A 50 meter tall Helter Skelter, made cylindrical rather than conical, thus resembling a large, vertical Archimedian Screw.
The structure has a solid core to allow access to patrons up an internal staircase, and to support the external, suspended, rotatable sleeve that has the spiral slide winding
around it. The spiral slide pitch, in the upper part of the tower, is quite steep - 45 degrees.
At the base of the ride (mostly barely visible through the crowd of litigation personal injury lawyers) is a deep, gymnastics training-style foampit.
The rotating sleeve is connected to a very large conical gear belt drive system, which has been designed to have the effect of accelerating the sleeve at close to 9.8 meters per second squared. (There is quite a 'thump' through the whole tower when the drive kicks in)
Thus, when a 'rider' sits at the top of the slide and the 'ride' starts, they will have the sensation of free falling for the height of the tower while only being ever a few centimeters above the surface of the 'slide' for most of the way down.
The problem comes at the bottom, where the rider has gained a dangerous amount of momentum and the rotating sleeve has reached a very high speed. The foam pit by itself would not prevent injury from a 50 meter free fall, so for the last, say, twenty meters the pitch of the 'slide' lessens, at an increasing rate of lessening, from 45 degrees to 15 degrees. The last few meters of the slide also begins to slope outwards laterally. The latter arrangement should serve to 'catch' the free falling rider, comfortably decelerate them, then pitch them away from the whole apparatus, into the foampit, at the end of their ride.