Browsing by Subject "Rigid Body Dynamics"

Now showing 1 - 5 of 5
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    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.
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    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.
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    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).
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    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.
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    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.