London — About 20 miles north of here, on the all-electric route to Glasgow, is the Bushey (Hertfordshire) curve. It's an "S" bend that engineers aboard British Rail express trains treat with respect. They take it at 80 miles an hour, the official speed limit.
But on this test run the sleek new Advanced Passenger Train (APT) takes the bends at a clean 125 m.p.h. Not only that, but the soup doesn't spill from the bowls in the dining car and the coffee barely ripples in the cup. The chairman of British Rail, Sir Peter Parker, dangles a pocket watch on a long chain.
Through the curves it remains perpendicular to the floor, indicating that the tilt, 13 degrees in some instances, exactly compensates for the speed around the bends.
The APT, 14 years in the making and currently the most technologically advanced train in the world, is to be brought in service on the curve-filled London-to-Glasgow run at around Christmas. It is capable of cutting the time over the 400 serpentine miles from 5 hours to 4 hours and 10 minutes, including stops in between.
In the mid-1960s, British Rail took a somewhat controversial stand: It would develop a superfast train that could use conventional track, tight curves and all, unlike other nations, which were developing fast trains that would require specially laid track.
The doubters said it couldn't be done. The answer came: "Let's try."
The initial design team drew on conventional railroad engineers and on many from the aerospace industry as well.
Besides front and rear streamlining, smoothing out the side profile became important, too. Doorknobs had to be recessed and window projections all but eliminated. Below 80 m.p.h. this is not so important, but above 100 m.p.h.it becomes vital.
Most important of all was the need to increase speed through existing curves. That meant a total redesigning of the suspension system, including the wheel-assembly trucks, or bogies, as railroad men here call them. Wheel profile was also redesigned.
So successful were the final designs that the wheel flange no longer makes contact with the side of the rail. This was discovered by the simple expedient of rubbing chalk on the flanges and seeing if any of it wore off during a journey, and later through the installation of closed-circuit television cameras.
The new trucks made it possible to take trains through curves at speeds 20 to 40 percent faster than conventional trains. It then became necessary to make adjustments for passenger comfort. A train hitting a curve at better than 100 m.p.h. would throw a passenger to the other side of the carriage in short order and propel a dinner plate through the air like a discus shot in flight. The answer was to tilt the carriage.
Carriages will, in fact, tilt 9 degrees in either direction. This, added to the 4-degree cant of the rail bed around curves, makes a 13-degree tilt for the passenger aboard the APT. Taking the Bushey "S" curve, for instance, produces a full 26-degree difference from one side to the other.
To the riding passenger the sensation is much like that of an airplane when it banks to make a turn.
The train has reached speeds of 160 m.p.h. in tests, but for now it will be limited to 125 m.p.h. because of the much higher fuel consumption at the higher speed.
Significantly, its lightweight alloy construction (40 percent lighter than conventional steel cars) allows the APT to achieve the same fuel efficiency at 125 m.p.h. as a conventional train gets at 100 m.p.h.
British Rail plans a fleet 20 of the $6 million trains to serve the London-Glasgow route, and ultimately hopes for a fleet of 60.