The present invention relates to a device for checking the function of a de-icing means, consisting of at least one elongated container, which is arranged to reversibly increase its volume under the effect of a gas brought to the internal cavity of the container with a pressure superceding that of the surrounding atmosphere, the container being attached with a at least partly elastic wall to the external wall of an aircraft wing or horizontal tail, the interior of the wing or horizontal tail standing in gas pressure levelling connection with the surrounding atmosphere.

Ice formation on aircraft is a problem that has been much noted, particularly in connection with accidents where it is presumed that ice formation has been the cause. It is especially common, that ice is formed on the leading edge of wings and horizontal tails during weather conditions that favour ice formation. In order that such ice that is formed on aircraft wings and horizontal tails shall be possible to remove, aircraft are provided with containers of the kind mentioned above. They are called "boots" and are arranged in groups of several such containers parallelly on the leading edge of wings and horizontal tails. They are manufactured from combinations of synthetic rubber and raw rubber and fabric that is more or less elastic. When the pilot observes that ice of a certain thickness has been formed on the leading edges of the wings, he initiates a pressure increase in said containers, i.e. the "boots" so that the ice is cracked into pieces and is removed from the airspeed wind. This is achieved in that gas under overpressure in turn is led to sections of containers on the leading edge, of the two wings and horizontal tail respectively. The pilot has here only an indication that the pressure has increased in the pipe thaτ: leads to the section of containers in guestion. If this pipe should be blocked by ice, or if the container should lie flattened out, frozen, in such a case, pressure increase is also indicated, without any volume increase intended to crack the ice has occurred. Naturally, this means an uncertainty that may cause danger.

The object of the present invention is therefore to provide a device of the kind mentioned in the introduction, which is simple and inexpensive,

and gives great reliability when checking the correct functioning of the de-icing means.

According to the invention, such a device is primarily characterized by an opening in said external wall, covered by an elastic part of said wall of the container, at which opening a sensor is arranged to sense occurring pressure difference between the internal cavity of the container and the interior of the wing and the horizontal tail, respectively, and to emit a corresponding signal. If such a pressure difference of adequate size, for example 150 kPa, is idicated, there is great certainty that the container indeed is increasing its volume, so that the ice is removed. The sensor is of course connected with an indication instrument or the like inside cockpit, so that the pilot will receive a direct acknowledgement of his action to increase the pressure in the de-icing means. The above-mentioned elastic part of the wall of the conatiner needs only be so elastic that a sensor can indicate a convexity.

In a preferred embodiment of the device according to the invention said sensor consists of a relatively stiff but flexible plate carrying a strain gauge, the plate being fixed relative to said external wall, arranged to be mechanically acted upon by the elastic wall of the de¬ icing means that is located over said opening, the strain gauge being arranged to emit a signal in dependence on occurring pressure difference between the internal cavity of the container and the interior of the wing and the horizontal tail, respectively.

The device according to the invention is described in more detail in the following with reference to the accompanying figures, of which

Fig. 1 schematically shows an aircraft in perspective, with markings of the parts of the wings and horizontal tails that are exposed to ice formation;

Fig 2 schematically and in perspective shows a part of a de-icing means on a leading edge of wing, with a number of containers, i.e. "boots";

Fig 3 schematically and in perspective shows a part of a container on the external wall of a wing with an opening for mounting a plate with strain gauge; wheras

Fig 4 schematically shows a longitudinal section through the external wall of a wing with opening and the elastic wall of a de-icing means on one side and a plate with strain gauge on the other side.

In Figure 1 an aircraft is shown with wings 1 and horizontal tails 3,

4. On the leading edges of the wings de-icing means 2 are arranged, and on the horizontal tails the de-icing means 5. These consists, as is evident from Figure 2, of a number of elongated containers, so-called

"boots" 6 arranged parallelly beside each other. In Figure 3 a part of such a container 6 is shown glued on the external wall 7 of the wing

1, in which wall an opening 8 has been made. The container is manufacted by synthetic and raw rubber and fabric and a part of the container that extends over the opening 8 shows a however moderate elasticity. A plug

9 of relatively hard rubber is shown, intended to be brought into the opening 8 with the object to cause mechanical contact between the container part over the opening and a plate 10 with a strain gauge 11, schematically shown in connection with an indicating instrument 12. From Fig 4 it is more clearly shown the sensor for sensing occurring pressure difference between the internal cavity of the container, marked with 13 and the interior of the wing 14, which as already meantioned stands in connection with the surrounding atmosphere, so that atmospherical pressure exists there. The somewhat elastic wall of the container is designated by 15.

The plate 10 stands in rigid connection with the external wall of the wing. When an overpressure, for example in the order of 150 kPa, is led to a container, to the degree this overpressure is brought unhindered to the container, there appears a pressure difference between the internal cavity 13 of the container and the interior 14 of the wing, which is. marked with arrows in Figure 4. The strain gauge 11 is acted upon, as the plate 10 is exposed to a certain, if small, bending, and a signal is emitted to the instrument 12, showing that an overpressure exists in the container, which is a certain indication that the internal cavity of the container 6 has been exposed to overpressure and that ice is

cracked away frcm the leading edge of wing, or as the case may be the leading edge of a horizontal tail.

The device shown in Figures 3 and 4 according to the invention constitutes only an example of embodiment, and other sensors are conceivable within the scope of the invention.