My project to build a ballon-launched high-altitude automnomous glider as a step up from the normal styrofoam box HAB projects necessitates the development of an airframe.
Initially, I was intent on using the Skyfun platform but my calculations and other's experiences of it as an FPV platform suggests that it will be difficult to keep the centre-of-gravity in a useable location, especially if I remove the motor to turn it into a glider...
When I spotted the clever www.crashtesthobby.com Assassin finless flying wings, I decided that the simplicity and flexibility of a custom designed flying wing might yield a better optimised airframe for the project, so I began to work through the design
On-board will be the decased HD-170 camera, a Futaba R167FS-driven APM, a MediaTek MT3329 GPS, HMC5843 magnetometer and MPXV7002DP pitot-static system. I will probably also include a MaxSonic range finder for sonar altimetry for use with Autoland experiments. All of this will be powered by a 2S 1800mAh LiPo battery. For flight development, a 25g brushless electric motor and controller will be fitted as a pusher arrangement. This may also stay on-board for HAB flights (if I get that far) due to weight and balance issues.
Estimated flying weight at 550g, 1270mm wingspan, 0.3m^2 wing area gives a wing loading of 1.67kg/m^2 My current W+B calculations put the CoG roughly in a similar position to the Assassin.
The airframe is intended to be fabricated from EPS, hot wire cut wings and a CNC machined fuselage section. I am still working on the spar arrangment and how I will install and access the payload contents - so far I'm leaning towards a partially PVA glued-together construction with flying leads to access charging and data requirements. Still some work to be done here...
The camera is oriented to place the horizon at a third of the frame in level flight and to avoid intruding on the 170° field of view. Obviously I want to give the lens some crash protection as well...
This is all ideas-in-progress, so I welcome all your comments. I don't promise updates to be very frequent though!
More pictures are available in my album, which will be updated as and when
Comments
Ritchie have you ever moulded a foam shape like that? I've been toying with the idea, what foam did you use? did it work?
And Andrew this is exactly what I have been wanting to do for a while but have been too busy...hopefully in summer I will start design and build.
looking forward to seeing how this goes!
Excellent ideas. If I were going to do what you intend I would try to fabricate a mould for the foam rather than machine it as a one off.
CNC your design into wood mould (your 3D in half along the leading and trailing edges). Add dowels for support to your electronics (so they will be level in the airframe). Heatshrink any sensitive stuff. Boxes for the servos (put extensions on the electronics so you don't seal the connections away ;D). Put the spars where you want and don't forget to ridge the mould for a thin part for the elevons. Once poured you could cut the elevons install the servos and launch.
Hi Jonathan,
I think there are more than a few working on high altitude glider projects - it's good to hear from you all out there!
I'm sure the skyfun is a good choice and a faster route to a flying result. I may still consider building up a skyfun to get some experience with real-world APM flying, but at the moment I am away from home on business and so most of my work is theoretical, based on X-plane HIL simulations, Excel spreadsheets and SolidWorks modeling. The renderings were done in PhotoView 360, part of the SW suite.
While my idea is essentially for it to be a glider, I have found that CoG constraints of a flying wing mean it's difficult to dispense with the electric motor on the back, so I have decided to make it in effect a self-launching glider, which will allow me to do initial non-balloon-borne test flights.
As far as heating, I was thinking of using the APM relay control to PWM at low frequency some strategically located resistors to keep everything above zero. I might consider carrying a seperate arduino-based heater management system though, just to avoid the risk of melting the thing in mid-space! Also, I will probably use a nichrome heated wire release mechanism at some point too, as used and described by Art Vanden Berg in the above link.
Good luck with your project and let us know how you get along!
Wow Andrew! I'm starting the design of what you were doing as well! Skyfun-based glider with GoProHD running 720p for the entire flight. I'll be using 2x5,000mah hobbyking batteries http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=.... And a redundant BEC (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...).
The skyfun will be covered in fiberglass to get some more strength. I know my weight will be high (~1,500g) compared to skyfun capability but that's OK since I'll need some high speed to pass through the jetstream on the way down back to the launch point. I plan on doing 3 different flights, 1st from 10,000ft, then 50,000ft and finally 100,000ft.'
I was thinking of running the multipilot 32 (from Roberto / virtual robotix team) w/ mediatek GPS.
For landing, I was thinking of deploying a chute at 400ft and let it glide down from there.
I'm wondering about heating (hot pads) and pressure variations, so wanted to seal off the electronics area. This is where the fiberglass will come into play.
What are you using to model your plane in? (what software)?
thanks!
Marc,
Yes, high altitude is a challenge. I intend to put some form of APM-controlled electrical heating inside and also I have chosen EPS partly for the insulation properties as much as anything else.
I have been doing a bit of number crunching and my calcs estimate my stall speed (TAS) at 100000' or 30km(NASA atmospheric model) at 177km/h (M=0.16), which if dropped straight down from a balloon could be achieved in about five seconds and about 400'. It will obviously need more speed than this to allow for stable flight. Guaranteeing this to happen without initiating any spin condition could be a bit tricky though.
I've seen the GPS boomerang website before - interesting how far it falls before establishing controlled flight, or at least non-vertical flight
There's also Art Vanden Berg's work here which is another interesting datapoint (or five)
Hi,
nice idea. Whats your targeted altitude?
Thin air and low temperatures can be challenging. I would try the APM in the fridge first to see how especially the gyros perform.
There is already a commercial product doing HAB gliding home: http://www.gpsboomerang.com/ . Their principle is using a stable platform and only steer with the rudder. Could be a good idea. Question is if you get your flying wing out of a fast spin when its coming down without lift at first (see this plots: http://www.gpsboomerang.com/content/view/24/36/). Seems like lift is working from 11km down...