One reason I recently bought RockSim 10.2 to augment my trusty OpenRocket was its onboard Ring Tail modeling feature, an awkward maneuver in OR. So, I set about modeling a simple rocket with a ring tail to test how different ring tail lengths effect stability and saw a surprising result: as the ring tail length was decreased the rocket’s margin of stability actually increased.
Starting with a 1.00”, BT-80 ring located 1.50” from the bottom of the body tube (see attached model #1), loading an Estes D12-3 with a 0.50” overhang produced a stability margin of 1.57 cal.. OK, reasonable enough I thought.
However, as I incrementally reduced the ring length, and correspondingly the ring surface area, the stabilizing effect of the ring did not grow smaller as anticipated, but instead got larger. While I maintained the ring’s center point distance to the rear at a constant 2.00” by adjusting the ring location slightly each time, successively smaller test lengths moved the CP rearward, not forward, on the rocket and the marginal stability got a little bit bigger.
At the extreme limit (see test model #2), a virtually non-existent 0.001” long ring tail still yielded a stability of 2.07 cal.! Where are my calculations going awry?
Starting with a 1.00”, BT-80 ring located 1.50” from the bottom of the body tube (see attached model #1), loading an Estes D12-3 with a 0.50” overhang produced a stability margin of 1.57 cal.. OK, reasonable enough I thought.
However, as I incrementally reduced the ring length, and correspondingly the ring surface area, the stabilizing effect of the ring did not grow smaller as anticipated, but instead got larger. While I maintained the ring’s center point distance to the rear at a constant 2.00” by adjusting the ring location slightly each time, successively smaller test lengths moved the CP rearward, not forward, on the rocket and the marginal stability got a little bit bigger.
At the extreme limit (see test model #2), a virtually non-existent 0.001” long ring tail still yielded a stability of 2.07 cal.! Where are my calculations going awry?
