Water Rocket Drag Race ??

Having had a number of recent successful Water Rocket launches, I thought it might be a fun suggestion 
              ( if agreed to and permitted by the Club ?? )

                     to have a   Novelty Drag Race

Water Rocket   vs    (whoever might be interested)
If the Club thinks this is a good idea, the Challenger should know that I estimate that my water rocket to go about 150 feet 

That said, maybe it's too low of an altitude to make sense OR to be of any interst.
Anyway, it's food for thought; any comments folks ?

I intend to be at the Aug 17 launch should anyone be interested.
Dick Pelle



 

I'm stoked to see how well your water rockets have been working at the last couple of launches.
I expect they'll continue to improve on performance.
I loved playing with water rockets as a kid. I had a virtually unlimited supply of "fuel" thanks to the 18' aboveground pool on my parent's backyard.
The temptation even then was to experiment with different water and pressure combos to see how well they would fly. It wasn't long before I discovered that more pressure makes for higher flights. Eventually, of course, one of my rockets burst from applying too much pressure.
My concern here is shrapnel resulting from a rocket bursting under pressure. Those 2 liter soda bottles don't seem too hazardous, but suppose someone uses more solid material such as PVC or composites in order to contain more pressure? Such material might fracture and send chunks of itself shooting toward the crowd.
Not trying to be a buzz kill here but something to think about.
Do please keep working on your designs, though, and maybe one day I'll have a go at it. There's a lot of potential in this area.
Rick

Hi Rick,
Thanks for your comments.                                   

You are 100% CORRECT in questioning the burst pressure of a water rocket. That was my major concern when I first began building water rockets;   namely safety.

Over the past years I’ve  “googled” what is the            burst-pressure of a 2-Liter bottle?

As I expected, the responses were all over the map (be they calculated, emperical, opinion etc. etc. ) with numbers ranging from 135 to 195psi.  That’s a large spread. 

My pressure vessel…..is made of two 2-Liter bottles spliced together. 

My launch ‘fuel ratio' is 1/3 water 2/3 air for optimum altitude.

With Safety in mind:

(a) I set my launch pressure between 90 and 105 psi 
(which I chose, keeping in mind the  LOWER 135psi value above) 

(b) When I first make my pressure vessel (before I use it in a rocket) I do a hydrotest on it to 120psi.  

Relative to hydrotesting, I took my initial concern of BOTTLE burst pressure up one level……to include concern for that of the SPLICE burst pressure.   I’ve read lots of articles which said, if done right, the splice burst pressure is as good as, or better than, the bottle itself.   

The phrase above that stands out like an elephant in a room, is…….”if done right”.                         
Having  followed the instructions on how to do a splice, the only way I would know “if I did it right” would be to test it.

My hydrotest-pressure is ABOVE my launch pressure and BELOW the low-end burst pressure.         

As an aside:   A hydrotest is filling the pressure vessel with close to 100% water then pressurinzing it.   
An explosion with basically water (which is incompresible) is much less violent than testing the pressure vessel          with just air.

So I feel I’m on the conservative side of safety.

Rick, as to your comments about concern from      shrapnel from high pressure water rockets made of PVC or composite material (instead of 2 liter plastic bottles)
is also 100% CORRECT.  I read about the World Record for water rockets (3,200+ altitude, with over 1,000 psi)  and should that explode, I agree, shrapnel would be a         deep concern.   

That said, at 80 years old, I have no intention of using anything other than 2-Liter plastic bottles.

Again, thanks for your comments. I’m all ears when it comes to how to improve safety.   Also, as you can imagine, I enjoy talking to people about  my water rocket and encourage questions, suggestions and criticisms from all.  

Dick Pelle