An alternative igniter
Big Clive has an igniter here - extremely cheap, probably very reliable, but does require a 12v power source:
http://www.bigclive.com/ignite.htm
LOHAN fires up sizzling thruster
Things are moving apace at the Low Orbit Helium Assisted Navigator (LOHAN) headquarters, and last weekend we did a first test firing of the proposed powerplanet for the Vulture 2 spaceplane. Click here for a bigger version of the LOHAN graphic The thruster in question is an AeroTech RC 32/60-100NS, specifically designed for …
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Tuesday 20th December 2011 12:49 GMT Wombling_Free
Alternate igniters
Presumably the igniter is doing as simple a job as the super-fragile igniters that come with A to D class rockets you get from hobby stores.
Back in the day we used a far simpler system that was robust and reliable - a matchstick with a small piece of nichrome wire (fuse wire) wrapped over it. This was inserted in the nozzle of the rocket, 9V was applied and WHOOSH. I'd send a sketch, but I can't. We used to use such igniters for our own air-fired rockets - either rockets slung beneath a glider, or gliders with remote-triggered rocket boost. Fun stuff!
I must admit to being thoroughly underwhelmed by the noise of the G - the old black-powder D series have quite a loud roar when they fire!
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Tuesday 20th December 2011 17:13 GMT Anonymous Coward
Good idea
Once demonstrated how to set off some home-made gunpowder with a piece of brillo pad wire and a 9v adaptor. I left the idea in the capable hands of my fellow inventors - ie more 2nd year (Scottish) undergrad students - to retire to my room and read a book.
Not long afterwards I became aware that the air in the flat had a acrid taint. I opened my door to find the corridor uncommonly "cloudy" . When i reached the lounge I discovered that my friends had not "learnt the lessons taught by the British battlecruisers at Jutland" : failure to take adequate anti-flash precautions (they had left the lid off the margarine tub) had meant that a stray spark from the experiment in hand had ignited the reserve of blackpowder.
The former marge tub was gone, replaced by a sizeable dent in the melamine and underlying chipboard of the table. The breadboard served as a temporary cover against official eyes until a second layer of melamine was added during the Easter hols.
Anon for usual reasons
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Tuesday 20th December 2011 13:44 GMT horsham_sparky
Fair enough! Just don't put your electronics anywhere near it, specially radio devices (e.g GPS, radio modem etc). They typically have Temperature or Oven controlled crystals in them to ensure they can tune accurately to the correct radio bands. These might have difficulty doing that if they rapidly move between extremes of temperature
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Tuesday 20th December 2011 12:51 GMT Keller Drozdick
Good test, questionable units
Nice test, and I was impressed by the rocket performance, particularly compared to my long ago experience with amateur rocket engines in the US (Estes), which put out huge volumes of smoke.
However, thrust in grams? Really? Can you not use an anglocentric unit like the Newton at the test center in Spain? Or did you try to compose the video after a trip to the pub, forgetting mass vs. force?
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Tuesday 20th December 2011 18:19 GMT Dyspeptic Curmudgeon
Loved the opening of the video, Nice work, Good practice for the upcoming main feature.
But the sound effects have to go.... that sounded like a puny 4 cylinder Cessna 152 flying by.
If you are going to do sound, then it should at least be a jet.
Try this: http://www.therecordist.com/assets/sound/mp3_09/Jet_A10_Warthog_Pass1.mp3\
Or maybe steal the audio from here, and substitute 'Lohan' where necessary.
http://www.youtube.com/watch?v=cLv4Nhoxz5M
Plus of course, it should start with the opening bars of 'Also Sprach Zarathurstra',
I mean, gee, get with the program, guys!
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Tuesday 20th December 2011 22:47 GMT another_vulture
Temperature in vacuum
In addition to worry about hotspots, you also need to remember that convective cooling does not work very well at reduced pressure. Fortunately, in this case the total heat is in bounded because the motor quits after a few seconds. I do hope you continued to monitor the temperature for at least a minute after the end of the burn, since it takes a few seconds at least for the heat to migrate from the inner wall of the chamber.
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Wednesday 21st December 2011 09:01 GMT 8-{>
Crapperheads....
Copperheads are more commonly known as "Crapperheads". Essentially they are double sided copper clad filmwire cut in to narrow strips with one end stamped in to a zigzag crinkled shape for about 5 to 10mm and then dipped in a pyrogen. Which, I think, is mixed with carbon to make it slightly conductive/give it enough resistance. As mentioned they are notoriously unreliable.. Often fine copper whiskers from their being guillotined in to strips short the two copper layers out.
Look for e-matches like Davyfires or similar. These are the proper tool for the job.
Also there should'nt be any heat issue with the casing temp. Part of the US regs (NFPA 1127 iirc) which the motors must meet to be allow them to be sold define max external temp the motor casing can reach. Also remember that most hobby rockets of the size that take these motors use a cardboard or phenolic impregnated paper/card motor tube for the motor mount. They dont have any issues with the temperature that the casing reaches.
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Wednesday 21st December 2011 09:16 GMT Kevin McMurtrie
Need space for more thrust
That tiny jet of exhaust is probably creating a vacuum over the nozzle, like a venturi pump would. Since the nozzle cap has more surface area being sucked on than the jet has area being pushed on, atmospheric pressure is not in your favor. This rocket could chemically perform worse in space yet end up producing more thrust.
Pedantic science nazi: Why put the rocket in a sliding holder for a bathroom scale? Surely you could get the difference in measurements from before and during the test when the whole apparatus is on the scale. How much is a gram in space?
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Wednesday 21st December 2011 13:18 GMT fighne
temp measurements in reduced pressure
two things from an old instrumentation technician;
1) thermocouple connectors are different colours across the cold bridge- leading to incorrect readings
2) thermocouples need a transfer medium-partial vacuum will lead to incorrect readings
Back in the day we used laser thermometry in low temperature and partial vacuum in the ultra low fridges at Oxford Instruments
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Wednesday 21st December 2011 16:19 GMT sisk
Copperheads?
It's been quite a while since I've flown model rockets, but it used to be a weekly event. Back in those days of yore when I had time to do things like spend whole days building model rockets and chasing them down I found copperheads to be the bane of my hobby. Sadly they were all I could get around here. As if the failure rate wasn't bad enough, safety pactices (at the time enforced by elders carrying titles like 'Dad') demanded that we take a ten minute break from launching just in case the motor decided to spontaniously ignite. To be fair it did happen on occasion.
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Monday 2nd January 2012 23:41 GMT Guido Brunetti
Thrust measurement
What is the weight of the fuel? You have to add that to the measured thrust over time to get the real thrust. Near the end the real thrust would be the measured weight on the scale plus the weight of the already burned fuel since the initial "0" measurement included the fuel weight.
So if your fuel weight was, say, 500g, the peak thrust would actually have been measured at roundabout 1900 grams near the end.
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Biting the hand that feeds IT
