Talk:Servo tab

(Servo/balance, pro/anti)
The given description of a servo tab is actually more accurately applied to a "balance tab" since the action merely serves to assist the pilot's input. With a true servo tab, the pilot's input is not delivered to the main control surface at all, but only to the tab. The aerodynamic force exerted by the tab is therefore the only means of operation of the main surface. It follows that there can be no such thing as an "anti-servo tab."

The example shown in the photograph is in fact an "anti-balance tab." It allows the pilot to control the main surface directly, but creates an opposing force that is directly related to control deflection, thus diminishing any tendency to over control. — Preceding unsigned comment added by 70.27.165.5 (talk) 18:35, 18 December 2005


 * Ugh, yes, mostly agree with the above; this article seems to conflate balance tabs with servo tabs (the latter is more correctly used as a synonym for "control tab" or "flying tab"). (The term may be used somewhat generically in other languages, and yes, "antiservo tab" is a legit synonym of "antibalance tab," but I just checked the FAA PHAK, and confirmed that they define "servo tab" as distinct from "balance tab," i.e. for the former "Only the servo tab moves in response to movement of the pilot’s flight control, and the force of the airflow on the servo tab then moves the primary control surface.") Jelliott4 (talk) 22:37, 14 January 2022 (UTC)

Expert tag
The information on this page doesn't match some of the information I read in some aviation books. I think it requires expert attention and reliable sources. There are some good German sites on the subject such as this one but I am neither native English nor German speaker therefore I am not gonna try to edit the article.--Abuk SABUK (talk) 23:18, 1 March 2013 (UTC)


 * As a published author in the field I would probably qualify, so I have reviewed it and removed the Flettner claim. It can be put back in with a proper ref cited. Otherwise the rest of the text is either cited or is correct. - Ahunt (talk) 13:09, 2 March 2013 (UTC)


 * OK, thank you. While searching about this dilemma I stumbled accross this forum site. It looks like somebody who were also searching the subject himself came here and edited the article without enough info or relevant sources. In my language flettner is used for other secondary control surfaces such as trim, servo, balance etc. as well but that may well be a false friend.--Abuk SABUK (talk) 21:24, 3 March 2013 (UTC)

Control surface =rudder ?
Can we use the word rudder instead of "control surface"? Andries (talk) 20:32, 7 August 2015 (UTC)
 * Already solved by adding a wikilink. Andries (talk) 08:17, 8 August 2015 (UTC)

Unmasked See-also
I summarized
 * /* References */ It can't be a ref, w/o linking to the fact it verifies -- see talk pg under "Unmasked See-also"

bcz what i converted from a fake ref to a "See also" has a single page number (suggesting it is alleged to document one or more specific statements rather just be of interest to the article's readers). If it's intended as a ref, it must be linked using the facility from each factual assertion that it verifies. If we could link to an online source of that page, it would probably be practical for some editor who doesn't own the work in question to clean up after the lazy or markup-ignorant colleague. (However, it might be of substantial value to know whether the same edit, or at least editor, were responsible for both the citation and one or more specific facts, as indicated by the edit history of the article.) But you'd be foolish to wait more than a week for me to be the one who examines the edit history even far enuf to have an opinion on the prospect of it helping at all. --Jerzy•t 13:31, 25 December 2015 (UTC)
 * OK, i gave it 5 minutes; see the 5th contrib to the accompanying article, which is that contributor's 1st of something like a two-digit count of contribs. And AFAIC foresee, count me out. Jerzy•t 14:03, 25 December 2015 (UTC)


 * I can't understand what you have written here, but paper refs cannot be listed under "see also". I have fixed the ref and the article. - Ahunt (talk) 14:51, 25 December 2015 (UTC)

Anti-servo as trim device
Hi User:Ahunt. You added the following:


 * An anti-servo tab may also function as a trim device to relieve control pressure and maintain the stabilator in the desired position.

This looks like an error in the source. An anti-servo tab could not serve as a trim device. They do not relieve control pressure, they increase it, as the other sources say. Probably it's a typo in the source for servo tab, not anti-servo. cagliost (talk) 10:44, 14 October 2022 (UTC)


 * No it is not an error in the source. I owned the AA-1 in the photo that illustrates this article and that is how it works on that particular aircraft. It operates both ways, as an automatic, geared mechanical surface that increases control forces for handling reasons, as you move the controls and as an adjustable surface that acts as a trim device, balancing out the forces. When you think about it, has to work both ways, unless you install a separate trim tab that works against the anti-servo tab. Of course that would act more as a speed brake like that when they are deployed in opposite directions. - Ahunt (talk) 12:01, 14 October 2022 (UTC)

Thanks. Does it make sense to describe it as an anti-servo tab? It sounds like it is a tab that can work as both a servo and anti-servo tab. When operating as a trim tab (i.e. in the same direction as the control surface, on net) it would make sense to call it a servo tab.

If so, it would make sense to put it in a separate section, rather than in the Servo tab or Anti-servo tab section. cagliost (talk) 12:36, 14 October 2022 (UTC)


 * I just go with how the refs classify it. - Ahunt (talk) 13:01, 14 October 2022 (UTC)

That's not good enough. The claim (anti-servo tabs relieve control pressure) is false, and contracts the other sources and the rest of the article. Frankly, the FAA sounds like a more authoritative source than Macdonald (even if the FAA do sometimes make mistakes). cagliost (talk) 13:11, 14 October 2022 (UTC)


 * It is another function of anti-servo tabs, as the ref notes. I think the way it is organized now makes complete sense. I can expand it a bit if you think it needs further clarification. - Ahunt (talk) 13:26, 14 October 2022 (UTC)

Please do. Including a quote from the source in the ref might also help. cagliost (talk) 13:42, 14 October 2022 (UTC)


 * ✅ - Ahunt (talk) 13:55, 14 October 2022 (UTC)

The article currently reads
 * An anti-servo tab may also function as a trim device in a similar way as trim tabs, to relieve control pressure and maintain the stabilator in the desired position. This obviates the need for a second device for trimming, which would increase drag.

I'm sorry, but this is false. This applies to a servo tab, not an anti-servo tab. The source is wrong, and contradicts the other sources. I'd like to gather consensus to remove this. Or, if you agree, I'll remove it right away. cagliost (talk) 15:45, 14 October 2022 (UTC)


 * It is not false. We have a reliable source that says this and an actual aircraft design that uses it in this way. Perhaps what we need is some more editor input here. - Ahunt (talk) 16:14, 14 October 2022 (UTC)

I think we need to make clear that when an anti-servo tab (which moves in one direction in response to pilot input to increase control forces) doubles up as the trim tab, it moves in the opposite direction. I.e. if the pilot were to push the stick forward, the tab would move in one direction, but if he then trimmed off the control force, it would move in the other direction. Is that right? cagliost (talk) 16:26, 14 October 2022 (UTC)


 * Actually, no that is not right. The trim wheel function moves the anti-servo tab to a new static position relative to the elevator, but when the yoke is moved for pitch control, the control surfaces all still move in the same direction as before - up when you pull back and down when you push forward. - Ahunt (talk) 21:34, 14 October 2022 (UTC)
 * What I mean is, if pilot held the yoke forwards, the elevator would move down, and the anti-servo tab (functioning as an anti-servo) would move down relative to the elevator. Then, the pilot trims: the tab moves up relative to the elevator. So in the tab's capacity as an anti-servo, it moves in one direction relative to the elevator, but in its capacity as a trim tab, it moves in the opposite direction relative to the elevator. Is that right? cagliost (talk) 09:39, 15 October 2022 (UTC)
 * Not precisely, no. It depends on which way you are trimming, nose-up or nose-down. If the trim applied is nose-down then the tab will move further down, if nose-up then the tab will move up. But then as you move the elevator it moves relative to the elevator surface though the mechanical gearing, but from its new datum position. - Ahunt (talk) 12:46, 15 October 2022 (UTC)
 * If the pilot pushes forward on the yoke, the anti-servo tab moves one way, but if the pilot then trims off the control force, the tab will move the other way? cagliost (talk) 17:31, 15 October 2022 (UTC)
 * That all depends on which way the trim is applied. It might move the opposite way or the same way, depending on the setting. - Ahunt (talk) 18:20, 15 October 2022 (UTC)
 * That's why I said "trims off the control force". cagliost (talk) 17:27, 16 October 2022 (UTC)
 * You are corrector an Anti-servo tab. It increases force required when acting as designed so if you want to use it as a trim tab it must move in the opposite direction to reduce force required. 77.58.34.170 (talk) 01:57, 12 March 2023 (UTC)

Stability of aircraft or stability of control surface?
The article makes two distinct claims about stability:


 * it is commonly used on aircraft where the controls are too light or the aircraft requires additional stability in that axis of movement. The anti-servo tab serves to... increase the stability of that control surface

The claim about stability of the control surface is sourced, and makes sense. The anti-servo tab prevents control surface movement running away with itself.

However, the claim about aircraft stability along an aircraft axis is unsourced. Is it true? If so, it needs a source, and also clarification about how it works. cagliost (talk) 11:12, 14 October 2022 (UTC)