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Set Duration
B Streamer Dur. Multi-Round
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D Eggloft Altitude
Research & Development

Set Duration

Thanks to Lee James & Kevin Trojanowski for assistance withthis page

Also see LeeJames' Tips Page with tips for Predicted Durationevents.

For NARAM-50, the Set Duration event has a target time of50 seconds.

Set Duration has the challenge of building and flying a model thatcan achieve a known target time as close to the time as possible.

With the Target Time of 50 seconds, the objective is to make themodel fly EXACTLY 50 seconds, from liftoff to landing. Only oneflight 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. Inthis case, it means you must fly Set Duration before you fly BStreamer Duration Multiround.

The event is open to any single staged rocket.

The model cannot use radio control or any other device to make itland at a certain time. The model cannot be caught.

For the full rules for this event, please see the PredictedDuration Rules on the NAR web page.

Scoring - For Set Duration, the actual model flight time iscalculated against the 50 second target time to produce a percentageerror. Lowest percentage error wins.

For example, if one model flies for 55 seconds and another modelflies 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 secondswould get a 2% error.

Design considerations - To use a rocket that will flyconsistently to the same altitude, and which uses a type of recoverythat will make it descend consistently. Then to "tweak" that model orrecovery device to try to dial it in to fly as close to 50 seconds aspossible.

It is not practical to produce a list of plans or kits, since thisis so wide open. You certainly do not have to build a special modelfor this event, you can make use of an existing sport model if youwant.

A person could try to use a flight simulation program likeRockSim. But a lot of fliers will take a model and fly it to try todial in the performance. Even those who use RockSim will tend to usethat only to give them some idea of what model to use, then do sometesting.

The most consistent type of descent rate tends to come more fromstreamers than with parachutes. So a good strategy is to use astreamer, and then try to figure out what sort of model, with whattype of engine, will go high enough for the relatively fast decentrate of a streamer to take about 50 seconds from liftoff tolanding.

The streamer type also matters here. Do NOT use a contest durationtype of streamer that flaps around, as those fall slower and areaffected a lot more by thermals and such. Use a simple rolled-upstreamer such as made out of flagging tape.

Most of those who take the top places in this event will havetested out their models and dialed them in to fly close to 50seconds. 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 staywith that engine but do something to either make the model fly loweror descend faster. Or both. A simple tweak to a model that flies 60seconds would be to add some weight so it will boost a bit lower, andalso 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 couldtry using a longer and wider streamer, though that might add enoughmass to be counter-productive. It might even be worth going to adifferent model type, starting over, than trying to tweak a modelthat 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 almostcertainly is going to vary in how long it is up. There may bevariances between engines, differences in the wind that make themodel weathercock differently, and also possible thermals. You cantry to address the engine consistency by using engines from the sameproduction run (check the production codes), ideally from the samepack. The wind, try to fly in the same kind of wind each time. Andthermals .... normally in contest flying we LIKE thermals but in thiscase you want to avoid flying when there is a thermal nearby. Youwant to fly in "neutral" air.

So, hopefully your testing will result in a model that can flyclose to 50 seconds, and you will have a decent shot at taking aplace with it at NARAM-50.

I have not done any flights for this event. It may requiresomething like an Alpha on C6, or smaller lighter higher flying modelon 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 secondswith the kit-provided chute, but as mentioned models with chutes tendto vary more from flight to flight. But at least that is one actualkit I can mention .A person can try to tweak that down by eitheradding some mass, reefing the shroud lines a little bit, or using alittle bit smaller chute.


Kevin Trojanowski mentioned: East Coast competitors have hadsuccess lately using the Estes Baby Bertha as the basis for PrecisionDuration models. They are reliable, accept motors from 1/2A to Dimpulse, and can accommodate many different sizes of recoverydevice.

Ed Giugliano wrote an R&D report on the Random Duration eventthat allowed him to create an equation for finding the parachutediameter and ballast weight to achieve a target duration.


Please check back for Updates. I am hoping that some more peoplewho have done some test flying might be willing to provide someinformation on the models they are using.

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 Last Updated   5/28/2008