• Technical Field

Aviation, propulsion, and energy.

• Background Art

- Jonathon P. Baker and C.P. van Dam, "DRAG REDUCTION OF BLUNT TRAILING- EDGE AIRFOILS", BBAA VI International Colloquium on: Bluff Bodies Aerodynamics & Applications, July, 2008,

- U.S. PATENT DOCUMENTS 5,871,174 2/1999 Hannay . 244/199.

AS the prior patent, US5871174, proposes discontinuity pattern all along the span of the trailing edge. The method achieves reduction of tip vortex by splitting the flow leaving the foil resulting in smaller vortices at trailing edge and not allowing the flow to accumulate to a large tip vortex.

• Disclosure Of Invention

- Introduction

Wandering birds refers to bird species that have dietary habits involving traveling for prolonged periods in search for food. These species have

developed means to maintain low energy consumption to allow for maximum mobility with the least effort.

These bird species have a distinctive feature in their wings, that is, oddly protruding primary feathers near the tip of the wings. Figure 1 shows the protrusion of the primary feathers on th _a e wings of a wandering falcon, the design proposed is inspired by these protruding primary feathers.

The Invention Summary

Inspired by nature, the proposed invention utilizes rounded chevrons attached to part of the trailing edge of foils to increase their lift. It achieves said effect by increasing the speed of the downwash of the fluid leaving the foil. Occupying only half (at most) of the wingspan, it has less weight than previous state of the art designs in the arena of Lift/Drag ratio increase, maximizing the sought-after foil performance enhancement.

The Invention Details

The insertion of tabs on the trailing edge of a foil will trigger three major effects: a) Increase in lift due to increase in surface area of the foil, this is the moststraight forward effect. b) Increase in induced drag due to the same reason in the previous point. c) Interruption in trailing-edge vortices formation.

The weight of the first and second effects needs to be carefully assessed to ensure an overall positive outcome is achieved from implementing such trailing-edge modification.

Implementing the tabs all along the trailing edge as shown in figure 3 has shown negligible positive outcome in terms of Lift/Drag ratio. This is mainly due to the highlighted increase in drag accompanying lift increase from said tabs.

With the tabs modified to occupy nearly one third of the wingspan, as shown in figure 4, they have shown net positive increase in lift by 4%. The tabs delay the formation of the starting vortex forcing it to develop further downstream of the main foil, that delay results in increased intensity of said vortex, and hence increased lift.

At the same time the now discontinues trailing-edge with implementation of the invention plays a rule in deterring formation of tip vortex by interrupting buildup of trailing-edge vortices. That cancels out any increase in drag developed by foil area increase, conserving the achieved Lift/Drag ratio increase.

• Brief Description Of The Drawings

- Figure 1 Falco Peregrinus (wandering falcon)

- Figure 2 Typical foil with smooth leading and trailing edges

- Figure 3 shows the same foil from figure 2 with straight leading edge and with tabs occupying all trailing-edge

- Figure 4 is the same foil with no changes to the leading-edge and the invention trailing-edge attachment example (occupying 33% of trailing-edge on tip side)

- Figure 5 Top view of the foil described in figure 4

- Figure 6 defining characteristics of one tab-attachment