So the most outrageous homework you have had to "help" with so far is... ?

[kalniel]

I was actually thinking about that when I was sanding a bit off the O ring. Might have sanded a bit too much off, it was hard to get the bottle on so I kept sanding when I should have just slapped a bit of vasaline on there!

Who's homework was it again?

[DanceswithUnix]

Who's homework was it again?

Hence the word help in quotes in the subject line

She did do a lot of work on it to be fair, but some was or had to be down to me (sharp craft knives aren't something I want her handling just yet).

[GoNz0]

I was actually thinking about that when I was sanding a bit off the O ring. Might have sanded a bit too much off, it was hard to get the bottle on so I kept sanding when I should have just slapped a bit of vasaline on there!

Personally I always find vaseline helps if I can't get it in.

[k-c]

Was in flight for about 8 seconds, came down so fast the nose was buried in the ground!

Hope the kids at school have somewhere to run and shelter when it comes back in to land!

Sounds like a brilliant project though, I love these kinds of things. I remember hearing somewhere that the aerofoil device on top of lorry cabs was invented after a school project. I have no idea if that's true or not, but it would be great if it was!

[Bagnaj97]

Hope the kids at school have somewhere to run and shelter when it comes back in to land!

No no no, you just need to extend the project - parachute deployment and recovery system!

[scaryjim]

... Was in flight for about 8 seconds, came down so fast the nose was buried in the ground! ...

I just happen to have a handy spreadsheet here for calculating speeds/distances in freefall (yes, I really AM that much of a geek; plus I wanted to know how hard I'd hit the ground if I fell off an 8m cliff ).

Making some fairly raw assumptions (that it went up for exactly 4s then down for exactly 4s, it didn't reach terminal velocity in that time, etc.);

A 4s free fall would occur from a height of 78m, and the rocket would hit the ground at roughly 88mph!

Tasty

[DanceswithUnix]

Nice!

Terminal velocity I think is supposed to be about 50mph, so it won't have gone that high.

Plugging numbers into http://polyplex.org/rockets/simulation/

I set the launch pressure to 40psi and launch tube length to 300mm (guessing tube length), and it says to expect 44m apogee and 6.15s flight time. Well, the cone isn't very heavy so the rocket slid down sideways a bit so probably didn't reach the expected 50mph terminal velocity so I think it got up there OK and the extra flight time is a long glide down (or my counting seconds is rubbish and I should use a stopwatch ).

Intended launch is 100psi, which that simulation says should reach 76m, but I need to do some safety pressure tests before I put that much energy into it!

[scaryjim]

I'd guess the upward flight actually lasts a little longer than the fall back down to earth, but I'd be surprised if you didn't break 40m! Look forward to hearing the outcome of further test flights