Finding Height Using Estes Alti Trak Altitude Finder

With my science activities I am trying to incorporate more math to go along with the project build ideas.  A very common application is determine the maximum height of a model rocket launch using the "tangent" function in trigonometry. My first attempt at using this method I used a protractor with a string tied to it and a weight hanging down. I launched a water rocket by myself using the 25 feet of line on my launcher but measured the rocket was 33 feet away. When siting at such a close distance the angle comes close to 90 degrees which does not give an accurate estimation. I had wrote down 85 degrees which using tangent  gives an altitude of 377 feet plus my height while holding would add another 6 feet to the result. This appears to be a reasonable result in that I have read water rockets often reach a few hundred feet.  However if the reading was actually 86 degrees this would have given an altitude that was almost 100 feet higher.

Estes Alti Trak Altitude Finder

Pull in trigger until sited

Protractor With Weighted String Hanging Down

Estes the model rocket company sells a device known as the "Estes Alti Trak Altitude Finder" which I purchased hoping it might be a little more accurate. With the Alti Trak line up the sites while pulling in a trigger when the point is found release the trigger and the angle is locked in.  I started testing the unit on a utility pole and then a rubber powered model helicopter.

Utility Pole

For the utility pole I computed it was 44 feet tall which could be fairly accurate as I read a standard utility pole is 40 feet tall but can be as tall as 120 feet.  I then tried to estimate the maximum height of simple rubber powered helicopter in windy weather. The helicopter drifted downwind a fair amount so I subtracted 10 feet for the drift as the helicopter was coming down. Angle reading was 28 degrees which gave a tangent reading of .5317094311661 which multiplied by 89 feet gives an altitude of 47 feet which sounds reasonable.

Tape Measure Extends to 100 Feet 

I plan to demonstrate this in some of the activities I do with kids. Even if it is not completely accurate I think showing how the math works is more important and to discuss where inaccuracies could be. To test it further I want to use this on a known height and see how accurate this is. I would also like to find a metric tape measure.

Bill Kuhl
http://www.ideas-inspire.com