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Gas springs give watchers a birds eye view

01 December 2008

They are usually employed to hold open car boots or prop up heavy covers allowing access to industrial machinery, but gas springs have proved they can have a softer side by allowing enthusiasts to get closer to one of the country’s rarest birds

Six Camloc gas springs have been purchased by the Forestry Commission Scotland and fitted to a bird hide which will allow dozens of watchers an unobstructed view of magnificent white-tailed sea eagles in their natural habitat.

The hide, operated under the Mull Eagle Watch partnership, is the only organised hide in the world to offer a view of a white-tailed sea eagle nest, and is situated on the banks of Loch Frisa in a remote area of the Isle of Mull.

It has canvas interpretation panels and two TV screens featuring live footage of the eagles, the UK’s largest and most endangered birds of prey, which is beamed into the hide from CCTV cameras placed close to the nest.

However, earlier this year, the Commission got in touch with industrial components suppliers Jet Press, based in Huthwaite, Nottinghamshire, with a challenge.

At the front of the hide are three wide windows, which each weigh 6kg and are hinged so that they can be opened to allow watchers to rest their elbows on the window frame and scan the skies through their binoculars. However, weather in Mull is changeable. The Commission wanted a mechanism that would keep the windows open securely on windy days, but one that could be closed easily, safely and quickly.

The task to find a solution to this problem fell to Forestry Commission building surveyor Steve Wassall, who decided that what was needed was a set-up similar to an open car boot. He realised that he needed two gas springs for each window, but was unsure of what specification they would have to be.

He approached Jet Press and outlined the problem to its technical manager, Martin Belcher who, given the remoteness of the site, would have to do everything over the telephone. Jet Press stocks gas springs manufactured by ArvinMeritor.

“Gas springs are used for an incredible number of different applications, but this was certainly a new one to us,” said Martin. “They are, however, perfect for the job, although the application required some communication between Steve and myself to establish the type of strut and the mounting point positions to achieve the required action.” After getting Steve to weigh and measure the windows, Martin worked out what was needed.

“The range of gas springs we stock can handle lid weights from 5kg up to 250kg, and we can normally calculate the gas spring force required to suit the application,” he said. “But small changes in the centre of gravity, temperature or the mounting position can radically alter the handling characteristics of the gas strut. Add to this the changeable weather conditions in the Mull, and calculating the optimum gas pressure for the strut soon becomes an almost impossible task.”

In the end, Martin decided that the task would be best served by using a Varilift gas strut in the 8-18 range. Varilift features a gas release valve, which would allow the fitters to release small amounts of gas from the strut until the correct “feel” could be achieved.

“Another consideration was the need to open the windows safely,” Martin continued. “After all, we did not want the window to spring open as soon as the catch was released, as this could cause injury to anyone stood nearby.” This involved accurately working out the static and dynamic mounting points so that the window had a slight self closing action over the final 5 to 10 degrees of movement, whilst still keeping them in an achievable position for the frame and window constraints. This solved one problem. Next, Martin had to consider the possibility that the weather could cause the window to slam shut in a gust of wind.

“The sensitive nature of the birds means that there is always a ranger present, but at the end of the day, they are often alone, so one person needs to be able to close the windows,” Steve said. “Because of the size of the windows, it would be impossible for them to reach and activate the locking mechanism on the gas struts on both sides of the window at the same time as closing the window.

“These problems forced us to consider the Econoloc range, which has a locking shroud which springs into place once the gas strut has reached its full extension,” Martin explained. “It acts like a mechanical lock, preventing closure of the window without manually releasing the locking shroud.”

After a flurry of telephone calls and paperwork between Nottinghamshire and Scotland, the problem was solved. The hide has one Econoloc strut fitted on one side of the window and a Varilift Swift & Sure on the other, which allows one ranger to operate the locking mechanism with one hand and close the window with the other.

The springs were sent to Mull in February, allowing Steve to fit them will in time for when the eggs hatched – affording the best opportunity for the watchers. All of this went unnoticed by the eagles – which is as it should be - but has made a significant difference to the watchers’ experience.

“We are delighted to have solved the problem,” said Martin, “especially since we were not able to see the hide at first hand. We hope that the gas springs add, if only in a small way, to everybody’s enjoyment of watching the sea eagles in their natural habitat.”

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