Chapter 15

 

Chapter 15

Tail Units: Control surfaces, various attachments.

WE can build rudders and tail-planes in the same way as wings. The main difference is that the tail unit can be made rather lighter. We can, for instance, use 1/8in. x 1/16in. balsa for the leading and trailing edges, 1/16in. x 1/16in. balsa for the main spar, and 1/32in. sheet for the ribs. This will be strong enough for quite large models, and the ribs should be made to the section known as R.A.F. 30. They can have holes cut in them to make them lighter, and should be spaced about 1 1/2in. apart. If the tail-plane is a small one, say not more than

8 in. span, there is really no need for a main spar, but when we do use one it should be continuous if possible from tip to tip, and attached to formers or spacers put in the fuselage for the job. Formers should also be arranged for attaching the leading and trailing edges. The method of glueing the spars to the formers is shown in Fig. 45.

Fig.45Fig.45

We can, if we like, make the tail-plane and fin (or rudder) detachable for ease of transport, or in some cases for access to the rear motor fixing. We can use a bamboo dowel, plugging into a paper tube, a piece of wire in aluminium tube or into balsa, which should have plenty of cement in and around, or we can use a rectangular bamboo plug and balsa box.

Very satisfactory results have been obtained from a rectangular plug fitted at the main spar, letting it project into the rudder and tail-plane

about 1 1/4in., with a short plug poking through a hole in the first rib just ahead of the trailing edge (Fig. 46). The hole was strengthened with an extra thickness of balsa on the inside. This rear attachment serves to prevent the surfaces from altering their incidence. A certain amount of slackness developed, but was easily taken up by glueing a strip of tissue paper to the inside of the balsa box or hole. This was accomplished by putting a spot of glue on the paper, pushing it down the box and putting the tail-plane or rudder on to the plug and withdrawing it before the glue could set.

Another way of making the fin and tail-plane detachable is to have them fixed together and to the top of the fuselage, and have this top half of the fuselage detachable. If we look overleaf at the drawing of the Kestrel Trainer, we can just distinguish this feature. If we look carefully we can see two fuselage formers just in front of the fin; one is marked H and the other J. H is attached to the fuselage proper, and J is fixed to the detachable part. Just below the letter J we can see two longerons, one of which passes right down the fuselage to the sternpost, and the other is from former J to the fin post on the detachable part. There is a view just below the fuselage of locating strips, with an arrow pointing to the point where the longerons are broken away, to show the motor attachment. These locating strips can be balsa, about 1/8in. x 1/16in., and are glued to the inside of the detachable longerons to butt against the main longerons to prevent the top part from sliding about. This unit is held in place with rubber bands fastened to the fuselage and fitting on to hooks on the detachable part. We can see these hooks on the drawing; there is one on each side, fastened to former J, and marked-rubber fixing; and another one on the fin post against the word "hinge."

Fig.46Fig.46

Although it is best to have the tail surfaces fixed so that there is nothing to get out of trim, it is sometimes useful to have some sort of trimming device, which is usually a part of the surface made to hinge. The most popular method is to use small pieces of aluminium plate or soft iron wire let into the balsa to act as hinges. We can then move the hinge, but it will stay put. Another method is to make the elevator or rudder a tight fit between two ribs, and in the end put a short pin to act as a hinge. If it should not be tight enough, a paper washer will remedy matters. These hinges are shown in Fig. 46a.

Here is Mr. Howard Boys with two tail-less models of his own design. They hold the British records in their class, one for hand-launched flight and the other R.O.G. Mr. Boys successfully treats his scale models very much like tail-less machines for stability, the idea being that a very small tail-plane is little better than none.Here is Mr. Howard Boys with two tail-less models of his own design. They hold the British records in their class, one for hand-launched flight and the other R.O.G. Mr. Boys successfully treats his scale models very much like tail-less machines for stability, the idea being that a very small tail-plane is little better than none.

In fixing the tail-plane and fin we must get them square and true with the fuselage. This is best done with some form of jig, which can be blocks of wood, books, tins or anything that will stand up on a flat table, and small wedges of balsa carl be used to give a final adjustment. A piece of thread tied at the top, with weights on the ends, can be used to keep the fin upright. It is best to pack up the rear of the fuselage until the centre-line of the tail-plane is level.

Fig.46aFig.46a

Take measurements carefully, and do not trust to what seems right to the eye. Measure from the table to get the tail-plane level, and to get the fuselage and fin upright a setsquare will be most useful. When all is set up true we can touch the parts to be glued with a spot of glue on the end of a piece of wire and spread it along the joints very carefully. A photograph showing a set-up as here described is on page 101.

THE REAL THING?

The photograph shows a Sopwith Camel which has crashed behind the German lines. The pilot is being marched off under escort, whilst the propeller and other parts are salvaged. An excellent example of table-top photography staged by Mr J. H. P. Green, of Dundee, who took the photograph and also constructed the model.The photograph shows a Sopwith Camel which has crashed behind the German lines. The pilot is being marched off under escort, whilst the propeller and other parts are salvaged. An excellent example of table-top photography staged by Mr J. H. P. Green, of Dundee, who took the photograph and also constructed the model.

 
Next | Prev

Contents Page