As far as I am aware, there have not been any model aircraft that have successfully circumnavigated the Earth without stopping. Few trans-Atlantic attempts have succeeded (see: The Spirit of Butts' Farm). My question is: what makes long-range model aviation so difficult? Is the small size of model aircraft disadvantageous when traveling long distances? Or is success just a question of improving the materials and propulsion, and flying during good weather?
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1$\begingroup$ I'd think that regulatory approval from all overflown countries and access to a powerful enough control and telemetry radio setup would be the most challenging... we already have fully solar-powered UAV aircraft that can theoretically stay airborne forever. I have no sources for these theses though. $\endgroup$– ifconfig ♦Commented Aug 3, 2020 at 4:30
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So many different issues, I study a lot of the FAA regulations closely but have contemplated this same question a few times.
- The power and weight of gear is heavy, so to make it all the way around is not going to happen without a lot of hacking. (solar proof of concept or similar notwithstanding)
- Efficiency of solar (power and weight) is a problem. The square feet of solar needed is quite large and disproportionate to how we conceptualize "RC planes". These vehicles are really flying solar arrays.
- Data, control, tracking, and safety assurance is much harder half way around the globe, even with satellite assistance
- Satellite data and connectivity hardware is still big leaving this type of task to the larger military units.
From a regulatory perspective
- FAA would rather cut their hand off than issue BVLOS waiver
- Patchwork problems internationally exist not only for aviation, but also frequency use . EU radio freqs are very different. When traveling to fly internationally it takes a while to make sure I am legal or have legal gear.
- Clearing airspace for these attempts is a serious undertaking of budget and politics.
Weather is a huge concern for small craft. Variations in the strata of the atmosphere are no joke. Be it thin air at altitude, winds, cold/hot temperature, all of this is hard for a small craft to manage.
"At heights of 7 to 16 kilometres, the air in jet streams moves at constant speeds of over 25 metres per second or 90 kilometres an hour." source
The US Military is one of a few orgs with advanced programs for this type of use. The U.S. military UAS groups has Tier 2+ with a '3,000-nautical-mile (6,000 km) radius'. These devices range from sub-55 pound to 2+ ton vehicles.
For what it is worth, I know some people with ties to a successful cross Atlantic RC plane flight. The stories they tell underscore how hard this task is to pull off.
In the end our number one obstacle for extended UAV flight of this type (and in general) is the same problem we have for phones and laptops. Our current battery tech is 20-30 years behind the technology it powers. The physics community engaged with this part of the equation frequently try to move the ball forward but the person to make a lighter and better battery will win the internet. Other fuel types are out there too, for example Hydrogen where the MFD3000 by Bobby Watts is available with a hydrogen fuel cell providing some interesting performance and represents good progress.
I think anyone with some expertise in mechanical, electrical, aviation, fuel and power train, etc could stop by and add a few more reasons why this is generally out of reach right now.
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$\begingroup$ The link to the MFD3000 page is broken. $\endgroup$– FluxCommented Jan 26, 2021 at 15:43
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$\begingroup$ @Flux looks like it is the 5000 now: wattsinnovations.com/pages/mfd5000 $\endgroup$ Commented Jan 27, 2021 at 16:14
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$\begingroup$ Frequency use issues can be danced around by operating in the amateur radio bands, as these are pretty standardized across the globe. The only thing you need is to be a licenced ham and operate all the hardware officially under your callsign. As an added benefit, you could use frequencies that are generally really hard to get permission for as a regular citizen, but are freely available to any ham. $\endgroup$ Commented Aug 26, 2021 at 11:24
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$\begingroup$ @FlashCactus you are totally correct, I have all my HAM lics, indeed there are a lot of amazing things to be done in the EM world. This is still a serious obstacle for 2 reasons. First, you will need to re-modulate the data for control and vision (assuming FPV use) - send/rx. Second, particular to FPV, is the underlying bandwidth requirements to transmit usable video. In LR flight there are already various systems for 900, 1.3, and a few other bands. Generally, 900 is the low side I see used (a junk band AFIK, commonly for control). I am aware of 1.3 video systems. $\endgroup$ Commented Aug 26, 2021 at 18:21