There were three Cub Scout water rocket flights in 1998 by the Bear Den, Pack 74, Baden-Powell Council, Boy Scouts of America.  All three flights were in rockets made from 2 liter soda bottles. Fins were taped to the sides.  The messages/covers were placed in a zip lock bag and taped to the sides.  The bottles were partially filled with water and then the bottle was pressurized with a foot operated air pump.  The rockets rose 40 to 60 feet above ground level.  A parachute was used to slow the decent.

One was a test flight in my back yard.  Of the three flights this was the only one where the items were mailed.

The next flight was at a Cub Scout meeting as a demonstration.  The message included the Cub Scout Promise

The third flight was held during a Cub Scout overnight where each Cub Scout built his rocket.  The flown message included an image of a water rocket and a listing of the activities on the overnight.

Special Thanks to Ed Engelman for sharing his experiences!