Cluster Failure Frequency

[SteveA]

I've been reading through the latest cluster threads and have noticed several comments of misfires and related cluster failures. So far, I'm 3 for 3 but I only recently delved into clustering this summer. I sort of figured that if I do this long enough that it will happen to me, but I was wondering just how often you'll have something like this happen?


Steve

 

[gpoehlein]

I just started flying clusters this past year or so, and I've yet to have a single failure. But then, I've also been using Quest Q2G2 igniters for all my cluster launches, and they really do make a difference!

 

[edwinshap1]

I just started flying clusters this past year or so, and I've yet to have a single failure. But then, I've also been using Quest Q2G2 igniters for all my cluster launches, and they really do make a difference!

they really are super amazing igniters.

i haven't clustered, but they are what i use in every one of my DD ejection charges. They fire so easily and readily that i'm willing to spend a dollar per even if they have short leads compared to e-matches. that and they have pyrogen which will gaurentee an ignition.

if you're using a club launch system with a 12v battery you're good to go for a pretty big cluster of bp motors. apcp motors are more complex, but if they're short you can use the 8" q2g2 leads and dip them in pyrogen which should ignite, but isn't recommended.

 

[[POW]Eagle159]

....I've had one using a scratch built and the Estes ignites.:wink:

 

[jimzcatz]

Umm, nope...not gonna say a word!!! :jaw:

 

[plano-doug]

I've been reading through the latest cluster threads and have noticed several comments of misfires and related cluster failures. So far, I'm 3 for 3 but I only recently delved into clustering this summer. I sort of figured that if I do this long enough that it will happen to me, but I was wondering just how often you'll have something like this happen?


Steve

I've had three unfortunate outcomes in all my cluster attempts. I also have several flights where one motor didn't light, but the flight was otherwise OK. But on those three occasions...ouch!

Most have been BP clusters. In one case, the soft, brittle clay booster nozzle didn't retain the ignitor plug with the result that only 2/3 boosters lit. The rocket gravity turned badly and was going lickety split horizontal at touchdown. In fact, that happened twice with that rocket, but it's been rebuilt both times.

Otherwise, my BP cluster flights have turned out well. I've used Estes ignitors in all those flights. While not as easy to light as Q2G2's, they are still quite good for clusters provided you have a decent launch controller. That is, if you go back to the old days of bare nichrome and the old "Astron" ignitors, you find Solar ignitors very reliable by comparison

As for APCP, I've tried to air start 2 RoadRunner G80's using stock ignitors. Got 1/2 lit. Excellent recovery. I also tried ground starting 4 of those using home made ignitors. Got 2/4. Not pretty.

So APCP clusters are definitely in a tougher league. But, even with BP - even using Q2G2's - you need to have the discipline to give yourself the best chances of success.

The ignitors need to all be securely installed against the propellant. And the nozzles must be clean prior to inserting the ignitors.

The leads all need to be securely tied together with no chance of shorting or coming open. Cluster clips (ie, Clip Whips) are not very reliable and prone to shorting and/or coming off. It's better to use more permanent connections such as twisting wires together or soldering.

Even with low current ignitors, there are still many ways a cluster launch can go awry, so it's important to make sure everything is done correctly if you want consistently good flights.

Doug

Super Big Bertha with all nine motors lit using Solar ignitors


.

 

[gpoehlein]

I should point out that I use the Q2G2 igniters in all my cluster flights not so much because of their low current needs, but because of the long insulated wires that come attached to the leads. It is simplicity itself to untwist the wires a bit so they can open them out, then twist the ends together in parallel. I bend the end of the twisted leads 180 degrees, which gives a bit more security when attaching the clip, and also helps to keep the ends twisted together and keeps them from "unraveling". Of course, the straw that comes with each igniter does a great job of holding the igniter in the nozzle (I crease each one longways with my thumbnail, flatten and fold it to form kind of a V shaped channel for the igniter - as it tries to unfold itself it holds more firmly in the motor). Because the leads are longer and insulated, there is little chance of shorting one or more of the igniters. As a result - I've had no ignition failures to date, and I've probably launched about a dozen clustered flights this year so far.

 

[Wayne's World]

A couple of months ago, I started flying a Starlight Sieron 3 (3x18mm). My first flight, on A8-3's, was perfect - straight as an arrow. Last Saturday, I tried with C6-3's. Only one lit, and the bird went sideways. The plugs held in the other two motors, and pulled the ignition cable off the pad until it was taut, and the rocket hit the ground, popping ejection a couple of seconds later. I used a whip and insulated the leads from each other with tape. After inspection, I found that one igniter had a broken bridge wire and the other had shorted in the motor. I launched it again this morning, wiring the igniters in series with no whip, and had a great flight, at least twice as high as on the A8's. I learned that I have to pay closer attention to my motor prep.

 

[Fe Dude]

Another +1 for the Q2G2 igniters. I have a few rockets that use cluster, all BP, the quest igniters are a snap to wire together, no need for a clip whip most of the time, and you don't have to worry about shorts between the igniters in the cluster. Well worth the extra $$ to get those in place of the estes ones.

 

[Verna]

I can only address black powder engines but we've been flying BP clusters for many years with tremendous success using only Estes engines and igniters. In over 100 clustered flights (3-5 engines each) using more than 400 engines we've missed a total of 2 engines. Both were attributed to smooth clips slipping off from wiggling in the wind when they sat on the pad too long. When I see other people have failures it's almost always due to the power supply. Sure, you need good connections, and igniters in good shape, and we are careful when choosing them for clustered flights but you have to have a power supply that far exceeds what you need so there is no lag when you push the button. Can't beat a full size car battery, 800 cold cranking amps will do it everythime.

Verna
www.vernarockets.com

 

[modeltrains]

Re: "Cluster Failure Frequency"
Oh, thought it was going to be about Washington D.C. or the Kansas City city council.

 

[MarkII]

Not very often, but sometimes stuff happens. Or in this case, doesn't happen. Careful preparation will help to minimize the frequency.

 

[bjphoenix]

I've flown a good number of clusters with Estes 18mm engines in the distant past, both 2-motor and 3-motor clusters. I always used a 12V car battery and never had a failure.

 

[dpower]

Since I started using the Q2G2, I've flown over 100 motors in 2..7 cluster flights, not a single engine failed to light. Before that, I had an occasional failure, when using clip-whips, when I wasn't careful enough cleaning them. For me, the ease of use for clusters is worth the cost (I purchase packs of 24 direct). I really like the straw type plugs too, since they're easier to put in, and stay in better.

 

[stealth6]

In my small experience, I've had mostly good luck with Estes igniters, and perfect performance with Quest (firing black powder motors). I would definately choose Quest every time all things being equal.

But of course they never are (equal, that is). I've always got tons of extra Estes igniters in my range box (so they are in essence "free"), and Quest ones are either hard to get, or not available at all, and/or come at a cost - which is hard to justify sometimes when I've got "free" Estes ones already, which do MOSTLY work just fine.


But I have a question:
I'm just starting to play around with clustering composite motors and in fact just today bought a few AT E20s for a project that is nearing completion. I've not used FirstFire igniters before, but figured I would use them as that's what came packaged with the E20s (and are - again - therefore "free").
But the little "how to" sheet that comes with them specifically states NOT to use them in clusters. ?!?!?!?

Anyone know why?

s6

 

[qquake2k]

I've got probably a dozen or so cluster flights with my 2x24mm Double Pumper, 2x18mm Double Pumper Jr., and 3x24mm Integrator. All were with Estes motors and igniters with plugs, and no failures (knock on wood). For the 3x24mm Integrator, I soldered insulated wire leads on the Estes igniters. One thing I always do is check the continuity of each igniter individually with a multimeter, before I twist the wires together. That way I know that none of the bridge wires are broken, and that there are no shorts.

 

[bobkrech]

Two ways to minimize the chance of a having a bad igniter in you cluster rocket:

1. Install all igniters and then check each one separately for continuity.
2. Use a wire wrapping tool, not clip whips, for paralleling igniters.

Bob

 

[dpower]

But I have a question:
I'm just starting to play around with clustering composite motors and in fact just today bought a few AT E20s for a project that is nearing completion. I've not used FirstFire igniters before, but figured I would use them as that's what came packaged with the E20s (and are - again - therefore "free").
But the little "how to" sheet that comes with them specifically states NOT to use them in clusters. ?!?!?!?

Anyone know why?

s6

AP starts much slower than BP, so is more difficult to cluster; White Lightning, in particular is quite a challenge to cluster, Blue Thunder, less so. The FirstFire Jrs that come with the E20 (3") are different than the normal FirstFire Jr., shorter, with less pyrogen. Not sure how well they would cluster. Oh, they'll ignite quickly, being a low current igniter, but the smaller amount of pyrogen, combined with WL, may not cluster well.

 

[MarkII]

AP starts much slower than BP, so is more difficult to cluster; White Lightning, in particular is quite a challenge to cluster, Blue Thunder, less so. The FirstFire Jrs that come with the E20 (3") are different than the normal FirstFire Jr., shorter, with less pyrogen. Not sure how well they would cluster. Oh, they'll ignite quickly, being a low current igniter, but the smaller amount of pyrogen, combined with WL, may not cluster well.

Black Jack is supposedly the hardest propellant to light.

Many folks who want to cluster composite motors use CTI reloads. The ignition pellet at the top of the grain, combined with their ematch igniter makes for instant ignition, especially with their Classic propellant reloads.

 

[grouch]

So far I have only had two cluster launches and both were flawless. Both were CTI motors so I am sure that had something to do with it. To me, clusters are about the coolest things going.

 

[Cluster King]

A lot of good advice here.

My largest cluster was 14 bp motors (D's and E's). Used Quest igniters. Two launches 1st was100% ignition. 2nd flight one failed to ignite and one spit nozzle.

3 AP cluster with CTI last year, 1 54mm and 2 29mm, 100% success.

I have a flight set to use mixed BP and AP. I'm confident using quest igniters for BP and CTI for AP will do the trick.

Tsolo Dann

 

[BobH48]

I use extentions added with a wire wrap tool on Estes igniters.

In the second picture, you can see that I put clear tape on both sides of the wires. This keeps the wires from flexing much while wrapping the extentions and also prevents them from moving and shorting out when the plug is installed.

Since I started using these igniters, I have had only one motor fail to light.

When I checked the igniters after the flight, all of them had fired so I assume it was "operator error" installing it.

 

[cbrarick]

I clustered 3 F39's in my upscale Tres. I tossed the crapperheads and put in some firstfire jr's --- lit all three, no problems! It was gone so fast I was surprised it didn't superroc-fold.

So, I agree, it's picking the right propellent to fly (or company) and using a good igniter.

 

[Micromeister]

As club Tagged mrcluster i've been flying clustered BP motors more then 30years (2 to 16 BP motors).

I agree with everything others have already mentioned about the wonderful introduction of Quest Q2g2 Igniters for geneneral purpose clustering. These low current igniters make 3-5 bp motor clusters almost as easy as single motor models. I prefer in most cases to use my own Igniters particularly in Upscale D12 powered MPR models.
That said there are many factors to consider when clustering BP motors.

Over the years and Thousand Plus Logged Clustered flights I can still report a total of only 13 unlit motors combined, 3 of which were intentional "test" mode no installed ignitor motors, so the misfire rate is still will under 1%

Personally I always use a relay ignition system with ALL clustered motor models moving the power source from the controller side to the Launcher side of the system with the leads kept as short as practical between relay and ignitors.
* Do not rely on clipwhips; If clips are used at all, they should be mechanically fastened/soldered to the relay leads and well soldered to the lead wires.
* TEST, TEST, TEST!!! each and every ignitor or continuity before, and after installation in the motor and ONE last check on the launch pad.
* Use as heavy (High amp rating) a battery as your budget will afford with Clustered motors. Keep the old rule of thumb in mind " 2amps per ignitor". Yes we're well aware this was/is intended for Estes type solar ignitors but it doesn't hurt anything even using Q2g2's.

 

[robbdm]

Only been clustering for a year.

Using a Fliskit Tres, mixed results with stock Estes three C6-5 and stock Estes igniters using a wip clip. Always one motor ignites late. First flight was saved due to rusty launch rod keep rocket on pad till all motors ignited. Next flight, lift off on just two motors and third didn't have a chance to ignite. Resulted in low arch flight into the dirt two broken fins, repaired but never flow again. See photo of the last flight.


On my LOC Magnum DD, ground igniting central 38 mm AT J350 using First Fire, then air start two G53 or similar using XAVIEN XCIC-1 to ignite First Fire jr is three for three.

 

[Larry Curcio]

As it happens, the chance of a misfire on any motor in a cluster is very slightly positively correlated with that on any other motor in the cluster. If we assume that the chance of any motor misfiring is independent, therefore, our conclusions should be very slightly optimistic. Let's try that.

Let the chance of a misfire be represented as P, so that the chance of a successful ignition for any motor is (1-P). The chance of N motors igniting successfully, under the assumption of independence, is (1-P)^N.

Here are the chances of successful ignition in clusters of sizes 1-20, given (1-P)=0.99 and (1-P)=0.95. Again, these are slightly optimistic. (*** added just to space the columns)

You can get an order of magnitude handle on P by your experience with single motor launches. That's not a perfect estimate (You might take more care on a cluster and use different igniters. OTOH, single ignitions don't have a strict time limit as cluster igniotions do.). I suggest the comparison just to demonstrate that (1-P) is not unity or extremely close to it.

Most N's would likely be small, and three or four consecutive successes are quite likely. There's still that chance...


HYPOTHETICAL SUCCESS CHANCE TABLE

N
1 0.990000000 ***0.95
2 0.980100000 ***0.9025
3 0.970299000 ***0.857375
4 0.960596010 ***0.81450625
5 0.950990050 ***0.773780938
6 0.941480149 ***0.735091891
7 0.932065348 ***0.698337296
8 0.922744694 ***0.663420431
9 0.913517247 ***0.63024941
10 0.904382075 ***0.598736939
11 0.895338254 ***0.568800092
12 0.886384872 ***0.540360088
13 0.877521023 ***0.513342083
14 0.868745813 ***0.487674979
15 0.860058355 ***0.46329123
16 0.851457771 ***0.440126669
17 0.842943193 ***0.418120335
18 0.834513761 ***0.397214318
19 0.826168624 ***0.377353603
20 0.817906938 ***0.358485922

Luck and Regards,
-LarryC