An excellent way for students to gain a feel for aerodynamic forces is to fly a kite. Students can also use math techniques learned in high school to determine the altitude of the kite during the flight.

On this page we show a simple way to determine the altitude of a flying kite. The procedure requires an observer in addition to the kite flyer, and a tool (like the one shown in the upper portion of the figure) to measure angles. The observer is stationed some distance (d) from the flyer along a reference line. (You can lay a string of known length along the ground between the flyer and the observer to make this reference line. A long line will produce more accurate results.) To determine the altitude, the flyer calls out "Take Data", and measures the angle (c) between the reference line and the location of the kite. Notice that this measurement is taken parallel to the ground and can be done by the flyer measuring from the kite string to the reference line laid on the ground. When the observer hears the call, "Take Data", the observer must face the kite and measure the angle (a) from the ground to the kite. The observer must then measure the angle (b), parallel to the ground, between the direction the observer is facing and the reference line in the same manner as the flyer. (Notice that angle (a) is measured in a plane that is perpendicular to the ground while angles (b) and (c) are measured in plane parallel to the ground).

With the three measured angles and the measured distance between the flyer and the
observer, we can use **trigonometry** to give us an equation for
the altitude (h) of the kite. The equation is:

h = (d * tan a * tan c) / ( cos b * (tan b + tan c))

where the tangent (**tan**) and the cosine (**cos**) are trigonometric
functions whose values are determined using a calculator.

If you are **really good** in math, see if you can derive
this equation using the information given above. You can check your answer
against my
derivation.
You can use this same equation to determine the height of any object
from a tall tree to a flying
model rocket.
If you do not know trigonometry, you can still determine the altitude of the kite
by using a
graphical solution.

Navigation..

- Beginner's Guide to Aerodynamics
- Beginner's Guide to Propulsion
- Beginner's Guide to Model Rockets
- Beginner's Guide to Kites
- Beginner's Guide to Aeronautics

Go to...

- Beginner's Guide Home Page

*byTom
Benson
Please send suggestions/corrections to: benson@grc.nasa.gov *