Modeling wings or foils in heliciel
wing or blade tip Losses
The length of the blade or wing:
The third dimension of leaks:
the losses at the blade tip ..

wing or blade tip Losses


It is important to remember that the formulas of drag and lift force, provide theoretical values​​, not taking into account some losses. These Drag and Lift, measured in the wind tunnel or calculated by numerical methods are called performance 2D (two-dimensional) or "wing of infinite span performance." 2D, because it does not take into account the phenomena of the third dimension: the length of the blade or wing. The lift is the result of the pressure difference between the top and bottom of the wing.

 

But the more the pressure difference is important. more leaks are important because the more fluid want to get to the other side by the shortest path it finds! The shortest path is the wingtip.

The overpressure zone and the suction zone of a wing, and causing the bypass blade tip losses

wing or blade tip Losses

 

So: When we calculate the performance of a propeller or a wing in a free flow (where the fluid is not forced and can freely bypass the wing or propeller), a "tip blade loss factor " is used to take into account the phenomenon.
See: tip loss factor expressed by Prandtl :, this factor is integrated into the blade element theory and Heliciel software incorporates this factor in the calculation of the propellers..

 

The apect ratio helps us to assess the losses to wingtip:

aspect ratio = Span(lwing length)/ Chord(width of the wing):

Aspect ratio( all forms)= wing length/(wing area

Example of the impact of the shape and the aspect ratio vortex and losses wingtip 4 wings of shapes and different aspect ratio, shown schematically in the software Heliciel

Rectangular wing length of 2 meters Aspect ratio = 4 ratio (Lift / Drag) =16

Rectangular wing length of 9 meters Aspect ratio = 18 ratio (Lift / Drag) =32

   
Triangular wing length of 2 meters. Aspect ratio = 5 ratio (Lift / Drag) =19. Triangular wing length of 9 meters. Aspect ratio = 33 ratio (Lift / Drag) =36

 

A high aspect ratio, it is a lift distributed over a large area. So a pressure difference between the lower and upper surfaces not giving too fluid the desire to get to the other side. If the lift is distributed as far as possible the tip of the wing that will make more road to get to the other side, and this will limit leakage. The wing shape theoretically distributed lift farthest from the end, that is the ellipse. Some aircraft therefore quite simply adopted elliptical wings.

elliptical wing spitfire lift as far as possible the wing tip focuses

the spitfire and elliptical wings focusing lift as far as possible from the tip of the wing to prevent leakage. In practice, a trapezoidal shape is sufficient to benefit from an effect close of the optimum. Heliciel allows to calculate the performance of propellers and wings incorporating tip losses , but it is possible to exclude tip losses to assess the max gain of a system winglets. In fact whatever the configuration it will not be possible to completely eliminate tip losses.