Presentations and Working Papers

Persistent link for this collection

https://hdl.handle.net/11299/167311

Included are presentations and working papers for the PAAW Program.

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Now showing 1 - 18 of 18

Application of MIDAAS to BFF Models
(2014-11-23) Danowsky, Brian
Modal Isolation and Damping for Adaptive Aeroservoelastic Suppression (MIDAAS) was applied to the BFF model at various flight conditions. All available control surfaces were used with nine sensors. MIDAAS synthesis produces a gain matrix feeding back all outputs to all inputs. Using these inputs and outputs, the resulting gain matrix is 9 by 8. Solutions were obtained for 3 different flight conditions (42, 44, and 50 knots). For each flight condition, a solution was obtained for two models, 1) bare airframe dynamics and 2) full system dynamics including bare airframe, actuator and sensor dynamics.
CFD/CSD-based IOROM Construction for mAEWing1 initial design
(2015-09-15) Danowsky, Brian
This working paper summarizes the construction of the Input to Output Reduced Order Model (IOROM) for mAEWing1. The linear time invariant (LTI) IOROM is based on a fixed trimmed flight condition and is represented as a state space system with the traditional four matrix quadruple: [A, B; C, D]. These IOROMs are entirely software-based models that start with a detailed Computational Fluid Dynamic / Computational Structural Dynamic (CFD/CSD)-based model built in the CMSoft, Inc. AERO software suite. The nonlinear full order AERO model (NFOM) is millions of degrees of freedom and is unsuitable for open loop dynamic analysis and control system design. From this model, a linear time invariant reduced order aeroelastic model (ROM) is built describing the modal structural dynamics coupled with the unsteady aerodynamic forces. This model is represented in an inertial frame since that is the frame for the finite element model (FEM). This ROM is sent to the STI ASETool software where the structural rigid body states are cast into the traditional body-fixed frame, and the input and output effect is added with user defined descriptions of actuation and sensor nodes resulting in the IOROM. The IOROM is a linear model of significantly reduced order that is in the ideal form for dynamic analysis and control system design. It includes all rigid body states, structural modal states, and unsteady aerodynamic states. The 12 rigid body states include the translational and rotational displacements and velocities and are represented in their traditional body-fixed frame of reference, making this model in an ideal form for complete control system design that includes primary flight control and flutter suppression. Stability and control derivatives can be directly extracted from the IOROM for direct comparison to experimental test data or other analytical models. These models are also used for novel system analysis using phasor diagrams where rigid body and flexible dynamic coupling can be clearly characterized. Approximate linear parameter varying models can also be created from the IOROMs that are dependent on a variable trim velocity. These models can be used for traditional flutter analysis (e.g., V-G diagrams, etc.) and LPV control design.
Classical Control Design Feasibility Study with BFF Models
(2014-11-18) Lee, Dongchan; Danowsky, Brian
This working paper documents an initial control feasibility study to determine if classical control techniques could be utilized to favorably augment the stability of the BFF vehicle. This study focused on the lower speed models which have stable, or slightly unstable aeroelastic dynamics. Future studies will explore the higher speed models with highly unstable aeroelastic modes. The final control solution will incorporate stability augmentation with aeroelastic suppression, including flutter suppression to stabilize the vehicle beyond the flutter boundary. The principal goal is a defined strategy, process and supporting software tools to develop a full envelope controller for flexible aeroelastic vehicles with significant rigid body and flexible coupling. Focus will be on blended wing-body vehicle designs like the BFF and X-56A. The purpose of this study is a background feasibility investigation.
Flight-Dynamics, Flutter, and Active-Flutter-Suppression Analyses of a Flexible Flying-Wing Research Drone
(As presented at the NASA Armstrong Flight Research Center Edwards AFB, CA, 2015-06-15) Schmidt, David
Flight-Dynamics, Flutter, and Active-Flutter-Suppression Analysis of a Flexible Flying-Wing Research Drone
(Aerospace Flutter and Dynamics Council (AFDC) Meeting, Spring 2015, 2015-04-16) Schmidt, David
Investigation of suitable flight test inputs for system identification of low frequency dynamics for the mini MUTT
(2015-01-16) Dongchan, Lee; Danowsky, Brian
The purpose of this document is to investigate suitable excitations for flight test to identify rigid body dynamic characteristics. It is understood that the stiff wing mini MUTT (Fenrir) will be flown soon for identification of rigid body dynamic characteristic. The flight test data will further be used to identify unknown system parameters offline. The model system considered in this study is the BFF model at 40 kts as this is the lowest flight condition available and displays the least amount of coupling between rigid body and flexible dynamics. It is noted that this model still displays coupling between the pitch dynamics and the 1st symmetric wing bending mode. The objective is to focus on low frequency dynamics as it is expected that the stiff wing mini MUTT (Fenrir) should display similar low frequency dynamics. Different input sequences for the elevator and aileron control inputs, are investigated. The sensors investigated are the roll and pitch rates at the aircraft center body IMU.
Investigation of system input and output blending for zero placement
(2014-11-25) Danowsky, Brian
The zeros are a function of the system input and output. Appropriate selection of sensor outputs and control inputs influences the zeros of the open loop system and this directly influences the effectiveness of any resulting controller. The purpose of this working paper is to summarize the investigation of appropriate input and output blending for zero placement as applied to an aeroseroelastic pitch-plunge model.
mAEWing1 Design Review
(2015-02-27) Taylor, Brian
MATLAB-Based Flight-Dynamics and Flutter Modeling of a Flexible Flying-Wing Research Drone
(2015-05-19) Schmidt, David
A relatively low-order, linear dynamic model is developed for the longitudinal flight- dynamics analysis of a flexible, flying-wing research drone, and results are compared to previously published results. The model includes the dynamics of both the rigid-body and elastic degrees of freedom, and the subject vehicle is designed to flutter within its flight envelope. The vehicle of interest is a 12-pound unmanned, flying-wing aircraft with a wingspan of 10 ft. In the modeling, the rigid-body degrees of freedom (DOFs) are defined in terms of motion of a vehicle- fixed coordinate frame, as required for flight-dynamics analysis. As a result, the state variables corresponding to the rigid-body DOFs are identical to those used in modeling a rigid vehicle, and the additional states are associated with the elastic degrees of freedom. Both body-freedom and bending-torsion flutter conditions are indicated by the model, and it is shown that the flutter speeds, frequencies, and genesis modes suggested by this low-order model agree very well with the analytical predictions and flight-test results reported in the literature. The longitudinal dynamics of the vehicle are characterized by a slightly unstable Phugoid mode, a well-damped, pitch-dominated, elastic-short-period mode, and the stable or unstable aeroelastic modes. A classical, rigid-body, short-period mode does not exist.
Modal Identification from Sköll flight tests
(2015-06-20) Danowsky, Brian
Modal identification was performed on flight test data using the Curve Fitting Frequency Domain Decomposition (CFDD) method. The emphasis is to identify aeroelastic modes rather than rigid body modes. Consequently, the aeroelastic short period mode was identified in addition to several higher frequency aeroelastic modes. All of the modes identified reflect complex-valued aeroelastic modes, as opposed to real-valued dry structural modes. The following flights were used for identification: Sköll Flight 3: 20 m/s flight condition; Sköll Flight 4: 30 m/s flight condition.
Parameter identification studies using SIDPAC with Fenrir’s 1st flight data set
(2015-03-06) Dongchan, Lee; Danowsky, Brian
This document summarizes the process of identifying unknown dynamic systems from measured flight test data. Several available system identification tools were evaluated based on accuracy and robustness. Among them,SIDPAC developed by NASA was chosen. The objective of this study is to lay out the procedures to identify unknown systems from flight test data and to provide recommendations for following flight tests. Data from the Fenrir’s flight was used.
Performance Adaptive Aeroelastic Wing Kickoff
(2014-09-23) Taylor, Brian
Preliminary Open Loop Analysis of BFF Models: Concentrating on low frequency dynamics
(2014-11-17) Danowsky, Brian
This working paper documents preliminary open loop analysis of the Lockheed Martin BFF models. These models were delivered to Systems Technology Inc from the University of Minnesota under a different contract. The focus for this study is on the rigid body dynamics which are in the lower frequency range. This vehicle has high coupling between rigid body and flexible dynamics so traditional classic rigid body modes do not exist. Regardless, the low speed models do exhibit some behavior familiar to traditional aircraft dynamic modes (e.g., short period, phugoid, dutch roll, roll subsidence, spiral).
Preliminary system identification studies with the stiff wing mini MUTT Fenrir
(2015-03-16) Danowsky, Brian
A short successful flight test with the stiff wing mini MUTT, named Fenrir, was conducted on 9 February 2015. The purpose of this flight was to gather preliminary data for system identification focused on low frequency rigid body dynamics.
Stability Augmentation and Active Flutter Suppression of a Flexible Flying-Wing Drone
(2015-05-19) Schmidt, David
Integrated control laws are developed for stability augmentation and active flutter suppression (AFS) of a flexible, flying-wing drone. The vehicle is a 12-pound unmanned, flying- wing research aircraft with a 10 ft wingspan. AFS is flight critical since the subject vehicle is designed to flutter within its flight envelope. The critical flutter condition involves aeroelastic interactions between the rigid-body and elastic degrees of freedom; hence the control laws must simultaneously address both rigid-body stability augmentation and flutter suppression. The control-synthesis approach is motivated by the concept of Identically Located Force and Acceleration (ILAF), successfully applied on some previous operational aircraft. Based on the flutter characteristics and on conventional stability-augmentation concepts, two simple loop closures are suggested. It is shown that this control architecture robustly stabilizes the body- freedom-flutter condition, increases the damping of the second aeroelastic mode (which becomes a second flutter mode at higher velocity), and provides reasonably conventional vehicle pitch- attitude response. The critical factors limiting the performance of the feedback system are identified to be the bandwidth of the surface actuators and the pitch effectiveness of the control surfaces.
Survey of Existing Aeroservoelastic Models
(2015-05-04) Danowsky, Brian; Schmidt, David
This working paper documents a survey of existing mathematical models of aeroservoelastic aircraft. For the purposes of this working paper, the primary purpose of such models is for control analysis and design. Enhanced validation and simulation (piloted and non-piloted) are also important.
System identification studies with the stiff wing mini MUTT Fenrir – Flight 20
(2015-06-11) Danowsky, Brian
A successful flight test with the stiff wing mini MUTT, named Fenrir, was conducted on 27 May 2015. The purpose of this flight was to gather preliminary data for system identification focused on low frequency rigid body dynamics. No augmentation was used during the 1st flight on this day, which is formally flight 20. This working paper analyzes flight 20 only. 3-2-1-1 pitch excitations were sent to individual symmetric surface pairs coincident with normal pilot inputs. For reference, a preliminary model of the stiff wing Fenrir (developed by D. K. Schmidt) at a flight condition of 65 ft/s (19.8 m/s) indicates a short period mode at 9.02 rad/s with a damping ratio of 0.658 and a phugoid mode at 0.569 rad/s with a damping ratio of -0.0251. It is expected that the actual aircraft dynamics will differ but these dynamic parameters provide a good baseline for ballpark values for comparison to the flight test data. Analysis of these data were performed in both the frequency and time domains. Short period system parameters were identified using two approaches: 1) frequency domain equation error, and 2) subspace system identification in the time domain.
Year 1 Review
(2015-10-29) Taylor, Brian