Take a look at all Boeing models starting with the 707.......horizontal stab is inverted.......as is the 727, 737, etc.....as Paul said....this makes the trim less sensative.....and allows autopilots to use a "Cruise Trim Motor" which moves the stab.....which can hold altitude much better......also helps control mach tuck.....with a very small actuator that trims the elevator.....which in turn.....with the neutral shift mechanism....will trim the stab.........and keep airplane @ selected altitude........Bill...