suicide by autopilot

[FADM Stern GNSF]

I have a strange problem that occures every now and then, especially after long flights (1-2 hours) that maybe someone has seen before.

 

I fly along happily, trimming as I go, and it flys so nice. Go into a hover and all is well, bag a few targets and move on. Then, out of no where (and usually when Im not doing anything) the helicopter will have what can only be described as an epileptic fit, bobbing and bouncing all over the place.

 

While I used to end up dying from this, I now usually dont as I know what the problem is, BUT not the cause. Seems that for some reason (and thats what im trying to figure out) all three auto pilots turn off. If I hold the trim button I can usually get the chopper steady until I can turn them (with a quick left hand RSHT-H, P, B i think). Then all is ok again most of the time (on rare occasions, they WONT turn back on, but simply all flash).

 

I know that no failures have been set in the missions Im flying, but for the life of me cant figure out why this happens (not counting any time I have taken fire, as I assume they are caused by damage)

 

Any ideas ?

 

Thanks all

[Lobo_63]

Is this happening at very low alt? I think the ap kicks off below a certain height...

[FADM Stern GNSF]

No, usually its at altitudes well about 50m (most of the time around 200m, but once [and fatal, at 3400]).

Most of the time (about 90 %) it hapens when Im in a nice stable hover, usually not even holding the cyclic. Im not sure if it only happens during hover and not flight because when I fly I dont use route mode, and make all adjustments with the trim held, only releasing when Im again stable.

 

I was wondering if I somehow triggered something with my mouse (while looking around out the windows), but last time I was simply hovering, let go the stick and started to head for a quick bio-break. While hovering over flat land at about 250m I heard the cat lady yelling and the buzzer going. I ran back qucik and managed to save the chopper by flicking them back on once I had it stable. It didnt loose a lot of altitude, but was spinging and leaning bad.

[Inseckt]

I think I read a similar thread where it was explained that if you overtourqe the engines or something like that, you lose power for a second, and tthen the INU goes haywire becose a part of the system does not back up on batteries... And the autopilot needs the INU to function... Give the INU thre minutes to reallign or something...

[okolovos oko]

That is happening only with taliban autopilot..does it scream Alaaaaah Ukbarrr before crash?? if so change chopper!!!

Edited February 19, 2009 by okolovos oko

[auricom]

This seems to happen if you overtorque or enter into a vortex ring (which results in substantial overtorque) and recover.. Like someone above said the INU goes haywire and the AP channels die.. you'll see the AP channel buttons flashing..

 

Usually just turning the channels off and back on resolves the issue, you may have to wait a minute (or three) for the INU to re-align..

 

As for this resulting in death, I would recommend practicint (At altitude) flight with all AP channels disabled.. It's actually not too hard once you get the hang of it.. Good practice for when this happens in the field..

 

Also watch your collective position and vertical rate indicator like a hawk when transitioning to a hover.. for me that was when I'd usually get stuck in this unfortunate situation as I was descencing too rapidly and not watching descent rate while trying to slow to a hover

 

Good luck :)

[FADM Stern GNSF]

LMAO no, so far no taliban screams, as that would just have me reaching for the eject button. I figure that your point of an INU failure is correct as the autopilots do go out to lunch. The big problem is finding what is cusing it. In a lot of case, just doing a mad stab to turn the three autopilots back on will fix it, which seems to indicate the INU is fine (or else it would not help).

There must be a reason (maybe through some pilot error) that the autopilots say "lunch time, clocking out", I just cant seem to find a reason or common occurance at the time (as I said before, its usually on a hover or stable forward flight (under 200K).

[ZaltysZ]

There is such thing as autopilot oscillations, when autopilot over controls and makes need for more correction and then over controls once again and so on. Maybe Ka-50 is smart enough and turns AP off when these oscillations are detected?

[AlphaInfinity]

I have had this happen to me a few times:

 

1. The INU is not aligned

2. I overtorque the engines, rotor rpm's drop during an extreme nose pitch to bleed speed and some systems go offline due to the lack of power.

[Inseckt]

@Alphainfinity: Would reason nr. 2 also normally result in the famous recalibration screen of the schval display? Just a side-question... Don't have the possibility to test it my self for some time...

[Mugatu]

Is the autopilot disabling below 4 feet a bug or a feature? Why on earth would you turn off all channels in auto hover just because you go below 4 feet, what were they thinking ... "hmm lets make the chopper go out of control because the pilots dropped below the minimum autopilot hover alt, and lets do it when there's something to crash into."

 

Same goes for in the vortex (more understandable if the FCS can't work out what's going on).

[Zorrin]

It will disable altitude hold below 4 metres (c. 13ft) and it is designed to do that.

 

It's hardly a life threatening situation to fly the Shark without an autopilot. While it is of course much much harder, it is perfectly doable.

 

The Shkval display will "restart" when your power drops too low. The engines aren't turning fast enough to power the generators.

[FADM Stern GNSF]

Well, it still does happen (and about the Shkval calibration screen, mine does that every now in then while flying, just figured that was normal)

 

I know its an autopilot and/or INU problem, but when it happens is usually while IN a stable hover (in hover hold, while moving the shkval box around locking up targets) or when I am in controled flight (smooth flight between 100-200K).

 

Most of the time, at least when its the biggest headache, is when I have been in a stable hover for a while (sometime Hover hold on, sometime not), as this is when the helicopter goes nuts. Now it may be that the autopilots turn OFF after the oscillation point mentioned above, but either way once I have got the chopper controled again and check, the autopilots are off. Most of the time I can turn them back on and all is fine again. I have died a few times, but that is usually when I get caught off guard and cant react fast enough. I guess the biggest mistery is why, when floating there ina stable hover for 10-15 min, scanning for targets, al of a sudden all goes nuts.

 

I have on a few occations flown back to the airport without the autopilots (happened twice when they got destroyed in combat), and while a pain in the arm, I can fly fine without them.

 

While I know all of the good listed points above can cause this, the times I am confused about is when it happens when all is fine (cant get much better than a smooth stable hover).

 

Thanks for all the idea's, and while it does still happen, at least now I have a very good saviour rate based on reaction without thinking lol. Maybe one day I will figure it out. As for the test pattern that popps up on the Shkval every now and then (for about 6 seconds, then returns to normal), I though this was normal ?

Edited February 22, 2009 by FADM Stern GNSF

[Weta43]

The test pattern on the Shkval is normal.

Most of the time, ..., is when I have been in a stable hover for a while (sometime Hover hold on, sometime not)...

Are you sure sometimes not?

Just thinking 'aloud', but I wonder if you've got auto-hover engaged, but as trimmed still have some groundspeed, & eventually drift far enough that you reach a point at which the AP can no longer compensate?

Edited February 23, 2009 by Weta43

[Mugatu]

Cost me a few lives, I've sunk a little low while attacking and the thing turned off, span wildly and smacked rear end first into the mountain behind me. No audio warning etc.

 

The design certainly wouldn't get through western airworthiness boards.

 

It will disable altitude hold below 4 metres (c. 13ft) and it is designed to do that.

 

It's hardly a life threatening situation to fly the Shark without an autopilot. While it is of course much much harder, it is perfectly doable.

 

The Shkval display will "restart" when your power drops too low. The engines aren't turning fast enough to power the generators.

[FADM Stern GNSF]

Just to be sure I will watch for the next occurance. A lot of the time I am probabaly in hover hold, so this could well be the problem. I will do a few test by moving a bit (say 5K) and engaging the hover hold. Then sit and wait and see.

If I find that is the cause, will trimming while in hover hold help prevent that. I normally trim all the time, but in a stable hover where all is clam I dont trim at all.

 

Thanks for the help, as now I have something to watch for to know once and for all.