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So, I know nothing about aviation. I'm a student studying maths and computing and I feel like building a high altitude glider controlled by a Raspberry Pi and Arduino as a personal project.

First things first, I'll be launching using a weather balloon or something to reach a given altitude (references to any information on glide ratios as you get to higher altitudes would be much appreciated). Once it's high enough the balloon will be deflated and released, the glider will then be dropped and start its descent.

Assume I've control of the glider in the form of waypoints I can plot on a map to be put into the onboard computer beforehand (or from signals sent from a computer). How complex an autopilot would be required to follow a set of coordinates (pre-calculated so they fit the descent pattern) and then release a parachute for a safe landing?

I was thinking of purchasing a basic glider structure as to have the maneuverability from the professionally built wings and stuff, so construction shouldn't be a problem. The main concern is how plausible a project like this would be considering I'll be building the flight computer myself and I know basically nothing about flight control.

Any other material you have on flight control, flight computers, personal projects like this would also be much appreciated.

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  • $\begingroup$ The first project I heard doing this were a couple of Canadian students who launched a glider via weather balloon that sent GPS coordinates back via radio so they could retrieve it. They lost it somewhere in the mountains. This was back in the early 2000s. Probably 2002. Their flight could have taken place in the 90s. The most well known successful attempt is probably this: youtube.com/watch?v=rpBnurznFio but make sure you get clearence from your government if you plan to release that high $\endgroup$ – slebetman Oct 19 '15 at 9:19
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This idea is entirely plausible and has been tried before, and even successfully. But I guess you have already read through all the pages which you can find via Google.

Several things are to be considered:

  • It is really cold up there (see below), and the ascent will take long enough that you need to heat the batteries and to remove grease which will likely freeze solid up there. It would be a shame if the onboard camera cannot document the flight because its battery was too cold.
  • Due to the low air density, flight speed will be high, so your sailplane will likely experience flutter if you try to use a regular RC glider. A more sturdy configuration which is less optimized for high glide ratios might serve you better.
  • Winds can be very high at altitude, especially between 10 and 16 km height. You need to factor wind drift into your planning. Try to launch on a calm day (calm all the way up, that is), or the plane might not reach the waypoints.

Temperature over altitude chart

Since lower temperature means a lower Reynolds number, viscous effects will be higher at altitude than on the ground. This means that your glider's drag for a given lift will be higher at altitude. How much depends a lot on the choice of wing airfoil. If you go with an existing model, pick one which flies well over a wide speed range. A reasonable glide ratio for a model at altitude would be between 10 to 15, so it will glide 10 to 15 km for each km of altitude.

The maximum altitude in which subsonic flight is possible depends on the wing loading (among other things), so try to keep masses down.

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There is a rule in the FAA part 101 regulations that has been interpreted to mean that you cannot launch anything from a high altitude balloon... "(b) No person operating any moored balloon, kite, unmanned rocket, or unmanned free balloon may allow an object to be dropped therefrom, if such action creates a hazard to other persons or their property."
That seems to be for security, keeping people with bad intentions from launching bombs on rockets, etc. Same with most GPS devices being limited to 20,000 ft. However, it you obtain permission to do it, please post a video! Good luck.

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    $\begingroup$ Not that I don't believe you, but linking to the appropriate part of the FAA regs in addition to quoting them is considered standard practice around here. Oh, and welcome! Your recent answers indicate an interest in ballooning - that will provide an interesting viewpoint to all the pilots we get here. :) $\endgroup$ – FreeMan Oct 16 '15 at 16:48
  • $\begingroup$ Considering that unmanned rockers, by design, allows itself and parts to be dropped, I guess the real important part of that regulation is "if such action creates a hazard". Multi-stage rocketry is perfectly legal. That means that the first part of the rule alone does not disallow you to do things. Rocket launched gliders are also a thing which used to be popular in the past at AMA free-flight events. $\endgroup$ – slebetman Oct 19 '15 at 9:13

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