1. The problem statement, all variables and given/known data In designing a hemispherical parachute, i´ve come across conflicting information regarding whatever to use a constructed (ortographical projection) vs. a nominal diameter in calculating the necessary area required in the parachute. Sources using constructed diameter in equations: http://en.wikipedia.org/wiki/Drag_(physics) http://my.execpc.com/~culp/rockets/descent.html [Broken] http://physics.info/drag/ Plus a few more. The main source promoting a nominal diameter is a specialist professor in the area, making me doubt my previous decision to use a constructed diameter (which seems physically reasonable): http://www.pcprg.com/rounddes.pdf 2. Relevant equations The equation for drag, computed from a mix of bernoullis equation and pressure over an area, with a coefficient for drag resistance added, C. F= 1/2×c×p×v^2×A 3. The attempt at a solution Choosing the constructed diameter in my further equations, because of the assumption that an inclined surface should, because of the steep angle of approach relative the air-particles, affect them (summarized) in an ortographical manner. The paper is due friday, and thus i would very much appreciate a quick answer.