Weird flight behaviour

[Johnny Dioxin]

Hi guys,

 

I was test flying the Hip at NTTR (screenshots here), when I suffered a very unpleasant situation:

 

 

Just flying serenely along in a straight line, at cruising speed, not moving any of the controls at all and suddenly it stands on it's tail.

 

I did have this happen a couple of times in the past, in 1.2, so it isn't an alpha thing.

 

Wasn't using any trimming or anything. i took off, pulled around and as said, flew in a steady, straight line,

 

Was a real challenge getting control back, too, though I did manage it, after rescuing a steep dive, probably as a result of a stall.

 

This happened to me for the first time in v1.2 in the mission where you fly with a Mi-24 along the coast and land. Same situation and same thing happened.

 

Because I was not actually doing anything to invoke such a response from the aircraft, I'm stumped.

[Cibit]

Track would have been better but it sounds like this

[ame]

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https://en.wikipedia.org/wiki/Retreating_blade_stall

 

Or you accidently disengaged pitch and yaw channels

Edited December 6, 2015 by Cibit

[Slazi]

Could be an input problem. If you're trimmed and flying normally, you can afk and it will stlll be on course.

Check your stick, throttle, keyboard, mouse, pedals, gamepad etc.

[NeilWillis]

Make sure you have set up the controls options correctly. Duplicate axis inputs abound.

[Looney]

What was your speed while cruising and, if left alone, would the helicopter self-correct the problem?

[Johnny Dioxin]

Thank you for your replies.

 

the track was no good, as it showed the helicopter flying along at 138-140 and then just nose-dive into the ground.

 

I'd been flying at that speed for a few miles, at the same altitude and keeping all the controls steady.

 

The helicopter would not have recovered on its own, as this sudden climb at that angle (doesn't even happen in the track) caused it to stall, and nose-dive. Once sufficient speed and lift was attained, I was able to pull it up, but it took a few seconds.

 

Rest of the flight passed without incident.

 

I've had this very thing happen to me once before, in DCSW 1, and that time I was slowly approaching an airbase at low altitude when exactly the same thing happened, but on that occasion, I was too low to rescue it.

 

I may have that track still somewhere.

 

Don't have record of the other times, but it is remarkably similar to an old Ka-50 issue.

Edited December 8, 2015 by Brixmis

[gospadin]

a sudden climb + torque to the left = retreating blade stall

 

Figure out if your speed was close to 260km/h at the time it occurred, and that's probably it.

 

If 240 or below, it likely isn't RBS.

 

Edit: 138-140, even in mph, isn't fast enough for RBS.

[Rogue Trooper]

RBS or Pitch Yaw stabilizer off is the only thing that I have seen that is similar.... especially the pitch stabilizer being off.

[Johnny Dioxin]

What is mistifying me is that I didn't operate any switches or press anything on my HOTAS - not even a flight input - just holding steady as I was flying along at around 140 Km/h. I'd already flown a small circuit.

 

I was about to join to land on the helipad, but this happened. I did still manage to land on the helipad, but this was a bit of a fright. If I'd been lower, it would have all been over.

 

Only thing I can think of is either autopilot over-correction of some kind or some other protection system that's kicked in and thrown the thing into a climb. Doesn't really make sense, though.

Edited December 9, 2015 by Brixmis

[BitMaster]

Do you by chance ecxperience the same erratic rudder behaviour as I described in my Mi-8 thread ? Where your controls still centered/trimmed the way the were the moment before hell broke loose ??

 

Having a similar issue, maybe there is a link.

 

my probelm: http://forums.eagle.ru/showthread.php?t=155088

[Slazi]

Icing might be a factor, but unlikely. Either bug in the current version or control input is my bet.

[Dave317]

I've had this before. If you pull too much power your pitch stabiliser will switch off under the load. You can switch it back on again but if you are not on level ground when you switch it on it will cause weird pitch problems in flight. I tried contacting belsimtek about it but no one answered.

[Corrigan]

I don't know that much about helicopters, so maybe someone else can let me know whether this is plausible or not: maybe your collective was set so high that the rpm fell below what's needed to power the alternator, and that caused the pitch stabilisation to disconnect?

[Johnny Dioxin]

Thanks for the suggestions. I'm still at a loss, but I don't know the Mi-8 in detail, as I've had little time for flying the last few months. And nearly every time I get to fly online in a group, they always want to fly the A-10C! :mad:

 

Do you by chance ecxperience the same erratic rudder behaviour as I described in my Mi-8 thread ? Where your controls still centered/trimmed the way the were the moment before hell broke loose ??

 

 

I'm not sure - I could have a play with that setting. To be honest, I didn't use the trimmer switch for the entire flight, as I've not used it much on the Hip before, and wanted to make sure I kept control (massive failure there! :doh:) as it was only a quick circuit. I used the full autostart as I was short of time and it would have taken too long referring to the start-up list and hunting for switches.

 

What I did experience from take off was very strong yaw to the left. I'd never had that before, and though it was very strange - but then there have been some updates to the model since I last flew it, so I thought it may have been that. It convinced me this was the case, when it got less and less as the speed increased. If I centred the pedals at any stage, though, the nose would snap to the left.

 

So I was holding some right pedal in order to fly straight - but I had been doing that all along, so...

 

I'll have another flight later and see what happens. I'll try and fly the same path as that flight.

 

I know my input config is okay, as that is part of what the session was for - I'm checking all input configs for all my modules before testing them in NTTR.

[gospadin]

If I centred the pedals at any stage, though, the nose would snap to the left.

 

If rudder trimmer is enabled, you need to press the trim center button, then return all controls yourself to neutral. If you're releasing then returning to the previous position, you'll experience these snaps.

 

What's the deadzone on your stick/pedals?

 

If you're applying an input just outside the deadzone, centering, then briefly entering and exiting the deadzone, it may cause these snaps.

[Johnny Dioxin]

Rudder trimmer is disabled.

 

I just flew pretty much the exact same course and had no issues.

 

the helicopter is still pulling to the left, though - I spent a lot of time looking at the pedals in the aircraft, and when they were level, the aircraft was pulling quite hard to the left to start with, but again, as speed increased, so I could slowly release the pressure on the right foot - but never all the way. Even at cruise speed, a little right pedal was required, which may be accurate?

 

Anyway, the nose-up and dive dance didn't happen this time. I even tried being rough with it, just to see, but nope - on its best behaviour.

 

Which does make the original behaviour weird. I'll report back the next time it happens (if it does) - be interesting to see how long before then.

[gospadin]

Rudder input to counter the change in torque caused by change in collective is normal.

 

At cruise speeds (~150km/h) you can center the pedals, but in most other flying conditions, you need some left or right pedal.

[Looney]

if you use the heading autopilot channel you are not required to move the pedals as the autopilot will trim the pedals based on current flight parameters.

 

Once the small N symbol appears on the heading autopilot display, the autopilot is then actually actuating the rudder pedal element and you can see the pedal move. This all provided you are not touching your pedals.

 

This causes confusion because you are not moving the pedals yourself, your real life pedals are still centered and the virtual counterpart has been offset.

 

If, at any time, you decide to use the pedals, some quirks will turn up where you cannot use full deflection or enough deflection to get the helicopter to do what you intended.

 

The only way to counter this is to keep watch on the heading autopilot indicator and if you see it move to the left or right side, deflect the pedal yourself. It will reset the heading autopilot channel (seen by the fact that the white bar will be centered) and pause the autopilot channel (the white bar is centered and doesn't move) until you let go of the pedals once again and are on a steady heading.

 

The other option is to fully reset the trim. I don't know if there's a way to reset pedal trim only.

[Cibit]

Read this and thought of you @Brixmis

http://forums.eagle.ru/showthread.php?p=2594379#post2594379

 

Is this a possiblity?

[gospadin]

QFE vs QNH shouldn't matter in this case (though it's a huge problem with ATC giving you QFE altitude adjustments for airfields that are 1.5km ASL)

[Johnny Dioxin]

Due to time constraints, as mentioned, I used the autostart procedure - my main aim for this flight was just to check that my assigned flight controls were all working okay.

 

So if the AP is set during the autostart-up, then that's how it was set, if not, then not.

 

I set neither AP nor any kind of trim myself - the entire flight was controlled manually, with just stick, collective and rudder inputs. All of my axes on this helicopter are set to linear.

[Cibit]

The AP for pitch and yaw is the last thing set during autostart.

Just a quick question. You say you fly without trim? Like really no trim input at all:joystick:

[Johnny Dioxin]

Normally I use it - for this flight I didn't.

 

It was less than 10 minutes - a quick loop around that end of the airfield and that was it. :pilotfly: