21-10-2016, 04:23 PM
1460397503-DesignofaMAV.docx (Size: 1.16 MB / Downloads: 5)
Design of a MAV Vehicle: When flapping a wing the flow of air is highly turbulent and producing more lift compared to the fixed wings flight (means Reynolds no. is more than 500000). These changes are because of the continuously movement of the wings.
1) During downstroke with a high angle of attack the flow seperates from the wing and the vortex evolve along the leading edge of the wings . Due to the high turbulence the flow reattaches from the wings before reaching the trailing edge, the vortex result in a significant, higher lift than could be observed in laminar flow.
2) The extra lift generates due the circulation effect of wings, At the end of each stroke some insect and birds rotate their wings so that result in a positive angle of attack.
3) Flapping wing motion are highly unsteady and turbulent.
4) Turbulent flow in case of atmospheric air is the variation of pressure due to the movement of wings in surrounding.
5) The arrangement of 4 wings with the help of 1 motor is such that, right side top wing is attached with the left side bottom wing and vice-versa making a 180 degree movement pair.
6) Upper wing and lower wing are attached to the geared train motor for the relative motion of the wing.
7) The forward movement of the MAV is controlled by rudders which is attached on front portion of it.
CALCULATIONS:
The lift that is produced by flapping the wings is characterized by highly unstationary aerodynamic effects which makes it difficult to predict the resulting lift force for a given wing. In order to get a rough idea, we have a boundary for the total weight of the MAV, Some simplifications are necessary, which allow applying the 2-dimensional airfoil theory with the formula for lift:
L = Cl*ƿ*v2*A/2
Where Cl = lift coefficient
Ƿ = air density
V = local Air velocity
A = Planeform
The flapping wing requires the following assumptions:
• Unstationary effects that occur only when the wings are flapping are neglected.
• The lift coefficient Cl is independent in time and location on the wing.
• Induced inflow is disregarded.
Aerodynamic for hovering insects flight
Most insects hover with an approximately horizontal stroke plane which is the plane designed by the flapping motion of the wings. Variation in the wing elevation angles perpendicular to that plane are relatively small typically less than 5 deg, and at worst less than 10 deg.
Study shows that the high speed films of hovering insects indicate that the wings generally generates lift on both downstroke and upstroke. Angle of attack are 35 deg for outer wing region.
Visualization study on the hawkmothManducasexta (flapper MAV)
During the downstroke air Swirls around the leading edge and rolls up into an intense leading-edge vortex (LEV). A Laminar leading edge vortex is to be expected at these chords-based Re (less than 5000) for thin wings with sharp leading edges operating at high angles of attack for brief period ; generating extra lift before it stalls.
The dynamic stall has long been in a run for explaining the extra lift of insects wings, but 2-D aerodynamic studies shows that the lift enhancement is limited to about 3-4 chord lengths of travel, the LEV(Leading Edge Vortex) grows until it becomes unstable at that distance and breaks away from the wing, causing a deep stall.
SIMILARITIES
1. Lift Enhancement by the spiral leading edge vortex bears several similarities to the high lift divices employed on certain man made wings .But the axial flow component is essential for the stability of such vortices.
2. The axial flow can be induced by active spanwise suction or blowing over the upper wing surface.
3. The axial flow over insect wings is due to the dynamic pressure gradient associated with the spanwise flapping velocity gradient.
SELECTION OF WING PLANEFORM SHAPE
In order to determine which wing shape is best suited for a micro aerial vehicle, wind tunnel experimental data was used to develop an empirically-based design and analysis procedure. In a series of experiments, four wing shapes with aspect ratios of 1 and 2 were tested.
The wings had zero camber and a thickness-to-chord ratio of 1.96%.
FABRICATION
We Desire to build MAVs using composite materials. The wings were initially constructed using a single or double layer of carbon fiber cloth wetted with epoxy resin. The carbon fibercloth was molded on a specially constructed base which had the contour of the desired airfoilshape. When cured, the wing was very strong and extremely thin.
A number of trials using carbon fiber cloth strips, composite frames, carbon fiber-balsa sandwiches and other techniques yielded amazingly resistant structures which weighed too much.
The airplanes built using the more conventional method of balsa wood were found to be significantly lighter than their composite counterparts. Carbon fiber strips and small patches of fiberglass cloth were used to reinforce critical areas of the airframe such as the nose,
leading edge, and wingtips. This balsa structure was found to be durable but not indestructible.