Unpowered avian flight principles - 2 Flashcards
What forces are involved in gliding flight, and how is gliding initiated?
Lift, drag, and weight. The bird needs to lose altitude to maintain forward speed (“powered” by gravity”). Powered forward flight stops producing thrust and starts to glide by tilting the direction of motion forward.
What are the glide angle and ratio, and how do they characterize glide performance?
Glide angle (gamma) is the angle at which the body glides once the forces are balanced, and it is defined in terms of the horizontal and vertical distance covered, gamma = arctan(delta h / delta x). The glide ratio is delta x / delta h (distance covered per altitude unit). Glide performance is affected by the glide angle since gamma is related to the L/D ratio, namely, gamma = arctan(D/L), so a smaller glide angle means a higher L/D and greater glide distance. The glide ratio is proportional to L/D.
What types of soaring are there?
Static and dynamic soaring.
What are basic principles of static soaring and dynamic soaring?
Static soaring is based on updraughts (upward currents of air) -> the bird finds a region where the air rises as fast or faster than the bird’s own sinking speed.
Dynamical soaring takes advantage of changes in wind velocity with altitude. Requires horizontal wind with a vertical velocity gradient. The basic principle is to climb by gliding into the wind (upwind) starting near the surface and then doing a cyclical pattern of up and down.
What forces are involved in soaring flight?
Lift, weight, drag, and soaring force.
What benefits could soaring capabilities bring to MAVs?
Extended endurance, reduced power consumption - improve energy efficiency, exploit features in specific environments such as oceans or urban environments.
What are some examples of MAV research involving soaring?
Trajectory optimization and path planning, wind field estimation/prediction for autonomous soaring, and efficiency optimization.
What parameters can birds influence through wing morphing?
Area, AR (Aspect Ratio), sweep, twist, and camber.
How can wing morphing influence flight performance?
Area increase allows for higher lift, higher AR leads to a higher L/D ratio, hence higher efficiency, while lower AR allows for better maneuverability (rapid take-off), higher camber means higher lifter with higher drag which is good at the start, while lower camber allows better L/D ratios good for gliding and cruising, twisting does a variation of the angle of attack distribution along the span which can improve the lift and sweep allows increase in stability (backward) or increase in maneuverability (forward).
What benefits could morphing capabilities bring to MAVs?
Larger range of flight conditions can be covered, improved performance, and have more elaborate and effective actuation and control
