I had a pack of BT-56 tubes, and no idea of what to do with them. I didn't even have a nosecone to fit. One day while looking at them, trying to figure out how I could get rid of the things, I started playing with the idea of building a Mean Machine clone. Well, one thing led to another, and instead I decided to do a long tube finned rocket. Since the body tubes are 18" long, by cutting one into 3" pieces, I'd use the entire package up and add another tube fin bird to our fleet. This one is D-powered, to go along with our mini-engined Finite Loop and the regular sized Groove Tube clone.
If you've never built a tube fin rocket, you will be amazed at how easy and quickly you can do it. The Empress does add the complexity of mid-body separation, an ejection baffle, and a boattail. To make this a true beginners level project, ignore the boattail and baffle, and use regular nose-cone separation.
Why use the "optional" stuff?
Well, the boattail will allow the rocket to go higher. There's a whole lot of complicated mathematical formulas that explain why in aerodynamic terms, but it's all pretty much beyond me. Besides, I like the way they look.
The ejection baffle eliminates the need for recovery wadding. I don't entirely trust them, and usually wrap the chute in one square of wadding anyway, just to be sure.
Mid-body separation means that instead of blowing the nosecone off, the body itself comes apart, releasing the recovery system. The main advantage for this rocket is that I don't have to haul around this loooooooong rocket in the car. It breaks into two shorter sections.
Yellow glue is plenty strong enough for this rocket. I used Elmer's Fill'n'Finish for fillets between the tube fins and to smooth the boattail.
2. Ejection Baffle. Take one of the BT-56 couplers, and cut a disk from balsa or thin cardboard, one for each end (See the diagram below). Glue it together and let dry.
hint: if you use thin cardboard, try sandwiching 2 layers together and soak them in CA (superglue) to toughen them up. Coat Balsa with yellow glue to add stiffness.
3. Mid-body separation coupler. Cut a disk from balsa or cardboard and glue it into one end of the second coupler. Don't put any holes in this one, it's a solid bulkhead. See the hint in step 1 about how to strengthen it easily.
4. Tube fins. Cut one of the BT-56 tubes into six 3" long sections. Glue pairs together so you have three pairs, let dry.
5. Assemble the motor mount. If you are using the boattail, the rearmost centering ring goes 1 1/8" from the end, otherwise follow the motor mount instructions. See the diagrams below for an idea of what this should look like. Let it dry.
6. Mark the body tube 1" from the end where you'll be installing the motor mount.
7. Glue the motor mount from step 5 into the body tube. The rearmost centering ring should be slightly inset from the rear of the body tube.
8. Boattail. Cut the appropriate sized shroud pattern from an Estes transition pattern sheet (available from Estes or at Jim Z's site). Or print one using VCP or other software. The completed boattail should be 1" long, with one end the diameter of the BT-56, the other end BT-50. Glue it into shape, and when dry glue it into place. You can use thin CA or yellow glue to strengthen it. I used a little Fill'n'Finish to smooth the glue joints and the seemingly inevitable minor wrinkles. You may need to cut a slight notch for the motor hook, use an X-acto for this.
9. Glue the pairs of tube fins around the body on the 1" line you marked in step 6.
10. Install the baffle. Glue the baffle into the rear body tube. Make sure it gets in there at least 3 or 4 inches.
11. Install the mid-body separation bulkhead. Glue it halfway into the front body tube, with the solid end closest to the nosecone. This is the coupler that holds the two body tubes together!!! Make sure you glue it in straight.
12. Shock cord mounts. I used the Estes paper-sandwich type. Glue one onto both ends of the 40" long elastic, and another onto the 12" long elastic. Three total.
13. Install the shock cords. Glue one end of the 40" shock cord into the bulkhead coupler, and the other end into the lower body just above the baffle.
14. Just for backup, glue the last (shortest) shock cord into the upper tube to secure the nose cone. This way, if the nose cone should accidentally come loose, it'll stay attached to the rest of the rocket.
15. Install the launch lugs. I cut mine in two. One was installed inside one of the tube fins (closest to the main body), with the other about 12" up from the bottom.
16. Finish and paint as desired. This is a long rocket, so lighter colors are recommended. Dark colors tend to get hotter in the sun (like in your car), and it could warp the tubes.
I painted mine white, and sprayed light blue up from the back end, fading about halfway up. Next I sprayed dark blue up from the back, fading at the quarter mark. Add some cockpit windows to the nose, some striping along the sides, and some windows to make an interplanetary liner. Be creative, have fun!
Flight Report - 7/18/98
Maiden flight, and I set it up with a D12-5 engine and a vented 18" parachute. Good boost with maybe a slight wobble off the rod. It climbed much quicker than I expected, but not a neck-snapper. Couldn't estimate altitude because I launched tilted into a pretty stiff breeze, but it was pretty high. Fine recovery, with ejection just after apogee. After-flight inspection showed that the baffle worked perfectly, with no charring to the shock cord or chute.
Flight Report - NARAM - 8/5-8/98
The Empress flew several times at NARAM. A large tube-fin rocket like this makes an impression! Perfect flights every time, including one using a 4"x40" streamer due to gusty wind conditions.