Hinge Thing

These days when we need to hinge a control surface such as an elevator, aileron, or rudder, we troop off to the model shop and select an off-the-peg commercial solution. All well and good. However, in ye olden days we used to sew control surfaces to flying surfaces with ordinary cotton thread. As a young bloke, sewn hinges contributed to the viability of my scratch-built control-liners, free fight power models, and early radio jobs. They also remain an excellent engineering solution on ultra-light models and el*ctric jobs, where foam or balsa control surfaces may be too thin to take a modern plastic hinge.

So, sewn hinges are a classic solution, and if carefully executed, are flexible, durable, non-binding, and slick. What’s more, they’re surprisingly rewarding to do, and they may also embody something approaching ‘retro-cool’. Just the job for a classic plan-built project, a full refurb’ of a well-loved old timer, or the finishing touch to a newly resurrected Brit. kit CNC re-design.

Tool Up

To get sewing you’ll need the following:

  • Cotton yarn or thread.
  • A big-ish darning needle.
  •  Balsa cement or medium cyano.
  • A 1mm drill or a thin panel pin.
  • A scalpel.
  • A 12” rule or straight edge with clear divisional markings.
  • Masking tape or Magic Tape.
  • Bulldog clips with DIY balsa jaws.

In addition, an off-cut of thick foam is handy to protect and support the control surfaces, fin, and tailplane as you work on them. Likewise, a bench drill is useful but not necessary. A thimble might stop you drawing blood, though!

Embroidery Floss

I get my modelling thread and needles from the haberdasher’s shop, craft shop, market stall, or anywhere with a sewing machine in the window. I usually code the colour of the thread to match my covering. Thus, a two colour covering scheme might need two different coloured threads. I’m terrible with colours, so I take samples of my projected model covering (Solartex, Solarfilm etc.) to the shop to ensure a good match. Recently, I’ve been buying Korbond brand embroidery floss which has six strands and around seven metres per skein. This is mercerised cotton, with that classic pearly look to the yarn, which although much thicker than normal darning thread, I find most attractive. More importantly, it’s perfect for the job. I don’t use synthetic threads since they can be a bit sharp on the edges of the balsa. Moreover, they’re sometimes not as flexible, and don’t seem to take the balsa cement or cyano well.

Method

Let’s hinge an elevator to a tailplane. First off, prepare the balsa tailplane and elevator control surface for covering in the normal way and finish with a light sanding. Next, gently bevel the elevator leading edge but leave the tailplane edge square. I use a David’s Plane here, this being a mini woodworking plane that uses razor blades.

Cover the surfaces as normal. In our example I used Solarfilm. Using Magic Tape, masking tape, or DIY Bulldog clips fitted with soft balsa jaws, clamp the tailplane and elevator in precisely the right position, leaving your two hands free to do the sewing! Now, before taking up needle and thread, we need to accurately mark out and drill the elevator and the tailplane with a staggered set of 1mm (or smaller) holes. Being a savage, in the past when lacking said 1mm drills, I’ve resorted to mini jeweller’s screwdrivers, bodkins, darning needles, and even the odd thin panel pin to podge through such holes.

Marking out is accomplished with a metric or imperial rule. Start by scribing a very light pencil line on the tailplane for a neat set of equidistant holes, say about 1/8” in from the projected hinge line. Next, choose a sympathetic spacing (or pitch) for these holes lengthwise along the tailplane and elevator to suit the size of the model. Aesthetically, it’s important to get your stitching looking proportionally correct, so that the distance between the run of holes on each component matches the pitch of the holes themselves. Note that a bigger model can take a larger pitch, giving bigger hinge stitches. So, for example, on my 52” span model shown here, a 1/4” pitch for the holes along the length of each surface goes well with the aforementioned 1/8” hinge line offset, thus making the line of the tailplane holes and the line of the elevator holes exactly 1/4” apart. Centimetres and metric divisions would work just as well. Just remember that when marking out the elevator - in order to yield a neat chevron stitch - the pitch between these elevator holes remains the same as those on the tailplane, but their start position must be shifted to fall exactly half way between those in the tailplane.

As I’m sure you can tell from the photos, it’s harder to explain than do. I find it helps to visualise a zigzag of holes hopping across from tailplane to elevator and back. You’ll also note from the photos that I have a Rollertec roller ruler (bought at a summer show tool stall) which has handy constant pitch holes along its straight edge. This guarantees a correct hole spacing, and is ideal as a drilling / podging template.

So, supporting the tailplane on some soft foam, drill your marked out holes with a 1mm or smaller bit, or just push them through as suggested earlier with the bodkin and thimble. Obviously the smaller the hole, the neater and tighter the final hinge.

 

It's all so easy

Since I’m not exactly needlepointing new models every weekend, it’s easy to forget the knack of hinge crossover stitching. Therefore, I confess that I usually mock-up a dummy elevator and tailplane from scrap balsa and have a quick dry run on that. If it’s your first time stitching, don’t skip this important dummy run!

Also, when you’re stitching, it helps to hold the surfaces together in correct alignment with the aforementioned masking tape or bulldog clips. I usually begin with a simple retaining stitch at one end of the surface, and seal that down with cement. This locates the yarn and the surfaces, and helps keeps them together as you begin the crossover stitching.

A normal hinge sewing routine is to push the needle up through from below the elevator, taking the thread over the top of the surface, and then passing it down between the tailplane and elevator to pass up through the tailplane from on the other side. Remember you’re zigzagging the stitches, over one surface and under the other. Repeat this process, being careful to keep the pressure on the yarn as you go, pulling the surfaces together in a herring bone fashion, until you end up with a hinge. If it starts to look a bit drunken, stop, go back and pull it tighter as you proceed.

Once the finished hinge is tight, yet loose enough for the control surface to fall under its own weight, seal the yarn to each hole with a dab of balsa cement or cyano, and then loop the end hole once or twice, and seal that with a dab, too.

And that’s it - job done. Just avoid cementing the hinge line! Hinges made this way are very durable. I have some that are forty years old, and they’re very light, non-binding, and efficient. I also think they add an authentic and aesthetically pleasing touch to any retro-classic.

Also, don’t forget that such needlework techniques are very handy when you come to tackle a scale prototype, such as a W.W.I bipe or golden age Moth with their stitched canvas edges, sewn wing tapes and inspection panels. By the way, I’m buying some crochet hooks and skin moisturiser next week...