Sunday, 11 January 2009

First Aileron Complete and a New Hat Shelf

A few photo's of the completed starboard aileron showing the strenghtened but rib.

The tip end rib also had to be replaced as the wood was cracked and had lost much (if not all) of it's residual strength.

Two general pictures showing the end result.

Although I will be starting on the second aileron next week I have also started looking at the design of a map shelf to fit behind the baggage sling. The design (I admit) was taken from that used by Rob in the restoration of G-BREY. Steel tabs will be welded to the fuselage so that the aluminium shelf can be screwed in place with machine screws. The map shelf is large enough that it require stiffening to prevent it from sagging even though it is not intended to support any real weight. It is far enough to the rear of the aircraft that any weight in this area will impact on the c of g of the aircraft.
Next week I'll post more details on the design of the map shelf and the stiffeners to be used.

Thursday, 1 January 2009

Completing the first Aileron

By early December the spars have had all the plywood doublers glued in place, drilled for the aileron brackets and varnished with Randolf spar varnish. The ribs are in place but not yet nailed and most other components are primed ready for reassembly.

The first job is to nail the ribs in place. To achieve this I jigged the spar by mounting it onto the workbench with brackets attached with AN3 bolts through the holes drilled for the aileron brackets. I used the old nail holes to locate the position of each rib, and for completeness, screwed the trailing edge to the ribs. I was also able to offer up the leading edge skins to ensure the screw holes still lined up. Once confident that everything is in place, I nailed the ribs to the spar.

Following advice from Rob Lees (G-BREY), I decided to reinforce the butt rib as this has a tendency to bow in with the tension of the fabric when it is applied. A wedge was made from 0.020" 2024T3 aluminium which would fit inside the rib preventing it from warping. The wedge was riveted in place with blind rivets as I couldn't get a bucking bar in the space available if I was to use solid aluminium rivets. The three pictures below show the assembly of the wedge.

The aileron is made up mainly from aluminium parts except for the tip bow which is a 1/2" 4130 steel tube bent to shape and all screws which are stainless steel. Because there is the possibility of dissimilar metal corrosion where steel and aluminium come into contact (even though all parts are primed) I used Duralac, either painted on using a brush or as a dip with the screws which will act as an additional barrier preventing corrosion. The Duralac was wiped off after assembly to keep the structure clean.

The inside of the 4130 steel tip bow was treated with Lanolin (oil) to protect it from moisture which will also cause corrosion. Lanolin is the traditional British treatment whereas America tends to use Linseed oil instead. The downside to Linseed is that it is flamable which can be a problem if a weld repair is required at a later date.

Finally, the leading edges were screwed into place using the old screw holes. Oversize nails were used to secure theleading edge to the spar and the aileron brackets were bolted on.

The aileron will then be checked against the wing to ensure that the brackes align correctly before the aileron is put into storage. I will cover the aileron along with the rest of the aircraft after the final rigging is complete. This is probably better done without fabric on.