At the risk of being a spoil sport, it seems to me that it would be pretty easy to do a solo, around the world, unrefueled flight by taking a 747, stripping out all the seats and adding additional fuel tanks in the cargo hold and the passenger compartment.
You'd probably have to overload it a bit and the takeoff would be a little hairy, but that also seems to be the case with Rutan's design.
Check the numbers. It will either never leave the ground or it will not make it around the earth.
Not enough lift in the wings of a 747. Look at the wings on that pic and consider that it is all composite.....a lot lighter than aluminum.
current Max range = 6100 miles
Earth circumference = 24901 miles
you would need fuel in fuselage for 18801 extra miles or about 3 times current Max range
and therefore 3 times current main tank capacity in the fuselage
(not considering increased GW effects on range which is stupid but ok to make this silly point)
fuel for current max range = 48445gals
6.7 lbs/gal * 48445 gals = 324581 lbs (you probably see what's coming)
weight of fuel needed in fuselage = (324581*3)lbs = 973774 lbs
This is an order of MAGNITUDE greater in weight than the current max passenger weight. The whole plane weighs less than 800,000!!!!
Thank you for playing.
I will venture to guess that Rutan's designing/building/test flying of this plane costs magnitudes less money than buying a 747 and then installing tanks and modifying it. Sure, a billionaire is funding the flight but there's no fun in using a 747.
Sorry for the late response...I've been offline for a week and just saw this thread.