Saturday, April 5, 2014

Dirty Birds, Starlings & Educational Rockets

Way back in 2002, I wanted to find a way to manufacture some inexpensive model rockets for teaching purposes. After having a couple of students make what could only be described "death machines" (and which I would not allow to fly), I felt the need to design something a bit more stable, inherently. 
Plastic fin sets were the logical choice, but the rockets that were available at the time that had these, the venerable Estes Alpha III, their smaller Gnome, or a couple of the Quest kits, were not cheap enough, not when compared to the Estes Vikings we had used.
Which was really a pity. The Viking started off as a Centuri rocket meant for the Boy Scouts of America. It has five fiberboard fins that can be arranged in a number of ways, allowing for full customization of each rocket. There are problems with this approach, though.
The first, and perhaps greatest, is student patience. They rush the construction, and this leads to other problems. 
These other problems are unevenly spaced fins, fins too far up the rocket (playing deadly games with CG/CP), weakly and poorly attached fins. Other problems had to do with the manner in which the rockets were built. Good old white glue, like Elmer's Glue All, is sufficient, but sometimes you find, especially in classroom situations, that someone has refilled the student bottles with Elmer's School Glue, a thinner, weaker variant. 
All of these problems came home to roost in the summer of 2002, when I had to tell a couple of students that their rockets couldn't fly.
I wanted to avoid that.
So, I set out to find an inexpensive alternative.

This quest to find the perfect educational model rocket actually began in 2001 while I was at the South Florida Science Museum. A year or so before I arrived, they received some kits from Pitsco. These rockets are unique in that they require that the student roll their own body tube. I was asked to evaluate one. I found that with my years of experience rolling the tube really wasn't that hard, but I wondered how easy it would be for a student, especially younger ones. From that point on, I concentrated on using the kits from Estes and Quest. Still problems persisted, as I previously mentioned.
About the same time, I was looking into the history of model rocketry and perusing some online scans of old model rocket newsletters. One of these, "Model Rocketry News", volume 2, number 1, February 1962, contained a plan by the one and only G. Harry Stine, one of the originators of the hobby and for many years its most prolific advocate. This rocket was the "Dirty Bird III". It utilized plastic components that Estes sold at the time, components that clearly showed their firework roots. The model was built around the BT-40 body tube, an old size that also has its origins in fireworks. 

I wanted to build my own copy of this model, and asked around online to the various model rocket groups I belonged to. Someone suggested that I check Firefox Enterprises, as they carried fin sets, tubes, and nose cones that matched the ones used on the Dirty Bird III.
Wanting to be sure, I contacted the company to check on the shape of the fin unit, and sent them a rudimentary GIF drawing. The salesperson replied that yes, those were the fins. The body tubes were shorter, however. She also mentioned that the cones were just that, cones, though she didn't know what I meant when I asked about how they fit on the tubes. 
Feeling confident, I ordered the components. I went one step further, however. These rockets were ordered for my rocketry class at the Talcott Mountain Science Center. If the Dirty Bird III was really made from similar components, these would be equally easy. 
What arrived, though, was not quite what I was expecting.
The fin units did not quite match those found on the original Dirty Bird III. 

Not only that, the opening in the bottom was around 9/16" (14 mm) in diameter, perfect for mini-engines, not standard 18 mm engines that we had in abundance. The nose cones were not quite what I was expecting, but not really surprising either; they were the standard "sky rocket" type that fit over the tube. The tubes were also a little rough, but at least they were colored.

Undaunted, I pressed on. I'd make do.
Thus was born the "Starling", my own little "Dirty Bird" (if you know birds, you will understand the reason for that name). 
I had to produce thirty kits. The first thing I did was to open up the fin cans to allow 18 mm engines.

To retain the engine, I made engine hooks from coat hangers. This entailed cutting and shaping thirty of them. The rockets would use crepe paper streamers; I've been using this for years, as it is flame retardant and very inexpensive, as well as light. Thirty were made, each 18" (450 mm) long. Each kit contained an elastic shock cord, also 18". Rounding out each kit was a launch lug, made from yellow hard plastic tubing used for mylar balloons. These were cut to 2" (50 mm).
There were some quirks that I didn't like. My original method for mounting the shock cord to the nose cone didn't work, so we went to making a small hole in the side of the cone, running the cord through, and knotting it. The engine hooks were made from soft coat hanger wire, which bent easily, and had to be mounted externally, slightly marring the rockets appearance. 
But even with these quirks, the rockets flew fine, and in fact were pretty tough. Every one of them flew. Every student was happy, though I heard from parents that the rockets did look like fireworks. They usually found it humorous. 
In 2005, I made a second batch for EcoEd in Jacksonville, "Starling-A". These had one modification; the nose cones now had the shock cord attached to the inside of the nose by means of a wooden bead, that I threaded the cord through and epoxied in place before hand. I also picked up a new batch of white tubing for the launch lugs that was supposed to be the same size as the previous yellow lugs. What happened, though, was that these little tubes were not consistent. Some were less than the advertised 3.5 mm internal diameter, and ended up jamming on the launch rods. I was horribly embarrassed. 
I gave up on the design. Until recently.
Once more, my mind has turned to the problem of the best educational rocket, and again I wonder if these components can be used to produce something truly useful. To that end, a test rocket has been assembled, the first "Starling Mk. II", Little Aerospace Model R-2. I am awaiting the arrival of more components. This is to be a small field bird, and a low altitude one at that.
With any luck, the STA (Starling Test Article, designated R-2X) will reveal any short comings in the design. That's my hope, at any rate.

We'll find out soon enough.

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