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Model Forum / General / Models / September 2009Wing-fuselage mismatch
While this always has been a potential problem, I find it occurring more regularly these days. The problem is a mismatch between the airfoil thickness on the actual wing versus the thickness on the fuselage- that is on the outboard edge of the fillet that should join to the airfoil. It seems more and more the case that the thickness of the wing is less than allowed for by the fuselage fillet. If one merely putties the bump, one produces a fillet that goes out on the wing farther than it should. Grinding of the portion on the fuselage is required- a very difficult job. Why is this happening? I am wondering if the upper wing sections are flattening out after the kit is produced. This would give that effect. Even some mfgs with very expensive prices and an otherwise good reputation are putting out kits with this problem. Seems to me there could be a stub spar molded into the upper and lower halves of the wing to hold the thickness. > While this always has been a potential problem, I find it occurring more > regularly these days. [quoted text clipped - 16 lines] > Seems to me there could be a stub spar molded into the upper and lower > halves of the wing to hold the thickness. This isn't as new a problem as you'd like to think. A couple fo years ago, I put an antique Frog Morane Saulnier MS.409 together and if I'd have built the wing/fuselage join as indicated, I'd have had about a 30 degree dihedral. I had to grind the bottom half of the wing and fill the upper half. Later somebody (otherwise well-meaning) gave me another on (Novo, I think) and it still had the same problem. I've seen other kits with this join problem as well. Have you tried putting a spacer in the leading edge of the wings to bring it up to match? Then you'd only have to putty the leading edge. Have you tried making your own spars? They wouldn't have to go too far into the wing so you wouldn't need to match the whole interior shape. KL > While this always has been a potential problem, I find it occurring more > regularly these days. [quoted text clipped - 7 lines] > one produces a fillet that goes out on the wing farther than it should. > Grinding of the portion on the fuselage is required- a very difficult job. This would raise the front and rear parts of the fillet on the wing. The problem is the curve of the airfoil is flatter on the wing than the fuselage. It is like the upper wing surface "relaxes" and looses the curve. Is there strain in freshly die cast plastics? When released do they tend to flatten out? Or is this just a problem with the designer not getting the curve right in the mold? > Have you tried putting a spacer in the leading edge of the wings to bring it > up to match? Then you'd only have to putty the leading edge. [quoted text clipped - 15 lines] >> one produces a fillet that goes out on the wing farther than it should. >> Grinding of the portion on the fuselage is required- a very difficult job. > Is there strain in freshly die cast plastics? When released do they > tend to flatten out? Or is this just a problem with the designer not > getting the curve right in the mold? Sounds like the plastic is too thin and not strong enough to hold its shape. I've seen this on a lot of vaccuumed-formed kits. >This would raise the front and rear parts of the fillet on the wing. >The problem is the curve of the airfoil is flatter on the wing than the [quoted text clipped - 23 lines] >>> one produces a fillet that goes out on the wing farther than it should. >>> Grinding of the portion on the fuselage is required- a very difficult job. Had this issue with an ICM Israeli Spitfire LF Mk IXe. The fuselage/wing match at the rear fairings was appalling and took a lot of filler to overcome and the wing to rear fuselage was quite a step before filler.. : This would raise the front and rear parts of the fillet on the wing. Can you glue the upper wing panels to the fuselage, and then glue the lower wing panel to the uppers/fuselage? Can you add a "step" of your own to support the upper wing in the fillet area, forcing the upper wing to assume the same curve as the fillet? : The problem is the curve of the airfoil is flatter on the wing than the : fuselage. It is like the upper wing surface "relaxes" and looses the curve. Keep in mind that glass is, technically, a plastic material. Granted that glass has an extremely high viscosity, but it does flow. Bruce  Signature------------------------------------------------------------------------ "I like bad!" Bruce Burden Austin, TX. - Thuganlitha The Power and the Prophet Robert Don Hughes |
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