Stabilator vs Stabilizer in airliners.

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Caldemeyn
Master Sergeant
Posts: 1101
Joined: 01 Feb 2011
Location: Poland

Stabilator vs Stabilizer in airliners.

Post Caldemeyn »

Hi all

A question if i may. What would be your opinion on why are stabilators not really used on modern airliners (besides the L-1011, why was it used here ?) What are the advantages of a trimmable horizontal stab vs a stabilator for an airliner ? I have my own suspicions but would like to hear your thoughts first.

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AKar
A2A Mechanic
Posts: 4661
Joined: 26 May 2013

Re: Stabilator vs Stabilizer in airliners.

Post AKar »

Simplified, a stabilizer is mechanically held in its position by the jackscrew usually employed to drive these. Stabilators typically are driven directly by hydraulic servos. So, a stationary stabilizer is a static thing whereas a stabilator is actively held in place by the hydraulics and the control system feedbacks.

In theory, a hydraulic servo could also hold a locked position, but in reality they have slight but not negligible internal leakages when stopping the movement and then holding their position against a significant load. It also follows that the stabilizer is momentarily fail-safe against loss of hydraulic power whereas stabilator would just fly free, causing instant and rather violent loss of control.

It also follows that the stabilator is more difficult to control, from hydromechanical point-of-view. You need to have a servo system in place that is both fast and very powerful, as both the fidelity to be the primary pitch control and the strength to reposition the entire tailplane are required from the same unit. In principle, one could have a telescoping tandem-servo kind of configuration, but this is something I'd only consider on a paper!

-Esa

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