Solid cylindrical centripetally burning propellant with four convex arced lobes

A solid elongated externally burning propellant element, the external configuration being such that the element retains its general configuration during combustion, the configuration of the element being such that the element may be inscribed in a cylinder of radius R, the cross section of the element having a contour comprising four identical connected lobes, said element having a first and a second perpendicular planes of symmetry, said element exhibiting mirror-symmetry with respect to said first and a second perpendicular planes passing through the axis of said cylinder of radius R, each lobe comprising a convex arc of a circle of radius e whose center is at a distance (R - e) from the axis of the cylinder, where e is the combustion thickness of the element, said arc being tangential to said cylinder, and each arc contains only one point at the minimum distance e from the axis of the cylinder, the four points of the arcs at said distance e being symmetrical with respect to the axis of the cylinder, the thickness of relative combustion e/R varying at a continuous rate during combustion, whereby the combustion of the element leaves only two combustion residues.