Custom tension gas struts used in aircraft control system

The certification of the WT9 Dynamic two-seat sports aeroplane was already behind schedule when the UK Civil Aviation Authority (CAA) test pilot decided that the mechanical flap actuation system was too heavy to operate. Built in Slovakia, the entire aircraft would have to weigh no more than 256kg to receive the CAA's approval.

Yeoman Light Aircraft Company Limited (YLAC), the manufacturer, urgently needed to find a solution to this problem. After considering a conventional spring, then a rubber bungee, the company's designers thought that a gas spring might hold the answer. The idea was that this would increase the forces for the first part of the flap selection, then 'pay back' in the key later stages. But it still did not solve the problem.

YLAC chief engineer Tomas Prihoda concluded that what was really needed was a gas spring that worked in the opposite sense to the usual ones. After some internet searching, he found a tension gas strut that would reduce flap forces throughout the whole movement range.

Prihoda formulated a specification for a theoretically optimum gas strut, but the next problem was to obtain a lightweight strut that complied with the specification and was sufficiently robust for use in an aircraft.

Nick Marley, YLAC managing director, explains: "After searching around on the web, we were starting to despair. When we found Industrial Gas Springs, we felt that our prayers had been answered. Right from the start, IGS had a 'can do' approach. They had informative material on their website to help Tomas perfect the design and, most importantly, recognised the urgency for quick delivery of a test strut. Two custom-made struts were delivered within a week of our initial enquiry."

Certification achieved

The test struts were fitted to the prototype aircraft overnight and flown by YLAC test pilot Tom Porteous the following day. He says: "It was brilliant. The flap selection was much lighter and our problem was solved - the struts worked exactly as we intended."

This view was confirmed by the CAA test pilot, allowing the Dynamic to receive its certification. YLAC immediately placed its initial order for 15 tension gas struts for production aircraft, which, again, was fulfilled in record time.

Steve Woolcock, managing director of IGS, comments: "We were very pleased to be able to come to the assistance of YLAC in getting their project back on track. While we have supplied gas springs for installation on both civil and military aircraft, this is the first time one has been used in a key control system, and naturally I am delighted at the recognition of the quality and reliability of our springs that goes with it."