Has anyone ever tried making a two-piece backpack system where:
Piece 1 is a stiff frame and all the pads and straps that snuggly hug your body
Piece 2 is just a big storage compartment, which can be detached from Piece 1.

I realize that the number-one concern in a backpack is getting close to your body and supported in a way that doesn't stress, but it still seems like you could have a Piece 2 that you "slide in" to a series of straps on Piece 1 and then cinch them up so it's tight against your body.

If there are some commercial offerings like this, please post them to serve as inspiration.

http://www.ula-equipment.com/epic.asp

I believe Zimmerbuilt has some interesting designs you might want to check out.
Steve

That ULA Epic looks like exactly what I have been looking for.

Is there a generic name for the type of pack? (the kind that is just a system of straps made to hug a separate bag)
What would be my search term?

The Molly Mac Pack is very similar to what you're talking about. MacEntyre (the manufacturer) even has a couple of pouches (they're in the "Order" section) that fit gear instead of having to use stuff sacks; they come in 15 and 30 L sizes.

Hope it helps!

Check out granite gear flatbeds, mystery ranch crewcab, eberlestock just one, or get a simple frame, cut off the bag and add a beavertail with straps. You could pick-up a beefy frame that fits you well and cut, hack and sew.

Good luck,

Dave

NRS is your cheapest option: http://www.amazon.com/dp/B000STB52K

LOL. I think every external frame pack ever made fits this description.