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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

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At my wit's end figuring out o-ring seal on launch tube

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
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Onboard video: why?

Postby anachronist » Wed May 24, 2017 7:00 pm

I'm curious why an onboard video camera is required for competitions. What value does this add? I mean, those onboard videos are interesting and all, but the real proof is the ground-based video that shows the altimeter after recovery.

I'm concerned about the potential loss of equipment due to trees and other hazards that make the rocket un-recoverable. It's bad enough to lose an expensive altimeter. It would be nice to avoid the potential loss of an onboard camera too.
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Re: Onboard video: why?

Postby WRA2 » Wed May 24, 2017 9:46 pm

There are multiple reasons for the requirement of the onboard camera.

1. The onboard camera is guaranteed to capture the entire flight. (even the best ground camera operator may lose sight of the rocket)
2. It has been a requirement for almost 15 years (it would not be fair to previous competitors to have a weight advantage that would be obtained by omitting the camera).
3. The cost of these cameras has decreased significantly over the last 10 years and they only cost a fraction of what they did back in 2003.
4. Adds to the "technical challenge"

Hope that helps.
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Re: Onboard video: why?

Postby anachronist » Wed May 24, 2017 10:20 pm

Thanks for the explanation.

I thought the reason (at least for class D) might be to record the descent time to verify descent rate when one has a peak altimeter, but that reason is negated by having a logging altimeter. The reasons you listed don't include that, but I understand now, thanks.

As for weight advantage of having no camera, I find in my simulations that being too light is a disadvantage, as is being too heavy. Eliminating the camera might actually create a disadvantage depending on what else the rocket carries.

My background is physics. I just spent the last month or so of my spare time creating a spreadsheet simulation of a water rocket flight that accounts for launch tube, adiabatic expansion effects on pressure as the air expands, humidity effects, wind resistance, choked airflow of the final burst of residual air, and a number of other things. There's definitely a sweet spot for the amount of ballast you have -- and the right amount of ballast is just about in the range of electronics available today.
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At my wit's end figuring out o-ring seal on launch tube

Postby anachronist » Fri Jun 02, 2017 1:02 pm

THIS IS THE FIRST POST OF THIS THREAD. THE POSTS ABOVE ARE FROM ANOTHER THREAD THAT MERGED WITH THIS ONE AFTER A DATABASE PROBLEM AT WRA2.

I've seen the tutorials and watched the videos about installing an o-ring onto a launch tube. They boil down to:
  • Manually carve a groove into the tube
  • Join two tube
s with another tube that fits inside[/list]
The first method results in an unreliable seal, and weakens the tube.

The second method provides a better seal, but it's impossible.

Why? Because I cannot find ANYTHING that fits snugly inside a 1/2" diameter schedule 40 PVC pipe!

One tutorial on this site suggests using a 3/8" PVC pipe. NOBODY carries this product. The big-box hardware stores in my area (Home Depot and Lowes) don't sell any 3/8" PVC. The Orchard Supply and True Value hardware stores don't sell it either. A local plumbing supply doesn't have it. I can order it online in huge quantities for a huge shipping cost... and I still don't even know if it will fit. I need to see it in person.

1/2" copper pipe is a bit too big to fit. I found a 3/8" copper sleeve that looked promising, it turned out to be pretty loose inside the 1/2" PVC pipe.

None of these stores carry the required 1/8" thick O-rings of 7/8" outer diameter either, but these are easy to find on eBay or Amazon. I bought a pack of 25 for about $3.

So, how did anyone else here build a launch tube?

-Alex
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Re: At my wit's end figuring out o-ring seal on launch tube

Postby anachronist » Tue Jun 06, 2017 3:26 pm

Hmm, since the database got messed up and then restored, it looks like an old thread got prepended to this one.

Anyway, I'm going to buy a 5/8" countersink and see if I can use it as a reamer to ream out a 1/2" PVC pipe an additional 0.003" to fit a 1/2" copper tube, which has an outer diameter of 5/8". That may provide a good seat for the o-ring.

I am curious how everyone else is doing it. The available tutorials may have worked in the past, but they are not possible to follow now.
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Re: At my wit's end figuring out o-ring seal on launch tube

Postby anachronist » Wed Jun 07, 2017 9:31 pm

The 5/8" countersink did the trick.

To ream out the inner diameter of a 1/2" PVC pipe to 5/8" so that it fits a 1/2" copper pipe insert, first cut your PVC pipe perfectly perpendicular to the length. I use one of thos disc cutters for copper pipe, which you rotate around and around, tightening as you go, until the pipe is cut.

Then get a cup of water. You'll want to dip the end of the pipe and the countersink bit into the water every few seconds.

Wet the pipe and the countersink. Use a HIGH SPEED electric drill. If you try it with slow speed, it will just bind and get stuck.

Put the countersink bit into the end of the pipe and give it a burst of power. Just half a second, or enough to bore down 3 millimeters or so. Pull the bit out while it is still spinning. If you let it come to a stop inside the pipe, it can get stuck.

Use your finger to clean out the burrs in the pipe. Wet the pipe and countersink again, and repeat until the countersink bit goes about 2-3 mm below the end of the pipe.

Avoid the temptation to go too fast or too long in each burst. If you do, the bit will get stuck in the pipe!

After you're done, you can cut a piece of 1/2" copper pipe to the length you need to fit into the bored holes. The fit will be easy, but snug enough that PL adhesive should create a good seal. Remember to lightly sand the pipe where you are going to glue it, and squirt some water on the PL adhesive (because it cures with water) before you insert the copper pipe into the PVC pipe.

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