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  #1  
Old 04-19-2011, 08:39 AM
dyaugo dyaugo is offline
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Default CC Express Booster design modifications

I'm working on a modified version of the Estes CC Express. The upper stage will have (3) 18mm motors using CHAD staging and the booster stage will be the same as the original design except for some changes. I want to design the booster so the engine ejects out after it ignites the upper stage. The reason is because I want to make it as light as possible when it tumbles downward to avoid it getting damaged. I launch on a dry lake bed and it seems you always have to over chute your rockets because the surface is so hard..if you don't you do a lot of damage....

Also one other change I am making to the booster is to use a tube coupler to hold the stages together. Not sure how much of the coupler actually needs to be fitted into the upper stage...I was thinking maybe a 1/4" and sand it to make it fit nicely, but not too snug.

Thanks for the feed back...
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  #2  
Old 04-19-2011, 09:10 AM
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chadrog chadrog is offline
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If you blow the motor out of your booster, how does the booster detach from the sustainer? If your booster motor kicks out, the booster body is going to stay where it is,and get torched by the sustainer motors. If you want to fly this again in a two staged configuration, I think you're going to have to risk the possibility of some landing damage.
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Old 04-19-2011, 09:19 AM
dyaugo dyaugo is offline
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Quote:
Originally Posted by chadrog
If you blow the motor out of your booster, how does the booster detach from the sustainer? If your booster motor kicks out, the booster body is going to stay where it is,and get torched by the sustainer motors. If you want to fly this again in a two staged configuration, I think you're going to have to risk the possibility of some landing damage.


After it ignites the upper stage should pull away? I know maybe I will be stuck with some damage.
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Old 04-19-2011, 09:23 AM
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Doug Sams Doug Sams is offline
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Quote:
Originally Posted by chadrog
If you want to fly this again in a two staged configuration, I think you're going to have to risk the possibility of some landing damage.
Yes. In fact, if anyone wants to fly staged BP rockets, they will risk booster damage. It comes with the territory.

Boosters tumble down and hit the ground, and occasionally get a ding or broken fin. I just patch 'em up and keep flying them until they get so beat up as to needing overhaul in which case I maybe replace a fin or two, sand things down, fill, prime and repaint.

But trying to build a BP booster wherein the staging event separates the booster and ejects the booster motor is very iffy. In all likelihood, either they stay together at separation, or the booster motor ejects leaving the booster stage to get fried by the sustainer exhaust.

Doug

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  #5  
Old 04-19-2011, 09:32 AM
dyaugo dyaugo is offline
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Quote:
Originally Posted by Doug Sams
Yes. In fact, if anyone wants to fly staged BP rockets, they will risk booster damage. It comes with the territory.

Boosters tumble down and hit the ground, and occasionally get a ding or broken fin. I just patch 'em up and keep flying them until they get so beat up as to needing overhaul in which case I maybe replace a fin or two, sand things down, fill, prime and repaint.

But trying to build a BP booster wherein the staging event separates the booster and ejects the booster motor is very iffy. In all likelihood, either they stay together at separation, or the booster motor ejects leaving the booster stage to get fried by the sustainer exhaust.

Doug

.


Thanks Doug for the input...it's much appreciated. I just thought maybe there was a way of avoiding damage...do you think having the tube coupler 1/4" in the substainer is enough to hold it in place and still separate?
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  #6  
Old 04-19-2011, 10:00 AM
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Quote:
Originally Posted by dyaugo
Thanks Doug for the input...it's much appreciated. I just thought maybe there was a way of avoiding damage...do you think having the tube coupler 1/4" in the substainer is enough to hold it in place and still separate?
In brief, yes. A quarter inch is plenty to join the two sections. Extra coupler length is usually employed to align the sections. For example, if you're not real good at cutting tubes and the ends are not quite square, the tubes tend to form a kink when butted up against each other and a long coupler can hepl correct for that.

That said, it depends on what type staging you are doing. In tape-together staging, the tape is often all that's needed to hold the stages together until separation. The coupler doesn't provide much extra friction to hold them together. Hence, a 1/4" being enough. (To be clear, in tape-together staging, the sustainer motor is frction fit into the sustainer, the cellophane tape joins the booster motor to that, then the booster section is sorta loosely friction fit to the booster motor. And an aft motor block in the booster ensures the booster stage comes off with the booster motor.)

In your case, you are gap staging (implied by the fact you're staging one booster motor to three sustainers). In that case, the upper and lower motors are not joined to each other. So you need some way for the booster section to stay attached to the sustainer and not drag separate, not separate too easily. For that, I add some friction tape to the booster, and adjust it before the flight. I want the booster to stay attached long enough for the sustainer(s) to have the best chance of igniting.

In the pic below, you can see the friction tape applied to the coupler. It's maybe a half inch long piece of 1/4" masking tape, and it helps the booster section to snugly join the sustainer.



I'd say, as long as both tubes are square cut, that a 1/4" long coupler is enough. It gives you enough tube to add a bit of tape to for doing this trick.

One extra thought, I add lots of CA to my exposed couplers (then wipe off the excess) and let them dry, then sand them smooth. This helps keep them from geting the "fuzzies" due to repeated insertion/extraction from the sustainer, and it also protects the paper from the tape when it's removed, keeping the paper from delaminating.

HTH.
Doug
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  #7  
Old 04-19-2011, 10:23 AM
El Cheapo El Cheapo is offline
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I've never built a cc express nor used this technique so I'm just kind of throwing this out there. Would there be enough room to pack a Streamer and use a burn string?
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  #8  
Old 04-19-2011, 10:24 AM
dyaugo dyaugo is offline
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Quote:
Originally Posted by Doug Sams
In brief, yes. A quarter inch is plenty to join the two sections. Extra coupler length is usually employed to align the sections. For example, if you're not real good at cutting tubes and the ends are not quite square, the tubes tend to form a kink when butted up against each other and a long coupler can hepl correct for that.

That said, it depends on what type staging you are doing. In tape-together staging, the tape is often all that's needed to hold the stages together until separation. The coupler doesn't provide much extra friction to hold them together. Hence, a 1/4" being enough. (To be clear, in tape-together staging, the sustainer motor is frction fit into the sustainer, the cellophane tape joins the booster motor to that, then the booster section is sorta loosely friction fit to the booster motor. And an aft motor block in the booster ensures the booster stage comes off with the booster motor.)

In your case, you are gap staging (implied by the fact you're staging one booster motor to three sustainers). In that case, the upper and lower motors are not joined to each other. So you need some way for the booster section to stay attached to the sustainer and not drag separate, not separate too easily. For that, I add some friction tape to the booster, and adjust it before the flight. I want the booster to stay attached long enough for the sustainer(s) to have the best chance of igniting.

In the pic below, you can see the friction tape applied to the coupler. It's maybe a half inch long piece of 1/4" masking tape, and it helps the booster section to snugly join the sustainer.



I'd say, as long as both tubes are square cut, that a 1/4" long coupler is enough. It gives you enough tube to add a bit of tape to for doing this trick.

One extra thought, I add lots of CA to my exposed couplers (then wipe off the excess) and let them dry, then sand them smooth. This helps keep them from geting the "fuzzies" due to repeated insertion/extraction from the sustainer, and it also protects the paper from the tape when it's removed, keeping the paper from delaminating.

HTH.
Doug
.



Epoxy on the inside of the coupler would help too.
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  #9  
Old 04-19-2011, 10:24 AM
dyaugo dyaugo is offline
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Quote:
Originally Posted by El Cheapo
I've never built a cc express nor used this technique so I'm just kind of throwing this out there. Would there be enough room to pack a Streamer and use a burn string?


I never tried that technique, but it might work?
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  #10  
Old 04-19-2011, 10:51 AM
jdbectec jdbectec is offline
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Quote:
Originally Posted by dyaugo
I'm working on a modified version of the Estes CC Express. The upper stage will have (3) 18mm motors using CHAD staging and the booster stage will be the same as the original design except for some changes. I want to design the booster so the engine ejects out after it ignites the upper stage. The reason is because I want to make it as light as possible when it tumbles downward to avoid it getting damaged. I launch on a dry lake bed and it seems you always have to over chute your rockets because the surface is so hard..if you don't you do a lot of damage....

Also one other change I am making to the booster is to use a tube coupler to hold the stages together. Not sure how much of the coupler actually needs to be fitted into the upper stage...I was thinking maybe a 1/4" and sand it to make it fit nicely, but not too snug.

Thanks for the feed back...



How do you plan on fitting (3) 18mm motors into a BT-55? Also you could attach a streamer to the booster.

http://plans.rocketshoppe.com/pubs/...am_roc_v5n1.htm

The unibird plan shows one way of doing this.
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