Yet another Oly2S build question

[merlinmurph]

OK guys, new builder here working on his Skybench Oly 2S.

I finally got some time this weekend to start the wing. I spent yesterday morning dry-fitting parts to see how it all goes together. This is the first decently sized wing I've built and had never really seen how things are engineered. Definitely a very cool learning experience.

Q #1
Got a question about the whole wing joiner area.
Reading the instructions and looking at the plans, it looks like you glue all the ribs in first. Then, you actually cut away the appropriate ribs to fit in ply joiner pieces W-11??? Is there a reason you don't cut the rib into pieces first, then build up from there?

Q #2
Step 8 in bobby legue's instructions is a little vague. It says "Remove the portion of the ribs 2 and 3 above and only the width of the spar". I'm not sure what this is saying, but I think it's related to Q #1 above where we need to make room for the W-11 ply joiners? I'm not sure what I'm missing.


Q #3
A fellow club member and longtime builder/pilot is trying to convince me to wrap kevlar tow to the spar. I had already semi-planned on adding the tow, not exactly knowing how it would be done. At the recommendation of the same club member, I have already made my own spars by laminating hard balsa to tapered carbon fiber on the top and bottom spars, like the Allegro-lite and Bubble Dancer.
If I were to add the kevlar tow, this changes the whole build procedure. I'd have to build the whole spar/rib assembly first, then add the sheeting. Got any input about adding the tow? If I were to add it, got any suggestions/warnings with the build steps?
One thing I can think of is that I would want to test fit all the ribs to make sure they would contact the bottom sheeting, as Ray suggests. Anything else?

I'm thinking of maybe skipping the tow (that is, follow the directions) on this build and use the tow on the next one (Oly 3??).


Thanks guys,
Murph

[lincoln]

1 I bet it's to make it more likely you get everything lined up nicely.
2. You're going to be filling that area with epoxy goo to hold the joiner tube, I bet. If you didn't do this you would at least need to drill holes for the joiner tube. It would be messy. BTW, I find the instructions vague at step 8. I believe he wants you to put in only the FRONT joiners at that step, so the back will be open for epoxy goo. However, if you put them both on you could probably stand the wing tip down, root up and pour in. Might be worth making sure there was no place for it to run out first. And whatever trick you did to jig the joiner tube would have to be done on a vertical surface. The rear joiners will be a tad stronger if you make sure the microaballoon mix doesn't slop over and cover the spar to joiner joint area. Use straight epoxy there, or else mix in a bit of that fumed silica or whatever they call it to thicken it, but don't use microballoons. Microballoons are probably ok for holding the joiner tube, though. Make sure the END of the joiner tube is securely closed. It might be worth soldering in a metal disc. It's a realy pain when the wing rod starts to push through the end of the tube.

If you don't want to use as much epoxy, I believe it's safe to make some plywood trapezoids to fill in the gaps a bit. But make sure they're glued in all over and that they are GOOD plywood. Not some splitting luan. Say5 ply stuff, marine or aircraft. I suppose end grain bits would work too. (I mean with the grain vertical). But epoxy only is probably fine and the easy way.
3. If you don't wrap, you should probably replace the hard balsa with something stronger where the joiner is, because that's what's holding the joiner. Balsa might split, would be my guess. Probably best to make a tapered joint between the two. As an alternative to kevlar wrap, fiberglass with the weave on the bias is supposed to work too. Might be a good idea to round the edge of the carbon a bit. I'll bet that the wrap works best if it's really tight.

I haven't done the wrap, but I've done several wings with joiner tubes.

[lincoln]

P.S. I haven't done an Oly either, but I had a student who mixed the microballoons in and THEN the epoxy components. Don't do that! It might not set right. BTW, it helps to be really careful about epoxy quantities when mixing. You don't want a batch that won't go off. Also, don't use fast epoxy for this if you don't like stinky smoke in your work area. Best to use the really slow stuff. It's stronger too. Even the slow stuff can smoke if you mix a few ounces at a time (boat) and it's warm.

[bobby legue]

Merph,
Yes you can cut the ribs first and glue in the wing joiner sides if you are carefull. If the ribs are glued in first you have a visual reference of where to cut and there is less chance to overcut. Really your choice.
As for wrapping the spar, there is no one who will claim that this will not add strength BUT Ive never done it and haver never failed a wing on launch!
Bob

[efowlerpreston]

If you find something vague, take a look at the instructions for the OLY III. There's a lot a similarities between the two planes, and sometimes, a step (or photo) is much clearer in the other instructions. Also, I found building to be much easier once I realized that the instructions were only "guidelines", and stopped trying to follow them to the letter. There's often more than one reasonable solution to a problem.

Regarding Question #1, I shared your concern. However, I ended up following Bobby's instructions, and it turned out to be easier than it sounds.

[bobby legue]

Regarding question 1, Dont glue the rib to the lower spar area and removal of rib center will be a snap.

[merlinmurph]

Thanks guys:

Lincoln: Thanks for the heads up on epoxying the joiner tube area. Somehow, I was envisioning filling from the top, not realizing the top spar would be there.

bob l: I started down this road, so I think I'm going to end up wrapping it. I folded the wings on a Majestic last summer (bought barely used), and would like to do what I can for strength. Though, I also need to learn not to stomp the pedal so much. Stay tuned, there will be more questions, I'm sure. Thanks again.

efowler: Have you got the OLY 2S, too? I agree on reading the Oly 3 directions - they can fill in some gaps.

Thanks again guys,
Murph

[ciurpita]

some suggestions:

1) i followed the instructions on one wing, but had a lot of difficulties trying to glue the shear web in between the spars after they were glued to the ribs. on the other wing, i glued the top spar in after i cut the shear web, gluing the top spar to both the ribs and shear web at the same time. (that first wing suffered from flutter because the shear joint did glue properly.

2) i sheeted the front half of the inner section of each wing (i.e. D-tube). i never had any problems launching using a strong winch. this not only made it stronger, but maintained a better airfoil shape (less sag).

3) i made a leading edge shaping tool from a piece of foam (2x2x4") by cutting out the leading edge shape with a hot wire, and lining it with some self-stick sand paper. i was told that the leading edge of the airfoil is by far the most important part of the airfoil.

4) i was unable to fit the standard size servos i had in sideways, like the plans suggested, because the fuselage was too narrow. i wish i had made the fuse wider.

[efowlerpreston]

I only have an electric Oly 3, but have been very tempted by the Oly 2S, especially since I have found someone with a winch about an hour away. I miss not having a woody plane on the building table.

[Ray Hayes]

Lots of ways to build a woody, part of the fun of it. Best advice I can give is:

avoid changing the front portion of the ribs ( from spar to LE ), that can cause the leading edge to change the entry point of the ribs that you cut. I have seen this on other kit build theads, end view pics that show the leading edge at the root was either higher or lower than ribs located further out from the cut ribs.

I use a stick of wood under the bottom sheeting, positioned near the front edge of the ribs. The stick starts out board of the cut ribs and runs past rib 1. Somewhere in my photos for several of my kits are pics that show this set up. The stick is my insurance the cut ribs are in line and not going to create a wave in the leading edge.

I'm building my proto WF-XL and will post a pic here shows what I'm talking about, I hope.

I have never wraped a wing, I fly contests and launch hard, the plywood shears on the sides of the spar have worked for me. It does two things ( if you don't cut the supplied ply shears into pieces and fit the pieces between the ribs ), the plywood obviously creates a very stiff wing, it also locks the the top and bottom spars to the vertical shear webs between the spars. Look at the cross section this type of construction makes.

Wrapping a spar is more or less creating the same cross section. The shear point on the wrap are the spar edges, the shear point on the plywood is the thickness of the top and bottom spar sides. The wrapped spar strength comes from the spar itself. using carbon spars and plywood is really strong.

However, carbon doesn't adhere to anything very well and commonly fails when the surface ( spar material ) seperates from the carbon. This is what created spar
wrapping.

BAck to my building board and vacation from Sky Bench. I'm getting burned out on Sky Bench, love everything but the work. :-) I will be closing several times this year, must be old age .......

Let it be know that I really appreciate Bobby Legue and all the help he has given to folks with Sky Bench kits. Thank you very much Bobby.

PS. ... I use a 2" Zona Saw to cut the ribs, blade is very thin, and a Perma Grit Sander with fine grain to clear the saw cut, sand any residue from the spars/vertical balsa shear webs. Google for scource of these woody tools.

Ray
http://www.skybench.com
Home of Wood Crafters

[bobby legue]

Thanks Ray,
Its an honor to be part of the Skybench team.
Bobby

[merlinmurph]

Thanks for the explanation, Ray. One of the main reasons I'm building the Oly is to learn a few things. I want to learn build techniques. I also want to learn about the engineering of the wing, why things are done a certain way. And I also just wanted to know what a shear web was. :D Anyways, I appreciate your input, it has definitely helped me understand a few things. Guys like you have forgotten more than I'll ever know. Now, get out of the shop and go flying! Good cure for burnout.

And I agree, Bobby L has always been there for people with questions about Skybench products. He has been a great ambassador for Skybench.

Thanks again guys,
Murph