Micro air vehicle motion tracking and aerodynamic modeling

unsteady aerodynamics;Micro air vehicle (MAV);flight dynamics;motion tracking;Vicon;modeling;separation parameter;MAV performance

Uhlig, Daniel

关键词: unsteady aerodynamics;    Micro air vehicle (MAV);    flight dynamics;    motion tracking;    Vicon;    modeling;    separation parameter;    MAV performance;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49560/Daniel_Uhlig.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Aerodynamic performance of small-scale fixed-wing flight is not well understood, and flight data are needed togain a better understanding of the aerodynamics of micro air vehicles (MAVs) flying at Reynolds numbersbetween 10,000 and 30,000. Experimental studies have shown the aerodynamic effects of low Reynoldsnumber flow on wings and airfoils, but the amount of work that has been conducted is not extensive andmostly limited to tests in wind and water tunnels.In addition to wind and water tunnel testing, flight characteristics of aircraft can be gatheredthrough flight testing. The small size and low weight of MAVs prevent the use of conventional on-boardinstrumentation systems, but motion tracking systems that use off-board triangulation can capture flighttrajectories (position and attitude) of MAVs with minimal onboard instrumentation. Because capturedmotion trajectories include minute noise that depends on the aircraft size, the trajectory results wereverified in this work using repeatability tests.From the captured glide trajectories, the aerodynamiccharacteristics of five unpowered aircraft were determined.Test results for the five MAVs showed the forces and moments acting on the aircraft throughout thetest flights. In addition, the airspeed, angle of attack, and sideslip angle were also determined from thetrajectories. Results for low angles of attack (less than approximately 20 deg) showed the lift, drag, andmoment coefficients during nominal gliding flight. For the lift curve, the results showed a linear curve untilstall that was generally less than finite wing predictions. The drag curve was well described by a polar.The moment coefficients during the gliding flights were used to determine longitudinal and lateral stabilityderivatives. The neutral point, weather-vane stability and the dihedral effect showed some variation withdifferent trim speeds (different angles of attack). In the gliding flights, the aerodynamic characteristicsexhibited quasi-steady effects caused by small variations in the angle of attack. The quasi-steady effects, orsmall unsteady effects, caused variations in the aerodynamic characteristics (particularly incrementing thelift curve), and the magnitude of the influence depended on the angle-of-attack rate.In addition to nominal gliding flight, MAVs in general are capable of flying over a wide flight envelopeincluding agile maneuvers such as perching, hovering, deep stall and maneuvering in confined spaces. From the captured motion trajectories, the aerodynamic characteristics during the numerous unsteady flights weregathered without the complexity required for unsteady wind tunnel tests. Experimental results for the MAVsshow large flight envelopes that included high angles of attack (on the order of 90 deg) and high angularrates, and the aerodynamic coefficients had dynamic stall hysteresis loops and large values.From the large number of unsteady high angle-of-attack flights, an aerodynamic modeling method wasdeveloped and refined for unsteady MAV flight at high angles of attack. The method was based on aseparation parameter that depended on the time history of the angle of attack and angle-of-attack rate.The separation parameter accounted for the time lag inherit in the longitudinal characteristics duringdynamic maneuvers. The method was applied to three MAVs and showed general agreement with unsteadyexperimental results and with nominal gliding flight results.The flight tests with the MAVs indicate that modern motion tracking systems are capable of capturing theflight trajectories, and the captured trajectories can be used to determine the aerodynamic characteristics.From the captured trajectories, low Reynolds number MAV flight is explored in both nominal gliding flightand unsteady high angle-of-attack flight. Building on the experimental results, a modeling method for thelongitudinal characteristics is developed that is applicable to the full flight envelope.