How Weather Affects Performance

[marauder]

It's well known that wind can have a major effect on range. I am curious, though, if humidity, temperature, dewpoint, or atmospheric pressure can affect stream speed, stream coherency, range, output, or shot time. I would imagine that streams would fly faster in warmer weather since molecules are more spread out when they are warm, but that is just a guess.

[SSCBen]

I can think of one thing you've missed: the performance of water guns is pretty much irrelevant when it's raining.

Humidity, temperature, and atmospheric pressure will not affect water gun performance significantly because they don't vary enough to do so. Water's density is more or less independent of pressure and temperature in the range of conditions where you'll survive. Atmospheric pressure doesn't vary enough to change the pressure differential between the water chamber and atmosphere. Humidity probably has no significant effect on performance at all (or at least I can't think of any one right now).

The main things we should focus on in performance are water pressure (and how it varies through the shot), pipe and nozzle diameter, and the quality of the flow paths (specifically, how liable they are to generate turbulence). If you include the possibility of adding glycerin or some other additive to the water, consider the effect of water's viscosity and density too. Wind will blow streams around too, as you said. So unless the weather affects these things, weather won't change performance much.

I don't know that much about the actual break-up and atomization of water streams, but I work with some guys who do, so I'll ask them about how wind could change the atomization.

Edit: Here's Wikipedia about the mechanism that breaks streams up: https://en.wikipedia.org/wiki/Plateau%E ... nstability

It's somewhat technical, but it makes me think that wind might cause the streams to ripple and break up because of that.

Edit #2: Here's what appears to be a good review article about research into stream breakup: http://sscentral.org/Lasheras_Hopfinger_2000_ARFM.pdf

It's very technical, though, so perhaps it's not for everyone. But someone might appreciate it. (I haven't read it, but it appears to address the wind issue too. When I get the time and motivation I intend to read a lot about this to make better nozzles.)

[isoaker]

I more-or-less agree with Ben. There may be, at best, some effect, but with the variability inherent in a basic shot, not sure we'd be able to really see the differences.

[SSCBen]

The surface tension of water varies with temperature more than I would have expected. I'm not sure how strong an effect this'll have on water gun range, but it's worth mentioning.