ORIGINAL: HighPlains
As far as a ''scale''detail - Please. The R3 is fictional, never sprang forth from the Grandville Brothers shop.
Sorry about that.... Lots of shade tree aeronautical engineers back then did cute tricks like lifting tails for dumb reasons. So the designer of the model did the same.....
A tail that lifts down - you are not the first to do this. I believe if you check out a Lockheed C-130 carefully, they do it too. Actually most conventional aircraft have downforce from the tail when the aircraft is in level unaccellerated flight. Draw out the force diagram of the center of lift and the center of gravity and you will see which way the lift from the tail has to go.
As for the tail of your model lifting down... or up.... or sideways.... don't assume that just because one side of the stab is fat that the plane is going to suddenly be carrying weight back there... or not carrying weight being upside down. It ain't how it works. We trim our models in flight to fly level. In fact, full scale usually does that too. What that level flight trim does is adjust the tail to produce whatever lift is needed to point the plane level. That lift might be up (don't bet on that however). It's usually down, but usually not enough to need special profiles. Since our models don't have much CG movement in flight, and aren't used anything like the Hercs are, with hugely varying loads from overloaded to empty, they don't have variable incidence or any major trim adjustments available or needed.
Your tail isn't going to lift down more than it would with symmetrical tail after you've found out and dialed in whatever trim is needed. It might produce a bit more drag than it would with a symmetrical tail, but then, that's probable had it been glued in upright.
Your model design didn't need the tail to lift up to begin with. If the designer of that fictional beast cared about the efficiency of his design, and still wanted the camber, he would have designed the angle of incidence of that tail to suit the demands, which would probably have negated the value of the stab camber.
The negative camber on the Herc is there to deal with the massive pitch stability problem the design experiences when the wing has to produce massive lift to carry massive loads. And there is an extra trim device in that little monster to crank the LE of the stab up or down to suit the loading. They need to be able to fly the plane when it's empty and when it's overloaded. Their world is a lot more demanding than ours. You aren't planning to carry a tank in that model, or chute it off the ramp in flight. .... although that'd be sorta kewl to do with a model..... hmmmmm