Set Duration Thanks to Lee James & Kevin Trojanowski for assistance with this page Also see Lee James' Tips Page with tips for Predicted Duration events. For NARAM-50, the Set Duration event has a target time of 50 seconds. Set Duration has the challenge of building and flying a model that can achieve a known target time as close to the time as possible. With the Target Time of 50 seconds, the objective is to make the model fly EXACTLY 50 seconds, from liftoff to landing. Only one flight is allowed. At-field practice flying is not allowed on the day of the event. You must fly this event before you fly any other duration event. In this case, it means you must fly Set Duration before you fly B Streamer Duration Multiround. The event is open to any single staged rocket. The model cannot use radio control or any other device to make it land at a certain time. The model cannot be caught. For the full rules for this event, please see the Predicted Duration Rules on the NAR web page. Scoring - For Set Duration, the actual model flight time is calculated against the 50 second target time to produce a percentage error. Lowest percentage error wins. For example, if one model flies for 55 seconds and another model flies for 45 seconds, both being 5 seconds off from the target of 50, both would get a score of 10%. A model that flies for 51 seconds would get a 2% error. Design considerations - To use a rocket that will fly consistently to the same altitude, and which uses a type of recovery that will make it descend consistently. Then to "tweak" that model or recovery device to try to dial it in to fly as close to 50 seconds as possible. It is not practical to produce a list of plans or kits, since this is so wide open. You certainly do not have to build a special model for this event, you can make use of an existing sport model if you want. A person could try to use a flight simulation program like RockSim. But a lot of fliers will take a model and fly it to try to dial in the performance. Even those who use RockSim will tend to use that only to give them some idea of what model to use, then do some testing. The most consistent type of descent rate tends to come more from streamers than with parachutes. So a good strategy is to use a streamer, and then try to figure out what sort of model, with what type of engine, will go high enough for the relatively fast decent rate of a streamer to take about 50 seconds from liftoff to landing. The streamer type also matters here. Do NOT use a contest duration type of streamer that flaps around, as those fall slower and are affected a lot more by thermals and such. Use a simple rolled-up streamer such as made out of flagging tape. Most of those who take the top places in this event will have tested out their models and dialed them in to fly close to 50 seconds. If your model test flies for 30 seconds on a B engine, you'll have to try a C engine next time. Whatever engine, if your model flies for say 60 seconds, then stay with that engine but do something to either make the model fly lower or descend faster. Or both. A simple tweak to a model that flies 60 seconds would be to add some weight so it will boost a bit lower, and also come down a bit faster. If on the other hand you have a model that flies for 40 seconds, it is hard to do a tweak to squeeze out another 10 seconds. You could try using a longer and wider streamer, though that might add enough mass to be counter-productive. It might even be worth going to a different model type, starting over, than trying to tweak a model that flies for 40 seconds to fly for 10 more seconds. Now, consistency is key, both for contest day and for test flying. If you fly the model three times exactly the same way, it almost certainly is going to vary in how long it is up. There may be variances between engines, differences in the wind that make the model weathercock differently, and also possible thermals. You can try to address the engine consistency by using engines from the same production run (check the production codes), ideally from the same pack. The wind, try to fly in the same kind of wind each time. And thermals .... normally in contest flying we LIKE thermals but in this case you want to avoid flying when there is a thermal nearby. You want to fly in "neutral" air. So, hopefully your testing will result in a model that can fly close to 50 seconds, and you will have a decent shot at taking a place with it at NARAM-50. I have not done any flights for this event. It may require something like an Alpha on C6, or smaller lighter higher flying model on C6, to fall for about 50 seconds using a simple streamer. I do know that a Baby Bertha on C6 will fly for roughly 60 seconds with the kit-provided chute, but as mentioned models with chutes tend to vary more from flight to flight. But at least that is one actual kit I can mention .A person can try to tweak that down by either adding some mass, reefing the shroud lines a little bit, or using a little bit smaller chute. ------ Kevin Trojanowski mentioned: East Coast competitors have had success lately using the Estes Baby Bertha as the basis for Precision Duration models. They are reliable, accept motors from 1/2A to D impulse, and can accommodate many different sizes of recovery device. Ed Giugliano wrote an R&D report on the Random Duration event that allowed him to create an equation for finding the parachute diameter and ballast weight to achieve a target duration. http://www.narhams.org/library/rnd/PredictedDuration.pdf -------- Please check back for Updates. I am hoping that some more people who have done some test flying might be willing to provide some information on the models they are using.
Last Updated 5/28/2008 |
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