Elevator Systems of the Eiffel Tower Part 2

Adaptation of the motor to the direct drive of an elevator machine was quite another matter, the difficulties being largely those of control. At this time the only practical means of starting a motor under load was by introducing resistance into the circuit and cutting it out in a series of steps as the speed picked up; precisely the method used to start traction motors. In the early attempts to couple the motor directly to the winding drum through worm gearing, this "notching up" was transmitted to the car as a jerking motion, disagreeable to pa.s.sengers and hard on machinery.

Furthermore, the controller contacts had a short life because of the arcing which resulted from heavy starting currents. In all, such systems were unsatisfactory and generally unreliable, and were held in disfavor by both elevator experts and owners.

[Ill.u.s.tration: Figure 17.--Siemens' electric rack-climbing elevator of 1880. (From Werner von Siemens, _Gesammelte Abhandlungen und Vortrage_, Berlin, 1881, pl. 5.)]

There was, moreover, little inducement to overcome the problem of control and other minor problems because of a more serious difficulty which had persisted since the days of steam. This was the matter of the drum and its attendant limitations. The motor's action being rotatory, the winding drum was the only practical way in which to apply its motive power to hoisting.

This single fact shut electricity almost completely out of any large-scale elevator business until after the turn of the century. True, there was a certain amount of development, after about 1887, of the electric worm-drive drum machine for slow-speed, low-rise service (fig. 19). But the first installation of this type that was considered practically successful--in that it was in continuous use for a long period--was not made until 1889,[7] the year in which the Eiffel Tower was completed.

Pertinent is the one nearly successful attempt which was made to approach the high-rise problem electrically. In 1888, Charles R. Pratt, an elevator engineer of Montclair, New Jersey, invented a machine based on the horizontal cylinder rope-geared hydraulic elevator, in which the two sets of sheaves were drawn apart by a screw and traveling nut. The screw was revolved directly by a Sprague motor, the system being known as the Sprague-Pratt. While a number of installations were made, the machine was subject to several serious mechanical faults and pa.s.sed out of use around 1900. Generally, electricity as a practical workable power for elevators seemed to hold little promise in 1888.[8]

[Ill.u.s.tration: Figure 18.--Motor and drive mechanism of Siemens'

elevator. (From Alfred R. Urbanitzky, _Electricity in the Service of Man_, London, 1886, p. 646.)]

[Ill.u.s.tration:

_Morse, Williams & Co._,

BUILDERS OF Pa.s.sENGER AND FREIGHT ELEVATORS.

ELECTRIC ELEVATOR.

Write us for Circulars and Prices.

Main Office and Works, 1105 Frankford Avenue, PHILADELPHIA.

New York Office, 108 Liberty Street.

New Haven " 82 Church Street.

Pittsburg " 413 Fourth Avenue.

Boston Office 19 Pearl Street.

Baltimore " Builders' Exchange.

Scranton " 425 Spruce Street.

Figure 19.--The electric elevator in its earliest commercial form (1891), with the motor connected directly to the load. By this time, incandescent lighting circuits in large cities were sufficiently extensive to make such installations practical. However, capacity and lift were severely limited by weaknesses of the control system and the necessity of using a drum.

(From _Electrical World_, Jan. 2, 1897, vol. 20, p. xcvii.)]

[Ill.u.s.tration:

MILLER'S PATENT LIFE AND LABOR-SAVING SCREW HOISTING MACHINE, FOR THE USE OF Stores, Hotels, Warehouses, Factories, Sugar Refineries, Packing Houses, Mills, Docks, Mines, &c.

MANUFACTURED BY CAMPBELL, WHITTIER & CO., ROXBURY, Ma.s.s.

_Sole Agents for the New England States._

The above Engraving ill.u.s.trates a very superior Hoisting Machine, designed for _Store and Warehouse Hoisting_. It is very simple in its construction, compact, durable, and not liable to get out of order. An examination of the Engraving will convince any one who has any knowledge of Machinery, that the screw is the only safe principle on which to construct a Hoisting Machine or Elevator.

Figure 20.--Advertis.e.m.e.nt for the Miller screw-hoisting machine, about 1867 (see p. 23). From flyer in the United States National Museum.]

[Ill.u.s.tration: Figure 21.--The first widespread use of electricity in the elevator field was to drive belt-type mechanical machines and the pumps of hydraulic systems (see p. 14) as shown here. (From _Electrical World_, Jan. 4, 1890, vol. 15, p. 4.)]

The Tower's Elevators

A great part of the Eiffel Tower's worth and its _raison d'etre_ lay in the overwhelming visual power by which it was to symbolize to a world audience the scientific, artistic, and, above all, the technical achievements of the French Republic. Another consideration, in Eiffel's opinion, was its great potential value as a scientific observatory. At its summit grand experiments and observations would be possible in such fields as meteorology and astronomy. In this respect it was welcomed as a tremendous improvement over the balloon and steam winch that had been featured in this service at the 1878 Paris exposition. Experiments were also to be conducted on the electrical illumination of cities from great heights. The great strategic value of the Tower as an observation post also was recognized. But from the beginning, sight was never lost of the structure's great value as an unprecedented public attraction, and its systematic exploitation in this manner played a part in its planning, second perhaps only to the basic design.

The conveyance of mult.i.tudes of visitors to the Tower's first or main platform and a somewhat lesser number to the summit was a technical problem whose seriousness Eiffel must certainly have been aware of at the project's onset. While a few visitors could be expected to walk to the first or possibly second stage, 377 feet above the ground, the main means of transport obviously had to be elevators. Indeed, the two aspects of the Tower with which the Exposition commissioners were most deeply concerned were the adequate grounding of lightning and the provision of a reliable system of elevators, which they insisted be unconditionally safe.

To study the elevator problem, Eiffel retained a man named Backmann who was considered an expert on the subject. Apparently Backmann originally was to design the complete system, but he was to prove inadequate to the task. As his few schemes are studied it becomes increasingly difficult to imagine by what qualifications he was regarded as either an elevator expert or designer by Eiffel and the Commission. His proposals appear, with one exception, to have been decidedly retrogressive, and, further, to incorporate the most undesirable features of those earlier systems he chose to borrow from. Nothing has been discovered regarding his work, if any, on elevators for the lower section of the Tower. Realizing the difficulty of this aspect of the problem, he may not have attempted its solution, and confined his work to the upper half where the structure permitted a straight, vertical run.

[Ill.u.s.tration: Figure 22.--Various levels of the Eiffel Tower. (Adapted from Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, pl.

1.)]

The Backmann design for the upper elevators was based upon a principle which had been attractive to many inventors in the mid-19th century period of elevator development--that of "s.c.r.e.w.i.n.g the car up" by means of a threaded element and a nut, either of which might be rotated and the other remain stationary. The a.n.a.logy to a nut and bolt made the scheme an obvious one at that early time, but its inherent complexity soon became equally evident and it never achieved practical success. Backmann projected two cylindrical cars that traveled in parallel shafts and balanced one another from opposite ends of common cables that pa.s.sed over a sheave in the upperworks. Around the inside of each shaft extended a spiral track upon which ran rollers attached to revolving frames underneath the cars. When the frames were made to revolve, the rollers, running around the track, would raise or lower one car, the other traveling in the opposite direction (fig. 23).

[Ill.u.s.tration: Figure 23.--Backmann's proposed helicoidal elevator for the upper section of the Eiffel Tower. The cars were to be self-powered by electric motors. Note similarity to the Miller system (fig. 20). (Adapted from _The Engineer_ (London), Aug. 3, 1888, vol. 66, p. 101.)]

In the plan as first presented, a ground-based steam engine drove the frames and rollers through an endless fly rope--traveling at high speed presumably to permit it to be of small diameter and still transmit a reasonable amount of power--which engaged pulleys on the cars. The design was remarkably similar to that of the Miller Patent Screw Hoisting Machine, which had had a brief life in the United States around 1865. The Miller system (see p. 19) used a flat belt rather than a rope (fig. 20).

This plan was quickly rejected, probably because of antic.i.p.ated difficulties with the rope transmission.[9]

Backmann's second proposal, actually approved by the Commission, incorporated the only--although highly significant--innovation evident in his designs. For the rope transmission, electric motors were subst.i.tuted, one in each car to drive the roller frame directly. With this modification, the plan does not seem quite as unreasonable, and would probably have worked. However, it would certainly have lacked the necessary durability and would have been extremely expensive. The Commission discarded the whole scheme about the middle of 1888, giving two reasons for its action: (1) the novelty of the system and the attendant possibility of stoppages which might seriously interrupt the "exploitation of the Tower," and (2) fear that the rollers running around the tracks would cause excessive noise and vibration. Both reasons seem quite incredible when the Backmann system is compared to one of those actually used--the Roux, described below--which obviously must have been subject to identical failings, and on a far greater scale. More likely there existed an unspoken distrust of electric propulsion.

That the Backmann system should have been given serious consideration at all reflects the uncertainty surrounding the entire matter of providing elevator service of such unusual nature. Had the Eiffel Tower been erected only 15 years later, the situation would have been simply one of selection. As it was, Eiffel and the commissioners were governed not by what they wanted but largely by what was available.

THE OTIS SYSTEM

The curvature of the Tower's legs imposed a problem unique in elevator design, and it caused great annoyance to Eiffel, the fair's Commission, and all others concerned. Since a vertical shaftway anywhere within the open area beneath the first platform was esthetically unthinkable, the elevators could be placed only in the inclined legs. The problem of reaching the first platform was not serious. The legs were wide enough and their curvature so slight in this lower portion as to permit them to contain a straight run of track, and the service could have been designed along the lines of an ordinary inclined railway. It was estimated that the great majority of visitors would go only to this level, attracted by the several international restaurants, bars and other features located there.

Two elevators to operate only that far were contracted for with no difficulty--one to be placed in the east leg and one in the west.

To transport people to the second platform was an altogether different problem. Since there was to be a single run from the ground, it would have been necessary to form the elevator guides either with a constant curvature, approximating that of the legs, or with a series of straight chords connected by short segmental curves of small radius. Eiffel planned initially to use the first method, but the second was adopted ultimately, probably as being the simpler because only two straight lengths of run were found to be necessary.

Bids were invited for two elevators on this basis--one each for the north and south legs. Here the unprecedented character of the matter became evident--there was not a firm in France willing to undertake the work. The American Elevator Company, the European branch of Otis Brothers & Company, did submit a proposal through its Paris office, Otis Ascenseur Cie., but the Commission was compelled to reject it because a clause in the fair's charter prohibited the use of any foreign material in the construction of the Tower. Furthermore, there was a strong prejudice against foreign contractors, which, because of the general background of disfavor surrounding the project during its early stages, was an element worth serious consideration by the Commission. The bidding time was extended, and many attempts were made to attract a native design but none was forthcoming.

As time grew short, it became imperative to resolve the matter, and the Commission, in desperation, awarded the contract to Otis in July 1887 for the amount of $22,500.[10] A curious footnote to the affair appeared much later in the form of a published interview[11] with W. Frank Hall, Otis'

Paris representative:

"Yes," said Mr. Hall, "this is the first elevator of its kind. Our people for thirty-eight years have been doing this work, and have constructed thousands of elevators vertically, and many on an incline, but never one to strike a radius of 160 feet for a distance of over 50 feet. It has required a great amount of preparatory study and we have worked on it for three years."

"That was before you got the contract?"

"Quite so, but we knew that, although the French authorities were very reluctant to give away this piece of work, they would be bound to come to us, and so we were preparing for them."