Thermite ignition tests

[Disclaimer: I assume no responsibility for use or misuse of this information. It's available elsewhere on the Internet and I'm simply sharing my engineering interpretation of that information. Use these materials with great caution. Do not mix reactants until just before use. Do not mix or ignite them anywhere near flammable materials. Do not look directly at the reaction as harmful UV radiation is emitted. Be careful!]

If you watch Mythbusters then you'll likely have seen their experiments involving thermite. According to Wikipedia Hans Goldschmidt discovered and patented this thermite reaction in 1893 and used it to both cut and weld metal. These powdered mixtures require very high ignition temperatures (2000˚F) but then burn at 4,500˚F swapping oxygen, producing molten metal, and releasing a bunch 'o' heat and UV radiation. Common reactants include elemental aluminum or magnesium with metal oxides like copper (II) oxide (cupric oxide) or iron (III) oxide (ferric oxide).

Many folks in high-power rocketry are successfully using thermite as a source of instant ignition of even the largest rocket motors using a guideline of roughly 1 g thermite per 1000 N•s of total impulse. I'm intrigued both by the reaction itself and its utility in this hobby so I decided to give it a try. I ordered 1 pound each of aluminum powder, cupric oxide, and ferric oxide online. I'm quite certain I overpaid as well so you should definitely compare prices on the Internet(s). :) I was finally able to use my chemical engineering degree and calculated the appropriate mass ratio of the reactants using stoichiometry and atomic and molecular weights. For the aluminum + ferric oxide reaction it's:

Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat + UV

2 moles of Al = 26.98 g/mol * 2 moles = 53.96 g

1 mole of Fe₂O₃ = 159.69 g/mol * 1 mole = 159.69 g

So the mass/weight ratio is almost exactly 1:3 Al:Fe₂O₃

For the aluminum + cupric oxide reaction it's:

3CuO + 2Al → 3Cu + Al₂O₃ + Heat + UV

CuO: 79.545 g/mol * 3 mol = 238.635 g
Al: 26.981g/mol * 2 mol = 53.962

Mass/weight ratio: 4.4:1 CuO:Al

I set up my video camera intending to share the clips here but the ignitions were so fast that they only show up on about 4 frames at 30 frames per second. As such I've simply grabbed the key frames and assembled sequences for both tests. This camera method also eliminated the need to directly observe the reaction although the emitted UV might have improved my tan a bit. Here a single electric match ignites 0.5 grams of a molar ratio of ferric oxide + aluminum powder thermite:

Ignition was fairly rapid but continued to sputter for about 30 seconds afterward. In this second experiment I again used a single electric match to ignite 0.5 grams of a molar ratio of cupric oxide + aluminum powder thermite:

This second combination appeared to be far more energetic and burned to completion without sputtering. Most folks have been using this cupric oxide+Al combination but I wanted to try the classic ferric oxide+Al combination as well. It's clear that cupric oxide works way better so I now have my empirical answer. Again... exercise caution!!

CD3 ejection ground test for M750 flight

It worked perfectly with only 12g of CO2!

CF minimum diameter build progress

So I've made some progress on the Viciously Mean Machine and unnamed 38mm spike below. I've applied Cotronics 4525 high-temperature epoxy fillets to all fin/body interfaces and laid up tip-to-tip carbon fiber reinforcement on all fin pairs with Aeropoxy. I've also post-cured both tubes in the oven for 1.5 hrs and, let me tell ya, those fins aren't budging even 1mm!!

This week I plan to build/reinforce the payload sections and couplers and start the finishing process. Both should be lookin' purdy by PB.

M750 for EM-SEM-FITY

One 9,345 N•s, 14 second burn M-motor now in stock for Plaster Blaster:

Thunder & Lightning mark II pix

Thanks to Jeremy Rich for these shots of the I357/I211 flight covered below!

A reminder that... yes I did get all parts back intact. I don't buy into miracles yet I'll admit that this vessel should not be sitting in my garage ready to fly again immediately!

Even more carbon fiber success

I was finally able to lay up two new 38 and 54mm minimum diameter designs with 2 wraps of 6 oz carbon fiber cloth and cure them in 1 hour with a nearly perfect finish. The key seems to be plugging in the curing oven right when you place the part and then unplugging at exactly 1 hr. I then let both tubes cool down in the oven for about 1/2 hr then pulled the Mylar™ film and release fabric off while they were still warm to the touch. Here are the finished tubes and I'm tacking the fins on with JB Weld Quick:

I have one batch of high-temp black epoxy left and I want to use it on both designs so all fins need to be tacked down and ready. Knowing that Derek Zoolander stands 5'6-1/2" tall I've built this comparison to my new designs for scale:

I really shouldn't even be talking about these designs because they're really-really, really-really, ridiculously good looking.

Lucerne launch report, 9/12/09

I arrived on the playa at about 8:45AM yesterday to extremely calm conditions. Jack Garabaldi had already opened is awesomely stocked What's Up Hobbies store and I dove right in buying components and new motors. The ROC folks were just beginning to set up the range but this seemed fine due to the complete lack of wind.
I'd begun prepping my main Thunder & Lightning mark II flight the night before to save time on Saturday morning. It still took another hour to assemble the motors, finalize the electronics and black powder charges, pack the 'chutes, and load up the tracking beacon. Just as I was finishing the preparation i felt the "breeze" kick up. This rapidly increased to 10-15 MPH winds so once again Mother Nature enjoys throwing challenges our way. Rockets and wind simply don't mix. I'd intentionally chosen a punchy booster motor, the AT I357 which burns for 1 second, and also shortened the sustainer's AT I211 ignition delay to only 1 second after booster burnout. Both of these tactics targeted minimal wind arcing to improve the likelihood of success.
I got everything set up on pad 21 but then asked the launch control officer to wait for a lull in the wind before launching. When finally launched everything on the I357 boost looked good. The one second delay before the I211 ignited in the sustainer felt more like three seconds. Then the I211 chuffed and conveniently popped off the booster section thus eliminating flame damage. After another chuff the I211 finally pressured up when the rocket was roughly 40 degrees from vertical. Oops. It powered off into the desert blue and, after I lost it visually for a bit, I again saw it drifting downward under the main 'chute. I had to walk roughly 1.2 miles out to retrieve it and the whole time I could see the parachute popping up and dragging my beautifully painted rocket along the lakebed. Here I've tucked that main back in and shot a quick photo indicating the distance:

Nice. Did I mention I'm not a huge fan of wind? I was surprised to see that the main parachute ejection charge had not worked. So why had the main popped out? Dunno yet but I considered myself very fortunate and would analyze the next day.
After gathering up both the sustainer and booster. I started cleaning the cases and it became very apparent that the wind wasn't planning die down any time today. I packed up and headed to the Pomona Fairplex to view a Dock Dogs competition.
Fast forward to today, Sunday, and I was able to disassemble the sustainer's electronics to analyze the near failure. I was surprised to see that the 9V NiMH rechargeable battery had bloated and warped in several directions. Also the electrical tape had burned a bit so something must have shorted after the drogue charge popped and killed the battery before the main charge could kick off:

The force of the drogue ejection must have fortuitously popped the nose cone and released the main 'chute thus saving the rocket to fly again.

Based on some reading on the ARTS2 altimeter I rigged up the above battery connector to bypass the current limiter and run both the flight computer and pyro charges off of a single battery that fits in PML's CPR3K ejection system. I've flown this configuration successfully several times but took a bit of damage on the battery connector cap last time. I thought the electrical tape would have sufficed to insulate the connectors but either that or one of the battery wires must have failed. I'll build another bypass connector and replace the battery to get back on track. I should also note that the I211 I used was manufactured in 2001. I've never had issues with older motors when ground starting but another important precaution in the future will be to only use fresh Aerotech motors in upper stages or air-start clusters. I think the instant-on nature of Cesaroni motors also lend themselves very well to these air-start configurations.

I wasn't able to take any flight photos but a flyer named Jeremy Rich did snap some and gave me his card. I e-mailed him this morning and look forward to hearing back. I'll post his photos here when I receive them.

Thunder & Lightning mark II

Several years ago it took me 5 years to build and fly my first PML Thunder & Lightning. I was psyched on the paint job at the time and my amazing and beautiful ex took this photo for me:

Unfortunately I set the upper stage timer for three seconds rather than 0-1 seconds and that beautiful rocket powered into the hard desert dirt at about mach 1 on its maiden flight. That flight also killed my prized AltAcc2A altimeter. Undaunted I lucked out and replaced that altimeter with the 2C version and purchased another T&L kit. While I had this kit lying around for about a year and a half I finally started it and finished the sustainer build and paint in under two weeks. It'll look very much the same as my first build above with one exception: car paint!:

Now that's some gloss!! This was my first and only paint job in the paint booth below before I realized it wasn't going to work and abandoned it. My final option to master car paint will require adequate ventilation in my garage and I'll park my car outside while I paint. The 500th time's the charm right?!
Finally I should note that, while I'm leveraging the original booster, I still have parts to build a second booster for a 3-stage version:

I'm a bit surprised that it remains totally stable without additional modification. That should be a fun flight if/when I attempt it.

Spray booth as dust buster?

It's seriously frustrating to build something for weeks or months then only to fail on the last step, the paint job, due to dust. I bit the bullet and built a semi-permanent paint booth in a spare area of my house. Fisheye lenses make indoor photography a snap and here's a side view of the booth:

Here's the entrance view:

And here's the lovely view I'll enjoy while spraying fumes:

That fan is very powerful and pulls the 4-mil plastic walls all the way inward with it's high setting. I think it'll remove most of the fumes and overspray particles on its low setting. I plan to try some clear coat as a test this weekend and this setup should nail the problem.

L610 motor build in only 1 minute!

Clearly this must be a new record:

Man I'm fast! :)