Blackburn Flyers Newsletter
Issue 16 – August 2015
Bonding Aluminium Spars to the Laser cut Birch ribs were July’s task. We needed to identify the right adhesive and the correct procedure to make the lower wing. Initially we wanted to identify a suitable adhesive and after a bit of discussion with the design team we have selected West Systems adhesives as the one to use. I’ve contacted the local supplier Kildale Marine in Hull as the selected adhesive is designed to repair wooden/aluminium boats which makes it ideal for our use.
In detail we’ve gone for the three part West-System 105 epoxy, 205 hardener and 406 filler, however after consulting the manufacturer with our selection, they recommended a different epoxy with more filling properties and durance. With their suggestion a repair kit containing G/Flex epoxy was purchased and a sample rib was bonded for the structural testing.
The bond appears very durable and there is a plan to carry out structural testing to measure the strength of the bond.
Different methods of mixing and application were considered. The recommended 1:1 ratio requires an equal amount of the resin and the hardner to be mixed. At room temperature, this mixture has an application life of over an hour and the cure time of 24 hours.
We followed the manufacturer’s guidance on their website which utilises a syringe to fill the gap between the rib and spars, but after experimenting with different spachlers, wooden stick and other tools to force the adhesive in the joint we discovered that using a cotton bud is the most practical way of pushing the glue from the sides of the spar to the gap.
Preparation of the surface was also very easy, we used Scotch-bright used in the paint shop to clean the Aluminium spars without the use of any solvent.
It was decided to build the tailplane first as we have all the components in hand and is a typical sub-assembly with the ribs joint in two sections to the spar. Main spar is a full ring and the rear spar on one side only. Inivitive minds came up with a simple solution of using elastic bands to hold them in place whilst the adhesive is applied.
And here are the first manufacturing volunteers fully geared up building the tailplane.