An Amphibious Track-layer a Single Propulsion System
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Emergencies Frequently Call for Vehicles of Specialized Type. The Roebling Amphibian is Designed to Meet Contingencies on Land, Sea or Swampy Undeveloped
Terrain
admirably the wheeled vehicle is admirably suited for use on nor mal roads, -it does not function, as is well known, so efficiently on a loose or shifting surface and, at the best, yields but uncertain results on rough terrain. It is for this reason that vehicles of the track-laying type have been evolved, the . area of contact which they provide with the ground being sufficiently great to give adequate adhesion even on loose sand.
It is to this class of vehicle that the Roebling Amphibian belongs. In contrast, however, with normal track-laying types, it is serviceable, as its name implies, not only upon land but also in water.
The dual-transport vehicle of this kind is, in itself, not an entirely new development, experimental -models"having been produced both in America and in Italy at least 20 years ago. • A Unique Feature.
The Roebling Amphibian, however, is unique in that a single propulsionr system serves for both land and water travel. Built by Donald Roebling, of Clearwater, Florida, the machine was designed, in the first place, for exploratory work in swamps and jungles. It is the outcome of experiments which were begun in 1933, as a result of suggestions made by John A. Roebling, who was responsible for the provision of much of the transport in the Florida Red Cross relief work in the Okeechobee Lake region. Although its use 'for such purposes was not originally envisaged by the designer, the Alligator, as the vehicle is called, would appear to offer considerable possibilities for adaptation to military uses, particularly in undeveloped tropical country. At the present juncture, therefore, it may not be inappropriate to present a detailed account of its construction and operation. In the building of the Alligator, notable use has been made of aluminium alloys, not only in purely static parts, such as bodywork, but, as will be shown, in the propulsion system itself, which is subjected to extremely high stresses. Primary requisites in a vehicle of this A28 type are, clearly, low weight, flexibility of manipulation and maximum durability under the most severe conditions. In so far as structural materials are concerned, aluminium alloys were, after careful thought, selected for many important parts in the hull and treads.
Exclusive of fuel and tools which, together, are assumed to weigh about 800 lb., the total weight of the Alligator is about 31 tons. The hull is 20 ft. long and 8 ft. wide, with a forward height at the cabin of 7 ft. 9i ins., and a rear height of 6 ft. 8 ins, For emergency purposes this provides sufficient room for approximately 40 passengers, or, alternatively, a load of about 3 tons may be carried.
Propulsion is achieved, as may be seen from accompanying illustrations (reproduced from our associate journal, Light Metals), by means of endless chains, one on each side of the vehicle, the chains being fitted with curved cleats made of a strong aluminium alloy in the form of a T-section, the stem of which is 7 ins, long, the top width being 4 ins.
On land, the Alligator rides on the lower edges of the cleats, which are shaped so that in water they act as efficient paddles. On level ground, the speed of the vehicle is from 15 to V m.p.h., whilst in water speeds of 8-1 to 10 m.p.h. are readily obtained.
The construction of the propulsior system is relatively simple. Tension or the driving chains, which operate th, treads, is secured by moving forwar( the front idler sprocket against heav: coil springs. In this way, an efficien shock-absorbing system is provided t meet the exigencies encountered in use
Complicated Devices Avoided.
The fact that a single system is en ployed under all conditions of travi constitutes a great advantage, becaui complicated and costly dual-transmi sion devices -are not required. Furthe more, the absence of paddle blades propellers decreases the danger I breakdown should the vehicle stril submerged objects while in the wate or suddenly run aground.
The chains carrying the aluminiu cleats do not run on idler wheels, . in the conventional track-layir vehicle. The idler wheels are integr with the chain in the form of seal, roller bearings of a diameter somewh larger than the thickness of the chai the driving-sprocket teeth being cut fit these rollers.
The chain is of double width, and is kept parallel to the machine by a steel channel which takes the side thrust in turning and prevents the chain from moving out of the correct line of travel. Motive power is supplied by a Ford VS .ngine with "Federal Mogul Hi-Comiression "; the unit develops about .10 b.h.p. at 3,800 r.p.m.
Power is delivered to the tread chains hrough a standard Ford clutch, and hence through 1 to I spiral-bevel gears /Inch drive a shaft at right angles to e:-motor. The engine-room deck and Fie' cooling system mounted beneath it laybe' removed as a unit to permit se removal of the engine.
The Alligator is steered by disengagtg the drive and stopping the chain h the side towards which the turn is to 3 made. For very short turns, one ack of cleats may be put in reverse id the other forward.
The vehicle is provided with the conntional instrument panel, upon which are mounted a fuel-flow meter, an oil. pressure gauge, ignition switches, etc. Two fuel tanks are provided, each of 50 gallons capacity and enough petrol is carried for a cruising radius of about 400 miles.
Ample storage lockers are provided in, side pontoons which open into the engine compartment and cab. In these are carried tools and equipment which may be needed to enable repairs to be effected during running. At the bottom of the pontoons are mounted bilge pumps for use when travelling in water, The driver's cab is 6 ft. 4 ins. wide, 5 ft. 6 ins. high and 5 ft. 6 ins, long and is designed to accommodate the driver, his_relief and a radio operator. Windows are glazed with Plexiglas. The passenger or cargo compartment 75 9 ft. 6 ins. long, 5 ft. 4 ins, wide and 3 ft. 2 ins, deep.
It is interesting to note that, in the unloaded state, the vehicle draws less than 3 ft. of water and when fully loaded it is assumed to draw not tench in• excess of-5 ft: Numerous"tests have been tarried out with the Alligator and -these have demonstrated that it is even more seaworthy than a normal boat of similar size.
No trouble with'shiftifig cargoes has been experienced in tests, nor does the Alligator sink if the cargo cbrnpartment he filled with Water. The shockresisting powers of the ,vehicle have 'been demonstrated 13)./. 'driving from a sea-wall '6 ft. above the water line straight into deep water. No injury restated to the driver, and there was no tendency to capsize.
Tests Show Good Results.
On land, says Light Metals, other tests have shown that it may be run on road surfaces of any type with no damage either to the treads or to the road. At the moment, the Alligator is being built only to order, and mass production has not yet been contemplated. Its approximate cost is £3,600.
Readers will recall that, in previous issues of The Commercial Motor, articles appeared discussing from various angles the use of light alloys in transport vehicles-. Reference should be made to these articles regarding any queries which might possibly arise as to the suitability of aluminium-base alloys for vital components in a heavy-duty machine such as the Roebling Amphibian.
Marine practice has provided sufficient data to enable it to he stated quite definitely that -suitably selected aluminium alloys may be used with • perfect safety under marine conditions. These entail exposure to strongly corrosive salt-laden atmospheres, as well as to the directly corrosive and errosive effects of -salt water, loaded, in many cases, with suspensions of•abrasive mineral matter. Painting is advised as an additional protection.