JPS6133687A - Ski stabilizing apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] FIELD OF THE INVENTION The present invention relates to a ski stabilizing device.

Skis are subject to various factors that change their behavior and lead to instability, which in particular causes the generation and persistence of vibrations.

Such vibrations reduce the contact area of the ski with the snow, making control of the ski more difficult.

Various measures have been proposed to reduce this vibration and suppress TFC. These measures are based in principle on the installation of an oscillator whose frequency is selected so as to attenuate at least a portion of the ski's oscillating frequency.

Namely, German Patent Publication DE-A-2, 747.

No. 084 relates to such a system, and discloses a device in which a mass is vibrably mounted within a housing by means of a spring-bearing or resilient material, such as an elastomer or plastic foam material.

DE-A-2,820,649 also discloses a similar solution, French patent publication FR-A-2,383.

No. 680 relates to a vibration damping device having a mass elastically held in a rest position and movable in a direction transverse to the longitudinal direction of the ski.

The various proposals described above have a number of deficiencies, especially as they increase the volume and mass of the ski, creating other problems that are just as troublesome as the vibrations they have been dampened.

A solution has been proposed in the European Patent Publication EP-A2-0102653 which can be integrated in part with the ski and does not have the above-mentioned disadvantages. A moderate effect of reducing acceleration by at least a factor of 2 within the Hz frequency band can be obtained.

In order to investigate the cause of ski instability, we investigated the behavior of skis, especially the spatula-like part, from an aerodynamic perspective.

It is well known that an airfoil whose lift force has a component in the direction of motion is unstable in a fluid flow, and that this instability manifests itself in the generation and persistence of vibrations. This is a well-known phenomenon that occurs when a constant wind, even if weak, acts on a wooden power line due to hoarfrost or rain ice, and the profile, which is no longer cylindrical, expands in the vertical direction, causing the so-called 1
The resulting lift force has a component in the direction of motion. This instability results in vibrations with large amplitudes, which can lead to wire breakage. It goes without saying that other phenomena caused by this phenomenon are also included, and these phenomena can also generate vibrations with large amplitude when the frequency of the excitation force is equal to the natural frequency of the ski, and this amplitude is equal to the area and the square of the velocity.

Swiss Patent Publication No. CH-A-573,256 discloses that the spatula-shaped part of the ski is streamlined starting from its tip, forming a convex curve and making the ski surface continuous with the rear of the spatula-shaped part. Methods have been proposed to reduce the drag generated by the shaped parts. This proposal claims to suppress the vibration of the spatula-shaped portion at high speeds. If it is true that such streamlining suppresses the vortices that occur behind the spatula and cause instability, then, conversely, the lift coefficient 07 of the streamlined profile decreases with the angle of incidence and this causes instability, and the fluid layer on the convex streamlined surface rapidly separates, which generates vortices.

Also, Austrian Patent Publication AT-A-344.

No. 049 proposes to provide a wedge-shaped element at the rear of the upper surface of a jumping ski in order to exert downward pressure on this part of the ski in mid-air.

This device was not proposed to eliminate the aerodynamic instability caused by the spatula of the ski.

It is an object of the invention to propose a solution which makes it possible to at least partially eliminate the aerodynamic instability phenomena caused by the spatula profile of the ski.

In order to achieve this objective, the present invention is disclosed in claim 1.
Provides a ski stabilization device as described in paragraphs.

The accompanying drawings are perspective views schematically showing two embodiments of the device according to the invention.

As is well known, when an airfoil is placed in a fluid flow, the lift coefficient C2 is a function of the angle of incidence i that the flow direction makes with the airfoil axis. According to the equation of motion regarding the static equilibrium position of this airfoil, (d
C,/di) ) (If l, a stable state is obtained.

On the contrary, an airfoil shape that is unfavorable from an aerodynamic point of view,
That is, there are many airfoil shapes in which the lift coefficient Cz, which has a functional relationship with the incident angle l with respect to the fluid direction, exhibits a negative slope, that is, (dc,/az)<O. Such an airfoil that does not satisfy the stability conditions of the equation of motion will lead to periodic instability, which appears in the form of vibration, and the effect is greatest when it resonates with the natural frequency of the structure that makes up the airfoil. becomes. Such effects are known, with the most dramatic example being around 70 kIII/h.
The destruction of the Tokoma Suspension Bridge occurred on June 1, 1940 under the influence of constant winds.

One of the causes of vibration in skis is aerodynamics.
In this case, the spatula of the ski has an unfavorable airfoil shape, i.e.
While the lift coefficient 07 plays the role of an airfoil that exhibits a negative slope depending on the air incidence angle i, it also causes a Karman vortex to be generated behind it.

It is well known that theoretically a cylinder suspended flexibly in a flow can oscillate due to the presence of Karman vortices. The frequency of the excitation force is proportional to the flow velocity, and the amplitude of motion is a function of the square of the velocity and the area of the airfoil.

In the embodiment of the device according to the invention shown in FIG. 2, the tip of the front end of the ski 1 constitutes a spatula 2 and thus an airfoil that causes aerodynamic instability phenomena. Said spatula 2 is truncated at the front end along a line intersecting the longitudinal axis of the ski, and is constructed with a wing 3 selected from a series of high-lift airfoils to overcome the destabilizing effect of the spatula 2. Coordinating the second airfoil introduces an aerodynamic stabilizing element. In addition to the stabilizing effect, the direction of the cross-sectional shape of the wing 3 has a pressure effect of several Newtons at a speed of approximately 100 tan/h, which increases the contact force between the ski and the snow, and therefore increases the control effect of the skier on the ski. Set it to increase to generate negative lift.

Both ends of this wing 3 are formed as a protection plate 4 that produces the effect of extending the wing, and are connected to the ski with two struts 5.

This embodiment was attempted essentially for experimental purposes. Although this embodiment can overcome the instability effects caused by the cross-sectional shape of the spatula 2, it cannot overcome the instability effects caused by Karman vortices. In practical terms, this embodiment has the disadvantage that the wing is not integral with the ski. Not only is the appearance unfavorable, but the fixation of the blade is likely to be impaired, and the space between the tip of the spatula-shaped portion and the front of the blade 3 is likely to become clogged with snow.

The embodiment shown in FIG. 3 solves these problems. That is, here there is no blade like the blade 3 in the above embodiment, and the spatula-shaped portion is formed in a streamlined shape. Specifically, the profile surface 6 is connected to the front line of the spatula 2 along a line intersecting the longitudinal axis of the ski. This profile surface 6 acts as a downstream profile of the high-lift blade, and the two side plates 7 forming green around the entire circumference of the profile surface create an extension effect in the cross direction with the profile surface 6, making the profile surface 6 into a spatula-shaped part. It also plays a role of closing the space between the profile surface 6 and the spatula-shaped portion 2 from the side. This free space can be used, for example, to fill it with a vibration-absorbing material as disclosed in EP-A2-0102653, thereby increasing the effectiveness of the syphrofil surface 6.

The embodiment shown in FIG. 2 not only has an excellent appearance, but also has the advantage that, since the profile surface 6 is connected to the spatula-shaped portion 2, Karman vortices behind the spatula-shaped portion can be avoided. Therefore, the second cause of aerodynamic instability is at least alleviated. Furthermore, since the profile surface 6 is connected to the front end of the spatula-shaped portion, the space between the front edge of the spatula-shaped portion 6 and the front edge of the spatula-shaped portion 2 will not be clogged with snow and will not interfere with the function of the device. . Such a streamlined fixation to the spatula is also easier and more reliable than the embodiment of FIG.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between lift force and angle of incidence, FIG. 2 is a perspective view of the front end of a ski showing a first embodiment of the present invention, and FIG. 3 is a perspective view of the second embodiment. 1...Ski, 2... Spatula-shaped part, 3... Wing, 7...
... Side plate, 1... Angle of incidence, C2... Lift coefficient.

Claims (1)

Claims: 1. A ski stabilizing device, characterized in that it is in the form of a profile member in which the variation of the lift coefficient C_z as a function of the variation of the angle of incidence i is such that dC_z/di>0. 2. The device of claim 1, wherein the profile member is located near the front end of the ski and oriented so that lift is directed toward the ground. 3. According to claim 1, wherein two plates forming flanges around the profile of the profile member are arranged at both ends of the member to enhance the effect of extending in the transverse direction. Device. 4. Device according to claim 1, characterized in that the leading edge of the profile member is end-connected to the leading edge of the spatula of the ski. 5. Claim 1, characterized in that the spatula-shaped leading edge of the ski extends along a line intersecting the longitudinal axis of the ski.
Equipment described in Section.