Ideally, of course, no torque is required, once the cylinder has reached 50 rotations per second. Torque is only needed to get it to that speed, and then, at speed, only to counter the effects or wind drag and friction in the shaft bearings.

Assuming you are rotating the cylinder around its axis, then the cylinder can be modeled as a ring, or a disk, depending. If all of its mass is at the circumference, then the cylinder can be modeled as a ring. Short answer:

Moment of inertia I when the cylinder is filled, equal density mass = 1/2 m r2

If all the mass is at the circumference, I = m r2

Torque is angular force, so it is applied to get the object to rotate from one angular rotation rate to another angular rotation rate.

Tau = I * angular acceleration

The more rapidly you want to achieve 50 Hz rotation rate, the more torque is required, but for a shorter period of time. It's analogous to F = ma.

http://physics.bu.edu/~okctsui/PY105%20Lecture_notes/Notes/class24+25_Torque+Rotation+Equilibrium.pdf

http://www.maplesoft.com/content/EngineeringFundamentals/4/MapleDocument_30/Rotation%20MI%20and%20Torque.pdf

I used to calculate, friction and windge  loss using simple rope used as dynamometer,  with two end spring balance, (S1-S2)r, where, r the shaft radios. Same practical method could be used....