TIP FOR STRAIGHT WINGS
01-21-2005, 12:07 AM
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TIP FOR STRAIGHT WINGS
The site says, Tips and Techniques. So here's a tip for building straight wings.
Locate the tip and centerline rIbs, and mark a centerline from the center of the leading edges to the center of the trailing edges....similar to plotting for cutting a foam wing. Now glue a 3/8"X3/8"X3" balsa stick below or along the line. The stick provides a shelf on which you can place a small plastic line level. Now you have a way of determining when the wing panel is exactly straight. As long as the root and tip rib bubbles agree, the wing panel will be straight.
After a lifetime of modeling, I've built my share of crooked wings. Using this method gives me absolutely no excuse for building-in a warp. And, although it sounds a bit more trouble, I think it's actually a little faster as a wing can be built with very few pins....using a little spray glue to keep things in position in lieu of pins. Wings usually require only about a half dozen pins and a couple shim sticks to build.
Locate the tip and centerline rIbs, and mark a centerline from the center of the leading edges to the center of the trailing edges....similar to plotting for cutting a foam wing. Now glue a 3/8"X3/8"X3" balsa stick below or along the line. The stick provides a shelf on which you can place a small plastic line level. Now you have a way of determining when the wing panel is exactly straight. As long as the root and tip rib bubbles agree, the wing panel will be straight.
After a lifetime of modeling, I've built my share of crooked wings. Using this method gives me absolutely no excuse for building-in a warp. And, although it sounds a bit more trouble, I think it's actually a little faster as a wing can be built with very few pins....using a little spray glue to keep things in position in lieu of pins. Wings usually require only about a half dozen pins and a couple shim sticks to build.
01-21-2005, 04:19 PM
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RE: TIP FOR STRAIGHT WINGS
Nice idea. I usually rely on tab ribs for controlling the wing twist but when you pop the wing off the building board to skin the bottom side, you have to trim off the tabs and can introduce a little twist if not careful.
I think I will start laser cutting little reference marks on my ribs for your method.
Allan
I think I will start laser cutting little reference marks on my ribs for your method.
Allan
01-21-2005, 09:42 PM
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RE: TIP FOR STRAIGHT WINGS
Yeah, I know what you're saying. No matter how much pinning down you do, sooner or later you have to sheet that last side...if that isn't straight, you're screwed. That last sheet is the one part that can make or break a straight wing.
Didn't mention it, but most times a piece of tri-stock works pretty well as a crutch for the trailing and leading edges. And, the accuracy of those little levels is remarkable. Also, on a constant chord wing, it doesn't even matter if the datum line is true to the centerline of the each end of the rib...just that the root and tip ribs share the exact same datum. What is quickest and most accurate is to mark one rib, then lay it over the other, push a pin through the datum line at each end of the rib and the second rib will be perfectly indexed with it's counterpart.
One last small point: Use a spot of hot-melt glue to semi-permanently attach the levels to the ribs. Makes things a little more organized. Good luck with it......if you hate guesswork, you ought to like the method.
Didn't mention it, but most times a piece of tri-stock works pretty well as a crutch for the trailing and leading edges. And, the accuracy of those little levels is remarkable. Also, on a constant chord wing, it doesn't even matter if the datum line is true to the centerline of the each end of the rib...just that the root and tip ribs share the exact same datum. What is quickest and most accurate is to mark one rib, then lay it over the other, push a pin through the datum line at each end of the rib and the second rib will be perfectly indexed with it's counterpart.
One last small point: Use a spot of hot-melt glue to semi-permanently attach the levels to the ribs. Makes things a little more organized. Good luck with it......if you hate guesswork, you ought to like the method.
01-25-2005, 09:59 AM
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RE: TIP FOR STRAIGHT WINGS
There's been a question regarding the first sentence of my explanation of one way to make sure your wings are straight.
To elaborate, select which ribs will be the tip and root ribs. On those ribs, draw a straight line from the front to trailing edge. The line you've drawn represents the airfoil's chord line....we are simply using it as a reference line for building purposes. On symmetricle airfoils, the line you've drawn will be right down the center of the rib.
If you are building a flat bottomed wing, simply use the bottom of the wing as a reference and tack glue your 3/8X3/8 "shelf" flush with the bottom edge of the rib.
On semi-symmetricle wings; outline the root and tip ribs on butcher paper. Plot where the trailing edge and leading edge tips should be. Draw a line from each point. That will establish the airfoils chord line which you will be using as that rib's reference line .
To elaborate, select which ribs will be the tip and root ribs. On those ribs, draw a straight line from the front to trailing edge. The line you've drawn represents the airfoil's chord line....we are simply using it as a reference line for building purposes. On symmetricle airfoils, the line you've drawn will be right down the center of the rib.
If you are building a flat bottomed wing, simply use the bottom of the wing as a reference and tack glue your 3/8X3/8 "shelf" flush with the bottom edge of the rib.
On semi-symmetricle wings; outline the root and tip ribs on butcher paper. Plot where the trailing edge and leading edge tips should be. Draw a line from each point. That will establish the airfoils chord line which you will be using as that rib's reference line .
01-26-2005, 08:36 PM
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RE: TIP FOR STRAIGHT WINGS
Excellent tip ddubya! I never thought of that one.
I've built lots of wings and just finished one that is not only warped, but skewed as well. It was straight when I was building it, but I think when I put on the trailing edge sheeting I skewed the wing as it was still very flexible.
Anyway, it was uncerimoniously crunched up into a little heap of balsa and disposed of. The bad part is this wing has about 36 rib/half ribs in it and I had to cut out another set.
But the important thing is that it will be right when it's done. Much better to get it right than to fly a crooked airplane.
I've built lots of wings and just finished one that is not only warped, but skewed as well. It was straight when I was building it, but I think when I put on the trailing edge sheeting I skewed the wing as it was still very flexible.
Anyway, it was uncerimoniously crunched up into a little heap of balsa and disposed of. The bad part is this wing has about 36 rib/half ribs in it and I had to cut out another set.
But the important thing is that it will be right when it's done. Much better to get it right than to fly a crooked airplane.
