Model glider restoration

I've had a Precedent Hi-Fly model glider lying around waiting to be repaired for years now. I originally built it with my dad. Well, he did most of the building; I suspect my main contribution was nagging him to get it finished. Unfortunately, we didn't really know what we were doing, and it took some damage after very little flight time. We attempted to use a plastic AA battery box which broke as we launched the glider and left us with no control.

Before

The nose of the model was damaged when it landed, and it was put in storage for many years, during which the wings got warped. A year or so ago I decided to restore it, I finally made a start on it last week.

I decided to completely rebuild the wings, as the warp in the originals was enough that it would be very difficult to remove without weakening them. First off I dug out the plans and found an image showing the typical wing section. I traced this in Draftsight to provide the shape for the various wing ribs. The tip ribs where the wing tapers had to be generated by measuring the plan, then scaling and fixing up the slots.

Ribs redrawn in Draftsight

Unfortunately in my hurry to get the ribs cut I drew them in a hurry and made a few mistakes. I missed the asymmetrical spar slots on the inner ribs and added a slot where the shear webs were drawn on the plan, leaving me with two part ribs. I didn't catch this before laser cutting the parts, but I was able to work around the problems and avoid wasting the cut parts. I guess the moral of the story is "Don't design in a hurry". The drawing shown above includes the corrections I made later. The thin ply end plates had to be cut by hand around a template as I couldn't find laser safe 1/32" ply.

Cut ribs

I traced the plan onto some greaseproof paper since the original plan was too creased to build on top of.

Layout

The actual wings went together fairly quickly once I got started. The spars were pinned to the board and the 1/8th inch ply and balsa inner ribs were laid on top. They were packed to sit level because they're cut 1/16th of an inch undersize so they can be sheeted later. I then added then top spar and supported it at the other end. A small template was used to set the angle of the root rib, to give the wing the correct amount of dihedral.

Inner ribs

Between each pair of ribs is a shear web that locks the spars together, and prevents the wing from twisting or flexing. These came in handy to hold the front end of the ribs in place, meanwhile the rear ends of the ribs were pinned. A set of building block blanks from Homebase came in handy to make sure everything was square. I tend to clamp them to parts until the glue sets to keep them oriented correctly. Fortunately I had enough clamps that by the time I ran out the glue on the first pieces was dry, so the clamps could be reused and the build went fairly quickly.

Lots of clamps

Once the rear ribs were in place, I marked the positions of their ends on a piece of trailing edge stock. I cut out notches then glued and pinned it to the board. This kept the rear ribs safe while I moved on to the front section of the wing.

Due to the mistakes I made when drawing the parts, the inner ribs were 1/16th of an inch longer than the outer ribs. To work around this I glued a strip of 1/16th balsa to the rear of the leading edge stock I was using, stopping where it met the inner ribs. I glued this to the inner ribs and pinned and clamped it in place, then installed the front rib half at the tip of the wing. This had to be clamped in in place with a pair of building blocks to keep it at the right angle. I then pinned the leading edge to the board to make sure it was straight according to my drawn layout before fitting the rest of the front rib halves.

Front rib halves

Once the ribs were installed, I had to do some sanding to fix my design mistakes. I then fitted a piece of sheeting between the spar and the leading edge on the top side of the wing. This is designed to be glued into the top of the leading edge and then sanded to blend it in later.

Leading edge sheeting

Once sanded, the sheeting gives a very neat and uniform look, which hides many of the problems caused by the drawing issues. The curved tips play a perspective trick in the photo above, making the sheeting look flatter than it is.

The next task on the wings is to build up the tips and install the inner sheeting. I also need to drill a hole in the inner ribs to hold a tube into which the wire wing joiner will slide. Later, I will need to fix up the fuselage, but this should be a simpler job.

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