The whole story.....
In the winter of 2014 we removed the port aileron of NX611 as we had noted a deterioration of the fabric covering, something that is a common problem on vintage aircraft as the Irish Linen historically used has a short life due to the affects of moisture and UV light.
As soon as work started on the removal of the aileron we knew this wasnt going to be a small job but we didn't realise thr full extent of what was about to unfold.
The overhaul of the port aileron is a good example of why we struggle to answer the question 'When will NX611 fly again?'. It is only once you start an overhaul of a system or part that you truly know the amount of work required.
The first problem we found was that the attachment bolts were corroded within the rase of the bearing they sat in. The main treatment of this is a thorough and prolonged soaking with a fluid such as Penol to ease the bolt out.....oh and some elbow grease.
Once the aileron was finally parted from the airframe we could set to work removing the rotting fabric and revealing the 'skeleton' structure. Looking back at the history of NX611 we fully expect that the fabric had not been renewed for over 30 years.
Sadly once all of the fabric had been removed we found areas of corrosion within the leading edge that had eaten from the inside through to the outside. The leading edge is exposed to the elements at each end (inboard and outboard) due to 'lightening' holes in the structure (a system implemented to reduce weight but maintain strength), We also found atleast one birds nest and a vintage crisp packet, evidently remnants of her past life stood on the gate at RAF Scampton.
The presence of the corrosion meant that we knew atleast two of the leading edges would have to be removed and replaced. Not only that but looking at the aileron and comparing it to the drawings it became apparant that at some point in its life it had suffered a blunt trauma to a corner; most likely it had been dropped at some point. This had damaged the alignment of the structure. It was decided that the only way to make the aileron airworthy once more was to completely dismantle the structure, jig the spar and rebuild it replacing parts where required. Sounds easy when its written doesn't it!
Further cleaning and inspection of the aileron identified damage to the pinion covers and ribs/formers. Drawings were sent off to Cunningham Aero for the leading edges, formers and covers in order to get the build underway.
The spar that forms the strength of the entire structure has the leading edge riveted to it and it's also bolted to the pinion which is in turn bolted to the control rod on the aircraft.
The major problem we found with the rebuild of the aileron centred around the pinion. It is a forged item and uses a riveting proceedure called 'plug riveting'. This required a rivet to be beaten into a blind, threaded hole. As long as you get the rivet the correct length the process of beating the rivet is simple, the hard bit is tapping the hole. We had the drawings for the tap but we spent around 3 months trying to find a company to agree to manufacturing it for us! The majority of companies argued that the tap would not work as it is too coarse thread and as soon as it met the bottom of the hole it would snap as there is no way of stopping the tap from 'bottoming out' (even though it had been used successfully hundreds of thousands of times in the 1940's!)
We eventually found a company who agreed to make the 5/32 Acme threaded tap (we ordered 2 just in case!) and the tapping of the holes was entrusted to Maurice Hammond at Eye Tech engineering who hand tapped all 50 holes.
The forging was returned to us ready for paint and we had received the new parts from Cunningham aero. Both leading edges were made over sized and needed to be trimmed and filed to fit leaving just the difficulty of backmarking and drilling the holes from the spar and forging into the new leading edges- a time consuming job as we didnt want to make a mistake and have to have a new leading edge remade and trimmed again!
Lots of new sheet alluminium parts we made in house to replace the parts of the aileron where the fabric is clamped between two pieces of alluminium and riveted to the former. All of these new parts had to be backmarked and drilled to match the original holes in the formers.
After the leading edges were trimmed to fit and all holes drilled to match the spar, pinion and internal formers of the leading edge it was time to start riveting. The internal formers had to be riveted to the leading edge first and then the edge riveted to the spar along with the main hinges. This of course had to be done while keeping the aileron straight and true to avoid any bends in the final structure.
Once the leading edge was riveted on the formers could be riveted and the cloaking strips that cover the top of the aileron could be attached. With formers riveted the trailing edge could be riveted on and all checked to make sure it was straight and true.
There were slight issues with alignment depending on what order it was all attached but this was all overcome and the aileron is ready to be coverd and painted in winter 2016.
Aileron work was completed by our airframe engineer Bob Mitchell with help from Sean Taylor (during the winter of 2014)
