Fixed membrane wings for micro air vehicles: Experimental characterization,numerical modeling,and tailoring

Fixed wing micro air vehicles (wingspan between 10 and 15 cm) are aerodynamically challenging due to the low Reynolds number regime (10⁴–10⁵) they operate in. The low aspect ratio wings (typically used to maximize area under a size constraint) promote strong tip vortices, and are susceptible to rolling instabilities. Wind gusts can be of the same order of magnitude as the flight speed (10–15 m/s). Standard control surfaces on an empennage must be eliminated for size considerations and drag reduction, and the range of stable center of gravity locations is only a few millimeters long. Membrane aeroelasticity has been identified as a tenable method to alleviate these issues: flexible wing structures with geometric twist (adaptive washout for gust rejection, delayed stall) and aerodynamic twist (adaptive inflation for high lift, larger stability margins) are both considered here. Recent investigations in static aeroelastic characterization, including flight loads, wing deformation, flow structures, aeroelastic-tailoring studies through laminate orientation, as well as unconventional techniques based on membrane pre-tension, are reviewed. Multi-objective optimization aimed at improving lift, drag, and pitching moment considerations is also discussed.     

Space radiation concerns for manned exploration.

Spaceflight exposes astronaut crews to natural ionizing radiation. To date, exposures in manned spaceflight have been well below the career limits recommended to NASA by the National Council of Radiation Protection and Measurements (NCRP). This will not be the case for long-duration exploratory class missions. Additionally. International Space Station (ISS) crews will receive higher doses than earlier flight crews. Uncertainties in our understanding of long-term bioeffects, as well as updated analyses of the Hiroshima. Nagasaki and Chernobyl tumorigenesis data, have prompted the NCRP to recommend further reductions by 30-50% for career dose limit guidelines. Intelligent spacecraft design and material selection can provide a shielding strategy capable of maintaining crew exposures within recommended guidelines. Current studies on newer radioprotectant compounds may find combinations of agents which further diminish the risk of radiation-induced bioeffects to the crew.     

Optimal thickness distributions of aeroelastic flapping shells

The severe weight limitations of flapping wing micro air vehicles necessitates the use of thin flexible wings, which in turn requires an aeroelastic modeling tool for proper numerical characterization. Furthermore, due to the unconventional nature of these vehicles, wing design guidelines for thrust and/or power considerations are not generally available; numerical design optimization then becomes a valuable tool. This work couples a nonlinear shell model to an unsteady vortex lattice solver, and then computes analytical design gradients: the derivative of aerodynamic force/power quantities with respect to a large vector of thickness variables. Gradient-based optimization is then used to locate the wing structure that maximizes the thrust, or minimizes the power under a thrust constraint, for a variety of shell boundary conditions. Changes in the topological features of the optimal wing thicknesses highlight important aeroelastic interactions that can be exploited for efficient flapping wings.