INS aligment
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I would guess that the F-16 does not derive latitude for navigation purposes but does check the calculated against the entered as large discrepancies will prove to be unusable in flight.
The system doesn’t have any error checking for what is entered for lat/longs. If you enter something grossly off the system cannot align and would be completely unusable.
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My 1984 D1 says the HSI compass card is the “INS magnetic heading”. I didn’t find that it was computed from True North. And the HSI compass card is INS servo driven just like the ADI.
The HSI displayed magnetic north but once again the HSI gets all of it’s information from the INS system when in NAV mode. If what the INS system sensed on alignment was true heading and as is agreed that the HSI is displaying magnetic heading how else do you think that was done?
Mag heading is given by software computation based on location, true heading and known Mag variation table.
The statement above is correct.
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page 1-163
I do not understands much (certainly not this), but I do not think this says anything about INS using magnetic heading, I will keep looking.
Caper is correct in that the compass card is displaying magnetic heading.
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@Gas Now there is a gyrocompass. That was my missing link. There had to be a compass some where. And would ya know that the FOG suite is used to allign it.
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@Gas Now there is a gyrocompass. That was my missing link. There had to be a compass some where. And would ya know that the FOG suite is used to allign it.
There is NO COMPASS used to align any version of the INS system. Just accept it already. I’ve used the term gyrocompass alignment more than a few times and that doesn’t mean there is a compass used to align the system. Good God.
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There is NO COMPASS used to align any version of the INS system. Just accept it already. I’ve used the term gyrocompass alignment more than a few times and that doesn’t mean there is a compass used to align the system. Good God.
That’s not what I said. I just the FOGs are used to align the gyrocompass.
If the gyrocompass was used to initialize INS after alignment, you wouldn’t find in your end-user docs away.
BTW we did design an INS without FOGs and gyrocompass. It use a fluxgate compass and rate gyros. It also feed data to the FLCS. We were not the first.
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That’s not what I said. I just the FOGs are used to align the gyrocompass.
It isn’t aligning a compass or being aligned by a compass there is NO COMPASS in the INS system at all. There is nothing more than the face of the HSI which isn’t a compass but as you pointed out just a servo controlled face with a compass printed on it.
If the gyrocompass was used to initialize INS after alignment, you wouldn’t find in your end-user docs away.
That is non-sense. After the INS is aligned it doesn’t need to be initialized. I am not using “end user docs” for this information but the CDCs that talk about how and why things happen in the INS system. I fixed that system for a living for 19 years.
BTW we did design an INS without FOGs and gyrocompass. It use a fluxgate compass and rate gyros. It also feed data to the FLCS. We were not the first.
You guys might have designed one but the SINS and/or the RLG INS work like I am describing. I would have to call BS for you saying gyrocompass yet again since that isn’t a part of the INS system. Merely gyros, either physical or laser and accelerometers.
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@Gas Now there is a gyrocompass. That was my missing link. There had to be a compass some where. And would ya know that the FOG suite is used to allign it.
I will look see if I find something but AFAIK, Stubbies2003 is a SME on this.
P.S.
SME=Subject Matter Expert -
Just so I understand, if you guys would please humor me.
- OP just wanted to know if INS alignment time can be changed to match JA-37?
- caper; You are saying INS or more specifically the INU uses gyros (not the sandwiches, ) and a gyro-compass to align?
- Stubbies2003; You are saying that the INS, more specifically the INU does not use any compasses to align?
Is that the sum of the conversation?
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I will look see if I find something but AFAIK, Stubbies2003 is a SME on this.
P.S.
SME=Subject Matter ExpertWe covered useing the FOG to align true north a day or so ago. I saw it a non LM f-16 web page years ago.
At least he’s not talking about the pilot’s backup compass.
The only INS package that does not ingrate a compass that I know of, is a Honeywell smart bomb INS. The flight is so short there is no drift to correct. However, that’s early 90s stuff.
I think Subbies been trying to say that FOGs don’t drift and don’t need to be correct by a compass. I could understand that. But he does not want to be that direct on the subject.
I post about flight operations and he replies with alignment proceedures.
I don’t really care anymore. -
Nope you must enter the coordinates for each normal/gyrocompass alignment even if they are correct for SINS/RLG INS systems. The combined INS/GPS units might be different but what is simulated in BMS would require entry.
I wasn’t talking necessarily about F-16 system …
Software mag heading is compared with mag heading coming from “heading central” (do not remember English name).
It use a fluxgate compass and rate gyros.
Fluxgate! Here is the word I was looking for! Thank you.
If you takeoff without allignment there is no heading tape?
Unless you can select manualy the INS or the FLUXGATE as heading sources … yes.
On my a/c, EHSI’s heading of 1st pilot is coming from INS, and BDHI (sort of RMI) heading is coming from FLUXGATE, for the 2nd pilot, it is the reversal … sources can be switched manually if needed.
It will be “the same” on my future a/c .
Does INS heading drift?
Yes. But heading drift is minimal compared to position drift.
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gyrocompass is a compass, just not as the general known by the mean ppl:
" A gyrocompass is similar to a gyroscope. It is a compass that can find true north by using an electrically powered, fast-spinning gyroscope wheel and frictional or other forces in order to exploit basic physical laws and the rotation of the Earth. Gyrocompasses are widely used on ships. Marine gyrocompasses have two main advantages over magnetic compasses:they find true north, i.e., the point of the Earth’s rotational axis on the Earth’s surface, as opposed to magnetic north, –an extremely important aspect in navigation, and
they are unaffected by external magnetic fields which deflect normal compasses, such as those created by ferrous metals in a ship’s hull.
Contents1 Operation
2 History
3 Errors
3.1 Patents
4 See also
5 References
6 External links
OperationA gyrocompass is essentially a gyroscope, a spinning wheel mounted on gimbals so that the wheel’s axis is free to orient itself in any way. When it is spun up to speed with its axis pointing in some direction other than the celestial pole, due to the law of conservation of angular momentum, such a wheel will normally maintain its original orientation to a fixed point in outer space (not to a fixed point on Earth). Since the Earth rotates, it appears to a stationary observer on Earth that a gyroscope’s axis is completing a full rotation once every 24 hours. Such a rotating gyroscope cannot ordinarily be used for marine navigation. The crucial additional ingredient needed for a gyrocompass to seek out true north is some mechanism that results in an applied torque whenever the compass’s axis is not pointing north.
One method uses friction to apply the needed torque: the gyroscope in a gyrocompass is not completely free to reorient itself; if for instance a device connected to the axis is immersed in a viscous fluid, then that fluid will resist reorientation of the axis. This friction force caused by the fluid results in a torque acting on the axis, causing the axis to turn in a direction orthogonal to the torque (that is, to precess) towards the north celestial pole (approximately toward the North Star). Once the axis points toward the celestial pole, it will appear to be stationary and won’t experience any more frictional forces. This is because true north is the only direction for which the gyroscope can remain on the surface of the earth and not be required to change. This axis orientation is considered to be a point of minimum potential energy.
Another, more practical, method is to use weights to force the axis of the compass to remain horizontal with respect to the Earth’s surface, but otherwise allow it to rotate freely within that plane. In this case, gravity will apply a torque forcing the compass’s axis toward true north. Because the weights will confine the compass’s axis to be horizontal with respect to the Earth’s surface, the axis can never align with the Earth’s axis (except on the Equator) and must realign itself as the Earth rotates. But with respect to the Earth’s surface, the compass will appear to be stationary and pointing along the Earth’s surface toward the true North Pole."
From: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Gyrocompass.html
So if a micro earthguake takes place during those 8 minutes INS Allignment is Fubared? Wonder if that caused or causes problems to Greek and Japaniese pilots as both are highly sismogenic areas.
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So if a micro earthguake takes place during those 8 minutes INS Allignment is Fubared?
IMO, there are filters smoothing any perturbation during alignment. On my a/c, moving it during alignment will make the IRS furbared. However, we can load the plane and sometime, it is shaking (when loading an 8T vehicle!) … no problem for IRS.
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Here is a IRS.
equipped with 3 gyrolaser like this one:
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You can only base very little when comparing BMS with 1984 F-16. The only similarities is that it is still an F-16 and…. yeah all the system are different. Engine, avionics, hell even the structure is different.
This one is better but still only a reference, nothing more and not 100%for those without facebook account:
http://publicintelligence.net/hellenic-air-force-f-16cd-flight-manuals/
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For grins, I googled “IRS compass” the other day. Got no hits:( I guess nobody makes a handheld. I wanted one to buy one so I can align my mobile Satelite TV dish the same way the f-16 aligns the INS. The mag compass sux. Get it close to the dish and never lock on to the Satelite. But that car compass with the adjustment screws maybe the ticket.
Here is a IRS.
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Just so I understand, if you guys would please humor me.
- Stubbies2003; You are saying that the INS, more specifically the INU does not use any compasses to align?
Is that the sum of the conversation?
Correct. It uses gyros for the platform (physical spinning gyros for SINS, strapped down laser gyros for RLG/EGI) and accelerometers to sense movement in the 3 planes.
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At least he’s not talking about the pilot’s backup compass.
The backup compass does nothing more than serve as it’s name implies. A back up for the pilot when all other NAV systems have failed.
The only INS package that does not ingrate a compass that I know of, is a Honeywell smart bomb INS. The flight is so short there is no drift to correct. However, that’s early 90s stuff.
I am not talking about a “package” but the INU which during alignment derives true north via gyros and accelerometers readings and not by some built in compass.
I think Subbies been trying to say that FOGs don’t drift and don’t need to be correct by a compass. I could understand that. But he does not want to be that direct on the subject.
I post about flight operations and he replies with alignment proceedures.
I don’t really care anymore.I have zero idea of how you think I’m ever saying that INS DON’T drift when all I have ever said is they DO. It is impossible to make an INS that does NOT drift. You can only use external help via GPS to keep it in line.
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Does the F-16 have a magnetic influence compass in it somewhere (other than the ball in fluid backup instrument)? I think the A-10 has one in the right wingtip.
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Does the F-16 have a magnetic influence compass in it somewhere
I hope it have. (not necessarily a compass … but a flux-gate … I’m almost sure! There is no reason not to have one for crosscheck of computed mag heading and as a backup for IRS heading.)