controls (530) (2019)
    In:  CASI
    Details
    Publication Date: 2019-10-30
    Description: No abstract available
    Keywords: Aircraft Stability and Control
    Type: AFRC-E-DAA-TN74004
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  • 4
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    Dynamics and Control of In-Flight Wing Tip Docking (2018)
    In:  CASI
    Details
    Publication Date: 2019-10-19
    Description: Project Link! is a NASA-led effort to study the feasibility of multi-aircraft aerial docking systems. In these systems, a group of vehicles physically link to each other during flight to form a larger ensemble vehicle with increased aerodynamic performance and mission utility. This paper presents a dynamic model and control architecture for a system of fixed-wing vehicles with this capability. The dynamic model consists of the 6 degree-of-freedom fixedwing aircraft equations of motion, a spring-damper-magnet system to represent the linkage force between constituent vehicles, and the NASA-Burnham-Hallock wingtip vortex model to represent the close-proximity aerodynamic interactions between constituents before the linking occurs. The control architecture consists of a guidance algorithm to autonomously drive the constituents towards their linking partners and an inner-loop angular rate controller. A simulation was constructed from the model, and the flight dynamic modes of the linked system were compared to the individual vehicles. The main contributions of this work are twofold. First is the introduction of close-proximity aerodynamic effects to create a realistic simulation framework for this problem. Second is the application of a sophisticated leaderfollower guidance algorithm to achieve in-air wingtip docking. Simulation results for both before and after linking are presented.
    Keywords: Aircraft Stability and Control
    Type: NF1676L-28646 , Journal of Guidance, Control, and Dynamics (ISSN 0731-5090) (e-ISSN 1533-3884); 41; 11; 2327-2337
    Format: application/pdf
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  • 5
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    MRAC with Time-Varying Reference Model from Convex Combination (2019)
    In:  CASI
    Details
    Publication Date: 2019-09-13
    Description: An extension of model reference adaptive control is presented that accommodates use of a time-varying reference model. Specifically, the reference model is taken to be a time-varying convex combination of two linear, time-invariant models. The design is intended to act as a way to smoothly transition between two different reference models without resorting to a scheduled switch. It also provides the ability to use an interpolated reference model when the plant is operating between design points. The time variation of the combination must satisfy some requirements to ensure stability but is otherwise user choice. Subject to these requirements, bounded tracking error behavior is demonstrated via Lyapunov stability analysis for the single-input, single-output, output feedback case. Tracking error convergence is asymptotic when time variation ceases. The proposed design is demonstrated in simulation of a numerical model.
    Keywords: Aircraft Stability and Control
    Type: ARC-E-DAA-TN66631 , American Control Conference; Jul 10, 2019 - Jul 12, 2019; Philadelphia, PA; United States
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  • 6
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    Joint Technical Conference on Slush Drag and Braking Problems (1961)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: No abstract available
    Keywords: Aircraft Stability and Control
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  • 7
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    Formation Flight System Extremum-Seeking-Control Using Blended Performance Parameters (2018)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: An extremum-seeking control system for formation flight that uses blended performance parameters in a conglomerate performance function that better approximates drag reduction than performance functions formed from individual measurements. Generally, a variety of different measurements are taken and fed to a control system, the measurements are weighted, and are then subjected to a peak-seeking control algorithm. As measurements are continually taken, the aircraft will be guided to a relative position which optimizes the drag reduction of the formation. Two embodiments are discussed. Two approaches are shown for determining relative weightings: "a priori" by which they are qualitatively determined (by minimizing the error between the conglomerate function and the drag reduction function), and by periodically updating the weightings as the formation evolves.
    Keywords: Aircraft Stability and Control
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  • 8
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    Method and System for Weakening Shock Wave Strength at Leading Edge Surfaces of Vehicle in Supersonic Atmospheric Flight (2015)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A method and system are provided to weaken shock wave strength at leading edge surfaces of a vehicle in atmospheric flight. One or more flight-related attribute sensed along a vehicle's outer mold line are used to control the injection of a non-heated, non-plasma-producing gas into a local external flowfield of the vehicle from at least one leading-edge surface location along the vehicle's outer mold line. Pressure and/or mass flow rate of the gas so-injected is adjusted in order to cause a Rankine-Hugoniot Jump Condition along the vehicle's outer mold line to be violated.
    Keywords: Aircraft Stability and Control
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  • 9
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    Method and system for control of upstream flowfields of vehicle in supersonic or hypersonic atmospheric flight (2012)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The upstream flowfield of a vehicle traveling in supersonic or hypersonic atmospheric flight is actively controlled using attribute(s) experienced by the vehicle. Sensed attribute(s) include pressure along the vehicle's outer mold line, temperature along the vehicle's outer mold line, heat flux along the vehicle's outer mold line, and/or local acceleration response of the vehicle. A non-heated, non-plasma-producing gas is injected into an upstream flowfield of the vehicle from at least one surface location along the vehicle's outer mold line. The pressure of the gas so-injected is adjusted based on the attribute(s) so-sensed.
    Keywords: Aircraft Stability and Control
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  • 10
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    Aerodynamically stabilized instrument platform (2012)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A suspension apparatus for suspending instrumentation from an airborne platform may include a generally longitudinal boom having a payload end and a tail end. Yaw and pitch stabilizers may be disposed at the tail end of the boom. A mast that may be selectively translatable on the boom may connect the boom to a tether line of the airborne platform. The payload may be attached to the payload end of the boom. The mast may be positioned axially along the boom at the center of gravity of the combination of the payload, boom, pitch stabilizer, and yaw stabilizer.
    Keywords: Aircraft Stability and Control
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