Whilst the top wings were drying (after gluing in place the bell-crank boxes etc.) I started work on the lower wing panels. The top wing panels require sanding and shaping, rigging brackets and plates gluing in position and other items to finish, I'll get round to those later. But first back to the construction of the lower wing panels.
I had to cut up the plans again (I really don't like doing that) to speed up the build and so that I could construct the port and starboard lower wing panels at the same time, this task was done to the right hand side of the work bench. On the left hand side of the bench the plans were cut again, again so that all of the tailplane components could be laid out at once and constructed along with the lower wing panels.
I started construction on the wing panels first by making sure ALL the wing rib cut-outs fit the spars, leading edge and trailing edge material.
The wing ribs being pre-fit to the spars, leading and trailing edges.
The main problem that I could foresee with these wing ribs were the 2 thick balsa root ribs. These ribs lean over at quite and acute angle and the ones supplied with the kit were cut at 90 degrees so I re-cut these to the correct angle.
Having these ribs cut at the correct angle allows the top plywood centre section sheeting to sit tightly against the top surface of each rib and the bottom angle of the rib allows the fabric covering to also adhere tightly against the rib surface.
The angle is quite apparent compared to the kit version on the tight.
The next stage was to pin down the leading edge, pinning first one end then the other and placing a straight edge between the two ends and pushing the centre of the leading edge up tight against the straight edge to ensure the wood was free from curves, the centre was then pinned in place.
Leading edge pinned down and the ribs ready to be glued in place.
After pinning the leading edge in place I pinned down a piece of scrap wood to ensure the spars, leading edge and trailing edge were all correctly aligned. This makes the task of fitting the wing tip that much easier.
Scrap wood used to align spars etc.
This picture also shows some of the components glued in place.
Setting the root rib angle with a plastic template.
Root rib comparison - 90 degree cut and angle cut.
The above picture shows the difference between the 90 degree cut root rib compared to the revised rib cut with an angle. It would not have been possible to sand down the kit supplied ribs as they would have ended up being much too low in profile and not the same height as the other wing ribs, noticeably so.
Part finished lower wing panels.
When dry the lower wing panels can be removed and all the remaining work can be undertaken without pinning the panels back to the plan. At this stage the plywood webbing between the spars, the area where the steel bracing plates bolt to, has only been fixed to one side. The captive nuts have not yet been installed. The holes will be drilled and captive nuts fitted after the brackets have been made. I will then use the finished brackets as a hole drilling template, this will ensure perfect alignment of the holes, and all brackets will be marked so they can be put back in the same place during final assembly.
All the riblets have also been 'thoroughly' glued into position as we don't want them breaking away from the main structure after covering. Again make sure you 'pre-glue' all the end grain joints.
Closeup showing plywood webbing glued in place.
A second plywood web will be glued to the other
side after the installation of the captive nuts.
Next, the wingtips can be fitted. These items are both made up of 3 pieces of 4 mm thick balsa sheet that require gluing together and trimming to shape. They need to be made a little longer than shown on the plane so as to allow for the curvature of the finished wing tip, about 5 mm will suffice. After making the 2 wingtip blanks fit the 4 lower wingtip supports 2 to each wingtip. They extend from the front and rear spars. These pieces also require a slight angle sanding to the top surface to allow for the curve of the wingtip. I used cyanoacrylate for these bottom supports so I could forge ahead with the wingtip construction, for the remainder I used wood glue.
Wingtip blanks - cut oversize in length.
2 bottom supports glued in place and sanded to the
appropriate angles to allow for wingtip curvature - port wing.
'dry-fitting' the wing tips.
Note the direction of the grain - running perpendicular to the tip rib.
After fixing the bottom supports in place the wingtips were glued to them with wood glue and the top supports (4 in total) were then glued and pinned in place and their bottom edges sanded to a slight angle to allow for the tip curvature as before. There were also 4 leading edge tip blocks fitted, 2 to each tip, 1 on the top and 1 on the bottom. Whist the glue was drying the tapers were marked on the tip supports, these will be trimmed and sanded later.
edge tip block also shown - starboard wing
The topside of wingtip glued in place with leading
edge tip block shown - starboard wing.
Whilst the glue was setting I marked the 'taper' lines
to the top and bottom tip supports.
At this stage I have not fitted the brass tubes that hold the piano wire wing attachment rods. The fuselage has already been built and the wing attachment brass tubes already fitted into the fuselage. The lower wing plywood facing root ribs will be checked against the fuselage wing attachment tubes first. If the fuselage tubes align correctly with the holes in the plywood facing root ribs then they will be glued in place on the lower wing panels. The existing holes in the plywood facing root ribs can then be drilled through the balsa wood root rib. The lower wing panels can then be fitted one at a time to the fuselage checking the dihedral as you line up the brass tubes on the second balsa wood rib. When the second tube hole is positioned correctly the second hole can be marked and drilled out.
When the 4 wing attachment brass tubes have been 'dry fitted' in both lower wing panels and the dihedral is correct then the tubes will be glued in place with epoxy. There are also 8 square plywood reinforcement plates that have to be glued to all the wing ribs that the brass tubes fit through. I will post pictures of this stage when I get there, but that's the gist of it.
Workshop Tip No. 2
When removing pins from a finished wooden structure care should be taken whilst pulling them out.
Always hold down the structure around the area of the pin so it does not pull up the wood and crack a joint.
If a pin has been put though a glued joint the pin inevitably drags glue into the second piece of wood whilst being hammered into the building board and when the glue dries it also glues the pin into the second piece of wood. In this instance make sure you twist the pin before you pull it out, this will break the glue around the pin. Again hold down the structure around the pin to prevent the structure lifting and cracking a joint.
After fitting the wingtips the lower wing panels were put aside to dry and I moved on to the construction of the tailplane components.
The next post will cover the tailplane construction and hinge detail
To be continued...
The next post will cover the tailplane construction and hinge detail
To be continued...
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