Cessna's and Piper's have dihedral also, and they will still work themselves into a steepening spiral without any help.
I have never noticed such tendency. In steep turns 45-55 degrees most Piper's and Cessna's are very much stable and require only little correction to keep level altitude. I would argue that much bigger and heavier airplanes indeed would go to spiral and usually restricted by 30-35 degrees of bank
Well, you might not be alone in having not noticed it, but if you look for it you will see that it's there. Even in your example of a Cessna or Piper, and well before you reach even 45 degrees of bank it should be obvious if you look for it. Next time you are flying roll into that 45 degree banked turn, and once established just look at your hands or get video of the stick/yoke during the turn and you will certainly observe that you are holding constant aileron pressure opposite the direction of the turn. . .if you were not, you'd be inverted long before you've completed that turn thanks to roll-wise instability
that is a characteristic of every conventional design.In fact you should be able to observe it in cruise flight even in a Cessna. Go out on a clam day, trim for cruise as best as you can, make no power changes after that, if you've got rudder trim, go ahead and center the ball and then put your hands in your lap and your feet on the floor (obviously using no autopilot). It will not take long before you absolutely WILL observe roll instability even from this best case scenario. Most of us correct these roll deviations without thinking about it. . .but they are still there.
Many of the biplanes I fly have dihedral either on both sets of wings, or just the lower wing. . .even going from upright to inverted I do not see a significant difference in roll-wise stability, and of course when inverted I've now got anhedral instead of dihedral. . .it's just not that strong.
I've never flown an Se5a but I've heard from multiple pilots that do fly them that they fly and feel very much like the Great Lakes, which I have flown in all attitudes. . .and like every other thing I've flown, they still have that spiral character.
