Does this plane have fixed horizontal stabilizers and elevators or has it been fixed with stabilators instead?
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2 Answers
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A Boeing 737 has a movable horizontal stabilizer for pitch trim with elevators for pitch control (also known as a THS – Trimmable Horizontal Stabilizer). This is true for all 737 variants, including the MAX. Note: The term stabilator is typically used when the entire tail is rotated for pitch control, like e.g. on a Piper Cherokee.
The following image (taken from this question) shows the horizontal stabilizer (the black arc indicates the range of movement of the whole stabilizer):
From the 737 NG FCOMv2 9.20.7 (Flight Controls - System Description):
Pitch Control
The pitch control surfaces consist of hydraulically powered elevators and an electrically powered stabilizer. The elevators are controlled by forward or aft movement of the control column. The stabilizer is controlled by autopilot trim or manual trim.
Elevators
The elevators provide pitch control around the airplane’s lateral axis. The elevators are positioned by the pilots’ control columns. The A and B FLT CONTROL switches control hydraulic shutoff valves for the elevators. Cables connect the pilots’ control columns to elevator power control units (PCUs) which are powered by hydraulic system A and B. The elevators are interconnected by a torque tube. With loss of hydraulic system A and B the elevators can be mechanically positioned by forward or aft movement of the pilots’ control columns. Control forces are higher due to friction and aerodynamic loads.
[...]
Stabilizer
The horizontal stabilizer is positioned by a single electric trim motor controlled through either the stab trim switches on the control wheel or autopilot trim. The stabilizer may also be positioned by manually rotating the stabilizer trim wheel.
Stabilizer Trim
Stabilizer trim switches on each control wheel actuate the electric trim motor through the main electric stabilizer trim circuit when the airplane is flown manually. With the autopilot engaged, stabilizer trim is accomplished through the autopilot stabilizer trim circuit. The main electric and autopilot stabilizer trim have two speed modes: high speed with flaps extended and low speed with flaps retracted. If the autopilot is engaged, actuating either pair of stabilizer trim switches automatically disengages the autopilot. The stabilizer trim wheels rotate whenever electric stabilizer trim is actuated.
answered Aug 1, 2019 at 11:14
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$\begingroup$ Thanks so much for this elaborate answer. It's very clear and to the point. $\endgroup$– AnshCommented Aug 1, 2019 at 11:26
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1$\begingroup$ Trivia: The L-1011 Tristar is the only jet-liner I know that has a proper stabilator with a geared (anti-servo) elevator. $\endgroup$– user14897Commented Aug 1, 2019 at 11:28
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$\begingroup$ The trim system is pretty much a bigger version of a Super Cub's or Cessna 180's, with an electric motor added. $\endgroup$– John KCommented Aug 1, 2019 at 12:58
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The B737 has an all moveable stabiliser. It has fully irreversible hydraulic flight controls, with Q-feel loading in pitch. The neutral point of the elevator moves with stabiliser angle, and the stab provides pitch trim and pitch column zero feel.
When the stabiliser is activated, it sets to a new position and moves the trim point of the column as well. So if the pilot holds the stick and he selects the trim button, they will feel the holding force increase.
The stabiliser has a large area and therefore large authority on the aircraft trim. It can be very hard to overcome the stabiliser trim setting by trying to deflect the pilot flight control column.
