I've got one in the workshop which the gradweans think is brilliant. I did buy it and it wasn't expensive. I'll try and take some photos and post them on here but they will be inside on the bench – it's gusting over 60knots here just now

Hi Jacob ,

(1) If your water rocket has any significant amount of water in it then the acceleration characteristics given by a plain nozzle are best you can do .

This is not quite the place to discuss projectile dynamics but in essence take off is at maximum weight and initial thrust is maximum . As water is disipated weight comes down and reduced air pressure reduces thrust .

Given a bit of luck it all balances out for itself .

(2) Need to decide though whether you are building a water rocket as such or a powered aircraft – the design rules are very different .

(3) For a water rocket launch initially at a steep angle from horizontal and let rocket follow a modified parabolic path for maximum range .

(4) For a powered aircraft launch at a much more shallow angle .

I don’t see any practical problem in fitting normal wings . The wing load is going to be very small and speeds are going to be definately well subsonic so ‘barn doors ‘ will suffice and can’t see any attachment problems . May need to be very light weight though .

(5) Take care with this project – it’s only toy size I know but there is still potential to hurt someone quite badly if things go wrong .

Get back to me if you have specific questions .

Regards ,

Michael Williams .

Hello again ,

Conventional thin aerofoil rectangular planform wings are probably all you need .

Do some numbers –

if you know the acceleration levels and wing load you can make definate decisions .

Needn’t be all that accurate – just ball park figures .

Regards ,

Michael Williams .

Jacob

Have a look on Utube, I seem to remember that they have videos of bottle rockets that have achieved altitudes of around 1000ft and descriptions/walk throughs showing launch rigs, release mechanisms, nozzles etc. Also shown are multistage rockets, using parts of a standard garden hose connectors that has been modified. Some of the launch videos are very impressive with a couple that that burst/exploded prior to launch completely destroying the launch rig.

Good luck

Martin

PS

Douglas, when one thinks what these bottles are designed to go through, hot environments and violent shaking and that before the kids get hold of them, I suspect they are designed to take pressures well above the 'normal' whatever that is. That said I agree with you that caution is required, especially after seeing the videos of some of these things exploding during pressurisation. Some rocketeers actually join bottles, cut and shut, by gluing a band made from another bottle around the join, to me that's inviting catastrophe.

Edited By Martin W on 23/02/2014 11:52:57

Hi

If trying to use the rocket in a glider then there is going to/or is likely to be a major change in the centre of gravity as the water is expelled. Also if the angle of launch is too shallow and the acceleration low then there could be a possibility that the water will not be expelled when the pressure is at its optimum thereby reducing total effective power. In the extreme all the water may not be expelled and could just become a load to be carried during the free gliding stage of the flight.

Are you allowed to any form of active control i.e. electronics, on the model? If so then a simple multi-axis accelerometer and servo system may help to stabilise and extend the glider phase.

Cheers

Martin

This is just a guess. Launch as a mortar for max. hight, at this hight the speed is nil for a moment. Have a mechanism to unfold wings and glide to earth. Balance before launch to suit empty bottle.

launching at a shallow angle might result in the air escaping through the nozzle, while there is 25 degrees worth of water still in the bottle. You need a water pickup tube that is at the bottom of the almost horizontal bottle. Also as mentioned massive change of C of G. Years ago I saw a design which was a model air craft that basically had a second smaller one pivoting on its top. The idea was that changes in the relative trim between the two resulted in the elevators on the main wings being tweaked by the action of the smaller one, so as to keep level flight.

At School we had a craze on plastic rubber band launched delta planes. When launched because of the very high acceleration they would loop, then level out and fly normally. Very robust and long lasting. I think most ended up in the roof gutters!.

Frank

I'd make a glider basically, gain maximum altitude, as quickly as possible, as the water is expelled the COG should shift to the front, ie. gliding angle, balsa wood is your friend here – I doubt it will snap, as others have mentioned the initial weight of the water is going to restrict acceleration,

The wing span obviously wont be large enough to support the weight of the water, but as it all exhausts and then levels its light weight gliding all the way.

I wonder if you could discharge the water bottle using a sort of level/pressure trigger & maybe a small weight could control small ailerons to keep her level…. I'm probably the king of impossible ideas, but hey, man's been to the moon and back……..

The direction of the wind will be a major factor in gliding, I guess you need control of the direction you launch in

Mylar or basically cling film .

Jacob

Any merit in using carbon fibre or similar composites in the more highly stressed areas. Some time ago I got hold of some thin walled tubular offcuts, about 5mm diameter, and while being very light they were almost indestructible.

Martin

PS

Plenty on Ebay at a reasonable price.

Edited By Martin W on 25/02/2014 14:05:40

As a kid I used car valve rubber thing..just fitted a well known washing up liquid bottle neck…add water add foot pump..and when the bottle feels the urge to fly..no release just when grip fails. ..best results found for quarter fill..but certainty discharged all reaction mass “in one”..13 mm nozzle..