Hi everyone

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.

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That is true but at some point there will be a pull out maneuver required that will stress the heck out of the wing. Oh it has been tried with regular gliders and they always shred their wings. This was actually done way back in the 80's by a fella in Canada.

He never succeeded in the pull up maneuver. I suppose it may be possible with a drogue chute but having tried that the chute is very likely to get entangled in the plane.

There is a lot of stress as you slow down in the thicker air.

Just simplify it and use a delta. That's just my advice. But hey I'd love to see anyone try it! 

Another tip: Use only quality METAL gear servos. The plastic ones can freeze up and break. Metal hinges metal links and attachments.

I have imagined the same project, but never attempted to do anything about it.   Have you seen this video?   FPV From Space.  This one uses a Funjet and LRS.   It was done by David Windestål who I think has also done stuff for Flight Test.  

Very cool project - would love to hear how it evolves.

Thanks for your reply rocketman! We are going to try and keep this simple so aren't using fpv at all. We are going to use a radiometrix telemetry module on the telemetry output of the apm, for a one way telemetry link sending out only important bits of data. We used a high gain yagi antenna with our first HAB and this was sufficient to pickup telemetry throughout the whole mission (we got to around 25km), so we're going to use this system again.

The spaceplane sounds amazing with the booster rocket, maybe we'll give it a go if this project is successful!

Our thoughts so far are that when the plane detaches, it will simply tumble for a quite a long way, and once it can glide the apm will sort that out and try and get it heading in the right direction. What is the INS? Do you think we will need to decrease the G sensitivity if we only intend to be able to glide once the air is thick enough?
Thanks so much for all the guidance. It's so helpful to know what's been tried and tested. Because it's a school project our budget is limited, but it isn't small, as we are keen for it to work! I'll have a look at the skyfun. Good point Jerry. Would our X-5 be okay if we were to put a couple of carbon rods through it to stiffen it up?
Yeah I have seen that Bill! Absolutely amazing. I was lucky enough to meet David at a hobbyking flying event in the UK and asked him about that project. He told me he actually only retrieved the plane because someone found it and phoned him up! Absolutely amazing video though. If we could get footage flying through the clouds like that we'd be extremely happy!

I like heavy and fast for these types of missions but you can try light and slow. Pretty much the choices. Light and slow will travel farther away. If you go light enough the wings may survive. I don't know what a X-5 is by the way.

So I am working on a high altitude balloon self guided return package at this moment.  We are using two APM boards for cut away and telemetry on the way up.  RFD900 radios on one, the other just datalog.  We will cut the the return package (glider) away before the balloon fails.  We are plan on using a triple redundant system for this, one is servo cut main board, the other is a hotwire on the second APM, third will be a timer.  The release will be scripted with altitude.  The first balloon went up about a year ago, we are using the data from that to give us a release before the balloon fails.  I believe this to be the trickiest part, ISA deviation, baro pressure, the balloon itself, all change the altitude the balloon will fail.  Large margin of error... I think we re going to release around 80,000. 

The plane itself we are building, a foamy. Gliders will not work as people above has stated you could easily rip the wings off.  We thought about a spaceship one type feathering system, but the 4 pound limit on a balloon telemetry package doesn't allow for such fancy.  So you end up with a shorter wing aircraft delta or a flying wing type swept plane.  Something to keep in mind is the ability to fly fast enough to cause a high speed stall, 77,000-250kts-Mach 0.80 this is a real possibility and a straight wing will stall at this speed and aircraft starts to spin that's the end.  So a swept wing with a low camber is needed read a bit about coffins corner. Airspeed seems like a must, can't go to fast nor to slow, the to fast problem will only exist for a few minuets, but if you pitch to an airspeed of 230kts you should be good, we still have to figure out how to script that.  To assist in supporting this wing we will have multiple spars in it We want the ability to support 7g's for a short period of time this stress is a very good probability. 

Warming of the batteries and electronics also seem very important temperatures of -70F around 50,000 feet.  So an extra battery to provide heat plus a temperature sensor for the electronics along with a voltage fail safe for the release.  

Also hydrogen balloon vs. helium the hydrogen is 1/2 the cost a more lift. 

We plan on April launch.... any thoughts you have would be greatly appreciated.  I'd also be happy to keep you informed on our progress. 

 

Contrary to popular belief heat can be more of a problem than cold at high altitudes above 50kft. So you do need some type of control to turn off heat if needed.

Hydrogen is the goto gas. Just read up on safety and make sure you know what you are doing. Use a ground strap on the bottle. If a weather balloon full of hydrogen pops it won't explode unless you somehow let air into the balloon during filling. Make sure you don't let any air in and the most you have to worry about is some falling latex. Normal clothing and safety glasses hat and gloves will protect you nearly completely.

Normal Lipos are fine in fact preferred.

Do not think about flying above 50kft aint gonna happen without thrusters IMO. You might get something around 70kt but you probably can not hold it.

 The plane will fall around it's CG for the first part of the drop at or above 80kft

 There is a trick you can use to gain attitude control a little faster and that's a sliding CG. Slide your CG to the nose if you have a naturally stable aircraft you can slide the CG back and it will catch hold.

 If you do this too early it will stall out and start the process all over again.

 Let me know if you need other help I have a machine shop and I can help you out a little in my spare time. If you like.

 Post Photo's! :)

 

I disagree with the apparent concensus that you can't fly above some specific altitude. I think it's perfectly possible if you understand the limitations you need to work with. Because the Reynolds number is very low (20-50k) the useable lift coefficient range shrinks dramatically, but still leaves enough to make something of it. That means limiting g loading, steep descents and shallow turns. APM et al would need some detailed rework to add features that would control within these density altitude-dependent limits

Will the G loading really be that high while tumbling from say 100k down to 50k? The whole reason it will supposedly tumble is the air density is so low the aerodynamic forces are to low to allow controlled flight. So if the aerodynamic forces are super low, what would cause significant g-loading other than rate of spin? 

My gut says that from when it drops to when it stabilizes in a nose low descent will occur rather quickly. Are there any youtube videos showing a drop from that high other than RC Explorers? He got tangled up, so that's not a fair example. 

Gravity will accelerate it until the aerodynamic forces create equilibrium. If you do the sums you'll find out that it will be going very quickly very quickly indeed!

If the flight controller is reacting to the change in orientation by moving control surfaces inappropriately, the risk of breaking something is quite high at Mach 0.75, which is easily possible

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