Want thoughts on a cluster idea

[Veracity]

To all,

Although launching is not new to me, I have only built five rockets of my own design. My next project will be my first foray into the world of cluster launching.

My new idea is to create a BT80 size rocket...two tube lengths long (30 in.?) and make it D/E capable. (I already made a rocket like that and it flies beautifully.) This time, I'd like to experiment with two small "booster rockets" which would be mounted to the sides of the BT80, at the base. BT20s with cones on them. No engine mounts...just a small ring inside the tubes which keeps the engine from breaking its way up through the cone.

When their ejection charges fire, the booster engines will push themselves out of the tubes. The main engine, the D/E will supply the ejection charge.

I just downloaded SimRoc and it's amazing. I cannot seem to get it to simulate this for me (I'm new to it). but I wanted to get some opinions from the forum readers.

V

[CPMcGraw]

...When their ejection charges fire, the booster engines will push themselves out of the tubes...

And to think most of us spend an inordinate amount of time trying to keep motors from doing this very thing...

Are you doing this to prevent the deployment charges of these motors from activating the recovery package prematurely? Or are you just trying to dump the mass of the motors?

In either case, my recomendation is don't. Instead, plug the top ends of the booster tubes and open up multiple 3/16" or 1/4" side vents from each booster to let the pressure out. You can dress these up to look like APU exhausts...

RockSim is a great tool, and you can use it to work up some interesting designs. It has a learning curve, which can be stiff if you've never seen it before, but it grows on you after a while.

[Veracity]

Craig,

Because those booster engines would be outside of the BT80, I figured it might be easier to let them blow themselves out. That way, I wouldn't have to worry about engine mounts, vent holes, taping engines because they aren't snug enough, etc.

My only real concern was stability. My exposure to other rocket designs other than Estes is extremely limited...and I don't remember seeing a cluster rocket that was anything other than all engines crammed into the main body tube.

I'd like to try something different.
Thanks for your reply.
V

[tbzep]

If you've flown models such as the Estes Streak, Mosquito, or Centuri/Semroc Lil' Herc, you know that ejecting motors is within the safety code. There's no reason for you to abandon this approach unless you are going to be flying it around a lot of people, especially kids who's parents look for any tiny little reason to sue you or your club or school (if you do school demos). "My little Johnny got hit in the head by a tiny paper wound tube with some clay in it and now he's an emotional wreck. He can't go to the bathroom anymore because he's afraid of all cardboard tubes. We are suing you and your club/school for $1,000,000." :rolleyes: I say go for it unless you are launching around a lot of people that don't do rocketry.

[JoeLaunchman]

Hey Veracity: That sounds like a great idea for parallel staging. You may want to consider using plugged engines in the parallel stages, they're made for rocket gliders but may serve your purpose, no ejection charge and no hot flaming particles out the front, but you're carrying the full weight of the spent tube all the way up. The idea should work in theory, but with all that tailweight you'll need some extra-large fins. Please check stability on Rocksim ahead of time or the people you launch with may find themselves ducking a heavy, E-powered, corkscrewing projectile.

I have no clustering experience but perhaps others on the board who have done this could propose some good ideas.

[CPMcGraw]

Craig,

Because those booster engines would be outside of the BT80, I figured it might be easier to let them blow themselves out. That way, I wouldn't have to worry about engine mounts, vent holes, taping engines because they aren't snug enough, etc.

My only real concern was stability. My exposure to other rocket designs other than Estes is extremely limited...and I don't remember seeing a cluster rocket that was anything other than all engines crammed into the main body tube.

I'd like to try something different.
Thanks for your reply.
V

I think I'd still opt for keeping the spent cases in the tubes instead of expelling them. TBZEP is right, concerning some very popular models that are still flown, about allowing the cases to blow out. I have a clone Gyroc...

I've also had cases from that Gyroc drop within inches of my own head from 300' up, so Tim's other comments do have merit...

On one of the two major plan sites -- YORP or JimZ, I don't remember which (Scott???) -- I think there is a plan scan (FSI?) for a drop-off booster similar to what you're describing. Granted, the whole booster drops, like the Space Shuttle SRBs, but it offers the ability to allow them to drop gracefully with a streamer or small parachute.

[ghrocketman]

Accchhhh.....
I say keep the design as planned and EJECT the spent casings.
Whaddaya want the old, spent, useless motor casings for anyways....they are made of bio-degradable material, so the green-police can't whine about littering (not that I care) either.
I actually like the menacing-mayhem action of the possibility of having to dodge the ejected casings....it makes for the possibility of a more exciting flight. :rolleyes:
Unless YOU actually get beaned by an ejected motor more than once, I would not worry about it.

Seriously though, as long as it is not over a person crowded area and the terrain is not dry as a tinderbox, motor ejection poses no real hazards.

[barone]

Accchhhh.....
I say keep the design as planned and EJECT the spent casings.
Whaddaya want the old, spent, useless motor casings for anyways....they are made of bio-degradable material, so the green-police can't whine about littering (not that I care) either.
I actually like the menacing-mayhem action of the possibility of having to dodge the ejected casings....it makes for the possibility of a more exciting flight. :rolleyes:
Unless YOU actually get beaned by an ejected motor more than once, I would not worry about it.

Seriously though, as long as it is not over a person crowded area and the terrain is not dry as a tinderbox, motor ejection poses no real hazards.
Give everone a butterfly net and make a game of it.....see who can catch the spent casings! Heck, Estes did something similar with the Pop Fly :rolleyes:

[DaveR]

Accchhhh.....
I say keep the design as planned and EJECT the spent casings.
Whaddaya want the old, spent, useless motor casings for anyways....they are made of bio-degradable material, so the green-police can't whine about littering (not that I care) either.
I actually like the menacing-mayhem action of the possibility of having to dodge the ejected casings....it makes for the possibility of a more exciting flight. :rolleyes:
Unless YOU actually get beaned by an ejected motor more than once, I would not worry about it.

Seriously though, as long as it is not over a person crowded area and the terrain is not dry as a tinderbox, motor ejection poses no real hazards.

I've noticed a LOT of cynicism in your posts lately, are you taking your meds? :D

Trouble is, I agree with just about everything you post. :rolleyes:

Back on topic: I agree eject the spent casings as long as you won't be launching around crowds. The detachable booster is a novel idea as well.

[Doug Sams]

To drop or not to drop...

It's basically a club launch thing. At small launches, spitting motors is usually not a big deal. But at a club launch, it can be an issue. Ejecting one motor from a Streak or Mosquito is one thing, but spitting 4 or 5 motors from a cluster is quite another. So it deserves a little extra consideration IMO.

Getting hit (say, in the head) by a spent motor casing _probably_ won't cause harm, but the right impact could actually burn someone. Not severely, but no one wants to deal with an upset mom. In my mind, the greater danger is looking up and getting hit in the eye.

My take is to at least explore the options before committing to any one approach. For example, I air-started some RoadRunner F60's recently, but had removed the ejection charges and pluggeg them first. While it's not kosher per the code, we can all agree it was the safer way to go.

For my other clusters, I either use the motor to eject the laundry or I plug them. In the case of 18 and 24mm BP motors, it's quite easy to plug boosters. There's no ejection charge to remove so it's a very safe procedure. I just cut some short lengths of the appropriate sized dowels and epoxy them into the voids at the forward ends of the motors. For example, most 1/2" dowels fit nicely in 18mm casings. A 1/2" long piece works well.

In my 5x18mm cluster, I usually have 3 motors ejecting the chute and 2 plugged.

I've never used pods before, but I do know that you need extra eyes to track and collect them, so if you use that approach, make sure you have plenty of folks watching the flight. I have used booster motors with breakaway fins, which is similar to pods. Needing 5 or more trackers is not uncommon on my clustered-staged flights.


Doug

[ghrocketman]

Sandmug,

Nope no meds, just my normally semi-cranky slightly-warped-sense-of-humor self.

[DaveR]

Sandmug,

Nope no meds, just my normally semi-cranky slightly-warped-sense-of-humor self.

OK just checking. :cool:
Personally speaking I like it.

[snaquin]

My exposure to other rocket designs other than Estes is extremely limited...and I don't remember seeing a cluster rocket that was anything other than all engines crammed into the main body tube.

V

This EMRR review of the ARC {Advanced Rocketry Corporation} 1813PSR rocket may give you some ideas you can borrow for you own design.

http://www.rocketreviews.com/reviews/kits/arc_1813.html

ARC lists two "parallel staged" models on their website. I've never tried their kits before but they do look interesting.

http://www.advancedrocketry.com/

.

[CPMcGraw]

...This EMRR review of the ARC {Advanced Rocketry Corporation} 1813PSR rocket may give you some ideas you can borrow for you own design...

Nice design, Steve. Thanks for the link. After reading the review and the construction report below it, I'm still trying to figure out their booster hold-down and release. Have you seen this model up-close?

[DaveR]

IIRC The Seattle Rocket Works "MIRV Gryphon" uses detachable boosters, not exactly the same concept we are discussing here but could possibly be modified to work. Here's the link: http://www.oldrocketplans.com/srw/srwMG/srwMG.htm

[Doug Sams]

IIRC The Seattle Rocket Works "MIRV Gryphon" uses detachable boosters, Close. The 4-tube booster is a single unit, but the upper section is four separate - detachable - sustainers. Definitely not something you want to fly without lots of eyes :D And some 1/2A3-0T booster motors would be real welcome, too.

So it is in fact quite close to the concept of strap-ons. Perhaps more challenging - when the strap-ons separate, they've already burned and will thus be descending at that point whereas with the MIRV-Gryphon, the sustainers will be under power at separation and thus get scattered to the four corners of the planet :)

IIRC, when LawnDart Rocketry was selling this kit, Dale offered separately packaged, replacement sustainers.

From what I've seen, Rob Edmonds needs to do that for some of his newer kits, too :)

Doug

[Veracity]

You guys are a great source of info. After using those links and seeing those parallel staging rockets, I feel confident enough to proceed as planned.

I think that trying to recover two or more objects as they fall to earth is too adventurous for me. My approach is much more "Caveman like".

"See chute. Chase pretty colors. Catch big stick. Good."

That's about it.

V

[CPMcGraw]

...I think that trying to recover two or more objects as they fall to earth is too adventurous for me. My approach is much more "Caveman like".

"See chute. Chase pretty colors. Catch big stick. Good."

That's about it.

V

That's a good approach. Simple, effective, no multi-prepping, less to lose...:D

I can relate...:o

[snaquin]

Nice design, Steve. Thanks for the link. After reading the review and the construction report below it, I'm still trying to figure out their booster hold-down and release. Have you seen this model up-close?

Craig,

I haven't seen the design in person. Chan Stevens wrote the review & I think I figured out how it works and it appears to be a well thought out design.

If you look close at the pictures the two "tabs" on the boosters are offset and lock into the slots where the fins meet the main airframe tube. Since they are offset, looks like one tab on a booster sits on top of a tab from a booster on the other side - if this makes sense.

The two "rails" on each booster appear to take up the slack between the two fins the booster mounts between to keep the booster from moving side to side. Boosters appear to have dowels that slide into launch lugs from the bottom side so when ejection occurs the boosters slide off the the rear of the rocket. The transition in the design keep everything tucked up nicely, more streamlined.

http://www.rocketreviews.com/reviews/kits/arc_1813.html

Maybe Chan has some comments but the more I look at the design the more I realize I probably couldn't come up with a better system than what's shown here.

Pretty cool!

.

[Maniac BAR]

Close. The 4-tube booster is a single unit, but the upper section is four separate - detachable - sustainers. Definitely not something you want to fly without lots of eyes :D And some 1/2A3-0T booster motors would be real welcome, too.

So it is in fact quite close to the concept of strap-ons. Perhaps more challenging - when the strap-ons separate, they've already burned and will thus be descending at that point whereas with the MIRV-Gryphon, the sustainers will be under power at separation and thus get scattered to the four corners of the planet :)

IIRC, when LawnDart Rocketry was selling this kit, Dale offered separately packaged, replacement sustainers.

From what I've seen, Rob Edmonds needs to do that for some of his newer kits, too :)

Doug


Just got around to this post. I have a MIRV G. and fly it on a fairly regular basis. Surprising enough each time it had good sustainer ignition they all appeared to head straight up. :p

After five flights, there have been only two times that they all lit. The dang thing stages so far up with A10-0 boosters that all you see is two, three or four little currly que smoke trails heading further up! However, on all the flights, the sustainers have all come back down within a 50 to 100' circle of each other! On one of the completely sucessful flights you could see four orange streamers heading down in a tight bunch. All of them were recovered about 50' from the pad and in about a 20' circle or so. I too made some extra sustainers figuring they would go with the wind but so far that has not been the case.

I think Dale provided extra sustainers because of the high failure rate of staging. When it doesn't stage the booster with sustainer comes in ballistic and just about destroyes the stuck sustainer. They are only BT-5 tubes and the booster has four empty casings in it to drive the whole thing in hard. :eek:

And to think I was going to make a BT-20 size version of this kit!!!! I just might do it anyway. :o