Talk:Aircraft dynamic modes
|WikiProject Aviation / Aircraft||(Rated C-class)|
|WikiProject Physics / Fluid Dynamics||(Rated Start-class, Mid-importance)|
Poor choice of title?
"Instability modes" implies that the modes are not stable. This is untrue, at least closed-loop, for every aircraft flying today, with the notable exception of the spiral mode (where on some aircraft the pilot closes the loop to stabilize the mode). "Aircraft dynamic modes" strikes me as a better description of the contents. I don't know if I'm allowed to move pages, but if I can I may if there's no objection, and if it doesn't disturb the proposed merges. Patrick O'Leary 19:11, 15 November 2006 (UTC)
- I'll give this a little more time, but I do see the merge proposals have been dropped from the page. Patrick O'Leary 17:50, 27 November 2006 (UTC)
Merge w/ Flight Dynamics?
Now I'm wondering if this article should really exist at all, given that all the good math is already in the Flight dynamics article. Perhaps a merger is in order? Patrick O'Leary 14:54, 14 December 2006 (UTC)
- Perhaps, but is this article really it? I know I just moved it to this title, but I would guess that anyone looking for information on aircraft dynamics and using the word "mode" is probably at least somewhat knowledgable in the math. I think if there were to be separate "basic" and "advanced" flight dynamics articles, we'd have to re-edit both this and flight dynamics to pick and choose, and that the bulk of this article should be under the title flight dynamics and the bulk of that here--that is, get the math into the more technically titled article. Patrick O'Leary 01:59, 20 December 2006 (UTC)
I like this article and, though it needs improvement and expansion, it is notable in itself. The FD article is afflicted with math and pedantry and an over expansive subject. This has the potential to make the subject actually usable by lay readers. "Mathematics lets fools do what only geniuses could do without it." (http://www.uh.edu/engines/epi1534.htm)
The Pendulum Effect is a Myth
"Also, a non-aerodynamic force is imposed by the relative vertical positions of the c.g. and the lift, creating a roll-in leverage if the c.g. is above the centre of lift, as in a low wing configuration; or roll-out if below, as in a high-wing configuration (a pendulum effect)."
Chief author(s), please remove any reference to the "pendulum effect." Although, unfortunately, it's an all too common belief, it nevertheless is a myth.
When a symmetric airplane banks, the projections on the roll plane of the of the lift and weight lines-of-action must intersect near the CG. Therefore they cannot form a couple, cannot create a restoring rolling moment and cannot contribute to the dihedral effect.
The case of a pendulum is different and irrelevant. In a pendulum, the weight acts downwards at the bob and the reaction acts upwards at the point of attachment. When the pendulum is displaced, the weight and reaction stay parallel to each other but displaced from each other, thus forming a restoring couple. There is no attachment point and no reaction in a free-flying airplane, therefore the pendulum analogy is invalid.
Yet, an upper wing configuration does contribute, significantly, to the dihedral effect, but the reason is aerodynamic, not mechanical. It has to do with wing-fuselage flow interaction: the fuselage creates a "fence" effect on the windward wing root and a "shadow" effect on the leeward wing root so that a marked difference in wing lifting efficiency appears between the wings, providing a strong restoring moment.