46 ounces will work Ok with 7 cells, not great,.. assuming that's the weight WITH the motor and battery pack, ready to go. An endoplasma (kyosho car motor, has large comm and brushes), with a 13X8 prop , geared 4.6 to 1 will pull it, even with a 12X8 it should be OK, not stellar performance, but should takeoff nicely from grass and fly. With that small wing, you might want to go a bit higher pitch speed and sacrifice some thrust, so a 12X10 might be in order. This is all assuming your weight (46 ounces) is with everything on board. If that is without power system, then you'll be at about 4.5 lbs ready to fly, which is gonna be very difficult to make "go" on just 7 cells. Possible, but not what I'd want to fly. For a "reality check" on weight,.. my E3D kit is 600 square inches, 52 inches long, and built and covered they end up in the 16 to 18 ounce range, with equipment about 22 or so, with motor/gearbox/prop, just no batteries, 32~34 ounces. If you want to see how an endoplasma works, the E3D video on my site (www.gwmp.net) is an E3D, stock, 56 ounces flying weight (that's with 10 sub-c cells) and an endoplasma. It has flown well on 6 cells, going up to a 15X10 prop, but speed is low on that plane anyway, not exactly what it sounds like you have. It's very very easy to get TONS of thrust from relatively low power input on an electric motor, just gear high and swing a really big prop. It becomes much more difficult when a fair amount of speed is required. Power requirements go up exponentially with speed requirements.