Step Three – Scratch Building Model Airplanes
Last week I managed to reach the stage of finishing the basic build of my fuselage and create the cockpit/removable battery compartment cover.
As I said at the end of the post, I hoped to have the cockpit glazing finished. Unfortunately, I am a simple human with foibles and occasionally forget to check the status of certain material requirements. I have to admit to running out of canopy glue!
Who said that scratch building model airplanes was easy and always ran smoothly? I have ordered a bottle of said glue but I don’t expected it to arrive until next week.
Finishing The Tail Feathers
I explained in my last post how I created the rear end fairings between the stabilizer and fin. The next step in this part of the build was to glue the stabilizer to the rear of the fuselage which, again, was explained last week.
Once the epoxy glue had dried I fitted the fin into its slot and checked for vertical alignment and that it was true to the centre line of the fuselage. This simplified diagram shows how I check this centred alignment.
Once dry, I was able to fit the previously made fairing blocks either side of the fin. a little lightweight filler rubbed into the join lines and sanded when dry gave a smooth streamlined shape ready to take the final covering.
Building The Wings
There is no actual dihedral built into the wings but a naturally created angle is obtained by building the wings inverted. This occurs because when the top spar is fastened down flat on the building board, the wing taper causes the underside of the wing to take on a positive dihedral angle from root to tip.
The wings are swept back at quite an angle so each panel has to be built separately. They are then glued together inverted with the spars flat on the board and the trailing edge blocked up to the correct height at the centre and at each tip. We will look at how this is done in due course.
You may recall that I had decided to use a set of mechanical retracts I found in the spares box. This has meant re-engineering the undercarriage mounting arrangement. Instead of fixed leg hardwood blocks being glued into the underside of the wing, I have had to cut 6mm (1/4″) plywood plates with the appropriate cut-outs for the legs when in the retracted position.
In the first of these posts I said that I had cut out the wing ribs following re-drawing the wing plan as a built up construction rather than balsa clad foam cores.
Now I was ready to start laying down wood to create the first wing panel. The first thing to do was to pin the top main spar down over the plan, not forgetting to cover the plan with glue resistant clear polythene sheeting first.
Next I cut two small blocks of scrap balsa to act as spacers for the trailing edge. These were cut so that when spaced off the bench, the centre of the trailing edge was at the same height as the centre line of the ribs.
Once all of the ribs had been glued to the top spar and to the trailing edge, I fitted the bottom spar (remember the wing is upside down so this spar is on the top). When all joints are firmly set the leading edge was glued to the front of the ribs.
It is worth mentioning at this point that the root ribs (the ones that will be glued together when the wing halves are joined) are from 3mm (1/8″) plywood as are ribs 3 & 4 to which the retract plate will be glued.
So far, so good! The wing is now a strong rigid structure ready to have the retract unit and pushrod fitted. Structurally it will be finished with vertical 1.5mm (1/16″) webbing between the main spars. A central retract servo housing and supports for the aileron servo mounting plate will be fitted. Once these are all fitted and the two panels have been glued together and braced, the whole wing panel will be covered with 1.5mm (1/16″) balsa.
In the photo (right) you can see the cut outs for the retract plate, pushrod clearance and for the wheel-well. Its interesting to see that although the wing tapers quite dramatically, it looks to be almost parallel because of the angle at which it was taken.
Till The Next Time
Next week I hope to have built the second wing panel, joined the two together and fitted the various accessories within the wing structure ready for the covering.
My fresh supply of canopy glue should be available so that I can fit the rest of the canopy glazing to the battery compartment cover.
I hope you are enjoying following my explanation of scratch building model airplanes. If you have just discovered this post, please take a look at the previous two posts covering the start of the project, starting with “how to scratch build rc planes“
Please feel free to share this post and the others with anyone you think could benefit from its content. If you are new to rc model planes and want to know how to get started successfully, please visit my website www.rookiercflyer.com. You will find everything you need to know.
Catch you next week.