Streamer Duration
OVERVIEW
Streamer Duration is about building a light, low drag rocket that can boost very high and still carry a large enough streamer of the right material and design to descend slowly. The model has to remain in one piece throughout the flight and cannot be staged. The streamer must be at least five times as long as it is wide, must be made of a single material, and must be connected to the model by a single line going to one of its narrow ends.
For the full rules for this event, please see the Streamer Duration rules in the Model Rocket Sporting Code.
SCORING
The contestant may make one or two flights. Up to two models may be used. The score is the sum two flights, as long as one of the models is returned.
GENERAL TIPS
by George Gassaway, NAR 18723 and Trip Barber, NAR 4322
Design Considerations. There are trade-offs between the model’s performance and the streamer’s size. Low-mass and low-drag models are generally preferred but may not be strong enough to survive boost. Increasing the size of the streamer means the streamer will need more room inside your rocket. A bigger streamer is also heavier, which could weigh down the model too much.
Streamers. Streamer choice and preparation is important. Simple crepe paper just doesn’t do it. Some people use a certain grade of tracing paper, while others prefer to use 1 mil Mylar. The tracing paper can perform well, but also can rip more easily than other materials. Therefore, 1 mil Mylar is recommended. For A and below power 4 x 40″ streamers are a good size. For B or C power, 6″ by 60″ streamers are about right.
The design goal for a streamer is to have it flapping and coning vigorously during recovery, creating drag from this action. A wide range of creasing and folding techniques are used to achieve this action. Streamer sizes vary from 4 x 40 inches (for 1/2 A and A) to 8 x 80 inches (for D), depending on the weight of the material used. Heavier materials are stiffer and hold creases better (this is good for drag), but they have to be smaller or their weight becomes a problem that reduces boost altitude and increases the fall rate on recovery despite their drag. Streamer mass should not exceed that which puts the model at optimum boost mass, nor should it exceed the weight of the rocket body with buned-out motor casing.
The trick to good performance out of the streamers is to put folds into them. The folds improve the “whip” action of the streamers. Some people use simple accordion type folds, or pleated folds, with the folds spaced about 1/2″ apart or so. Just pressing the folds is not good enough for Mylar streamers; the folds will not set as well as desired for good performance. Heat from an iron is better. Either use an old iron or apply some scrap cloth over the iron to protect the iron. Lay the iron over the folded or rolled/flattened streamer and let it heat as deeply as possible for many minutes. After you are done, place the streamer under some heavy object to keep the folds tight while it cools off.
The “Roll Fold” (sometimes referred to as the “Scorpion’s Tail”) is another simple approach for streamer creasing in common use. It can only be used with stiffer Mylars, 1 mil in thickness. This type of Mylar is sold in 50-inch-wide rolls as window film for hydroponics greenhouses. Make up streamers in batches at a time by rolling full-width 1-mil Mylar around a 10mm body tube then remove the tube, squash the streamer material flat between a long wooden clamp made from 1x4s and carriage bolts, and bake this inside an oven at low heat (150 degrees) for a few hours. Then slice the roll into individual streamers and add the shroud line. Leave the streamers in their tightly folded condition until they were ready for use, and store together those made from a single batch. Streamers made from the same batch behave very consistently. Straight out of the oven, “Roll Fold” streamers are too tight to be used as-is. As part of the prep routine, open up the streamer by gently pulling on it. Pay close attention to the degree that you open the streamer up. Too little or too much will hurt the streamer action. Pull and release the streamer until it naturally wants to roll up and assume a triangular shape, i.e. folds at 60 degrees, that just fits in the 40mm body.
The “Heat Sink” creasing technique is much more complex and time consuming, but appears to be closer to the state of the art in other countries, at least for A power class and below. This technique (described in the article posted below) produces a very large number of very tiny folds in the streamer material, and uses thinner (1/2-mil) material than the “Roll Fold”. This type of Mylar is commonly available, in rescue blankets and from model rocket hobby sources. Streamers made using this technique can be large (6 inches by 90) without being excessively heavy; using a length-to-width of up to 15 is common in East European models that use techniques and streamers similar to this.
Shock Cords. Kevlar shock cords of 100 pound grade are recommended. Use a 3 to 4 feet length from the main body to the streamer. Attach the cord securely to the streamer so that it cannot come off. Many people like to use a 1″ wide piece of tape folded across the bottom of the streamer, trapping the shock cord. But the cord could still slip free, so put a few knots into the portion of the cord that will be under the tape. The adhesive tape should be a type that will not rip easily, not scotch tape or masking tape. For extra strength, you can add a piece of 1/2″ wide strapping tape as shown. Connect the anchor line of the shock cord external to the body of the rocket, in the root of one of the fins. Secure it to the body above this point, at the balance point (center of gravity) of the empty airframe with burned-out motor casing, using a piece of tape or some CA glue. This will ensure that the rocket body falls sideways during recovery, adding its significant sideways drag to the drag of the streamer.
MOTOR SELECTION
This is an altitude event flown with big streamers. So the best motor selection for this event is one with low average thrust, the smallest possible diameter, the highest total impulse that fits within the power class being flown, and a long delay time. If you have a choice between a 13mm motor and an 18mm motor for this event, always use the 13mm motor. Streamer models tend to need long coasting times after motor burnout in order to reach their maximum feasible altitude, so always use the longest available delay time for the motor type you choose. In some power classes, particularly “A”, the longest delay time currently available for the smallest-diameter available A, the Estes A3-4T, is far too short for maximum altitude but you don’t have any alternative choice. Be careful in C streamer duration to use larger fins, as the heavy C motor in the tail with a light streamer often makes SD models in this class go unstable.
KITS
–Straight-Up kits (1/2A through D) – Qualified Competition Rockets
–13mm & 18mm kits (1/4A through C) – Aerospace Specialty Products
–Blue Streak kit (B – C) – Apogee Components (can be adapted)
–Competition streamer materials – Aerospace Specialty Products
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