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I was doing a question about a fully hydraulic elevator and it's position in relation to the trimmable horizontal stabiliser and the explanation of the answer contained the word "redatum". What does it mean?

Full question, answer and explanation:

Q: What is the position of the elevator in relation to the trimmable horizontal stabiliser of an aeroplane with fully hydraulically operated flight controls that is in trim?

A: Elevator deflection is zero

A fully hydraulically operated flight controls is an irreversible system, and the trim is a redatum, as there is no physical connection between the stick and control. Therefore there will be no elevator deflection when trimmed.

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  • $\begingroup$ My first reaction is that it's a typo since "redatum" is not in any dictionaries I have. Searching the interwebs I find that it is a commonly used word in geology papers. The papers are all super technical and I know nothing about geology, so it's a bit tough to discern the meaning. But what I can gather the word is used in data analysis of seismic or radar returns. If you don't get an answer hear you might try at English.se $\endgroup$
    – TomMcW
    Sep 18, 2017 at 16:04
  • $\begingroup$ I'm pretty sure that has nothing to do with this case, but thank you very much $\endgroup$
    – Jonecat
    Sep 18, 2017 at 16:06
  • $\begingroup$ I think in the geology papers it is being used similarly to what Koyovis says. It seems to be a way of removing aberrations from data by setting an artificial reference plane against which sensor output data can be analyzed. Or something like that. All the sources I find on the web are from technical geology papers. So what Koyovis says makes sense $\endgroup$
    – TomMcW
    Sep 18, 2017 at 16:11
  • $\begingroup$ You must have accidentallly asked your elevator question on a geology website :P $\endgroup$
    – TomMcW
    Sep 18, 2017 at 16:13

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I've never heard of the term, but from the context of the explanation it appears that they refer to a situation where the elevator neutral position is relative to the stabiliser, not to the aircraft. So stick moves elevator relative to aircraft and stabiliser, trim moves elevator relative to aircraft only because the elevator neutral position follows the stab position. Like the stabiliser/elevator arrangement on the B737.

enter image description hereImage source

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  • $\begingroup$ That's what I thought too, and it agrees with the anser as well. Thank you! $\endgroup$
    – Jonecat
    Sep 18, 2017 at 15:53

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