Loiter normally attempts to circle around a position and maintain the altitude where the mode was entered.  I would like to have my plane circle around a position, but allow the plane to rise and fall within a specified min and max altitude.

I am building a RE powered glider and wonder if APM could be used to circle in a thermal.  (manually triggered)  In this case, the loiter radius would be relatively small.

The other use would be to explore the max duration of my power system (constant airspeed with power) while allowing the plane to rise should it encounter thermal lift - without the AP trying to maintain target altitude. In this case, the loiter radius could be 1 km.  I feel the constant pitch/throttle adjustments used to maintain target altitude is unnecessary and potentially inefficient for the task.

Thanks in advance for any feedback.