What difficulties would it take to build a glider without ailerons? I read that "if you can control the turns with the rudder maybe you don't need ailerons." Well, apart from the fact that it would only slide to one side, I was wondering if there was a rudder-elevator combination that would allow bank angle turns or is it something that only ailerons can do. (We must be able to achieve with 42° bank angle)
Without ailerons you can get a bank angle only as a side effect of the sideslip introduced by the rudder.
This side effect mainly depends on the sweep and dihedral angles and on the position of the wing (high, middle, low).
So if your bank angle has to be perfectly controllable (as I suppose it should be) then it would be better to rely on ailerons.
Sideslip is also caused by lateral gusts, so if you design an airplane which rolls only due to sideslip then it is going to be sensitive also to lateral gusts.
One really would not want to design a glider without ailerons because:
minimizing drag is key to achieving the greatest lift to drag ratio.
You glide much farther by flying coordinated. With ailerons, you set your bank. The rudder need only keep the nose "into the wind", compensating for adverse yaw from the downward aileron.
Without ailerons, one must push the nose out of the relative wind with the rudder in order to create a "crosswind component", which rolls the aircraft. This does work, but is far more draggy.
But spoilerons are an interesting alternative, currently being used on many long range aircraft where fuel economy is of primary importance.
One may test to see if the rudder/vertical stabilizer, usually shaped as a vertical airfoil, is actually of lower drag (in combination with ailerons) than raising a spoiler into the airstream in order to turn.
By setting the rudder up very high on a high tail one could increase its bank effect. You would have to counter steer: turning the rudder to the right would wrangle the plane into a left bank.
In effect this is a vertical aileron; imagine a second rudder underneath the plane that turns the opposite direction.