Aligning IRS/INS on aircraft carrier?

[Bbow]

Just wondering, how do you align an IRS or INS if you are on an aircraft carrier that is moving?

[The B Word]

You can align INS in flight so what's the problem with a ship travelling at 20odd Kts?

[NoHoverstop]

1. Switch it on and wait for it to say it's in standby.
2. Tell it to "Air Align".
3. Wait and watch as 11 out of 12 cheeses fill in quite quickly.
4. Wait some more.
5. Wait even more while the elusive 12th cheese is found by the software.
6. Have a bit of a moan at "Telemetry".
7. Distract yourself by seeing if you can get the AHRS, a distinctly land-lubberly system that is actually nowt to do with the INS, to produce a heading output even vaguely close to reality.
8. Get prompted by "Telemetry" to the effect that the INS has actually quietly finished aligning whilst you were distracted on the wrong HUD format.

...is one way. Other methods may exist.

[Bbow]

Sorry guys, perhaps I should have stated that I not a military pilot, but commercial. Our IRS systems will not allign on the ground if the a/c moves, that got me wondering about aligning on a moving platform.

We can do an inflight alignment, but it's crude, not very reliable and would only be done if it failed inflight.

So I presume that the system is clever enough to cope with being moved along at 20Kts, unlike airliners.

[airborne_artist]

Our IRS systems will not allign on the ground if the a/c moves

Just as well the conveyor-belt runway idea was scrapped, then...:ok:

[ORAC]

In Days of Old, when Knights were Bold (http://www.pprune.org/tech-log/146822-ins-alignment-aircraft-carrier.html), and solid state ring-gyros and GPS weren't invented...

[galaxy flyer]

BBow

Basically, the plane is plugged into the carrier's SINS platform (very big in the old days) and the plane aligned off of it. Your plane and the ship didn't move in relationship to each other. Cue, Mr Einstein.

GF

[budgiep]

Whilst aligning to the ships inertial is a valid and widely used technique; these days a GPS aided alignment is also available. Without SINS or GPS the INS will be unable to align with sufficient accuracy to be of much use. Even if the ship is tied up alongside the wharf a 'normal' INS alignment is difficult to achieve (personal experience).:ok:

[woptb]

During the Falklands War we used FINRAE to do on deck alignments,although it didn't seem particularly good kit.To be honest I don't remember how it worked,if I ever did! Assumed it was slaved to something external of the airframe?

[Triple Matched TQ]

......I just tell the observer to "do it" and presto it works

(sometimes)

[vecvechookattack]

In the olden days when we used a plotting board, tracing paper and a pencil we used to ask the ship where we were.........and then along came GPS and it ended up with the ship asking us........

[Nozzles]

Bbow,
I beg to differ with Budgiep. In the absence of a Transfer Align from the ship's INS, the additional info (compared to a land align) the aircraft's platform needs is: ship's course and speed and aircraft heading on deck (relative to ship's course). This tells the platform what its translational velocity is while it is aligning. The velocity info can come from GPS or can be manually inputted (carrier videos sometimes show the deck crew holding up a small whiteboard to the pilot with Lat, Long, course and speed on it). Relative heading needs to be manually inputted or derived via standard INS gyrocompassing techniques. Software can average out the ship's pitch, roll and heave during the align process. INSs that can align at sea have to be marinised and the align accuracy will never be as good as that of a stationary align. However, the solution is useable. More modern INSs will have their velocities damped by GPS, thus slowly tightening the navigational solution. Older systems use other forms of damping, such as a downward-facing Doppler radar.

[Double Zero]

I'd suggest holding up a ( info' ) board is very much a failsafe Plan B, there is a discreet system whereby a carrier sends the data to the aircraft.

[WeekendFlyer]

USN aircraft have for years used alignment with the Carrier's INS, via a cable connection or low power radio datalink. Our Harriers used to use a non-GPS sea-alignment, where the INS was told its heading with respect to the carrier's course and then sorted out the rest with clever filtering. But now GPS is almost standard, our Harriers use a GPS-based sea alignment process where the GPS provides the velocity solution to aid the alignment.

I am surprised modern airliners cannot do this, but then perhaps that is because they tend to have inertial reference units rather than full inertial navigation systems? Even so, i would have thought a GPS-based air alignment process would have been fairy easy to implement.

[agincourt]

For the RN there is no direct feed from the ship's INS - data can be passed verbally via telebrief. The IRU can be started in DECK LEVEL mode at sea (as opposed to GYRO COMPASS mode ashore) since the Magnetic Detector Unit is unreliable close to a big lump of steel.
Probably as much of an issue is the fact that GPSs don't like initializing several hundred miles away from where they were when they were shut down.

[bayete]

When the RAF was first trialling the GR7 on board carriers they were not able plug into the ships INS so they had to manually input the ships position, CSE and speed (read from a card on the bridge) and the difference between their heading and the ship's (measured with a sextant on the ships datum line). And I seem to remember the pilots had to do some additional jiggery pokery when they hit the ramp on takeoff to get another vector to complete the align.

I'm sure someone from ETPS at the time will have more info.