The time from the late 1940s to the late 1950s is the period when almost all car factories in our country were actively working on cross-country vehicles. Direct descendants of some all-terrain vehicles designed at that time are still being produced - suffice it to recall the Ural-4320 or the Ulyanovsk "loaves" and "tadpoles".
Soviet designers, who had real experience in creating fairly progressive all-terrain vehicles, in those years, in fact, could be counted on the fingers of one hand. And where did this experience come from, if even in theory the questions of the patency of wheeled vehicles in our country have been studied very poorly. And direct copying of the ideas inherent in foreign designs did not always lead to a positive result: it is enough to recall the "somersaults" GAZ-64 or the ZIS-151, which has a weak cross-country ability with increased "gluttony". However, the gaps in theory began to be actively filled with a colossal amount of practical research: such a number of fundamentally different experimental models of all-terrain vehicles throughout the post-Soviet space, perhaps, have not been created in any other decade! It was thanks to those development work that the "postulates" were gradually formed, on the basis of which some of the most advanced all-terrain vehicles in the world were subsequently created in the USSR.
It should be understood that many fundamental points in matters of further development of the domestic "all-terrain" school, which became obvious to designers and testers, in those years, for various reasons, found many ardent opponents both among the factory bosses and among the army leadership (the direct customer of such machines type). The fact that a real pneumatic all-terrain vehicle should have single wheels with the same track and a centralized tire pressure control system has not yet been recognized as an axiom! There was no consensus on the selection of tires - in particular, the understanding that the specific ground pressure is an important, but not a fundamental characteristic, did not come immediately. Much more important is the optimal ratio of the specific pressure to the dimension of the tire, which determines, among other things, the rolling resistance and, to some extent, the vehicle's ground clearance. The need to implement certain solutions had to be proved, and the best evidence was demonstrative tests of various types of equipment. Our today's story will be about one of such comparative races, conducted on August 1, 1956 by specialists of the Autotractor Directorate of the USSR Ministry of Defense.
The purpose of these tests was the accumulation of materials for a comparative assessment of the passability of vehicles in wetlands. Almost all modern Soviet all-wheel drive vehicles (with the exception of amphibians) took part in the races from among automotive vehicles - a total of 15 units. Of this number, seven cars were completely serial - these are GAZ-69, two all-wheel drive "Pobeda" M-72 (one had tires with a nominal pressure of 2 atm., The second - lowered to 1 atm.), GAZ-63A, ZIL- 151, MAZ-502A and YaAZ-214. Another GAZ-63A was equipped with experienced wide-profile tires 11, 00-18, inflated to 0.5-0.7 atm. The remaining seven vehicles were experimental designs: these are the GAZ-62 and GAZ-62B "hoods", an early prototype ZIL-157 with an inflation system with external air supply to the tires, an armored personnel carrier ZIL-152V, equipped in a pilot manner with the latest tire inflation system with internal air supply (subsequently mass-produced as BTR-152V1), as well as three mock-up vehicles of the 134th series, created at the SKB V. A. Grachev in Moscow.
A wide open area of wetland with flat relief was chosen as a testing ground. The task set for the participants included the passage of the maximum possible length of the swamp section. If the vehicle did not show the possibility of loss of passability in these conditions, it was considered sufficient to pass a 50-meter corridor through the swamp gradually increasing from 20 to 70 cm in depth, otherwise the movement continued until the complete loss of mobility. The time to complete the route was not in any way a critical parameter, but it was measured and taken into account later when analyzing the results obtained. For greater clarity, the corridors for the movement of all vehicles participating in the event were laid parallel to each other. In case of suspicion of the inadequacy of the result obtained (due to a piloting error, incorrect choice of tactics of movement in these conditions, etc.), it was allowed to use a second attempt to pass a similar route.
Cars went to the distance "by seniority", more precisely - based on weight and dimensions. Thus, the M-72 model with tires inflated to the nominal value fell to open the "parade". In the first low gear, the all-wheel drive "Pobeda" was able to overcome only 5 meters of the way, after which it was firmly "buried" in the quagmire. Measurement of the parameters of the swamp in the place of jamming gave the following results: the depth (vertical distance from the surface to solid ground under water) was 250 mm with the strength of the sod layer of 10 kgm (the latter parameter was determined experimentally by measuring the resistance to turning of a special stamp of Professor Pokrovsky). The depth of the track left by the car was 210 mm. Exactly the same M-72, but with lowered to 1 atm. wheels, improved the performance of his fellow tribesman three times at once, having already passed the 15-meter corridor in just 20 seconds. True, further advancement of the car was absolutely impossible. Measurement of the parameters of the bog gave a limiting depth of 260 mm with a cover strength of 6.5 kgm.
The GAZ-69 all-terrain vehicle with normal tire pressure, which had the same chassis and transmission units as the M-72, moved forward very hard, but stubbornly. After 6 minutes 5 seconds of slipping on the first low one, he finally froze at around 14, 5 m, just a little ahead of the all-wheel drive "Pobeda" with flat tires. Measurement of the parameters of the bog showed a depth of 230 mm with the strength of the sod layer at the level of 6, 3 kgm. But the depth of the track, due to the excessively long slipping, turned out to be even greater than the depth of the swamp itself - 235 mm.
The larger all-terrain vehicle GAZ-62 with lowered to 0.7 atm. with tires, thanks to a more high-torque 6-cylinder engine, he set off to storm the off-road in low gear and in 2 minutes 19 seconds he reached the 30-meter mark. There, however, he remained, having thoroughly sat down on the bridges. The depth of the bog in this area was 350 mm, the strength of the sod layer was 6 kgm, and the average rut depth was 305 mm.
But the first race of the formidable-looking "four-axle" GAZ-62B ended in fiasco. Briskly starting to move on II low, with an increase in the depth of the swamp to a half-meter level, the driver was faced with an acute lack of engine torque. An attempt to quickly switch to first gear was unsuccessful, since during this time the car managed to stop, but it could no longer move. The result is 35.5 m in 8 seconds with a finish in a 55-centimeter swamp with a cover strength of 4 kgm and a track depth of 300 mm. It can be assumed that at that moment in the location of the generals observing the maneuvers in the air there was a question about the competence of the designers who worked on the GAZ-62B. And in fact: the transmission has become twice as complicated as on a simple 62nd, an inflation system has been introduced, elastic tires operating with ultra-low pressure have been used - and the car “does not go” …
However, the second race put everything in its place - GAZ-62B took revenge. Smoothly starting in low gear I, the crew of the "four-axle" broke through to the 46 m mark in 1 minute 46 seconds. The loss of maneuverability occurred in a 50-centimeter section of the bog with an extremely low bearing capacity of the sod layer (1-2 kgm), and the depth of the track left by the car was 205 mm.
Interesting are the results shown by the GAZ-63A trucks. If the variant on standard tires was able to slip through 29 m of the swamp in 17 seconds, standing in a 35-centimeter "slurry" with a strength of 2, 66 kgm, then its namesake on wide-profile lowered wheels in the same lower gear II made its way by only 1 (!) M further, while spending incomparably more time - 3 minutes 45 seconds. The depth of the swamp at the point of stuck was even slightly less (333 mm), as well as the depth of the track due to the low tire pressure (245 mm instead of 320). Obviously, a negative role in this case was played by an increase in rolling resistance and a lack of adhesion properties of the test tires while maintaining all other parameters of the car at the same level.
The next in the "swim" went the standard truck ZIL-151, however, due to the gable wheels and modest ground clearance, its chances were initially very modest. This was confirmed by practice: after 8 minutes of swinging and slipping in low gear II, the car stopped just 10 m from the start line. The parameters of the bog in this place were found to be 290 mm (depth) and 7 kgm (strength).
Results close to the GAZ-62B could be demonstrated by the then experienced "three-wheel" ZIL-157 with a tire inflation system. When vented to 0, 4 atm. pressure in lower gear II, the machine “ironed” 40 m of the swamp in 68 seconds, until it sat down on the bridges. The depth of the swamp in the place where the passability was lost turned out to be 510 mm with a low cover strength (1-2 kgm), and the depth of the left track was 430 mm. A re-run at a faster pace, just in case, revealed practically the same results: the distance covered was 44 m in 45 test seconds. Moreover, this time the car was forced to stop by an impressive shaft of ripped sod that had accumulated in front of the bumper and front axle. Due to the somewhat denser and stronger surface of the "track" (the value of the resistance to turning the Pokrovsky stamp was 3 kgm), the depth of the track left was significantly less than in the first race - only 270 mm.
The closest relative of the "one hundred and fifty-seventh" - the ZIL-152V armored personnel carrier - showed practically the same passability reserves. A solid weight gain was compensated by more favorable parameters of geometric cross-country ability and tires operating at a slightly lower pressure (0.3 atm instead of 0.4). As a result, in the first race, using low gears I and II, in 10 minutes he was able to overcome 40 m of the swamp, getting stuck in a section with a depth of 600 mm with a sod strength of 1-2 kg and leaving behind him a 430 mm track.
During the re-run, during the same time, the conveyor moved only 2 m further and stopped in a swamp with a depth of 475 mm with a coating strength of 2 kgm. The depth of the track left this time did not exceed 290 mm. It is worth noting that the common characteristic moment during the movement of the ZIL-157 and ZIL-152V cars in such conditions was the tearing off of the sod cover by the elements of the undercarriage at a swamp depth of more than 350 mm, while wide-profile tires were subject to "blurring" to a much lesser extent than tires high pressure for GAZ-63, ZIL-151, etc.
The best cross-country performance in the group of pneumatic-wheeled vehicles was shown by the models of SKB Grachev. Even the first of them - the most cumbersome ZIS-1E134 - was formally able to fulfill the task: in the first race, when driving in I lower gear with locked differentials, the loss of patency occurred only 6.5 minutes after the start at around 52 m in a 675-mm swamp with turf strength 1 kgm. Thanks to the ultra-low tire pressure (0, 1 - 0, 2 atm.), The track depth did not exceed 350 mm, which was even less than the ground clearance. In the second race when leveled to 0, 2 atm. pressure in the tires ZIS-1E134 traveled exactly 50 m in 9, 5 minutes and got stuck in a 730-mm "buchil", leaving behind a rather modest 360-mm track.
The second model - ZIS-2E134 - during the first attempt made its way to the mark of 59 m in 14 minutes, where it finally got up on a site with a depth of 700 mm with a turf strength of 1 - 2 kgm. At the same time, the depth of the left track did not exceed 300 mm. During the second race, the tire pressure for the experiment was increased from 0.2 to 0.25 atm. However, under such conditions, moving in the same lower gear, the car could not go beyond 47 meters. The time spent on this path was 3 minutes. The parameters of the bog at this point were 700 mm and 2 kgm, and the track depth, as expected, increased by 5 cm.
As for the lightweight (only 2, 8 tons) model ZIL-3E134, he was able to cover the entire 50-meter distance in 1 minute 48 seconds, without showing the possibility of loss of patency. The movement was carried out vnatyag in 1st gear with a tire pressure of 0.2 atm. The greatest depth of the swamp along the route of the vehicle was 800 mm with the strength of the turf cover at the level of 1 kgm. The depth of the track in the half-meter swamp section did not exceed 130 mm, since along the entire route of the ZIL-3E134, due to the low specific pressure on the ground, it did not destroy the upper sod cover at all. We can say that the ZIL-3E134 was the first domestic prototype of modern all-terrain vehicles on low-pressure pneumatics!
The tests were completed by heavy trucks MAZ-502A and YaAZ-214. Only this conclusion turned out to be very peculiar. Due to the large mass, multiplied by the high specific ground pressure, both of these trucks could not even really start. MAZ-502A, moving in lower gears I and II, completely lost its cross-country ability only 1.2 m from the edge of the swamp, not even reaching the start line! The depth of the swamp at this point turned out to be only 200 mm with the strength of the sod cover more than 14 kgm. In this case, the track depth turned out to be equal to 220 mm due to the destruction of hard soil by the wheels at each attempt to move from a standstill.
The performance of the three-axle YaAZ-214 turned out to be even sadder. Despite the fact that it moved as much as 6 m from the edge of the swamp (of course, never reaching the start line), the depth of the swamp in this place turned out to be even less - only 175 mm with a cover strength of 18 kgm. At the same time, a track with a depth of 365 mm remained behind the car! This fact clearly demonstrated the vital necessity of equipping cars of this class with centralized tire pressure regulation systems.
