Su27 Wing Thing

[jackmckay]

ED please explain to me what was the case here, I'm not sure is this realistic?

 

I was flying at 7,3km ASL, at Mach 1,26, roll rate was 23 deg/sec going inverted into the dive at AoA 1.7 deg and 3,9G, wing normal was at 167deg, fuel status was less about 70%, carrying ECM pods with extended combat load (4x27ER, 2x27ET, 2xR73)... this means I was extremely careful not to over stress the air frame. Since it was first serious maneuver the air frame wasn't able to accumulate stress prior to disintegration. Why did the wings broke off?

 

(Attachment below, callsign *NOB*Birdstrike, track time +00:14:05)

NOB vs TAW 1.zip

[GGTharos]

You are rolling and pulling at the same time, so there may be something to this.

 

You're in the most vulnerable regime (M1.26), so you have the absolute least resistance there.

 

IIRC it's 139/GW, so you're at ... 27000kg or so.

 

So 139/27 = 5.14g.

 

You are already pulling 4g, it's possible that your roll speed adds the 1g to the wing ... or there is a bug.

 

In any case, I believe you start to stress after 5.15g, actual breaking should occur at either:

 

5 x 1.3 = 6.5

 

or

 

5 x 1.5 = 7.5

 

Do you have a track? The reason I ask is that tacview typically shows an averaged value, so you may have been pulling more G than you believe you did.

[ShuRugal]

One thing i have noticed since the wing damage update is that every time i pull the wings off, Betty is silent. This strikes me as odd, why would there be an audible G-limit alarm if it doesn't go off until after the wings are gone?

[GGTharos]

Because it's tuned for a 21T aircraft under non-lateral g, IIRC. Basically you need a more modern nadia.

[Ktulu2]

You are rolling and pulling at the same time, so there may be something to this.

 

You're in the most vulnerable regime (M1.26), so you have the absolute least resistance there.

You are already pulling 4g, it's possible that your roll speed adds the 1g to the wing ... or there is a bug.

 

It would make sense : He's over MAC1 at a moderate altitude, the aileron that induced the roll will have been under an important force, which could easily add up to > than the weight of the wing.

 

There would be an easy way to find out, if we could get the Su-27's inertia and the wing weight (to figure out local G).

[jackmckay]

here's the track

SATAC 2016 mission-20160924-193008.zip

[Ktulu2]

The moment of Inertia is the measure of opposition to a rotation movement, like mass opposes a change in velocity. It is something that ED used that probably is in the game coding, but I do not have the knowledge to find it, it's not something I can get from a track.

 

Realised I used inertia in the first post...derp/bad habits

[jackmckay]

I saw it now after watching track, actually G-meter shows more than 9G! for a second after rising even AoA indicator wasn't moving so hard .. it looks like plane somehow accumulates Gs in a inverted dive.. weird, I didn't had feeling of high Gs.. I was counting on negative 1G due to the inverted flight that would subtract total G count but Gs are constantly rising and stick is not moving to aft(!)... There's great difference between .ACMI and .TRK files readout though.

Edited September 25, 2016 by jackmckay

[DarkFire]

I saw it now after watching track, actually G-meter shows more than 9G! for a second after rising even AoA indicator wasn't moving so hard .. it looks like plane somehow accumulates Gs in a inverted dive.. weird, I didn't had feeling of high Gs.. I was counting on negative 1G due to the inverted flight that would subtract total G count but Gs are constantly rising and stick is not moving to aft(!)... There's great difference between .ACMI and .TRK files readout though.

 

A couple of points:

 

1. Combining roll with pitch will produce much more G than either roll or pitch alone. It's very, very easy to go in to an over-G condition with even a modest amount of roll if you're doing a hard pull.

 

2. The G you'll experience in an inverted dive is dependent on trim. If you're trimmed to pitch up an inverted dive can easily contribute to the total G load on the airframe.

 

3. Difference between the track file and the tacview file: Tacview only records parameters at certain intervals. For all it's an awesome tool (essential IMO) it doesn't do well at recording sharp spikes in any particular parameter.

 

4. At M1.26 you're well within the G notch on the speed/max-G chart. With a relatively high load your actual maximum safe G loading may be as low as 5 or thereabouts:

 

 

The graph is for an all-up weight of 21,400Kg which is what the in-game nagging nadia is calibrated for. Higher weight = lower permitted G. Tests have shown that destruction of airframe occurs at somewhere between 1.3 - 1.5 x maximum permitted G load shown on the graph.

Edited September 25, 2016 by DarkFire

[jackmckay]

1. - wasn't case cos I first rolled then pulled

2. - plane was trimmed down(!) since plane has tendency to nose up on high speed

3. - right, data blending

4. - tried to keep it under 5G for sure, inverted flight should subtract 1G and I was also trying to imitate ballistic dive, something that NASA uses to imitate 0G environment. In chart above 'Height factor' is missing cos air density IS most influencing force factor on wing. I was at 7.6km ASL, air there isn't that solid to induce that much force on wings and going mach 1.3 at that height won't induce equal force on wings as going same mach at sea level. So IAS is factor of most importance for G scale.

 

Somehow plane build up 9+ Gs continuously on inverted ballistic dive even stick wasn't pulled so hard aft and wasn't moving radically. Structural limit could be close, true, but I have some weird feeling that something isn't right there.

Edited September 30, 2016 by jackmckay
IAS, typo

[DarkFire]

1. - wasn't case cos I first rolled then pulled

2. - plane was trimmed down(!) since plane has tendency to nose up on high speed

3. - right, data blending

4. - tried to keep it under 5G for sure, inverted flight should subtract 1G and I was also trying to imitate ballistic dive, something that NASA uses to imitate 0G environment. In chart above 'Height factor' is missing cos air density IS most influencing force factor on wing. I was at 7.6km ASL, air there isn't that solid to induce that much force on wings and going mach 1.3 at that height won't induce equal force on wings as going same mach at sea level. So IAS is factor of most importance for G scale.

 

Somehow plane build up 9+ Gs continuously on inverted ballistic dive even stick wasn't pulled so hard aft and wasn't moving radically. Structural limit could be close, true, but I have some weird feeling that something isn't right there.

 

Hmm that's really strange. I've tried to re-produce the fault & wasn't able to do so. Tried it under vaguely similar conditions and the maximum G I experienced during the inverted dive was between 1.3-1.7.

 

Sounds like you encountered a problem of some sort. Are you running any mods that might effect the performance characteristics of the jet?

[jackmckay]

No performance mods. I have StarwaysBlackSea2.0 and Reshade&SweetFX. Its MP so it has to pass integrity check.

[DarkFire]

No performance mods. I have StarwaysBlackSea2.0 and Reshade&SweetFX. Its MP so it has to pass integrity check.

 

Ah, multiplayer. That might be the issue. Occasionally some very strange things can happen in multiplayer that never do in single player. As an example, very very rarely when I'm flying around in MP the ACS will drop into manual mode, completely of its own accord. Never happens in single player.

 

Try to reproduce the problem in a single-player mission. If it still happens than I'd suggest that you possibly have some problem with your DCS installation. Try doing a repair. If it doesn't happen then it may simply be one of those weird un-reproduceable things that happen in MP.

[jackmckay]

I tried in single player at same alt, higher speed(max), full load, fuel max.. couldn't broke wings, pulled 5G max, plunged down for 5km in a seconds.. alter I pressed "The S" key then I broke them but had to pull full aft max.

[jackmckay]

then it may simply be one of those weird un-reproduceable things that happen in MP.

 

Right, in official SATAC match (lucky me). So you say MP "accidentally" diabled my FCS or pressed <S> in short at right exact point in time? Seriously, I wouldn't mind at all if there wasn't official team.vs.team match because "Wing Thing" happens all the time in the DCS now.. but..

 

It looks like that even with a fine tuned PFM and stricken flight limits the Su-27 is still in BUG mode which makes this aircraft useless and unreliable in serious MP matches (at this point) regardless of piloting skills and logic.. or my system is vulnerable to some sort of MP intrusion with "backdoor open" support.

 

DCS looses a lot of juice by crippling this plane so much, 'cos who's gonna play Eagle targets with some hope of survival as AMRAM's won't score as they should since Sukhois are breaking wings too often.

 

Could this happen to F-15 sometimes soon too?

[DarkFire]

I wouldn't say it's at all useless, or even unreliable. It's just that on a very small number of occasions, maybe 1 in 50 flights, strange things can happen in MP games. ED are still working on the network code for DCS World.

[jackmckay]

Unreliable at my point of view. My fairness logic says that ED should have implemented unified flight physics applied on all planes not push just some special treatment for su27. They should make flight dynamics countable for all planes equally or no plane at all until ready to do so. Things set up that way could have been easier for them as developers and us as beta testers too. Thank you DarkFire on comments.

[Ktulu2]

Well, to be fair, Su-27 was the 1st supersonic plane that received breakable wings from ED. If you think about it, M2K FBW stops it, the F-15 doesn't have enough hydro force to truly break them instantly...

[GGTharos]

I see this as nothing but trying to point the blame anywhere but on the pilot right at the moment. If there's an actual bug to be looked at, the player's track is needed for analysis.

 

Until some type of bug is confirmed, it's just pilot error.

 

And no, it doesn't have anything to do with MP. You need multi-crew for that :)

 

It looks like that even with a fine tuned PFM and stricken flight limits the Su-27 is still in BUG mode which makes this aircraft useless and unreliable in serious MP matches (at this point) regardless of piloting skills and logic.. or my system is vulnerable to some sort of MP intrusion with "backdoor open" support.

[jackmckay]

Here's acmi .. I can't find the track but you can try to repeat the same condition and if you brake it (out of "S" mode off course) I'll withdraw everything I said and apologize to DCS community. Conclusion will be it was my mistake but first brake them.

Tacview-20161001-232559-DCS.txt.zip

[kobeshow]

It looks like that even with a fine tuned PFM and stricken flight limits the Su-27 is still in BUG mode which makes this aircraft useless and unreliable in serious MP matches (at this point) regardless of piloting skills and logic.. or my system is vulnerable to some sort of MP intrusion with "backdoor open" support.

 

 

I would even go as far as saying that missile performance and netcode make DCS useless for "serious" multiplayer matches.

Such a small thing as a lag spike can break your wings in the flanker if it happens at the wrong moment (similar to sudden instant blackout, which also does not happen in SP, only in MP, although it never happened to me after the breaking wings patch since you cannot afford to pull that many G anyways)

[GGTharos]

The ACMI doesn't help unfortunately, because it smooths/averages what's happening. If you had a g-spike it won't show.

 

I can assume what you did, but this is not good enough and it's obviously useless for debugging as well.

 

So I'll point out again: If you cannot reproduce it, it's pilot error or much less likely, a bug so intermittent that we just can't chase it down without that track.

 

 

Edit: I see you have the track up there. I'll try that. Do you recall which version of DCS was in use exactly?

Edited October 2, 2016 by GGTharos

[GGTharos]

Lag spikes don't cause g-spikes to the ownship. There's nothing in the MP code that will cause your aircraft to experience forces, other than another aircraft warping into it.

 

The ONLY time something is affected like this by a lag-spike is multi-crew, which is N/A to Su-27.

 

I would even go as far as saying that missile performance and netcode make DCS useless for "serious" multiplayer matches.

Such a small thing as a lag spike can break your wings in the flanker if it happens at the wrong moment (similar to sudden instant blackout, which also does not happen in SP, only in MP, although it never happened to me after the breaking wings patch since you cannot afford to pull that many G anyways)

[rrohde]

Until some type of bug is confirmed, it's just pilot error.

 

+1

[GGTharos]

So, from the track we have:

 

Fuel 6200Kg ~0.66%

Altitude 7000m

Speed ~M1.25

 

So, GW is 26377 kg.

The speed requires us to apply the 139t threshold, giving us a safe margin of ~5.3G

The max pull in ~8.5g

 

The 'wings break' g-value will be around 8.0g (139/26.4*1.5).

 

1) Max stick pull in the first image

2) Almost Max g even though the stick appears to have been released - so looks like there's some inertia carrying the aircraft through the maneuver still

3) Right after the wings break, indicating the Max G of 8.5+ (as indicated by the 'max g' yellow marker), but the most interesting thing is that the G suddenly drops from there on - which could be due to the missing wing surface.

 

 

While there may be something odd happening in there, there's no doubt that you applied a certain amount of stick pull and the safe G margin was severely exceeded.

Edited October 2, 2016 by GGTharos