So I could use some advice on the engine setup. I have seen some videos online of guys flying four engine planes and were being pulled all over the circle. I also saw Paul Walker fly his B17 at either the 2001 or 2002 nats and if he was having a hard time hanging on it did not show.
As one of the few people to fly the B-17, I can assure you that the line tension was pretty darn heavy, and the control loads were remarkable. I flew it in the dead calm and it was near my limit. I could have done 4 flights a day, maybe, with some conditioning, but it was *very stout*. Paul worked out regularly until he could manage proper posture and body positioning to be competitive, but it was at least double the normal stunt plane.
It may have been far less than some of the scale models because the scale models tend to be built like bricks, they seem to be in love with plywood. Paul's airplane was built by a master and it was dramatically lighter (at 100ish ounces) than most scale models, and, it was balanced with a relatively aft CG.
Of the two issues, the control loads were probably more daunting than the line tension itself. I have no doubt it would turn plenty hard enough *if* you had enough forearm. I think you have to consider some assistance, like Howard's boost tab/servo tabs. Solve that, keep the weight in bounds to control the tension and speed, and I think you have it. Even if the plan is just to fly scale and not aerobatics, build it like a stunt plane from the 70s - weight control.
Brett