I have read a couple of discussions on this already but it seems no one has asked about this for over a year and I wondered if there have been any advances that would make this easier since then.
So last year my school sent a weather balloon to space with a payload containing various sensors and a camera, and after a lot of searching with a yagi we managed to find it! This year we want to do something a bit more interesting, and so plan to take another balloon up with a glider, and have it autonomously glide down to a predetermined location. We have a skywalker x-5 that we've assembled and got flying, and decided on an APM. (We decided against the pixhawk because it's outside of our budget). We are ordering an neo-6m gps unit for it, and aren't sure about whether we should get an airspeed sensor or not. Should we get one? And will we need to modify any of the code to make the APM do what we want or can we just put it into RTL mode on takeoff and have it glide down once it is detached from the balloon?
Any help is greatly appreciated.
Oh you can fly but you do need the appropriate speed and I'm pretty sure you can't achieve it with just a glide. Also there is still some issues we have not solved completely with the APM speed density algorithm for high altitude flight.
If you slide the CG forward on an aerodynamically stable craft it does help you go faster and become stable sooner. But it's not as soon as we would like.
Starting out I'd not try it until you have more experience with actuality making some attempts and getting a feel for what's going on.
Look at the NASA Ares project if you want to see how the pros do it.
These guys did it and used a chute to stabilize.
Some GPS's will not work above 60,000' at all, so that is a consideration. Pick the right one. Does anyone have input on the common GPS's we use with APM/Pixhawk whether they work that high?
Edit - I just noticed they only went to 6 km altitude ~ 20,000. Not really representative I suppose
The Mediatech does not but all the Ublox do. They are good to about 250k. It's a lot easier now to find supported GPS. The LEA is the only other GPS we have flown. That module is in the Big Red Bee APRS tracker. There are lots so one you may already have should work.
Here is a list it may be dated now.
How about, not powering APM until say, 20 K feet, and until then, have some feathering mechanism, ala Space Ship 1, or a drag 'shute ?
APM Needs a reference for cal on the ground.
Here's some video of ARES flying at 125k feet. Pretty impressive!
(starting at 5:08)
Very impressive indeed! Also highly funded. There is a good chance we can develop the capability but starting out I have to suggest starting out by getting experience flying back.
Our project started 8 years ago and has developed toward high altitude flight over the last 3 or 4 years. Mistakes can be expensive and time consuming.
Know that what your attempting if you intend to fly at very high altitudes is not going to be a piece of cake. But you can have a ton of fun making the progress needed to gain enough experience to achieve it.
GO FOR IT!
Thanks for pointing it out RocketMan. In all the research I have done on high-altitude flying, I hadn't seen that before. Looking at the design they've chosen, I can begin to see some interesting features and the reasons behind them, mainly surrounding the requirements for flight at low Re.
Note how the airframe appears quite stubby, rather than the high aspect ratio design of, say, a U2. The reason here is, I believe, to keep the chord as long practicable to increase the Re as best one can for a given wing area. At low Re, the stall angle of attack for an aerofoil can be surprisingly low and the drag very high.
It also looks a bit like they started out with a blended-wing body design and ran into pitch control issues, hence adopting the rather ungainly tail sprouting out the back. I have been here in my design processes and pleasingly also arrived at the up-turned V-tail idea as well. I might be reading too much into this though.
Has anyone thought of using TWO balloons?
One would obviously fail before the other and then you would gently descend to a reasonable altitude where you would cut the tether and glide back home.
Yeah I'm still waiting on your plane Andrew! Good luck with that. I remember listening to you back when we all got started doing this.
Just a thought, would the air emprisonned in the foam would explode the aircraft as it goes up in low pressure atmosphere... the weather balloon does take a huge amount of volume as its climbing... so would the foam...