Thanks again guys! Hrm - That link doesn't work. Sorry about that. Flak: I've no idea! I won the rocket design competition at Uni 2 years back - so I can vouch for all the equations I've used. I'll have to wait until the 'consultation' to see what their motives are. D@M: MathCAD all the way! Said rocket (that was also the inspiration for 'Apogee') was designed in MathCAD. Its my favourite engineering tool. I've also used it to design a glider, a flying taxi, a next-gen badminton shuttle and a mars rover. All of which worked! :biggrin: