The Beauty of Metal Skis

I recapitulate from Mathematics and Skis that the idea was to lay the different layers of the cross-country ski on top of each other with a temperature of maybe 90 degrees centigrade (so that the are thermally expanded), then glue them and then bring them down to snow temperature.

After I had implemented my beam model (in plain FORTRAN 77, of course), we (i.e. the ski manufacturer) produced some skis made of purely metal layers (to be more specific steel and aluminium layers). Why that? The material properties (i.e., the thermal expansion factor and the mechanical stiffness parameters) of metals at these low temperatures (low for metals) are very well known. Hence, we could use the very first experiments to identify the gluing temperature.

With that temperature fixed, we were able to reproduce the results of all metal ski experiments (different number of layers, different thicknesses, different order of materials) within a tolerance of less than 5 percent. The computing time for one experiment was about 3 minutes on a central IBM monster machine at Linz university (with a computing power much lower than today's cellphones).

Image Sourece: European Patent Office, Patent Nr. 0086983. This patent has nothing to do with our developments.

Now it is time for the bad news: When it came to the real skis (made of wood), it turned out that the material parameters of wood used for ski production differed by a factor of 4, even for wood layers produced form the same batch which should have identical parameters. We had asked the ski manufacturer several times if it would be possible to obtain the material parameters in a reliable way and had got the answer "Yes, certainly." Maybe we should have been more insisting.