WaterWar.net

Right, this is going to be a strange request.

Basically, for a uni project, I have to design a system which can be put on an aircraft in order to allow it to fight fires - a water gun on a larger scale!

My idea is to use 2 tanks - 1 of compressed air, 1 of water/fire retardant. I'm looking for a way to be able to calculate how much air, and at what pressure/compression ratio it needs to be at in order to give a given flow rate of water out of the tank. I think the main problem will be that the air pressure will drop as it expands into the larger water tank, so I need to know how I can compute this drop.

I understand this is a water gun forum, but I'm sure the physics is similar, just on a slightly bigger scale!

Any help would be MUCH appreciated!

SSCentral should be able to help you out at least a bit.

http://www.sscentral.org/physics/equations.html
http://forums.sscentral.org/showthread.php?t=5149

Just to mention Super Soaker Central is now in archive mode, everyone from that forum moved over here, so those topics are just for reference. It's a shame Ben doesn't visit the forums much anymore, he'd know how to do this for sure.

Thanks for the links, you have no idea how much better that explains things than previous sources I've looked at!

I'll have a try with some numbers later and get back.

I think most fire-fighting air craft use gravity fed release systems, but I may be mistaken.

Yeah, I think so.

If you used a regulator, you wouldn't have to worry about pressure drop, like on the SuperCAP. http://www.sscentral.org/homemade/supercap.html

Gravity would make the most sense to me for most applications too, but it wasn't asked for.

And yeah, I was about to mention the use of a regulator before martianshark ninjaposted. This also gives you a lot more power to work with along with no dropoff for most of the air release.

3rd/4th year engineering project?

I'd also go with the regulator, but you will obviously need the air supply tank to run at a much higher pressure than the other to provide maximum output for longer (that or you make that tank ridiculously larger than the other).

Out of interest, what kind of nozzle(s) were you thinking of using. I'm assuming you'd want to spread the stream to cover more area, rather than using a narrow stream, either by using many nozzles, or one fan-shaped nozzle.

Thanks again for the replies.

The main reason not for using a gravity feed system was because it requires a fairly large 'hatch' to come out as fast as we would like, and this means there is a lack of control of the flow coming out. We want the retardant to come out in a fairly narrow stream as we're aiming at it being more able to contain fires by dropping retardant in strips around the fire.

As for nozzles, it's something we haven't really looked into, but as I said, we'll likely use a fairly narrow nozzle (in fact, 4). What sort would you recommend? I'd think maybe one that has the sort of honeycomb structure to try and keep the water as streamline as possible.

An issue we may have is that we'll be using a cylindrical tank for the water and it will lie flat along its long axis and the exit nozzle will be at the middle of one the ends for structural reasons. Will this cause issues once the water level goes below the hole?

You could just use one big nozzle. If you want it to spread slightly, use several smaller nozzles. But make them close to each other.

A diagram of what you're planning would help a lot.

Set it up like a "clunk" style r/c aircraft fuel tank- there's a very flexible silicone line with a weighted intake that flops around the inside of the tank to keep it in the fuel or in your case water- you could also have a dual-layer setup like WWII-era fighters with the actual water container being a bladder of some sort and then you could pump your air into the metal tank around the bladder- that would also work handily to keep from running dry.

A single honeycombed nozzle could work well for a wider but still concentrated stream of retardant.

Anybody else thinking what I'm thinking?

atvan wrote:Anybody else thinking what I'm thinking?

How to dominate a water war:

Step 1: Be that dude with the aircraft.