Gazzalene Posted February 7, 2013 Share Posted February 7, 2013 Being a newbie i hope this is not a really stupid question.The kit i am building as balsa spars top and bottom.The wing is flat bottomed so that easy.But i do not know the norm form the upper spars.The area where the notch is, to the eye looks flat ain the curve at that point.Do i make the spar flush at the top OR leave proud then sand.If left flat i have no idea how this looks at the covering stage. Quote Link to comment Share on other sites More sharing options...
Andrew767 Posted February 7, 2013 Share Posted February 7, 2013 The plan should show this but they normally fit flush. Hope this helps Andrew Quote Link to comment Share on other sites More sharing options...
Gazzalene Posted February 7, 2013 Author Share Posted February 7, 2013 The plan does show a cross sectin of the wing BUT the thing is the curve there is very slight.to the eye it looks flat but obviously a curve is there and i do not lnow if this still needs leaving proud and sanding.or will a flat spar show.this is where my lack of building hinders me. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted February 7, 2013 Share Posted February 7, 2013 I wouldn't have thought that the curve would be significant, say less that 2 or 3% of the wisth of the spar. If so, I would leave if flush as suggested. You will never notice it in the air. If it is meant to be curved then shape it a suggested, but I have never seen a curved spar on the surface a model yet. Martyn Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 7, 2013 Share Posted February 7, 2013 Gazzalene Would I be correct in assuming the wing is an 'open' structure to be covered with a film or tissue? If so when the covering is taught it will not follow the correct curve of the upper surface in the area between the wing ribs so whether the top of the spar is curved or flat is not really significant. If the spar was particularly wide it would then have to take the curvature of the wing section into account. Quote Link to comment Share on other sites More sharing options...
Gazzalene Posted February 7, 2013 Author Share Posted February 7, 2013 Simon, you are correct that the wing is open structure,its a semi scale T Moth. I do not understand your point though.i thought when covered the material will touch every surface of the wing,and the spar being flat was my concern. Again sorry for my ignorance here. Quote Link to comment Share on other sites More sharing options...
IanN Posted February 7, 2013 Share Posted February 7, 2013 Gazza, no need to apologise. It's a perfectly fair and reasonable q for a first build, and that's what the forum is for As per all the above, leave it flat - it will be both visually and aerodynamically insignificant Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 7, 2013 Share Posted February 7, 2013 Gazzalene Yes the surface will touch all the structure but imagine the shape of the top surface of the covering midway between the ribs. Because the film will be taut in all directions it will sag a bit so looking down the wing from the tip the surface will non be smooth but it will undulate slightly over the ribs, hence their name! You can see this effect of this picture of a tiggy. The point is this means the cross section of the wing will not be exactly the rib shape at the mid point between them. The flat top to the spar will be insignificant. On the full size the spar tops are set slightly below the surface so the covering does not touch them. In ths way although the covering does sag beteeen the ribs it atleast gives a smooth curve front to back. It is very encouraging that you spotted this as it means you are thinking about things as you go along. The fact you asked about it is even better! Keep it up. Quote Link to comment Share on other sites More sharing options...
Gary Murphy 1 Posted February 8, 2013 Share Posted February 8, 2013 Thanks for the encouragement guys. Get your point now Simon thanks for taking the time to explain.I also get the point about the spar being lower than the ribs in the real aircraft.Can i ask why that is not done in models.you now set marginally lower. Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted February 8, 2013 Share Posted February 8, 2013 If you have stringers on a fuselage where the curvature is much greater then I would always GENTLY sand them to conform to the shape .On open structures on wings -don't bother 'cos the shrunk covering will still show up the slope between the spar and the leading edge .The tension takes the path of least resistance ie flat ,so all you'll do is minutely change the airofoil section which varies between each rib. Best bet is to sheet from the spar to the LE .From there back,the curvature is much less pronounced and won't look like what we call the "starved horse" effect.Capping the ribs helps too .Look at any of Peter Millers designs to get the idea .By the way,ALWAYS use a sanding block -never freehand or by eye no matter how skilled you are IMHO. Quote Link to comment Share on other sites More sharing options...
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