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So, to complete the tail feathers. The fin is a built up aerofoil section and the rudder, on the plan, a simple solid sheet sanded to shape. I'm planning to glass cloth all the surfaces and spray paint finish so the fin and rudder are simple and cheap components to practice on and easily replaced. I have used lightweight glass cloth before some years ago and it's not as daunting as you may first think. Even so I would welcome any suggestion you may have and include them here. |
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Start as before cut marking out the ribs using your preferred method. Cut the rear post and leading edge and slot both to accept the ribs. Now, building over the plan is not as straight forward as it first seems. I toyed with the problem for some time and came up with all sorts of elaborate packing options. Then an epiphany, what I needed was a gadget. Not any gadget but something technical.
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Obtained under the pretext of making sure any shelving would be put up straight, I found under the bench, still not used, one of these sprit levels with a Lazar light. Position the ribs in the slots of the rear post ensuring they are at 90 degrees. Then, only thing left is to make sure all ribs align. Placing the lens to shine a vertical line I made sure it lit up the tips of the ribs then adjusted to hit the centre mark on all. Once dry I found this much easier to lay over the plan and add the leading edge, adding packing as required. One small anomaly is the lower rib being larger than the rear post and un proportionally larger than the other ribs, yet I could not see then or now why this was. |
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After sanding the leading edge, top block and rear post to continue the profile of the ribs I added the sheeting to one side and pinned down. |
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After building the tailplane I was a little concerned at the minimal material in the trailing edges to accept the hinges I had chosen so I added an extra block to take the centre hinge. More about the hinges in a minute. |
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When dry, everything was sanded to shape. Now remember back when sheeting the tailplane I mentioned leaving extra sheeting hanging over the trailing edge spar, well the fin also has this shroud. The idea is to fair-in the moving surfaces and help seal the gap between them. To make any flying surface effective you need to maintain pressure on each side, whether it be higher or lower pressure. When you change the path through the air one surface will have a different pressure than the other, however, air flow is lazy and if it can, will leak through a gap to the lower pressure. The shroud guides the air over the control surface and maintains the efficiency. (Someone is bound to have a comment here and I know it's a simplification but it fits my needs for explanation) |
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The plan has the rudder as one piece 1/2 inch (12.7 mm) sheet. Being a bit of a tight sod I didn't see the point of making a huge barn door in solid block only to have most of it end up on the workshop floor. I choose to make mine from a medium 1/4 inch (6.4mm) sheet for the centre core, sanded to a taper at the trailing and top edge, and two outer sheets of 1/8 inch (3.2mm) to make up the 1/2 inch (12.7mm) at the leading edge. |
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Note the lightening holes, I put these in to off set the weight of the glue. With engine and motor designs giving much more grunt relative to size, we tend to forget weight still matters. Still, I'm conscious of the narrow wing on this model and a high weight to square inch of surface or wing area means you need to fly at a very high un-scale like speed and your final approach can be 'adventurous'. |
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Once all is dry sand to final shape including rounding off the leading edge and fit the top cap. The top cap is something of a complex shape. Aerofoil shaped at the front (use the fin to get the shape) then tapering to the rear. However, the tip to the rear has a rounded shape that accommodates the tail navigation light in the real aircraft. I've sanded this to shape but you could use round dowel and fair in with filler. I will add the lamp detail when finishing and on a model this size there's no need to go overboard. |
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I mentioned hinges earlier. Because of the shroud I've decided to use Robart pin hinges. These will allow me to recess into the leading edges and make the pivot point similar to the real surfaces. Also, it should maintain a minimal clearance within the shroud without fouling. | |
