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cwc
24th Sep 2009, 07:43
From the manual of aviation meteorology-put out by the commonwealth bureau of meteorology in Oz.

After a very un-comprehensive definition of what it is they state "Pilots must make navigational corrections to allow for Coriolis effect"

I have never intentionally done that....what are they talking about. What is the adjustment? Is it in the planning stages, the inflight stages etc.

Help would be appreciated.

Runaway Gun
24th Sep 2009, 07:51
Good question. Maybe they are talking about re-aligning gyros, or updating Inertial Nav systems? Or dodging Cyclones? :ok:

BOAC
24th Sep 2009, 07:54
cwc - I think you can relax. I have got away with it for years. IF you conduct your navigation on a space-frame orientation you will probably need to correct for Coriolis. IF, however, you navigate between points on the earth's surface using earth-based references (heading, track, 'normal' INS, drift etc) you should be OK. If, however, you consistently find yourself missing your destination to the left in Oz, I would tweak it a couple of degrees right.:)

Any chance of a link to the "commonwealth bureau of meteorology" article? I'm always looking for a new drift on ideas.

Capt Pit Bull
24th Sep 2009, 08:54
I've wondered about this.

As a 'northern hemisphere guy' I have noticed that students seem to be more liekly to end up off track to the right. But of course that could be due to some other factor - maybe a sub conscious tendancy to want to unmask the area beneath the left hand side of the nose.

I guess it would be worth calculating it.

ISTR reading that it's a significant factor in long range gunnery. So if its a factor for guns firing shells at ? several hundred metres a second for a few miles, it ought to be a factor for aeroplanes travelling a bit slower but far further.

I might do some sums later ;)

pb

john_tullamarine
24th Sep 2009, 10:03
.. then again, for those with my standard of navigation excellence ... Coriolis considerations tends to get lost in the scatter .. and, as I recall, I've never ended up more than just a teensy bit lost for a minute or so.

Brian Abraham
24th Sep 2009, 11:07
I've never ended up more than just a teensy bit lost for a minute or so
Must be the consummate aviator JT. I can remember being lost to the point of fuel exhaustion, despite the other seat saying "I know where we are".

john_tullamarine
24th Sep 2009, 11:17
Must be the consummate aviator JT

Not at all, Brian .. just had a very sheltered and protected life.

Plus, in periods of navigational terror, time slows right down .. maybe I embellished the story a tad ... the worst might have been that time where I had not the slightest idea where I was during a tow from A to B with two on lines ... had to outfield and ask a farmer where I was .. thank heavens for the flexibility of SuperCubs ... we'd been running around thunderies and in and out of scud for the previous couple of hours or so. We knew where we were probably to an accuracy of 40 or 50 miles but that wasn't much use on the day ... so an outfielder it was ...

Sometimes I wonder how any of us survive being young, overconfident, stupid and overflowing with testosterone.

The best tale, although I can't recall the TP's name just now, was the fellow who observed in respect of the SR71 .. "you ain't never been lost ... until you've been lost at Mach 3".

Microburst2002
24th Sep 2009, 11:43
I had a Navigation teacher from the Air Force who was considered the expert of the experts. He used to say:

"When you have applied a wind correction angle you have also allowed for Coriolis" because the wind direction and speed was determined by Coriolis effect and the airplane is "inside" the wind.

He added that, unlike the artillery guys, pilots did not need to allow for Coriolis. Maybe he just wanted us to stop making questions on that matter...

Maybe it has to do with time? A shell from a gun gets from A to B in a very short time, and moves real fast. Let's suppose that the air mass within which it moves has not the time required to make the shell drift as it would make it if it remained a longer time in the air. Airplanes, however, stay in the air for hours so they are drifted (and "Coriolisized") by the wind.

What do you think?

davestewart
24th Sep 2009, 11:51
And there was me thinking that the Coriolis effect only applied to helicopter:)

RedPortLeft
24th Sep 2009, 12:06
In my simple world there are 2 big differences between artillery and aircraft which make it not worth worrying about Coriolis effect in the latter.
Firstly once a shell is fired that's where it's heading so all the calculations beforehand have to take everything into account, whereas an aircraft can be constantly corrected until the destination.
Secondly, a shell is relatively small, dense and fast compared to most aircraft and so the effect of wind, etc will be relatively less and other effects relatively greater. In an aircraft wouldn't the wind effect make any Coriolis effect negligible ?
Cue someone to tell me I'm talking rubbish :(

haughtney1
24th Sep 2009, 12:17
Coriolis?

I thought that was what you got after a bad chest infection? :}

BOAC
24th Sep 2009, 13:31
As JT says Coriolis considerations tends to get lost in the scatter The effect is all due to the rotation of the earth in space and your motion around an object. The black magic' involved in constraining the space-frame references to the earth-frame are wondrous..(refer Newton's First Law).

If you were able to 'hover' over a point on the equator for 12 hours, starting facing east and making NO changes to your 'space' attitude, you would finish up inverted and pointing west.

Similarly, if you started 'hovering' at 60 North, facing north and made no changes, you would arrive inverted and severely 'nose-up' after 12 hours but still 'pointing' north.

Setting off from the UK, pointing east (with a space referenced attitude) and aiming to fly to a point 'due east' you would see that point gradually move to the left of your nose as the earth rotates until it arrives behind you after 12 hours. This is the dilemma the poor old shell faces since its motion vector is 'in space'. Since your aircraft's motion is also a vector 'in space', you are a little like the shell. However, unless we are planning a long period of 'DR', as JT says, the Coriolis effect is lost in the constant corrections you make to stay 'on track' with wind changes, heading deviations and the like, not to mention using 'magnetic' directions with varying variation............. To stay pointing 'east' (magnetic) requires constant changes in some or all of pitch, roll and yaw to maintain - again fixed changes due to earth's rotation and variable according to your speed. Once you start following a 'line on the map' or tracking a radial or following an INS track, the 'corrections' required just 'happen'. The line on the map and the radial are all based on an earth reference and thus correct automatically. The INS has built in corrections to its space reference for earth rotation (earth rate) and your movement across the surface (profile rate) so it 'knows' the corrections it needs to apply to your space attitude to 'allow' for earth rotation and your motion across it. If I were Sir Francis Chichester in 'Gypsy Moth' aiming for that little island in the Pacific 10 hours away, yes, I would allow for it. For 'modern' flying, as I said, just relax:)

Phew!

jimtherev
24th Sep 2009, 22:08
Sorry, the 'board won't allow a one-word response, BOAC... I just wanted to say

WOW

john_tullamarine
25th Sep 2009, 00:21
Three observations ..

(a) BOAC knows a lot more about Coriolis than I

(b) all roads lead back to Einstein

(c) all wisdom may be found neatly encapsulated within one limerick or another .. while the following is probably more useful when talking about wormholes and time dilation considerations, it must be relevant to Coriolis somewhere along the way ..

There once was a lady named bright
Who traveled much faster than light
She departed one day in a relative way
and came home the previous night.

FLEXPWR
25th Sep 2009, 01:19
Mmmhh... I thought Coriolis was applied to moving systems, not fixed ones..as far as I remembered.

But what BOAC presented, although entirely correct, seems to be "just" gyroscopic precession, not Coriolis effect, which in itself does not exist for a fixed object, but applies to a moving system, like the curve induced on a bullet trajectory (thought minimal) or a weather system.

Please correct as needed,

Flex

VinRouge
25th Sep 2009, 07:32
I know long range artillery make corrections for it, not sure about us though....

Artillery and Coriolis (http://www-das.uwyo.edu/~geerts/cwx/notes/chap11/artillery.html)

More recent developments in the science of ballistics make the Coriolis effect more significant. For instance, a German gun of 21-cm bore called �Big Bertha� was used in 1918 to shell Paris from a distance of 122 km. Over such distances the inclusion of the Coriolis effect is at least as important as the consideration of deflection by the wind.

Its all to do with reference frames, so probably has an effect on INS?

Coriolis effect - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Coriolis_effect)

BOAC
25th Sep 2009, 08:25
Yes - I'm stunned too:)

Flex - NB I did include "your motion around an object" but the point I was trying to make was, as JT said, that the Coriolis effect, for controllable objects (unlike Big Bertha - she was wild:)) is effectively lost in all the other 'tweaks' we automatically make every second or so. EG did you realise that as you fly around the globe at, say, 450kts you need to keep adjusting your pitch nose down by 0.125 degrees a minute? I guess not. Heading north from the equator there will initially be a similar correction required in roll - all due to our 'motion' being relative to a space frame, but conducted in an earth-frame. All of this, of course, taken care of by our attitude reference systems (be they Mk I eyeballs, gyro Art Horizons, IRS or a black cat sitting on the coaming with its tail hanging over the panel) which are artificially 'tied' to the earth frame and we just do not see it. The ISS and Shuttle do not care much for all of this and generally maintain their 'space' attitude. Now convince me we will 'notice' the Coriolis effect!

Incidentally, it is the other gyro 'property' - 'rigidity' - not 'precession' that we are talking about. If I may summarise - Coriolis effect is there. It does affect our motion around the earth. It is just not really relevant for normal flights. None of the above applies to artillery shells, wind or black balls on blue turntables.

If you want to 'blow your brains' further, the Wiki reference is comprehensive and good, and will tell you that due to the Eötvös effect you can get away with eating more crew food when east-bound than west-bound.:)

Typo edits

cwc
25th Sep 2009, 21:33
BOAC-thanks.

Had a last minute flight last night...just me and two engineers off to fix a stranded boat. Midnight, quiet night, and conviently flying 3 hours north on the same heading( quite convient actually- and boring). Your post was great and I suddenly clicked to how it all worked as I sat there looking at my instruments and thinking how it all worked with relation to what you had written. My mind can now rest.....

Ive never been one that can settle for the "becasue it just is that way". Thank goodness there are smarter people than that out there that can explain it to those of us who dont get it first time round, or fourtieth for that matter.

Thanks again.

BOAC
25th Sep 2009, 21:41
3 hours at night on the same heading:eek::eek: - and you FOUND the boat! :)

cwc
25th Sep 2009, 23:43
I found the airport, that had the helicopter that flew the guys out to the boat. The boat just conviently broke something as it was passing near an a strip.

muduckace
25th Sep 2009, 23:53
I had understood it to be a variance in the gravitational effect on gyro's being more at the equator and less at the poles due to the earth's rotation as a simplified explanation.

iceAxe
13th Oct 2009, 19:24
Not a pilot, but a scientist who stumbled across this discussion. :-) I doubt anyone is watching this thread anymore, but here's a perhaps more intuitive answer.

The circumference of Earth at the equator is roughly 40,000 km. Earth rotates once per day, so a point on Earth at the equator travels 40,000 km in 24 hours, or has a speed of about 1600 km/hr. The circumference of Earth at 60 deg. N. latitude is half that: roughly 20,000 km. But, a point on Earth at 60 deg. N also completes 1 rotation in 24 hours, so its speed is about 800 km/hr.

Now, say you fly south from 60 deg. N to the equator. You are departing from an airport that is moving to the east at 800 km/hr, but your destination is moving to the east at 1600 km/hr. If you fly directly south, when you reach the equator you will be thousands of kilometers to the right (west) of the airport. Once airborne you are no longer in contact with the ground, and as you fly south the ground beneath you is moving increasingly faster to your left.

Over small distances north and south this difference is minimal and, I'm guessing, very small compared to more routine navigational considerations and corrections. But for long flights north or south the correction is a necessity and--I'm guessing again :-) --probably computed by navigation software w/o the pilots ever seeing it. Again, not sure about the piloting parts--but the Coriolis stuff is correct., fwiw.

Dimitris
15th Oct 2009, 12:13
@mudacacke
hmmm.... 1600km/h is ~400m/s, if what you say holds, then someone that jumps from a 1.5m wall to the ground stays in the air for ~0.5s, which means that the ground has moved by 200m in that time...?

From physics, Coriolis is a force that is exerted at a body that moves (even at constant speed) in a rotating reference frame. The speed is constant but the direction changes (due to the fact that you are on a rotating reference frame), so a force is needed to make equations right --> coriolis force. Greater the speed/angular speed the greater the force.

Apparently it's the reason that rail tracks are not evenly worn in trains that travel north-south (subtle effect). The effect on aviation is not the one you mention I believe. I think you are mixing the coordinate frames. Someone with better physics background can explain it better.

Basil
15th Oct 2009, 13:05
someone that jumps from a 1.5m wall to the ground stays in the air for ~0.5s, which means that the ground has moved by 200m in that time...?
but so, of course, has the jumper.