# Talk:Longitudinal static stability

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WikiProject Aviation / Aircraft (Rated Start-class)
Start  This article has been rated as Start-Class on the project's quality scale.

## Incorrect diagram

In all conventional aircraft, the center of gravity must be ahead of the center of lift of the main airfoil in order to achieve positive static stability. The diagram in this article incorrectly shows the center of gravity behind the center of lift.

As the center of gravity moves aft toward the center of lift, stability decreases and is lost when the center of gravity is behind the center of lift. Some modern aircraft do fly with reduced or even negative static stability because static stability is achieved with a drag penalty created by the drag produced by the negative lift of the horizontal tail. This penalty can be reduced in civil aircraft to reduce drag and thus fuel consumption. Static stability can be virtually eliminated in some military aircraft in the interest of extreme maneuverability. There is a cost for this. These newer aircraft can only be operated safely by relying on active computer assisted controls. The controls must counter every disturbance from trimmed flight, perhaps many times per second. Otherwise these disturbances may cause the aircraft to depart controlled flight altogether. —Preceding unsigned comment added by 69.255.237.10 (talk) 16:39, 5 February 2010 (UTC)

The above asserts that; 'the drag produced by the negative lift of the horizontal tail.' I am of the opinion that the tailplane in modern commercial aircraft produce a vertically upwards lift component, not downwards. Downwards lift would make the aircraft dynamically unstable.
58.8.235.159 (talk) 07:09, 8 March 2010 (UTC) R.A.P
Disagree with "Incorrect diagram"
It is common for cg to be aft of wing aerodynamic center. -Krebs — Preceding unsigned comment added by 2620:0:10F2:FD00:755D:E84A:3B5D:4449 (talk) 20:23, 17 August 2015 (UTC)
Either condition is common enough (it is a popular fallacy that the tail must always exert a down force), in fact the lowest-drag ideal is for the tail force to be zero and for the centres of wing lift and gravity to coincide. Real life often approximates this condition and sometimes passes through it. Another popular confusion is that between the centre of lift and the aerodynamic centre. The fact that one is usually in front of the centre of gravity does not mean that the other one necessarily is too. These confusions are all present in the above discussion: read the article carefully and you will see that all is explained. — Cheers, Steelpillow (Talk) 09:00, 18 August 2015 (UTC)

## Wrong axis

Longitudinal Stability describes what a layman would call "Roll." LATERAL Stability is Pitch..... —Preceding unsigned comment added by 71.194.185.138 (talk) 03:58, 13 January 2011 (UTC)

No. — Cheers, Steelpillow (Talk) 09:01, 18 August 2015 (UTC)

## Cleanup Protocol?

There are comments below [above], all now either invalid or actioned (corrections implemented in the article), so I think the balance of this page is defunct, and would like to delete it. That feels capricious & unilateral so I won't. Instead I'll do some research to see what the habitual techniques of maintenance and housecleaning before presuming to delete. Meanwhile, any reading this be advised (one person) thinks the article's pretty good and the below [above] comments no longer relevant. Markrkrebs (talk) 13:29, 13 May 2012 (UTC)

All is as it should be. This talk page stands as a record of the discussions. If it ever gets too long, then the earlier discussions can be archived. I moved your comment down to the correct place - new topics go below earlier ones - and edited it accordingly. — Cheers, Steelpillow (Talk) 09:04, 18 August 2015 (UTC)