I may be wrong . But throwing it even from an aircraft wont actually destroy the data on the disc . You may damage the Hdd casing and the read/write head but the data on the mag disc ( if u find the discs

) can still be taken out , though it will require some patience .
U can destroy data using an electromagnet (simple wire coiled conductor with power supply ) it will modify the data and in most cases data wud be rendered unreadable .
OR
store full 8 GB crap like music , movies etc and then do a zero level format .
my first choice wud be gg_3000's method and can be an easy an fun to do option LOL .