This would make a great episode, the Josh's could explain the different altitude ceilings for each radio type 2.4ghz, 900mhz, 30mhz, that kind of thing. Even if they made a scratch build for maximum altitude that would be a cool show to watch.
The free space is normally no problem as the commercial flights are a lot higher 10 000 m/ 30 000 ft.
Most radios should manage the distance in m - not in ft with normal long distance receivers. The problem is to see the plane to be able to control it. I tried to find the world record but did not see it at the moment. The pilot are sitting in a chair looking at the plane with a telescope.....
I believe that you need a jet enginge/turbo charger/compressor or thermal to get really high in the "thin air".
Normal cars without turbo are "weak" when driving in the rockies 14 000 ft above sea level.
Yes it would but beating Trappy (Isn´t he the one with the furthest distance) will be a pretty tough challenge!
If thin air is even better then in theory you should get more signal range with the direction up so away from the centre of earth then you would get tangentially to to the surface of earth. So in difficulty decreasing with distance as the air gets thinner and thinner.
@pgerts: Antennas have the "Weak spot" at those points directly above or under them. With a normal rubber ducky antenna the antennas themselves should always be staying parallel otherwise ending up with sagnificant loss in connection.
Don't forget approaches and non-jet aircraft. You should definitely check out a map of the airspace and routes in the vicinity of the place you are flying at. Being right on a airway would mean trouble.
It'd probably be best to design a plane with a really low wing loading and try to catch some thermals on the way up rather than building a super heavy sport plane and trying to muscle the way up with a huge motor and heavy batteries. I've had my ember 2 up so high it was just a speck, I know that isn't saying much seeing how small it is, but when I caught the thermals it was like an elevator going up!
With a little 500mAh 2S you would power the receiver only which would only have to keep in touch with your TX and power a few servos. Some kind of a slope soarer for flying around and a Mini FPV gear which doesn´t need much power as well.
I think catching thermals is quite difficult though. I fly in a region which is straight next to a forest and a lot of air turbulances are around there as well.