Dick Hanson wrote:
well -an empty balloon may weigh a gram -but it can be filled with light gas to almost zero weight on any scale under conventional weighing conditions.
An empty balloon that weights one-gram will still weight at least one-gram after it has been filled with light gas, despite the scale will show less weight due to the Archimedes' principle:
A buoyant force is exerted on an object submersed in a fluid. The pressure beneath the object is larger than the pressure above. The resultant force on the object is upward, opposing the force of gravity.
When an object is partially or fully submerged, the buoyant force, or apparent loss in weight, is equal to the weight of the fluid displaced.
Dick Hanson wrote:
My point was that as we approach zero wingloading-the HARD rules soften/change -and when extremely light -the aircraft is far less critical to cg -
That's a much less controversial assumption, which has already been addressed several times here in this thread.
Below are some of the postings:
http://www.rcuniverse.com/forum/m_11...tm.htm#1579840
http://www.rcuniverse.com/forum/m_11...tm.htm#1611105
http://www.rcuniverse.com/forum/m_11...tm.htm#1614766
http://www.rcuniverse.com/forum/m_11...tm.htm#1797383