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Josef Bartoska1

1 Forest Research Institute Zvolen, Oravsky Podzamok, Slovakia.


This paper deals with existing problems and possible solutions in various areas of timber transportation in the forestry management of the Slovak Republic. It addresses the areas of environmental emissions; pollution of the environment by fuels, lubricants, and hydraulic fuels; and damage to carriage ways of forest roads caused by excessive axle loads.

In the field of environmental emissions, it deals with the possibilities of reducing emissions through the establishment of new hauling arrangements by optimizing organizational measures.

Possibilities to reduce environmental pollution by use of ecologically friendly fuels, lubricants, and hydraulic fluids of domestic production are presented.

In the area of damage to carriage ways of forest roads by excessive axle loads, the paper deals with correct combinations of vehicles and their allowed loads.

In the final part, the paper presents the measures included in the research programme of the Research Station of the Forest Research Institute Zvolen in Oraveky Podzamok specialized in the research solution of timber transportation issues in the forest management of the Slovak Republic.

The situation in timber hauling in the forests of Slovakia after the separation of the CSFR

Before the separation of the Czech-Slovak Federative Republic into two independent states, the trucks for timber hauling were manufactured mostly in the Czech Republic. A decline of these production capacities followed in the Czech Republic, and in Slovakia these trucks started to be fitted with specialized equipment for timber hauling in three manufacturing enterprises and at the Research Station of the Forest Research Institute in Oravský Podzámok.

In the years 1989-1993 a slow-down in the innovation and replacement of the hauling fleet occurred in the forests of Slovakia. In 1992 the number of trucks used in forestry increased only by 2 new TATRA 815 trucks. The prevailing trend was a decrease in the number of trucks due to the privatization of the state forests and the transfer of ownership to private forest owners and companies. So only existing, worn-out trucks were used

After 1993 some private forest owners, wood-processing companies and newly established transport companies started to fit their trucks with equipment for timber hauling since the price of new trucks was very high (TATRA 815 6 x 6 - CK 2 300 000 + VAT).

Since 1994 a certain revival of the interest in the restoration of the hauling fleet also in the state forests of Slovakia can be seen as a result of the improvement of the economic situation as well as the breakdown of the existing fleet and necessity of replacement.

In the forests the mostly used trucks are TATRA 815 6 x 6 and LIAZ 111.800 4x4. The use of other types such as TATRA 148, SKODA 706, PRAGA V3S and some types of LIAZ used in forest management has been decreasing.

The situation of timber hauling by log trucks in the state forests of the Slovak Republic up to the 1994 is illustrated in Figure 1.

The aspects of timber hauling ecologization

The critical environmental situation in Central Europe calls for urgent need to orientate towards particular fields of forestry with recovery measures, not excluding timber hauling by log trucks.

To reach the targets of timber hauling ecologization we consider necessary to realize the following:

1. purposeful innovation of the hauling fleet;

2. measures aimed at the elimination of environmental pollution by emissions, leaking fuels with hydraulic pressure liquids (media);

3. measures reducing the damage of forest roads due to axial overload on hauling trucks.

With the innovation of the hauling fleet we consider it necessary to select the basic chassis to be fitted with timber hauling equipment according to their techno-economic characteristics and in compliance with existing legislation with regard to their harmful effects on the natural environment. Our objective is to modernize TATRA and LIAZ frame chassis meeting EURO I or II criteria, with new constructionelements, an acceptable noise level, lower fuel consumption and better technical characteristics exhibited at international truck competitions. We take into consideration off-road conditions of the forest transport network in Slovakia and the experiences with the use of single types of chassis in these conditions.

To find a solution to the questions of environmental pollution by leaking fuels and lubricants we studied:

1. the use of alternative fuel for diesel engines - biofuel (RME) and the possibility to use liquefied petroleum gas engines in trucks under suitable operational conditions

2. the substitution of mineral pressure media in hydraulic systems of hauling trucks by ecological pressure media;

3. the establishment of legislative regulations securing the reduction of the danger of natural environment contamination as much as possible;

4. the optimization of timber transport to consumers.

With regard to the introduction of alternative fuels for trucks, we cooperate closely with the manufacturers of trucks run on gas and biofuel.

When trying to introduce trucks with engines run on biofuel we met with some obstacles due to the attitude of the truck manufacturers against the use of biofuel in their trucks. The manufacturer TATRA a.s. Kopýivnice from the Czech Republic, covering at present approximately 56 percent of the trucks of the State forests in Slovakia, has not allowed the use of RME in its engines up to now. Laboratory tests on the TATRA 815 6 x 6 engine shows operational unreliability due to higher fuel efficiency in the air-cooled engine, fall of performance by almost 25 percent, the occurrence of resin muds in the valves and other reasons. However, the manufacturer of TATRA vehicles allows the use RME in his engines after testing of RME in a mixture with petroleum base, which could eliminate the unfavourable effects of RME on the engine. However, mixing RME with a petroleum base and other additives decreases its biodegradability.

In 1995 the manufacturer of LIAZ vehicles - LIAZ a.s. Jablonec nad Nisou in the Czech Republic, covering at present approximately 40 percent of the vehicles used in the forests of Slovakia, approved the use of alternative fuels in accordance with regulation Vyhl. Ÿ. 102/95 concerning technical qualifications and technical demands of road traffic valid in the Czech Republic.

According to this regulation the use of alternative fuels in spark ignited engines from the viewpoint of acceptable limits of air pollution and environment protection (gaseous emission, solid particles, fumes) is approved by the Ministry of Transport of the Czech Republic. The manufacturer of vehicles (engines) approves the use of these fuels in particular types of vehicles. A similar regulation should also be issued in the Slovak Republic at the end of 1996.

Regarding the alternative fuel BIOFUEL (trademark NATUR DIESEL, ND-21) the manufacturer of LIAZ vehicles LIAZ a.s. Jablonec NAD Nisou elaborated a regulation, which approves its use of LIAZ engines run on biofuel. This conclusion is based on internal tests to verify the interval of oil exchange (refuelling) and life cycle when using biofuel NATUR DIESEL, ND-21 of the manufacturer ADW s.r.o. Sedlec in the Czech Republic, as well as tests on the starting capacity of the LIAZ engine at low temperatures. LIAZ a.s. Jablonec nad Nisou indicates in its instructions for the use of NATUR DIESEL that the decrease of engine power should not exceed 5 percent although there are no restrictions concerning its use on their side,

After the creation of favourable legislative conditions (the regulation Vyhl. Ÿ. 248/91 Zb. was issued) the manufacturer of vehicles TATRA a.s. Kopýivnice in the Czech Republic also solved the problem of gasification of the vehicles TATRA 815 S1 and 535n including the rebuild of a vehicle run on compressed natural gas. Thus the vehicle is able to run on compressed natural gas (20 MPa) ignited by pilot injection of diesel fuel or only on diesel fuel. The scheme of dual fuel vehicle T 815-2 S35 28 195 6 x 6.2 is given in Figure 2.

The use of vehicles run on gasified fuel is impossible in the forest in the case of long logs hauling when the space behind the cabin is used to mount an hydraulic arm or a cab/protective shield. It is possible when the hydraulic arm is mounted on the rear of the vehicle, but its use is meeting problems (with the vehicles TATRA 815 for long logs hauling) connected with the decrease of effective weight by approximately 600 kg due to the installation of 10 pressure tanks (60 kg each tank), the need to build connections and stations for compressed natural gas filling, as well as the costs of own rebuild of the vehicles. The introduction of TATRA 815 vehicles on CNG (compressed natural gas) has not spread in forest work in Slovakia up to now but we want to carry out experimental tests of the vehicle run on LPG under suitable operational conditions.

A T 815 engine run on liquefied petroleum gas seems to be a better solution for the future. It will be definitely ready for use after a solution is found to the problem of gas leakage from the cryogenic tank of liquefied gas during long standstill of the vehicle; better heat insulation is also required.

Compared to the Tatra engine run on CNG, this application seems to be better with regard transport to the place of use, smaller dimensions, as well as lower weight of the cryogenic tank.

With regard to solving the problem of substitution of mineral pressure media used in loading and hauling vehicles the situation is as follows:

In hydraulic systems of forest machines mainly mineral pressure medium OHM-46 is presently used in the Slovak Republic. It is hydraulic oil of petroleum origin, biologically undegradable and insoluble in water. This would have a serious impact on the environment in case of undesirable leakage from the hydraulic system, for example due to an unexpected accident or loose connection.

For this reason the majority of developed countries require that pressure media used in machines operating in the natural environment should be biologically degradable, innocuous for food, non-toxic for bacteria, water animals and man.

The chemical industry of the former Czech and Slovak Federative Republic had not dealt with the development of ecologically compatible pressure media up to 1990. Therefore, in first studies of the possibilities of their use in forest machines we were entirely dependent on their import from abroad. At that time legislative regulations preventing natural environment pollution by the lubricants of power-saws had been already established, and the use of ecological pressure media in mobile machines operating mainly in the regions important from a water management viewpoint was tested. Information on the results of these tests frequently disagreed and led to different recommendations. Also in several cases the use of ecological pressure liquids based on polyglycols and esters was recommended. The price of these liquids is 2.5-6 times higher than the price of mineral pressure liquids (DM 2-8 per kg). This fact was not very attractive, in spite of their longer service life compared to pressure liquids of rape origin (which in a certain way compensates for the high price).

Also after 1993 the chemical industry of SR started to pay increasing attention to the development of ecological pressure and lubricating liquids, and thus it was necessary to compare the created liquids with foreign ones according to the same methodology and to elaborate the recommendations for their use. Within research projects carried out after 1993 at FRI Zvolen we used samples of 28 brands of pressure liquids of local as well as foreign manufacturers to perform compatibility tests of packing of ESSEL hydraulic arms manufactured in SR with these media and standby tests of some linear hydraulic motors of hydraulic equipment used in the forests of Slovakia. During the tests we cooperated with the Institute of Forestry and Wood-technology Mechanization of the Faculty of Forestry VæZ Brno in the Czech Republic. The recommendation to use particular ecological pressure media in ESSEL 80 hydraulic arms (Table 1) is one of the results of these tests.

The recommendation concerns mainly Slovak and Czech pressure media, but we also recommend to use with our assistance media CONNEXOL HD 32-68 from Germany, MOBIL EAL 224H and OMV AG-Biohyd MT from Austria for the hydraulic arm ESSEL 80.

From the results obtained it is obvious that different types of mineral pressure liquids are only slightly different with regard to their utility properties, and mainly their price is the dominant criterion in the selection of a particular medium. Another criterion considered is medium durability because the durability of mineral pressure liquids is quite low compared to synthetically made media.

At present FRI Forest Station in Oravskl Podzmok aims at the introduction of the results of research of ecological pressure media into forest management. The behaviour of ecological media at minus temperatures is an important aspect of their tests on hydraulic arms considering the severe conditions of northern Slovakia. It was found that total crystallization of RME occurred at a temperature of -37°C under laboratory conditions.

With the implementation of the measures to eliminate the effect of overload on the axles of hauling vehicles we aim to:

1. determine the optimum structure of the hauling fleet and suitable combinations of logging trucks for long logs and stacked wood;

2. ensure running control of axle load in hauling vehicles by means of on-board electronic scales sensing and displaying axle payload;

3. develop truck trailers for long logs hauling with sufficient loading capacity;

4. introduce heavy haulers more suitable for the conditions of wood transport on forest roads.

One of the important criteria for efficient timber hauling is make maximum use of the effective weight of the hauling trucks. From an analysis of the conditions of optimum use of effective weight of different truck and trailers combinations it can be concluded that it is important to choose a proper combination, to know how their distance affects their mobility in sharp bends, and how the use of different trucks with different loading capacity affects the distance of timber transport.

Cases of improper truck and trailers combinations for long logs, trailer overload or great distance between them, can make them subject to fines from the competent authorities. Improper truck and trailer combination results in increased wear of roadways and consequent surface erosion, as well as increased wear of the hauling vehicles due to their overload.

Vehicles overload is also in contradiction with regulation Vyhl. Ÿ. 41/1984 Zb. prescribing the conditions of vehicles operation on roads, and that was the reason why our research institute started to study the problems of sensing, displaying and assessing hauling vehicles overload. In accordance with above-mentioned regulation the maximum overload cannot be more than 3 percent of total weight of the vehicle in operation to avoid pollution whereas in our field tests we found an average overload of 14 percent for the TATRA 815 6x6 (24 t) truck, 15 percent for the LIAZ 4x4 truck and almost 50 percent for the one-axle trailer DAV-8 (10 t). We found that double-axle semitrailers DA-5 without shaft are fully adequate for any combination with truck. This proves the important role of trailer loading capacity as with a proper arrangement of truck and trailer the latter can take a significant part of the truck load.

The problem of vehicle overload, especially trailers for long logs, is solved abroad by the use of on-board electronic scales sensing and displaying payload. We had the idea of developing such equipment already in the 1970s but were discouraged by the high price in comparison to the price of hauling trucks. In 1986 we developed a more simple equipment for sensing axle overload in the LIAZ truck and trailers and in trailers with plate springing based on deflection of elastic elements of axles. Due to its simplicity it was not suitable for use in the TATRA vehicles with swing half-axles.

After the rapid price increase of hauling vehicles in 1991, our interest in the development of high price equipment was restored. This equipment should meet the requirements of weighing accuracy and its price should be proportional to the price of trucks. For this reason, cooperation was established with the company ESA Mestechnik GmbG Munchen, well established in Bohemia, and with the Czech Republic. The scheme of this equipment and front panel is given in Figure 3 and Figure 4.

A mean accuracy of 1.72 percent was reached in sensing of truck load; with the trailer it was 0.02 percent (the accuracy increased with the increase of "load on the stakes").

The price of the equipment is approximately SK 100 000 and, compared to the price of TATRA 185 6 x 6 (SK 2 250 000 + VAT) and the price of the trailer DAV-14 (SK 450 000 + VAT), it is acceptable.

This equipment can be used in the future for the sorting of long logs according to weight, and with timber import it will ensure truck and trailers passage through the border without any fear of exceeding allowed loading capacity of vehicles.

This equipment includes also sound alarm, which is activated in the case of vehicles overload during loading in the forest.


We believe that our efforts will result in successful solution of all mentioned ecological problems and we will contribute to the decrease of unfavourable impact of forest machines on natural environment. But still we must do a lot of work to implement research results in forest management.


Bartoška, J. & Urban, C. 1988. Základné podmienky efektívneho odvozu kme ov z h adiska optimálneho vyu itia u ito nej hmotnosti odvozných súprav (Conditions of effective hauling of logs from the viewpoint of optimal use of effective weight of truck-and-trailers]. Vedecké práce VÚLH Zvolen [Scientific works of FRI Zvolen]. pp. 181-196.

Bartoška, J. & Urban, C. 1990. Use of ecological pressure liquids in machines operating in a natural Environment. Lesníctví, 36 (LXIII), No. 11. pp. 969-977.

Bartoška, J. et al. 1993 Pou itie ekologicky neškodných tlakových médií v hydraulických systémoch lesných strojov a ekologizácia odvozu dreva The use of ecological pressure media in hydraulic systems of forest machines and ecologization of timber hauling]. Zá vere na správa iastkového projektu [Final report of partial project]. LVÚ Zvolen. 43 pp.

Bartoška, J. 1994. Rozbor sú asného stavu pohonu nákladných vozidiel plynom a mo nosti jeho vyu itia v lesnom hospodárstve [The analysis of present state of vehicles on gas engine and possibilities of their use in forestry]. Lesnícky asopis Forestry Journal 40:3 pp. 215-221.


FIGURE 2. Rear Dumper TATRA 815-2 S1S 28 195 6x6.2

Engine T3A-929-80

Modes of work:

- only with diesel fuel
- with methane gas and pilot injection of diesel fuel

No. of cylindres




Rated power (both modes of work) at 2200 RPM

195 kW

Max. torque at 1200 RPM

950 Nm

Compression ratio

16,5 ± 0,7

Weight of engine

1160 kg


Curb weight

12 500 kg

Pay load

16 000 kg


28 500 kg

G.V.W. distribution

- front axle

5 800 kg

- rear axle

2x 11 350 kg


Body volume

9 m3

Body inside length

3 700 mm

Body inside width

2 290 mm

Body inside height

1 000 nun


Max. speed

89 km.h-1

Max. climbing ability

28 500 kg 38%


800 mm


12 R 20

Fuel consumption

When running on gas, 50 - 70 % of diesel fuel is replaced by gas with the ratio of approx. 1 m3 of gas/1 l of diesel fuel.

Diesel fuel tank capacity

230 l

CNG tanks capacity

120 nm3




















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* 1 - (R) Rape oil
* 2 - Determined according to international metodology CEC L-33-T-82
* 3 - + yes, - no
* 4 - Information provided by manufacturers to March 1996



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