Tuber and Uber-Tuber - Tube Finned Multi-Stage Rockets

Tuber and Uber-Tuber
Tube Finned Multi-Stage Rockets

Photo courtesy of Bill Gee - Mar-16-2002

The original Tuber was one of my standard fliers; I flew it nearly every time out.

Inspired by the Rocket Vision Six Pack, the upper stage of the Tuber used six tube sections (BT-55) as its fins. To complement the six tubes, the booster was equipped with 6 balsa fins. It came out looking quite good. And the Squirrel Works were impressed enough to kit the Tuber.

In the original, both stages used 18mm motors. It flew great on B's and C's, and with its high drag, the Tuber was great on small fields using a B6-0 to B4-4 combination.

And the tube fins proved quite rugged. The original Tuber had a history of accidents. At least three times it came in on plastic wad recovery, or worse, stuck chute. In some cases, it seemed the parachute just stepped aside and allowed the ejection gasses to escape without ejecting the chute. But each time it was able to fly again without repair.

Over time, Tuber's nose cone got dinged up some, and there were plently of cracks in the paint, but it proved to be quite rugged, and always entertained me. However, it met its demise just before Christmas of 2002 when it core sampled in a concrete parking lot. It was almost totally destroyed, but the nosecone was salvaged, and used on its successor.

The replacement featured 24mm motor mounts and an extra booster stage. The repaired nosecone had a slightly rounded tip, but otherwise, the rocket's shape was true to the original. A nice decal adorned the new Tuber.

Soon after entering service, on a 2-stage flight, the upper failed to light, and the resulting lawndart accordioned the airframe and destroyed the nosecone

So the new Tuber was repaired. I turned a replacement nosecone out of cedar, and spliced in a new section of airframe. Some dings on the second stage booster were repaired and painted blue. Rebuilding the rocket, I was a little too creative and failed to be true to the original. The nosecone was too long and the wrong shape. And the repaired airframe was too long as well.

At left, the rocket is ready for its only flight in this configuration. The motor stack was D12-0 to D12-0 to D12-7.

Here's a liftoff shot of the D-D-D combo. The rocket was too heavy for the single D12-0 in the first stage, and crawled off the rod. It soon began turning into the wind, and by the time the third stage motor lit, it seemed like it was going horizontal. Don Magness helped me track the flight, and we had a long walk but managed to recover all the pieces.

The lengthened body tube and heavier nosecone proved to be unnecessary and were in fact detrimental. They contributed to weather cocking and gravity turning.

The lesson learned was that more thrust is needed to fly a stack like this.

Photo courtesy of Pelham Swift

Below is a great liftoff shot. The rocket is in a rare configuration with the airframe cut back to the original length, but still sporting the cedar nosecone.

Photo courtesy of Tim Sapp

Uber Tuber - 3 Stage Tuber with Clustered First Stage Booster

Having flown the 3-stage Tuber variant on a D12-D12-D12 combo in late 2004, I knew it needed something different. As it was, it crawled off the rod, lumbering into the sky. By the time the third stage lit, it was nearly horizontal. It needed a better first stage thrust curve; something like a D30 or E30 would be just right. But since no one makes one (in black powder), the next best thing is a clustered booster (clooster?).

Having successfully clustered boosters on my Thridget and Midget70 birds, I knew just what to do here.

Adding three 18mm outboards to the first stage solves the problem, and does so without needing an FSI E60

Here's a look at the aft end of the first stage booster. The three outboards were built and finished first, then glued onto the booster. Tape was used to mask off unfinished strips where the glue was applied. On the booster, the red paint was sanded down to the bare wood to accept the glue.

The three motor hooks are clearly visible here.

The forward ends of the outboards are beveled to reduce drag and to improve looks. Drag looks ugly, right?

The vent holes are just visible here. The beveled plug is made of balsa, and also functions as the engine block. The plugs were bored axially then radially. Any ejection gases will pass forward through the plug then radially out the vent hole.

In this shot, the burn string attach points are visible. Piano wire was bent into two U-shaped pieces, then epoxied through the aft centering ring into the anular space between the motor tube and airframe.

The burn string is critical. The center motor lights the next stage, so the rocket must be held on the pad in case is doesn't light. Otherwise, things will get ugly.

Photo courtesy of Tim Sapp

With the enhanced first stage booster, the Uber-Tuber is a real winner. At left, all four booster motors lit and the rocket had a great flight.

Here's another 3-stage flight. It had the maximum impulse load: three C6-0's and a D12-0 in the first stage, a D12-0 in the second, stage and an E9-6 in the third stage. Altitude estimates were around 3000'.

October 26, 2008

5-28-2010