I started building a Mid-Star 40 kit. I started with the right wing but didn't realize there was a bow in my building surface until too late. I've attached pictures and wonder if anyone has any ideas to take the bow out. I've put a sand bag on the middle on a "Flat" surface, grrrr.

What I have done, tried but not tested yet is cut through the trailing edge and removed enough material to allow the warp to relax. I then glued the TE back together and epoxied a ply plate to the front of the TE to strengthen the glue joint. I cut through the TE at the center of the rib bays to allow more surface area for the glue bond. I was able to catch the warp before all of the sheeting was put on and picked up some heavier balsa sheet to use on the TE.

Strike what I said before!!! I just realized it is bowed, not warped. Is the wing thinner in the middle along the spar and thicker at the end or is it bowed equally on top and bottom. If so, dampen it with water or Windex (to keep the grain from rising) and block it in the oter dirrection and I put weights made from a bag of BBs on the ends and the next morning it should be fine...make sure to get the spar wet but if it won't straighten then if you can cut some reliefs (I've done this too if it's bad)

That's not A bad warp. I put the wing on two built up surfaces, one on the tip and one on the center, spray the wing with A 50/50 blend of water and ammonia then put A small bag of lead in the center and let it sit over night.
Another way is when you cover the plane you can have A friend hold or bend the wing straight and use the heat gun on the bottom and tighten it up, this works on small warps but may need to be done more then once before the covering is shrunk correctly.
I just had to straighten up one of the ailerons on the plane I'm building now and the water mix worked great. To keep from warping too far you can put something under the center so when it's straight it won't warp to far the other way.

Baldeagle, don't worry about it.

That's not a warp, it's a bow - and it's not even a bad bow.

It will not affect how the plane flies, and unlkess you look right down thw wing (like in your pic) no one will ever see it.

Don't even mention it, and we'll keep your secret

Thanks for the replies! When I built my first plane, Goldberg Eagle II, the wing was in stroage so long, one side did look like it had a similar bow. The plane flew fine as well. The only problem I had is the aeilerons didn't move smoothly. I'm trying the ammonia/water tip right now and see if that does the trick. Thanks again!

Just a little extra dihedral. You probably wont even know the difference if you're like 90% of sport flyers. I flew a plane for 10 minutes of hard aerobatics on one aileron and I just thought the rates were a little low! My linkage was flapping in the breeze.