Light twin pilot reported an NMAC shortly after takeoff at RUQ airport when another aircraft executing a training maneuver descended into the downwind leg of the pattern.

Narrative

After turning left crosswind following departure on Runway 20 at RUQ; a near miss occurred when an aircraft; presumably piloted by an instructor with student; executed a steep spiral descent into the downwind leg. The aircraft was above me and never seen until after it had passed overhead; traveling from my right to left. My TCAS warning system alerted me to the aircraft proximity and evasive action was taken. Although the presumed instructor had called his intention to execute the practice steep spiral descent into the downwind leg earlier; some time had elapsed by the time I departed and turned crosswind and his position was unclear. In addition; there were 4 aircraft; including my own; in the pattern at this small airport; with one taking off behind me. My concern is that practicing steep spiral descents at this small; relatively busy; airport may place other aircraft in the pattern at risk for mid air collisions. Consequently the suitability of performing this procedure at this airport should be examined and perhaps restricted to times when the airport traffic is less dense.