Horizontal Stabiliser

Horizontal Stabiliser

The horizontal stabiliser will be the largest component I have attempted so far. It is 90″ wide which is longer than the workbenches I have access to. Whilst I could have daisy-chained two benches together, I would need a much larger surface when it came time to tackle the fuselage construction. Therefore, I decided to go ahead and build a single large bench that can handle the horizontal stabiliser, fuselage and wing assemblies. The process of building the new workbench is documented in its own post.

The construction of the horizontal stabiliser differs slightly from the previous empennage assemblies I have built. The design calls for a diagonal truss of 1/2″ x 3/4″ bracing members to span between the centre beam and trailing edge. The rest of the design is very similar to the rudder/elevator.

The first step as usual is to draw out the outline of the members onto the work surface. This is followed by some basic blocking so that the constituent members can be inserted into the fledgling jig. The members are then cut to length so that the basic form of the assembly can be seen.

Once again, the outer perimeter members require a T-shape profile to be cut into the timber to create a rebate for the ribs to sit in. This T-shape profile was cut using the rebate plane and a lot of elbow grease in my rebate jig.

A template for each of the gussets was drawn on paper – this process sometimes requires multiple iterations to get the correct [graceful] curves. The template is then traced over on the members in the jig so that the extents of the rebates can be accurately determined. The template is also used to trace out the gusset profiles on the plywood. There seems to be a consensus that plywood is strongest parallel to the outer ply direction – therefore, where possible, the ply direction was arranged perpendicular to the butt joints. This should hopefully increase the bending capacity across the joint.

Shims were used to align the centreline of adjacent members – this is very important as we are dealing with members of different thicknesses. Once the gusset rebates were cut and the shims installed, a final dry-fit was performed to check that everything fit correctly. Once I was satisfied, the frame components were glued using a T-88 at each of the butt joints.

With the glue cured, each joint is attacked with the chisel and file to remove any excess glue that would foul the fit of the gusset. Following this, the gussets are glued onto both sides of the horizontal stabiliser (in two separate glue-ups). 

The ribs are then glued onto the frame – this ties the three main beams together and provides a significant boost in stiffness to the assembly.

After a couple of days, the staples get removed and the leading edges and corners get rounded over. A final sand of everything finishes up the horizontal stabiliser.