Hi,
I have done quite a bit of flying in the Seneca, the mark 1, 2 and 3. I have flight tested many and spoken to Piper on many occasions about various aircraft, from time to time. The type was conceived as the twin Cherokee six. The prototype crashed after shedding a wing panel in the VNE dive. I think it killed Piper's test pilot. It's along time ago now, so I can't remember the full story.
The Seneca's wing has quite a bit of wash-out, even though it might not look it. All Cherokee's were designed with wash-out after about number 70. The type originated from the Thorpe Sky Scooter.
The wash-out is there to make the root stall before the wing tip, and was increased a bit in the twin because of the prop wash. The wash-out is there to allow aileron control into the stall. Without it the aircraft had a vicious tendancy to end up inverted in a full stall. Pilots, it seems, have an instinctive reaction to control the roll with aileron, particularly approaching a stall that is 'unplanned' or unexpected. The use of aileron in the stall simply stalls the wing on the downgoing aileron side, as it further increases the angle of attack on that side, and causes the aircraft to roll in the oposite direction to aileron input. On the Seneca this was quite vicious and as I said, the aircraft would quickly be on its back. Most aircraft today are manufactured as best as possible so it will stall straight and stable, so unless it is an advanced aerobatic aircraft, the wings will wash out so as to stall after the wing root, which after stalling will pitch the nose down. Fly a Seneca today and this can be demonstated to very good effect. Stall the aircraft and do what you shouldn't and control the roll with aileron, you will be amazed that the aircraft has positive aileron control even during the stall.