Colin Theodore

Rapid Frequency-Domain Modeling Methods for Unmanned Aerial Vehicle Flight Control Applications

Modeling of the flight dynamics of unmanned aerial vehicles (UAVs) poses unique challenges that are not present with manned aircraft. The use of analytical modeling methods based on first principles is often difficult for UAVs because of short design cycles, reduced development costs, and many unconventional designs. Also, without the need to carry a pilot, UAVs are often much smaller and lighter than manned aircraft. The lower weights and inertias result in higher natural frequencies and quicker vehicle responses requiring high bandwidth dynamics models. Frequency-domain system identification is especially well suited to the modeling of UAVs. With the availability of flight hardware early in many UAV programs, dynamic response models of the vehicle can be identified and validated rapidly with flight data. The system identification method also allows for rapid updating of vehicle response models as physical changes are made to the vehicle configuration. The use of frequency-domain system identification in the development and operation of a number of UAV programs is discussed. The example aircraft programs include Northrop Grumman’s Fire Scout vertical takeoff unmanned air vehicle demonstrator based on the Schweizer 300

Performance Evaluation of Vision-Based Navigation and Landing on a Rotorcraft Unmanned Aerial Vehicle

A rotorcraft UAV provides an ideal experimental platform for vision-based navigation. This paper describes the flight tests of the US Army PALACE project, which implements Moravecs pseudo-normalized correlation tracking algorithm. The tracker uses the movement of the landing site in the camera, a laser range, and the aircraft attitude from an IMU to estimate the relative motion of the UAV. The position estimate functions as a GPS equivalent to enable the rotorcraft to maneuver without the aid of GPS. With GPS data as a baseline, tests were performed in simulation and inflight that measure the accuracy of the position estimation

System Identification of Large Flexible Transport Aircraft

This paper presents results and lessons learned from a proof-of-concept study that used frequency-domain system identification to extract models of the lateral-directional flight dynamics of a large transport aircraft. These identified models are intended to be used for simulation model validation and upgrade, and for flight control law development and validation. Both of these applications require models that are accurate over a broad frequency range. For large transport aircraft identifying such models can be challenging given that: 1) the lower-frequency rigid-body dynamics modes are often lightly damped and difficult to identify accurately, and 2) the flexibility of the aircraft structure can significantly affect the response of the aircraft in the frequency range that is important for flight control and therefore must be accounted for in the dynamics models. A model structure is developed that is used to identify simultaneously the rigid-body aircraft response dynamics and the structural flexibility modes of the aircraft from flight data. Comparisons between the model responses and time history data collected during flight-testing show that the models are highly accurate in predicting both the rigid-body and structural responses. The paper presents details of the flight test procedures, frequency response and dynamics model identification, and the coupled rigid-body / structural flexibility model structure.

Aerodynamic Analysis of the Elytron 2S Experimental Tiltwing Aircraft

The Elytron 2S is a prototype aircraft concept to allow VTOL capabilities together with fixed wing aircraft performance. It has a box wing design with a centrally mounted tilt-wing supporting two rotors. This paper explores the aerodynamic characteristics of the aircraft using computational fluid dynamics in hover and low speed forward flight, as well as analyzing the unique control system in place for hover. The results are then used to build an input set for NASA Design and Analysis if Rotorcraft software allowing trim and flight stability and control estimations to be made with SIMPLIFLYD.

Vibration Analysis of a Composite Helicopter Rotor Blade at Hovering Condition

The helicopter is an essential and unique means of transport nowadays and needs to hover in space for considerable amount of time. During hovering flight, the rotor blades continuously bend and twist causing an increased vibration level that affects the structural integrity of the rotor blade leading to ultimate blade failure. In order to predict the safe allowable vibration level of the helicopter rotor blade, it is important to properly estimate and monitor the vibration frequencies. Therefore, the mathematical model of a realistic helicopter rotor blade composed of composite material, is developed to estimate the characteristics of free and forced bending-torsion coupled vibration. The cross-sectional properties of the blade are calculated at first and are then included in the governing equations to solve the mathematical model. The natural frequencies and mode shapes of the composite helicopter rotor blade are evaluated for both the nonrotating and rotating cases. The time-varying bending and torsional deflections at the helicopter rotor blade tip are estimated with suitable initial conditions. The validation of the model is carried out by comparing the analytical frequencies with those obtained by the finite element model.