How straight do wings need to be

I believe that the wings on a cub should be straight across (no sweep back for forward). How accurate does this measurement need to be? If I pull a string along the front spar from tip to tip then how far aft of the spar can the string fall at the root ends of the wings for the wings to be considered "straight"? Does anyone have a cub with a wing that is swept more than an inch that still flies just fine?

you measure from say... tail spring bolt to same place on each wing, I use rear strut attach fitting on wing... have seen 5" difference... most planes are over 1" different...

its quite an optical illusion looking at the string like you say.... might put strait edges up from spar faces to near string.....

are these wings covered?

are tanks & the tube installed and bolted in??(wings sweep back with tube disconected..)(just reassembling some wings that some rocket scientist redrilled the tube and tab so it was almost a 5/16" slot with a -3 bolt...thunk thunk.... instead of having someone push the wing forward to make it fit...)

it will probably be fine.....

mike mcs repair said:

you measure from say... tail spring bolt to same place on each wing, I use rear strut attach fitting on wing... have seen 5" difference... most planes are over 1" different...

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That could also be a tail that banana-ed during welding. Steve Pierce said its common to find cubs sitting a few inches off his tail stand rest in the jig. Also I heard its good to weld left and right as you move through the clusters, or you cause the banana.

mike mcs repair said:

are these wings covered?

are tanks & the tube installed and bolted in??

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Wings are covered. I will go back to hangar today and raise the tail enough so the spars are perfectly vertical. Then the string's catenary will be drooping straight down at the root. This will decrease the optical illusion. (I'll still put a straight edge on the wing mount bracket as you suggest to get a more accurate measurement) But when I sight down the wing's spar one or both are clearly swept back. And since the distance to the tail is different, I can determine that they are not equally swept back.

How about propping the tail up and dropping a plumb bob down to the floor from the LE at the outboard and inboard points, on both wings, so 4 marks on the floor.

Then snap a straight line as a reference point, amd measure to it. That and measuring off the tail should get you close enough.

I've seen a couple of cubs that had wings "rebuilt" by amateurs -- they bowed like a banana, with the middle of the wing set back further than either the root or the tip, and some wings that were swept forward and some swept backwards. They had to wallow out the wing attachment fittings and bend the aileron and flap attachment brackets to make them fit. Scary!

Like the 50 yard paint job, it's hard to spot from the "for sale" ad photos posted and it's one more thing to be wary of before you buy a plane "sight unseen."

You need to figure out if it's the wings or the top deck that is out of whack. Take the wing root fairings off and measure across the front and rear spar carry through from the C/L of each attach bolt hole. I believe the measurement should be 26 3/4"

Either way I can't think of an easy fix.


Jason

Check the forks on the struts...


is one side short and the other long???

Start simple, work expensive.

A well placed tree on one side mite bring stuff back to square if the appropriate speed is induced:help

How hard were the wings to install? Uncquare wings are a pain to get on. I have removed some that were that way. The top deck could be un-square as well.