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  #11  
Old 02-18-2007, 09:07 AM
Ltvscout Ltvscout is offline
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Quote:
Originally Posted by JRThro
Scott, do you mean Launch Pad 2000?

That's the one. Thanks for posting the link, John.
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  #12  
Old 02-19-2007, 12:05 PM
SaturnV SaturnV is offline
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Okay guys, I found some older A-10-0T engines locally. Bought all they had (4 packs). hope these work, I really didn't want to mess around modifying engines. I travel a lot and will start hitting the hobby shops looking for these now obsolete engines. Thanks to all of you.
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  #13  
Old 03-17-2007, 01:43 PM
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handeman handeman is offline
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Quote:
Originally Posted by Doug Sams
Here's a shot of my 2.2X upscale Midget just coming up to pressure. That's 3 outboard B6-0's (or C6-0's) and a centerline D12-0 in the booster. I think that's the burn string falling away just below the burn stick. Or maybe it's one of the ignitor lead extensions.


Doug,

Looking at the picture and reading, what is the upper stage? Is it a single D?

I've never tried to cluster multi stages and didn't think it could be done reliably. Can it and if so, How?
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  #14  
Old 03-17-2007, 05:47 PM
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Quote:
Originally Posted by handeman
Looking at the picture and reading, what is the upper stage? Is it a single D?
It's a single motor, but I'm not real sure which type. Probably a D12, but might be an E9. I've flown both.

Doug
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  #15  
Old 03-17-2007, 06:32 PM
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Default Re: Clustered staging

Quote:
Originally Posted by handeman
I've never tried to cluster multi stages and didn't think it could be done reliably. Can it and if so, How?
There are basically two configurations that work well, with minimal risk. One is a clustered booster to single motor next stage. The other is a clustered booster to clustered next stage, but the booster breaks away in pieces. That way, if one booster motor burns out sooner than the others, its separation won't force the others to separate prematurely. A single piece clustered booster is just asking for problems.

For the first case, you use a burn string. This holds the bird on the pad, releasing it only if the center motor lights and burns the string holding it. That way, it is assured that the motor that lights the next stage has indeed been lit.

Here's a pic of the burn string attachment points on my Uber Tuber:


You can see my burn stick in the earlier pic. It mounts on the rod and projects under the center motor. The stick is coated with ablative epoxy, but can also be drilled and replaced if/when it gets too charred.

The string attaches as shown here:


The transparent gif doesn't work well on the blue background. You can see it better here along with more info: http://home.flash.net/~samily/burn-string/

The second method puts a separate motor tube and fin on each booster motor. Each one falls away as its sustainer lights without need for perfect synchronization with the other booster motors.


More details here: http://home.flash.net/~samily/motor-eaters/ and a few more pics here: http://home.flash.net/~samily/thridget70/

Also, here's a shot from LDRS last summer. Dave Schaefer and I were racing similar 3-to-3 motor clustered stagers. One of mine didn't light Its rod speed was marginal on two, and weathercocked badly in the Texas wind resulting in a near power prang when the sustainers lit. But it might just finally make its post-repair debut flight next weekend


Doug
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  #16  
Old 03-18-2007, 11:32 AM
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Quote:
Originally Posted by Doug Sams
There are basically two configurations that work well, with minimal risk. One is a clustered booster to single motor next stage. The other is a clustered booster to clustered next stage, but the booster breaks away in pieces. That way, if one booster motor burns out sooner than the others, its separation won't force the others to separate prematurely. A single piece clustered booster is just asking for problems.

Doug


Doug, you are the "Rocket" man.

A clustered booster to single upper stage I pretty much figured out, except for the burn string idea. Never heard of one before, but will never try a cluster to single without it. It may have occurred to me after a lawn dart to two.

The separate tubes and fins for the booster cluster also makes a lot of sense. Again, something I hadn't thought about. I probable would have figured it out, eventually, maybe.

Time to get to the workbench. It’s amazing how many ideas pop up when you get a little more good info.

Thanks
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  #17  
Old 04-08-2007, 12:15 PM
SAABMaven SAABMaven is offline
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Thumbs up Excellent ideas and info!

Doug,

Thanks for documenting that so well. The burn string idea is brilliant! The pictures and diagrammes are all printed out and on my work table... for the next few weeks merely to think about.

Clusters are interesting but also complex in a staging environment. Have you (or anybody else) considered using a larger D-motor in the first stage(s) and then a smaller C-motor in the upper stage(s)? Will the smaller upper motor ignite?

The numbers say that the initial thrust of a D12 motor is 30 newtons for ~0.26 seconds, wheras a cluster of three A8 motors also thrust at 30 newtons for a slightly shorter time. Assuming the same design weight, is not the choice of a single D12 the simpler design?

Clustering on the first stage is attractive, I've got to admit. My staging experience was never something about which I could boast... the flights were unimpressive and stressful... a few metres off the ground slowly, enough for the gusty wind near the ground to have an effect and tip the rocket alarmingly off vertical before the second stage ignited. Slow flight is nice for video cameras but too mich time is spent in turbulent air.

The only other first stage clustering idea that I've been thinking about is to cluster a single D12 motor with three A-10PT (Plugged) motors for an initial thrust of 60 newtons at 0.2 seconds into the flight. The A-10 motors burn only half as long as the D12 motor, they are just empty weight; but it seems to me that the initial second of flight, so close to the ground turbulence, is critical. Your thoughts?

Cheers,
Rob in Vermont
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  #18  
Old 04-08-2007, 01:36 PM
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Quote:
Originally Posted by SAABMaven
The burn string idea is brilliant!
I can't recall where I got it - maybe from an Estes catalog back when I was a kid - but it's someone else's and not mine.

Quote:
Have you (or anybody else) considered using a larger D-motor in the first stage(s) and then a smaller C-motor in the upper stage(s)? Will the smaller upper motor ignite?
That's how the Estes Comanche works, staging a 24mm motor to an 18. Mine is gap staged and properly vented. It works great. And if I ever build a Farside-X clone, I'll likely do the same thing.

Quote:
The numbers say that the initial thrust of a D12 motor is 30 newtons for ~0.26 seconds, wheras a cluster of three A8 motors also thrust at 30 newtons for a slightly shorter time. Assuming the same design weight, is not the choice of a single D12 the simpler design?
That's a good observation. Both my one-piece clustered boosters are clustered only because a solo D12 won't do the job. Extra motors are needed.

That said, I've tinkered with the idea of playing with a cluster of A10s in a booster, although in this case, they would be three or four A10-0Ts in a multi-piece booster staged to 3/4 sustainer motors. The idea was to do a small field version of the Thridget.

Quote:
The only other first stage clustering idea that I've been thinking about is to cluster a single D12 motor with three A-10PT (Plugged) motors for an initial thrust of 60 newtons at 0.2 seconds into the flight. The A-10 motors burn only half as long as the D12 motor, they are just empty weight; but it seems to me that the initial second of flight, so close to the ground turbulence, is critical. Your thoughts?
The idea is to get lots of thrust without lots of total impulse. It gives good rod speed but doesn't put the bird in orbit. I've flown a D with three Bs and also with 3Cs. Three As would work, too. In my case, tho, Rocksim showed a rod speed I didn't like with 3 As, so I never tried it. It probably would have been OK, but there wasn't any extra margin in case one of the outboards didn't light.

On a lighter rocket, I'd give it a try, though.

Doug
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  #19  
Old 04-08-2007, 02:38 PM
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Quote:
Originally Posted by SAABMaven
My staging experience was never something about which I could boast... the flights were unimpressive and stressful... a few metres off the ground slowly, enough for the gusty wind near the ground to have an effect and tip the rocket alarmingly off vertical before the second stage ignited. Slow flight is nice for video cameras but too mich time is spent in turbulent air.
Rob,

It sounds like your birds were just too heavy - or the rods too short - to get sufficient speed before clearing the rod. Most Quest and Estes boosters are what I'd consider medium thrust motors. B6-0 and C6-0 motors are fine on ordinary two-stage rockets, but are gonna be grunting in the first stage of a 3-stager or in some of the heavier 2-stagers out there. The D12-0 and rare C11-0 are well suited for this, tho. The Estes Echostar, for example, is one 2-stager that looks marginal on an 18mm booster, and begs for upgrading the booster to 24mm.

Generally speaking, BT-20 (ie, minimum diameter) and BT-50 based 2-stage rockets work great on B6-0s and C6-0s. If you build really light (impossible for me) and use a long rod, a 3-stager is possible, typically min diameter. A light BT-55 2-stager can also be done, or even a BT-60 if you build really light.

So, if your staging experiences have been slow and nearly horizontal, besides clustered boosters, you can try lighter rockets and longer rods, which may in turn dictate bigger lugs. For example, all my 24mm powered stagers use 1/4" lugs so they can be flown off 6' rods.

There are lots of plans for stagers here and on JimZ that should fly great on B6 and C6 boosters.

For 24mm stagers, anything BT-55 to BT-60 works great. When you start approaching 2" diameters, you gotta be careful. It's easy to end up too heavy for the D12-0. (That's how my clustered booster Midget-70 came to be.)

For 13mm stagers, if you have a stash of A10-0T booster motors, you can have lots of cheap fun. These work great up to BT-50 for 2-stagers, and I've even flown a 3-stage Midget variant without problems (other than losing sight of the sustainer). The big thrust spike of the A10 allows it to do more than a typical A (eg, A8-0).

Staging is probably my favorite thing to do in this hobby. That "free kit" Midget Estes shipped me in 69 or 70 has made a staging monster out of me

Doug
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  #20  
Old 04-08-2007, 07:01 PM
SAABMaven SAABMaven is offline
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Thanks Doug!

I'll have a closer look at those plans over the next week or so. Appreciate the insights.

Cheers
Rob in Vermont
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