EGI Alignment on the ship

[Admiral_ZIPANGU]

I look forward to the release of Apache.

I am hoping to build a mission to fly Apache from LHA-1 Tarawa after its release. Just wondering, is it possible to align the EGI of the Apache on a ship underway?

[Dragon1-1]

The Apache is not a naval helo, so it probably doesn't have the datalink needed for that. You may need to do an in-flight alignment.

[MrNelz]

6 hours ago, Dragon1-1 said:

The Apache is not a naval helo

Try telling the British that.......

 

 

[Dragon1-1]

Yeah, that's not an AH-64.  The ones seen here seem to be AW-built Apaches AH Mk.1. They are, AFAIK, quite different from the original. Among other things, they have folding rotors and other equipment for shipboard operations. They also carry CRV7s instead of Hydras, and probably lots of other changes I'm not aware of (Brits love doing things their own way). 

[ghost84]

1 hour ago, Dragon1-1 said:

Yeah, that's not an AH-64.

but these are:

https://www.navalnews.com/naval-news/2020/04/u-s-navy-esb-u-s-army-ah-64e-apache-conduct-integration-operations-in-arabian-gulf/

[Dragon1-1]

That one is not a D, though. It seems to be something they're just starting to try out on the E. I've never seen any evidence of a US Army AH-64D being able to operate from a ship. I don't know how they do that, perhaps they can use a radio datalink for INS alignment, but this is something they must have introduced recently either way.

[TheGuardian]

Other than training missions, I've never heard of one operating from ships. Sure they have landed and rearmed or refueled but that is all. Given EDs past releases and comment history I wouldn't expect them to make this a feature for our AH-64D.

 

[Raptor9]

Yes you can operate D or E models from ships. There is a single button that is pressed to change the alignment mode between land or seaborne operations. Everything else is completely automatic. Doesn't require datalink or anything.

[Nealius]

On that note, do D models have TACAN equipment for either land-based or ship-based operations? I think presence/absence of TACAN in US Army Blackhawks is spotty. I wonder if it's the same for the Apaches.

[AlphaOneSix]

3 hours ago, Dragon1-1 said:

Among other things, they have folding rotors

I've seen this a number of times. They have the exact same rotor system as every other Apache on the planet. They are all "foldable" in a sense.

[Raptor9]

22 minutes ago, Nealius said:

On that note, do D models have TACAN equipment for either land-based or ship-based operations? I think presence/absence of TACAN in US Army Blackhawks is spotty. I wonder if it's the same for the Apaches.

Only E models have TACAN, primarily for joint operations with other services. The US Army as a whole doesn't use TACAN.

[Floyd1212]

What is EGI Alignment?

What is TACAN?

Inquiring minds want to know...

[LooseSeal]

5 minutes ago, Floyd1212 said:

What is EGI Alignment?

What is TACAN?

EGI is a fancy way of saying GPS-based navigation. So, you don't need to enter coordinates yourself, the GPS will know where you are. Which is handy on a ship, because by the time you've put the coordinates in... you'll have moved!

TACAN - Tactical Air Navigation. A radio system used by (most?) Western militaries that broadcasts on ultra-high frequencies. Think VOR in a Cessna, but for the military.

[Floyd1212]

Thanks!

[Dragon1-1]

1 hour ago, Raptor9 said:

Yes you can operate D or E models from ships. There is a single button that is pressed to change the alignment mode between land or seaborne operations. Everything else is completely automatic. Doesn't require datalink or anything.

How does that work, exactly? I was under impression that most such systems need to either be stationary, or know how and where the ship is going and how fast (which is what the datalink is for in Navy aircraft). Does it just use GPS to compensate, or is it something that can be used in GPS denial conditions, too? 

1 minute ago, LooseSeal said:

EGI is a fancy way of saying GPS-based navigation. So, you don't need to enter coordinates yourself, the GPS will know where you are. Which is handy on a ship, because by the time you've put the coordinates in... you'll have moved!

Except that's not the whole story. EGI is a system that combines GPS with a gyroscopic INS system. The big difference is, with GPS, when you don't see the sats, you don't get any sort of fix. With an EGI, once it's aligned, the INS component will still report position in case GPS signal is lost, although it'll degrade over time (and it can be aligned the old-fashined way, by inputting coordinates). It's important because GPS might be unavailable, for example if it was jammed or if the sats were hit by enemy ASAT weapons.

[MrNelz]

4 hours ago, Dragon1-1 said:

Yeah, that's not an AH-64.  The ones seen here seem to be AW-built Apaches AH Mk.1. They are, AFAIK, quite different from the original. Among other things, they have folding rotors and other equipment for shipboard operations. They also carry CRV7s instead of Hydras, and probably lots of other changes I'm not aware of (Brits love doing things their own way). 

We sure do! Yep, added flotation gear (still wouldn't want to ditch in one these even with flot!). The UK variant had more powerful RTM322 (from the Merlin) engines (great for over torquing the transmission at sea level in a temperate climate) and the CRV7 has a higher velocity than Hydra so some extra kinetic energy to add to the bangy stuff. Otherwise it was just a licence built Block II D model with extra funky bits. I was a bit late to the Apache party and never got to operate these off of HMS Ocean as I'd moved onto Wildcat after only 18 months. 

[MrNelz]

50 minutes ago, AlphaOneSix said:

I've seen this a number of times. They have the exact same rotor system as every other Apache on the planet. They are all "foldable" in a sense.

Indeed, but it is a highly technical process that requires specialist calibrated tools to remove the leading edge blade pin.......ie a bloody big mallet

[QuiGon]

3 hours ago, Raptor9 said:

Yes you can operate D or E models from ships. There is a single button that is pressed to change the alignment mode between land or seaborne operations. Everything else is completely automatic. Doesn't require datalink or anything.

But I assume that's only true if GPS is available, as GPS can probably compensate the movement aboard a ship? What if it's a GPS degraded environment and a classic INS alignment has to be done? Is there a special mode to do that on a moving ship?

Edited March 3, 2022 by QuiGon

[Raptor9]

5 hours ago, QuiGon said:

But I assume that's only true if GPS is available, as GPS can probably compensate the movement aboard a ship? What if it's a GPS degraded environment and a classic INS alignment has to be done? Is there a special mode to do that on a moving ship?

Those are questions I can't answer due to sensitivity reasons.

But the main point is it doesn't need a datalink from the ship.

Edited March 3, 2022 by Raptor9

[whiteladder]

Quote

17 hours ago, AlphaOneSix said:

I've seen this a number of times. They have the exact same rotor system as every other Apache on the planet. They are all "foldable" in a sense.

 

ALphaOneSix is correct,  although they are foldable they are design to fold for transport and not really like a helicopter designed for maritime operations.

 

When the British were initially operating the Apache from HMS Ocean (MrNelz Photo is Ocean) they had to fold the rotor to take them down to the hanger on the lift.  Now they can Operate from the Queen Elizabeth Class carriers they don`t have that problem any more.

 

 

Edited March 4, 2022 by whiteladder

[FalcoGer]

On 3/3/2022 at 4:02 PM, LooseSeal said:

EGI is a fancy way of saying GPS-based navigation. So, you don't need to enter coordinates yourself, the GPS will know where you are. Which is handy on a ship, because by the time you've put the coordinates in... you'll have moved!

TACAN - Tactical Air Navigation. A radio system used by (most?) Western militaries that broadcasts on ultra-high frequencies. Think VOR in a Cessna, but for the military.

EGI is only in part GPS (that's the G part). It stands for embedded GPS/INS. INS is the other big part of it, being the inertial navigation system, which is the part that actually needs the alignment. In the AH-64D the EGI is a dual redundant system, the INS consisting of 3 laser ring gyros each (one for each axis of rotation). While mechanical INS systems (using actual spinning gyros) drift over time, the laser ring gyros are very precise in measuring acceleration and rotation. Alignment time is 6 minutes. I can't remember the specifics about stored alignment, alignment after moving the chopper with power off, no GPS alignment, etc. They're all different though.

Physically alignment is done by measuring acceleration forces that the earth exerts on the unit. GPS greatly aids in the process but is not strictly required. Acceleration is measured by a split laser beam moving in two different directions around the gyro and recombining. If the gyro moves, then the path while the light travels around the gyro will change in length differently. The resulting interference pattern will shift, which is measured by a sensor. From this acceleration is inferred.

Putting the thing on a ship (or even bumping it) would really mess the process up and probably requires special hardware. That is why EGI alignment on commercial aircraft is done before boarding and engine start.

Edited March 13, 2022 by FalcoGer