This makes more sense, thanks.
I still don't understand why the trim is "stronger" on these planes than a fully pulled back column. Is this necessary on large planes?
I still don't understand why the trim is "stronger" on these planes than a fully pulled back column. Is this necessary on large planes?
On the 737 the trim adjusts the entire rear stabilizer (the entire horizontal structure of the tail), while the elevator is a sub-component of that stabilizer.
So, when you adjust the trim, it's a much larger surface area that is moving. Ultimately, the stabilizer just has more aerodynamic control that the elevator, due to the larger surface area.
I have no idea why the design is that way, though.
Cost, maintenance, weight, etc., probably. The only jet airliner I can think of that uses an "all-flying tail" is the Lockheed L-1011. Nearly every other plane you'd be riding on will have a big stabilizer and a smaller elevator.
If both redundant hydraulic systems to the elevator fail, or the elevator gets stuck for other reasons, the emergency procedure is to control pitch with just the stablizer trim alone.