(You deserve a response for your excellent grammar - I was offered mozarella and sundried tomato Panini in the deli this morning and hadn't the heart to explain that I only wanted a panio)
I think that's the main point I was trying to make about why Pendolini only use the leading pan.
You've picked up quite rightly on a very complex factor to evaluate. In early APT trials, they fudged several factors such as the weight and gauge of the conductor and pressure of the pantograph to simulate the intended high speed operation - and in the recent French APT trials even the measuring equipment available today struggled to quantify the problems - which, with just one pan, is similar a mix of static oscillations and a "moving standing wave" (which is hard to grasp in itself). Its obvious that (for a given spacing of anchorages) that any OLE will hit its resonance at some speed or other (like an instrument string). But the problem is not just the pan has to rise to maintain contact when the cable is high and fall when its low, but the weird forces required during the transitions (ie as the cable is falling then the pantograph has a higher lateral force from the falling cable and as it is, relatively, rising, then extra pressure is required to maintain contact despite the rising cable providing a forward pressure).
It only becomes
really interesting at high speed when these movements are close to the four-fold wavelength (or other multiple at other speeds or other train lengths) of a train with
two pantographs, when there will always be one frequency which produces a violent resonant oscillation.
(Forgive me for jumping topic for a sec - you recall that old film of the San Fransisco suspension bridge oscillating and collapsing? Or the wine glass shattering at a certain pitch?)
You can see extraordinarily violent cable movement when you combine the 3 factors:
the static oscillation of cable over a certain length of track with fixed-interval support;
the moving standing wave caused by the two pans at a fixed spacing between them (moving with the train);
and the moving wave-front caused by the simple pressure of the train's impact (combined air and pantograph pressures) on the OLE and its suspension).
To develop one of O L L's points about wear, the wear from steady passing friction may not be great, but the erosion from arcing/flashing when the cable is moving can lead to spiralling wear at certain points - and these would be on high speed lines where the above 3 factors combine with a built rise and fall of catenery such as level crossings and over-bridges. Once pitting of the conductor begins at these points then it reduces the evenness of contact and jerks the position of the conductor which are both hysteric - ie they accellerate their own causes.
There's a lot of technical papers published on the subject for those interested and these are largely high speed issues (which the Pendo was designed for).
Me? I prefer the French approach (above) of applying two solutions to each train so you've got both options covered! Never mind the technolgy - lets just make it work
mon ami
(now, time for supper, will I have another panino or just a sarnie?)
