Over-g'ing the INS: Permanent or salvageable?

[Voyager]

So I'm given to understand that if you pull to many G's then the INS gyros topple and you lose your platform knowledge in the F-14B, but I'm missing whether this is a "pour the old one out and bolt a new one in" type of failure, or whether you can fix it in flight?

 

Thank you,

 

Harry Voyager

[Wizard1393]

I've heard you should be able to realign. But Idk how. Maybe it's not implemented yet.

[Super Grover]

Usually, it's a mechanical failure, which means that the whole INS has to be replaced by the ground crew - only DCS "repair" function can make your INS fully functional again.

 

In terms of in-flight re-alignment, it's impossible with the F-14A/B. You can erect the IMU to a state where it can serve as the attitude source, but you can't restore full INS abilities.

[Voyager]

Thank you. That clears up my question on operational g limits; basically keep it under 6G unless not doing so would be a hill loss.

[Jansgi]

Thank you. That clears up my question on operational g limits; basically keep it under 6G unless not doing so would be a hill loss.

 

You can exceed 6 G's and even max out the accelerometer up to 10 G's for a split second in dire situations without damaging anything. From my experience prolonged 7 G maneuvers haven't damaged anything for me so far.

[Whiskey11]

Usually, it's a mechanical failure, which means that the whole INS has to be replaced by the ground crew - only DCS "repair" function can make your INS fully functional again.

 

In terms of in-flight re-alignment, it's impossible with the F-14A/B. You can erect the IMU to a state where it can serve as the attitude source, but you can't restore full INS abilities.

 

Is this implemented? I don't think it is... at least... I've yet to get it to work. I pulled an 8G (yeah, 8G) turn and the INS went.... heading off by 30 degrees and HUD ladders rotated about 5 degrees to the right.... landed to repair, ground crew wont repair with aircraft completely cold and dark. No other damage either.

[Super Grover]

It worked the last time I tried it (although some time ago), and the code is there. And you shouldn't be able to break the INS at 8G, at least the threshold in the code is set higher than that.

 

 

Oh, and BTW, if you have "Random System Failures" set to on, the INS and other devices will sometimes break too (maybe the INS a bit more often than the rest).

Edited June 10, 2019 by Super Grover

[Voyager]

It worked the last time I tried it (although some time ago), and the code is there. And you shouldn't be able to break the INS at 8G, at least the threshold in the code is set higher than that.

 

 

Oh, and BTW, if you have "Random System Failures" set to on, the INS and other devices will sometimes break too (maybe the INS a bit more often than the rest).

 

Ok, so we've got two separate way the INS outputs can go bad? One by introducing to much maneuvering driven drift, and the other by inducing physical failure in the INS, and that the physical structure of the INS is rated for 8+ G's, but the accuracy drops off very quickly as you go up in G's.

 

If I'm following that correctly, that seems to imply that one should always have a alignment point available if one may need to dogfight, but that one should not be limited to <6G when manuvering, unless you don't have an available alignment point.

 

That sound right?

[Talonx1]

Dont know if it was due to over g but after playing around a bit around the carrier I noticed my compass was off by 10 deg. Only fix I could come up w was setting compass to DG mode and turning the knob to match my heading up to the carriers brc. (Also used info bar to confirm it was set properly as it will show you actual that you can compare to your instruments)

[Super Grover]

@Voyager

The INS accumulate drift all the time, not only at high G. Of course, high G manoeuvres may introduce more significant errors. However, those are mostly position errors, and attitude errors are less pronounced.

On the other hand, there are two ways for break the INS completely: by pulling too much G, and as a result of a random failure (emulating all other aspects why the device can break).

 

One common misconception is that the skewed pitch on the HUD comes as a result of a broken INS (IMU). Quite often the scenario is: the IMU breaks, the AWG-9 detects that failure and automatically switches to AHRS/AM, the AHRS becomes the attitude source for everything, including the HUD. However, the AHRS can easily tumble, because it's designed to work for +/-82° only. Usually, that shifted/rotated pitch ladder is just a result of heavy manoeuvring in the combat phase before the IMU broke. As an exercise showing the limitations of the AHRS, you can manually switch the INS mode to AHRS/AM, do some aerobatics, and observe how the accuracy of the attitude displayed degrades.

 

 

@Talonx1

The magnetic compass/sensors are sensitive to the magnetic field of the carrier and can easily be off by 10° or more.

[Whiskey11]

One common misconception is that the skewed pitch on the HUD comes as a result of a broken INS (IMU). Quite often the scenario is: the IMU breaks, the AWG-9 detects that failure and automatically switches to AHRS/AM, the AHRS becomes the attitude source for everything, including the HUD. However, the AHRS can easily tumble, because it's designed to work for +/-82° only. Usually, that shifted/rotated pitch ladder is just a result of heavy manoeuvring in the combat phase before the IMU broke. As an exercise showing the limitations of the AHRS, you can manually switch the INS mode to AHRS/AM, do some aerobatics, and observe how the accuracy of the attitude displayed degrades.

 

So I think what happened on my flight is this, but if the INS grenaded like this, a repair would fix it no? I was shut down on the tarmac, engines off, canopy open... No repair.

 

In an earlier session I did successfully repair a collapsed landing gear from a PIO during landing causing the left gear to collapse, so I know aircraft repair works for that.

 

Maybe I'll have to do some free flights and intentionally break things to test it :D Sounds like the kind of testing Grumman did in making the aircraft! Just a shame they didn't make the INS system to the same standard!

[Top Jockey]

Hello everyone,

 

As I'm still updating my DCS version, and I'm not all that knowledgeable about the INS and its repairing possibilities after the harsh maneuvering, I do have some doubts:

 

At previous updates, I did recal it wasn't always possible to repair the INS.

But now I've seen at the 2.5.5.31917 open beta (pic below, red box) something about that possibility.

 

So can anyone tell what exactly does that mean - can Jester effectivelly re-align / repair the INS or not ?

 

Thank you.