A lot of posts got dumped in the site maintenance from yesterday. I lost a few myself.
The tips on a swept flying wing are highly washed out so that they can provide stability to the design. So they are not flying at the same angle by a long shot. Because of that washout angle they are flying at a much lower lift coefficient compared to the center part that is more forward. As a result you cannot use the whole wing when determining your flying and stall speeds. The tips are just not pulling the same load as the rest.
If you try to avoid that and make the wing with no washout then it'll be unstable in pitch unless you reflex up the elevons to a high degree like Zagi's and other stuff like that does. But that's a highly inefficient way to get your stability as well and it still pushes those airfoils into a non lifting mode since the angled up surfaces act like spoilerons ALL THE TIME while providing the needed stabilzing forces. At least with the washout angle they still help out a little.
Wander over to
www.b2streamlines.com for some tech articles on designing flying wings. Lots of good info there. In particular check out the Panknin swept wing washout tool that runs in Excel or using the spreadsheet in Open Office (a free download that opens and runs Microsoft Office Word and Excel files
www.openoffice.org )
And you will NOT be able to throw that size and weight of model at that speed unless you're facing a 15 to 25 mph headwind..... unless you can morph into the Incredable Hulk. Sorry But if you want to try it then buy a 10 lb bag of sugar or get a 10 lb hunk of 2x10 and try throwing it and see how far it goes. It won't be far and it won't be fast. With a good headwind you MAY get away with it but is far more likely just a matter of time until you don't have enough headwind or you don't throw it quite hard enough and it stalls and flips over for a cartwheel crash. Mind you with a good hand hold and at 5 lbs it'll fly a lot slower so no problem. It's only when loaded up that you should not be trying to hand luanch this thing.
Definetly plan on some landing gear even if it's just a dolly that the wing flys out of when up to speed. Be sure to include a streamer on the dolly so you can find it later. It's amazing where they can get to.