This rocket was inspired by the Little Beth X-2 which was a Design of the Month plan in an old issue of Estes Model Rocket News.  I wanted a rocket similar in design but larger. Hence, the Big Beth X-2.

Parts List

1 BT-60 body tube, 36" long
1 BT-60 body tube, 2 3/4" long
2 BT-55 body tubes, 9" long each
1 JT-60C tube coupler
1 PNC-60AH nose cone
2 PNC-55AC nose cones
3 BT-50 tubes for motor mounts, 2 3/4" long each
2 engine hooks
3 AR-2050 centering rings for engine blocks
4 AR-5055 centering rings
2 RA-5060 centering rings
1 1/4" diameter launch lug, 1" long
3/32" basswood for fins
1 18" parachute
1/4" wide elastic shock cord
 
 
 
 

1.  Glue the JT-60 coupler half-way into the short (2 3/4" long) BT-60 tube.

2.  Glue the 2 BT-55 tubes onto either side of the short BT-60 tube.  The bottom ends of all 3 tubes should be even.  Reinforce the tube joints with glue fillets.

3.  Assemble two motor mounts for the BT-55 tubes using 2 BT-50 tubes, the 2 engine hooks, 2 RA-2050 engine blocks, and the 4 AR-5055 centering rings.  When dry, glue one engine mount into the bottom of each BT-55 tube.  Ensure the end of each engine mount is even with the end of each BT-55 tube.

4.  Assemble the remaining engine mount for the BT-60 tube using the remaining BT-50 tube, 1 AR-2050 engine block, and 2 RA-5060 centering rings.  When dry, glue this engine mount into the short BT-60 body tube which is inbetween the 2 BT-55 tubes.

5.  Cut 4 fins for pattern #1 from the basswood.  Cut 2 each of the other 2 fin patterns from the basswood as well.  Round all edges on the fins, except for the root edges.

6.  Glue the 4 fins from pattern #1 along the bottom of the long BT-60 tube.  The fins should be spaced equally around the tube.

7.  Glue the 2 fins from pattern #2 to each of the BT-55 tubes.  Glue the 2 fins for pattern #3 to either side of the short BT-60 tube.

8.  Place glue in the bottom of the long BT-60 tube.  Now glue the short BT-60 tube to the long BT-60 tube via the JT-60C coupler.  The fins on the long BT-60 tube should be evenly spaced between the 2 BT-55 tubes.

9.  Cut the launch lug in half.  Glue one launch lug half next to and even with the bottom of a fin on the long BT-60 tube.  Glue the other launch lug half 15 1/2" from the bottom of the long BT-60 tube and in line with the other launch lug.

10.  Attach shock cords using desired length to each body tube (BT-60 and the 2 BT-55's).

11.  Add about an ounce of nose weight to the PNC-60AH.  Tie each nose cone to a free end of a shock cord.

12.  Assemble parachute and tie to PNC-60AH nose cone.

You can fly this rocket using 3 D12-7 motors.  An alternative would be to use a D12-7 in the center and 2 D11-P's in the BT-55's.  If using all D12-7's, be sure to place wadding in the BT-55's to protect the shock cords.  You could also glue on the PNC-55AC nose cones and cut vents near the top of the BT-55's for the ejection gases.

One other alternative:  You can make this a two stage rocket with 3 motors in the booster stage and 1 motor in the top stage.  (This is my original plan.)  To do this, do NOT glue the long BT-60 tube to the short BT-60 tube.  Instead, build another motor mount and glue it into the long BT-60.  Attach 12" parachutes to each of the BT-55 assemblies.  To fly in this configuration, use D12-5's in the BT-55's, a D12-0 in the short BT-60, and a D12-7 in the long BT-60.

Good luck with your Big Beth X-2.

I have flown the Big Beth X-2 four times.  The first 2 flights used the 2 stage configuration.

1st Flight

On the first launch, the launch wires some how got tangled on the first stage.  This held the rocket on the pad, but at staging the second stage took off just fine.

2nd Flight

The second flight was also in the 2 stage mode.  This time the first stage worked perfectly, a straight boost. At staging, however, a fin broke off of the second stage.  The second stage became unstable at this point but the parachute did deploy and it was recovered with no damage other than the one broken fin.

3rd and 4th Flights

For the 3rd and 4th flights, I had glued the two stages together, making the Big Beth X-2 a 3 cluster, single stage rocket.  I flew it both times with three D12-7's.  Each of these 2 flights was perfect.  Straight flights and good recoveries.