[onewhippedpuppy]

All certified multi-engine aircraft have to meet a minimum engine out rate-of-climb and takeoff distance. The idea is if you lose an engine on takeoff without room to stop the aircraft, you still have enough power to liftoff, climb out, and return to the airport.

I don't know the Skymaster all that well, but I'd guess that the fuel system issues come from location. A conventional twin has the engines mounted on wing nacelles, and fuel storage in the wings. So it's a simple, short route from the fuel to the engine. The Skymaster has engines front and back, but I assume it still uses a wet wing as most aircraft do. So you have additional issues routing the fuel front and back, as well as balancing the fuel quantity between the wings.

The Skymaster is a neat plane, there's one that flies over my house pretty often. Very unique sound. To add to Paul's (Seahawk) critique, they also had cooling issues with the rear motor.

Jeff's comments are spot on regarding the advantages of centerline thrust, but it comes down to one thing: insurance. It's the reason for the Skymaster, as well as the Adam A500. It's very difficult to get insurance on a twin without a lot of hours in a twin. So if you're wanting to buy, you have to rent until your insurance company is satisfied that you're sufficiently experienced. Without the asymmetric thrust issues of a conventional twin, a centerline thrust twin is a bit more idiot proof, and easier to insure.