Dynamic soaring of a sailplane in the earth's atmospheric boundary layer was computationally investigated over a range of conditions to explore the feasibility of flying over a large vertical extent over open fields. A point-mass sailplane model was studied as well as a full six degree-of-freedom (6-DOF) piloted sailplane model. For the point-mass model, parameter sweeps were performed around a baseline 3-m (9.58-ft) wingspan sailplane having a weight of 15 kg (33 lb) and aspect ratio of 20. Results from the point-mass model show that in certain high wind conditions, dynamic soaring energy-conserving orbits are possible for flight trajectories extending from the ground to 185 m (607 ft) aloft. A 6-DOF piloted flight simulator was used, and it produced similar results that showed dynamic soaring over open fields for large vertical extents. Together these results support the conclusion that it is possible to perform dynamic soaring in high wind conditions through the full extent of the atmospheric boundary layer to high altitudes over open land with model-scale unpowered sailplanes having both high wing loadings and high lift-to-drag ratios.
This paper presents wind tunnel results of wings of low-to-moderate aspect ratio (2≤A≤5) at low Reynolds numbers (60,000 to 160,000). Tests were conducted in the low-turbulence wind tunnel in the Subsonic Aerodynamics Research Laboratory at the University of Illinois at Urbana-Champaign (UIUC). A 3-component force/moment balance was designed and fabricated. The balance design methodology and validation are described in detail. Low Reynolds number tests performed on a wing having an aspect ratio of 4 and using the Wortmann FX 63-137 airfoil showed the existence of a critical Reynolds number of 90,000 for which a jump in performance characteristics was observed. Pre-stall and post-stall hysteresis was captured at the critical Reynolds number. Flow visualization photographs for the wing at different angles of attacks are presented. Finally, aerodynamic performance measurements taken for ten flat-plate rectangular and tapered wings are also presented and discussed.
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