[ALREADY REPORTED] Viper FCS "Death Rattle" Question - ED Forums
 


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Old 10-27-2019, 02:43 AM   #1
November Charlie
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Question [ALREADY REPORTED] Viper FCS "Death Rattle" Question

Hey all,

I just wanted to query a thing I've found with the Viper at Low altitude (at or below 300ft, although in the vid it happens up to 2500ft), and at high speeds (650-700)<. I have found that in these conditions, the Viper initiates a wobble, similar to an Underdamped door which increases in severity as it continues, in straight and level flight, during acceleration, deceleration or sustained speed (it always ends in decel as the viper strays left and right as seen below). It looks as if the rudder is attempting to correct a minor oscillation but underdamps and starts oscillating around the velocity vector. This behaviour can be seen below. This was performed at between 2/3 fuel and under.

https://www.youtube.com/watch?v=SIo-ot5vDHE

Would this be considered normal behavior for the Viper IRL? The I have not noticed this in any other aircraft, and I am wondering whether this is an anomaly in the FCS or an actual noted real world problem with the aircraft. It has been noted by various other sources that the Viper can fly in autopilot under these conditions with the LANTIRN pod, which makes me think that this may be an anomaly within the DCS FCS coding? Would much appreciate clarification.

I noticed this while using terrain masking while out for CAP, and as such when I took out the airframe for some envelope pushing and familiarisation, I recorded the above footage.

Cheers,

Charlie.

Last edited by November Charlie; 10-27-2019 at 03:29 AM. Reason: Formatting; Fixing Youtube Link; More detailed info.
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Old 10-27-2019, 04:05 AM   #2
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This has happened to me a couple times and as recently as tonight. Originally I thought it might be ground effect from heat rising in the hot desert..... seriously lol. However, no other module does it. It happened tonight when running from 31's while Winchester. When I was able to climb up again, I realized my stores of 4 CBU97's hadn't dropped when I hit emergency jettison earlier.
I know you're not supposed to approach Mach speeds while CAT3. Having 4 CBU97's is definitely CAT3. You will break the pylons if you do. I don't know your total loadout as I didn't watch the video but at least in my case that was the problem. I've flown low and fast in it many times now and only experienced the problem twice. That's my guess anyway.
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Old 10-27-2019, 10:45 AM   #3
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This has been reported previously. The current FLCS has some areas of dynamic instability at high speeds. You are overspeeding the plane by quite a margin before the oscillations start, so i'm not sure if it is that much of an issue.
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Old 10-27-2019, 07:31 PM   #4
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The load out in the video was clean, no weapons. As sobek states, I was over speeding the airframe (max speed was 0.25 M over the max speed (1.25 M) at the fastest point, but about 0.08M over at most points. It’s good that it’s been reported because this kind of *FLCS* (not FCS sorry) could very well black out the pilot if even slight stick inputs are applied.

Cheers guys,
Charlie
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Old 10-27-2019, 07:42 PM   #5
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What I did notice is even below the max speed the instability was happening, not to the over speed degree but enough to climb out and drop speed out of worry of killing the aircraft if I descended. I’ll record some more instances of it happening when I have the time for reference. I also originally thought it was ground effect but I think that dynamic instability sounds about right in this case.

Thanks again,
Charlie
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Old 10-27-2019, 08:29 PM   #6
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Check out the 5:35 mark in this video. It looks like something similar is happening in other modules as well. Maybe a recent change in the PFM in general?

https://www.youtube.com/watch?v=VMFpI4P8xxg

Last edited by antsh; 10-28-2019 at 12:15 AM.
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Old 10-27-2019, 10:05 PM   #7
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pimp my viper hahahahaaaa
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Old 10-27-2019, 10:20 PM   #8
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I had this in the f16 the other day, flying low with no weapons. But it wasn’t left and right it was up and down like going over speed bumps. I thought it was odd, but is it supposed to happen?
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Old 10-28-2019, 01:43 AM   #9
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Happens to me a lot too. I believe you need some turbulence in the mission weather settings for it to happen (or at least that helps).
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