- Dream of the paraglider scientist -

PART 1: Notes on the 3D formation of the leading edge in a paraglider, using ripstop fabric.
PART 3: Negative 3D-shaping
PART 4: A device for experimental study of deformations and wrinkles

In this PART 4 we propose a construction that can be used to study experimentally the effect of different values of skin tension and 3D-cuts in the surfaces shapes.

The amounts of skin tension, the position and depth coefficient of the 3D cuts, can be determined from the following elements:
- Numeric values known previously (publications, data files).
- Previous experience.
- Geometry intuition.
- Calculations the geometrical and physical calculations, based on theories.
- Numeric models.

But it is a difficult task, and the final quality of the wing will depend on to choose properly this values. In addition, the values can change for each profile and for each wing shape. For this reason, an additional element of study can be a "device" for studying individual cells without the need to build an entire wing. We can imagine two rigid profiles located next to one another in the position of study. Between the two profiles, we can try different ripstop surfaces of ripstop, which have been calculated with the help of a program like LEparagliding, with different values of skin tension and 3D-shaping. The two profiles can be exactly the same, or slightly different (to simulate changes in curvature at the leading edge). The fact that they are completely rigid can simulate an ideal situation of symmetrical forces on each side, which is not always the case, but sufficient for the object of study.

An initial study could be to create two exactly equal and completely parallel profiles, and to create different collections of panels with 3D cuts with amplified effect to observe the differences.

The device, described in the accompanying drawings, will be exposed to a uniform wind and and observations will be visual and tactile (to verify tissue pressure and stability) to detect areas of wrinkles, deformations, high pressure or low pressure. From the analysis of different test surfaces a conclusion will be reached on the best values for a given profile. There is the possibility of mounting another pair of rigid profiles symmetrically on the other side of the supports and thus directly compare two identical cells but with different panels.

Device 3D_1
Figure 1. General concept of the device for experimental study of 3D curvatures and wrinkles.

Device 3D_2
Figure 2. Placement of panels on the profiles.

Device 3D_3
Figure 3. 3D view of the dispositive.

Ideally, the profiles to be studied should be on a real or 1/2 scale. They will be cut into pieces of plywood that will be joined together by 3 or four threaded steel bars of 6 or 8 mm. A spacer washer will be attached to one of the outer sides of the profile, which will be the horizontal axis for adjusting the angle of attack. Here will be fixed a wooden support that will continue in a metal tube, which will be the vertical axis to face the wind. Alternatively, one or more fans may be used in indoor installations. The vertical axis will be fixed to a firm vertical support or tripod fixed to the ground.