The wings of my Oriental ARF looked like they had a twist and so I got the incidence tool on the wing and discovered that I have a twist of 1.8 degrees Positive incidence measured at the outboard tip.

I  accepted that the controls would have to be replaced and other mods performed but then discovered I would have to replace the flaps, and now this with the wing

I will get the iron on the covering and see if I can get some movement but the wing seems pretty solid.

I aim to get my models as spot on as I can but wondering how close do I need to get it so that a trim tab would sort things out? I am at the learning stage and so I guess it does not matter if it is not perfect.

One of the problems with iron on covering is that the wood never gets reshaped when you take out a warp/twist.  Unless you dampen the wood it never relaxes and assumes the new shape entirely.   If the wing is yet to be mounted it is probably a twist.  They are a real SOB to get out once the wing is glued in and the center section cannot flex.  On a twist both the LE and TE will appear straight when looked at individually, but they will have opposing incidence if measured. Which one is yours?   Are you concerned about appearance?  I have a MonoKoted plane that had a twist in one wing but trying to heat it out with an air gun just turned it into a warp.  I cut the covering off of two panels on the bottom and used the hole to dampen the entire structure with steam.  That let me take out the twist by blocking the tips to level and letting it dry for two days.  Recovered the panels with the same color monokote and then reshrunk the top covering.  Added some trim to hide it.  Two years later and it is still at -0- incidence relative to the center.

If you are using a "wart" to correct anything but hinging, you are making a mistake.  If you need a tab you are never going to get the plane into "perfect" trim if that is even possible.  Find a way to get the wing straight.

"I guess it does not matter if it is not perfect."  That is true to an extent.  Looks wise it is 100% true as you learn but trim wise it matters a lot.  Many, or even perhaps most crashes while you are learning can be avoided if the plane is trimmed properly.  Learning to compensate for the plane only leads to learning bad habits and avoidable crashes as you learn how to recover from bad situations.

Ken

NOW , you wont believe this . But a 2 foot x 6 inch piece of 5/8 in. steel ways a bit . TWO weigh twice as much . then theres the other bits . a hammer or bech vice . whatevers handy .

out on the LAWN , where its NOT got rocks or hard bits , You pack  the swine , use a 4 x 4 if its inverted . under the spar . Cut a piece of foam from a styrofoam lid from the green grocers , or case .
Sit the thing flatish , Put a stick along the trailing edge , say1 inch x 3/8 x 24 inch . Put another long ' packer ' on that . Sometimes a piece of tin . knife blade , sticky tape , is used to positify location .

a thinner one along the spar ( maybe ) .

THE TRICK is to carefully , judiciously , evenly , and slowly , ( Dont drop it 1  ) the steel , ON . Then Another on that .

i did the Spitfire like this a few weeks back . Six hours on a Sunny day , and it was twisted six times further the other way . Par Tickly WHERE it exited the Fuse. T.E. we're sorting out here , Getting it to comply .
This wasnt the desired conclusion . Left a day or two . They ALWAYS come back a way .

Did it opposite , paying attenntion to the T E . ( 1/2 sq. on a silk covered detroiter with spruce spar caps with vertical shear web . ) 
About three or 4 hours with it less odiously levered , and it came off pretty well spot on .
Got to check again . Dosnt seem to like being stored by the leadouts . tho its the OUTER that wasnt sitting right .

the PRINCIPLE is twist it the f* the OTHER WAY . ( twice to four times the twist ) Leave it for a week . Eyeball . Often itll have gotten itself spot on . You gota go softly  easing the weight .
Tho you get more daring . Used two car batteries on a fully sheeted wing once , on planks .

George, you may want to consider another approach which is either great or a complete brain fart.  if it is what I think it is, your center planking was put on with the wing not solid in a jig (don't ask how I know that).  If this is the case you are going to have one hell of a time ever getting that wing straight.  Since it is not mounted, consider taking the covering off out to 1 rib past the center and remove the center planking behind the LE Sheeting, get the twist out and re-plank it.  Or wet it down and see if it will reshape.  Recover and you have a natural place for trim lines.

Plan "C" would be to completely recover the wing and get the twist out while it is uncovered using steam and profanity.  If it is wet, you can reshape just about anything.

At this point nothing is too "off the wall" to try.  Every one of the tips you got here and on other threads came from somebody a long time ago trying something new out of frustration...that worked!

Ken