Cluster or 24mm?

[tdn]

I'm contemplating the construction of my next rocket. It will be either and egg-lofter, or an all-purpose lofter (I wish to loft both water and small cameras, thought not at the same time). It will essentially be a clone of the Apogee Stonebreaker(?) with a BT-70 body tube. I estimate the weight to be around 4 oz., or 12 oz. if I'm lofting water.

My question is how I would power it. I've never used a motor above a C before. I would either want to go the D or E route, or use a cluster of 3.

I've clustered before, when I was a kid, but that was in the days of car batteries. I'm afraid my little Estes Electron Beam with 4 AAs will be under powered for a cluster.

Are there any commercially available high-powered launch systems available? If you were building this rocket, what would you do?

 

[powderburner]

If you want to use an E you will definitely need to cluster. A single E is not a load-lifter-type motor. Note the total impulse that the Estes E delivers: it is really only a D-and-a-half.

You might do better to cluster some D motors for higher peak thrust.

If you have not clustered motors (of any size) before, you may want to simplify things and use a single composite motor. Mid-power motors like Aerotech E and F are just about ideal for this application.

 

[r1dermon]

yeah man, i'd go with a composite motor, something with some kick in the pants. the E30 is 24mm and gives a NICE kick. also, as powderburner stated, an E9 will give you more overall thrust than a D12, meaning, if you have a light rocket that's going for altitude, its great, but a heavy rocket would be better off on a higher thrust, shorter burn motor. the D12 burns shorter than the E9, however, it has more PEAK thrust. so its max thrust is higher than the E9's. meaning it will lift the rocket off the pad a lot faster and more effectively. also getting it to stable speed before it leaves the rail/rod.
BTW, what pad are you using?

 

[GL-P]

Yeah, and if you build solidly with a 24mmt, you can use more exotic motors like Ellis Mtn and AT Fs and Gs.

You could always build a removable mmt to hold clusters and single configs.

3 D12s would put out quite a boost

 

[tdn]

Originally posted by r1dermon
BTW, what pad are you using?

One that I wouldn't use with this new rocket, most likely. I have only a standard 36" rod (in two thicknesses). As I said, I've only launched A-B-C rockets so far. I have a few bigger ones I haven't flown yet, so I'm going to have to upgrade.

Reccomendations?

 

[powderburner]

r1dermon and glp are correct about most of their comments, but I still think you probably do *not* want to try a cluster

Yes, three D12s will give you a solid boost off the pad----if you get all three lit, and together. Pardon me if I make a bad assumption here dtn, but from your question I am guessing that you don't have a lot of background with D/E/F-powered motors, or with clusters?

The challenge with clusters (now I didn't say 'problem' because some people like a challenge) is getting good ignition. If one motor does not start, you have an immediate penalty with additional dead weight of the inert motor (the other operating motors won't lift the total rocket as well), off-center thrust, and a heavier model landing at a slightly increased sink rate. You add the complexity of a more fancy launch pad (clip whips may not be a big deal, but the big battery to simultaneously fire all your igniters *is*). You also add the risk of reverse-ignition of the motor (ejection charges from the working motors ignite the front end of the un-ignited motor, and it burns and vents forward into the guts of your rocket).

If some of your cluster lights on time but other motors start late, your peak thrust is changed and the rocket's acceleration off the pad is all different. Probably you would still have enough velocity to be stable at the end of the launch rod/rail. With one or two late ignitions you would still utilize all the impulse. But if you are trying for one specific target altitude, your rocket's performance can be significantly changed by one tardy motor burn.

You can avoid all that by using one good E or F motor.

 

[tdn]

Originally posted by powderburner
Pardon me if I make a bad assumption here dtn, but from your question I am guessing that you don't have a lot of background with D/E/F-powered motors, or with clusters?

As I said, no experience with larger motors, and the last time I tried clustering was when I was a kid (I had 2 rockets that I launched maybe once or twice each). I'm aware (not through first hand experience) of what can happen if the motors don't all light at the same time. Hence this thread.

If I am to build this rocket, I'm going to have to move into the world of either clustering or larger motors. Either way, it's a step into more advanced rocketry for me. The last time I clustered was with a car battery, and I've never used composite motors.

Even though I've launched rockets since the Nixon administration, I'm still a bit of a newbie. So I guess I'm asking which route might be easier or more logical for my next step towards mastery.

 

[jflis]

Challenge is good.
Clusters are cool.

My motto? "Cluster's rule, mono's drool"

If you understand clustering, take your time and follow some simple rules, clusters are not difficult, nor are they unreliable. My success rate on clusters is about one failure out of every 300-500 cluster launches and anybody can match that rate easily.

If you purchase a cluster kit from FlisKits you will get a short hints and tips sheet on clustering which will answer most of your questions. Don't want to buy any of our kits? No problem, just send me an email and I'll get the sheet off to you.

If you are going with a BT-70 tube, I would recommend a three motor 24mm cluster. You can do this scratch building easily and/or purchase an engine mount kit for the job (FlisKits has 2 versions of this very kit in stock)

Using such a cluster would allow you to fly with C11, D12 or E9 motors for some fantastic flights, easily lifting your payload. Your only concern (after motor ignition) is selecting the proper delay charge depending on the mass of your rocket at liftoff. Our Richter Recker , for example, at nearly 16oz liftoff weight on D12 motors uses a 5 second delay charge.

To be successful with clusters, follow these simple rules with each and every flight:

- Using standard ignitors that come with the motors, match them up for size and shape (They don't need to be big (lots of pyro) or small, just similar in size)
- Do a continuity check on each ignitor before using
- If uncertain, gently scrape the fuel area inside the nozzle to remove any foriegn residue
- CAREFULLy install each ignitor making sure the tip of the ignitor touches the fuel inside the motor then use the provided plug or a ball of recovery wadding to hold in place.
- Plug the top of each motor with a small ball of recovery wadding held in place with tape. In the event of a misfire on one motor, this will prevent the other motor from igniting *this* motor in reverse when the ejection charge goes off.
- If applicable, twist the leads together tightly or use a clean clip whip to hook up all the ignitors
- NOTE: CRITICAL: Always hook your ignitors up in PARALLEL, never in series
- NOTE: CRITICAL: Always use a good strong power source. My recommendation is to use a car battery or equivilant. If you are using club equipment with LONG leads, make sure they use a "Relay System".

That's it. It sounds involved, but really you should perform pretty much these same steps for every launch, cluster or not, so as to not waste ignitors and time.

Keep watch over FlisKits before the end of the year for 2 clusters models (3 18mm and 3 24mm) coming out soon

jim

 

[Mike]

How about you do a simulation of it in RocSim or SpaceCAD (demos available) and see what happens with different motor possibilities/payload weights. You should get an idea which configurations give what altitude or if its even got enough power behind it to fly. With that you'll be in better position to judge what motors are best for you.

Yep, you're right in your first post you Estes controller won't have the power to cluster.

HTH

 

[r1dermon]

tdn, if you go with larger motors, i personally think you'll be much more pleased. there's a lot more power per lb, a lot more options in smaller diameters, which means your rocket can be smaller in diameter. F21's are 24mm, and would give you solid boost. composite motors arent really difficult. a lot of people are scared by them because of the strange ignition. however, they're a lot easier than you think. i think your best bet would be to go with a 29mm mmt (unless the rules specifically call for a 24mm mount). that way, you can utilize a TON of different motor configurations. in-fact, i believe ellis mtn makes an I motor in 29mm. so you can get E through I power with a 29mm mount, i'd say thats pretty versatile. not only that, but the consumer motors available for 29mm are insane. the G80 is a nutty motor and is extensively used in mach buster rockets. all the way down to the F20 econojet, which lb for lb gives off the best roar you've ever heard. and that sends my 8oz aura to 2700ft(simmed but never attempted) it certainly would lift a 12oz lofter up there. its also a great way to step out of the limiting realm of estes, to the limitless realm of mpr/hpr rocketry.

 

[powderburner]

If you use a cluster of big BP motors you are probably going to have more 'dead' weight after burnout than you will with a single composite motor. This might be bad-----the extra weight might pull down your maximum altitude, and the extra base-drag area might count against you too. This might be good----the extra mass on board might add enough inertia to help you coast a little higher. You will have to figure this out for yourself with some analysis. If you don't want to buy a $100 copy of Rocksim to check this, you can download a trial version for free (an earlier release, without all the features, but enough stuff to run a sim).

I think this choice boils down to whether you want to play (have a little more challenge learning how to master a cluster) or whether you want to work (get your payload delivered simply and reliably).

 

[eugenefl]

Originally posted by tdn
I've clustered before, when I was a kid, but that was in the days of car batteries. I'm afraid my little Estes Electron Beam with 4 AAs will be under powered for a cluster.

Are there any commercially available high-powered launch systems available? If you were building this rocket, what would you do?

For igniting clusters I would recommend the Estes/NCR Command Control launch controller. There's one going on eBay right now. See auction <a href="https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=2567&item=5926107754&rd=1&ssPageName=WD1V">here</a>.

Also, TRF member DynaSoar spotted some of these controllers at a local hobby shop for $29. You may want to get in touch with him and see if they are still available. He posted a thread here - <a href="https://www.rocketryforum.com/showthread.php?s=&threadid=12218">NCR Controller</a>.

Hope this helps. I say go cluster!

 

[DynaSoar]

Originally posted by tdn
I'm contemplating the construction of my next rocket. It will be either and egg-lofter, or an all-purpose lofter (I wish to loft both water and small cameras, thought not at the same time). It will essentially be a clone of the Apogee Stonebreaker(?) with a BT-70 body tube. I estimate the weight to be around 4 oz., or 12 oz. if I'm lofting water.

My question is how I would power it. I've never used a motor above a C before. I would either want to go the D or E route, or use a cluster of 3.

I've clustered before, when I was a kid, but that was in the days of car batteries. I'm afraid my little Estes Electron Beam with 4 AAs will be under powered for a cluster.

Are there any commercially available high-powered launch systems available? If you were building this rocket, what would you do?

OR?

Consider: build a motor mount that holds a BT60 sized "motor".
Make that "motor" be a 24mm motor tube bult into a BT60 sized tube, AND a 3x18mm cluster built in the same size tube. You can then fly it both ways.

The AA batteries may well be underpowered and result in the igniters not heating up close enough together to start all three motors. Some might go off sooner. Open up the EB and replace the wires with heavier speaker/lamp wire and it'll run off a car battery if you want.

 

[KarlD]

There are plenty of plans on the internet for good low cost 12V relay launchers.

My Favorate is the Launcher on info- central. It is a multipad unit, but it has a plan for a single bay launch box.

Just remeber to solder a diode reverse biase across the relay coil leads to damp the coil field collaspe pulse...

 

[OARJeepr]

I'm building a dual egg lofter myself right now. I went the single motor rout. Its built around a 29mm mount because that's the hardware I have. In that size however you can get everything from E to low H motors. I'll post a pic when I get the construction done.

 

[r1dermon]

i think DR rocket has a 29mm I motor...

 

[JStarStar]

I think many if not most launch control systems will work on higher voltage, the only caveat is that you must replace any continuity light bulb with a higher voltage bulb so the bulb doesn't burn out when you give it the juice.

I have a 1970s-vintage Estes Launch Control System, brown zip cord for the leads, connections, etc., it still works great. A few years ago I opened up the casing and soldered all the wire connections - that thing is like it's bulletproof now. Plugs into a cigarrette lighter socket, works fine.

We have on another thread a discussion about using portable battery booster units as power sources. They deliver plenty of jolt to fire up the clusters.

JFlis was on target in his post - just follow his checklist regarding connections, clip whips, continuity, making sure igniters are installed correctly, etc.

My own preference, usually I prefer to use the fewest number of motors possible for whatever it is I want a particular model to do. While ignition reliability is still ok with clusters, it isn't as good as it is with a single engine.

Your ignition-failure rate does increase proportionally with the more motors you have to ignite. Clusters are cool, but you do have to take into acccount they're somewhat more challenging. Which of course sometimes is a lot of the fun.

 

[Mad Rocketeer]

Good points have been made here on both sides.

Single motors are all or nothing on ignition. They either light up or they don't. If they do, you're set. If they don't, you fix the problem then try again.

Clusters can partially light. If you're careful, use the right equipment, don't skimp on the checklist, and remember not to take your thumb off the button the moment you hear a whoosh, you should be able to get good relaible flights that way too.

I'm like you. I've flown since the Nixon years, had a long pause for college and young married life, and have recently returned to the hobby as a BAR. I've never flown a cluster or a motor larger than an Estes D.

I can't wait to try both though. I bought three kits from Fliskits about a week ago, two of them cluster models. If you've not been to see the Fliskits stuff, open another browser and look before you even finish reading this. His stuff is beyond cool, IMHO. [I bought an Acme Spitfire, a Deuces' Wild, and a Richter Recker.]

Dynasoar had a great idea there. Build yourself a swappable mount, if not on this rocket then on another one soon. I plan to do the same. You could pre-load both and fly the rocket back-to-back in the time it takes to fire it, retrieve it, reload the chute and wadding, swap the mount, and push the button again. Compare and contrast. Wow your friends. Have a great time.

 

[sandman]

I've flown since the Nixon years,

Oh ohh!

That made me think and then it hit me....

I've been flying rockets since...Oh **** ...Eisenhower!!

 

[tdn]

Originally posted by sandman
Oh ohh!

That made me think and then it hit me....

I've been flying rockets since...Oh **** ...Eisenhower!!

Wow. So did you, like, know Orville and Harry and Vernon? Ever been to Coalwood?

 

[WiK]

I would say go with a 3 D cluster. It'll be a good experience. You'll have to learn clustering sometime, why not now? Then again I can't comment on AT motors.


Phil