Airspeed Indicator?
Ham radio license, small gps, single chip TNC (tinytrak maybe...) and small ham tx. (yaesu vx-1r or icom credit card radio) total weight would only be a couple of ounces, nothing for a plane of that size.
This would allow you to send down gps data (including speed and alt), although only once a second, and receive it on a computer.
Ryan
KC0LMO