Precision Duration is a simple yet surprisingly challenging event. There are three options for the event:
- Predicted Duration. The competitor specifies the duration that his/her model will have.
- Set Duration. The target duration is specified in advance when the contest is sanctioned.
- Random Duration. The target time is randomly selected immediately prior to flying the event.
The declared time for Predicted Duration must be 30 seconds or greater (although the model itself may have an actual flight duration of less than 30 seconds). For Set Duration and Random Duration, the duration target must be from 30 to 120 seconds, in five second increments.
Precision Duration must be flown before any other event of a contest.
For the full rules for this event, please see the Precision Duration rules in the NAR Pink Book.
The score is based on the absolute value of the error ratio between the actual duration and the predicted duration. Lowest error wins. See the Pink Book for the exact calculation method, or use the Contest Manager software to calculate it.
The strategies for this event vary depending on the flavor of the event.
Predicted Duration. The obvious strategy for this event option is to fly a rocket many times and record its duration. The rocket should have durable construction so that the model’s performance does not change significantly due to accumulated flight damage. A rocket that flies high and has a reasonable (yet safe) rate of descent will be less perturbed by wind or thermals. Parachute recovery may not be a good approach since parachutes can be erratic (broken or tangled shroud lines, melted canopy, etc.). Streamer recovery is probably better since streamer drag is reasonably repeatable. Helicopter recovery can be an excellent way to achieve repeatable performance since the drag is produced by structural components.
Set Duration. The strategy for this event is straightforward: build and fly a durable/repeatable model, and then see how its duration compares to the target duration. If the duration is too long, then decrease the size of the recovery device and/or add weight. If the duration is too short, switch to a higher impulse motor. Keep tuning the model until you match the target duration. As before, it’s probably better to use streamer or helicopter recovery to achieve better consistency.
Random Duration. This is a very challenging event since the target duration is not known until immediately before the event. One strategy is to have single model that can be widely adjusted including mass, recovery device size, and motor impulse/size. A second strategy is to have a family of models that are targeted to specific durations or ranges of duration. For either strategy, many test flights may be needed to tune the model(s).
Almost any durable kit is a candidate for this event. Kits that use plastic fin units may be more durable and repeatable than models with balsa fins. A kit that includes a payload compartment may be useful to more easily adjust the weight of the model.