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

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Daddyisabar

Oddroc scum. Mindsimmer.
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After the unmitigated disasters of the Prinz Eugen, Egg and Whack Wocket, it looks like days of my silly oddrocs might be in deep trouble. The flight card of the Egg has been placed in my permanent record with the red stamp of “Inherently Unstable Design,” a direct violation of the RSO’s zero tolerance policy towards unstable oddrocs. You only get one chance with these things and they had better work. As in the Animal House movie, with the Dean of the college dropping the Big One, my only course of action is to try something new and completely stupid. Yes, a gas dynamic stabilized, yet finless and scale like model rocket might fit the bill for the home coming launch. With all the hype surrounding the Apogee newsletter it must be good rocket science and hopefully I can drop some fancy college terms that will get me a coveted pad assignment. Who needs stinking fins! Who needs no good, stinking, performance robbing nose weight? Who needs bigger, punchier motors? Gas Dynamic Stabilization will be the answer to all of my prayers, I am sure of it; confidence is Key. Even the rivet counting scale guys might like it, no more Lexan. Early hope sims are good, then comes the build using left over parts from the headache box.

There have been threads where small A 10 motors have been successfully fired down a ducted tube, so I am going for some ultra-high by pass air action with a 24mm motor on this one. All that cool air flow and expanding gas will surely stabilize the rocket just like if it had big old fins. But then more mind sim problems arise as massive doubt and angst set in. How to manage motor heat that can easily burn right through a steel blast defector? What about all those sparky bits that shoot out the back on my lovely E9 motors? What about that hot burning delay melting away the pretty plastic bits on the back of the rocket? Will I be able to take the heat damage or will I become so distraught from black soot, peeling paint and melted plastic as to just give up. Will the “shaping fins with fire during flight” argument hold up again? But most important, will it look good?

No silly mid or forward canted tractor motors on this one. The motor must point down. Rocket science is all about efficiency. Variable nose weight capability will be required for the scheduled test flight program. It will first fly as a “Saturn” like rocket and as the nose weight comes off it will look more “Titan” like. The first flight will have to be off a long quarter inch rod. No rod whip allowed. Launching off the little stand like in the Apogee newsletter article is just a dream. Thank goodness I was able to dig through some High Power trash and score some igniter packaging tubes I can use for launch lugs.

As the build progresses I decide the induction tube at a minimum of two diameters is just too restrictive and will burn up even with lots of holes. Just putting spaced ring fins on will allow more airflow and burning gas to stabilize the rocket . . . right? I feel the good rocket science slipping through my fingers as my silly mind sim mods add up. Is it really worth all this just to move the motor up and eliminate fins? Will the model rocket Jedi Masters at the club see this and move me back in with the Younglings? I decide to hack the openings above the motor and around the motor tube to max. Max airflow over the motor must be achieved. I try to hide a little lip to bring in more airflow using rail road corrugated metal. Some use beer can metal for the induction tube. I fear little drops of molten metal falling on the crowd. Just CA soaked tube and hardware store hardwood Poplar rods will have to do. A final decision to add some launch lugs and cut nose cones for pretty silver nozzles to make it look good and hopefully endear it to the old school Jedi before launch. One shot, it must work. Help me gas dynamic stabilization, you are my only hope!

GD 7.jpgGD 6.jpg
 
Enhance yer ignitors (er, 'motor starters'-ya know plants crave electrolytes, right?) and cross yer eyes for spontaneous combustion. (parachute?-The Emperor will be so proud of you-Won Ting Mi Sing!)
 
From now on all those Chinese e matches get a dip. This one is going to feel the burn of just one motor. Nice big nylon chute to bring it down slow, it will need some time to cool off. Short delays only to keep off the heat. Hope I get a lot of flame fin action and gas dynamic stabilization. All cooled by large amounts of passing air. Stable even through the coast when there is no motor thrust. It will be just like the reusable Space Shuttle Engines were supposed to be, a quick clean up and back in service with less nose weight.
 
This is a very cool design. I have never heard of this voodoo you call Gas Dynamic Stabilization, but it sounds sciency, so it is probably good. It's so crazy, it just might be genius! Whether it works or not, it should be pretty fun to watch --- I'm visualizing smoke and flame billowing out of the open part of the structure during flight.
 
This is a very cool design. I have never heard of this voodoo you call Gas Dynamic Stabilization, but it sounds sciency, so it is probably good. It's so crazy, it just might be genius! Whether it works or not, it should be pretty fun to watch --- I'm visualizing smoke and flame billowing out of the open part of the structure during flight.

https://www.apogeerockets.com/education/downloads/Newsletter379.pdf This will blind you with Science. I know voodoo economics, not science. Hopefully it will not fly the Laffer curve. All the blow out will keep it stable with out fins.
 
This is Spartaaaaaa!

Big deep wells with out protective rails scare me!

AAAAHHH my rocket is falling in flames having kicked out the motor!

The Athenians have much better science, but our RSO can be a bit Spartan, so hopefully he won't reject my mutant rocket at birth and throw it into the pit. I must consult the Oracle - that is nothing some but high end mindsimming!

What are 300 against the Immortals and a Legion of War Elephants?
 
Big deep wells with out protective rails scare me!

AAAAHHH my rocket is falling in flames having kicked out the motor!

The Athenians have much better science, but our RSO can be a bit Spartan, so hopefully he won't reject my mutant rocket at birth and throw it into the pit. I must consult the Oracle - that is nothing some but high end mindsimming!

What are 300 against the Immortals and a Legion of War Elephants?

If the RSO gives you any trouble, you can just yell, "This! Is! STAAAAABLE!!!" Then kick him into the abyss.
 
If the RSO gives you any trouble, you can just yell, "This! Is! STAAAAABLE!!!" Then kick him into the abyss.

If only life was more like the movies. Only pure science will work. This is the age of reason and the scientific method. The good old days of fighting spirit and skill have given way to push button technocracy. Your shield is your laptop, your spear is your hard lab data, your helm is the Rocsim output that guarantees your success. No yelling allowed, just steady applause as the data streams in.

That 300 was a good show.
 
I like it!
It's high time someone around here started playing with the concept.
It's on my "To do list".
 
:
Do you have an ECD (Estimated Crash Date) for this thing?

Hopefully the flood waters will have receded and we can get to the club launch site for July 18. Also hope everyone will be in the mood to see a real good crash and have a jolly belly laugh. That always seems to help break the tension. If you fly yours before hand give us some photos and video, (unless it is top secret for national security purposes.) Then I can show the guys it is sound and proven rocket science and can be done by someone who actually knows what they are doing.

Since I have decided not to go with a proper induction tube they will classify it as just silly ring fins and let it burn-burn-burn-burn. Just a little bit more tube with lots of holes and I coulda been a contender, but the mind sim didn't work out that way. Too lazy to cut out all those holes. That will be soon cured when they put me in the orange jump suit and have me out recovering the parts from the crash. I'm diggin' those holes holes holes holes, I'm diggin' those holes!

These GDS rockets are so easy to make maybe I will get out the hole punch and build some more for fun. A BT-70 version? I do have some Boddingtons, Speckled Hen and Young's Double Chocolate Stout in the fridge. Maybe some of those tall cans can fly, and the plastic plug balls would make great Sci-Fi external fuel tanks. Now that does sound satisfying and delicious! I like that kind of rocket science! I must sacrifice to get the parts I so desperately need to build GDS rocket ships! :cheers:
 
From Apogee Newsletter #379 Engine-Driven Gas-Dynamic Stabilization:

...this mass flowrate is about 15 times the mass flow rate of the engine alone, so the mass flow rate of ambient air is about 14 times the mass flow rate of the engine. This high 15:1 increase in mass flow rate provides the means by which angular momentum about the rocket’s pitch and yaw axes is depleted.

From Apogee Newsletter #195 Basics of Dynamic Flight Analysis (Part 3) - The Damping Moment Coefficient:

Propulsive Component of the Damping Moment Coefficient

The propulsive component is commonly referred to as jet damping. What happens is that the gases coming out of the nozzle seem to make the whole rocket harder to turn. This is similar to increasing the moment-of-inertia of the rocket.


So this GDS technique is greatly amplifying the mass flow rate of the engine via ducting to make the normally insignificant (in model rocketry at least) propulsive component of the damping moment coefficient very significant?
 
Have you seen any reports of a fully successful GDS rocket flight here? It's a very interesting technique. The only mention of a flight I've seen was here:

https://www.rocketryforum.com/showthread.php?126525-Gas-dynamic-Stabilization&p=1468873#post1468873

It's not 100% conclusive that the GDS actually stabilized the rocket. It did appear stable at the start of the flight. I'm going to try it again in July. One thing to note is these will go unstable after burnout, so short delays are in order.
 
It's not 100% conclusive that the GDS actually stabilized the rocket. It did appear stable at the start of the flight. I'm going to try it again in July. One thing to note is these will go unstable after burnout, so short delays are in order.
I'm really looking forward to videos of one of these flying. Via a Google search on various related keywords I find a number of references to different individuals making and flying these over a number of years, even photos of their various models, but no videos anywhere.

On the stability issues during low and no thrust conditions, I think 3 or more very small, slightly canted fin tabs at the base of the rocket might impart some spin stabilization to remedy that. If they could withstand the exhaust plume, they could even be hidden inside the body tube.

I found this, but while it's a very interesting video, it's referring to the wrong type of "induction" rocket:

TELSON : INDUCTION ROCKET SYSTEM

[video=youtube;x0FG7S3E070]https://www.youtube.com/watch?v=x0FG7S3E070[/video]
 
Have you seen any reports of a fully successful GDS rocket flight here? It's a very interesting technique. The only mention of a flight I've seen was here:

https://www.rocketryforum.com/showthread.php?126525-Gas-dynamic-Stabilization&p=1468873#post1468873

A couple of years ago there was a guy from the UK that flew an old design from the late 50's on an A 10 with a deeply recessed motor and lots of airflow past it. I can't find that thread anymore. Other than that it is just the guys here and the newsletter. I have had visions foreseeing the flight of my rocket but that is just the Dark Side of the Force invading my mindsims. Stable all the way through but oh the BURN!
 
From Apogee Newsletter #379 Engine-Driven Gas-Dynamic Stabilization:

...this mass flowrate is about 15 times the mass flow rate of the engine alone, so the mass flow rate of ambient air is about 14 times the mass flow rate of the engine. This high 15:1 increase in mass flow rate provides the means by which angular momentum about the rocket’s pitch and yaw axes is depleted.

From Apogee Newsletter #195 Basics of Dynamic Flight Analysis (Part 3) - The Damping Moment Coefficient:

Propulsive Component of the Damping Moment Coefficient

The propulsive component is commonly referred to as jet damping. What happens is that the gases coming out of the nozzle seem to make the whole rocket harder to turn. This is similar to increasing the moment-of-inertia of the rocket.


So this GDS technique is greatly amplifying the mass flow rate of the engine via ducting to make the normally insignificant (in model rocketry at least) propulsive component of the damping moment coefficient very significant?

I am going to memorize this for my pitch to our RSO. All of the above with no Krushnik Effect and manageable burn damage. No fins, little or no nose weight, no launch rod, scale good looks, in short; TOTAL AWESOMENESS! That is a best laid plan of Mice and Men.
 
Hee-hee-haa-haa
To the funny farm
Where life is beautiful all the time

I think I have lost it! Daddyisabar, your Saturn-like creation has motivated me to build my own Saturn-like GDS. Why the heck should I wait to see of my first one actually works...or wait to see if your's does...now THAT would be crazy!

Here's a photo of the induction tube. There are going to be ducts at the point of the 1st transition to feed air along side the motor. There is also going to be the compulsory air gap.

It has fins, so it's probably cheating.

18715700714_261fc3ec2f_z.jpg
 
Hee-hee-haa-haa
To the funny farm
Where life is beautiful all the time

I think I have lost it! Daddyisabar, your Saturn-like creation has motivated me to build my own Saturn-like GDS. Why the heck should I wait to see of my first one actually works...or wait to see if your's does...now THAT would be crazy!

Here's a photo of the induction tube. There are going to be ducts at the point of the 1st transition to feed air along side the motor. There is also going to be the compulsory air gap.

It has fins, so it's probably cheating.

WOW! That is a real GDS rocket. Fins look good on that one. The real rocket scientists will be amazed: " You are flying that Saturn V what motor? With how little or NO nose weight? AND it stable off the pad! WOW! GDS is the way to go!" Yeppers, rocket science is all about efficiency. Just swab the soot out of the induction tube if you wish and ready to fly again. Reusable and safe rocket ships are here to stay.

Hiram Maxim and John Browning used the gas wisely and their stuff is still around today.

Don't worry if the guys in white coats that want to put you in that really long sleeved jacket are at the launch. Don't even worry if the uniformed guys who want to put you into and orange jump suit and load you onto the big white bus are present. But keep a sharp look out for the Black SUV's and the guys in dark blue with gold letters on the back of their coats. If they see a successful GDS launch you might just disappear to Club Gitmo for a permanent vacation outing.
 
This had become one of my typical real time builds...ending up something other than what I expected. It started as a nice light paper rocket that would be easy to stabilize with all that mass flow. Now it looks like it might be a tad overbuilt. Has a 29mm mount so it may need a SU G. May need away cells...

And I did a great job hijacking your thread. Ooops. My bad.
 
This had become one of my typical real time builds...ending up something other than what I expected. It started as a nice light paper rocket that would be easy to stabilize with all that mass flow. Now it looks like it might be a tad overbuilt. Has a 29mm mount so it may need a SU G. May need away cells...

And I did a great job hijacking your thread. Ooops. My bad.

Keep on hijacking, I don't mind at all when we all get to see the twisted inner workings of the Rocket Dungeon. Making GDS work with bigger motors is AWESOME. It is like Hulk Hogan prancing around saying "FEEL THE BURN!"

Yes sir mister RSO. There are guys out there flying gas dynamic stabilized, Saturn V paper rockets on G 80's. What is there to fear from my small and not dangerous, E9-4 powered toy?
 
I am going to memorize this for my pitch to our RSO. All of the above with no Krushnik Effect and manageable burn damage. No fins, little or no nose weight, no launch rod, scale good looks, in short; TOTAL AWESOMENESS! That is a best laid plan of Mice and Men.
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.
 
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.
 
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