In the late sixties, the American company Grumman became interested in the problem of high-speed rail transport or other similar systems. Over the next few years, its employees developed a promising high-speed vehicle project, called the TLRV (Tracked Levitated Research Vehicle - “Experimental Rail Levitating Apparatus”). In addition, there is an alternative designation TACRV (Tracked Air Cushion Research Vehicle - "Experimental rail vehicle air cushion"). As follows from the two designations, the aim of the project was the development and construction of an experimental vehicle, which during the movement should not touch the road surface.
The TLRV project was developed with the active participation of the US Department of Transportation. At that time, this organization showed interest in various promising developments in the field of railway transport, including those that do not use traditional rail tracks. Starting from a certain point, the ministry took over part of the financing of the work, and also helped the development company with the construction of an experimental route and testing.
Some sources mention the connection of the TLRV project with the Space Shuttle program. Nevertheless, in reality, this project had nothing to do with the space program, although the prototype built by its futuristic appearance really looked like a Space Shuttle without wings.
During the preliminary work, the results of which formed the basis of the TLRV project, Grumman specialists found out that a corresponding route is required for the construction of a radically new vehicle. The use of the traditional rail track was considered inexpedient and a new version of the structure was developed that could be used by a promising vehicle. Instead of a pair of rails, it was proposed to use a flat concrete road with vertical sides on each side. The TLRV car was supposed to drive this “tray”, remaining at a certain height above its bottom. The boards served to keep the vehicle on the track, and also helped him to take turns.
Prototype on the track. Photo Evergreen.zenfolio.com
A new project was proposed to base on an air bed. This technology by then was well mastered and could provide the required characteristics. The rise of the air cushion vehicle made it possible to eliminate the contact of its structure and the track. In addition, due to similar equipment, it was possible to prevent the car from contact with the sides of the track. These, as well as some other considerations, ultimately affected the design of the experimental TLRV apparatus.
It was proposed to use several turbojet engines as a source of energy for moving the apparatus and supplying air to the pillows. The power of such a power plant was enough to maintain the car in the air, and for its translational movement at a sufficiently high speed. Thus, the TLRV, on the basis of the main features of its appearance, can be considered an air-cushioned express carriage. Also, it should be noted that she became one of the few representatives of this extremely rare class of technology.
The basis of a promising vehicle were to be two special-design trucks located in the front and rear of the car. Each of them had to have four small units to create an air cushion. Two were located under the bottom of the cart, two more - on the sides. It was supposed that the lower ones would lift the car over the road, and the side ones would hold the tracks between the sides and protect them from strikes against them.
As part of the TLRV, it was proposed to use two types of air cushions: it was planned to locate wider aggregates under the bottom, the side boards had a smaller width. The length of all the pillows was the same, and the overall design is similar. The basis of each pillow was a metal case with air ducts, on which a rubber skirt and shock absorbers were attached, protecting parts from damage when in contact with concrete. The pillows were oval in shape, ensuring maximum efficiency of work, as well as facilitating their location on the trolley.
For turning corners and compensating for different oscillations, all eight airbag pads were mounted on hinges, which allowed them to swing along the longitudinal axis. The cushion suspension system was also equipped with shock absorbers and hydraulic actuators to change the configuration of the chassis. The use of two groups of airbags made it possible to a certain extent to simplify and facilitate the construction, as well as to improve its performance during the passage of curved track sections. A device of similar dimensions with solid air cushions across the entire surface of the bottom and sides could not normally take turns due to the appearance of large gaps between the skirts and sides of the track. The two mobile carriages, in turn, made it possible to solve the problem of maintaining the correct position of the pillows.
As part of the back of the truck there was a large tank for the distribution of compressed air supplied by pumps. This tank was connected to the rear airbags using a pipe system. In addition, there were two pipes of large diameter, held under the body of the apparatus. In front of these pipelines there were units for transmitting compressed air to the front cushions. Wooden blocks were provided on the external surfaces of these pipes, designed to protect them from contact with the sides of the track-tray.
The body of the experienced TLRV aeronautical carriage was made in the form of an elongated carriage with a characteristic nose cone. Both trolleys with air cushions were hinged to his frame at the bottom. To facilitate the passage of turns carts could rotate around a vertical axis. Because of this, the nose fairing of the body was made as a separate unit and fixed on the front carriage. There is a noticeable gap between the fairing and the main part of the body. Initially, it was closed with a strip of fabric, but later this part was lost, which is why there is now an unclosed gap between the case and the fairing.
At the bottom of the fairing there was some vertical slot, the exact purpose of which remains unknown. It is possible that at one of the stages of the project, the U-shaped road was planned to be supplemented with a central rail, which should have been included in the notch of the fairing. Nevertheless, the constructed experimental route did not receive such a rail and the exact purpose of the slot in the fairing raises questions.
Directly behind the nose fairing there was a crew cabin with large frontal glazing and full-fledged workplaces for machinists. For access to the cabin, two doors of the gullwing construction were provided at the driver’s and his assistant’s places. In addition, in the sides of the hull there were several hatches for access to the internal units.
According to some reports, the middle part of the hull was given over to accommodate a set of special equipment, as well as fuel tanks for kerosene. In the tail part of the hull there was a wide pylon with three Pratt & Whitney J52 turbojet engines, which were supposed to provide air cushions and also be used as a propulsion device.
It can be assumed that a system of pumps and pipelines was organized in the engine pylon to supply atmospheric air to the air cushion tanks. Apparently, air was taken from the engine compressor, which was then distributed between the eight pillows. In this case, the engines remained a certain reserve of power, which could be used to move the car forward. Turbojet engines also proposed to use when braking. For this, the nozzle units of the engines were equipped with reversing movable nozzles located on a common axis.
TLRV on a trolley during transport from one museum to another. You can consider the elements of the chassis. Photo Pueblorailway.org
The experimental Grumman TLRV airliner was built in the 1972 year. This device had a weight of about 25 thousand pounds (11,35 t) and was equipped with a set of equipment necessary for testing. In this configuration, the car had to be tested on a special track.
Especially for checking the original project on one of the sites owned by Grumman (according to other data, at the site of the Ministry of Transport), an experimental track was built. A ring of concrete slabs of the appropriate width was laid, on the sides of which vertical plates were installed to hold the car. All subsequent checks were carried out only on this track. The construction of new highways or the modernization of the existing landfill was not needed.
According to calculations, a promising vehicle could reach speeds of up to 300 miles per hour and carry cargo weighing about 10-15 thousand pounds (4,5-6,8 tons). It took no more than three minutes to accelerate from zero to 270 miles per hour. In the future, it was possible to increase the performance through the use of new components, primarily engines, as well as with the help of major improvements in the design of the apparatus itself. Nevertheless, tests of the first prototype showed that such developments are not needed.
The original chassis of the TLRV wagon led to the adoption of methods of work from the sea hovercraft. Before the trip, the crew had to start the turbojet engines and bring them to the operating mode. After that, the air was taken into the tanks and piping of the airbags. Upon reaching the required pressure in the system, it was possible to turn on the pillows and raise the device to a small height above the track. Then it was necessary to add engine thrust and thereby begin acceleration.
According to reports, the first checks of the hovercraft aerobatic car were completed without any problems. All systems operated in normal mode and ensured correct acceleration to low speeds. The car gently took turns, side airbags kept him at a safe distance from the concrete. In addition, the passage of turns contributed to the presence of two mobile trucks. The authors of the project were satisfied and over time began to increase the speed of test runs.
The gradual increase in speeds was carried out without any problems, but soon the first serious shortcomings were identified. It was experimentally found out that the experimental apparatus could move at high speed only along straight sections of the road. In this case, by installing new engines and modifying the design, the speed could indeed be increased to 300 miles per hour. However, for safe cornering, it was necessary to slow down to 90 miles per hour. Despite the use of swiveling bogies and side airbags, at high speeds there was a risk of late response of the undercarriage with subsequent damage to it.
It is quite possible that it was precisely the problems with the high-speed cornering that prevented the TLRV from showing all its capabilities and developing the estimated speed. Tests on the test track lasted for several months. During the test runs managed to develop a maximum speed at the level of 258,4 miles per hour (415 km / h). Further overclocking in the existing conditions was not possible for a number of reasons.
The tests of the only prototype TLRV on the experimental track allowed us to test the viability of the original concept, as well as to identify its positive and negative sides. It was possible to find out that the proposed design of a promising high-speed vehicle really allows you to develop high speeds and reduce travel time. In addition, the possibility of full use of a group of airbags was confirmed by experience.
However, it was not without flaws. The most serious was not enough perfect design of the chassis, which could not provide the correct interaction of airbags and sides of the road at high speeds. Because of the high risk of hitting the concrete parts when cornering, it was necessary to slow down. When operating on real tracks, this could lead to the need for regular braking and acceleration, which, among other things, could seriously damage the efficiency of the system due to frequent changes in the operating mode of the turbojet engines. In addition, the regular need to change the speed complicated the management of the car, but in practice would lead to difficulties in planning flights.
Another serious drawback of the TLRV program, which by that time had already led to the closure of a lot of bold projects, was the need to build a special highway. The hovercraft could not use the existing rail network and needed special routes. For their construction required serious financial investments, which in theory could pay off in the process of operating a new transport. Nevertheless, even the existing advantages did not allow us to count on the return of investments within a reasonable time.
According to the results of testing on the test track, it was decided to abandon further work. In its current form, the new aero wagon had serious flaws that did not allow us to speak of its practical use. There were noticeable technical flaws, and in addition, there were serious doubts about the possibility of full practical operation of such equipment.
The tests were completed in 1972 and soon the experimental track was dismantled as unnecessary. The only prototype TLRV wagon was sent for storage. Soon, Grumman and the US Department of Transportation determined the fate of the device. Nobody dared to utilize the unique embodiment of original ideas and therefore the experienced aircar was handed over to the Pueblo Weisbrod Aircraft Museum (Pueblo, Colorado) Aviation Museum, where it was exhibited for several years. In the spring of 2010 aviation the museum agreed to transfer the “non-core” exhibit to another organization. In April 2010, the car was moved to the Pueblo Railroad Museum. There, the TLRV is stored to this day and is available to everyone.
On the materials of the sites:
Detailed photo review of the prototype TLRV:
Photos of the transportation process from the aviation museum to the railway: