With the exception of a few shunting engines, and the two “tunnel locos” 81 and 82, all of the fo’s motive power is equipped for rack and adhesion working (indicated by an “H” in the type designations) and can operate anywhere on the fo, the bvz, and the a.c. lines of the RhB. However, only the Deh 4/4 and the hgm 4/4 are allowed to pull (or rather push) trains on the 180 promille Schöllenenbahn section between Andermatt and Göschenen. While the older locos have adhesion and rack drive permanently coupled with a fixed ratio, the more recent engines (starting with the hgm 4/4) can disengage the adhesion drive when on the rack, which reduces track wear (the fixed ratio implies a certain amount of slip, unless the wheel diameter is exactly what it is supposed to be). The hge 4/4ii goes one step further, having a differential gear to divide the load automatically between the wheels and the rack.
These small rack/adhesion locos were built for the Schöllenenbahn (Göschenen-Andermatt) when it opened in 1916, using 1200V d.c. The two electric motors were permanently coupled to the rack wheels, while the drive to the main axles went through a clutch to jackshafts and coupling rods.
When the fo was electrified in 1941, the Schöllenenbahn was converted to a.c., and the locos received completely new electrical equipment, similar to that fitted to the `abdeh 2/4 railcars. From 1961 onwards they were renumbered in the fo series as 21–24, and repainted in the red fo livery. They remained in regular use until the introduction of the Deh 4/4 push-pull sets in 1972, when they were relegated to shunting at Andermatt and occasional SchB freight trains. All four were withdrawn and scrapped in the period 1976 to 1985.
The first locos built for the fo electrification in 1940 used a design based closely on the 1929 ‘Crocodiles’ (11–15) of the neighbouring bvz. Improvements in motor design made it possible to place the traction motors within the bogie frames and dispense with the characteristic croc noses. The bogies are very long in relation to the wheelbase, because the motors are displaced from the axles to make room for the gearing that drives the wheels and rack pinions via an idler shaft.
The locos were built to handle a six coach train (100 tonnes) on the rack sections, and can pull 160 tonnes elsewhere. There is a small baggage compartment in the loco body, with a capacity of 2 tonnes.
Four locos were built by slm/mfo in 1940, and a further three of the same type were added up to 1956. No. 35 was broken up after an accident in 1970; the other six remained in regular service until most of their remaining duties were taken over by the new `hge 4/4ii in 1989. Since then 31 and 34 have been put into store, and the remaining four serviceable engines used for extra duties of various kinds, e.g. the construction trains for the new low-level Gotthard rail tunnel. No. 37 was even rented out to the RhB for a while in 1992 to cover a motive-power shortage there.
This tractor was built in 1946, to the same design as similar machines built for the Brünig line and the RhB. For many years it was assigned to shunting at Brig station.
In 1972 the fo and bvz ordered a first batch of powerful units for operating push-pull services on the Schöllenenbahn and the main line. These railcars, (the fo units are numbered 51–55), were very successful, and were followed by further batches (Nos. 91–96) of a slightly modified design in 1979 and 1984.
Although they look like locomotives, these units are officially classified as motorised baggage cars (Deh 4/4), and can carry up to ten tonnes of mail or luggage. They have a maximum speed of 60km/h in adhesion mode and 30km/h on the rack. They operate most of the local trains on the fo, with a fixed formation of a driving trailer and two intermediate coaches (Deh + B + B + abt), but extra coaches or wagons can be attached to the rear of the set when required.
In the late sixties, the fo had the same problem as the RhB: in the event of any failure of the traction supply, the only reserve was an ageing fleet of steam locomotives. The two companies placed a joint order for two main line diesel locos each, to be suitable for pulling service trains in emergency, and for providing power for rotary snowploughs. The two fo examples, 61 and 62, differ from RhB 801 and 802 in the design of the bogies, which are arranged for mixed rack and adhesion working. Unlike the RhB electrodiesels (which can take 1000V d.c. from the Bernina traction supply), they can run only on diesel power.
With the opening of the Furka Basistunnel in 1982, the fo found itself having to cope with a big increase in through traffic. The elderly `hge 4/4 locos were no longer adequate for the heavily-laden Glacier Express services, and it was clear that new locos, with a higher maximum speed, were required.
The sbb were also interested in new metre-gauge rack locos for their Brünig line, so a joint protoype was developed. In total, eight locos were built for the fo, eight for the Brünig line, and five for the bvz, between 1982 and 1989. With a top speed of 90km/h (adhesion) and 35km/h (rack), these powerful locos now haul most through passenger trains on the fo and act as reserve for the tunnel locos 81 and 82.
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