S6A Streamer Duration Strategies
The strategy in S6 is pretty much the same as in NAR competition: Build light, boost high, get good streamer deployment and action, and hit good air. Simple enough, right? Let's look at each aspect:
A common goal in all incarnations of Streamer Duration is to build light. But in S6A, this is taken to an extreme. Built to the current rules, S6A models (empty; no motor, no wadding, no streamer) as light as 3 grams have been seen. (About the mass of a U.S. penny!) However, like in any other event, building excessively light in S6A is not without its risks. Many a competitor has "pushed the envelope" too far in S6A, the result being an embarrassing disintegration of model and ego shortly after launch, not to mention a disqualification and a zero score. So, while building light might improve your chances of winning, going too far will definitely destroy them.
An important aspect of a competitive SD flight is to boost high, just like the forefathers of SD competition had intended. Before the advent of size restrictions, this usually meant building a minimum diameter bird that was just large enough in diameter to house the motor. But with the current FAI diameter restrictions, you don't have much of a choice. You can, however, do things to minimize drag, including using a boattail, airfoiling your fins, getting a good finish on your model, using an efficient motor, and making sure your model is at optimum mass. A vertical flight for maximum altitude is also important, e.g. unless you're really confident that you can consistently boost straight off a piston without tip-off, you're better off without it. (Tipping off is actually a double-edge sword: A flight that tips-off not only suffers in altitude, but often winds up flying into an unintended portion of the sky, foiling with your efforts to launch into lift.) As with all duration events, consistency is important. A bad flight can really blow your chances for an individual and a team place because, like every duration event at the WSMC, every flight counts.
How does one get good streamer action? Streamers have been a debated topic from the very beginning of SD competition. What is the best size? What is the best material? What is the best method of packing? No one seems to know. SD has always been a "black art" that has few givens and a lot of unknowns. A lot of streamer studies, drop tests, and experimenting has been done over the years, some of which have had conflicting results. Furthering confounding the black art nature of this event is the fact that streamer models do not always behave consistently, despite efforts to control the variables. Even the same model flown by the same person can behave quite differently between flights. Because of the black art nature of Streamer Duration, it's really hard to say what definitely works and what doesn't. In SD, you have to keep experimenting until you find something that works for you.
So, what streamer system works for me? One can easily go nuts trying to consider all of the variables and possibilities. I think the key in S6 is to not go crazy! I like to focus on the no-brainers, then work on my own ideas on what I think works. My current thoughts on S6 are as follows:
- Build the model as light as you are willing to go, then size the streamer so that you are at optimum mass. Cramming more streamer beyond this might improve the sink rate, but will definitely lower the altitude. For my S6A models, my streamers (~3/4 mil Mylar) come out at around 4.5" x 45".
- Size the streamer to 10:1. This is the minimum aspect ratio mandated by FAI rules. A study by Trip Barber and the MIT Rocket Society in the '70s demonstrated that increasing the width of a streamer increases its drag, but beyond a certain point, the performance of a streamer actually decreases with increased length.
- Choose a readily-available streamer material to experiment with. A lot of talk has been made about "proprietary" and "secret" streamer materials. Aside from questionable claims as to how truly magical these substances are, usually such proprietary materials are in short supply. What's the point of experimenting and practicing with something that you can't get more of?
- Choose a folding technique that's easy to do. For one thing, a folding technique that's easy to do means a greater chance that different streamers folded the same way will behave in the same manner. Second (and most importantly), spending less time folding streamers gives you more time for practice! I roll my streamer material into a tube, squash it flat between wooden blocks, bake it at low heat for a few hours (instead of ironing), then slice it into individual streamers. This is quick, easy, and insures uniformity between streamers made in the same "batch."
- Pay close attention to the condition of your streamer between flights. The same streamer can act quite differently between flights. Obviously, one that is folded up tight versus one that has been flown a few times and has "stretched out" can't be expected to perform the same. Bunched up or stretched out, whatever streamer system you find that works for you must be accurately repeatable each time you fly.
- Nothing beats practice.
Item #6 is related to the last aspect of a good streamer flight: launching into good air. Picking good air to launch into is important in all duration events, but with S6 it is especially critical. This is yet another black art, one that can only be learned through practice. Like other black arts, picking air can be really frustrating. What works well one time might not work well at another time. The U.S. Team traditionally brings all kinds of equipment to the WSMC to detect thermals, including thermal poles, bubble machines, and temperature and wind sensors. This may sound really complicated, but the only thing this equipment does is give a competitor feedback as to what the air is doing. Is the air rising? Is it sinking? Is another thermal coming through the area? The equipment can give you clues, but it is up to you to determine what the air is really doing and to decide whether to launch or not. There are many articles written on this subject; I'm not really qualified to write on this. All I can say at this point is that this art can only be learned by doing.
In conclusion, there's quite a lot to this event that was originally conceived as a "beginner's event." S6 offers a lot of challenges to the modroc competitor. The demands of building super lightweight models using exotic building materials, coupled with the "black art" nature of streamer dynamics and thermal picking make this deceptively simple event an interesting challenge for any modroc competitor.