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[BUG] over 20g w/o break-up needing 21g's to break


cauldron

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I am a fan of the F-14 since childhood, so this comes from a fan.

 

posting pics and non-replay short vids showing the F-14 holding 17g's for more than a second and up to 20g's without a failure/damage or structural failure of any kind. to break it i needed over 21g's.

 

I did get it to break with wings extended at 13.6g's which also seems too high imo, but i don't have any real data to say where, i'll leave that to the devs to figure out.

 

the following vids and pics were made in 3rd person w/o the replay function as its not working.

 

the links to see the vids:

13.6g breakup:

16g no damage:

18g no damage:

21.7g before breakup:

 

My questions are,

 

How is the acceleration of the g's [m/s/s/s] and is it with constraints? How are the pilots not blacked out by the accelerated GLOC if its outside of the margins? Why can the F-14 attain over 20g's without breaking up, while in a slower wings out config breakup approaching 14g's? Which imo seems a little on the high side already.

602494174_F-1421.7gpicbreak-up.thumb.png.c81e1d3010ef56431686ce90b6a13c92.png

329812802_F-1418gpic.thumb.png.7934886d6621295a48b7a7c349e1fff8.png

894319142_F-1416gpic.thumb.png.dcccffc7689f8ada9ad5411f4afd3933.png


Edited by IronMike
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The Grim Reapers did a video on the structural damage model which might help explain it:

 

So, you can do brief forays at very high "g" but the plane will eventually break. Mine almost always breaks after I get above 13, though I rarely do that and haven't ripped the wings off in a long time.

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The Grim Reapers did a video on the structural damage model which might help explain it:

 

So, you can do brief forays at very high "g" but the plane will eventually break. Mine almost always breaks after I get above 13, though I rarely do that and haven't ripped the wings off in a long time.

 

I don't see how that has much relevance to the specifics of my post. Maybe they repeated what i did, it doesn't change the fact that this needs to be addressed. btw, in my tests the plane DID NOT break up to 20g's and was flyable w/o damage and no blackout.

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The video provides an explanation as to why the aircraft's wings come off, which I correlated to your question about why it is that the plane can hit such a high "g" a few times. That is the structural "point" system as described by the GR video. Your questions were more specific, however, so, sorry, my response wasn't adequate to those questions asked (e.g., high "g" not blacking the pilot out, why it seems to break more often at lower speeds and lower-high "g", etc.).

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With the wings swept back, the torque on the wing root is massively reduced and the wings can withstand much more Gs than with wings fully forward. 20G may be a little too optimistic but not entirely unthinkable with the wings fully aft. I'm also not sure if the pilot would black given the short amount of time the 20Gs are sustained.

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There are some explanations for you:

1. Afaik people do not instantly G-LOC at high Gs. 20G for a 1s should be managable.

2. Airframe limitation of 9G doesn't imply breaking beyond that value. It is usually higher (like 30%).

3. It's momentary (managable) vs prolonged high G (lethal) both for a pilot and airframe.

4. Even with wings in place structural damage may still occur but not visually evident. If implemented correctly damage should accumulate and weaken the airframe just to break even in prolonged flight under the limits.

5. Easier to over-G at lower altitudes than hig alt.


Edited by draconus

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To our knowledge it would hold easily to 25Gs in that configuration, if you ease it in, the aircraft will let you do it. As to why the pilot did not black out, I cannot answer, as pilot G-Loc is managed on DCS side, not on ours.

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Pilot has a 5 sec oxygen reserve, but that reserve becomes shorter as the g increase, and the onset time counts against it as well.

The player can also turn off the g effects.

 

As for 'easily managing 25g' ... I don't agree. things are going to come apart. Inside the fuselage if not outside. The engine housings and possibly the core will bend, the wings will bend, the longerons won't take another turn.

 

Failure should come well before you reach 20g.

 

We have an f15 that took 12.5g for some seconds and could not be salvaged. Another that broke up at 3g because the longerons were not manufactured to spec.

 

To say that the heavier tomcat, which was limited to 6.5g for lifespan purposes can take 25g in any configuration is beyond suspect. That sort of capability would have made it indestructible for the purpose of lifespan and a limit would have never been required.

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GGTharos, I agree with you, something is suspect, and needs investigating. Extraordinary claims like "easily 25g's" needs some commensurate extraordinary evidence.

 

Also... the rate of g' onset m/s/s/s is suspect as well, because afaik only unstable fighters can manage rates that could be dangerous, and they have the computer limit them. I don't know how far FM's in DCS can go on this, but i'd hope it gets some attention. For ref. the test history of the F-20 tigershark.

 

someone mentioned the torque: the moment arm for the outer wing does not change with sweep. What may change is its share of the load for a given g load upon the plane as a whole. It may well diminish thus transferring load to other lifting bodies of the plane to attain the said g. I was aware this was to be modeled with a flow and pressure model. But 25g's is very high indeed to reach.

 

For momentary vs prolonged loads on structures... its not so simple. Complex structures fail under rapid loads in a cascade of weaker components failing much earlier than the ultimate load as the loads increase to failure. This is designed for and planned for, how close to the limit this occurs is different for everything, and unique, but the ultimate failure occurs in mere fractions of a second. An optimal structure for strength may hold loads much higher but may not be desirable to a lower load limit due to a sudden and abrupt uncontrolled disassembly event, and may actually be not the best design - that's the engineers job and its a hard one at that, how this applies to this topic depends on a lot of things. But its clear it can be approximated to a reasonable level (and it already is), the question really is in the details, and is there enough information to support the claim above?

 

Altitude is a non factor, the loads and rates of loads are there or not regardless of altitude.

 

Do you happen to know of how much the F-14 static load to failure test got up to? That would be a great benchmark. The most vulnerable configuration as stated [see paper ref. below] was a transition from full sweep outwards as it would cause a friction lock and divert the load focus.

 

If you are interested (needs some math and structures knowledge but its a good read)

 

I have done my part in this posting, the developer has a clear opinion on this and that's that I guess.


Edited by cauldron
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Pilot has a 5 sec oxygen reserve, but that reserve becomes shorter as the g increase, and the onset time counts against it as well.

The player can also turn off the g effects.

 

As for 'easily managing 25g' ... I don't agree. things are going to come apart. Inside the fuselage if not outside. The engine housings and possibly the core will bend, the wings will bend, the longerons won't take another turn.

 

Failure should come well before you reach 20g.

 

We have an f15 that took 12.5g for some seconds and could not be salvaged. Another that broke up at 3g because the longerons were not manufactured to spec.

 

To say that the heavier tomcat, which was limited to 6.5g for lifespan purposes can take 25g in any configuration is beyond suspect. That sort of capability would have made it indestructible for the purpose of lifespan and a limit would have never been required.

 

 

That's not what I meant GG, I meant that if you ease it in (and for some reason your pilot does not gloc), she will not snap right above 13G, but let you pull through 25 before she crumbles into tiny pieces. Or in other words, if by some miracle you would get that far, the Tomcat does nothing to prevent you from it, but break it ofc you will. In that sense, it is exceptional if you manage to do that, she will usually go way earlier, INS above 9 (again depending how abruptly you pull, ease it in and you gain more), then soon thereafter your wings will come off and so on. I didn't mean to say that she holds against 25G without damage or that it would be the threshold. Anything above 13G and you risk breaking her.

 

This thread is anyway of a particular kind, if I may say, usually we see folks having issues with wings breaking too easily.

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I'm saying you'll never reach 25 - it does not logically follow :)

There is material strength that will simply yield the moment you reach a certain value, regardless of how you get to it.

 

An empty cat at 10g is 410000lbs. Every G adds 41000lbs. A loaded cat will add say 55000lbs/g.

 

It's just an enormous amount of force IM, it cannot follow that you can ease the force to a over a million lbs and not have the thing snap like a twig. If you call the F-14 a 9g bird at a certain weight, you should snap the wings (and other things!) at 14.5g every single time, and that's with a generous 50% engineering margin.

 

At any rate, the engines should be gone at this point as well as a bunch of electronics. I know you guys have done huge work on the DM and it's one of the best IMHO - the whole 'break thing at x g' is probably a minor detail.

 

And you're right, I'm OT. The fuselage/wings being too sensitive is worse than not being sensitive enough in most cases.

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If you call the F-14 a 9g bird at a certain weight, you should snap the wings (and other things!) at 14.5g every single time, and that's with a generous 50% engineering margin.

 

Which actually usually happens when i go online. At far lesser values as well. At first i wasn't sure why. But then i look at G-meter after executing the same merge i do offline and lo and behold. When i fly offline, it pegs at 8-9g, when i fly online it pegs at 9.5-10.5g. This is with a fairly benign ping of about 150 (reported). So while i only break a wing once in a blue moon when offline, when online it happens about 25% of the total times i performed the same maneuver. Heaven's forbid i should try that on a 300+ ping server.

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This thread is anyway of a particular kind, if I may say, usually we see folks having issues with wings breaking too easily.

 

So, this non bug-performance issue is awkward? I didn't mean to bug anyone or waste anyone's time, but i really thought that was the point of this exercise. My apologies for finding a fantastical result; outliers happen, i was pointing one out i came across. The F-14 module is amazing and this clearly is not a priority, as it is at the extreme end of the envelope. Some time ago the M2000-c module had a similar case, it was performing high speed Kulbits - a total outlier, not a high priority but they acknowledged it was happening and eventually got around to dealing with it. The difference is this is a sim, players are going to explore the boundaries of the envelope free from actual death and destruction that would be irl, pilots were given limits by the test pilots for reasons, those reasons fail in a sim where the only consequence is a need to respawn.

 

In my humble opinion i'm going to say you guys need to consult with an actual aerospace/mechanical engineer, make the same claim of an easy 25g's and a massive g/sec rate and see what they have to say.

 

Again, my apologies. And again thank you & Meteor for a great module, a truly enjoy it.

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Typically aircraft structures are designed with a factor of safety around 1.5 or 2. Keep in mind that the 6.5G limit imposed by the Navy was merely to extend airframe life, not because of any actual load restriction. Most operational load limits are fatigue and lifetime related and do not necessarily reflect on the ultimate load factor.

 

I've read that Grumman designed it to be a 9G airframe and bench tested out to 13G without issues, although they set the suggested carrier operation load limit to be 7.5G to increase the safety margin for lifetime shipboard operation. I don't have info on the ultimate load factor, although we can assume that it's at least 13G. I imagine other things like INS failure as well as bent engine mounts would happen before structural failure of the titanium wingbox or main spar above 13G. My "wild ass guess" number for wing structure failure would be in the 15-18G range.

 

Additionally, the physical toll of that many Gs on the human body combined with the fact that it would be nearly impossible to physically control the aircraft to that G loading makes this a rather moot point. We don't simulate physiology or human arm strength in this equation and we have no plans to.

 

All this being said, if you're routinely getting into that G range and have issues with your wings coming off, you need to re-examine your piloting skills and go back and do a bit of training.

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All this being said, if you're routinely getting into that G range and have issues with your wings coming off, you need to re-examine your piloting skills and go back and do a bit of training.

 

I like to point out that you yourselves have made all the extraordinary claims; I came to this forum to try to help and point out that the wings are NOT coming off until some very high loads - I acknowledged that it is a fringe event at the edge of the envelope and not a high priority- and I was polite . It is clear you did not bother to even read the posts. Anyways you've made my point all by yourselves. Just make up your minds if its going to be 25g's or 13-18g's or whatever.

 

 

Oh and by the way,

 

I have not insulted nor criticized you or anyone else's programming skills, development skills or there person, so don't insult my piloting skills which are still not bad after retiring from a lifetime flying many aircraft and a technical education, thank you.

 

Good Day.

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Catching up on this a bit, having done the tests in the cockpit (with the DCS information bar showing via CTRL-Y), the highest I've been able to get before catastrophic failure is 16.2 G, with everything else happening in the 14 range. The one interesting item of disparity to me at the start is that mine were clean, and presumably at lower weight to be absolutely guaranteed to hit the necessary G values for breaking the plane, whereas your exceedingly high touches were carrying no less than bags, and in the 18 and 21 runs Sparrows and Sidewinders. With the back end issues concerning stores drag, I'd be remiss if I didn't note there may be more at play than simply the raw F-14 model- especially when it works according to their state intent when there's nothing hanging off of it.

 

cauldron, you seem to be taken a bit aghast at something that wasn't intended; to be sure, you've accused fat of doing the same thing that you did to Mike- not reading his post. He made it clear that his intention was to state that there wasn't any prohibition in the aircraft to restrict the flight control system from delivering 25 G, and that it would do so on command- not that it wouldn't rip the jet apart by doing so, and that 13 is the point where they hold to things getting dicey. To that you said they should consult with aero engineers over the original statement, not his clarification.

 

Similarly, this is a peculiar series of events to note, having taken stock of the complaints herein about the wing break point- I'm not certain where you're mad that he's stating this is the first of its kind, which to be honest I thought was your original point.

 

So yeah- you have been critical of people. Nobody is giving you lip, and if you slow down a touch, there's not actually a major difference of opinion here. So relax.

 

As it were, unstable airplanes aren't the point where an airframe could be fundamentally torn apart by onset rates. The aforementioned Eagles tore themselves all to hell, and only had OWS as a polite suggestion. Onset rate could absolutely be delivered faster than the system would deliver the tones depending on the circumstances, and bring about a catastrophic failure or a permanent down airplane. Comparatively, F-14s weren't just bench tested to 13 G, but were considered in flight test to be such and flown accordingly. In other conversations it has been noted that there are a number of events taking them operationally into the mid to high 12s, inspected, and put back into service finding no issues. FBW and software limitations were created because airplanes were getting to the point they could rip themselves apart all on their own- they didn't become dangerous and limited from progressing into dynamic instability; the ability to make an airplane unstable was a byproduct of the technology, not the onus.

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I like to point out that you yourselves have made all the extraordinary claims; I came to this forum to try to help and point out that the wings are NOT coming off until some very high loads - I acknowledged that it is a fringe event at the edge of the envelope and not a high priority- and I was polite . It is clear you did not bother to even read the posts. Anyways you've made my point all by yourselves. Just make up your minds if its going to be 25g's or 13-18g's or whatever.

 

 

Oh and by the way,

 

I have not insulted nor criticized you or anyone else's programming skills, development skills or there person, so don't insult my piloting skills which are still not bad after retiring from a lifetime flying many aircraft and a technical education, thank you.

 

Good Day.

 

 

Cauldron, our apologies, I think we expressed ourselves poorly, which could have led to a misunderstanding. First of all, your report is appreciated very much indeed, we are just trying to understand it ourselves. What I initially meant was that, in the case gloc of the pilot is disabled, a tiny chance exists that it would indeed make it to 25G before being "pulverised" so to speak. Naturally it would lose parts and bits and wings along its way there, so if you arrive above 20G unscathed, then of course that is wrong. What we are trying to understand is if that is a one off glitch or a reoccurring bug.

 

 

My comment about this being a single report about wings not breaking, while most reports are about wings breaking too easily (which is what Fat Creason elaborated on, when he meant you need to fly it properly, he did not mean you with that), was not meant to in anyway downgrade your report, it was just funny from our perspective, as we usually hear the exact opposite (which I thought you were aware of as well). It does not mean that we do not believe you or anything like that.

 

Please note that I also said "Anything above 13G and you risk breaking her." which does not contradict Fat Creason's estimate of between 13 and 18G. However, as it is irrelevant, I should not have mentioned 25G at all. Again, if you arrive at anything above 18 without damage, then something is not right, you are absolutely correct in that. You should have also blacked out.

 

Please excuse us for this misunderstanding, please know that we value your input very much and no one would dare or want to do anything even remotely close to insulting you. If it sounded like that, please accept our sincere apologies, Fat Creason reassured me that this was most certainly not what he had in mind, and of course neither did I.

 

If this continues happening to you, please let us know. Thank you again for your kind input.


Edited by IronMike

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I am impressed, i did not expect to post again here.

 

I did just want to point out this outlier happening. If the the ultimate load strength is assumed (mentioned here to be just above 13g's) to be of a said value then any loads above that not causing a cascade leading to a destructive event are extraordinary, and need solid reasoning to back that up. I don't know how much detail is in the FM or the physics modeling, but my guess is that the g tolerance is not the only thing going on here - the rate of g' onset [g/s] seems too high at high dynamic pressure, but that's your job, not easy i am sure, and i don't envy your bug squashing efforts.

 

So far I think your team has done an excellent job. And again I do hope I have not wasted anyone's time with this issue, I know its at the edge of the envelope, but it was the test i was making at the time.

 

My regards, and best of luck to you and your team.


Edited by cauldron
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I am impressed, i did not expect to post again here.

 

I did just want to point out this outlier happening. If the the ultimate load strength is assumed (mentioned here to be just above 13g's) to be of a said value then any loads above that not causing a cascade leading to a destructive event are extraordinary, and need solid reasoning to back that up. That's your job, not easy i am sure.

 

So far I think your team has done an excellent job. And again I do hope I have not wasted anyone's time with this issue, I know its at the edge of the envelope, but it was the test i was making at the time.

 

My regards, and best of luck to you and your team.

 

 

Rest assured you did not waste our time at all, to the contrary, you invested yours to help us, and we appreciate that highly. We can now keep an eye out for it, and hopefully, if a bug exists, fix it. Thanks again. :)

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F14b 20g turns...

 

hello guys !

F14 is my real life favourite plane since...ever (especially D variant).

that said … i obviously like to see it on top of everything else (especially the evil competitor F15 , LOL) , but i really think this thing has gone way too far.

 

DCS F14 can:

turn 90 degrees in 1 second.

lose 160 knots in 1 second (from 460 to 300)

sustain a peak of 20g turns and "normal turns" at 13g-15g

(to be clear, i witnessed 25g wings opened turns, 17g wings closed, and a 34g finally breaking wings)

 

proof of this:

 

…while the REAL F14 had a soft limit of 6.5g . Grumman give it for +9g -5.5g .

now i want to belive, and i'll say that soft limits are for airframe life cycle purposes, and Tomcat can sustain with no trouble… lets say +9g.

lets even say that in an Emergency life-or-Death situation, pilot pulls 11g, its extreme but i'm still fine with that.

but if for example F15a ultimate g limit is 12g, what in the world make sense in making F14 pulling 20g as if was nothing multiple times in same fight, and have no effects on airframe, instruments, pilot and so on ?

for a simulation thats quite a sad "ace combat" feature.

 

i love F14... with all his strenght and its weakness. please respect it as it was.

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F14 (D variant) is my favourite plane ever.

i really wish to see it triumph over F15 and so on… but i feel something is way too over the line...

i share this little video to show what seems ...well… sci-fi.

 

i love F14 with all its strenghts and weakness. i really wish to keep it as it was.

(and hope you make F14D, LOL!)

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