Is clustering really that hard?

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horf

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I was reading the debate about letting people get L1 cert on clustered G motors and several people said that clustered Gs are at least as complicated as using a single H motor. It made me wonder: Is clustering really that hard?

I've done it with the 18mm estes motors (3 tightly packed). The hardest part was getting the igniter wires not to touch. Are there other issues with composite motors that I don't know about (since I haven't flown one yet)?
 
Clustering is fairly easy if you get yourself a clip whip. Then it's just a matter of hooking up each clip to the igniter. Forget trying to twist all the igniter's together, to difficult and don't always get all to light.
Lance
 
You're really talking about 2 different things there, horf.

Like Lance said, the simple - and quite reliable - solution to LPR/BP clutering is a clip whip. I can't remember where I bought mine (when it comes to me I'll post up) with 3 sets of clips for launching my BoRocks Flechette and my FlisKits Tres, and I also made one myself with 2 sets of clips for my FastForward. You absolutely should NOT attempt to cluster with the typical Estes Electron Beam controller; it just doesn't push enough current to reliably light both (or all three, or...) igniters AT THE SAME TIME. You need a 12V system.

Similar thinking applies for clustering AP. You need a good, strong 12V system, and the same clip whip can be used.

I saw your other post (in Dan's Mini Magg cluster); he mentioned air-starting some of the engines, which requires on-board electronics (timers).
 
Clustering BP and AP is two whole different worlds all together. It cannot be compared.
Clustering BP is fairly simple.
Clustering small AP motors is much harder than larger ones, because the small nozzle will not allow installation of decent low-current igniters.
Clustering AP is more complicated also because the ignition speed tends to vary with the size of the motor (unless you can use thermite or pellets, what in turns brings us back to point two: Can only be done on larger motors).

Juerg
 
Clustering BP and AP is two whole different worlds all together. It cannot be compared.
Clustering BP is fairly simple.
Clustering small AP motors is much harder than larger ones, because the small nozzle will not allow installation of decent low-current igniters.
Clustering AP is more complicated also because the ignition speed tends to vary with the size of the motor (unless you can use thermite or pellets, what in turns brings us back to point two: Can only be done on larger motors).

Juerg


What Juerg says.

What he is saying will be exemplified and made obvious to you the more you fly (or are around other people who are flying) G+ impulse composite motors.

To illustrate: When you launch a LPR rocket with an Estes motor (really doesn't matter what size) what happens when you press the launch button? Let's assume your batteries on your launcher are in good shape with plenty of charge and your igniters are installed properly.

What happens? Almost instantaneously, the motor ignites and leaps into the air. Focusing on the instant that the motor ignites, the time between "pressing the button" and motor ignition is very small and almost exactly the same every time for a given launching system (again, assuming the batteries are charged and the igniters are good and installed correctly)

Now - think about the G composites. What happens when you "press the button?" Is the time between pressing the button and motor ignition consistent? Hardly.

There are reasons for that, not the least of which is the many variables involved in how long it takes for composite motor pressurization and overall ignition (like: Is the igniter installed in the right place? How much pyrogen is on the igniter? What is the core diameter of the grains? What kind of propellant? What size is the nozzle? Did I bring more cowbell with me today? etc.)

The inherent variablity in ignition times of composite motors make clustering them seriously more complicated than clustering BP motors. Can it be done? Sure. Use ematches and BP pellets (like in CTI Pro38 motors) or use other "exotic" ignition methods other than just regular ol' igniters for example.

Personally, I'd say that clustering G's is *more* complicated than launching an H motor. Probably more complicated than launching an I. Think about that. To fly an H or an I, all you need to do is show up with a rocket that is suitable for launching in that impulse range (LOTS of kits out there in this size. A No Brainer) and build a reload and slap it in there. When actually launching it, you just want to get it off the pad. If it takes a half-second for the motor to pressurize before blasting skyward, who cares, right?

Now, for a clustered G rocket, you need a rocket that is designed for the impulse (now in the H range, see note above - not a problem) and stick more than one motor in there. Reload or single use. If you use reloads, you're adding to the order of magnitude of variability because of the possibility (however small) of user error when assembling the reloads. Anyway, when you get the rocket loaded and to the pad and wired up, you better have made all preparations to ensure that both motors light at the same time for ultimate success. What if one chuffs? What if one spits the igniter and the other pressurizes instantaneously? Hmmmmmmmm....


See my point? If you're flying a single H or I, and it spits the igniter, re-cycle the pad and try again. If one of your motors in a cluster spits and the others don't - Uh, Houston, we have a problem.
 
Clustering isn't difficult, rather a different set of skills to be learned, practiced and perfected, almost an artform if you will.
There is however much more to it then simply stuffing some igniters, hooking up some clips and praying for the best, I invite you do read Tech-Tip 006 clustering BP motors, in the library section of narhams.org for an in-depth look at bp clustering.
Clustering AP has even more to consider as Fore Check layed out.
 
Just one simple thought

Cluster + Ellis Mountain = Really Cool Flight

This is not to say Rob does not make good motors, I actually like them a bunch. They are just persnickety to light and the results can be, ahem, entertaining.
 
I was reading the debate about letting people get L1 cert on clustered G motors and several people said that clustered Gs are at least as complicated as using a single H motor. It made me wonder: Is clustering really that hard?

I don't think clustering is "that hard", but it's certainly more complicated (and more rewarding) than flying a single motor. You're dealing with the same amount of AP, the same total impulse, and the average impulse is likely to be higher with a pair of 120NS G's than a single 240NS H (assuming similar propellants). I suppose the assembly of the reload might be considered more difficult, but both G's and H's come in both single-use and reloadable flavors. I didn't find assembly of a 24mm reload to be any easier than assembly of a 38mm reload (sorry, I haven't tried the 29mm reload yet).

I don't see anything that's easier about the G cluster, which means it's got to be at least as difficult as flying a single H, and likely more so.

-Rick
 
Clustering is NOT hard...it is slightly more complicated than lighting a single engine but anyone with rudimentary electrical knowledge can wire 2, 3, or 4 igniters in parallel EASILY.:D
 
AP clustering can be a challenge (I am still working on my skills). My nike hercules flew great for its first four flights. On the fourth flight only one of the two engines lit. While the flight was safe enough with only one engine, the delay was too long and it is now in my rebuild pile as I need to replace the top tube.
 
If you want to practice AP clustering skills... Get a LOC Ultimate. 7x29mm motors. I loaded it up with 7 G77 SU motors, all ground started and all successful. I also loaded it up with 6xF42 and 1xG40 which was VERY cool. The 6 F42s started and came up to pressure instantly and the G40 came up to pressure about 1 second later (and about 30 feet above ground)

The key to AP clustering is good igniters, strong batteries(a relay is VERY helpful) and good wiring.

-Aaron
 
Just one simple thought

Cluster + Ellis Mountain = Really Cool Flight

This is not to say Rob does not make good motors, I actually like them a bunch. They are just persnickety to light and the results can be, ahem, entertaining.

*knockknock*
"who's there?"
"Land Shark!"
"what?"
"uhhh...Candygram..."
 
Study, read, resaerch, and ask alot of questions of your peers.

6cluster.jpg


6 "G64w" 's

Man I love this stuff, but just like anything else in life, it doesn't always go as planned.
 
The reason clustering AP (especially hard to light AP like Skids) can be entertaining:



(luckily, that design is stable on one motor...)
 
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