1/2" PVC motor updates

[joshb]

I've been doing some more static testing and have uploaded a batch of videos. Details and results are in the videos and attached descriptions on YouTube. The longest video is 2 min 19 secs.

This is my experimental rocketry video playlist:
http://www.youtube.com/view_play_list?p=97EE5FE286E611ED
The most recent videos are near the bottom.

The goals of these tests were to practice making fuel and different formula and methods and at the same time experiment with the behavior of PVC motors. I'm not attempting to "go big" so that I will minimize CATOs or other bad things while still learning. A side effect of this is many of my tests are long burns with low or no thrust, which lets me see what happens to PVC after long exposure to high temperatures (if not high pressures.)

Interesting things I learned from this series:

• PVC starts to get soft during burns as short as 15 seconds
• The PVC will reharden and can be reused (with caution), as long as you can still fit fuel into it. In a real rocket the motor mount may keep the PVC straight while cooling.
• My motors seems to lose around 2 grams after cleaning vs. pre-test weight. This doesn't account for build-up that I can't easily remove so it could be more. These motors weight 50-60 grams unloaded.
• The only CATO (Test 5) was due to using plastic cement instead of PVC cement and having a really crumbly fuel batch.
• Clay nozzles last longer than PVC.
• Starting with Test 8 I tried what I believe is Dan's flexible fuel method. This works very nicely and is easier for me to pack into the small motors and cases.
• The largest burn measurement I have so far is about a B3, though I think I can make a D or E in these motors. I'll need a larger scale though.

 

[joshb]

Test 11 completed and uploaded. Good test with surprising result: PVC glowed! No deformation and only 0.2g mass lost before to after the test, so I can reuse this.

The fuel was a single 24g fully-cored grain. It looks like as the fuel burned closer to the walls the chamber fire was intense enough to be visible through the PVC. The nozzle end started glowing about 1/4 second before the forward (bottom) end, making me think that ignition traveled down the core of the grain in about the same time. It stopped glowing in the same pattern. The clay nozzle area didn't glow (top 20 mm of motor.)

During the peak thrust the start of the plume looks about the same width as the motor, which I'm guessing shows underexpansion. The nozzle was 1/8" throat to 1/4" exit.

This motor simmed as a low F with max pressure of 3000 psi (assuming simultaneous ignition.) I didn't use my test stand since I suspected the motor would overpower it plus I was afraid this motor might explode.

Here is the full res version (9 meg):

Look for "save file" link in bottom right:
http://www.2shared.com/file/3706532/e186bada/PVC_Rocket_8-3-2008_Test_11.html

 

[Eagle]

Awesome! I'm glad it worked so well.

Would it be worth it to add a thin coating to the inside of the pvc pipe to protect it from ignition and make the chamber easier to clean. In that coating itself would be easier to clean/replace than bare pvc. Though just replacing it after a few uses works too.

 

[joshb]

It's pretty easy to clean anyway by poking and scraping with a dowel.

I have done some motors with fuel grain loaded into a cardboard tube, which is then loaded into the motor, rather than directly casting the fuel into the motor. In those cases there was some burnt paper leftover that cleaned out easily.

Yes, replacing it is typical too. Usually when something melts, but hopefully I won't have that problem too much more.

 

[joshb]

Test 12 and 13, launches:

 

[Eagle]

Nice. Any estimates about performances the last too launches?

One more thing, are you using any recovery methods, or just lawn darting?

 

[joshb]

Two estimates:
1) Fast
2) High

:speakcool:

Actually I have simmed the flight and took some crude measurements from the first few frames of each launch, and I think these rockets peaked somewhere between 700 and 1000 feet. The second one had more fuel and burned a little longer, so maybe went higher than that.

If one reached 700 feet, then the velocity at burnout would have been about 150 mph, and 1000 feet would have required 170 mph.

No recovery possible for these. I did try tying a string to the sticks but the string broke on liftoff. That's why the second rocket seemed to be delayed or stuck for a moment.

 

[Kyle]

Saw on youtube someone send a rocket up to 30,000 Feet.
I suggest you do a two stage rocket.

 

[Sherrif of Nottingham]

Sweet!!! They went high! Dang!

Um, if you really want to recover them you could try a battery powered LED. Or painting them a bright red color.

 

[joshb]

Test 14, 15, 16: