English Translation:
In the production plan for this year, the central car club of "Svazarm" has stipulated the production of the first types of a new small racing car with a capacity of 750 cc. These makes are intended for the training of new racing squads. In this article we describe the construction of the tentatively named T-605 racing car, which was built by Tatra designer Lubomir Szpuk. This designer writes the following about his new racing car:
“If a new sports vehicle with a small stroke capacity is to meet the requirements for racing, but especially for the training of new car racing squads, it must above all fulfill two conditions:
1. comply with the international regulations in force for speed competitions;
2. Its performance and driving characteristics must reach such a level that it can compete with all the latest sports cars in its class.
While the second condition is dictated by the desire of our top drivers for a new, faster car that can withstand all demands, the first condition has its origins in the possibilities of acquiring new experiences in international competitions.
Both conditions, even if they are actually very closely linked and pursue the same goal, are in great contrast to each other in the current situation prevailing in the CSR. The second condition would be relatively easy to meet if the vehicle weighs a corresponding number of kilograms, not exceeding the ratio of 6.5:1 hp (for an empty vehicle). The designers and drivers of our existing vehicle types achieve this ratio quite simply by doing away with the spare wheel, battery, starter, dynamo, etc., and by replacing the existing body with rigid fenders with a cigar-shaped body fitted with small, pivoting fenders. Of course, international regulations do not allow this type of execution, and therefore the vehicles "clipped" in this way only compete in our national competitions because of the generosity of the marshals.
However, since such "generosity" can no longer be counted on in national and international competitions in the future, the designers at Tatrawerke, who are currently working on the creation of a new small racing car, decided to use the experience they had gained during the construction of the Tatraplan sports car and the Tatra Monoposto and to use the knowledge gained in the construction of the new small racing car T-605.
The conception of the Tatra Monoposto, with its low weight ratios, stands out and was almost entirely adopted for the construction of the new T-605, whereby individual subgroups or details (e.g., the suspension of the rear axle, etc.) were simplified and others were reduced in weight, either by creating new shapes or through smaller dimensions. While the latter two types of design changes to subassemblies and details were dictated by reaching the chassis weight limit, the first change was prompted by the need for ease of manufacture. All of the above ways of achieving low weight would be useless if they were not based on the experience of previous, structurally similar vehicle types. The following comparison clearly shows how the weight of the vehicle can be reduced in the course of development.
The frame of the Tatraplan Sport, which was built without prior experience, consisted of a tubular steel construction and weighed 145 kg. The frame of the Tatra Monoposto, which was developed from the Tatraplan Sport construction, weighed only 35.5 kg. The load-bearing part of the frame of the newly designed small racing car, which was also created from the Monoposto frame using the proportional weight reduction method, weighs only 13.5 kg and after installing the necessary parts, such as engine mounts and torsion bars, the weight is no more than 18kg.
During sporting events, tests on the Tatraplan sports car clearly demonstrated the importance of the aerodynamic body for a racing car intended for speed competitions.
An aerodynamic pontoon body was chosen for the new small racing car, both for reasons of weight and to comply with international regulations, i.e., a body with rigid fenders that do not pivot with the wheel. If we didn't choose such a body, one would have to take into account that the coefficient of drag "Cw" would increase significantly. In addition, to comply with international regulations the mudguards would have to be of such dimensions that they cover the entire wheel, but also allow sufficient freedom of movement. However, fenders made in this way cannot compete with an aerodynamic pontoon body. The advantages of the latter body are proved by their frequent use. In practice we have seen a comparison when racing for the CSR Grand Prix in 1952 with the GDR drivers; such as Straubel, with his EMW collective, and on the other hand the IFA F9 car.
The loss of power in a car with a pontoon body at a speed of 140 km/h is 15 hp less than in a car with a cigar-shaped body with rigid fenders. Compare by diagram curve 2 of the Tatraplan Sport and curve 3 of the Frazer-Nash, which is 20 kg lighter. This means that the maximum speed is 20 km/h higher with motors of the same power. The acceleration of the vehicle, which is equal to the ratio G/N (total weight of the vehicle engine power), plays an important role and therefore influences the final shape. Examples are the cars that took part in the races in Mlada Boleslav, Lberec and Ecce Homo and abroad in the 100-lap race in Monte Carlo. Since the increase in maximum speed is guaranteed by the better acceleration, the aerodynamic pontoon body was provided for the construction of the new small racing car. Experiences with the body of the Tatraplan Sport, in which the aesthetic processing of the aerodynamic and technically flawless shape resulted in a deterioration of the coefficient of drag "Cw" (up to a value of 0.46), proved that it is necessary to design the body from the aesthetic side, for example, in order to create the required low body weight. The rear fenders are designed as stabilizing surfaces of a completely new shape. The basis here is the low vehicle body with covered fenders. By eliminating the sunken surfaces of both Tatraplan Sport bodies, which was achieved by installing headlights on the front fenders and openings for cooling air to the rear wheel brake drums (which, by the way, turned out to be ineffective even at speeds over 80 kph), the coefficient of air resistance should be reduced from 0.46 to 0.45.
Since the planned engine with a capacity of 630 ccm, which is already built as standard from a high-speed drive unit for stationary [motor] purposes, has been subjected to many tests with changing loads in the Tatraplan-Sport and Tatra-Monoposto in various races, it is certain that you will hardly get a power higher than 46 hp, at which the car reaches a speed of 170 kph if the total weight does not exceed 420 kg.
Comparing the new car with the Tatraplan-Sport, we find that the driver's resistance area to the oncoming airflow is 15 percent larger than in the Tatraplan-Sport. From this it can be concluded that the coefficient "Cw" will also be higher, namely at least 0.53. But even under these circumstances the vehicle would reach a maximum speed of more than 160 kph.
Great attention was paid to the duct for the inlet and outlet of the cooling air. Some progress has been made in this area over the course of development. In the case of the Tatraplan-Sport, the additional duct for the flow of cooling air to the engine began with an increase in the shape of the hood behind the driver's seat. By covering the passenger seat, the use of dynamic overpressure and airflow to support the dynamic suction of the cooling fan was considered. However, the practical investigations of the bodywork in the aerodynamic air duct have shown that the arrangement of the inlet opening was not exactly solved in a favorable manner. The air currents, the one. Bodies flowing around influence each other so that they avoid the body to be flowed at a certain distance. When the airflow stalls from the body, the turbulent airflows are not always parallel to direction of the original airflow but run parallel in the direction of the laminar airflows at or just before the point of rupture (of course, the merging of the air currents behind the body takes place in the same way.)
These basic characteristics of airflow must be kept in mind to understand how the windscreen in front of the driver's seat affects airflow. (See illustration.). This means that the shape of the windshield has an influence on the air flow. In order for the windshield to do its job with the smallest area of resistance (to bend the airflow so that it only minimally engages the protruding part of the body), it is necessary for the windshield to have relatively little curvature. Behind their edges, however, the air flow breaks off and the laminar flow (marked with straight arrows in the picture) hits almost a sixth of the total area of the inlet opening. The diagonally hatched part of the opening (section "C" - unshaded part) is caught by the whirling turbulent flow (helical arrows), in which the dynamic overpressure mentioned at the beginning does not occur. The air is sucked in this field by fans, causing a partial clinging of the air flow to the motor housing.
A well-known phenomenon of aerodynamics, namely the snuggling of the air-flow behind a spherical surface also occurs here (namely behind the driver's head) and a certain dynamic overpressure for the support of the suction of the carburetor is reached.
The diagonally hatched opening "B" is almost completely covered by the driver's back, and consequently no dynamic overpressure occurs here. Simple ducts feed air to the engine is marked as part "A". The dynamic overpressure at the front part of the vehicle, which has already been used by the oil cooler, cannot be conducted into the engine compartment in a technically simple way. The type of air cooling described can be found on both Tatra Monoposto cars. With this type of cooling, however, there have been some disadvantages, which consist in the fact that it cannot be prevented that parts of the car, such as parts of the swing axles, shift levers or even the shock absorbers, protrude into the cooling air duct, which causes the laminar flow and the like so that the utilization of the dynamic overpressure is disturbed.
By using the dynamic overpressure in connection with the oil-injector cooling, in order to create such cooling conditions in the car that sufficient cooling air is available even for an engine with cylinder fins, which was originally intended for the necessary cooling without a fan, it would be necessary for the excess pressure on the cylinders (at the point of air supply) to be at least a maximum value of 70 mm of the water column.
This would achieve a performance that would be sufficient to drive the vehicle, taking into account the fan. Future research will show whether such conditions can be created."
Ludomir Szpuk
Republished from “Ludovy Motorista”
Full edition:
https://gdrfahrzeuge.blogspot.com/2023/06/1954-illustrierter-motorsport-gdr-year_81.html
