Super Big Bertha scratch build with 2 D Or E motors

[Tazfire598]

Hello everyone. My name is Rob and I have been building Estes model rocket kits for about 20 years and I finally want to do something different. I was curious if anyone would be able to advise me on my current scratch build. I'm thinking of doing a SBB with 2 D or E motor cluster. This is my first build using more than one motor. Would this be too much power for this rocket to handle?

[GrossApproximator]

Not too much power. Normal tubes can handle the thrust of G motors, so a couple D or E motors shouldn't be a problem.

[scsager]

I have a Super Big Bertha built with standard Estes BT80 airframe, light ply centering rings, light ply (1/8") thru the wall fins, and a 29mm motor tube.

It flies great on E-H power (single motor) and hit about 2500ft at Midwest Power 9 using an H128


http://www.youtube.com/watch?v=fm2GEofo8tk

[jungmann1]

Yeah, not problem. I built a SBB, modified to 29mm and it loves the G64! Basically stock kit exept thru the wall balsa fins, and I made it zipperless design so it breaks i the middle instead of the top. Flies perfect. John.

[SacEsq]

If you are gonna use 24mm go for three motor mounts... seems more balanced. Otherwise why not a 29mm as suggested. Lots of options with a 29mm

[JPVegh]

Clustering a Super Big Bertha or other BT-80 rocket is how some of us got started with mid power. A double barrel SBB ought to be pretty cool as long as both motors light.

[Tazfire598]

Wow guys. Thanks for replies. I'm excited to do this build. I can see I'm in good hands with this forum. Looks like there's a ton of knowledge to tap into. Thanks again.

[jungmann1]

The only thing we ask in payment is a build thread with a ton-o-pics! We love pics. Carry on! John.

[Tazfire598]

I can do that. As soon as the build starts I'll get some pics up. Can't wait!

[Marc_G]

Taz-

Enjoy your build! And welcome!

Be sure to read up on igniting clusters. The general consensus is that for black powder motor clusters, the Quest Q2G2 igniters are the best. I use them all the time with great success. But be cautious ; the standard Estes controller can set them off with just continuity check current. Easy fix is to swap the bulb with an LED.

Have fun, ask questions, and for goodness sakes post pictures and video.

Marc

[KurtH]

You might want to consider getting a Semroc SLS brighton

http://www.semroc.com/Store/scripts/...s.asp?SKU=KA-9

It has interchangable motor mounts, you can fly it with 4 Cs, 3 D12/E9 or a single 29mm.

It flies great on e18s, f35, f39, f52s, and G75s.

It is my go-to rocket at launches, and it never fails to draw admiring comments.

Have fun what ever you decide!

[qquake2k]

I think a BT-80 based Super Big Bertha, if built light, would fly great on two Estes D12's or E9's. If you build it like a tank (like I do), then I'd go with a 3x24mm cluster. I've had 100% success lighting two and three motor clusters with Estes ignitors, but I know a lot of people here swear by the Quest Q2G2 ignitors. By the way, a good place to get components is Balsa Machining. They have body tubes, nose cones, plywood, balsa, basswood, launch lugs, motor hooks, parachutes, and cluster centering rings. Another place to get plywood, balsa and basswood is Michael's. I get a lot of my wood there, using their 40% off coupons.

[qquake2k]

I have a Super Big Bertha built with standard Estes BT80 airframe, light ply centering rings, light ply (1/8") thru the wall fins, and a 29mm motor tube.

It flies great on E-H power (single motor) and hit about 2500ft at Midwest Power 9 using an H128

Man, that was a straight boost! I love how you edited the video, too, with the stills in the middle. Very nice!

[qquake2k]

Speaking of tanks, here is my 3" Big Bad Burt, a Big Betty upscale, on a G53 Black Jack reload. He has a balsa nose cone, 1/4" plywood fins, center break zipperless design, and a 29mm motor mount. He weighs in at 28oz without motor.

[Tazfire598]

My only concern so far is the shock cord. In the original instructions they have you glue the shock cord inside the body tube. I'm thinking this isn't the way to go with 2 D or E motors. Would it be wrong to mount it through the top motor mount disk and use a longer cord? Should I go through the disk and tie a knot or screw an eyelet to the disk and tie it to there? I know to some of you this is probabaly the simplest thing but it is my first scratch build / clone of this size and power.

[o1d_dude]

There are any number of ways to attach the shock cord. Your plan to attach the shock cord to the top centering ring is one that many folks use. Some tie the shock around the motor mount and run it up through a slot or notch in the top centering ring. Others use an appropriately sized eyebolt drilled through the top centering ring and bolted in place from the back.

My own preference is to drill a hole through the body tube just below the nosecone and run the shock cord out through that. I then knot the shockcord and cover it with a fairing made from a split plastic nosecone.

All of these methods work.

[qquake2k]

Do you have Kevlar cord? If you attach your shock cord to the centering ring and it's not Kevlar, it'll likely burn through.