# Horizontal water rocket thrust calculations - HELP

1. Jul 31, 2011

### markmywords

Horizontal water rocket thrust calculations - HELP!!!

Hi All,

I want to accelerate a 90kg body at a rate of 2 m/s2 for a period of 1 second using thrust developed from a number of water bottle rocket jets. Based on the drag coeff calculated I believe I need to develop 190N of force.

A water bottle rocket uses a quantity of water as the working fluid which is propelled through a nozzle by a volume of pressurized air.

Where do I begin? Ideally I would like to use 3 or 4 separate rockets. How do I calculate the pressures, nozzle sizes, water volume, vessel volume/sizes required?

I have taken a look at http://www.sciencebits.com/RocketEqs but afraid my physics a bit rusty. Need some help negotiating these equations!!!

Many thanks

markmywords

2. Jul 31, 2011

### nickthrop101

Re: Horizontal water rocket thrust calculations - HELP!!!

im not sure, if you use F=MA, then the force you need is the acceleration that you want 90 times 2m/s, this should give you the force that you need to apply to the rocket to get a 90KG rocket to fly at 2m/s.

3. Jul 31, 2011

### A.T.

Re: Horizontal water rocket thrust calculations - HELP!!!

Have you tried this in the horizontal?

4. Jul 31, 2011

### markmywords

Re: Horizontal water rocket thrust calculations - HELP!!!

No I haven't tried a horizontal bottle rocket but if it develops thrust and I can achieve a reactionary force (pushing against something) then I see no reason why it wont work.

Thinking about angling the jets downwards to achieve backward thrust (forward movement) - so my force required needs to be recalculated taking into account the vector??

5. Jul 31, 2011

### A.T.

Re: Horizontal water rocket thrust calculations - HELP!!!

With normal bottles you will definitely have to angle them down. Otherwise much of the water will stay in the bottle. But you could keep the bottles vertical, and attach a 90° bent pipe to them.

6. Jul 31, 2011

### markmywords

Re: Horizontal water rocket thrust calculations - HELP!!!

AT, yes realise that I need to configure the vessel so that compressed air forces out all the water and a 90deg bend good idea. I need to work out what pressure, nozzle size, volumes required???????????????

7. Jul 31, 2011

### RonL

Re: Horizontal water rocket thrust calculations - HELP!!!

http://en.wikipedia.org/wiki/Robert_Truax

I bought a few book from this man before he died, if you search for his publications, you can get a wealth of information from his books. They pertain to steam (hot water rockets) but the information might help you in some way.
If you have trouble finding anything, let me know and I will find the publication numbers.

Ron

8. Jul 31, 2011

### dmriser

Re: Horizontal water rocket thrust calculations - HELP!!!

Check out the second page of this PDF, I have nothing to do with the creation of it.

It contains some relavent equations for the burn time and escape velocity of water from the nozzle. I would suggest creating an excel spreadsheet or using MATLAB to experiment with different nozzle sizes and bottle pressures to provide the thrust that you need.

Note also that the thrust depends upon the mass of the fluid exiting, some people add soap or foaming additives to the solution to give more thrust.

You may also want to simulate the effects of using different amounts of water. Here's the link, good luck.

http://sophclinic.pbworks.com/f/rocket_equations.pdf