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I saw two questions on locating these surfaces ahead of CG:

Vertical Stabilizer and Rudder

How are these the same or different control surfaces?

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    $\begingroup$ I find this question confusing. Are you asking about the conventional usage of these terms, or about how they would be applied to surfaces located ahead of the CG? If the latter, that would see to merit mention in the actual title of the question. Also, the two links no longer work. $\endgroup$ Commented Dec 6, 2022 at 18:34
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    $\begingroup$ @quietflyer The two answers provided cover all that I intended. I tried to update the links as the questions are on this site and are listed in the 'linked' section on this page, but they still don't work. $\endgroup$
    – Pilothead
    Commented Dec 6, 2022 at 19:11

2 Answers 2

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The vertical stabilizer is immobile (if it starts to move, you're in deep shit), and provides stability in yaw (it keeps the aircraft pointed more or less in the direction that it's moving).

The rudder is mobile, and typically attached to the aft edge of the vertical stabilizer. It provides controllability in yaw (it allows the aircraft, if necessary, to point in a different direction than the one it's moving).

The rudder allows the aircraft to slip sideways when you want it to; the vertical stabilizer keeps it from slipping sideways when you don't want it to.

enter image description here
(Original via flickr.com)

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    $\begingroup$ Would it be possible to get a picture of a plane with a bigger rudder to make the moving part more noticeable? Possibly something like an A-380 or 747 where the rudder is huge. $\endgroup$
    – dalearn
    Commented May 26, 2018 at 19:55
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    $\begingroup$ Where does trim fit in? Does the whole vertical stabilizer move the way the horizontal stabilizers do on jetliners? $\endgroup$ Commented May 27, 2018 at 0:13
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    $\begingroup$ @Harper -- the vertical stabilizer is fixed -- rudder trim is usually provided through a tab or sorts on the rudder $\endgroup$ Commented May 27, 2018 at 1:03
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    $\begingroup$ @UnrecognizedFallingObject - With the controls being irreversible on the big jets, the rudder controller just shifts the neutral position (same for the pedals), regardless of airspeed. $\endgroup$
    – user14897
    Commented May 27, 2018 at 16:09
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In order to deserve its name, a stabilizer must be located aft of the center of gravity. Once it is shifted ahead, it will become a de-stabilizer.

The only way to laterally stabilize an aircraft with a vertical surface ahead of the center of gravity is to make it moveable and actively controlled, either being slaved to a gyro or, even better, continually adjusted by a computer. In other words, any forward vertical stabilizer is a rudder.

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    $\begingroup$ "In other words, any forward vertical stabilizer is a rudder." Not true: SA-2/S75 missile's canards are definitely not rudders. They are fixed and used as destabilizers. $\endgroup$ Commented May 27, 2018 at 19:03
  • $\begingroup$ @user3528438: Exactly. DEstabilizers. Not stabilizers. $\endgroup$
    – Vikki
    Commented Dec 10, 2018 at 4:25
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    $\begingroup$ @Sean: Thanks! It feels so good to be understood. $\endgroup$ Commented Dec 10, 2018 at 17:50

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