Tail end of the tail
Now we are onto the last major element of the aircraft empennage – the vertical stabiliser. Whilst there is a [very] long road to go on the build, getting to this point provides some confidence that the rest should be achievable – given enough time. The vertical stabiliser is of similar construction to the rest of the tail components except that it has a radically different, triangular shape. The beam sizes are similar to the horizontal stabiliser.
The stabiliser will be connected to the horizontal stabiliser and the rudder. On the original plans, Mr Pietenpol uses wood screws for the connection to the horizontal stabiliser. However, I don’t know how I feel about wood screws in this application. Wood screws tend to be a bit weak in shear – probably not a massive concern given we are flying nice and slow but I like extra strength where possible. Hence, I think I will use some AN bolts if possible as this will be very strong and has the massive bonus of being infinitely removable which will make constructing and transporting the aircraft much easier.
The first step in the build of the vertical stabiliser is to draw the shape on the workbench using the dimensions in the plans. I have heard some rumours on the internet about the rudder being too long when constructed to the plans. Whilst the internet can breed some rather fanciful rumours, I think I will go ahead and add an inch or so to the height of the vertical stabiliser just to get it close – I don’t think that will cause too many issues.
With the main pieces cut to length and some blocking attached to the workbench to create a jig, we can see a large gap at the top of the vertical stabiliser. There isn’t a ton of guidance on the plans as to what goes here but it seems the general consensus is to just fill this void in with some timber that will be sandwiched between the gusset plates. Because the gussets will connect the leading and trailing edges regardless, I don’t think it really matters what you put in here – within reason.
To bridge this gap, I decided to cut some short strips of scrap spruce and laminate them together to create the approximate profile of the gusset plates. The strips were glued together with T-88 and then the glue joints were machined down to create a flat profile on each face for the gusset plates.
Once again, several of the members where profiled with the rebate plane into a T-shape profile. Once this was done, there was some profiling of the centre vertical support beam. This member was slightly tricky as the dimensions didn’t quite add up and it ended up too narrow where it joined the bottom chord The plans call for a small gusset plate to join this centre beam to the bottom chord however, the thicknesses wouldn’t allow the gusset to work correctly. Therefore, I ended up laminating two centre beams together to built up the thickness so that the gusset plate could sit correctly. The centre beam was then tapered at the top so it could join the leading edge.
The gusset plate rebates were cut with a chisel and coping saw. Once the fit was checked and the jig finalised with some clamping blocks – the frame was glued together in the jig using T-88. Once the epoxy was cured, the area for the gusset plates was levelled using a chisel and file and the gussets were epoxied into place with a few staples to keep them in place.
This procedure was repeated on the other side to attach all the necessary gussets. For the front, lower gusset – I decided to combine two gussets together for simplicity and to smooth out the stresses in the lower chord (which shouldn’t be too stressed regardless). The ribs are then glued in place and the whole assembly is given a final sanding and the leading edge is tapered with the block plane.
