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Veracity
11-02-2007, 07:40 PM
To all,

A friend and I were talking today about multi staging. I'd like to try a technique I read about in the Handbook of Model Rocketry. (Page 166 for all of the faithful out there.)

1) Regarding multi staging, are you guys pleased with your success ratio? Do those upper stages ignite often enough for you to feel it's worthwhile?

2) Have any of you tried the technique listed in the handbook? (No direct contact between the lower and upper stage engines.)

Thanks,
V

Phred
11-02-2007, 09:06 PM
I 'gap stage' all of my models, and have so far had a 100% success rate.

I have even converted some older 'tape method' staged models to gap staged, and they work fine.

The trick to gap staging is to vent the gasses, which allows the hot particles from the booster motor to ignite the upper stage. I typically vent via holes in my centering rings. This lets the gasses out the rear of the booster tube.

Phred

JoeLaunchman
11-02-2007, 10:12 PM
Is there any formula for the distance between the booster and sustainer engines? Does it matter if they're 18mm or 24mm? Is there any maximum distance that works between them? I've only multi-staged with the cellophane tape method and had good success with it.

CPMcGraw
11-02-2007, 10:43 PM
Is there any formula for the distance between the booster and sustainer engines? Does it matter if they're 18mm or 24mm? Is there any maximum distance that works between them? I've only multi-staged with the cellophane tape method and had good success with it.

The Handbook suggests an upper limit of about 12" between stages. When you imagine the mechanical movement of those particles, you picture them spreading forward and outward (in a cone pattern) from the top of the casing. As you put distance between the two motors, the quantity of particles moving straight ahead is reduced, probably at a mathematic-measurable rate of decrease. There's a point where you no longer have enough particles close enough together to get through the nozzle and carry on the chain reaction of the burning process. Additionally, remember that those particles are burning as they travel through the gap, and they are losing mass the whole time. At some distance, probably measurable based on the starting size of the particle, the mass is gone and the reaction stops.

Put in language for us shadetree rocket scientists, at some distance past a foot, there ain't enough sparks gettin' through that are hot enough to light the next one.

For practicality, a booster longer than a foot, for motors under "D" and "E", is not really a benefit and may be a liability. Keep the booster to a manageable length with a gap less than 12", venting the pressure correctly, and your stages should work reliably.

Veracity
11-02-2007, 11:04 PM
Excelsior_rocketry wrote
"The trick to gap staging is to vent the gasses, which allows the hot particles from the booster motor to ignite the upper stage. I typically vent via holes in my centering rings. This lets the gasses out the rear of the booster tube."

Nice! That seems like a really interesting way to go.

How many holes do you make...and what's their size? The handbook says 1/4 inch.

Regardless of where they are, the size seems like the key thing to me. Too small, the gas pressure pushes the upper stage away before the upper engine ignites. Too big, the pressure differential created by the slipstream would suck out too much of the "oooomff" created by the bottom engine...which would decrease the likelihood of a successful second stage ignition. (I believe that "oooomfff" is a technical term used by former Soviet block rocket designers.) :D

Maniac BAR
11-02-2007, 11:27 PM
Excelsior_rocketry wrote
"The trick to gap staging is to vent the gasses, which allows the hot particles from the booster motor to ignite the upper stage. I typically vent via holes in my centering rings. This lets the gasses out the rear of the booster tube."

Wow. That seems like a really interesting way to go.

How many holes do you make...and what's their size? The handbook says 1/4 inch.

Regardless of where they are, the size seems like the key thing to me. Too small, the gas pressure pushes the upper stage away before the upper engine ignites. Too big, the pressure differential created by the slipstream would suck out too much of the "oooomff" created by the bottom engine...which would decrease the likelihood of a successful second stage ignition. (I believe that "oooomfff" is a technical term used by former Soviet block rocket designers.) :D


My MIRV Gryphon has two 1/4" holes per tube in the booster. Each of the four booster tubes is a BT-5 size. The sustainer motor end is about 2" above the end of the booster motor. It has flown 5 times with full four motor ignition only twice. But lighting a 13mm motor is very difficult as is. The fact that they did all lite shows the principal is sound. :)

I built a three stage spool rocket just a few weeks ago and flew it for the first time last Sat. 11-3-07. It uses three D12-0 motors that are about 3" apart. The motor tubes are all BT-50MF. I placed one 1/4" hole right in the middle of the small 1" outside coupler used to hold the stages together. It had perfect ignition of each of the stages. :D

The success of the stages will depend more on the upper stage engine nozzle opening than on the distance they are apart as well as the size of the motor/body tube. However, the 12" rule is valid and should not be exceded. There have been some reports of larger staging distances using a very small wick (fuse) of thermallite placed into the upper stage nozzle. With that being said, remember the longer the booster stage is, the more likely it will come in ballistic and not flutter down! :eek:

At some point the booster will need its own recovery device. All this will not work at all on composite motors. All the upper stage motors must be end burners. There is no way the burning particials can get all the way up a core burner and would not be hot enough to start ignition anyway.

barone
11-03-2007, 09:23 AM
The Handbook suggests an upper limit of about 12" between stages. When you imagine the mechanical movement of those particles, you picture them spreading forward and outward (in a cone pattern) from the top of the casing. As you put distance between the two motors, the quantity of particles moving straight ahead is reduced, probably at a mathematic-measurable rate of decrease. There's a point where you no longer have enough particles close enough together to get through the nozzle and carry on the chain reaction of the burning process. Additionally, remember that those particles are burning as they travel through the gap, and they are losing mass the whole time. At some distance, probably measurable based on the starting size of the particle, the mass is gone and the reaction stops.

Put in language for us shadetree rocket scientists, at some distance past a foot, there ain't enough sparks gettin' through that are hot enough to light the next one.

For practicality, a booster longer than a foot, for motors under "D" and "E", is not really a benefit and may be a liability. Keep the booster to a manageable length with a gap less than 12", venting the pressure correctly, and your stages should work reliably.
At NARAM 47, Peter Bricker gap staged a Saturn V, not once but twice! (total of three stages) I think his max seperation was something like 18". And clustered....all motors lited.

CPMcGraw
11-03-2007, 04:27 PM
At NARAM 47, Peter Bricker gap staged a Saturn V, not once but twice! (total of three stages) I think his max seperation was something like 18". And clustered....all motors lited.

Wow!

That had to be right on the edge of maximum-gap, unless he did something internally to direct the particles in a straight(er) path, like a long, small-diameter stuffer tube.

Getting all of the motors in any cluster to fire at the same time, or at least within a couple miliseconds of each other, is an accomplishment; staged clusters can only be as reliable as the lighting of the first motors. It would have been a flight to remember...

Ltvscout
11-03-2007, 05:36 PM
all motors lited.
Lit. ;)

Did anyone get a video?

barone
11-03-2007, 09:18 PM
Lit. ;)

Old military term...lited....for troubleshooting...old habits die hard.... :D

Did anyone get a video?

Not that I know of......The article appears in the Nov-Dec 2005 issue of Sport Rocketry, page 26.....authored by Peter Alway....

"Peter Bricker's well executed Estes 30th anniversary edition Saturn V took fifth in static. But it was the insides that made the model special. He clustered five engines in the first stage - a D12-0 in the center and four b's for the outboard engines. While the B engines would eject parachutes, the D was to ignite a second stage engine across a nearly 2-foot gap. Assuming all the clustering and staging worked, the second stage would ignite a third. This ambitions plan would be carried out without any onboard electronics."

"The highlight of scale flying, however, was Peter Bricker's Saturn V. Peter had flown his cluster-stage combination before, and was confident it would function, except for the second stage parachute, which relied on the tug of a Kevlar line hanging off the rear of the third stage. Dozens of NARAM contestants gathered around to watch this flight. At ignition the spectators clearly saw five yellow flames. On cue, the second stage ignited. Then the third. Whooshhhh-Whooshhhh-Whooshhhh! The sky was full of Saturn stages, all on parachutes. Finally, the third stage ejected the Apollo capsule, which came down on three scale-like striped parachutes. Even the escape rocket came down on it's own streamer. The crowd cheered, and 175 mission points propelled Peter's Saturn V into first place."

The launch picture appears on page 22...photo taken by Ken Hutchinson. Looking at the picture, there are several folks in the background that look like they were recording it so someone has a video of the launch....

Tom Swift
11-27-2007, 04:18 PM
Is there any formula for the distance between the booster and sustainer engines? Does it matter if they're 18mm or 24mm? Is there any maximum distance that works between them? I've only multi-staged with the cellophane tape method and had good success with it.

Having the sustainer light up is not the only "gotcha" with multi-stage rockets. Recovery of the booster after it is dropped must be considered.

If you use the tape-the-motors-together method, then by necessity the booster is short. It is likely to tumble when dropped. A gap staged rocket though will have a relatively long skinny booster with the fins at the base. The booster stage is likely to be stable when dropped.

My only two stage rocket to date has a fairly short BT50 booster with a gap of only about 1.5 inches. With a spent engine in place, the CG is a little more than 1/3 of the way back from the leading edge of its fins. I thought it would tumble. Instead, it is remarkably stable and has come in ballistic 3 out of 3 times. :( I will try a little tail weight next time.

So what tricks do you use to destabilize a tumble-recovery booster? And/or what's your favorite design for recovering the booster under streamer or chute?

Doug Sams
11-27-2007, 05:10 PM
So what tricks do you use to destabilize a tumble-recovery booster? Well, the ultimate in bad boosters is the Estes Mongoose. It's so stable, you might say the booster uses destruction recovery. It's pretty much guaranteed to crush its forward end at impact :(

What I do on my stagers - when I'm not cloning, and sometimes even when I am - is to move the booster fins far enough forward to ensure it's unstable, but not so far forward as to make it stable in the opposite direction.

Rocksim will let you ascertain the CP and hence the stability margin of the booster - by deleting the sustainer :( - but at least you can analyze it. (Hopefully, one of these days, they'll enhance the product making that analysis a little less painful.)

When you're scratch building, one of the keys to unstable boosters, is keeping the fins fairly unswept. This moves the CP closer to the root chord (but obviously places additional stability demands on the sustainer).

Doug

dwmzmm
11-27-2007, 08:34 PM
The more recent staging model(s) I've flown used the tape-the-engines together method.
Two of these models were even clustered/staged. For a more "historical" perspective, see
my thread I posted not too long ago here:

http://forums.rocketshoppe.com/showthread.php?t=2318

Lot's of narration and pictures....

Tom Swift
11-28-2007, 08:07 AM
Well, the ultimate in bad boosters is the Estes Mongoose. It's so stable, you might say the booster uses destruction recovery. It's pretty much guaranteed to crush its forward end at impact :(
As a matter of fact, my booster is made with the fin can of one Skywriter and the sustainer is another Skywriter. So my two stage rocket is very much like a Mongoose. Fortunately our launch field is often muddy so there's been no damage yet to the booster on landing. Takes nice core samples though. :D

Mark II
12-06-2007, 12:32 AM
For a different take on staging, check out this design:

http://www.dars.org/jimz/eirp_10.htm

I built one of these earlier this year, but I haven't flown it yet. I added an actual booster stage module that would be recovered (in theory, at least) on a Mylar streamer (not yet attached in the pictures) after being ejected from the augmenter tube. (The streamer will wrap around the spacers on the outside of the "stage" and be held in place against the inside of the augmenter until the booster is ejected.) I also didn't bother hollowing out the nose cone, since I'm just using a streamer for the sustainer as well.

Back on the subject of gap-staging, though, didn't Centuri use some sort of external coupler for some of its gap-staged models? How did that work, exactly?

Mark

Tom Swift
12-07-2007, 11:12 PM
Back on the subject of gap-staging, though, didn't Centuri use some sort of external coupler for some of its gap-staged models? How did that work, exactly?

Mark
Same concept really. I used to have a later model Centuri Black Widow (http://www.ninfinger.org/~sven/rockets/catalogs/centuri74/74cen26.html) . The plans can be found here (http://www.dars.org/jimz/kb-6.htm) . See this page (http://www.dars.org/jimz/centuri/kb-6e.tif) and this page (http://www.dars.org/jimz/centuri/kb-6h.tif) in particular. It had large vent holes so that the expanding gases of the booster motor burn-through did not separate the booster too fast (before the sustainer lit).

The external coupler allowed the booster to be aligned and attached very securely, since the booster BT slipped between the sustainer motor and the coupler. But it also made it tough to get the spent motor out as I recall. Had to reach inside with needle-nose pliers.

I never did get that booster to glide well either... but a cool rocket just the same.

CPMcGraw
12-08-2007, 06:34 AM
...Back on the subject of gap-staging, though, didn't Centuri use some sort of external coupler for some of its gap-staged models? How did that work, exactly?

Mark

SEMROC sells the same coupler, HTC-7B. It's an external coupler for the Series-7 tubes, with two 1/4" holes at the center, 180 degrees apart.

The idea follows Stine's concept of 'pressure vents', although in a simplified form. Generally, the initial shock wave of the booster motor 'burst-through' begins to push the stages apart. Then the pressure rises inside the gap, sufficient to finish 'knocking off' the booster. These 'vent ports' allow that pressure to escape before ignition of the sustainer, keeping the booster attached for a brief fraction of a second longer. This allows the slower-moving burning particles to make their way up the nozzle of the sustainer and carry on the burn. The pressure from the sustainer burn is much greater than that from the 'burst-through', and that's what finally separates the stages.

gpoehlein
12-10-2007, 07:03 PM
Of course, you could always build a clone of the Centuri Black Widow - the booster stage was designed to glide back!

Greg

Mark II
12-10-2007, 07:37 PM
The external coupler allowed the booster to be aligned and attached very securely, since the booster BT slipped between the sustainer motor and the coupler. But it also made it tough to get the spent motor out as I recall. Had to reach inside with needle-nose pliers.
Yeah, I understand the technique of gap-staging, and have successfully used in in some of my clones. I had previously thought that minimum diameter designs couldn't use gap-staging, but I guess that's why Centuri came up with the external coupler - to enable gap-staging with minimum diameter and near-minimum diameter designs. Was that pretty much the idea?

Mark K.

Mark II
12-10-2007, 08:45 PM
I also had an interesting experience with staging at a launch in October. In anticipation of an old motor test launch being put on by my Section (ASTRE), I had obtained some A3-0T and A10-0T mini booster motors, and had built a clone of the Mini-Brute version of the Estes Midget.

At the launch, I spent a frustrating half hour trying to assemble the stages and prep the rocket for launch. With the booster and sustainer motors taped together, I just couldn't get the motors shoved all the way into either stage. It seems that the fit of the BT-5's was just too close to admit even a single wrap of cellophane tape at the junction of the two stages.

Finally, I just shoved each motor into its respective stage and fitted the two together, with the end of the sustainer motor acting as the stage coupler. I gave the rocket a 50% chance of staging successfully. As it turned out, in its only flight that day, using an A3-0T in the booster, the Midget staged perfectly (at 200' !!), with an audible "pop!" I was so pessimistic about this happening, that I only tracked the booster down during its long, leisurely flutter recovery. (Fortunately, two fellow ASTRE members followed the sustainer up and back down for me.)

So, is this a recognized staging technique, or was I just lucky? Is this what was once referred to as "pop and go" staging (by Estes, I believe)?

Mark K.

Tom Swift
12-11-2007, 03:16 PM
Yeah, I understand the technique of gap-staging, and have successfully used in in some of my clones. I had previously thought that minimum diameter designs couldn't use gap-staging, but I guess that's why Centuri came up with the external coupler - to enable gap-staging with minimum diameter and near-minimum diameter designs. Was that pretty much the idea?
Mark K.
Sounds right to me.

Maniac BAR
12-21-2007, 02:53 AM
I am no expert on this subject so as far as the tape needed on the two engines I can only speculate. My take on the subject would be that the tape was used to hold the two together not only for reliable ignition but to hold the booster engine in place and not possibly fall out of the rocket. There were some Estes kits where this could have occured due to the rocket booster design. :o
I have built a three stage ring fin rocket from some old MRN plans that doesn't use any tape to hold them together and has no vent hole at the gap area. The rocket, called Ring Fin Thingy, would be impossible to load with three engines taped together. As you can see, a standard BT-50 coupler is used to hold each section to each other. A standard 18mm motor mount was installed into each section as well. The sustainer has a regular motor block and each of the booster motor tubes are fully open through out. The sustainer was built first with 1/4" of the motor out the back and each booster was then fitted so that its motor butted up against the next upper one. The motor tubes did the same. The couplers butt up against the next up motor mount CR. The middle booster motor was allowed to also hang out 1/4" and the lower booster was fitted to it. Its motor has just enough clearence so that I can grab it to remove it. Because of the way this was built, each of the stages is more or less sealed to the next one in three different places!! :eek:
I was going to add vent holes but could not figure out how to place them to acutually work. :(
Each of the motors is friction fitted to hold them in place and so far I have had 100% ignitions on all stages. The interesting thing with this design is that the boosters have not only tumbled back down but on occasion will acutally glide back as well.
When the whole stack is assembled, each of the motors is touching the other but that is all. I think, because of the close proximity of each stage, the hot particules have just enough time to get into the next nozzle a milli second before they seperate.
Either that or I have been extreamly lucky!! :D
The Corona II from Flis is also flown with out using any tape to hold the two motors together and does not have any vent holes. It has flown 5 times with 100% ignition as well. I wonder if the nozzles and the booster engine charges have gotten that much better that the old methods are not needed now?
As for Marks rocket, I just added that one to my build que and am thinking of making it for a 24mm motor :p

barone
12-21-2007, 07:03 AM
I am no expert on this subject so as far as the tape needed on the two engines I can only speculate. My take on the subject would be that the tape was used to hold the two together not only for reliable ignition but to hold the booster engine in place and not possibly fall out of the rocket. There were some Estes kits where this could have occured due to the rocket booster design. :o
I have built a three stage ring fin rocket from some old MRN plans that doesn't use any tape to hold them together and has no vent hole at the gap area. The rocket, called Ring Fin Thingy, would be impossible to load with three engines taped together. As you can see, a standard BT-50 coupler is used to hold each section to each other. A standard 18mm motor mount was installed into each section as well. The sustainer has a regular motor block and each of the booster motor tubes are fully open through out. The sustainer was built first with 1/4" of the motor out the back and each booster was then fitted so that its motor butted up against the next upper one. The motor tubes did the same. The couplers butt up against the next up motor mount CR. The middle booster motor was allowed to also hang out 1/4" and the lower booster was fitted to it. Its motor has just enough clearence so that I can grab it to remove it. Because of the way this was built, each of the stages is more or less sealed to the next one in three different places!! :eek:
I was going to add vent holes but could not figure out how to place them to acutually work. :(
Each of the motors is friction fitted to hold them in place and so far I have had 100% ignitions on all stages. The interesting thing with this design is that the boosters have not only tumbled back down but on occasion will acutally glide back as well.
When the whole stack is assembled, each of the motors is touching the other but that is all. I think, because of the close proximity of each stage, the hot particules have just enough time to get into the next nozzle a milli second before they seperate.
Either that or I have been extreamly lucky!! :D
The Corona II from Flis is also flown with out using any tape to hold the two motors together and does not have any vent holes. It has flown 5 times with 100% ignition as well. I wonder if the nozzles and the booster engine charges have gotten that much better that the old methods are not needed now?
As for Marks rocket, I just added that one to my build que and am thinking of making it for a 24mm motor :p
That's a nice looking rocket. I've been wanting to build one but I've got too many irons in the fire. As for your gliding boosters, the ring is a natural gliding body. We used to make paper rings in high school, attach a small one to the front of a pencil and a large one on the rear and have an instant paper (and pencil) airplane. They don't thermal well but they can glide well :D

Maniac BAR
12-21-2007, 04:24 PM
That's a nice looking rocket. I've been wanting to build one but I've got too many irons in the fire. As for your gliding boosters, the ring is a natural gliding body. We used to make paper rings in high school, attach a small one to the front of a pencil and a large one on the rear and have an instant paper (and pencil) airplane. They don't thermal well but they can glide well :D


Thanks. I never knew that about the rings!! :eek:
Now I'll have to try that here at home!!
I wonder if we could make a rocket with those rings and get it to launch correctly and then glide back down. Talk about unusual !!! :rolleyes:
OK, just what I need, another holiday project! :D

Mark II
01-02-2008, 11:58 AM
Thanks. I never knew that about the rings!! :eek:
Now I'll have to try that here at home!!
I wonder if we could make a rocket with those rings and get it to launch correctly and then glide back down. Talk about unusual !!! :rolleyes:
OK, just what I need, another holiday project! :D
Hmmm, let's see (musing) - if you have both rings down at the aft end, but on opposite sides of the body tube at launch, and then have some mechanism that, when the ejection charge fires, causes one ring to slide up the tube while rotating 180 degrees around the vertical axis so that it ends up in line with the rearward ring...maybe using elastic and a burn string and a tube within a tube...hmmm...

Mark K.

barone
01-02-2008, 02:36 PM
Hmmm, let's see (musing) - if you have both rings down at the aft end, but on opposite sides of the body tube at launch, and then have some mechanism that, when the ejection charge fires, causes one ring to slide up the tube while rotating 180 degrees around the vertical axis so that it ends up in line with the rearward ring...maybe using elastic and a burn string and a tube within a tube...hmmm...

Mark K.
Ohhhhh...we got a thinker here. I'm interesting in seeing the design. Granted, it would be hard to thermal but this should get a very decent glide. I'm seeing an internal tube that slides back at ejection (with a rear ring). Perhaps an internal full length tube coupler with a spiral cut. Internal tube has a peg at the forward end that fits the spiral cut. At ejection, the internal tube slides back through the tube coupler, the peg, following the spiral cut, causes the tube to rotate as the tube slides back, reaching a 180 degree turn by the time it is fully extended....?

Mark II
01-02-2008, 09:56 PM
Ohhhhh...we got a thinker here. I'm interesting in seeing the design. Granted, it would be hard to thermal but this should get a very decent glide. I'm seeing an internal tube that slides back at ejection (with a rear ring). Perhaps an internal full length tube coupler with a spiral cut. Internal tube has a peg at the forward end that fits the spiral cut. At ejection, the internal tube slides back through the tube coupler, the peg, following the spiral cut, causes the tube to rotate as the tube slides back, reaching a 180 degree turn by the time it is fully extended....?
I was thinking of exactly the same thing! :D

Mark

Silverleaf
01-05-2008, 10:47 AM
On minimum diameter designs that employ gap-staging/Chad staging, you can add a couple pods to the sustainer proper and use one as a place to store a streamer/chute.

Nomex chute and Kevlar chord will suffice.

If you have a larger diameter design, you can create a small stuffer tube and have the chute/streamer inside. Included is a quick and dirty drawing I posted at TRF some time back.

Yes, this system does work very well.

Cheers,