[jameshart]

For flight, the problem is that the only acceleration that really matters is variation in vertical acceleration. Linear acceleration can briefly simulate that, but it can't be sustained. That's a fundamental problem that can only be dealt with by creating that kind of massive vertical acceleration environment - even that will be limited in terms of how long it can simulate sustained > or < 1g. You can create sustained accelerations by spinning something round on the end of an arm, but there's always that pesky downward gravity vector that keeps getting added to everything, unless you build your simulator in orbit.