What goes up – should stay up…
At this point in the journey, I have already made about three “practice” elevators. Whilst slightly annoying that I had to do so many, it is all part of the adventure. I have now obtained the correct materials – in the form of a Pietenpol fuselage and empennage kit from Aircraft Spruce & Specialty in the US.
The first step is the creation of a jig for the Pietenpol elevator on a piece of plywood. The jig was similar to the previous versions used for the practice pieces. However, after the practices, I have decided to forgo the aluminium clamps and invest in an electric staple gun. This has the following benefits:
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- The workpiece can be moved straight away – rather than having to wait several days for the glue to dry
- The gussets do not move around – when using the clamps, the gussets would glide over the thin film of glue too easily
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The staples do require caution to ensure they do not split the underlying timber or embed too deeply in the piece. The staples could be left in permanently however, I don’t like the idea of leaving an avenue for rust to exploit. Therefore, I will opt to remove the staples once the epoxy glue has dried. The jig is shown below with the blocks to secure each member securely.
Most of the members that make up the empennage require a T-shape profile to be cut into them. This profile will act to reduce the weight slightly and allow the gussets and ribs to be recessed flush with the member. Most of the practice elevators had this cut performed on a homemade router table. However, the router has unfortunately “eaten” a few pieces of nice spruce. I discovered {too late] that this was due to feeding the grain the wrong way. However, I must admit that I’m now slightly spooked about using the router on my nice spruce. The cross-sections required are shown below.
To cut the required profiles, I made a rebate jig out of some MDF board. I can insert a piece of spruce into the jig and run the hand rebate plane over it [many, many times] and slowly cut the profile into the timber. The rebate jig is shown below.
Once the rebates are cut, the pieces can be assembled into the main jig and cut to length using the band saw. At this point, I also figure out the shape of the 1/8″ plywood gussets.
The gussets require that the flange of the T-shape profile is removed where the gusset sits. Hence, there is a bit of work with the chisel to remove these flanges. We also have to do some other minor bevelling and tapering to ensure that there are no sharp corners where stresses can develop.
With all the rebates completed, the assembly is now glued up for the first time. Some T-88 Epoxy is spread on the butt joints and it is clamped together using the jig. Once the epoxy has cured for a day or so, the squeeze-out is removed with a chisel and file and the gussets are attached with more T-88 and staples. The edges and corners are then rounded with the band saw, block plane and some sanding.
One the gussets are installed, trimmed and looking good – the ribs are cut to length and attached. The ribs are small 1/2″ x 3/16″ members which tie the leading and trailing edge together with the centre beam. Once these ribs are attached, the whole assembly is very stiff. The finished elevator is soon joined by a second one built exactly the same.