The clearing of power line corridors using a vertical saw carried by a helicopter has proved itself to be most effective. One of the leading companies in this business is the German company Helimatic. They are becoming increasingly active in Switzerland, for example in the Tessin.
|Fig. 1 - Helicopter take off for the next assignment in a power line corridor.|
|Fig. 2 - The 8m saw is suspended on a 36m long aluminium tube which made up of 6m long individual tubes which are screwed together.|
A little way past the Alpine Transit building site in Biasca, in the direction of Malvaglia, a small tarred road leads to an elevated cow pasture. This is being used as a take off and landing place by the company Helimatic during their three day assignment. The pasture is situated at the foot of the around 1900 m high Monti Lesgiüna and offers an unimpeded view of the valley where the river Brenno flows in the south.
It is optimal flying weather today; the sky is clear with only an occasional gentle breeze. The muffled, thudding, roar of a helicopter can be heard. However, you have to look for a long time before you finally see it take off from the rich green, steep slopes which are interspersed with the pale yellow blossom of chestnut trees.
At present the pilot, Urs Aecherli, is busy clearing one of the Società Elettrica Sopracenerina’s (SES) power lines. His attention is constantly focused downwards. As though they have a life of their own his hands and feet carry out gentle movements, steering the SA 315 B Lama helicopter slowly over the steep slopes, whilst the saw hovers close to the overhead power cables cutting off any branches which come into its path as quick as a flash.
Sitting next to Urs Aecherli, and connected to the pilot with headphones and a microphone, is Peter Kechler, the technical manager and coordinator. He gives the pilot non-stop information about the position of the saw, the helicopter, and the distance of the rotor blades to the terrain.
From a distance the saw appears to be hanging on a rope. But in fact the "rope" is made up of 6m long aluminium tubes, technically known as slings, which are screwed together. There are two advantages to this system. Firstly, the working length can be adjusted to a maximal length of 40m and secondly, the 8m long saw can be controlled with more precision, even in windy conditions. On the inside of the tube there is a control cable which allows the saw to be operated from the cockpit, as well as a wire cable, which would secure the saw if the tubes were to break.
The 58 year old Swiss pilot, Urs Aecherli, has been flying for Helimatic, the company with the saw system, which is a part of the Otto Wolff group based in Cologne, for nine years. He has a total of 11,500 flying hours under his belt, 4,200 with the saw. And he has never had an accident. "You need luck", says Aecherli, "but also the ability to know your own limitations and those of the machine." The system is very safe and has proved itself over ten years. The manoeuvrable powerful robust Lama helicopter can fly safely even in wind, rain and light snowfall. It can be dangerous when there is a strong, gusty side wind: "if the 400 kg heavy saw starts to swing excessively it could unbalance the helicopter."
Whilst his colleagues are in the air the saw technician, Stefan Justen, is standing in the cow pasture watching the operation from a distance. In his VW van he has all the necessary tools tucked away to be able to service the saw after it’s circa one hour assignment, or to quickly repair any possible malfunctions. To service and refuel the 8m long saw it is laid on a 10 m long double axel trailer. When landing the helicopter hovers steadily over the trailer and descends centimetre by centimetre until Stefan Justen can catch the lower end of the saw and latch it into the carrier bar. Then Urs Aecherli lands the helicopter, together with the aluminium "rope" onto the ground behind the trailer.
|Abb. 3 - The saw technician, Stefan Justen, checks the 60 HP motor of the 10 blade helicopter tree saw after an assignment.|
Abb. 4 - The pilot, Urs Aecherli has been flying for 31 years, 9 of them for
Photos: Christoph Schwyzer
Abb. 5 - The tree saw can cut through branches with a diameter of up to 25 cm.
Abb. 6 - The overhead power cables of the Società Elettrica
Sopracenerina SES near Biasca after a successful trimming. The corridor had been
thinned out conventionally before hand.
Photo: Christoph Schwyzer
"We rarely have problems with the saw", says Stefan Justen. A key aspect is the precise adjustment of the torque speed of the ten carbide saw blades. "If they are too loose then they have no bite." The blades have a diameter of 55 cm and rotate 2,000 times per minute. A 60 HP Bombardier-Rotax motor, usually used for powering snowmobiles, provides the energy. The fuel is stored in the first tube above the saw (tank capacity 27L). If the saw is running at full power it can easily cut through branches with a diameter of up to 25 cm.
"In the beginning", according to Thomas Harbeke, managing director of Helimatic, "many foresters were sceptical about our method. They feared that the trees would be permanently weakened, infested by pests and would die." However, thanks to the many operations carried out since 1981 these reservations have been dispelled. The cut surfaces are extremely smooth and clean and they lignify very quickly. "In the short term there is a loss of increment, but this is good as the trees re-grow less quickly into the power line corridors again. Also because the branches are only cut on one side the main point of growth shifts from the direction of the power lines to that of the forest." After being cut the corridors do not need any further clearing for six to eight years.
And how do the forestry entrepreneurs see the situation? Is the flying saw a rival to their businesses? Harbeke says no: "Primarily we fly our assignments in steep, inaccessible terrain. That is to say, everywhere where it would not only be time and cost intensive to clear the power line corridors by hand, but also where it would be very dangerous. Where the access roads are good, the forestry entrepreneurs still do their job. On top of that they often carry out preliminary work, felling small, short trees." On average the helicopter saw, which has a cutting surface of 6 m, can trim a tree stand along a length of around two kilometres in one hour, at a cost of around CHF 4,000.- to CHF 5,000.-. "A forestry enterprise with five workers would need a week to do this work", says Thomas Harbeke.
Another advantage of trimming by helicopter is the minimum time the power lines need to be disconnected from the net. The future aim of the energy providers is to not have to turn off the net at all: "At present we are working together with the Berner Kraftwerke Energy Ltd (BKW Ltd) on a system which would permit us to work with live power lines. In the future we want to use carbon tubes instead of aluminium ones therefore completely decoupling the helicopter from the saw."
General Manager, Thomas Harbeke is not worried about getting jobs: in Switzerland especially but also in Italy and France he has ascertained that there is a considerable backlog of necessary maintenance to power line corridors.
Helimatic first worked in Switzerland in 2003 for the Romande Energie RE. Further customers are the Elektrizitätswerk Obwalden (EWO), the Elektrizitätswerk Reichenbach (EWR), the Berner Kraftwerke (BKW), the Aziende Industriali di Lugano (AIL) and finally in June 2009 the Società Elettrica Soprecenerina (SES).