Help me gas dynamic stabilization, you are my only hope!

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Actually, that wasn't so much a statement as it was a question about whether I was correctly identifying the stabilization mechanism involved.

Anyway, apparent success by others using that technique which provided stability in at least the powered portion of flight, the portion anyone should be concerned about, led to photographs of a number of different models appearing on-line with no "unsafe - don't build this!" warnings and I'd hope that would be enough to convince your RSO to allow a low power motor launch on an away pad.

Dude, when it comes to model rockets you are like the Dos Equis most interesting man in the world, your questions are the answers!

When Winston talks, E.F. Hutton listens!
 
I ignored your question. Not because it isn't a great one but because I don't know. Dean Black, the author of the Apogee article, would be best source for an answer but he has dropped out of sight. I tried him three different ways and didn't get a response. Hope all is well with him.
Tim VanMilligan of Apogee is an aerospace engineer who wrote those dynamic stability articles in the Apogee newsletter, so he'd probably know.
 
GDS might look good on paper, but getting it to work well in the real world of model rocketry might not look so good, especially in the beginning test flights.
Yeah, there are a huge number of variables in the rule-of-thumb general design rules and unless a formulaic method can be used, that means tons of experimentation changing one design variable at a time. That would be a great project for a NAR tech report.
 
Presenting the Saturn V, SA-666. You can read more about it here. I simmed it in Rocksim and it might be stable without any passed gas. If we had a long 1/4" rod, it could fly on an F15. I bet it might spontaneously disassemble on a G76. Oh well, I want to fly my Inductor again before I decide so August is the target launch date. Criticisms and jeers are welcome. :grin:

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Presenting the Saturn V, SA-666. You can read more about it here. I simmed it in Rocksim and it might be stable without any passed gas. If we had a long 1/4" rod, it could fly on an F15. I bet it might spontaneously disassemble on a G76. Oh well, I want to fly my Inductor again before I decide so August is the target launch date. Criticisms and jeers are welcome. :grin:

Super cool, looks good for a test rocket. A nice F15-4 or even a "naughty-fied" F15-0 if needed. A six foot 1/4 inch rod from the hardware store and you are golden. Could go with an internal lug on these. Just a question of burn and soot. If it works there can be all kinds of ways to hide the intakes and gap. Could also be cool on rockets with big inter-stage lattice works. Just go up to the guy with a traditionally built one with a big motor and tons of nose weight and challenge him to a pink slip race based on efficiency, a true rocket science challenge. If it could take off with a short rod (or no rod at all) that would be awesome dude.
 
Thanks. I'm pretty sure our club has longer rods. My latest thought is to use something like an F26 and use whatever old rod is set up. I had considered an internal lug but just slapped it on the outside for this one. The tongue depressors could go inside too for that matter. The inside of the induction tube isn't treated at the moment, but I might fix that before it flies.
 
Presenting the Saturn V, SA-666. You can read more about it here. I simmed it in Rocksim and it might be stable without any passed gas. If we had a long 1/4" rod, it could fly on an F15. I bet it might spontaneously disassemble on a G76. Oh well, I want to fly my Inductor again before I decide so August is the target launch date. Criticisms and jeers are welcome. :grin:
Very cool looking. Do you have plans to make a video of the launch?
 
I generally don't try on launches that I want to watch as I will both miss watching it and miss most of the flight on thw video too. I will see if I can wrangle someone else to shoot the flight.
 
If you can't dazzle them with brilliance, baffle them with bull#$%! The key to dealing with any jack-booted thug like the Pad Fuehrer is to stand strong, be confident, and spout just enough BS that they believe you know what you're talking about, but not so much that they think they're being played. This technique has even been known to work on the JBS' superior officers--the dreaded man in a dark suit carrying a clipboard.

I suggest memorizing four sentences verbatim from the Apogee article. Spout these off at the appropriate moments, then wave the article at the PF. Maybe exaggerate slightly the track record. If the worst happens, blame Apogee. I fear mentioning Krushnik may be overkill. Good luck!
 
Unfortunately, when dealing with the guys having graduated from CU and Colorado School of Mines engineering schools, rocket science talks and BS walks. If I use BS science it is just a vain attempt at comedy, maybe if I can get a laugh they might be in the mood to see if it works or crashes, but only if the conditions are right. The is no fooling the Pad Fuehrer, he is like a rock. Have seen several kids and club members walk away in tears, their rockets having been rejected. Most have been fixed on site, or have gone through the appeals process or modifications and flown at the next launch. Some rockets get banned and unbanned, others stay banned for life, kinda like Pete Rose. Will Pete make it into the Hall? Will a Cosmos Mariner ever get a a pad assignment? Who knows.

Never blame Apogee, Flis Kits, Semroc, or any of the Pad Fuehrer's other favorites. Blaming Estes or AT is fine and in rare cases even Cessaroni. Blaming the manufacture is a sure way to get a chuckle from the Pad Fuehrer, but he might just be laughing at you. No excuses for unstable rockets, just accept the harsh consequences and move on. Don't do the crime if you can't do the time. For oddroc flyers it is a hard knocks life. Have to build up your street cred, get your props from the MAN, or else he will put you down.
 
I am happy MDRA is largely Pad Fuehrer-less. When I walk up they generally just shake their heads and sign off. No fins? No problem! They have on occasion exiled me to a further away line of pads or 'recommended' the rod/rail orientation. I actually catch more crap when I bring up a 'normal' rocket. I say, who's to say what's normal?
 
You do get familiar hanging out at the back pads, and until GDS is proven it is far far away. The Pad Fuehrer is in some ways is like Darth Vader, he is more forgiving than the Emperor, so I think I am still in good graces, and I don't remember if he was there for the Easter Egg disaster so I might write it off as Hearsay. After so many of my oddrocs he has also mellowed a lot, sometimes just sitting back and watching the show.

For GDS a good strategy might be to play devil's advocate and use reverse psychology. Just put the rocket in each guy's hand and say "no way this thing can fly" and "GDS is all just a bunch of Huey." Then they might get curious and defend the cute little GDS rocket that could. Let them argue all the positive rocket science points about GDS and then I can be all grumpy and negative.

At least in the Saturn mode it has nose weight where I am almost certain it will be stable off a long rod. If it flies good then in the Titan mode it still may need a bit of nose weight. Then shorter rod - then less nose weight until GDS Nirvana is achieved.:smile:
 
At the possible expense of a tube fin or 3fnc cluster flight, I am putting the Saturn on the lineup for this weekend. Should it go before the finless Inductor or vice versa? Decisions, decisions.
 
It depends on the weather. If it is dead calm the nastiest one goes first.

It depends on my gut feeling. How much scare can I stand? With those tiny fins is the Saturn just another finless inductor? Does it really make any difference?

You may set up some wagering on a successful flight. The odds may change depending on flight order.

What is the crowd hollering to be flown first. They want to see a good crash.

Keep the prettiest for the finally.
 
Well, I flew both my finless Inductor and ducted Saturn V, SA-666 today. Here are the reports:

Inductor on an F35-4 - This flight was longer than the previous but ended the same. That is, it was stable off the pad, got a little wobbly at the end of the burn, and the went head over heals during coast. So, it appears induction stabilization is working when a lot of exhaust mass is flowing. However, at best you don't get much altitude because there is no coast phase. This makes it a poor use of an F motor IMO. I was surprised that the induction tube is sooty but not burned. I got a very bad video of the launch, there should be a better one coming in a few weeks.

Saturn V, SA-666 on an F44-4 - This was a wobbly flight that almost was lost to the soy beans. This model must have either been really draggy or Mr. Krushnik was at work. It didn't get any where near the altitude that it should of. On this one also, the induction tube was just a little sooty. However, the paper nozzles hang into the line of the tube are a little worse for wear.

That Saturn is probably retired, but I'm going to build another. The new one is a slight upscale to I can use mailing tubes (3.1" OD). I am thinking that the induction tube will have an internal cone, starting at the full ID and ending up at 1.5-2 inches on the base. Or maybe not, who knows?
 
Great reports. They flew with out serious bodily injury so it was a success! Glad to see you are building a new Saturn, it will be a New Hope for GDS rockets. Hopefully perfecting GDS won't take as long or involve as much effort as the Empire had to put forth in getting the Death Star to work, and rumor has it that there is still a fatal flaw the Emperor is waiting for the Jedi to discover.

Substantial lack of power sounds like Krushnik at work. More Holes? The F44 is a lot of power fast, maybe like an F-24???? The perfect balance of all GDS variables must be out there, but it is harder to find than that rebel base.

Good to hear about the lack of burn. That at least bodes well for the future.
 
Thanks. The Saturn surprised me. It had a wider gap and upper vents. I do agree with you assessment of the motor thrust. I generally don't have lots of candidates lying around and wouldn't want to order any special. Maybe I'll try the Estes F26 (?) if Hobby Lobby has them.

I hope the forthcoming video of the Inductor catches the whole flight. There is a poor video in this album, that at least shows most of the stable flight.

It appears, on a sample of 4, that these rockets are pretty safe. If stable, they go up. If not, they slough all their energy in the immediate vicinity of the end of the rod/rail.

When does yours go up?
 
July 18th and the weather is looking good. Fear of Krishnik is why I opened mine up a bit after the mindsim fueled by the Young's Double Chocolate. It took another Boddington's to convince me to put on the plastic nozzles even though they will get burned. All in the name of Science.:cheers:
 
From the pictures the damage did not look that bad. From the video it looked like it ripped off the pad real nice, that it liked the F 44. If it goes a bit unstable after thrust at least it is high up and gives a good show. As long as it deploys in time fix and fly again.
 
From the pictures the damage did not look that bad. From the video it looked like it ripped off the pad real nice, that it liked the F 44. If it goes a bit unstable after thrust at least it is high up and gives a good show. As long as it deploys in time fix and fly again.

That was the Inductor on an F35 reload. The Saturn got the F44. I can definitely mod these...but...have...compulsion...to...build...another...
 
Ha! If the criteria is only crashes, I have a 75% success rate! Note these will all tumble during coast unless maybe if you get them to spin too. ;)
 
Very cool, guys! I seem to recall a few people doing finless, canted clusters (mounted at the rear with the rod up the center) that semi-successfully spun stabilized. Maybe a combo of the two techniques would work even better? Or maybe not if the canted motors burn up the induction tube. Hmm... you'd probably need some other method to induce spin.

Congrats on furthering the science! Looking forward to the flight reports!
 
Like the fireworks we launch on the 4th you have to get that relatively narrow pyramid body spinning very fast before it can vertically take off. GDS holds the promise of not using silly canted or tractor motor set ups. Beautiful scale Minuteman missiles flying away into the sky. Spare the rod and spoil the rocketeer!
 
I don't know how you'd get an induction stabilized rocket spinning. Canting the motors at the wall of the induction tube doesn't sound like a good idea. Separate spin motors might work in theory but ignition delays would be problematic. I remember someone flying a football that was spun up on the pad....but how the heck do you keep the igniter in that thing??? All this makes me want to build a good ol' 3/4FNC!
 
Possibly. The trouble is you can't make them too small in diameter and you still have to make them so they hold up to the fire.
 
The baseline design for an induction stabilized rocket is attached. It had posted it before but forget where. Dean, who literally wrote the book on this class of hobby rocket doesn't discuss inlets above the motor and I'm not sure why. That didn't stop me from trying them.

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