Flapping-wing flight: aerodynamics - 3 Flashcards
What are some of the advantageous features of FWMAVs ?
The potential of miniaturization, power-efficient at low Re, highly agile and maneuverable, hover capabilities, extensive flight envelope, light, unmanned, safe, and inexpensive.
What is the stroke plane?
During the stroke, the wing motion is approximately in the stroke plane.
How do stroke plane orientation and direction of flapping change between forward and hovering flight?
For forward flight, the stroke plane is more vertical, and the flapping is more up and down (the more horizontal the stroke plane, the more forward and backward the wing motion and the slower the flight). We achieve hover flight when the stroke plane is completely horizontal (wing motion totally backward-forward).
How does the relative wind velocity vary along the wing span?
Near the wing tip, the relative wind is significantly influenced by flapping, whereas near the wing root, the relative wind is mostly due to forward flight and has lower velocity.
What phases are involved in a flap cycle, and what role do they have in force generation?
The flap cycle has two phases, upstroke and downstroke. Downstroke creates an overall resultant force tilted forward in forward flight. The upstroke produces much less force, especially in fast flight for birds (passive upstroke), or it can produce thrust for slow-flight insects (active upstroke).
What is wing rotation and why is it important?
Wing rotation allows for stroke reversal and consists of rapidly rotating the transfer phase between down and upstroke. It is important since it allows the leading edge of the wings to correspond to the aerodynamic leading edge, which is what allows the wings to maintain a positive angle of attack and generate lift during the entire flap cycle.
How does normal hovering work?
Wings beat approximately horizontally, and the body is pitched up. The process relies on wing rotation. Downstroke -> Stroke reversal so that lower surface faces up -> upstroke -> stroke reversal.
Which three non-dimensional parameters are important when analyzing flapping-wing aerodynamics?
Reynolds number (Re), Strouhal number (St), and Reduced frequency (k). They allow us to determine the main characteristics of aerodynamics and decide which assumptions are acceptable. This allows us to define aerodynamic similarity - the same behavior at different scales.
What aerodynamic force generation processes are involved in flapping flight?
Free-stream circulation, rotational circulation, delayed stall, leading-edge vortex, wing wake interaction, added mass, and clap-and-fling.
What is the effect of delayed stall?
Delayed stall comes from the formation of a leading edge vortex which allows for the delay of stall and lift increase.
How does wing rotation influence lift formation?
During wing rotation, added circulation increases lift and drag formation, although if it takes too long it can reduce lift. Depending on whether it is done before or after stroke reversal it can also produce higher or lower lift.
What is clap-and-fling?
The interaction (usually touching) of two wings leads to considerable lift enhancement, usually at dorsal stroke reversal. In clap, circulations cancel out, and lift production increases, and in fling, leading edge vortexes are formed due to increased circulation which also produces more force.
