Overview Block quotations in the following description are from the 1886
Scientific American article, and the description is based on this. The basic premise for the design of the system was to make the street-level footprint of the line as narrow as possible, to ameliorate the problem of shadowing created by conventional urban
elevated railroads. This entailed a single row of iron pillars of variable height, connected by single horizontal girders. On top of these girders was a pair of load-bearing rails, close together. In between the rails was a row of short posts, bearing a thick third rail. Each item of rolling stock (locomotive, tender or passenger car) had two trucks or
bogies, each with four wheels. These wheels were angled inwards to sit on the load-bearing rails. In addition, each truck had a pair of horizontal spring-mounted gripper wheels which pinched the central upper rail. In non-powered vehicles these were for stability and braking, but in the locomotive these provided the drive in addition. This central rail was not load-bearing. The gripper mechanism allowed trains to manage steep gradients. The rolling stock had the form of horizontal cylinders, including the locomotives, and the edges of the cylinders were rounded. This was an early example of the deliberate design feature of
streamlining, which featured in publicity: This system is as applicable for surface as for elevated railroads. It is cheaper to build than an ordinary road, as the design of the rolling stock allows the contour of the ground to be more closely followed. As an elevated road in cities, the permanent structure presents far less obstruction to light and air than the usual form. The center of gravity of the cars and engine is brought down as low as possible, thereby lessening the effect of leverage caused by wind pressure. The smooth, even surface of the exterior of the entire train serve to decrease the resistance to the wind, and permits a high rate of speed.
Permanent way The following description is for the expected standard iron construction. As the experimental line demonstrated, much of the construction could have been replaced with wood (timber). The hollow iron support pillars were made up of two C-shaped bars, back to back and bolted together with two strap bars. No specifications were given for the cross-section, "which may be varied as demanded by location", but a standard pillar was suggested at 20 feet (6 metres) comprising 6 feet (1.8 metres) underground on foundations specified for the local geology and 14 feet (4.3 metres) clear, with an additional 4 feet (1.2 metres) occupied by the permanent way at the top. These pillars were to be free-standing, not stayed. The permanent way on which the trains were to run consisted, firstly of a line of single iron structural support girders on the tops of the pillars. On top of these was a line of narrower single girders or
track beams (so-called) to which the load-bearing rails were to be fixed. A pair of U-shaped girders, facing upwards, was bolted to the sides of each track beam, and filled with longitudinal baulks of timber. The upper outer edges of the baulks were
beveled at 45 degrees, and the rails fixed to the bevel surfaces so as to be angled out at the same inclination. The rails, baulks and track beam were fastened together with single bolts passing clear through. The gauge of the load-bearing rails was 22.5 inches (57 cm) between the outer edges. The support girders were not stayed, either. The track beams were interrupted by short posts 42 inches (107 cm) high and sitting on the support girders, and bearing the central traction rail (also referred to as the
upper track beam) which was a girder 17.5 inches (44.5 cm) thick. This thickness included iron straps, replaceable when worn, which were fixed along the sides so as to leave a slot along the bottom of each side. The
flanges of the horizontal gripper wheels fitted into these slots. The support posts were supplemented by diagonal trusses, as seen in photos of the experimental line. The experimental line did not feature junction arrangements, so these only appear in print. A
swing bridge arrangement was envisaged: A junction switch is formed of a single swinging section, turning upon a hinge of great strength attached to one of the pillars. A movement of four or five feet (1.2 to 1.5 metres) by the free end of the switch was enough to permit the cars and trucks on one track to clear the end of the other track. The free end travels upon a carriage provided with rollers, moving upon a supporting rail. Suitable mechanism is provided for operating the switch and locking it in place. The switch would have had to be operated manually, somehow. Neither the experimental line nor published illustrations gave any indications as to how routine inspection and maintenance of the permanent way were to have been carried out, without recourse to ladders or scaffolding erected in the street below.
Wheel system Each item of rolling stock had two trucks or
bogies, with four flanged load-bearing wheels each. The major peculiarity of the latter was that they were not vertical, but angled inwards: Each truck consists of a horizontal rectangular
wrought iron frame, stiffened by
cast iron pieces and provided with stiff pedestals bolted to its under side, in which were fixed short axles for the wheels. Each truck had four wheels set at an angle of about 45 degrees, the axles being so inclined. Since the axles were fixed, the bearings would have been in the wheel hubs. Also, each truck had a pair of horizontal gripper wheels, located in between the two pairs of load-bearing wheels which were about 4 feet (1.2 metres) apart. These gripper wheels were 42 inches (107 cm) in diameter and 3.5 inches (9 cm) thick, and the two wheels rotated independently of each other, not being coupled. They were also flanged, on their lower edges, and these flanges fitted into the slots in the sides of the central traction rail. The vertical wheel axles slotted into box slides fixed to the frame, containing springs which pushed the wheels against the rail. The functions of the wheels were, firstly, to stabilise the vehicle against any rolling motion and, secondly, to be part of the hydraulic braking system. Meigs considered that the braking power of the wheels was adequate, but allowed that the load-bearing wheels could be provided with brakes too. The flanges of the gripper wheels were to hold the vehicle onto the track, so that it was unable to fall off. However, the truck frame was also provided with lugs in the event of wheel assembly breakage: In case any or all of the wheels should break, provision is made to prevent the cars from overturning or leaving the track, by means of a strong shoe, which would slide upon but could not leave the way. The horizontal gripper wheel design was also followed by the separate pair of traction wheels on the locomotive. The vehicle undercarriage consisted of two chassis frames, connected by side trusses on which the vehicle body sat and to which was fixed the floor assembly. Each chassis frame had four vertical tubes containing heavy spiral springs, and these fitted into spring sockets bolted to the underneath of the floor assembly. The chassis frame was attached to its truck frame by a centre turn pin stayed by rods attached to sliders, so as to allow free rotation of the chassis on the truck. When running through curves, the trucks turned on the gripper wheels and it was claimed that the design allowed for very tight turning: It has been found that, by reason of the independent motion of all the truck wheels, curves were followed so closely that the increase of friction of the car wheels passing through curves even as small as 50 feet radius, was too slight to be noticed or measured in a model one-eighth full size. This construction of the trucks would allow a car 50 feet (15 metres) long to from a street only 28 feet (8.5 metres) wide into another of the same width.
Passenger car The floor of the passenger car was a frame of
C-channel beams of 5 inch (12.7 cm) gauge. It was 51.16 feet (15.6 metres) long, and 7.5 feet (2.3 metres) wide. The cylindrical car body was formed of hoops of light iron T-bars bent into a circle of diameter 10.7 feet (3.26 metres). The publicity emphasised the luxuriousness of the
fitting out: The cars possess many novel features, both outside and inside. The circular section and rounded ends admit of the strongest possible construction, without an overweight of material. The framing of the body is filled in by panels covered with rich upholstering, which covers all the interior. The exterior is sheathed with paper and copper. While adding to the strength, this form is expected to diminish the wind resistance fully one-third. The interior of the car is light, roomy, and pleasing to the eye. The seats are upholstered like the rest of the car, and comfort and luxury have been carefully studied in every detail. At each window was a specially designed device for securing ventilation without the annoyance caused by dust. There is an entire absence of sharp corners, so that, in case of a serious accident, the liability of the passenger being greatly injured is largely avoided. There is no mention of any insulation, or of heating arrangements for winter. Despite the reference to
copper sheathing, the surviving photo of the fire damage indicates that the metal used in the experimental car was cheaper, with a lower melting point. The car had two rows of horizontal rectangular windows down each side, with the frames fitted in between the hoops and attached to them. The ends had open platforms for entry and exit, with canopies, and passengers passed into the body of the car via swing doors with glass panels and spring closures. Lighting was by hanging oil lamps. There was a continuous run of padded and upholstered seating down each side, with backs resting against the curve of the cylinder. In addition, there was a line of swivel or barbershop chairs along the major axis. The floor had a carpet. A photo survives with the annotation that there was seating for 72 persons. There was absolutely no provision for standing passengers -there was nothing for them to hold on to.
Tender The tender was a completely separate vehicle from the locomotive, only connected by the coupling, as discernible in posed photographs. Not described are the arrangements for the fireman to obtain coal for the locomotive's firebox without risking a fall into the street below. This vehicle was in the same style as the passenger coach, but without end platforms and shorter, at 24.5 feet (7.5 metres). It had the same two rows of windows on each side, but six in each row. Inside was a water tank, a bunker for the coal and "additional room for other purposes". The possibility of parcels traffic was not plainly stated.
Locomotive The locomotive also was in the same cylindrical style, with a floor 29.25 by 7.5 feet (8.9 by 2.3 metres) and having similar fenestration, with seven windows in each lower row. The upper window rows, however, were interrupted by a glazed turret which was the engineer's cab and so had five windows each. For the experimental train this cab only gave a view forwards and to the sides, but drawings of hypothetical trains in service show the cab to have a 360 degree view. Turning engines and marshalling trains to have the locomotive in front would have been very challenging to the system (the experimental line had no turntable), and running in reverse half the time would have been desirable. The front of the locomotive had a large circular door in plate glass panels without protection, and was fronted by an open access platform. There was no
cowcatcher. The two locomotive trucks were close together, but otherwise were of the same design as those of the other vehicle. Between them was a pair of gripper driving wheels, similar to the truck gripper wheels but larger at 44.6 inches (113 cm) in diameter. They had vertical steel (not iron) axles six inches (15 cm) thick. Each wheel had its own driving mechanism, fed from a single boiler. The following is the
Scientific American description of the locomotive specifications: The boiler was of the locomotive type (that is, a fire-tube boiler), 60 inches (152 cm) in diameter and 15 feet 94.6 metres) in length. It was placed over the driving mechanisms, its center line being 61 inches (155 cm) above the floor. There were 200 tubes, 2 inches (5 cm) in diameter and 7 feet (2.1 metres) long; the
firebox was 4.5 feet (1.4 metres) square. The crown sheet was arched, and inclined downward at the back end to allow of climbing and descending grades equal to 15% without exposing any uncovered part to the fire (and so causing an explosion). The cylinders were 12 by 22 inches (30 by 56 cm); their center lines were placed 18 inches (45 cm) above the floor, and 61 inches (155 cm) apart. The piston rods connected with independent
crossheads gliding upon steel girders, supported at their ends by standards bolted to the floor beams. The driving wheel axles extended through a sliding box containing the journals. The boxes slid in cast iron runners placed at right angle to the line of the engine, and each axle had a crank keyed upon its upper end. The well known
slotted yoke connection was used. The slide valves were of the usual locomotive form. The links were placed in a horizontal instead of a vertical position, and were operated by two
bellcranks. The throttle valve, link rod, brake and coupling rods, also the connection between the driving boxes for producing pressure against the rails, were operated by hydraulic power, although hand levers were also provided. Adhesion of the driving wheels to the rails was obtained by means of a cylinder and piston secured to the sliding boxes. The engineer had before him five hydraulic cocks, which adjusted the throttle, links, sliding boxes of the driving wheels, brakes and the coupling rods of the entire train, while just above were steam and hydraulic pressure gauges and indicators, whistle and bell ropes. The fireman was stationed behind the boiler, at the rear of the locomotive and so well away from the engineer. The reference to a control for coupling rods was as regards a claimed safety feature: One turn of the cock controlling the couplings unlocked them and divided the train into its component cars, each of which had a brake which acted automatically upon detachment from the train. This partially destroyed the momentum of the whole, and a collision could only take place by a succession of comparatively light blows from the engine and slowing cars of the train, instead of by a single blow with the momentum of the whole train. The brakes were operated upon the balancing wheels of the trucks. == Gallery ==