Tech Tip: Rigging Biplane Models
By Don Snedden
A biplane without rigging looks like a man walking down the street without any trousers. Rigging is not hard to do; it has a bad name because it is a slow and tedious job waiting until the glue on each wire is firmly dried before proceeding with the next step. Many good methods are available on the Internet. However, this article contains methods I have never seen in print. One friend did obtain the Aeroclub product and he said it did all that was claimed; only fault being it could not make the coffee. However, with the exchange rate being $A2.50 to 1GBP, after he had paid the exchange rate, postage and other add-ons a decision had to be made to give up eating or drinking for a fortnight. At the end of that time he was very hungry.
This why I (and many others) use Platyl fishing line which does all we need. Quite possibly there are other brands that will do the same job but Platyl is in plentiful supply here. How long does it last? I have no idea, the only evidence I can give one of my first efforts rigged 35 years ago has one wire fallen out and the unpainted fishing line yellow with age. I will use “wire” instead of “fishing line” in this article simply because it is easier to type.
Information received from the RAF Museum told me that the main wires, wings to fuselage and undercarriage were 9/64th of an inch which, in metric is .35mm line with a breaking strain of 20lbs or 9.1kgs. So I purchased such a line. Unfortunately their letter is lost amongst the myriads of papers so am unable to give the diameter of the thinner wires between the struts.
Many modellers prefer to use stretched sprue or fine stiff wire. Useful tip here is to drill the upper hole much deeper than the bottom which is little more than a scratch on the wing surface. Insert one end of your sprue or wire fully into the top hole, then cut the sprue/wire level with the entrance to the bottom hole. Let the sprue/wire slide to the bottom of the bottom hole and glue it into place at each end. If the glue should fail it still will be difficult for the sprue/wire to fall out.
A GOLDEN RULE is "if it looks tight it is right". In the early days I pulled the lines very tight when doing one wing. The other wing proved impossible to rig correctly and, looking from above I saw the first rigged wing was at a very very incorrect angle to the fuselage. Only solution was consigning it to the scrap bin. From this I learnt to pull taut – not tight- and also do one wire on one wing then one wire on the other wing and so on until the rigging is complete
Get a plan of the rigging, if you have to work from photos use a transparent ruler on photo’s wire line and you will be able to guess where a line ends.
Before any assembly of the model mark and use a pin vice drill to drill where each wire will go. The bit size is slightly larger than the wire you are using. You need something that will make a small dip into the plastic. Said dip prevents your drill bit from jumping out and marking the plastic. A small nail lightly tapped with a hammer is efficiently for this purpose.
If you have a radial engine check and see if the engine can be fitted after assembly and rigging. No great drama if this cannot be done. Just remember never to fit the control column into place when assembling the cockpit.
Two types of holes can be drilled, the choice of which to use is yours. One is a blind hole which only goes part-way through the plastic and the other which goes all the way through. Using a blind hole I tie a simple knot at one end of the line and trim off the surplus. The hole drilled is large enough to take the knot. Once the knot is in place then glue it. The knot means a greater gluing area therefore a stronger join. Which hole you use is a personal choice; I recommend use both and then make your choice. Through holes are what I prefer.
Blocking a Hole After the Wire is Fitted and Glued
When using a hole right through the wing the usual practice is to fill it with putty which, to me, means a lot of sanding, filling and much paint to blend the hole with the wing. Being lazy I swiftly adopted this method when I saw it in print. Stretch a piece of sprue and cut off one of the cone shaped ends. Trim the pointed end until it is slightly larger than the hole then paint the end with polystyrene cement and, when the plastic has softened, SCREW the end into the hole. It only takes about a half turn for the soft plastic to spread and completely fill the hole. Cut and sand down the protruding bit and you have a very neat fill. Naturally you have been cunning and chosen sprue the same colour as that of the wing. This so quick easy and makes a perfect block that I use it.
You will need a shepherd’s crook for easier rigging. This is made from thin piano wire with a fair bit of rigidity and in use you may have to bend the handle slightly. I use piano wire with some coloured insulation tape at the end for easier sighting on my workbench.
The length of the handle is from the front of the model to the cockpit with plenty of added length so you can grasp it firmly. Another way is cut all but one prong from a MacDonald’s take-away-fork, heat and bend over the remaining end and you have a good imitation of a shepherds crook. How to use it will be explained later on. Always commence rigging at the centre of the aircraft and work your way out wards.
All these drawings are not to any scale or size. Here your model has been painted, both wing and all struts cemented in place. I prefer not to assemble the undercarriage until later on, too much risk that it will be broken as you turn the model upside down. Very importantly ALL paint and glue is fully dry and hard. Thinking “it should be hard enough” leads to much trouble and often complete ruination of your model. Once I decided to be a Henry Ford and mass produce so I fed all the wires into the fuselage and finished up with such an intangible tangle so that the only solution was go back to square one. I wasn’t as smart as I thought.
Weak and Strong Joins
Wire B is glued at two small points at the wing and the fuselage and therefore very weak. Wire A has been fed through and bent so the depth of the wing and the fuselage hole are the glue points. This makes very strong join.
Each wire, one at a time, was fed through the wing then into the fuselage, more wire in the fuselage, easier for the Shepherds Crook to do its job. Slide the shepherd’s crook into the fuselage and fish around then pull out. It might take a few goes but eventually you will succeed in fishing out the wire. This moving around of the shepherd’s crook is why I do not fit the control column. Wire A runs down the inner wall of the holes and provides a strong join. After gluing wire A the surplus in the fuselage wire is fed into the jaws of a small pair of scissors and the scissors moved along the wire until they can go no further. Wire A is then cut. An alternative is to pull A out through the cockpit, tie a large knot in it, and trim off the surplus wire, put glue on the knot and the pull A taught through the wing and wire B fed though the wing and fuselage.
Actually I use this system for wire A and for the wing wires. With these it is the direction in which you pull makes the wire glue to the inner wall of a hole.
If the radial engine has not been fitted then you can also pull the wires through tthat open space.
Correcting Visible Sags
I say VISIBLE SAG because if the wire looks tight then it is right. Take a source of non flame heat, a cigarette, soldering iron are two. These work quickly, too quickly for my old reflexes so I use an incense stick, much slower but I have much greater control. With the incense sick I did try using the mystical "oooommmm oooommmm" but it made no difference. You heat one small section of the wire and when it tightens then quickly remove the heat source.
If the wire still has a sag then heat another section. Reheating the first section will snap the wire.
If the wire still has a sag the there are two things you must do. First heat a third section of the wire and secondly, next times do a better job of rigging.
Well that is my way of rigging and I hope it helps you. If you do find or come up with a better method then don’t be afraid to use it.