So I read up about how to get warps out of plastic parts and I'll describe the process I landed on below. First of all, here's the issue I was dealing with.
In the above pic, the wing underside is perfectly flat on the cutting mat and the fuselage seam at the engine bulkhead is perpendicular and aligned with the top centre of the roll cage. Now look along the line of the square and note how the vertical stab is tilted to the left. Also, a file has been inserted through the slots for the horizontal stab and you can see that the file is also tilted. The conclusion is that the whole rear of the fuselage is twisted counterclockwise as viewed from the front.
I learned on the interweb
here that styrene plastic has what's called a Glass Transition (GT) where the plastic moves from a being springy to where deformations can be induced. The key is to find the right temperature, high enough to allow the material to be reshaped but not high enough to melt it. Too low and you will remain in the springy zone and not accomplish anything. I started by heating a pot of water to 170F measured with a meat thermometer. I then immersed a long piece of sprue and tried bending it against the floor of the pot and withdrawing it. If the sprue springs back straight, the temp is too low. If the sprue stays bent, turn the heat off and move to the next step. I settled on a temperature of between 175 and 180 degrees F as the right place. Now, you need to have a way of forcing the material to go where you want to without causing local damage and, in this case, I used the file to force the twist. I immersed the back of the model into the hot water for 10 or 15 seconds, pulled it out and then began to gently twist the model using the file handle. I then held it firmly and ran the model under cold water and checked the shape. The twist was removed on the first try but the vertical stab still had a bend in it that was still noticeable. I repeated the process of dipping the model in hot water 3 times, bending the fin with my hands and then blowing on it to cool it while maintaining pressure. I checked the alignment after cooling with the model held against a cutting mat with a grid on it. I had to keep turning the heat up as the water dipped below the needed temperature quickly.
In the end, I managed to get rid of this warp after only about a half hour of effort and the result can be seen below:
This is the first time I managed to fix a warp and so I'm quite pleased with how it went. I wish I'd noticed it earlier on my IL-2. One down side was that the slots for the horizontal stabs did buckle a bit with a possible slight resulting bulge in the fairings. I'll need to check this area with some primer to see if it's actually bad enough to have to fix but it's very minor.
With this now done, I was able to get on with gluing the wing uppers on and set the horizontal stabs. The fit at the wing root is incredibly good and so I have applied glue to that seam only for now. After drying overnight, I'll glue the rest of the wing seams.
Thanks for looking in.