Looking back
also decided that the train would be the first on British Rail to meet the full international (UIC) strength standards. A new form of structure using aluminium extrusions was developed for the trailer cars. The extrusions included features such as air ducts and seat rails allowing the vehicle shells to be produced more quickly and cheaply than the steel built vehicles then common. A new weld preparation and clamp point was developed as part of the extrusions, which enabled multiple sections to be welded simultaneously producing a complete roof or floor section in one operation. This was later used extensively by overseas manufacturers but not by BREL, then the main UK rail vehicle builders.
New hydro-kinetic brake systems were developed to reduce the speed to a level where normal friction tread brakes could take over. We were required to stop from full speed in the same distance as a current train from 145 kph (90 mph). Our new brakes stopped the APT smoothly in 70% of that distance. At that time, in normal service the then new French TGVs simply cut power and coasted from top speed to a level where they could use friction brakes without excessive wear. If they had had to use their friction brakes for an emergency stop from full speed, the train would have been taken out of service for a complete brake pad replacement. Today’s TGVs have high performance brakes, which can be used at full speed.
The relatively light aluminium APT trailer cars had the potential to achieve the required strength and stiffness without much difficulty. The more heavily loaded power cars were far less uniform in cross- section making an extruded structure less appropriate, and steel became the material of choice. I managed the team designing the power car structures and worked with BREL to co-ordinate the build of six cars for three prototype trains. The maximum permitted load on the track is 17 tonnes per wheelset, which limited the total vehicle weight to 68 tonnes. With more than 30 tonnes of equipment to carry and two 12 tonne bogies, the power car shell could not exceed 13½ tonnes. Since this included the heavy structure round the couplers and other strong points, the main body shell, over 20 metres long, had to weigh less than 8½ tonnes. It needed to meet the UIC end load test requirements of 2000 kN compression and 1500 kN tension at coupler level and various
smaller loads at other positions. To meet the suspension requirements, it also had to have minimum body vibration frequencies of 12.5 Hz laterally and 10 Hz vertically, far stiffer than any similar power car or locomotive then in service.
Each power car had four body-mounted, 750kW, traction motors, each driving a wheelset via a gearbox on the body, a large Cardan shaft through the floor, a second gearbox on the bogie frame and a Quill drive. (A Quill drive is a tube around the axle connecting a gearbox mounted on the bogie frame to the back of one wheel via flexible mounts. This minimises the wheelset mass.) Since the bodies were to tilt to match the trailer cars, and the pantographs had to stay horizontal to pick up the overhead power, it was necessary to make space for an ‘anti-tilt’ mechanism through the body using long rods connected to the bogies. In addition, large air intakes and outlets for cooling air, doors and access panels all left the structural shell full of holes and space constraints posing challenging structural design problems.
After some four years from blank paper to complete vehicle, the first fully fitted power car was put into the laboratory for structural testing. It passed all the UIC load tests and had a lateral frequency of 12.6 Hz and a vertical frequency of 10 Hz.
The trailer car next to the power cars had a small guard’s compartment. BR insisted that we must carry all the equipment carried on current trains. The list included a first-aid box, a stretcher, track circuit clips and a large felling axe. We asked, “Why the felling axe?” “That’s for chopping into wooden coaches in an accident.” “But there aren’t any wooden coaches anymore!” BR withdrew more than 4000 felling axes from trains across the country. I’ve got one in my shed.
The tilt system on each car consisted of a complex hydraulic pack controlling cylinders on the bogies. These had been through a long development process to achieve the rate of tilt needed to react to the train passing through a set of curves at 250 km/h. The sensors measuring the side forces for each vehicle had to be put on the vehicle ahead to give sufficient time to react. As a result the early packs fitted for the first APT-P test runs had been modified several times and become less reliable. Replacement packs to correct the problem were being built when the BR
New hydro-kinetic brake systems were developed to reduce the speed to a level where normal friction tread brakes could take over.
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