thanks curt,
do you have any Idea what size the prop should be for it to fly slower?
I think I am going to do a wing, and maybe try to have solar sheets on it.
my sketch of what it might look like has it at a 3' wingspan.
Any recommendations for what to do?
I think your project will be the most satisfying if you do things the way you want. A forum is a great place to get advice (and there are lots of people here way smarter than me) but if you ask 20 people on a forum, you will get 100 different suggestions to sort through and you might never get anything started. There is value to planning ahead and there is value to making build/flight progress. You need to find a comfortable balance between those two opposing forces. Many great projects never get out of the designer's head because they just tried to do too many things at once. The design became too difficult to manage. Many funky builds never truly fly because the concept was ill conceived and hacked together too hastily. So aim for something in the middle of that. Come up with an initial plan, and then take the jump and make it work! And be flexible along the way: A project like this is kind of like walking through a crowd ... you have to adjust your path and sometimes your destination as you go to fit what the situation gives you. There's too many variables to plan it all out ahead of time, but some plan or strategy can help.
I don't know your level of experience, but be careful not to bite off too much at once. I really like the idea of building a simple prototype that you can fly successfully. Then iterate on that. For each new version, focus on a thing or two you really want to improve on or add.
So for example, build a simple 3' flying wing and get it to fly reliably. Maybe add battery capacity until it becomes too hard to manage reliable launches and landings. At this point you probably have a 100 things you want to improve structurally, or size wise, or flight characteristics you didn't like, etc. So pick a few of those things and make informed design changes. Now you know what you are improving and why and how to go about it. After a few iterations, you could have a pretty sweet design if you are thoughtful at each step of the way.
All that said, for an endurance plane, I would not recommend a flying wing. Fun wings are super light wing loading, way over powered, and fly great. Endurance wings are way overloaded with battery, way under powered for efficiency, and get extremely tricky and frustrating to launch and land.
Typically the larger the aircraft, the more relative weight it can carry (google cubed wing loading.) So generally, the larger your design, the easier it will be to make it fly a long time ... but with that said, there is still a lot you can do with a smaller design if you keep it light enough.
As you increase size and speed, then real aerodynamics become more important ... things like wing aspect ratio, airfoils, and drag do start to make a difference.
But don't forget, in the end it boils down to the simple observation that the slower you run your motor, the longer your batteries will last. So think about how you design an airplane that stays aloft with the least amount of power possible.