The Mk2 died off the weekend before the NPL competition. This was a little inconvenient, and meant a couple of evenings being devoted to the rebuilding it. The nose bottle was replaced as I was a bit worried about it bursting. Its replacement was a more normal, blunter, shape and so a nose cone was added; this also gave the rocket a bit of a 'crumple zone' rather than the pressure vessel taking the full brunt of the landing. The body is otherwise the same as the MK2a, being stiffened with wooden stringers and packing tape. The fins are again drilled out plywood but a slightly different shape.
Simulation
Input Figures
Rocket Volume - 6 l
Diameter - 100 mm
Coefficient of drag (guesstimate) - 0.68
Mass of ejected water - 1.6 kg
Launch pressure - 100 psi
Exhaust diameter - 10 mm
Exhaust loss coefficient (guesstimate) - 0.5
Spent weight - 0.6 kg
Results
Maximum acceleration - 5.4 G
Apogee - 194 feet
Burnout speed - 43 knots
Burnout altitude - 26 feet
Touchdown speed - 52 knots
Total flight time - 8 sec
I flew this for the first time at the NPL and the 'ooh!' from the crowd was quite gratifying. The small exhaust on this rocket give it comparatively poor acceleration but quite a long burn time. I think this makes it look better! It flies slow enough to watch and also see it ejecting water; most of the rockets there just went 'phut' and disappeared, only really becoming watchable again during the coast phase. Ours went whoosh! I think the photograph on the main page was taken about 0.4 seconds after launch. It looks a bit battered here as this was taken after the competition.
