Brief:
This rocket be designed because I wanted t' play around with several different things – cluster, arrr, 24mm engines, and aft ejection. Well, blow me down! When t' EMRR challenge came around, shiver me timbers, me bucko, this one be a perfect fit for the “Twice t' Thrust” part o' t' challenge. Aye aye! I ended up nay doin' t' aft ejection because o' all o' t' fins and pods on t' lower part but everythin' else pretty much stayed as planned.

Construction:
T' parts list for this rocket is quite extensive.

• 1 x BT-80 (18”)
• 1 x BT-60 (18”)
• 2 x BT-60 (10”)
• 4 x BT-20 (6”)
• 3 x BNC-60SV
• 4 x BNC-20CB
• 2 x TR6080
• 2 x 24mm engine mounts with E-size retainers and BT60-50 centerin' rings
• 2 x BT80 centerin' rings
• 6 x 1/8” balsa fins
• 1 x 12” parachute
• 1 x 24” parachute
• 1 x 3/16” launch lug
• 1 x BT80 baffle (optional)

Preparation has lots o' steps because o' all o' t' parts. Well, blow me down! Sand and fill t' seven nose cones and two transitions, ya bilge rat, fill t' spirals on t' eight tubes, ya bilge rat, shiver me timbers, shiver me timbers, sand and fill t' six fins. Ahoy! Avast, me proud beauty! Whew! Lots of sandin' dust here!

Cut a 1” x ¼” hole in one side o' each side pod just below t' nosecone. Blimey! Avast! Stand t' pods up next to t' BT-80 (with t' lower transition installed!) so t' bases are all at t' same level. Ya scallywag! Transfer t' location o' the duct hole t' t' main tube and cut t' same size hole on each side o' t' main tube. Ahoy! Ya scallywag! Make sure all o' t' holes line up properly! You may want t' coat t' holes with glue or CA t' help them withstand t' heat o' ejection. NOTE: t' holes described above were what I did on t' original build. As you will see, shiver me timbers, they are NOT large enough. Arrr! Begad! You will want much larger holes!

Install a block in t' main tube below t' duct hole. I used two BT-80 centerin' rings with t' centers still in (glued together for strength). Arrr! Blimey! Before gluin' t' block in punch two holes through t' rin' and run a Keelhaul®©™® thread through t' holes and tie it off. Aye aye! Ahoy! Be sure t' install t' block so t' Keelhaul®©™® thread is nay near either o' t' ducts!

At this point you have a decision t' make: t' paint scheme. Avast, ya bilge rat, me proud beauty! If your scheme will be complex, arrr, it may be a good idea t' go ahead and prime everythin' now (maskin' off t' glue points) and paint it all before puttin' it together. This is what I did.

Glue all o' t' nose cones and t' transitions into all o' t' appropriate tubes. Dry fit everythin' first to make sure each piece will fit correctly. Avast, me proud beauty! I had t' sand t' shoulders o' t' transitions and a couple o' t' nose cones. I put filler in t' seams and waited for it t' dry before sandin' it smooth. Well, blow me down! Do NOT glue t' upper transition into the lower BT-80 body tube. Ahoy! That’s where t' rocket separates for deployment! Cut t' lower shoulder off o' the transition on t' BT-80 lower tube (it will look like a very short boat tail). Aye aye! Begad! Sand t' cut end smooth.

Once everythin' is painted and dry, shiver me timbers, glue it all together! Blimey! Start with t' side pods, ensurin' they are straight and t' duct holes line up properly. Well, blow me down! Arrr! Once t' pods are installed and dry, glue on t' upper and lower SINGLE fins. Aye aye! Once those are dry you can either put t' end pods on or wait. Begad! Doesn’t matter but it is easier t' wait. Stand t' rocket on one side and glue on t' two side fins, ensurin' they are flat against t' upper and lower fins. Avast! You may want t' bevel t' root edges slightly t' ensure a proper fit. Glue t' tips together at t' end but don’t bevel them! T' pod will fit better if you leave them alone. Well, blow me down! Once one set o' side fins are done, repeat the process with t' other side. Ahoy! Begad! After everythin' is dry, glue t' win' pods on one at a time, ensurin' t' bottom o' the pods are even with t' bottom o' t' fins. Avast! In t' pictures I centered t' pods but on landin' t' bottoms o' t' pods got crunched.

Once all o' that is done, ya bilge rat, make t' two engine mounts and install them in t' two BT-60 side pods.

If you are usin' t' BT-80 baffle, matey, don’t bother doin' t' Keelhaul®©™® thread t' t' block as described above. T' baffle will come with an attachment point for t' Keelhaul®©™® thread. I ended up nay usin' t' baffle which is a good thin' because if I did thar would nay be enough room for the parachutes.

Assemble t' two parachutes, install t' screw eye in t' transition in t' upper section, and attach the 12” parachute t' t' screw eye. Ahoy! Tie one end o' t' shock cord t' t' Keelhaul®©™® thread and tie t' 24” parachute t' t' other end. Blimey! Arrr! As an alternate, skip t' 12” parachute and tie t' shock cord t' t' screw eye t' create a single-deployment. Blimey! Avast, me proud beauty! You will want t' increase t' size o' t' parachute, me hearties, shiver me timbers, though. Arrr! Ya scallywag! The Double Barrel comes down fairly smartly on a 24” ‘chute without t' upper section.

Install t' engines and you’re ready t' launch!

Flight:
T' first flight o' t' Double Barrel be at t' Alamo Rocketeers August launch in China Grove, TX.

T' DB was launched under t' power o' two C11-3s. T' boost was brisk and pretty much straight up despite a pretty stiff breeze. Arrr! Deployment was as expected with t' upper section separatin' cleanly with its small 12" parachute and t' lower section comin' down under t' 24" parachute. T' recovery be brisk, though, arrr, matey, and one of t' pods got crunched a little bit against t' hard ground. All o' t' fins were intact, though.

T' second launch was on two D12-5s. Again, ya bilge rat, me hearties, me bucko, t' boost was very nice but unfortunately we had an accident on ejection. Aye aye! T' duct holes were two small on at least one side and t' ejection charge blew a large hole in t' side of one engine pod up near t' nosecone. Blimey! T' upper section did deploy just fine, but t' parachute didn't come out for t' lower section. Aye aye! T' DB floated down end over end for a while but stabilized into a tail-first smash into t' ground. Avast, shiver me timbers, me proud beauty! Only one fin pod was damaged, though, matey, which is really surprising. You can see t' final descent on t' video.

I will have t' repair t' hole and make t' ducts larger in both pods before tryin' t' launch this again. Blimey! I really want t' see what it will do on two E9 engines!

Summary:
PROs/CONs: This be a fun rocket t' build despite all o' t' parts. Ya scallywag! Aye aye! T' fins were a bear because I don't have a good hand for free-cuttin' balsa, even with a metal ruler for a guide. Ya scallywag! Gettin' t' side engine pods on straight be also difficult. Despite all o' t' balsa, me hearties, this rocket is surprisingly light.

PRO: T' flight was beautiful! Straight up with a nice recovery.

CON: T' large fin area make t' DB difficult t' transport t' t' launch area. Paintin' can be a real challenge.

Other:
Ducted ejection can be hard! How large do t' holes need t' be? Well, me hearties, for D and E engines the holes need t' be larger than I made them. Begad! Avast, arrr, me proud beauty! I'm plannin' on cuttin' out a much larger hole in each pod if I can.