Main spar bow

[Darick]

I have the right wing top aft skin cleco'd to the rear spar. There is a slight forward bow to the main spar (prebuilt from factory). If I push the tip of the main spar towards the rear spar, the forward edge of the skin and the edge of the spar will line up. If I don't keep this pressure on (I'll use a clamp or jig of some sort) the forward edge of the skin and the forward edge of the main spar won't line up in the last 20 inches. At the tip, the skin will be back from the edge at least 1/16 inch.
Am I doing the right thing by putting this tension on the assembly to keep things lined up?

I searched the forum and found one previous discussion about a Zenos spar bow. The factory said not to worry as the spar will straighten out as you get the skin attached. I don't see this happening in this case as the skin will just lock the bow in place if not straight to begin with.

The photo exaggerates the miss match a little in the upper left corner of the photo.

[tonyr]

Hi Darrick,

Provided you cleco the wingskin exactly along the rear spar, when you progress to the forward spar, it will naturally pull the bow out as long as you push it into place before drilling. Position the forward spar where it needs to be and drill cleco the first hole.. The cleco will hold it. Move along the forward spar and make sure the bow is pulled out along the forward edge. It wont take much pressure to keep it straight.
Once you have one skin on do the other, making sure that the rear edge is aligned and any remaining bow is worked out of the forward edge. (The other side may have a small bow in it)

If you assemble the wing vertically using sawhorses, the bow is reduced a little by the weight of the wing structure.
I suspended a brick or two from the spar to pull it closer to straight.

Cheers
Tony

[Darick]

Thanks Tony and good luck with the paper work you recently submitted.

[Bryan Cotton]

Darick,
I will have to upload my hummelbird spar pictures sometime. The outer spars were bananas, and the plans call for bending them straight by propping them up on blocks and using a jack on the spar to try and lift your house. I used an old Dodge Omni jack. If you can pull the spars onto place by hand then you would not need to do anything so excessive. Spars tend to be strong in the up and down direction, like when you pull G. They tend to be weak in the fore and aft direction. The skins take those loads, as some of the skins will always be in tension. For fabric or wood wings they use drag/anti-drag wires in the wings.

CNC holes are a wonderful thing.

Sonex probably does not want you to bend your spars straight else they would tell you to. The Schweizers did not like the spar unbending. They used heavy duty tooling to hold the spars during riveting to prevent the bending. That works.

[wlarson861]

Align the aft edge of the skin with the aft edge of the rear spar and clamp it securely. This will pull the main spar straight. I built my wings verticaly on saw horses which made it very easy to square up and have access to both sides without flipping it over.

[tonyr]

Sonex probably does not want you to bend your spars straight else they would tell you to

Umm Not quite correct, if you search through the old Yahoo posts, there are quite a few posts about bent spars and how to fix.. several Sonextech replies included - they all say to correct the bend as described

Cheers
Tony

PS Darick re paperwork, yes in this neck of the woods the Aussie system is very S-l-o-w, hopefully not too much longer

[Bryan Cotton]

Tony,
Thanks for the correction!

[Bryan Cotton]

Here are my hummelbird outboard wing spars. Check out the bow! These spars are tapered.


A couple of views of the straightening operation. I used a hydraulic jack for this, the omni jack project was for bending a round hat channel.




That was my old EAA chapter.

[tonyr]

That's quite a bow you had there.. I'm glad the Sonex spars thin out towards the tips and are easy to move where you need them

Bet the roof was never the same after that exercise too ?

[Bryan Cotton]

Extra headroom in the clubhouse is always a good thing!