Gyroscopic Drift

[ardypilot]

Just revising through my PPL Tech subject here and thought I would see if I could replicate gyro drift accelerating error on the Directional Indicator gauge in FS2004- seeing it in motion would obviously help me to memorise the effect, which according to my manual, is in a southerly direction when accelerating and a northerly direction when decelerating (S.A.N.D) due to the magnetic meridians cutting through New Zealand airspace at 60 something degrees and the pivot for the DI needle being slightly off it's COG... and also, the turning error which is 10/20/30 degrees over towards the north and under towards the south (ON/US)... so, I fired up FS2004, went into the realism settings and pushed the 'Gyro' bar all the way to the right, and enabled it in the tickbox below- however, neither my DI or HI seems to be showing any lag when I performed normal rate 1 turns- surely this isn't correct? Is there a way I can replicate what I've just mentioned above? Have I missed some other settings?

I also set my airspeed to display as 'true' rather than 'indicated', however, when flying into a 12 knot wind from say 290 true, heading at 290 true, I don't notice any reduction on the ASI or difference in speed with the value shown in the red text 'ctrl+z' line at the top of the screen- any ideas on this one?

Cheers

[Alfashark]

Hmmm, I could be wrong, but the "gyro" slider refers to the gyroscopic/torque effects produced by the engine/prop combo...
Also, true airspeed, as I understand it, is more in reference to the actual speed of the aircraft through the AIR itself, taking into account density altitude (thinner air up high, hence IAS decreases with altitude) - If you were cruising at 100KIAS, heading 290, into a 290 @ 12kt wind, your GROUNDSPEED would be affected (100 - 12 = 88kt GS)
The last two Wave soaring flights I made in '01 out of NZTG had me decending downwind through 14000' with a GS of 290kt+ verified by both my trusty Garmin 12, and CHCH control

[pois0n]

QUOTE (Trolly @ Feb 21 2009, 01:13 PM) <{POST_SNAPBACK}>

Just revising through my PPL Tech subject here and thought I would see if I could replicate gyro drift accelerating error on the Directional Indicator gauge in FS2004- seeing it in motion would obviously help me to memorise the effect, which according to my manual, is in a southerly direction when accelerating and a northerly direction when decelerating (S.A.N.D) due to the magnetic meridians cutting through New Zealand airspace at 60 something degrees and the pivot for the DI needle being slightly off it's COG... and also, the turning error which is 10/20/30 degrees over towards the north and under towards the south (ON/US)... so, I fired up FS2004, went into the realism settings and pushed the 'Gyro' bar all the way to the right, and enabled it in the tickbox below- however, neither my DI or HI seems to be showing any lag when I performed normal rate 1 turns- surely this isn't correct? Is there a way I can replicate what I've just mentioned above? Have I missed some other settings?

I also set my airspeed to display as 'true' rather than 'indicated', however, when flying into a 12 knot wind from say 290 true, heading at 290 true, I don't notice any reduction on the ASI or difference in speed with the value shown in the red text 'ctrl+z' line at the top of the screen- any ideas on this one?

Cheers

IAS remains constant with an increase in alt compared with TAS which increases with alt, you're thinking of groundspeed in your example.

[ardypilot]

QUOTE

Hmmm, I could be wrong, but the "gyro" slider refers to the gyroscopic/torque effects produced by the engine/prop combo...[/quote]
Havn't learned about this yet, but I thought that effect was labeled 'P-Factor' in the FS2004 realism options?

I forgot flight sim had a 'help index' where you can search up things like this, so to answer my own question, I better go RTFM!

Just while I'm looking though- can anyone verify whether DI errors can or cannot be replicated in FS?

QUOTE

you're thinking of groundspeed in your example.[/quote]
Ah yep, my bad. Some aircraft have their airspeed seem to have their ASI measured in TAS (such as the default 172), and some in IAS (such as the Carenado 172)- does that mean the IAS will read lower when pointed into a headwind?

Last edited by ardypilot on Sun Feb 22, 2009 3:43 pm, edited 1 time in total.

ardypilot

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[happytraveller]

If I remember my CPL theory correctly, the effect is due to the Coriolis Effect,

http://en.wikipedia.org/wiki/Coriolis_effect

The rule for the northern hemisphere was BOSUN which translated as Bearing oversteer south, understeer north, so roll out 30 degrees later on compass turns when turning through south, and about 30 degrees before north when turning onto north. All the errors would be the reverse in the southern hemisphere. Bet that has now got you totally confused!!

Like many aviation laws, things are reversed between the two hemispheres.

Smooth landings (and turns onto headings).

[HardCorePawn]

What you're referring to are the dip and acceleration errors in the magnetic compass... the 10/20/30 degree ONUS thing is when doing compass turns! The DI does not suffer from these issues (or the problems associated with turbulence as much)... hence the preference to use it in 'modern' aircraft as the primary indicator of direction over the compass...

What the DI suffers from is 'drift'... where it loses its 'sync' with the compass due to the rotation of the earth, precession (when maneuvering) and friction etc... hence the need to include the DI in your SADIE checks every 15minutes or so to make sure it is aligned with the compass.

[happytraveller]

And about the differences between IAS and TAS, a headwind or tailwind would not make any difference, as the speed of the aircraft through the air remains the same. The speed of the aircraft over the ground does change though.

IAS is the speed indicated on the ASI. As this is a pressure instrument, then it relies on the force of air hitting a sensor to calculate the airspeed. As altitude increases, then the relative air pressure decreases, so that although the aircraft may be flying through the air at exactly the same speed, because the air is less dense then it hits the sensor with less force and shows a lower air speed figure (but it still shows the IAS, indicated air speed).

True Air Speed (TAS) is the aircraft speed through the air after a correction has been added to compensate for the less dense air. So when climbing into thinner, less dense air, the IAS may remain the same, but the TAS will actually be higher than the figure shown on the ASI.

I can remember many hours of correcting air speeds on the old navigation computer, all for the exams, but in practice in a normal single, you just take the IAS as the same as TAS.

smooth landings.

[ardypilot]

Thanks guys, that all makes sense that I had the compass and DI mixed up- I'd actually written it down wrongly in my notes which explains the confusian.

Cheers for the detailed explanation- will go make the required adjustments now

We've been learning about Corolis force in Met, but I thought that it did not effect the magnetic compass components, but that was due to the meridians 'cutting through NZ airspace' at the odd angle? From reading both HT's and Jarreds replies, I am still a little confused on this aspect... care to explain it further?

[Christian]

QUOTE (Trolly @ Feb 28 2009, 08:42 AM) <{POST_SNAPBACK}>

Thanks guys, that all makes sense that I had the compass and DI mixed up- I'd actually written it down wrongly in my notes which explains the confusian.

Cheers for the detailed explanation- will go make the required adjustments now

We've been learning about Corolis force in Met, but I thought that it did not effect the magnetic compass components, but that was due to the meridians 'cutting through NZ airspace' at the odd angle? From reading both HT's and Jarreds replies, I am still a little confused on this aspect... care to explain it further?

The coriolis force doesn't have any effect on your compass. The heading indicator is simply a spinning top (or similar). Now, I don't remember my physics anymore, but in one way or other the spinning earth affects your spinning top in your aeroplane. I'd need to look it up in a text book. As far as I remember, the Coriolis Force isn't actually a real force, but just an effect because the earth is bigger around the equator. Hope that's not too confusing The thing to remember is that the DI is a spinning top, gets out of sync and needs to be readjusted now and then to match the magnetic compass again.

Christian

[HardCorePawn]

Coriolis has nothing to do with magnetic compasses...

QUOTE (Trolly @ Feb 23 2009, 09:42 PM) <{POST_SNAPBACK}>

We've been learning about Corolis force in Met, but I thought that it did not effect the magnetic compass components, but that was due to the meridians 'cutting through NZ airspace' at the odd angle? From reading both HT's and Jarreds replies, I am still a little confused on this aspect... care to explain it further?

Not sure want you're wanting to know... I have no idea what meridians cutting through NZ airspace has to do with anything???

[pois0n]

Just use an HSI

[A185F]

QUOTE (pois0n @ Feb 21 2009, 03:20 PM) <{POST_SNAPBACK}>

IAS remains constant with an increase in alt compared with TAS which increases with alt

Whooaa dunno about that one there cuz


As you increase in alt the there is less air, there for there is less air to go into the pitot tube, there for a less indication.

At alt you might indicate bugger all compared to down low because there is less air going into that pitot, BUT because there is less air up there then there is less resistance to the fligth and the aircraft moves through the space faster (which is what TAS is in a nutshell)

As some personal e.gs I've had
When I was in a (semi) mighty C206 at 250000ft she would indicate bugger all (like 65-70kts in the cruz) but cos there is less air she was TASin at about 160-170 with about a 170kt ground speed.

The Mighty 185 down low 500-1000ft indicates about 145ish in at cruz power but at 12k its more like 90-100.

The Dornier will do 220kts indicated at 1000ft cruze with the power back but up at 10k its more like 170-180.

Some notable differences there...

[HardCorePawn]

QUOTE (A185F @ Mar 3 2009, 12:25 AM) <{POST_SNAPBACK}>

As some personal e.gs I've had
When I was in a (semi) mighty C206 at 250000ft she would indicate bugger all (like 65-70kts in the cruz) but cos there is less air she was TASin at about 160-170 with about a 170kt ground speed.

I hope you got your badge from NASA

[A185F]

QUOTE (HardCorePawn @ Mar 3 2009, 09:13 AM) <{POST_SNAPBACK}>

I hope you got your badge from NASA

Actually now that I think about it, I was tellin a little porkey there...
We had a little puf of wind up the cacker there to get the 170kts Ground speed, the TAS was more in the area of 140-160kts, still plenty and a huge difference from such a low Indicated speed.
But was a few years ago and only once and never again thank you very much
I was told by a mate who flys that aeroplane often that he's had it sucking the (little) air at 28000ft !!! Must have been a good day to coax the old girl up that high...

[pois0n]

lol, can tell its been a while since ive done any theory stuff

[ardypilot]

QUOTE

I was told by a mate who flys that aeroplane often that he's had it sucking the (little) air at 28000ft !!![/quote]
C206's aren't pressurised are they? How's it possible to fly that high for longer than 5 or so minutes without getting hypoxia?? Does your mate wear an oxygen mask or something?

Thanks for the explanation by the way- got a nice mid 90% mark today in the Tech practice exam.

Last edited by ardypilot on Tue Mar 03, 2009 5:00 pm, edited 1 time in total.

[A185F]

QUOTE (Trolly @ Mar 3 2009, 05:59 PM) <{POST_SNAPBACK}>

C206's aren't pressurised are they? How's it possible to fly that high for longer than 5 or so minutes without getting hypoxia?? Does your mate wear an oxygen mask or something?

Yes we all do, above 13k.

[ardypilot]

You all get hypoxia or you all wear O2 masks?

I guess that must be standard for skydivings ops- aren't most jumps from around 12,000 feet? Have been thinking about doing it myself out of Mercer sometime soon.

[A185F]

QUOTE (Trolly @ Mar 3 2009, 08:37 PM) <{POST_SNAPBACK}>

You all get hypoxia or you all wear O2 masks?

I guess that must be standard for skydivings ops- aren't most jumps from around 12,000 feet? Have been thinking about doing it myself out of Mercer sometime soon.

haha yea we all wore oxy masks, well by all I mean all 2, pilot and camera operator. Those high level flights were aerial survey, not skydiving (although I bet a freefall from 25000ft would be something !! )
Most skydive opps are around 10-13000 ft so no oxy required. Some places go up to like 15 & 16k and I think they just have oxy on hand usually, cant remember.