NPL Water Rocket Challenge, 2002
This is intended to provide a bit of information for those that are curious about quite what the Met. Research Flight did on 26th June.
What were the rockets?
We flew three versions of my Mk4b. The rocket flown before the competition and in the last round was an early version, simply the pressure vessel with a nose cone, and was there just for a laugh (and spare parts!). The two rockets flown 'in anger' used identical pressure vessels and fins, but the upper sections differed slightly.
Round One
This was the longer and heavier of the two being about 8' over all and weighing 700 grammes, dry. Directly above the pressure vessel sat the camera section and above that the parachute section. This was the smaller of the parachutes, about four feet across, flat. The parachute timer was externally mounted on this version with a fairing to comply with the 'no metal external parts' rule; although this arrangement is more reliable than the internal arrangement on the other rocket, it does carry a drag penalty. A string tied to the launcher ran up to a pin in the timer. When the rocket was fired, the pin was pulled and the timer gave about four or five seconds before the nose was pulled off, releasing the drogue which turned the rocket nose up again and extracted the main chute. The lines for the main chute pulled a pin from a three second timer on the camera.
Round Two
This rocket was about 130 grammes lighter than the previous effort as it did not carry a camera. The nose and drogue were the same as before but the main chute here was about eight feet across, flat. This is silly. I knew that but, hey, why not have a laugh? Knowing the performance of the small parachute, I assumed that if there was any wind at all I would loose this rocket and so was not really that surprised that it drifted out of the field. The timer in this case was mounted on the underside of the parachute container, just above the pressure vessel. Although this does get it out of the wind, there is a risk of the cord from the timer to the nose snagging and as the parachute section did not rest directly on the top of the pressure vessel, there is a greater risk of things moving around at firing - remember that the rocket will accelerate quite hard.
Both rockets were fired at about 140 psi about 1.9-2 litres of water onboard.
More Stuff
Instructions for building the MK4b.
Simulations of the three flights.
Pictures from the competition NPL.
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