S6A Streamer Duration Overview
Streamer Duration (SD) is an old event that has its roots as a "Poor Man's Altitude" event. Back in the early days, models under streamer recovery were generally thought to fall, more or less, at the same rate. Hence, by simply timing streamer-recovered models from liftoff to touchdown, one could infer that the model that stayed aloft the longest "obviously" flew the highest. Especially appealing to beginning competitors, Streamer Duration was a welcomed addition to competition here in the U.S. when it was officially introduced in 1971.
Of course, we know that just because one SD model stays aloft longer than another SD model doesn't necessarily mean the former flew higher than the latter. There are many variables that can influence the duration of an SD model, making the direct comparison of duration versus altitude invalid in most cases. Over the years SD fans have discovered that there are variations in streamer materials, packing procedures, attachment methods, building techniques, and flying strategies that can make the difference between a model that sinks like a rock in under 60 seconds, and one that blissfully hovers in the air for several minutes or more. Indeed, this deceptively simple event has received an amazing amount of attention from competitors seeking to gain the proverbial competitive edge.
The FAI equivalent of Streamer Duration is referred to as "S6." The power class of S6 traditionally flown at past World Spacemodeling Championships (WSMC) was "S6A," i.e. 2.5 Newton-seconds. In early 2001 the rules for the WSMC were changed and now specify the S6B class for Senior competitors, and S6A for the Juniors. (This article focuses primarily on the S6A class model, though the basic ideas and principals should generally be applicable to all classes of the S6 event.) Regardless of the specific power class, though, the basic idea of this event is the same as the comparable NAR event, i.e. stay aloft as long as possible using streamer recovery, but with a few interesting twists. As with all FAI duration events, S6 is flown in rounds with defined "maxes" (see Rules Section of this article). Standard NAR Streamer Duration is not flown this way. (Though a less frequently flown "Multi-Round" version also exists.) The most significant difference between S6 and NAR Streamer Duration is that the FAI imposes dimensional restrictions on contest models. Whereas in NAR competition one can build an SD model to any dimension one chooses, in S6, models must be built to meet certain minimum length and diameter requirements. For example, S6A models must have a minimum length of 350 mm and a minimum diameter of 30 mm over at least 50% of the model length. When you consider that the typical NAR "A" streamer bird is a tiny, minimum diameter model no bigger than 13 mm in diameter, the size restrictions for the equivalent S6A event seem awfully grotesque in comparison. A lot of competitors freaked out when these "crazy" rules requiring 30 mm models first came out in 1989. Under these rules, many a competitor had visions of large, heavy streamer models lumbering to low altitude and remaining aloft for only a few seconds. Among other more graphic names, many dubbed these beasts "Big Berthas." As radical as these changes were, however, they weren't without some redeeming value. Over the years since the introduction of the size restrictions (originally 18 mm, later 30 mm), the quality of S6A models has gone up significantly. By being forced to follow the new size constraints and wanting to still be competitive, modelers have sought out new building materials and revamped their construction techniques, resulting in substantial advances in SD technology. The technology has reached the point where the 30 mm Big Bertha streamer model of today can pretty much go toe-to-toe with the old 13 mm paper-and-balsa model of the '70s.
The evolution of S6A over the years is interesting. Originally, like in NAR competition, there were no size restrictions on S6 models. S6A models at early WSMCs weren't really all that different from what was being used in NAR competition and typically used commercially-available parts. Common S6A models at the '78 and '80 WSMCs were built around Estes or Competition Model Rockets (CMR) parts. Streamers were typically tissue, tracing paper, or 1/2 mil Mylar. Streamer folding techniques were very much in vogue by this time, culminating with the U.S. Team's convincing win in SD in 1980 using pleated tracing paper streamers developed here in the U.S. by Charlie Sykos. Picking "good air" (i.e. thermals) to launch into, first used by the U.S. in '78, was becoming increasingly popular, as was the related "piggybacking," where one would launch into good air found by another competitor. Motor technology was still in its infancy, with the motor of choice being the 13 mm blackpowder Estes A3-6T. The '83 WSMC saw substantial changes, with many Europeans using lightweight 11 mm diameter hand-rolled fiberglass models with tiny custom-made blackpowder micro motors. In '85 the FAI imposed the first of the dimensional rule changes, mandating a minimum diameter of 18 mm over 50% of the length of the model. This was in response to models as small as 6 mm (!) being flown at an earlier European Championship, which was viewed as a safety hazard. This rule change prompted the development of boattailed fiberglass airframes, which later evolved into the 30 mm boattailed S6A airframes of today. A later rule change limited motor diameters to no less than 10 mm. '87 saw the use of custom 10.5 mm core burning composite micro motors by the U.S. Team in S6A. In 1989 the current 30 mm/350 mm dimensional restrictions for S6A were introduced. In 2001 the rules were changed again to define larger dimensional restrictions for larger classes of the S6 event. Most S6A models since the '90 WSMC have looked very similar. The typical S6A model of today uses a lightweight composite airframe, a pleated Mylar streamer, and an efficient long-burning motor, such as the "Delta" brand of motors manufactured in the Czech Republic. These models typically reach altitudes of around 250 meters on an "A" motor and can achieve durations of about one and a half minutes in "dead" air. Pretty impressive, all things considered!