sorry or the late pic because I need to find out why one of the wing is stable and one is very easy to come off.
Let start for the wing modification STEP BY STEP
1) take out all the parts inside the wing engine. Use the following parts
And do like this
And put it inside
after I took those photo, I find that I have another parts can make it more stable, I Change the two 2x1 brick to one 4x1 black colour long brick, like this
Also l find a grey colour 1x4 brick for the other side, like this
After you finish the modification of the inside structure, you can put the wing on , like this, yes, did you see the grey colour 2x2 inter lock?
After that, You can design your no down side up wing by you own idea.