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

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rstaff3 said:
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!
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NO -NO! Not 3/4FNC! That would be way too sane, and smart, and nice, and safe, and traditional.

The real rocket science guys I have talked to say you just can't get a traditional model rocket spinning fast enough, soon enough to be stable at liftoff and still have a modicum of efficiency for flight. That 3/4FNC is just the way to go and that is that. Darn! Now I want to build 3/4FNC!
 
Daddyisabar said:
NO -NO! Not 3/4FNC! That would be way too sane, and smart, and nice, and safe, and traditional.

The real rocket science guys I have talked to say you just can't get a traditional model rocket spinning fast enough, soon enough to be stable at liftoff and still have a modicum of efficiency for flight. That 3/4FNC is just the way to go and that is that. Darn! Now I want to build 3/4FNC!
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But the spin may be enough to keep the GDS rocket from tumbling as gas output from the motor declines and the GDS effect decreases. As I've said, canted internal tabs could hide the fins, but they'd obviously need to be able to withstand the motor's exhaust. I don't think of small fins to induce spin as cheating as much as I think they may be something that is required to make GDS rockets eventually fly adequately.
 
Winston said:
But the spin may be enough to keep the GDS rocket from tumbling as gas output from the motor declines and the GDS effect decreases. As I've said, canted internal tabs could hide the fins, but they'd obviously need to be able to withstand the motor's exhaust. I don't think of small fins to induce spin as cheating as much as I think they may be something that is required to make GDS rockets eventually fly adequately.
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I see scratch built, high end induction rockets in your future!

An induction tube turbo fan would be awesome! It would be just like the old 70's commercial: DATSUN. . . TUUURRRBBBOOO DRIVEN!
 
If the posts between the motor and the induction tube were static vanes that cut a partial chord across the inner diameter, perhaps curved or airfoiled, wouldn't the incoming air make an internal vortex?
 
Charles_McG said:
If the posts between the motor and the induction tube were static vanes that cut a partial chord across the inner diameter, perhaps curved or airfoiled, wouldn't the incoming air make an internal vortex?
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The Vulcan ship passing through this sector has detected that beings living on the third planet are about to solve the mystery and finally utilize Gas Dynamic Stabilization in model rocketry. Are they going to land and make first contact?
 
I don't know about vanes, spinning and Vulcans...in fact I don't know much about this stuff in general.

As I was pondering what to do with the SA-666's successor, I went back to read some of Dean Black's write-ups. I don't remember seeing this in his Apogee Newsletter article but I find that, while an air gap behind the CG results in induction stabilization, an air gap ahead of the CG retards it. D'OH, that's what I randomly decided to add to the SA-666. When it comes to rocket science, you just can't make stuff up. But hey, I never claimed to be a rocket scientist.

So, I cut a paper transition to cover the gap, I covered the nozzles with metal tape, and cut some additional vent holes. It will fly again in August.

The photos are here.
 
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Don't know much about history
Don't know much biology
Don't know much about science book
Don't know much about the French I took

Don't know much geography
Don't know much trigonometry
Don't know much about algebra
Don't know what a slide rule is for

Good to know about that above CG gap thing!

Hopefully it flies tomorrow and I live to tell about it.
 
rstaff3 said:
Back from launch...waiting for your launch report :)
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It flew just fine, maybe a bit over stable as it weather cocked into a slight breeze. The crowd was eager to see GDS in action. Flew fine through the coast stage as it arced over and ejected as the nose went down on an E9 -4. Next time a D12 3 or E12 4 and less nose weight. Maybe I can scare up an F 12. It burned off two of the three launch lug brackets holding the nozzles. We found one at the edge of the range. That was a bit more burn than I predicted but right on line with what my trusty assistant predicted. He will down load some post flight pics and maybe part of a video. I am uploading the pre-flight photos now. Was it really GDS or just power, nose weight and a little luck?
 
Daddyisabar said:
It flew just fine, maybe a bit over stable as it weather cocked into a slight breeze. The crowd was eager to see GDS in action. Flew fine through the coast stage as it arced over and ejected as the nose went down on an E9 -4. Next time a D12 3 or E12 4 and less nose weight. Maybe I can scare up an F 12. It burned off two of the three launch lug brackets holding the nozzles. We found one at the edge of the range. That was a bit more burn than I predicted but right on line with what my trusty assistant predicted. He will down load some post flight pics and maybe part of a video. I am uploading the pre-flight photos now. Was it really GDS or just power, nose weight and a little luck?
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Awesome, I expected no less from one of your creations. I don't know how much GDS came into play or not. It looks kinda like one of the minimum diameter tube fins that the water rocket folks use. No matter, it looks cool and flies the same...minor burning is expected here.
 
The biggest challenge was to get the clips taped so they would not hang up and then to actually clip them to the starter. The ring was in the way of getting a good squeeze on the clips, but I found someone with small fingers that was able to do it. Why, they asked, did the tube fin have to go there? I said it had to be placed there due to the science. Hopefully we can get some video soon, if not I can shoot post flight burn photos.
 
What I do when there's a chance of clips hanging is scavenge used igniter wires from the HPR pads, restrip as required, and twist on to my short igniter wires. Works for my home made 12"ers, Quest, or even Estes. In the event you forget a plastic cap or other form of igniter retention it is easy to secure the long wire to a rod/rail so the igniter stays firmly where it supposed to be.

I learned about clip hang on a converted Shuttle what had fins on a long boom. It was just after getting back into the hobby (for the 1st time) and was still using the Estes controller from a starter set. Clip caught, rocket took the controller with it. Neither survived. I made a new controller but gave up on the Shuttle.
 
Daddyisabar said:
Don't know much about history
Don't know much biology
Don't know much about science book
Don't know much about the French I took

Don't know much geography
Don't know much trigonometry
Don't know much about algebra
Don't know what a slide rule is for

Good to know about that above CG gap thing!

Hopefully it flies tomorrow and I live to tell about it.
Click to expand...

Don't know much Scientology
Don't know jack 'bout da economy
Don't know much about rocketry
Don't know what them thar fins is for

But I do know that it must fly true
And if this one skinny tube will do
What a wonderful world this would be
 
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ThirstyBarbarian said:
Don't know much Scientology
Don't know jack 'bout da economy
Don't know much about rocketry
Don't know what them thar fins is for

But I do know that it must fly true
And if this one skinny tube will do
What a wonderful world this would be
Click to expand...

LOL, very funny :)
 
ThirstyBarbarian said:
Don't know much Scientology
Don't know jack 'bout da economy
Don't know much about rocketry
Don't know what them thar fins is for

But I do know that it must fly true
And if this one skinny tube will do
What a wonderful world this would be
Click to expand...

We can always count on ThirstyBarbarian to get the song lyrics just right!:rofl::rofl:
 
D - Congrats on the flight! I always wondered how one would insert the motor & connect the clips. Maybe future versions will have removable induction tubes? :)

TB - Ha! You mad lyricist, you! Pods! Pods! PODS!!! (no body snatching, please) :)
 
I have cut some spare pieces of BT 60 where I can close up the gaps however I want for more of an induction tube effect.

The motor slides easily on the wooden dowel "racks." Putting the igniter in is easy too as the induction gap is fairly large.
 
I have the top section of my next Saturn V, the SA-667 built. But now the harder part comes...to decide what the induction section will look like. My muddled thoughts are focussed on a smaller diameter induction tube. See attached diagrams. The one on the left with no inner tube is what I had on the Inductor and on the SA-666 if you ignore the upper vents. The same diagram is on the right of the other diagram, but just because I don't have another idea to fill in. I was going to add some which had a center tail cone to force air into the induction tube but canned the idea since tail cones, while aerodynamic, are destabilizing. Something these rockets don't need. My mind gave out when I tried to think about what a tail cone in the middle of a rocket would do. I didn't resort to 'what-if' models in Rocksim to find out. Plus, the top is built. :) I have a feeling that one of the options that start at the full diameter and transition to the smaller is the way to go.

BUT...I also am thinking about building a frame that can support different options. Not for scientific reasons but for fun. Here, my current insane idea is to attach aluminum tubes or threaded copper busbars to the upper. There would be one thin ring down a bit and a wider one to hold the Saturn nozzles, etc. Screws through these would help affix/center the induction tube and rail buttons would attach to one of them. Basswood is a probably a better option. And it won't start a discussion about using metal.

induction tube options.jpginduction tube options 2.jpg
 
Somehow, I suspect that Rocksim isn't going to be informative. Its not doing CFD and this kind of design is breaking lots of Barrowman assumptions.

I have a couple of thoughts (caveat, I'm a biochemist, not a rocket scientist):

1) Look at the Dyson bladeless fans. https://www.dyson.com/fans-and-heaters/cooling-fans/am06/am06-desk-fan-10-inch-black-nickel.aspx The inner surface is an airfoil, thick end on the draw side. They inject compressed air into a gap in the airfoil so it flows back, over the foil, and out and -induces- a larger draw through the middle of the fan. Isn't the induction tube analogous? Except the fast airflow is the motor exhaust. I'd try building an airfoil shape into the induction tube.

2) Does an aspirator have any relevance here? It uses the venturi effect to create a vacuum from a water stream. The internals have a nozzle jetting into an expanded volume, with a side tap. Which brings to mind the motor (in a boat tail, especially), the induction tube and the vent hole. A quick look at wikipedia suggests that it's not relevant - the draw would be upstream of the motor, while the rocket vent hole are down stream. Hmmm... still thinking about that one.
 
Option 1 sound interesting but as I understand it the air would be injected towards the motor and I don't know how that would be accomplished. I also doubt my ability to create and actual airfoil inside a tube. The two curved ones on the right hand diagram would employ a found object vs. be really building a structure in a tube.

Would the difference in diameters have an effect? I don't know.
 
I think the air flow is in the correct direction. At least from what I recall, looking at a display model at a Worst Buy a couple of years ago.

I gave an in-tube airfoil a lot of thought when I was experimenting with a ring-wing boosted glider. (a la https://www.spacemodeling.org/jimz/eirp_56.htm). I thought about ways to taper the thickness of the leading thick lip of the glider, wondering if an airfoil would be better than that simple lip. IIRC, when I searched on this kind of hand thrown glider, some people put side vents in just aft of the lip. It now sounds very familar. I never got my Stovepipe to come off the booster - even when I made an elastic driven sliding launcher on the core - and abandoned the rocket(s).
 
I guess I would need to think more about the issue. One issue here is that the induction tube will not last long and for me wouldn't warrant a lot of work. Sounds like we have another induction stabilized rocketeer?
 

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