Newbie Cluster Question

[PWALPOCO]

My (shy) freinds Woody , Alan and I will soon be entering a new plane of rocketry existance .... clustrering.

Ive been looking at clustering for a while now as a means of getting a bigger slow low flying rocket wheras Alan is probably looking for Altitude. Woody is probably in it for the same things I am.

The questions I have about Clusters are to do with redundancy of motors , ejection charges and so on.

My train of thought is that all the motors might not fire. Some may not fire or all may fire, or is this something that you should make totally sure of before ? Is Ignition a little hit and miss no matter how well you try to make sure ?

If total ignition can never be 100% guaranteed do you plan in redundancy ? I mean , if the rocket needs to have 3 motors to safely get off the ground , do you install 4 ? If youve got 4 , do you have just the 1 motor with an ejection charge , or maybe 2 ?

So many what ifs ! Guidance anyone ?

Paul

 

[rocket trike]

I have done 3 motor clusters and have all of the motor light everytime using a whip clip. When I launch a cluster I hook up the whip clip to the motors and have a freind check it over. I use all 3 motors with a ejection charge again with no problems. I hope this helps a little.

 

[jflis]

A similar question came up recently on ROL when a rocketeer was having trouble getting all the motors in his cluster to light.

Here is my response:
Using clipwhips is usually your best bet, but there's more to getting clusters lit properly and I hope these points help:

1) Make sure all 6 clips are *clean* and have good spring to them.

2) make sure the controller clips (the ones that will clip onto your clip whips) are clean also (many forget this point... )

3) When selecting your igniters, (i only use the ignitors that come with the Estes motors), select 3 ignitors that are about the same size/shape (same amount of pyrogen on the tip, etc)

4) If you've been having bad luck as you have, you may wish to do a continuity check on *each* ignitor befor and after installation in the motor. Also, check the ignitors *after* launch if you have a misfire. See if the ignitor burned. If not, you may have a back clip

5) While grasping the ignitor tip between your thumb and forefinger, slightly spread the leads going into the tip. This is a common area for a short circuit. Hold the tip helps prevent breakage while spreading the leads.

6) Be certain that the ignitor tip is *touching* the rocket fuel inside the motor nozzle

7) Use the provided plugs or a small square of recovery wadding (NOT tissue) to secure the ignitor in the motor. You should be able to hold the assembly by the ignitor and jiggle it without the motor falling off...

8) If you can, do a test with 3 ignitors on your clipwhip without the motors and visually gauge if they are firing at the same time. If they all fire at different times (even a fraction of a second), either clean all of your clips or look into a better power source. You say you are using a 12 vold battery system, but if this is made up of flashlight batteries, pitch it and go to a car or motorcycle battery.

One final point that many miss is protecting any motors that may not light. You want to put a small ball of recovery wadding in the TOP of each motor (in the case of D12 motors, you may have to use tape to hold it in place). The purpose of this is to protect that motor (and your rocket), should that motor not light. The ejection charge of the OTHER motors can ignite this motor in reverse, gutting your rocket (not a good thing )

Sorry so long winded. I hope this helps!

=================
FlisKits also has a hints and tips sheet on clustering. I have uploaded it and you can view it at: https://fliskits.com/free_dl/hnt-sl3cl.pdf (it is a 137KB file)

Let me know if this helps.
jim

 

[PWALPOCO]

Rocket Trike

So , you are saying having multiple ejection charges going off isnt a problem ? I had visions of scorched BT's , but seems I was wrong.

Paul

 

[rocket trike]

The ejection cahrges do not go off all at the same time. I out my lighting strike up on 3 B6-4 real kool flight slow lift off. Only got up about 300 ft the kool part is that you could hear all 3 ejection charges go off one right after the other. In other words they will not put all of the heat in the tube at one time.

 

[vjp]

I'd just like to add my 2c in here - I've found it to be a good practice to epoxy-coat the inside of Estes-style BT's, for a few inches ahead of the clustered motor mounts. Several ejection charges going off simultaneously (or close to it) can create a lot of heat in there, eventually causing charring and burning. The epoxy really helps to protect things.

 

[Rocketjunkie]

Originally posted by jflis
6) Be certain that the ignitor tip is *touching* the rocket fuel inside the motor nozzle

6a) Look into the nozzle and make sure you can see black propellant. If there's come clay covering it, gently scrape it out.

 

[Micromeister]

Paul:
My second love is clustering...
. Jflis gave you plenty of good points. If your using a standard ignition system make sure you have as large a amp/hr battery as you can get. Even with this heavier batter remember your loosing a lot of power from the batter to the igniters through that thin whimpy controller wire to the launcher. As this system sit's you'll have good to fair success with 2 and 3 motor clusters, 4 motors and up I'd strongly suggest a relay ignition system. with the batter at the launcher instead fo the controller. this allows heavier wire and shorter runs between the source and the igniters 3 to 4 feet vs. 25 or more.
Clustering, well consistant clustering is almost an art. You can't simply jam 3 igniters in 3 motors and expect them all to light.
If you think of Clustering as a 3 part system it will Greatly increase your success percentage.
1) Igniters, They need to be checked before and AFTER installation. Check the pyrogen for cracks or other defects, use Only pretested ingiters, check the gap between the leads a the pyrogen (spread slightly while holding the pyrogen tip tightly in the fingers if the leads are touching. Insert and recheck continuity.
2) Battery: as High an amp/hr rated battery as you can get.
3) System: 2 or 3 motors standard contorller is marginal but useable. 4 plus motors: a Relay ignition system is the best way to insure success. Check all micro clips before EACH launch, Clean before connecting to a cluster igniter (Every time) have a buddy check the connections to see none of the clip are shorting and all are connected correctly.
In Sept or Oct. of last year we had a long thread on "Clustering the Classic's" in this forum, A search will add alot of additional info.

 

[hokkyokusei]

Originally posted by PWALPOCO
My train of thought is that all the motors might not fire. Some may not fire or all may fire, or is this something that you should make totally sure of before ? Is Ignition a little hit and miss no matter how well you try to make sure ?

If total ignition can never be 100% guaranteed do you plan in redundancy ? I mean , if the rocket needs to have 3 motors to safely get off the ground , do you install 4 ? If youve got 4 , do you have just the 1 motor with an ejection charge , or maybe 2 ?

I've successfully clustered up to 9 black powder motors. I use two techniques. Up to about four motors I use clip whips as Jim described in his reply. Above 4 motors I tend to use quickmatch for clustering. You put a length into each motor and bundle the other ends together with a single igniter. Works well.

While clusteing can be very successful, it's always best to tink about what is likey to happen if some of the motors don't light. I don't think I'd attempt a flight where the failure of just one motor to light would mean a disaster! Generally, I'd use a greater "safe distance" for launching a cluster.

 

[Austin]

I think one of the rules of thumb in clustering would be to make sure you are not underpowered if you loose a motor or two...at least from a safety side.

Carl