- This article is about the event Air Trajectory. For the event Trajectory, see Trajectory.
Air Trajectory is a Division B and Division C event being held in the 2016 season that debuted in 2015 after being a trial event at the 2014 National Tournament. The object is to construct a device that uses only the gravitational energy of a falling mass to launch a projectile either directly or indirectly.
From at least 75 centimeters away, students must trigger a device that drops a mass and then converts the gravitational energy of the mass to air pressure or movement, which is used to launch the projectile. The device must start at ambient air pressure (i.e., the projectile should not launch without the mass falling).
There are two targets on the course, between 2.00 m and 8.00 m from the launch area, separated by a distance of at least 2.00 m. The near target is centered on the line that bisects the launch area, parallel to the launch direction, and the far target may be anywhere up to 2.00 m from the imaginary center line. The allowed intervals at which the target areas are placed are different for regionals (0.50 m), states (0.25 m), and nationals (0.10 m).
For each target, students may perform a maximum of two shots. The goal is to launch the projectile (i.e., tennis balls, racquetballs, ping-pong balls, or plastic practice golf balls) so that its initial impact is as close as possible to the center of the target. The maximum target score is 2000 for the near target and 4000 for the far target, minus the distance from the initial impact to the target in millimeters.
If the first shot at a target lands within 50.0 cm, a bucket shot may be requested, where a bucket is placed anywhere between 2.00 m and 8.00 m from the launch area, and 2.00 m from the imaginary center line facing up. A shot that lands in the bucket is worth 100 points, and one that hits the bottom face of the bucket is worth 200 more points for a total of 300 points.
In addition to device accuracy at the competition, the score accounts for a graph component, in which teams are to bring graphs for determination of the best launch parameters for a maximum of 400 points.
Therefore, the score is calculated as follows:
The maximum possible score is 7000.
One method to build a launch mechanism for an Air Trajectory device is to use an empty bottle (i.e. 2-liter soda bottle) and attach a pipe to it. To load it, you could put a ball in the pipe. Then you would drop your mass onto the bottle, forcing out the air inside it and launching the ball out of the tube. For this method, you would have to experiment with different masses for the short and long targets. This would not be a particularly good idea, because there is a total amount of weight you are allowed to bring in. A better way of calibration would be to change the different heights the weight is dropped from, having a standard way to measure different heights.
There are also other methods. Some involve air pumps, others use custom-made air chambers. But all of them can work- you just have to put them to the test!
- Soda Bottle - simple and easy, but can be unreliable and inconsistent
- Air pump - more consistent, but more difficult to incorporate and produce the needed air pressure
- Bag (of some sort) - upgraded version of soda bottle, difficult to find and incorporate
- Kickball - Difficult to incorporate and prevent leaks
- Custom air chamber - difficult to build, but constant and can be quite powerful
The overarching problem that can occur with all the above designs is that golf balls or ping pong balls must be used which can cause deviations in mid-air from small drafts
An advanced design that some teams choose to use is employing a swinging arm to throw a ball. This design is very difficult to build, but maintains a higher level of consistency.
Testing The Device
Testing the device is crucial to success in this event. Testing makes sure the device works as stated in the parameters. Testing should be done at many different humidities and temperatures so that these factors can be accounted for during the competition. Some regional and state competitions may have a wide range of temperatures and wind speeds if competition is outdoors, but Nationals is always done indoors in a controlled environment. Make sure that all other conditions are as close to competition conditions as possible, including using a level surface.
Consistency and reliability are the most important characteristics to strive for. The ideal device should be at a point where it hits the target every time. A device that hits the target 1 out of 3 times is unlikely to beat a device that can hit the target 9 out of 10 times. It is also important that the device is sturdy enough such that once calibration is completed, nothing will break or move (which would result in the need for re-calibration).
- Make sure to put a ball (or whatever is being launched) in before you launch, as sometimes it can be easy to forget to reload it. An inadvertent launch will count as one of your 4 possible launches, which wastes one of the four trials.
- While in the testing box, goggles must not be removed. Doing so will result in a large penalty.
- Make sure that all participants' hands and knees are always out of the launching box while launching.
- Try bringing a checklist, which can prevent the unintended omission of anything important.
- Check your graphs, what you did before can help you during the competition.
- Before you launch, make sure to notify the judges of the impending launch.
- Take your time - do not hurry to launch! Estimate where the projectile will land before launching.
- Make sure to not go over the weight limit. Be especially carefully if pistons are used because the piston weight counts for the falling weight.
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