cluster rocket delay time

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fr3nkd0gz

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I am currently trying to build an experimental lander prototype using model rocket engines. due to my design, I am going to need several motors that are about 10 centimeters apart so the risk of flipping is high if not all motors activate at the same time. I have looked for information regarding ignition variation between the same models but I haven't been able to find anything. I was wondering if anyone had any advice or data for how much variation in the ignition I should expect.
 

Antares JS

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For me to give you good advice on starting motors simultaneously, I need to know what kind of motors your are trying to start. Regular Estes BP motors or composites?
 

fr3nkd0gz

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I am looking at an Apogee Medalist motor F10-4, link below, I am just hoping for consistency under a second if possible or advice on how to build a super consistent ignition rocket.

 

Daddyisabar

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I don't know but I've been told, launching widely spaced motors is mighty bold! I have used only BP motors with Q2G2s, only with the best club relay or cluster box systems, only in the best conditions, only under strict RSO supervision and permission. Widely spaced motors are hallmarks of extremely poor rocket design! I use two widely spaced motors on my Arado 234 Blitz. Two motors can be worse than say eight on the Lancaster. Two motors must light and perform in synchronization, no where to spread the SIN!
IMG_20140620_213209129.jpg
 

samb

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I don't have any data on cluster motor ignition other than experience that yes, the instance of ignition varies on just about every flight. So relay systems, good starters, long leads are all important. My modified Estes SR-71 flies relatively straight on the center and either of the two outboard motors off a 5 foot launch rod. The long leads give the outboards a few more nano-seconds of contact if the center lights first.

Blackbird.jpg
 

samb

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Some info about rigging a burn string to prevent a rocket from leaving the pad unless the critical motor (like the one that controls the recovery system deployment) lights can be found in this thread:

Burn String | The Rocketry Forum
 

afadeev

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I am currently trying to build an experimental lander prototype using model rocket engines. due to my design, I am going to need several motors that are about 10 centimeters apart so the risk of flipping is high if not all motors activate at the same time.
How exactly many motors is "several"?
What is the overall shape and size of your model?
What motors are you planning to use, how how will the contraption be descending back to the ground (under chute? gliding?)

All things being equal, black-powder (BP) are easiest to ignite "nearly" simultaneously.
Whether or not "nearly" will be good enough for your application, is hard to determine, with the information shared thus far.

I have looked for information regarding ignition variation between the same models but I haven't been able to find anything. I was wondering if anyone had any advice or data for how much variation in the ignition I should expect.
It all depends on what types of rocket motors you are suing, how many rocket motors, what type of ignitors you are using, and what type of ignition system and ignition wires you plan on using.
If you want a deterministic answer, please specify all five (5) with maximum specificity.

Without that, my best guess is that BP-motors will be your best guess, and just might give you the desired outcome 2 out of 3 times.

HTH,
a
 

samb

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BTW, I'm convinced Daddy uses alien technology on his outlandish contraptions. ;) Don't try this at home ! :p
 

Daddyisabar

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I am looking at an Apogee Medalist motor F10-4, link below, I am just hoping for consistency under a second if possible or advice on how to build a super consistent ignition rocket.

Nope. Slow burn motors are no good. Are you trying to land under thrust?
 

Rocketjunkie

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Use Estes F15s instead. Also use electronic ejection in case they don't all light.
 

bguffer

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Believe his lander needs the 7 second burn of F10s.
 

bguffer

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Suspect you should check with club of where you will launch to see if they will be ok launching this. Will likely need to be launched on away pad, and a heads up flight. You can reassure them that a cluster of 3xF10 has been successfully launched (see the link above).

Bob
 

bguffer

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If you still need to acquire the F10s and can't buy the F10s locally, you may be looking at 60 dollars shipping/handling/hazmat.

Bob
 

bguffer

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"how much variation in the ignition I should expect"
Look at the 600 FPS slow motion video in the link above. I'm uncertain that the central motor lit before it left the 8' rail. Kinda hard to tell, given that F10s don't have much smoke/flame.

The F10s are cast using Blue Thunder propellant, which to my understanding was the easiest AP propellant to light, at least 10 years ago when i know all the different motor propellants.
 

bguffer

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Is the lander going up using the F10's, or is a different/larger motor putting the lander up in the air with the F10's lighting at apogee for landing purposes?
 

bguffer

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You might check if Joe Barnard has any experience with F10s

He was working on falcon 9 type recovery. Believe he focused on single motor designs, but his initial experimentation could have been clustered.

Bob
 
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