gyro nutation ?

[flame_bringer]

One time i was working on a 727 and the engineer asked me to power the aircraft from the APU ( im an apprentice ) and i powered the aircraft because we had to do a daily check and some preflight inspections but anyways , as we finished he asked me to shut the apu down , when i closed the APU and cut off the power i noticed something really dazzling on the standby artificial horizon , the whole thing started spinning clockwise and i was scared i thought i must have made something wrong and broke it , so i asked the engineer and he was like dont worry about it it happens all the time thats called gyro nutation , so i asked him whats a nutation he said to me go back to your school notes and you'll find something about it , so i went back to my notes but couldnt find anything about it and i researched in google and it did mention something about it but i dont see the relationship between it and the stanby horizon spinning clockwise :S all it says is that nutation is the slight irregular motion of a larg spinning mass.
So can anyone explain to me whats nutation ( gyro wise and not a larg mass spinning wise ) and how did it spin the standby artificial horizon.?
Thanks in advance

[flame_bringer]

anyone :( ?

[pyracantha]

All the avionics specialists have gone quiet now.. suddenly they are all busy doing stuff!!

If the light flashes, take the bulb out....problem solved.

[SeldomFixit]

It takes longer to erect than you had it powered so what you were seeing was the " I think I can, I think I can, oh , sod it, I,m not going to, I'm not going to " as you depowered - text book, even if do say so myself :ok:

[Sonic Bam]

Google is a wonderful thing. Try it with "gyroscope precession".:ok:

The answers are out here ........

[HubNuts]

:ok: Nutation

From Wikipedia, the free encyclopedia


Jump to: navigation (http://www.pprune.org/#column-one), search (http://www.pprune.org/#searchInput)
See also: Nutation in plants (http://www.pprune.org/wiki/Nutation_in_plants)
http://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Praezession.png/170px-Praezession.png (http://www.pprune.org/wiki/File:Praezession.png) http://bits.wikimedia.org/skins-1.5/common/images/magnify-clip.png (http://www.pprune.org/wiki/File:Praezession.png)
Rotation (green), Precession (blue) and Nutation in obliquity (red) of the Earth


Nutation (from Latin (http://www.pprune.org/wiki/Latin): nūtāre, to nod) is a slight irregular motion (etymologically a "nodding") in the axis of rotation (http://www.pprune.org/wiki/Axis_of_rotation) of a largely axially symmetric object, such as a gyroscope (http://www.pprune.org/wiki/Gyroscope), planet (http://www.pprune.org/wiki/Planet), or bullet (http://www.pprune.org/wiki/Bullet) in flight (http://www.pprune.org/wiki/External_ballistics). A pure nutation is a movement of the rotation axis such that the first Euler angle (http://www.pprune.org/wiki/Euler_angles#Euler_rotations) (precession (http://www.pprune.org/wiki/Precession)) is constant.
Contents

[hide (http://javascript<b></b>:toggleToc())]

<LI class="toclevel-1 tocsection-1">1 Of a planet (http://www.pprune.org/#Of_a_planet) <LI class="toclevel-1 tocsection-2">2 Of the Earth (http://www.pprune.org/#Of_the_Earth) <LI class="toclevel-1 tocsection-3">3 Values (http://www.pprune.org/#Values) <LI class="toclevel-1 tocsection-4">4 See also (http://www.pprune.org/#See_also)
5 External links (http://www.pprune.org/#External_links)[edit (http://www.pprune.org/w/index.php?title=Nutation&action=edit&section=1)] Of a planet

The nutation of a planet happens because of tidal forces (http://www.pprune.org/wiki/Tidal_force) which cause the precession of the equinoxes (http://www.pprune.org/wiki/Precession_(astronomy)) to vary over time so that the speed of precession is not constant. It was discovered in 1728 by the English astronomer James Bradley (http://www.pprune.org/wiki/James_Bradley), but was not explained until 20 years later.
Because the dynamics of the planets are so well known, nutation can be calculated within seconds of arc over periods of many decades. There is another disturbance of the Earth's rotation called polar motion (http://www.pprune.org/wiki/Polar_motion) that can be estimated only a few months ahead, because it is influenced by rapidly and unpredictably varying things such as ocean currents, wind systems, and motions in the Earth's core.
Values of nutation are usually divided into components parallel and perpendicular to the ecliptic (http://www.pprune.org/wiki/Ecliptic). The component which works along the ecliptic is known as the nutation in longitude. The component perpendicular to the ecliptic is known as the nutation in obliquity. Celestial coordinate systems are based on an "equator" and "equinox," which means a great circle in the sky that is the projection of the Earth's equator outwards, and a line, the Vernal equinox (http://www.pprune.org/wiki/Vernal_equinox) intersecting that circle, which determines the starting point for measurement of right ascension (http://www.pprune.org/wiki/Right_ascension). These items are affected both by precession (http://www.pprune.org/wiki/Precession) of the equinoxes and nutation, and thus depend on the theories applied to precession and nutation, and on the date used as a reference date for the coordinate system. In simpler terms, nutation (and precession) values are important in observation from Earth (http://www.pprune.org/wiki/Earth) for calculating the apparent positions of astronomical objects.
[edit (http://www.pprune.org/w/index.php?title=Nutation&action=edit&section=2)] Of the Earth

In the case of Earth (http://www.pprune.org/wiki/Earth), the principal sources of tidal force are the Sun (http://www.pprune.org/wiki/Sun) and Moon (http://www.pprune.org/wiki/Moon), which continuously change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes (http://www.pprune.org/wiki/Node_(astronomy)). However, there are other significant periodical terms which must be calculated depending on the desired accuracy of the result. A mathematical description (set of equations) that represents nutation is called a "theory of nutation" (see, e.g. [1] (http://www.iers.org/iers/earth/resolutions/UAI_b3.html)). In the theory, parameters are adjusted in a more or less ad hoc method to obtain the best fit to data. As can be seen from the IERS (http://www.pprune.org/wiki/International_Earth_Rotation_and_Reference_Systems_Service) publication just cited, nowadays simple rigid-body mechanics (http://www.pprune.org/wiki/Mechanics) do not give the best theory; one has to account for deformations of the solid Earth.
[edit (http://www.pprune.org/w/index.php?title=Nutation&action=edit&section=3)] Values

The principal term of nutation is due to the regression of the moon's nodal line and has the same period of 6798 days (18.6 years). It reaches 17″ in longitude (http://www.pprune.org/wiki/Longitude) and 9″ in obliquity (http://www.pprune.org/wiki/Axial_tilt). All other terms are much smaller. The next largest, with a period of 183 days (0.5 year) has amplitudes 1.3″ and 0.6″ respectively. Interestingly the periods of all terms larger than 0.0001″ (about as accurately as one can measure) lie between 5.5 and 6798 days and seem to avoid the range from 34.8 to 91 days. It is therefore customary to split the nutation into long-period and short-period terms. The long-period terms are calculated and mentioned in the almanacs, while the additional correction due to the short-period terms is usually taken from a table.
[edit (http://www.pprune.org/w/index.php?title=Nutation&action=edit&section=4)] See also

Axial tilt (http://www.pprune.org/wiki/Axial_tilt)
Euler angles (http://www.pprune.org/wiki/Euler_angles)
Polar motion (http://www.pprune.org/wiki/Polar_motion)
Precession (astronomy) (http://www.pprune.org/wiki/Precession_(astronomy))[edit (http://www.pprune.org/w/index.php?title=Nutation&action=edit&section=5)] External links

For a synopsis and comparison of recent nutation theories, see Cyril Ron, "The Tables of Differences Between the Nutation Series IAU2000, IERS1996 and IAU1980" (http://www.iers.org/documents/publications/tn/tn29/tn29_111.pdf) (PDF (http://www.pprune.org/wiki/PDF)), at iers.org.Retrieved from "http://en.wikipedia.org/wiki/Nutation (http://en.wikipedia.org/wiki/Nutation)"
Categories (http://www.pprune.org/wiki/Special:Categories): Astrometry (http://www.pprune.org/wiki/Category:Astrometry) | Precession (http://www.pprune.org/wiki/Category:Precession)



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[chapter22]

It just toppled!!

[SeldomFixit]

You said it so much better than I, Chapter :ok:

[flame_bringer]

Sonic Bam
i googled that too but i didnt get a precise answer.
HubNuts
thank you for trying to help but i dont see any association between this wikipedia paragraph and what i have seen .
chapter22
i know it toppled but what it caused this toppling ?this is my question.
SeldomFixit
please be more specific bro
you guys are just making me more confused with these incomplete answers :(

[chapter22]

The stby horison is a vertical gyro, as the speed reduces the precession increases and any out of balance of the gimbles will cause the gimble to drift when the gyro axis gets close to the longitudinal axis of the gimble the whole thing will start to rotate.
Thats my take on it anyway!!

[flame_bringer]

hey chapter22 yea i think what u said makes more sense because the rate of preccession is inversly proportional to speed so if it spins slow the rotor in the inner gimbal precesses the outer one and it starts spinning in the direction of the rotor torque .
yea this theory makes more sense
i dont see the correlation of this and nutation though :S
but thanks alot

[chapter22]

flame
I had never heard the expression gyro nutation before your post, so while I accept it is a fact as per the other reply I don't believe that it is in common use in the aviation circles and does not explain what you saw!! also the bible for training Avonic engineers the UK (my words!) Aircraft Instruments by EHJ Pallet does not even mention this term.
Dave

[chapter22]

Flame
Dont know wheather you can get acces to a stby horizon easily, the one you saw was probablly a Sefena one, if I remember correctly it has 2 screws on the back of the case which when removed the case can be slipped off. Now if you had a u/s horizon??! you could power it up then remove the case and could then precess the gimble by hand and see the effect!!! used to do this when balancing the gryo quite good fun!!! had a few years in a gyro shop many years ago.

[JEMAVION]

So what does conventional wisdom say you should do about it? Leave it to spin down on its own or cage it as I've seen some people do? An action which I suspect could do some damage.

[flame_bringer]

Anyways thank you very much ppl for your attempts to help
I tried my best to find an explanation to this and i came into a conclusion that its just due to precession due to torque applied by the rotor itself to the gimbals when they become orthogonal .