Clusters and Ejection

[DaveR]

Starting a new thread as to avoid hi-jacking another.

Just to help folks get a good grasp on things, the E9 peak thrust is more than 2N less than the C11 and only about 5N more than a C6. If you are afraid to launch a rocket with a C11, don't launch it on an E9!

Peak Thrust:

C6-x 14.09N
C11-x 21.73N
D12-x 29.73N
E9-x 19.47N

Just in case we forget....

Four C6-3 cluster: 56.36N peak thrust,
Total impulse 35.28N/s

I have very little cluster... OK no cluster experience :o (but I am willing to learn) but tbzep's earlier post about a cluster of 4 C6-3's got me to thinking.
Are there any "extra precautions" any of you guys take regarding the ejection forces produced by a cluster? For instance, longer and or thicker shock cords or exculsive use of baffles with a cluster.
As discussed elsewhere on this forum, today's Estes ejection charges tend to be a little "hot". Seems to me that 4 ejection charges going off in a paper tube at the same time (or close to the same time) could produce less than desirable results even with a baffle.

Would it be safe to cluster say, 3 C6-0 and 1 C6-3 together? ......Well maybe not, if the C6-3 failed to ignite that'd be ugly too. Maybe half and half? :confused:

[barone]

Starting a new thread as to avoid hi-jacking another.



I have very little cluster... OK no cluster experience :o (but I am willing to learn) but tbzep's earlier post about a cluster of 4 C6-3's got me to thinking.
Are there any "extra precautions" any of you guys take regarding the ejection forces produced by a cluster? For instance, longer and or thicker shock cords or exculsive use of baffles with a cluster.
As discussed elsewhere on this forum, today's Estes ejection charges tend to be a little "hot". Seems to me that 4 ejection charges going off in a paper tube at the same time (or close to the same time) could produce less than desirable results even with a baffle.

Would it be safe to cluster say, 3 C6-0 and 1 C6-3 together? ......Well maybe not, if the C6-3 failed to ignite that'd be ugly too. Maybe half and half? :confused:
Dave,

You got to be careful mixing boosters with regular motors. Unless you plug them or their motor tube, you'll get recovery deployment when they burn out vs when you reach apogee. And, put some tissue at the top (forward end) of the motors. This is to prevent hot particals falling into a motor that may not have ignited under boost (well, that's what I was taught and I think I read it somewhere too :confused: ).) As far as thicker/longer shock cords, just go with the normal ratio (not the Estes ratio). Shock cord should be a minimum of 1.5 X the body length (yeah, there's another thread where everyone has provided their $.02 on that matter too).

Now...that was $.02 worth.. ;)

[Doug Sams]

I have very little cluster... OK no cluster experience :o (but I am willing to learn) but tbzep's earlier post about a cluster of 4 C6-3's got me to thinking.
Are there any "extra precautions" any of you guys take regarding the ejection forces produced by a cluster? For instance, longer and or thicker shock cords or exculsive use of baffles with a cluster.Yes, beefing up the recovery harness is a good idea. I like to use kevlar cord for the part that remains in the airframe, and use a shock cord protector, also kevlar, over the portion of the shock cord that transitions thru the opening. Also, use extra wadding, too.

As discussed elsewhere on this forum, today's Estes ejection charges tend to be a little "hot". Seems to me that 4 ejection charges going off in a paper tube at the same time (or close to the same time) could produce less than desirable results even with a baffle.

Would it be safe to cluster say, 3 C6-0 and 1 C6-3 together? ......Well maybe not, if the C6-3 failed to ignite that'd be ugly too. Maybe half and half? :confused:Half and half is good. Just keep in mind, that even if one of the ejecting motors doesn't light, there has to be enough other ejecting motors to get the laundry out.

I plug C6-0 motors using 1/2" long pieces of 1/2" dowel epoxied into the end. You can also use plugged B6-0's if, for example, Rocksim says you need a little less total impulse. You can get A10-PT's and use them with 18mm adaptors, too.

Another trick is to use longer delay motors. For example, say that a 5 second delay is perfect for your 4xC6 cluster. You can use two C6-5's and two C6-7's. The 5's will get the chute out while the 7's will be ejecting into an open airframe.

You can mix different motor types, too, if you consider the total burn time plus delay time. For example, two B6-4's could be used with two A8-5's, with the B6-4's putting the chute out and the A8-5's firing ~0.7 seconds later. Or use B6-6's instead of -4's, and have the A8-5's put the chute out.

Lots of stuff you can do with clusters.

HTH.

Doug


.

[tbzep]

Don't forget to do everything you can to make sure they all ignite too.

Individually check igniters for continuity before twisting them together. One easy method is to install the igniters with the little plastic plugs before putting them in the rocket. Check continuity, then slip them into the rocket. Once you have them in place, twist the leads together making sure you don't pull an igniter lead in the process. If you use friction fit instead of hooks, it might be easier to put the motors in the rocket first, then install the igniters.

Use at least 12v for ignition.

[Gus]

The best way to learn clusters is to start with a simple 2 engine cluster kit.

Unfortunately nobody currently offers a really basic two engine, 13mm or 18mm cluster kit. I wonder why.

Fliskits Deuces Wild is a wonderful 2 engine 18mm cluster kit, but the motors are canted making construction and twisting the ignitor leads together a little more difficult.

Same for the Sunward Screamer.

Semroc doesn't offer a 2 engine cluster.

Neither does Quest.

Many of the other smaller companies make 3 engine clusters, but not 2.

Estes does offer the 36-D Squared, which is a non-canted 2 engine cluster but it uses 2
24mm motors, probably not the best idea for a first cluster attempt.

Commonwealth Displays still carries the Estes Thunderstar, which is a straight 2 engine 18mm cluster and might be a good place to start.

Clustering isn't really hard. But don't try it with a regular Estes Launch controller. It just doesn't have enough juice to light a cluster. Use a 12 volt system if launching on your own. If launching with a club, most club launchers have enough power to light clusters.

[Skippy]

The best way to learn clusters is to start with a simple 2 engine cluster kit.

Unfortunately nobody currently offers a really basic two engine, 13mm or 18mm cluster kit. I wonder why. [snip]

I got my initial cluster experience last year with a Thrustline Black Shadow, modified with a Fliskits EMK2-13-55 motor mount, and it flies brilliantly.

http://fliskits.com/products/01prod_fs.htm

Use this motor mount in any BT-55 based rocket designed for 'B' impulse motors and there is your basic two engine 13mm cluster kit.

[Solomoriah]

Take your Hobby Lobby coupon and get a Baby Bertha. Order up a 2x18mm engine mount kit (I've had good luck with Uncle Mike's Rocket Shack) and swap it for the standard engine mount. Add 0.625 ounces (about 18 grams) of noseweight; I used 16 standard computer screws with enough epoxy to hold them all in place.

Flies great, and excellent for a first experiment with clustering. I painted mine Fire Red. Estimated 260' with A6-4 engines, 300' with A8-3's, 680' with B6-6's, 1400' with C6-7's.

I've flown mine on A8-3's and C6-7's and can say it's a real crowd-pleaser.

http://rocketry.newcenturycomputers.net/fleet/doublebarrelbabybertha.jpg

[DaveR]

Wow, thanks for all the good info guys. All this info caused me to take a break from working on my new shop this weekend to try to finish up a couple of build projects I've been working on for a while now. Didn't finish anything but started a another project. I decided to go with 2 motor cluster to test the waters.

Here's a couple of pics of my scratch build 2 engine cluster that I came up with this weekend. (This build jumped to the front of a LONG build que)

The fins may be a little on the large size but they were already cut and I'd rather err on the side of caution in attempting my first cluster. I attached a 18" steel fishing leader to the engine mount (anyone else ever try that?) and have a 2X BT length shock cord. When she gets her clothes on, I'll swing test to see if nose weight is needed. Am I missing anything?

BTW, Sorry about the bad lighting in the pics but there is no electricity in the shop yet. Also, the engine mount is sticking out a little but it was not glued in place when I took these pics.

[Tom Swift]

The build looks great! But your work area is WAY too tidy. :D

A fishing leader works well but has a very small diameter. If it is long enough to extend out the front of the body tube, be sure to take precautions that it does not cause a zipper. A few wraps with tape where it touches the lip of the BT will help.

[DaveR]

The build looks great! But your work area is WAY too tidy. :D

A fishing leader works well but has a very small diameter. If it is long enough to extend out the front of the body tube, be sure to take precautions that it does not cause a zipper. A few wraps with tape where it touches the lip of the BT will help.

Thanks. I didn't think about the zipper effect of using a leader; however, it's about 3" shy of coming out the front of the body tube. Just to be safe, I'll wrap a little tape around it anyway.