Air Trajectory

Air Trajectory is a Division B and Division C event 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.

Competition
From at least 1 meter 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).

The goals is to launch the projectile (i.e., tennis balls, racquetballs, ping-pong balls, or plastic practice golf balls) so that it lands as close as possible to the center of a target placed between 2.00 to 8.00 meters away. The allowed intervals at which the target areas are placed are different for regionals (1.00 m), states (0.50 m), and nationals (0.10 m).

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.

=Construction= 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. 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!

Common types:

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 (duct tape works well for preventing leaks, can be consistent)

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 Your Device
Test your device so you can make sure it works as stated in the parameters. Then test it at different temperatures and different humidities and so on since the device can be affected by all or any one of those factors. Do your main testing at conditions as close as possible to what is expected at competition. In some regional and state competitions you may have to account for a wide range of temperatures and even wind speeds if competition is outdoors, but Nationals is always done indoors in a controlled environment. Make sure you are on level ground and are exact.

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 hit the target 1 time out of 3 is unlikely to beat a device that can hit the target 9 times out of 10. It is important as well that the device be sturdy enough so that once you have done your calibration, nothing will break or move (or you are likely to have to completely re-calibrate you device).

Tips

 * Make sure to put a ball(or whatever you are launching) in before you launch sometimes it can be easy to forget to reload it. An inadvertent launch will count as one of your 4 possible launches so you don't want to waste them.
 * While in the testing box, be sure that you do not remove your goggles. *Doing so will result in a large penalty.
 * Make sure that you and your partner are always out of the launching box while launching that means hands and knees also.
 * Try bringing a checklist, and before you impound your device, check that you have everything you need.
 * Before you launch, make sure to notify the judges.
 * Take your time - do not hurry to launch! Estimate where your projectile will land before launching.
 * Make sure you do not go over the weight limit. Be especially carefully if you have piston because the piston weight counts for the falling weight.

Files
[[Media:trajectorygraphs.xls|Graph Examples]]

Helpful Links
https://www.youtu