Helo INS wanderings

[PPRuNeUser0211]

Chaps,

Just a general inquiry. For those of you who have aircraft fitted with an INS available for use as a navigation tool, what kind of accuracy over time are you getting? Anecdotally I've heard of a laser ring system wandering around 1nm per hour in a rotary platform. Is that typical in actual usage or are modern systems (without the aid of gps) getting better than that?

Cheers!

[extpwron]

No longer at the coal face but I remember that in the early 80’s we had a Delco Carousel INS strapped down in the back of the Chinook to aid our long range navigation options (pre GPS!). It was very accurate for the first couple of hours (measured against Decca/Omega/Doppler) but several hours later (long range tanks fitted), low level over the water at night, we almost learned to our cost that a single INS is not that accurate. We learned about Schuler Loop that night!

ins/irs 'schuler effect' [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-119072.html)

[chinook240]

Ah, overwater nav, we must have together!

[JohnDixson]

Some ancient history: The S-67 upgrade in 1972 had a version of the Litton ASN-86 ( LN-39 I believe ) from the Army OV-1B Mohawk. It was used for nav, running a CDC ( Canada ) moving map display from the A-7E, for the 20mm aim point calculations which fed to the F-111 head up display ( we borrowed from everybody! ), and the helmet tracking system that ran the 3 barreled turret. For 1972 it was pretty good.

Anyhow, that inertial spec was 0.5 nm/hr as I recall, but we got numbers in the 0.3 nm/hr on occasion. The environment was INU friendly: fairly low vibration levels and air conditioning.

Are you thinking of a stand alone INU nav system?

[PPRuNeUser0211]

Aye, the system I've heard of is a modern laser ring system that has several blending options, but stand alone gives around the 1nm/hr or slightly better. Just can't quite believe that's up to industry standard based on fixed wing experience, but obviously the helo environment is not as ins friendly!

[catseye]

3nm plus 3t in hours used to apply for pre laser ring. Laser ring not much drift.