your best bet could be telemaster with a modified high lift aerofoil. wingspan 2 meters. I tried 10cc evolution gas engine. with 1.2 ltr of fuel. it gave three hours of cruise with a 11x6 prop. the max you can get is 10 hrs. the speed would be much lower 30 knots since it has a high glide aerofoil.
Aerosonde did exactly this sort of thing 15+ years ago with a twin boom pusher, superficially similar to a Muggin. I'm sure they can sell you what you need, but they are part of AII now so not at $5K :)
That aircraft has some interesting trade-offs. Catapult launch (or car rooftop contraption in the early versions) and belly or net landing, so it probably won't slow down much. The Muggin landing gear was a weak point in the version we used (it may have improved in future versions). The Aerosonde looks higher AR than the Muggin, but given NASA flew one version of them into cyclones I imagine those long thin wings are light and highly loaded == expensive. A few $k materials cost for the airframe sounds plausible but up-front investment in tooling and per-airframe labor components would be significant.
There used to be an interesting narrative online (sorry, couldn't find it now) about their eventually successful Atlantic crossing attempts in the 90's. The one that landed was full of rainwater (yikes!), they lost one due to using the wrong kind of sticky tape somewhere - exciting stuff, really pushing the envelope. Deliberately flying into storms means you probably want a high stall margin so you don't loose control with tail-gusts, so a different set of compromises to their long distance case.
I've played with the thought experiment of building a small, fast, fully sealed, lightening-proof chevron wing for flying into the big cumulus storm clouds we sometimes get around here, to see if I could catch and survive the 8km purple updraft. How heavy is your instrumentation? could you launch something like that into your storm from a long-range mother-ship?
The instrumentation would be 3 kg. NOAA moved to the mother-ship idea. But it's a big mother! They use the P3 to launch a Coyote UAV into the storm from a chute on the airplane. From what I've read the Muggin doesn't have a good wing for long endurance. Using manned aircraft as a mother-ship increases cost which reduces long term feasibility.
Hi Well you need to talk to the folks at Johns Hopkins Applied physics Labs in Md,also a talk with the Navy will help ...WCH
May I suggest the PaperDrone Disposable concept for Pixhawk?
what is the max altitude?
You left out a few zero's @ no. 4 :-)
As mentioned before by others, the specification except duration are probably doable.
To give you an idea just how demanding 20h duration is, the standard MQ-9 Reaper (aka. Predator B) using an efficient turboprop motor and a 20m wingspan, is still limited to about 25h flight duration.
Turboprops aren't that efficient, compared with a small-ish two-stroke engine. They are pretty much above the 0.5 lb/hp.h which a well designed 15kW/cylinder two-stroke engine should be able to better by some margin. Of course, the prop efficiency won't be as good due to scaling effects, but it doesn't have to be a million miles from what the MQ-9 can do.
Personally I have been building the FX-61 flying wing (with some custom mods) for people (Farmers, wildlife conservationsist, surveyors) And I will include a hard case with a Surface Pro Tablet for telemetry and loading flight plans along with a 9xr FrSky setup with an 7"monitor mounted on it and a Canon 260 camera in the belly of the plain with a hole cut out for the lens for taking the photos for mapping and I put it all together and sell it for $2500 or so.
I did have one guy who wanted to push the envelop and I upgraded the motor and rigged up an amp on the telemetry with a Omni - Directional antenna and a yagi hooked up to a tracking gimbal for max range along with 4 5000 amp batterys and I believe he got a couple hours of flight time out of it which was pretty good and he took it pretty high. I configured to RTL on low battery only so he could go out of range of the telemetry, FPV, and R/C and still complete the mission. I think that one came out closer to $5K. But with that build I used one of these:
But Ive found including a Microsoft surface Pro tablet is really a pretty good way to go so that the customers have everything they need all ready to go.