Hi all,
As I'm planning to use the APM2 to pilot a glider back from near space there are quite a few unusual questions etc that I need to clarify - so apologies for the many questions!
Originally I had thought about using my Lassen iQ, as this works about 18km (i.e. actually implements the CoCom limits properly). However, after reading the advice about avoiding NMEA if possible I've had a think and should be able to fly with the stock gps on board the APM2.
Firstly there isn't much "air" above 18km so it would probably be in free fall anyway therefore there would be no need to use gps. So - if I was to use the stock gps on the APM2 with the APM code - is there any software altitude limitations that I need to be aware of?
Also, a side question if any knows the answer - would I be able to fly the APM2 with GPS ON throughout the duration of my flight (up to ~30km) and then it would just work when it's below 18km? Or would I need to reboot the GPS below 18km for it to work again?
Many thanks :)
Replies
Ardupilot should keep running if it loses a GPS fix, which it will above that altitude, so you don't need any sort of reboot... if it gets a fix back it should start using it.
As you think about design... a couple of concerns. One - it's going to be falling FAST initially... as the atmosphere thickens a stable and balanced airframe will pull it's nose up... potentially WAY above the airframe's VNE... potentially ripping your wings right off?
Also, gps has trouble establishing a fix when it's in a dive.. and this will be compounded by the fact that the antenna will probably be oriented to point up towards the satellites when the aircraft is in level flight...
So.... as you think about solving the first of those issues (parachute that cuts away at a certain altitude... software designed to keep the plane in a dive until a certain altitude and then safely pull out... etc...) the second issue becomes a real issue.... your plane will lose lock when it crosses the 18km line, and may not get it back when you'd expect it to... so it may not know to cut the chute loose and fly, or when to pull out, etc.
Plus you want to know how high the balloon goes, right? I'd stick with a gps that can handle the whole flight and deal with the NMEA parsing issues... and then I'd design my vehicle for a descent profile that will do its best to keep the gps working and/or make command descisions based on when the barometer starts working again and/or make it stable and balanced and design it to not tear apart when it suddenly pulls out of a miles-long dive....
It's a big challenge!
Art
Fire up Xplane and HIL simulation for its Shuttle model and test out the altitude limits.