[markb846]

I understand the the reason why the class 81-85 had 2 pantographs fitted when new was because the aerodynamic forces on the pan were not fully understood at the time. However itg was soon found that 1 pan worked as well which ever direction the loco was running.
The second pan were removed as part of a life extention program, when this, and other redundent electrical equipment was either removed, or isolated. The roof space was used to house the additional air recievers needed for the locos to be able to work trains formed of air braked stock.
Dual voltage machines do normally have a pan for each of the voltage systems they are required to work through. Eurostar power cars have 2 pans fitted, 1 is for the 25Kv ac, and the other for the 3000v dc supply on the classic Belgium routes. That said they can also use the dc pan to work on 1500v dc routes sothern France, and Holand.
Some French, and Belgium locos were built with 4 pans, and could work on upto 6 electrtical supply systems.