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Moment equilibrium is usually called 'longitudinal trim'.Gordon Vigurs 13:33, 20 July 2006 (UTC)

A tailless aircraft may be statically stable, provided the centre of gravity is ahead of the aerodynamic centre.Gordon Vigurs 10:27, 29 July 2006 (UTC)

A stable aircraft cannot be flown 'hands off' for long, as the long period phugoid and spiral modes will become manifest. This article is restricted to the short period pitch response, the actual behaviour is somewhat more complex. See Flight dynamics. However, this is a reasonable qualitative introduction. Gordon Vigurs 10:36, 29 July 2006 (UTC)

Merger talks[edit]

I have added horizontal stabilizer to the definition and redirected it here, as I consider this article more specific than stabilizer (aircraft). I am also taking out the 'merge' template since the 'discussion' link in it points here, where there is no discussion of it. If anyone objects or questions any of these moves, please discuss here. Thanks, Crum375 13:03, 7 October 2006 (UTC)

I've added merge tags again. The content of both articles treats the terms as equivalent, which isn't to say that refinement isn't warranted, just that the distinction is unclear as things stand. ENeville (talk) 06:32, 26 February 2009 (UTC)

-- (talk) 15:06, 11 May 2012 (UTC)

Tailplane and horizontal stabilizer should both redirect to Stabilizer (aircraft). Tailplane is a redundant and less precise word for horizontal stabilizer, and horizontal stabilizers are just one form longitudinal stabilizers. Canard and tailless aircraft of all types use the aft edges of the main wing for longitudinal (or pitch) stabilization.

Actually 'tailplane' is the proper (and older) precise aeronautical term for that airframe component which fulfils the purpose of 'horizontal stabilisation' in an aeroplane.
Similarly the proper precise aeronautical term for the wing is 'mainplane'.
Notice they are each only one word.
Reference here: [1]


I can't help but feel that the stability & equilibrium sections need re-writing, with much of the equilibrium section moved to stability. All aircraft have the centre of lift above, below or coincident with the centre of gravity when in level flight, otherwise the aircraft would depart from steady, level flight even in the absence of a disturbance. It is the movement of the centre of gravity &/or lift which varies; in 'a conventional aircraft,' the centre of lift moves back when the aircraft pitches up (only then is 'the centre of gravity is ahead of the centre of lift') & vice versa.

In addition, the 'Tailplanes and Canard compared' section is rather narrow/incomplete. The main source of mass in a glider is the pilot, wings & engine (if one is present) all of which are fairly close together - you then have the choice of adding a long tail boom, allowing a small low drag tail plane to produce a stable glider, or a long nose boom, small low(er) drag canard, a large computer and even larger battery (or engine, fuel & generator) to keep the thing stable, so of course gliders employ a tailplane. Conversely, if you were to put a jet engine right at the back of a glide, shifting the centre of gravity much closer to the tail plane, the arrangement suddenly become far less attractive!

-- (talk) 15:06, 11 May 2012 (UTC)

--Stodieck (talk) 18:54, 10 May 2012 (UTC) I am planning a rewrite of Canards and Stability/equillibrium. Stability/equillibrium are the same thing. Visit stabilizer (aircraft) for a preview. I have just rewritten that. Stabilizer (aircraft), Horizontal Stabilizer, Flight control surfaces, Elevator (aircraft), and others are redundant and often contradictory and need to be aligned. Canards are very poorly understood by most editors.

"partial revert, equilibrium and stability are not the same thing, unstable equilibriums and stable non equilibriums exist" by Planetscared.

This is not the point of the article. Unless you can find an external reference on this point as it relates to "Tailplane" you are involved in "Original Research" which is verboten in the Wiki. This is an encyclopedia not a philosophy debate. It is a documentation process not a creative exercise. A horizontal stabilizer is not named a horizontal equilibrator. A pilot doesn't care that his craft is out of equilibria what ever that might mean. He would be very concerned if it were unstable. — Preceding unsigned comment added by Stodieck (talkcontribs) 20:03, 10 May 2012 (UTC)

An aircraft can be unstable, in which case the aircraft's nose will flip up, or down, and then the wings will fall off. That's unstable. Or you can be perfectly stable... in a screaming dive... because there's not enough (downward) lift from the tail section. The tail plane has to be designed for both stability and balance/equilibrium. That's what the body of the article currently says, and I completely fail to see that you can argue this to not be the case, and so I reintroduced it to the lead when you removed it.Planetscared (talk) 20:12, 10 May 2012 (UTC)

An airplane in a screaming dive is "out of control". It may be in perfect balance and equilibrium. The tail plane has to be designed for both stability and control not "balance/equilibrium". You are using overlapping redundant terms and confusing yourself with them.

It may or may not be out of control, but it's directionally stable. If you want to call equilibrium 'stability' that's fine. But it's a different sort of stability than the article refers to as stability.Planetscared (talk) 02:04, 12 May 2012 (UTC)

No. There is only one type of stability at issue here. If this article has created a new one it needs to be purged. The article needs external technical references, if you were to seek those out you would start understand what the problem is here.

"In a conventional aircraft, the center of gravity is ahead of the center of lift, which would cause the aircraft to pitch forward without the downward force of the tailplane to balance this." This statement is circular, "the center of gravity is ahead of the center of lift" because these planes are designed to use a horizontal stabilizer to achieve pitch stability.

"In cases where the two forces are close together, the control inputs required to fly the aircraft may be too difficult to apply precisely enough for many pilots to maintain control of the aircraft." "cases where the two forces are close together" is normal flight! This is near equilibrium! In normal straight and level flight the two force centers are normally on top each other with small excursions to either side. The average over time is dead center.

"Examples of aircraft that had this setup"! What setup? "With computer controls this is no longer a problem and aircraft as different as the Airbus and the F-16 are flown in this condition." Huh! What? Your talking about aircraft with a lack of static "instability". If you are using non-standard terminology it doesn't belong in the wiki. --Stodieck (talk) 03:37, 12 May 2012 (UTC)

Only just found this discussion[edit]

So I take this article as it is now.

My understanding of the aft-CG arrangement discussed under Equilibrium is that "issues with this arrangement that were beyond the capabilities of designers at the time to fix" is untrue. The British Army and Sopwith's were well aware of the handling difficulties of unstable or neutrally stable arrangements, but also understood that they were more maneuvrable than stable types. That was so important in combat that instability was accepted as a necessary compromise. — Cheers, Steelpillow (Talk) 20:06, 14 July 2012 (UTC)

I saw your note above, and was inspired to have a look at the section Equilibrium - it is very amateurish and needs a lot of work. Whenever we see someone writing about the center of lift we know they are out of their depth. There is no recognised term called center of lift. Even on Wikipedia it merely re-directs to aerodynamic center. The entire section is unsourced and I'm not surprised - it is material that will never appear in any reliable published source on longitudinal stability. I will try to do some work on it in the next week or so. Dolphin (t) 13:03, 15 July 2012 (UTC)
The term "center of lift" was used for many years and we all know what it means. It can be more intuitive for non-experts than the technically correct "center of pressure". The term "axis of lift" is sometimes used to describe the line through it on which the lift vector lies and is also technically correct, although the term "lift axis" is used more often in other contexts so usage in the present context is probably unwise. "Centre of lift" still seems to be in common use, so we do need to explain about it. The Center of lift page now redirects more correctly to Center of pressure, as the Aerodynamic center is a quite different beast. — Cheers, Steelpillow (Talk) 14:24, 20 April 2013 (UTC)
I agree that "center of lift" should redirect to "center of pressure", not "aerodynamic center".
You say "center of lift" was used for many years; and still seems to be in common use. That surprises me - can you give an example of a reliable source, or at least a popular source, that uses "center of lift?"
The explanation I have given students who have asked about "center of lift" is that lift and drag are not independent forces acting through the center of lift and the center of drag respectively. Lift and drag are merely the components of a force called aerodynamic force. The aerodynamic force is a surface force resulting from the variation in pressure around an airfoil so, as with all forces resulting from pressure variations, it can be considered to act through a point called the center of pressure, arbitrarily located on the chord line of the airfoil. Lift and drag are components of aerodynamic force so they must both be considered to act through the same point as the aerodynamic force - the center of pressure. Dolphin (t) 15:33, 20 April 2013 (UTC)
One reference is: Curtis, et. al.; Aerospace Engineering Desk Reference, Butterworth-Heinemann (2009), Page 498, Figure 7.2-4. The discussion focuses correctly on the centre of pressure, but the term "centre of lift" slips into the image caption. Googling "center of lift" and/or "centre of lift" (UK spelling) reveals plenty of popular sources. The other day it led me to Darbyshire, A.; Mechanical Engineering, Newnes (2003), but then showed me the wrong page. The actual page with the search hit seemed not to be viewable. I don't know whether this at could be considered reliable.
My understanding of the centre of pressure is that its location is not arbitrary: it is, as it were, the point of intersection of the lift and drag axes - or, more technically, the point on which both the lift and drag vectors act. (If I am wrong about the definition, please ignore this paragraph!). So it is not generally located on the main wing's chord line. For example a flying boat typically has a high thrust line and draggy hull, which places the axis of drag / centre of pressure well below the thrust line. this is quite independent from how high the wing is mounted, which will usually be well above the axis of drag / centre of pressure. (All this pitches the nose down, and is compensated for by trimming the tail to pitch the nose up. The centre of pressure can end up in quite an unusual place.) — Cheers, Steelpillow (Talk) 10:35, 21 April 2013 (UTC)
Thanks for the hints about the books by Curtis and Darbyshire.
My comments about aerodynamic force, center of pressure and lift were intended to apply to an airfoil or a wing rather than an entire aircraft. The concepts of aerodynamic force and lift are of great value in describing the physics of airfoils and wings but when we move on to consider the dynamics of the entire aircraft, they are of limited value. For example, the aircraft requires an upward lift force on the main wing and a downward lift force on the horizontal stabilizer, resulting in a net upward lift force and a nose-up pitching moment. Any axis can be considered the lift axis but the pitching moment varies with the choice of axis. Hence the attraction in defining the aerodynamic center, the point for which the coefficient of pitching moment is constant over a large range of angle of attack.
Your comments about the drag axis are correct. The center of pressure on an airfoil is arbitrarily located on the chord line but the drag on an entire aircraft acts along an axis that may be significantly removed from the chord line. (Any powered aircraft has a drag axis and a thrust axis. The vertical separation of the two is significant in determining whether the aircraft pitches up or down following a change in engine power or thrust.)
I don’t consider the Allstar website to be reliable. The following extracts illustrate what I mean:
  • lift is increased as the angle of attack is increased because there is more relative wind striking the airfoil's bottom surface, creating higher pressure.
COMMENT: As you know, with changes in angle of attack there are significant changes in the reduced pressure on the airfoil’s upper surface, but little or no change in the pressure on the airfoil’s bottom surface.
  • There is also an increase in the induced lift, because at a higher angle of attack the air has to travel even farther over the top surface of the wing.
COMMENT: This sounds like the equal transit time model, a model that has been discredited.
  • The aircraft's ceiling is that point in the atmosphere where the air is too thin to allow further increase in lift.
COMMENT: An aircraft’s ceiling is the altitude at which the maximum excess thrust is zero. It has nothing to do with lift. (Excess thrust is thrust minus drag.)
Dolphin (t) 14:09, 21 April 2013 (UTC)
Ouch! definitely not a reliable web site, then. Yes, whether one is concerned with the aerofoil in isolation or the whole aircraft does affect the simplifying assumptions one likes to make. For example, I guess the exact drag axis for an aerofoil seldom matters. — Cheers, Steelpillow (Talk) 18:49, 21 April 2013 (UTC)
I agree. The science of longitudinal static stability is all about the forces in the vertical direction - weight, lift and pitching moments. The drag axis, and the separation between the drag axis and the thrust axis, have little or no influence on the longitudinal stability of an aircraft. In our article Longitudinal static stability the word drag is not used! Dolphin (t) 12:36, 22 April 2013 (UTC)

Content moved over from Stabilizer (aircraft)[edit]


I am removing the content below from Stabilizer (aircraft):

"Adjustable stabilizers are usually adjusted with a positive displacement device like a jack screw or a hydraulic ram. Failure of the adjustment jack screw led to the crash of Alaska Airlines Flight 261. In aircraft with elevators, a trim tab on the trailing edge of the elevator is often used to move the elevator to alter the aircraft's pitch (see Douglas DC-3 or Cessna 172). The stabilized speed is known as the trim speed, and the trim is used to set the desired speed without having to hold the elevator out of its trimmed or faired (trail) position.
Other aircraft use an one-piece moving surface that serves the function of both a stabilizer and an elevator and is called a "stabilator" or "all moving tailplane". One example of a modern airliner with a stabilator used for flight control is the Lockheed L-1011 TriStar. Horizontal "Stabilators" are generally used for aircraft flying near or above the speed of sound because the formation of shock waves on the surface of the stabilizer tends to reduce the effectiveness of elevators. Stabilators may also use a trim tab to control the angle of the all moving stabilator surface, as on the Miles M.52. The North American F-86 Sabre initially used a fixed stabilizer and elevator with a trim tab, but later versions used a stabilator."

I think the content definitely belongs here in Tailplane, not over there, but it may need re-writing before being incorporated. Ariadacapo (talk) 12:18, 20 April 2013 (UTC)

adjustable tailplanes give fuel efficiency[edit]

are there any references on tailplanes that adjust size to use the Jetstream to greater advantage? Wikipedia Jetstream article says that the Jetstream gives about a third faster velocity with same energy, thus a tailplane like a hinged > could widen or narrow to optimize efficiency. another possibility could be a lifesaver or puffable tobe (sort of like a pencil grip) around the area of the plane between wings to tailplane.

Not sure if you meant to link to that article, but the jet stream just carries the aircraft along with it, it doesn't flow faster over the airframe. — Cheers, Steelpillow (Talk) 19:48, 19 June 2014 (UTC)

US versus UK English[edit]

I spotted the word "tailplane" on 1940 Brocklesby mid-air collision and wondered what it was.

The term is not listed an 1942 aviation dictionary that I have which also includes slang used by the American and British flying forces. That dictionary's definition for "tail" uses the wording ".. a group of stabilizing planes, or fins, to which are attached certain controlling surfaces such as elevators and rudders". I usually call them the horizontal stabilizers and vertical stabilizers and had to laugh when I saw that "horizontal stabilizer" redirects to the tailplane article.

"Tailplane" does not appear in the Shorter Oxford English Dictionary (1993 ed). It does show up in the online OED which says "British: Another term for horizontal stabilizer." and sources The British & World English dictionary. The online OED also has this record which says "British: A horizontal aerofoil at the tail of an aircraft." and sources their US English dictionary.

My question now is if the British often use "horizontal stabiliser." I'm trying to think of a clean way to reword the first sentence which has "A tailplane, also known as horizontal stabilizer (or horizontal stabiliser), ..." to indicate that "tailplane" is UK English, "horizontal stabilizer" is US English, and that in the USA we use "horizontal stabilizer".

For now, I updated the article to use "A tailplane, also known as horizontal stabiliser (and horizontal stabilizer in the USA), ..." but am not quite happy as someone might mistakenly believe that the word "tailplane" is used in the USA. --Marc Kupper|talk 18:06, 29 September 2014 (UTC)

No time now but as a Brit I find "tail plane" and "tailplane" to be common. Just to be annoying, our Oxford dictionary prefers "stablilizer" while the Cambridge one goes for "stabiliser" (I think it's that way round). Pedantically, in a relaxed-stability vehicle the tail plane is horizontal but one thing it is not is a stabiliser, it's just something to help the elevator work properly and the stabilising function is carried out by a system comprising the elevator and associated control software. Whatever we do, it will be nearly as mad as the real world. — Cheers, Steelpillow (Talk) 21:33, 29 September 2014 (UTC)
I would add further to what I wrote last night. The term "horizontal stabilizer" is understood by everybody and that is very important. However a canard forewing is also sometimes described as a horizontal stabilizer, and that can make the term ambiguous - especially on a three-surface aircraft. The British use of "tailplane" and "foreplane" for the two cases is more logical, being unambiguous, which is also very important. So we are caught between a rock and a hard place - do we accept some ambiguity or a term that not everybody is familiar with? It is not a nice problem. Turning to the Flight magazine archives, I find both "tailplane" and "horizontal stabiliser" (with an "s") in use, but "horizontal stabilizer" (with a "z") not at all. I wonder if the best approach might be to summarise the issues in the lead along the lines of, "In British English a tailplane, horizontal stabiliser or horizontal stabilizer, or in American English a horizontal stabilizer, is a small lifting surface..." and then add a rider that "The term 'horizontal stabliser' or 'horizontal stabilizer' can also refer to a small canard forewing."— Cheers, Steelpillow (Talk) 20:44, 30 September 2014 (UTC)
As a kid growing up in the UK in the late 60s/early 70s, and building lots of model planes, it would not have occurred to me to call it anything other than the "tailplane", which was how it always appeared in the construction instructions. -- Arwel Parry (talk) 22:35, 29 September 2014 (UTC)
Actually 'tailplane' is the proper (and older) precise aeronautical term for that airframe component which fulfils the purpose of 'horizontal stabilisation' in an aeroplane.
Similarly the proper precise aeronautical term for the wing is 'mainplane'.
Reference here in Flight International going back to as far as 1909: [2] — Preceding unsigned comment added by (talk) 10:22, 30 June 2015 (UTC)