Naval aircraft INS alignment

[RodBorza]

Hello all,

 

I was watching a good old History Channel show on You Tube about the development of the F/A-18 and then suddenly this doubt came to my mind:

How do airplanes and helicopters carried on ships do the inertial system alignment process prior to flying?

One thing is doing this on the ground, which is fixed in relation to the Earth, also which benefits from the computer memory to know its last location. But, doing this in a moving platform, with its twists and turns and where position information from your last landing is days old, I believe it to be way more difficult.

Do they take nav information from the ships computers? Do they use a more advanced/complex mathematics to account for speed and orientation of the ship to allow the alignment?

It is interesting because the inertial alignment process is a not easy feat in itself, even more if you consider that you are now in a moving, accelarating/deccelarating platform.

[EtherealN]

Global Positioning System. ;)

 

Also, movement does not preclude INS alignment. Remember that you can do this in the A-10C while in the air, for example. It makes it more difficult and probably less precise, but you can still do it.

[hassata]

Looks like GPS, as EtherealN said. This is from cmatt, and F-18 pilot over on the Seven-G forum:

 

"Skwabie - the INS has a GND and CV align mode. When selected to CV, the ship transmits the required coordinate information and updates it. Once the GPS kicks in, then it takes over. Normally about 4 - 5 mins for an alignment. Not normally a problem because you are busy doing other checks (radar, FCS, FLIR, programming IFF/AI etc)."

 

http://seveng.forum3.info/t8p15-questions-about-the-f-18

[RodBorza]

Thanks for the answers.

This question came because alignement is not that esay as many people think, the GPS is there to correct and diminish the errors that the INS tend to accumulate over time. Thus, you don't need to do the HARS fast erect anymore.

But my question was directed more on knowing how the system got its initial position. Good to know that it takes from the ship.