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Burn String

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Duderino

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I have been researching making a rocket with an engine cluster. I see a "burn string" mentioned several times as a precaution against the rocket lifting off without the main engine lit. But I cannot seem to find pictures of a Burn string.

Could you help me understand how it would be attached to the rocket and to the launch pad and what material it should be made from?

Thank you.
 

delta22

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Used a burn string once.
Fastened cotton string to bottom of rocket on opposite side from launch rail.
Other end of string was fastened to launch rail.
Idea was that central motor would need to burn through string before rocket moved up rail.
Flight was successful.

However, I much prefer to build the safety margin into the selection of motors in the cluster and ignition methods.
 

Duderino

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How did you fasten the string to the bottom of the rocket? I am trying to get an idea of a way to fasten it that will not damage the rocket from the thrust of the other motors firing, and the string pulling whatever it is attached to apart.

I am sure that this would be easier to answer if I was a little more specific. What I am looking at is the estes Saturn V that was re released. I would like to use a cluster, a central 24mm mount and 4x 18mm mounts. I have read about several builds using this configuration.
It seem that in most of these threads about the build, someone will recommend using a burn string in case the 24mm motor doesn't ignite.

That is why I am asking for more information on burn strings.

Thanks
 

delta22

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You could tie the cotton string around the motor sticking out from the bottom of the rocket that is opposite the rail/rod.
Or make a loop at the end of the string what could encompass the two fins away from the rail/rod.

But what I would really recommend:
1) Use 5 of the same motors, depending on the weight of the rocket 5x C6 or 5x D12.
2) Use Rocketflite MF igniter wires and CF Pyrogen kit. Easy to do and much more reliable than anything with Estes igniters.

I've done a lot of successful cluster launches, and building reliability into the basic launch plan is the most reliable way to go.
 

Bat-mite

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How did you fasten the string to the bottom of the rocket? I am trying to get an idea of a way to fasten it that will not damage the rocket from the thrust of the other motors firing, and the string pulling whatever it is attached to apart.

I am sure that this would be easier to answer if I was a little more specific. What I am looking at is the estes Saturn V that was re released. I would like to use a cluster, a central 24mm mount and 4x 18mm mounts. I have read about several builds using this configuration.
It seem that in most of these threads about the build, someone will recommend using a burn string in case the 24mm motor doesn't ignite.

That is why I am asking for more information on burn strings.

Thanks
No experience, so I can't help you. But, in those other build threads, you could find the user name of whomever suggested using a burn string, and PM that user. You might get a response to a PM, whereas they might not see this thread if they aren't looking.
 

KennB

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I've done a lot of successful cluster launches, and building reliability into the basic launch plan is the most reliable way to go.
Now you're just being modest.

In addition to your suggestion to use the same motors and home-made igniters, I would say your Cluster Box has helped ensure the good performance you've experienced. We always love to see you tote that little red box out to the pads. Even with good igniters, firing a cluster without a relay is an iffy proposition. Duderino, check out the Cluster Box page of Boris' website for some good info.
 

Tonimus

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+1 To Boris you listen. Cluster Master he is.
 

samb

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Yes, Boris can light a motor or 2... or 20 ! Amps and the right starters are key. As far as burn strings go, my friend Doug Sams had a nice write-up on his web page that you can find on the Wayback Machine. Unfortunately his pictures and diagrams didn't cache.

https://web.archive.org/web/20040724053048/http://home.flash.net/~samily/burn-string/

He's on a little sabbatical now but he may pop on and see this thread and offer some more insight. Hope this helps.
 
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