There has been a question on how the rules are interpreted on the 15″ parachutes for the 2011 competition. A 6 sided parachute will not qualify.
A question came up on if the top of the parachute, when inflated, was larger than the bottom where the shroud lines are connected. The answer is no.
From Trip Barber:
The challenge this year also specifically requires that the rocket, or at a minimum the part of the rocket containing the egg and altimeter, be returned to the ground under a 15-inch-diameter parachute. The TARC 2011 event rules describe what this means and how we will be measuring parachutes for compliance. Basically we will have a flat surface with 14 inch and 16 inch concentric circles. When laid flat, every piece of the outer edge of the parachute must be between these two circles. If the parachute is hemispherical we will use cut-outs of 14 and 16 inch diameter and verify that the 14 inch cutout fits into the inflated canopy and the 16 inch does not.
I have also attached a file showing a 6 and 8 sided parahcute in the allowed dimension of 14 and 16″. An 8 sided parachute will just fit, but very tight fit. There is also the extra weight and work involved with the extra shroud lines.
The 15″ round parachute from Sunward will qualify.