that is some good information from you deggy...!
i will take a close look at the material.
staying below 400' could be possible. it is not that close to the ground to fear collisions with random objects except tall buildings. but they are normaly found in city´s only. and we dont want to go there
it is possible to let the uav follow roads just like a normal satnav but maybe with a bit distance and keep away from towns/citys... that could do the trick for continental navigation. overseas is a bit easier.
the transmit power for the radio is only restricted in specific frequencies. there are open ones which can be abused like hell.. i´ve seen also some very impressive antenna designs for omnidirectional transreceiving. but i still need to do some more resarch in this direction.
about the hydrogen topic: NO WAY! it is true that i´m using a airtight construction in the end, but hydrogen is way to unsafe for this kind of project. the amount needed for the uav is high enough to be rated as a flying bomb. i will never get any flying clearance for the uav with this material inside. therefore i will only use helium.
@jonitan: it would be nice of you if you could calculate the volume needed. i´ll come back to you when i have all materials here to weight them.
all in all, there is still quite some work to do for the project. and also still some waiting time for materials from china... why the hell do they need %$#§ over 25 days to deliver... damn.