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by Cliff Charlesworth
Many gliders exist which have fuselages built up from steel tubing and wood and then covered in fabric. This article covers the manufacture of such a fuselage. First of all I will run through various types of gliders that carry this type of fuselage:-
These are only a few of the types that are flying today and the picture above shows such a glider which is a very common model on our gliding fields. Such a shape tends to put modellers off, so I hope after reading further you might want to have a go at one. The method of construction is extremely light but very strong and it looks very good when built. In actual fact, what you will be doing is simulating a steel tube fuselage in wood. For the sake of simplicity, we will deal with an existing model design, i.e. the Ka 8B is 1/4 scale, its span is 3.75m and it has an all up flying weight of 8.25 lbs., which is a nice weight for thermal soaring. All such types of fuselage need to be built as accurately as possible, so a fuselage jig is a mandatory requirement, so lets make a start. Here goesCut all fuselage formers and bevel the required edges and slots for the stringers. Draw a base line square to the formers, approx. 1 - 2in below the keel. This line will now represent the top face of your jig board. Measure from the front face of former No. 1 to the rear face of Cut the required pieces to length and glue and pin them together as in Fig.1. In Fig.2 you have a typical fuselage former set up. Be careful measurement from the baseline on your plan, you can quickly establish the height of the female jig formers, and once you have established this dimension you can determine the shape of the jig formers as in Fig.3. Don't forget to mark the vertical centre line on the formers. All jig formers should be cut out and the various edges chamfered to allow for correct seating of keel piece and fuselage formers. Now measure off the distance between each of your formers from the plan and mark in pencil the locations on the jig board. Stick all jig formers to the base. Those shown in the sketch are all at 90 degrees to the board, but you could have a former which slopes one way or the other, so your jig former would have to match it. You might choose a fuselage which has a shape like this, especially at the rear. If this was the case, your female jig former should be in two pieces and temporarily joined by glued balsa strips. See Fig.5. Don't forget your centre line on all jig formers needs to be carefully lined up with the centre line of the jig board. If you have followed me this far you obviously are serious about making such a model, so let's press on. ..and there's more A typical model on the jig Assuming you have finished the jig, it only remains now to fix two lightweight batterns. These will come in useful for clamping the high formers around where the wings are fixed. All other formers can be either clamped or taped to the jig formers to keep them steady during construction. O.K. so far? I assume you have bought your balsa and spruce, so lets make a start. First the keel piece has to be laid down into the jig. Generally this will be cut from l/8in spruce sheet which has a good straight grain. After cutting, soak it in boiling water to make it supple, or steam it, whichever you prefer, and bend it to the shape required. Note:- Never assemble timbers like this in a dry state because they will always be under stress. Lay the keel into the jig, tape or clamp it down, and proceed to assemble all the formers. When clamping tall formers, check that they are true and vertical. This can be checked by fixing a cotton line to the top centre of the jig headboards and using this as a reference against the centre line that you marked on the formers.
The next stage is to assemble all the major longerons. Always start at the bottom and work upwards. Soak or steam all your stock before fitting. Some of the longer pieces need care when sorting out their lengths, so don't go hacking too much off at once. It is at this stage that you will find out what kind of job you have made of the slots in the formers Generally, fuselages of this type do not have formers rearward of the wing fixing area, apart from the stern-post and a small one just in front of the After fitting the rear top keel fit in any infill sheeting that may be specified around the nose of the fuselage and, if you have a round front deck or a fiat one in front of the cockpit, now is the time to complete that operation. Once you are up to this stage, you should have a nice looking structure in the jig. One major piece of woodwork remains prior to removal from the jig, and this is the centre line stringer running from nose to tail. Thus is the one that gives the fuselage a nice shape after covering. See Fig.9. The stringer will fit into slots on the forward formers and slot into the two rear formers but it is what happens between that I want to tell you next. Before fitting the side stringers, don't forget to steam them to the curvature required, and when it comes to the spreader bar lengths, refer to the sections on the plan and the plan view of the fuselage. Once you have completed this operation, check all your joints, and your basic fuselage is complete. Items like wing root ribs, wing joiner, servo mounts, control runs and tail fixings can all be fitted to the fuselage while it's still in the jig. The use of a modelling knife around the front and rear faces of front and rear formers, and some gentle persuasion will be all that is required to remove your masterpiece from the jig
I hope I have enlightened you a little more on the building of scale gliders: I find it almost as enjoyable writing about it as building them! I'm beginning to see more and more gliders that have been built from plans, a trend which I hope will continue. |
the end former, add 1/32in - 1/ 16 inch to this dimension and this is then the length of your jig. Generally the width of the hoard needs to be approx. 6 inches and be about 1 /2in thick, and the end plates will be the same, so get yourself down to the timber merchants and look in his off-cut pile. Nine times out of ten you can get exactly what you need from off-cuts and the cost will be minimal. The battens, by the way, in stage 1 are purely as an aid for clamping the formers in position and have proved to be very useful.
tailplane, so the position of diagonal bracing should be marked on the baseboard of the jig and carried up to your longerons by means of a set square. Try to be as careful as you can when cutting diagonal bracing. Joint angles are important. On all diagonals in elevation view rear of the wings, I like to reinforce the joint by adding a l/l6in ply gusset. See Fig.8. Sand the edges of the ply gussets as they will show a little after covering, but it looks realistic anyway. Complete all your diagonals and then you can add the top keel-piece going rearwards from the centre section.
