3 estes bt-80 tubes on a 24mm tri cluster

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Tinker

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Care to explain? Im still not completely sure what exactly it all means. Im assuming its center of gravity. Nose cone is sealed off so i cant add any weight to it, but for a bulkhead a used a big round block of balsa that weighed like 50 grams instead of just capping a coupler so i hope that added plenty of weight. For shock cord ive got 1/2" x 92" estes pro series. Ive never used a chord this big, is it suppost to be that long or should i shorten it up?
I probably shouldn't do this as I am sure to get something wrong and get womped for it, but here goes. Yes CG is center of gravity. CP is center of pressure. The best understanding of this I could give (and I am probably wrong) is if you imagine your rocket being of uniform density, what point would it pivot on if balanced and a wind hit it sideways. (Where would the pole be in the weathervane?) If the CG is one caliber (Diameter of you airframe) forward of your CP, your rocket will fly stable. As the distance between those two points grows, you rocket will tend to weathercock more. So generally clustering BP rockets becomes problematic as you keep adding weight to the rear end requiring more weight up front (in some form) to keep that CG in front of the CP.

Tinker
 

neil_w

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I would sincerely suggest that you study up on your rocket stability basics before flying this rocket. A clustered D rocket is no small thing to fly without understanding CG/CP relationship. Also suggest downloading a copy of OpenRocket to experiment; in addition to giving you a decent stability report, it'll also help you figure out appropriate delay, whether you'll have enough thrust off the rod, etc.

A 50 gram bulkhead is a pretty substantial amount of weight, but since it's not all the way at the front of the rocket it won't have as much effect as pure noseweight. To really know you need to figure out your CG (which is easy, just load up three engines and see where the rocket balances) and CP, for which the easiest thing is to create a model in OpenRocket.
 

Trident

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Is it complicated to make your own?
Go to https://www.firefox-fx.com/ignition.htm

Their Liquid Element Conductive Pyrogen is great. No nichrome bridge wire to solder. I used pairs of wires from CAT5 LAN cable, stripped insulation off tips, and with about 1/16" gap, dipped. Fine for BP motors. Dip in one of their secondary pyrogens for hotter igniters, like for composite motors.
 

dippind27

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Progress. Weighs 410. I havent had a chance to get engines yet

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Daddyisabar

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She is not quite in drag queen territory, but definitely into fat bottomed girl territory. First flight on D12 -3' s! Like the song says, fat bottomed girls they make the rockin' world go round! Go to your local club and use their good 12v launch system. Nice long rod or rail, good conditions a must. Then if only two light you still have a very good chance. Use a bit of wadding in the top of each motor. After the first flight you can then decide to use the cheaper D12-5's readily available from Hobby Lobby.
 

dippind27

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She is not quite in drag queen territory, but definitely into fat bottomed girl territory. First flight on D12 -3' s! Like the song says, fat bottomed girls they make the rockin' world go round! Go to your local club and use their good 12v launch system. Nice long rod or rail, good conditions a must. Then if only two light you still have a very good chance. Use a bit of wadding in the top of each motor. After the first flight you can then decide to use the cheaper D12-5's readily available from Hobby Lobby.
Im in the process of building my own launch box to run off 12v. They are quite simple to make
 

DeeRoc29

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Use e-matches for ignition. I've had 100% success with BP clusters using them. Check eBay or Amazon for great deals. Chinese a okay.
 

dippind27

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Use e-matches for ignition. I've had 100% success with BP clusters using them. Check eBay or Amazon for great deals. Chinese a okay.
I ordered some first fire jr's. Ill look into them though
 

DeeRoc29

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I definitely wouldn't use the first fires for clustering as they require too much current. It may work fine if your controller is up to it, but I'd still go for the e matches.
 

bill_s

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I suggest not listening to anyone on the delay time. Run the simulations and ignore everyone!

I've been averaging 2 Estes "starters" per engine lit, perhaps this can be improved, but seems to me Clustering is dead with them. If you want to try clustering E motors, use the 29 mm or cluster only 2. The motors come in three packs, that leaves one to test burn first to see if you have a good pack. Sorry Estes. Or maybe just avoid Hobby Lobby, while I haven't had trouble with the 29 mm yet, the last 2 times I got E9s there they were bad. The same date code from Estes warranty or Hobbylinc were fine.

You could see if you can find any of the Estes Sonic igniters that were sold to use with composites (although were too weak for them), the FF Jrs. are not the smallest Aerotech igniter. The Aerotech Copperhead igniters were a pain to connect to, but if anyone has them they were cheap, especially the 3" ones.
 

bill_s

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Burning one motor from a pack of three does not guarantee the other two are good.
So far of probably 100 of E9's and a few E12's, I've never had a single bad motor. The 2 bad packs were bad for both motors fired so far from each pack, and one pack was grain-ejecting and one nozzle-ejecting, also consistent within... yes that leaves me now with 1 motor from each pack, which I'm tempted to set off at the same time (the nozzle CATO test was spectacular), maybe along with a fresh one.

So, true, but we are talking E9s and Hobby Lobby here.
 

Daddyisabar

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The D-12s are fine. My problem has only been with E9s as well. I have also used a lot over the years and it seems one or two bad batches seem to come out each year, either spitting nozzles or having cracks/voids/propellant mix issues. A real problem when clustering three motors. I have had one bad motor per pack and two bad motors per pack. That is consistent on what I have heard from others. Clustering E9s or E 12s is a matter of avoiding the bad date codes and having faith in Estes and their vendors. With the demise of Q2G2's and suspect BP E motors, clustering is becoming even more difficult.:(
 

Micromeister

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I've said this many times but it is worth repeating to anyone NEW to BP clustering:
RELAY IGNITION SYSTEMS are not A way to ignite clustered BP motor, It is the ONLY reliable way to ignite them.

There are 3 parts to reliable Cluster Motor ignition:
1) Check, Check, Check all igniters (Starters). Before installing in the motors, After installing in the motors, and one last check with the model on the pad.
This can be done easily with a Ohm meter or a pocket continuity checker (see diagram attached).

2) The Battery: Use as large a 12volt high Amp/hr battery as you can afford, for 1-3 motor BP clusters a Hobbico 7amp/hr Gel-Cell will do, For larger clusters I wouldn't use anything smaller than a 26amp/hr Gel-Cell for 4-12 motors. (REMEMBER 2amps per Igniter is the rule of thumb).

3) Most important "THE RELAY": For smaller 1-4 motor clusters a 10amp D.P.D.T. relay works just fine, for larger clusters I use a 40amp/contact power relay.
Why a relay? First the relay moves the power source from the controller side of the circuit to the Launcher side, shortening the amount of cable the power must go through to get to the igniters. Connect the relay to the battery with the heaviest and shortest length, stranded wire you can get (I use #14 to #2ga stranded copper). Use 18-20" micro clip leads mechanically connected to the Load side of the relay. 18" of micro clip lead allows a round of wire under the model to allow first motion of the model to raise some while all motors ignite before the clips are ripped off. Below is a drawing and photos of a "Range box Relay" that I've used successfully to ignite up to 10 motors.

4) Clip whips are NEVER the answer to cluster ignition! No matter how well made, a clip whip is ONLY an extension of the existing Launch Control system, In fact a clip whip actually decreases power transfer efficiency by adding inferior connections and added length to the already to long, small gauge controller wiring.

There is also an in depth Tech Tip-006 "Clustering BP Motors" a 6 page study of what has to happen in the first millisecond to gain successful Cluster ignition. Go to www.narhams.org look for the library tab on the left hand menu, click on the library tab then look for Tech Tips.
Since switching over to Relay ignition I've launched over 2000 2-10 motor clustered models with a total of 13 unlit motors in all those thousands of motors clustered. I haven't had an unlit motor since 1997. The system works!

Range Box Relay-a_system & magneium-AP igniters_01-31-96.jpg


Range Box Relay-b_Face lable Close_01-31-96.jpg


Range Box Relay-c1_5pic photos. dwg & parts_06-23-10.jpg


Range Box Relay-d_Inside the Box_09-16-05.jpg


View attachment RangeBox Relay-a2c_Rev Drawing & Wiring_01-31-96 Rev.06-23-10.pdf

12V Gel-Cell-b_ Batteries & Adaptor Charger(128dpi)_11-05.jpg


View attachment Cluster Wiring Diagrams-2c_Dwg(Revised)_09-17-12.pdf

1.5v-d2_Revised Pocket Continuity Tester 3pic_09-06-05.jpg


Relay Ignition system-a2_Inside the box_02-19-90.jpg


Relay Clip-Whips-sm_8m St-Stl microclip lead_03-09-91.jpg
 
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dippind27

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Despite everything you guys said i flew it as it was on 3 D12-3s and it flew just fine. No parachute issues everything went as it should. All 3 engines fired using the first fire jrs with no clip whip, just twisted them together. Also used my homemade launch controller with regular old speaker wire. It did end up landing in the lake but i jumped in after it and saved it. I will try to upload the launch video to youtube and post the link
 

dippind27

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Wish i could have done a recovery video but i was too busy running and trying to take my shoes off at the same time
 

TangoJuliet

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I've said this many times but it is worth repeating to anyone NEW to BP clustering:
RELAY IGNITION SYSTEMS are not A way to ignite clustered BP motor, It is the ONLY reliable way to ignite them.

There is also an in depth Tech Tip-006 "Clustering BP Motors" a 6 page study of what has to happen in the first millisecond to gain successful Cluster ignition. Go to www.narhams.org look for the library tab on the left hand menu, click on the library tab then look for Tech Tips.
Since switching over to Relay ignition I've launched over 2000 2-10 motor clustered models with a total of 13 unlit motors in all those thousands of motors clustered. I haven't had an unlit motor since 1997. The system works!
John - Thank you for sharing the images and diagrams, and for your vast knowledge. I'm a far cry from being electronically inclined, but I have friends who are and might be willing to assemble something like this for me if I provide the parts. It was a pleasure to get to meet you last weekend at ECRM44.
 

Micromeister

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Wish i could have done a recovery video but i was too busy running and trying to take my shoes off at the same time
Outstanding!
Great that you recovered your 1st cluster, Had a very similar experience years ago with my Magnum 2-stage upper stage landing in the Potomac River LOL. Went for a long swim to retrieve her but she still flies today LOL!.
 

dippind27

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Picture that my girlfriend took while i was trying to dry it off.

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tmacklin

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Nothing like a cool dip after a successful launch! Congratulations!
 

JPVegh

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Fantastic build and launch! GREAT JOB!!!
 

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