Su-27. Extreme G-loads... G=?

[DarkFire]

Can we safely assume that if we inadvertently over stress the airframe without any obvious signs of structural damage, we can then safely land and repair to reset that stress datum, like most other airframe damage within the sim? The last thing we need is to repair and remarm and then to find out that our airframe structure subsequently fails due to previous unseen collective damage.

 

What I'm asking is a) Are all over g stresses recorded within the sim to form some sort of cumulative airframe depreciation damage? b) Can we then repair and reset this value before continuing with any subsequent flights without switching aircraft. Although I do appreciate that switching AC is probably the most likely resolution in real life, should that pilot not be grounded for ruining a perfectly good bird. Although in the case of the sim, you do not have the luxury of a ground crew to analyse cockpit data or engineers to check the AF for structural damage.

 

This is purely guesswork on my part, but what I imagine is that the airframe has a certain quantity of "health." Any G conditions then remove varying amounts of that health based on the amount of G, with higher amounts of G removing much more health than lower amounts of G, and over-G conditions removing much more. I'm imagining some sort of y = x^4 relationship between degree of G and the amount of "health" removed, i.e:

 

Hcurrent ~ Hmax - k where k : (Gcurrent/Gmax)^4

 

This would account for the fact that severe over-G can subsequently result in destruction at what are ostensibly lower G values than the normal limit.

 

I could be wrong about all of this, but I suppose it might fit the observed behaviour.

Edited April 13, 2016 by DarkFire

[SinusoidDelta]

Who knows what kind of wizardry is going on in the FM. There are some clues in mods/aircraft/flamingcliffs/....

 

It's locked away in a dll. Unless YoYo spills the beans, we can only guess. Perhaps someone savvy could do some reverse engineering / detective work with export scripts but we don't even have export ability beyond the old LOGet stuff. All the EDFM stuff is top secret.

[Seaeagle]

..More on top if in the check prior to take off any of the FCS lights is on for any of the FCS channels the pilot must abort the flight.

 

I think you got that bit a little wrong.

 

The fly-by-wire system has quadruple redundancy and AFAIK the lights are indicating which FCS line is currently in use - counting down from number 4.

 

So if the system is operating correctly, number 4 should be lit.

[Esac_mirmidon]

According to the manual no light at all must remain ON in the SDU panel after the test of the system. From 1 to 4. ( if i have translated it right ).

 

If any CDU system-axis fails the lights related to that axis starts to blink for 3-5 seconds and after that the lights remain continuosly ON indicating a failure of the SDU in one or more systems. You must press the button/buttons to turn OFF the warning. If the light/lights comes ON again you must abort the flight.

 

 

[Ironhand]

Can we safely assume that if we inadvertently over stress the airframe without any obvious signs of structural damage, we can then safely land and repair to reset that stress datum, like most other airframe damage within the sim? The last thing we need is to repair and remarm and then to find out that our airframe structure subsequently fails due to previous unseen collective damage...

 

Tested this morning and, it seems, that repairs are made to the airframe. I stressed the airframe to 13 Gs and landed. Requested repairs and, 32 minutes later, was told that repairs were complete. Took off and flew repeated 8 & 9 G maneuvers without incident. Prior to requesting repairs, attempting those maneuvers resulted in wing damage.

[Axion]

Thank you Ironhand for testing, that really is good news. This flight modelling just gets better and better.

[*Rage*]

What's interesting is that, now that damage is being modeled you start paying attention to things you overlooked previously. I had, for instance, not noticed that you can easily pull more than 9 Gs with the limiter on:

 

 

This was just some preliminary testing I did. The Actual Gs column represents the highest value recorded during the turn--usually about midway through. The #s in the Max Op G (Maximum Operational Gs) column are calculated from the chart in the Su-27SK manual. I haven't flown the 29,000 kg weight yet. (I was going to do it this morning but decided to spend a pleasant half hour flying online instead.)

 

Based on some previous testing with the limiter OFF, I had a working hypothesis that, once you passed a factor of 1.5 Max G, bad things started to happen. But the Mach 1 figures seem to disproved that. Anyway, when I have a chance, I'll try to test and add more data.

 

Great info Ironhand.

[*Rage*]

Tested this morning and, it seems, that repairs are made to the airframe. I stressed the airframe to 13 Gs and landed. Requested repairs and, 32 minutes later, was told that repairs were complete. Took off and flew repeated 8 & 9 G maneuvers without incident. Prior to requesting repairs, attempting those maneuvers resulted in wing damage.

 

A normal repair takes 3 minutes. Did it realy take 32 minutes?!

[Ironhand]

A normal repair takes 3 minutes. Did it realy take 32 minutes?!

That plus a few seconds.

 

It's been ages since I've asked for repairs and had forgotten how long it used to take. I remembered it wasn't much. Waiting several minutes with nothing happening, I used time advance to speed things up. Let the clock advance 25 minutes and dropped back into real time. I concluded that nothing was being repaired.

 

But I was low on fuel and asked for 40%. Sat there for a bit while refueling was taking place and decided that would be a great time to grab a 2nd cup of coffee. Came back in time to see Repairs Complete on the screen.

 

So it could be that the refueling, come to think of it, delayed the completion of repairs. But it did take a l-o-n-g time regardless.

[Seaeagle]

According to the manual no light at all must remain ON in the SDU panel after the test of the system. From 1 to 4. ( if i have translated it right ).

 

If any CDU system-axis fails the lights related to that axis starts to blink for 3-5 seconds and after that the lights remain continuosly ON indicating a failure of the SDU in one or more systems. You must press the button/buttons to turn OFF the warning. If the light/lights comes ON again you must abort the flight.

 

Yes it sounds like I was wrong about what a lit lamp indicates - the reason I thought this, was that I have seen a picture of the SDU panel with lamp no 4 illuminated...I guess it could be showing an error or part of the test procedure.

 

On the other hand, a lit lamp might have one meaning during a test procedure and another in normal operation....but i don't know.

 

I still think you got the "axis" bit wrong though - i.e. rather than a lamp indicating a control axis failure, it is indicating a failure in one of the FCS' back-up channels(hence numbered 1-4).

 

Maybe we could ask in the Russian section and see if anyone knows more about this.

[Stuge]

Yes.

 

And also whats the point to turn supersonic at maximum G? Wider turn radious and more time to turn. No advantage at all.

 

Lol :)

 

Sorry :)

[Esac_mirmidon]

Lol?

 

Name one fighter with a supersonic corner speed.

 

Except i've missunderstood you.

 

And for axis-channels. You are right. The problem for me is to find the more accurated translation from russian manuals and for this topic sometimes it talks about axis channels, sometimes longitudinal channel others lateral channel, stabilizators, automatic handling control , etc

 

And also i'm not english native so i usually miss a lot naming things.

 

But in essence the SDU it seems to have four channels and controls several sub systems like the dampers , slats, flight control surfaces, etc. Every channel in the SDU has a light but reading the manual each light corresponds to more things than his channel. It blinks because more things not only his specific channel.

 

But at last the important thing is that the pilot would never take off with a SDU failure light on and in flight he never must turn off the AoA-G limiter under any circunstance. There are no real gain on it as the manual said and only produces a more dangerous flight and a real chance of loosing control over the plane or overstressing it.

Edited April 14, 2016 by Esac_mirmidon

[Ironhand]

Yes it sounds like I was wrong about what a lit lamp indicates - the reason I thought this, was that I have seen a picture of the SDU panel with lamp no 4 illuminated...I guess it could be showing an error or part of the test procedure.

 

On the other hand, a lit lamp might have one meaning during a test procedure and another in normal operation....but i don't know.

 

I still think you got the "axis" bit wrong though - i.e. rather than a lamp indicating a control axis failure, it is indicating a failure in one of the FCS' back-up channels(hence numbered 1-4).

 

Maybe we could ask in the Russian section and see if anyone knows more about this.

According to the manual he's quoting, those buttons will sometimes illuminate after engine start even though there isn't a problem. Don't know what the situation was in the picture you saw.

 

Here's a (mine) translation of the top half of Esac_mirmidon's image from the manual including the section he has "boxed":

 

While flicking Switch 1 up and down, you should feel an increased pulling effort on the control stick, followed by shaking, indicating normal operation of the α, G limiters during testing.

After testing, set the control knob in the neutral position, turn off switch 2, and with this the SDU indicator panel (lights) should go out.

Close the Switch 2 cover.

Set the mode switch of the SDU to the AUTO position, at the same time the SDU MODE SWITCH light will go out.

WARNING. Takeoff with CDU indicator lamps flashing is PROHIBITED.

During all of these tests of the SDU, no push-button lamp on the SDU control panel should be lit.

A flashing push-button lamp indicates the failure of a unit of the corresponding subchannel during which time the push-button lamp illuminates in flashing mode for 3 – 5 sec; after this flashing period it remains lit as a steady light until you turn on the subchannel.

If any of the checks shows a failure in a subchannel, then in order to engage the failed subchannel you must press the lit push-button lamp. When you enable the subchannels the lamp goes out. After that, test the failed subchannel twice.

If the button is pressed and the lamp failure is not removed, or upon retesting re-appears, takeoff is PROHIBITED.

These aren't backup channels. They are the various system subchannels each controlling their piece of the FCS. I think that's what he was trying to get across in describing each light as referencing a particular system-axis.

Edited April 14, 2016 by Ironhand

[Stuge]

Sorry, that wasn't very constructive I know.

 

I'll try this time..

 

Surviving a BVR missile shot in most cases is a combination of high speed and high G. Faster is better and more G is better. Why fast? Because a missile from rear or side aspect must chase you longer. Thus most often it is not beneficial to slow down to corner speed. Corner speed is most important for dogfights!

 

Extra speed in BVR is bad only if you are shot from the front sector and do not know it, then you will fly into the missile faster :)

 

In all other cases of BVR.. speed is life. It keeps you alive, and it gives your own missiles a longer reach.

Edited April 14, 2016 by Stuge

[Esac_mirmidon]

We are talking about different things Stuge.

 

I'm talking about flying outside airframe G limits overstressing it. And about people complains because wings are breaking off when this happens because people are pulling to much G for the weight and speed the Flanker is flying. And in this context you dont need to pull 15 G at mach 1 to fight WVR. Corner speeds are lower.

 

And for BVR you are right. Speed is life but also at supersonic speeds there are a limit in the maximun G available for not strresing the airframe. If you pull more be prepared to break something. Thats all. People must know that in the real Flanker there are limits. Is forbidden to turn off the AoA limiter or to take off with a failure light in the SDU and nothing about pressing the brakes to turn tighter.

 

Ironhand.

 

I assume that the description of the initial failures in the SDU panel is because engines start procedure. Is like when you starts your engines in the Black Shark abd the Ekran start to show oils pressure failures or hydraulic failures because is normal in a start up until or is running and activated.

 

It seems when you start the engines in the Flanker the SDU panel could lit up because hydraulic pressure is not in his normal levels until the secuence is complete and the system thinks there are a problem. When the engines are running and all pneumatic and hydraulic systems are online the pilot start the system checks and the lights that are on are pressed after the SDU test to turning them off.

 

If any of them remain on then he must repit the test two times and if they still are on abort the departure.

[CiberAlex]

From RU-section

Много откуда. Как вариант - из аэродинамики Су-27.

 

 

[Esac_mirmidon]

Thanks for the pics.

 

There are a more complete description of the G-Speed-Weight limits we have seen before here. Specifically about flying at 21.400 kg weight with 50% internal fuel and four missiles.

Edited April 14, 2016 by Esac_mirmidon

[mvsgas]

Thanks guys, cool info. Esac mirmidon, The SDU sounds a lot like the F-16/ F-117 FLCS.

[Ironhand]

...I assume that the description of the initial failures in the SDU panel is because engines start procedure. Is like when you starts your engines in the Black Shark abd the Ekran start to show oils pressure failures or hydraulic failures because is normal in a start up until or is running and activated.

 

It seems when you start the engines in the Flanker the SDU panel could lit up because hydraulic pressure is not in his normal levels until the secuence is complete and the system thinks there are a problem. When the engines are running and all pneumatic and hydraulic systems are online the pilot start the system checks and the lights that are on are pressed after the SDU test to turning them off...

That makes sense. :)

[GGTharos]

Sorry, that wasn't very constructive I know.

 

I'll try this time..

 

Surviving a BVR missile shot in most cases is a combination of high speed and high G. Faster is better and more G is better. Why fast? Because a missile from rear or side aspect must chase you longer. Thus most often it is not beneficial to slow down to corner speed. Corner speed is most important for dogfights!

 

Wait until guidance is fixed.

[esb77]

That plus a few seconds.

 

It's been ages since I've asked for repairs and had forgotten how long it used to take. I remembered it wasn't much. Waiting several minutes with nothing happening, I used time advance to speed things up. Let the clock advance 25 minutes and dropped back into real time. I concluded that nothing was being repaired.

 

But I was low on fuel and asked for 40%. Sat there for a bit while refueling was taking place and decided that would be a great time to grab a 2nd cup of coffee. Came back in time to see Repairs Complete on the screen.

 

So it could be that the refueling, come to think of it, delayed the completion of repairs. But it did take a l-o-n-g time regardless.

 

Hm, I dunno. If we're simulating here, I'm surprised they even got the airframe inspection done in just 32 min.

 

 

I would think that an over-g resulting in airframe damage would be more like, "Come back next week if you've finished the paperwork by then, and remember to bring us[the ground crew] a case of vodka when you do."

 

"More realism," is a doubled edged battle cry in some cases. ;)

[Seaeagle]

 

And for axis-channels. You are right. The problem for me is to find the more accurated translation from russian manuals and for this topic sometimes it talks about axis channels, sometimes longitudinal channel others lateral channel, stabilizators, automatic handling control , etc

 

And also i'm not english native so i usually miss a lot naming things.

 

Same as you :) - but in the case of this paragraph it only mentions "подканала", which I think translates simply to "sub channels".

 

But in essence the SDU it seems to have four channels and controls several sub systems like the dampers , slats, flight control surfaces, etc. Every channel in the SDU has a light but reading the manual each light corresponds to more things than his channel. It blinks because more things not only his specific channel.

 

Yes as I read it, a flashing "button-lamp" indicates element(s) of the corresponding sub channel failing to respond during test.

 

But at last the important thing is that the pilot would never take off with a SDU failure light on and in flight he never must turn off the AoA-G limiter under any circunstance. There are no real gain on it as the manual said and only produces a more dangerous flight and a real chance of loosing control over the plane or overstressing it.

 

No arguments there :)

[Seaeagle]

According to the manual he's quoting, those buttons will sometimes illuminate after engine start even though there isn't a problem. Don't know what the situation was in the picture you saw.

 

Neither do I - it was only number 4 that was lit.

 

Here's a (mine) translation of the top half of Esac_mirmidon's image from the manual including the section he has "boxed":

 

Yes thats pretty much what I arrived at as well.

 

These aren't backup channels. They are the various system subchannels each controlling their piece of the FCS.

 

I don't see how you can determine that based on the translation.

[DarkFire]

Hm, I dunno. If we're simulating here, I'm surprised they even got the airframe inspection done in just 32 min.

 

I would think that an over-g resulting in airframe damage would be more like, "Come back next week if you've finished the paperwork by then, and remember to bring us[the ground crew] a case of vodka when you do."

 

"More realism," is a doubled edged battle cry in some cases. ;)

 

Good point. This may be going slightly O/T, but if it were suspected that an airframe had been subjected to extreme over-G I'd expect it to be shipped (literally, not flown) to a 2nd line maintenance base where it would be totally stripped down to the bare airframe for inspection, or at least stripped down to the point at which the entire frame would be accessible. Then comprehensive testing, possible replacement or rebuild of entire sections of the airframe followed by reconstruction of the entire aircraft.

 

I'd be amazed if the pilot saw the aircraft again within 3-4 months. If the RuAF is anything like our lot, and I'd be amazed if they were not, then during such a deep inspection & rebuild absolutely everything is inspected down to the smallest detail and are very carefully re-constructed, tested, tested again, tested some more just to make sure and then inspected again to make sure. Only then would the aircraft be subject to further test flights before being finally signed off and released back for line squadron use.

 

Deep inspection / maintenance cycles are taken very, very seriously because so much is reliant on them: the life of the pilot and the national investment in an expensive aircraft.

 

Referring to the 2nd image that CiberAlex posted, I take it that the 5Km, 10Km, 12Km and 15Km lines on the G v Mach diagram refer to operating altitudes? That's really, really useful information to have, thanks for cross-posting from the Russian forum :thumbup:

[GGTharos]

Good point. This may be going slightly O/T, but if it were suspected that an airframe had been subjected to extreme over-G I'd expect it to be shipped (literally, not flown) to a 2nd line maintenance base where it would be totally stripped down to the bare airframe for inspection, or at least stripped down to the point at which the entire frame would be accessible. Then comprehensive testing, possible replacement or rebuild of entire sections of the airframe followed by reconstruction of the entire aircraft.

 

It would be as you say, but in the event that the airframe is actually warped, they'd just write it off.