Helicopter recovery model that releases the blades after boost by using the motor ejection charge to drop the fin can off the back attached to a Kevlar harness, eliminating the need for a burn string.  Blade shape no is accomplished by slicing the balsa blades diagonally lengthwise (partially, not a complete cut-through) then bending the balsa with the aid of pre-cut jigs and glueing the cuts to set the final shape.