Errorless Wing Construction
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Home > Articles & Tips Index > Construction > Errorless Wing Construction

[Courtesy of Pete Young, pwyoung "at" ix.netcom.com, June 2000]

I originally developed this technique when building A, B, and C gas free flight wings. As one might suspect, you have to build gas free flight wings very accurately as any undesired warps or misalignments can really reduce weeks of effort to matchsticks in a jiffy. 

George Voss wrote up his technique, very similar, in FM about a year ago. I don't have a better reference for that particular article, so you'll have to bear with lots of prose here. I've built about 3 dozen poly wings using this technique and the results have always been very satisfactory. As a matter of fact, you can use the same general technique for building almost any model wing, not just polyhedral glider wings. Read through this and you'll see what I mean.

As we all know, 99% of model kits say, in effect, "build individual wing panels over the plans", "join at the proper dihedral angles", "sand everything to fit". Well, this is just plain impossible to do accurately and repeatedly. 

For one thing, normal alignment tolerances make exact linear alignments impossible at the LE, TE, and spar junctions. And for dihedral braces at the poly breaks, it's very very important to have everything align with zero gaps. And once you start fine-sanding a spar, LE, or TE, it won't take much before you've oversanded in one plane or another and the joint may be almost right, but not perfect at all the intersecting joints. Agree? 

Let's assume for the sake of argument that we're building a four panel wing in one piece - a Gentle Lady for example. Let's call the panels Left Tip, Left Main, Right Main, and Right Tip.

First, build LM over the plans. Put down LE, TE, spars, ribs - except as will be clear, you may want to not add the ribs at the poly breaks right now. And also, don't put in diheral braces. Anyway, this step should take only a few minutes but be sure to cut the spars, LE, and TE to EXACTLY the right length. 

Now, prop up LM at the center joint to the right height - use some trig here starting from the poly dimensions conventionally given - so that you can build LT flat on the plans, and joined directly to LM which has its right hand edge propped up in the air. By the way, measure LM's rise height at both LE and TE so that you don't accidentally build in any washout or washin. Due to some idiosyncracy I haven't figured out, you can put a perfectly square block of wood under the panel but usually have to skew it to get both the LE and TE at the same height - I've given up trying to figure out why, so just double check both LE and TE dimensions

As LT's spars, LE and TE are a little overlength at this point, fine sand these joints so that the fit to its matching LM partners is PERFECT. Don't forget to perforate the endgrain of the wood with a pin to allow glue to go up into the joint by capillary action. So, glue LE, TE, and spars together and get those pesky alignments exactly right. There's no excuse for not getting perfect alignments since you're joining these panels directly together. 

The rest follows by extension: build RM directly to LM; and build RT directly to RM. Or do this in any sequence you want but keep the same philosophy: splice spars, LE, and TE to each other directly, achieve perfect fits before glueing. 

Once you build a wing this way, you'll never want to do it the old fashioned way, i.e. independent panels and hope for a good fit.

Here's another tip for building wings like the Majestic's or a BOT; or for any wing planforms with Phillips entry or a semi-symmetrical airfoil. The problem here is that the ribs should be aligned just perfectly with respect to each other, or else the LE sheeting will have a hard time aligning across the wing. 

Let's go back to the previous series of instructions and let's build LM. But this time, start by first gluing down two ribs which are as far apart on LM as possible. These are usually the rib next to the poly break; and a rib near the center of the wing. Glue these in, then draw an index line down the back of the LE between the ribs. Use this index line to sight in and install the remaining ribs. This procedure should insure that, within close tolerance limits, the ribs are aligned properly with respect to each other. 

If it's necessary to adjust the fit of a particular wing rib, this is usually done by trimming the fit of the rib to the spar. Do this carefully, removing only enough material to get the desired alignment. This series of steps will almost guarantee a straight and true D-box sheeted wing section.

On building the Majestic, these two procedures are IMHO essential to getting a true wing where everything fits closely and perfectly as the designer intended.

Let me know what you think of these. These two procedures are common sense and tested across many many completed projects. Do as I suggest and building a multi-panel glider wing will become almost boring - everything will fit and be aligned the first time without any strain!

Pete Young 
215 Belmont St., Apt #2 
Belmont, MA 02478 
e-mail pwyoung "at" ix.netcom.com

 


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