investigating G overload damage limit decreases with the increase of speed

[Northwind]

The current version of DCS F5E seems that the G overload damage limit decreases with the increase of speed.

At IAS 500 knots, it can pull more than 11g without overload damage.

At IAS 800 knots, overload damage occurs at approximately 7-8.x G.

Note that it is correct that F5E pulls about 11g without break up, and break up should occur at higher overload.

It's easy to reproduce. No track file.

DCS version:open beta 2.7.7.14727

 

[Northwind]

Track file.

This is not the Most extreme case.

f5e g overload.trk

[NineLine]

So what do you expect the limits of the F-5E to be?

[Snappy]

49 minutes ago, NineLine said:

So what do you expect the limits of the F-5E to be?

I think his point is not what the actual limit should be , but instead that this limit , at which structural damage begins to occur , should be consistent across the speed range.

G is G . There is no reason the airframe can sustain up to X G at low speed but not at high speed.It’s not like the G amount itself becomes more dangerous the airframe structure.The only thing that happens is at high speed the Gs usually come on quicker with less of a pull, so you are somewhat more likely to inadvertently pull more G than intended 

 

Edited November 1, 2021 by Snappy

[NineLine]

Not sure I agree with all that, but still not sure the point really, its well over where it should be flown, even if we made it fail differently, you probably shouldn't be actively trying to pull 11 Gs. I am not trying to be rude, but I am trying to figure out what it is you guys want fixed? Do you want to be able to pull 11Gs no problem no matter the speed?

[Snappy]

Best wait for @Northwind to reply, but I really think this is not about the airplane breaking apart at 11G , which is a generous limit.

But the point is if (in the simulation) the airframe gets damaged/breaks up at X amount of G, then this should be consistent across the speed range where the aircraft is available to generate that x amount of G.

I don’t see why it can take 11 G at somewhat lower speed and only 7-8 G at higher speed to cause damage. After all it’s the G-load that damages the airframe, not the speed. I think whatever upper limit ED wants to employ , be it 8, 9, or 11 G should be consistent across the speed range.

Sorry I really can’t explain it any more clearly.

As for your last question, no of course not. Below a certain point it should be impossible to reach even 7G , because the lower the speed the less G you can generate due to physics.(see my bold)

Edited November 2, 2021 by Snappy

[Machalot]

Measured G is not strictly the same thing at all speeds. The dynamic pressure and Mach number increase with speed, resulting in a different pressure distribution on the skin and structure, which changes the lift to drag ratio. The angle of attack required to deliver a certain G load decreases, and the G component measured by the accelerometer more closely aligns with the total G load. 

That's not to say the model is correct, but it's more complicated than "G is G".

[Snappy]

1 hour ago, Machalot said:

Measured G is not strictly the same thing at all speeds. The dynamic pressure and Mach number increase with speed, resulting in a different pressure distribution on the skin and structure, which changes the lift to drag ratio. The angle of attack required to deliver a certain G load decreases, and the G component measured by the accelerometer more closely aligns with the total G load. 

That's not to say the model is correct, but it's more complicated than "G is G".

Well for the purporse of this discussion I would say this makes no real practical difference. Because in the end G is G. You are talking about the indicated/measured G by the accelerometer which may differ slightly with speed. But this is about the actual G force on the airframe and the point at which it makes it come apart. And this actual G force limit at which damage occurs should be more or less constant under ideal conditions, which we have in the sim. ( putting aside real world factors  like airframe age ,fatigue, prior damage etc..)

BTW,  I don't think the difference between G measurement by the cockpit accelerometer and actual G force on airframge will ever amount to several Gs within the practicable speed range of the aircraft .That would make the acceleromater highly unreliable for use at higher speed, which is something a figher jet is expected to be employed at in combat , with maneuvering.

The F-5 has a symmetrical load limit of +6.5 and -2.0 G.  Plus the 150% design safety factor, we're at +9,75G. Like I said , 11 G is generous, I don't mind if ED makes the airframe starting to take damage at 10G or even 9,75 Galready. But I have severe doubts the aircrafts should fall apart at around 7-8G indicated , even at higher speed. 

Plus the design safety factor is very likely based on calculated real G load during the stress testing , not measurement by the accelerometer. So in my opinion at up to at least 9,75 (actual ) G the aircraft should not fall apart in its entire speed range in DCS.

But proceed as you must.

Edited November 2, 2021 by Snappy

[=475FG= Dawger]

3 hours ago, Snappy said:

Well for the purporse of this discussion I would say this makes no real practical difference. Because in the end G is G. You are talking about the indicated/measured G by the accelerometer which may differ slightly with speed. But this is about the actual G force on the airframe and the point at which it makes it come apart. And this actual G force limit at which damage occurs should be more or less constant under ideal conditions, which we have in the sim. ( putting aside real world factors  like airframe age ,fatigue, prior damage etc..)

BTW,  I don't think the difference between G measurement by the cockpit accelerometer and actual G force on airframge will ever amount to several Gs within the practicable speed range of the aircraft .That would make the acceleromater highly unreliable for use at higher speed, which is something a figher jet is expected to be employed at in combat , with maneuvering.

The F-5 has a symmetrical load limit of +6.5 and -2.0 G.  Plus the 150% design safety factor, we're at +9,75G. Like I said , 11 G is generous, I don't mind if ED makes the airframe starting to take damage at 10G or even 9,75 Galready. But I have severe doubts the aircrafts should fall apart at around 7-8G indicated , even at higher speed. 

Plus the design safety factor is very likely based on calculated real G load during the stress testing , not measurement by the accelerometer. So in my opinion at up to at least 9,75 (actual ) G the aircraft should not fall apart in its entire speed range in DCS.

But proceed as you must.

 

Snappy has it correct here. 

[Northwind]

15 hours ago, Snappy said:

I think his point is not what the actual limit should be , but instead that this limit , at which structural damage begins to occur , should be consistent across the speed range.

G is G . There is no reason the airframe can sustain up to X G at low speed but not at high speed.It’s not like the G amount itself becomes more dangerous the airframe structure.The only thing that happens is at high speed the Gs usually come on quicker with less of a pull, so you are somewhat more likely to inadvertently pull more G than intended 

 

 

 

5 hours ago, Snappy said:

But the point is if (in the simulation) the airframe gets damaged/breaks up at X amount of G, then this should be consistent across the speed range where the aircraft is available to generate that x amount of G.

I don’t see why it can take 11 G at somewhat lower speed and only 7-8 G at higher speed to cause damage. After all it’s the G-load that damages the airframe, not the speed. I think whatever upper limit ED wants to employ , be it 8, 9, or 11 G should be consistent across the speed range.

As for your last question, no of course not. Below a certain point it should be impossible to reach even 7G , because the lower the speed the less G you can generate due to physics.(see my bold)

 

 

3 hours ago, Snappy said:

Well for the purporse of this discussion I would say this makes no real practical difference. Because in the end G is G. You are talking about the indicated/measured G by the accelerometer which may differ slightly with speed. But this is about the actual G force on the airframe and the point at which it makes it come apart. And this actual G force limit at which damage occurs should be more or less constant under ideal conditions, which we have in the sim. ( putting aside real world factors  like airframe age ,fatigue, prior damage etc..)

That's what I mean.

And load limit of F-5E is +7 .33, -3.0 (T.O.1F-5E-1 Page 268)，Plus the 150% design safety factor，+10.995G.
So it is correct that F5E pulls about 11g without break up. The structural damage should be consistent across the speed range.

[Snappy]

35 minutes ago, Northwind said:

 

And load limit of F-5E is +7 .33, -3.0 (T.O.1F-5E-1 Page 268)，Plus the 150% design safety factor，+10.995G.
So it is correct that F5E pulls about 11g without break up. The structural damage should be consistent across the speed range.

Yes, you’re right - I looked at the limits with a certain stores configuration.

Edited November 2, 2021 by Snappy

[GGTharos]

1 hour ago, Northwind said:

And load limit of F-5E is +7 .33, -3.0 (T.O.1F-5E-1 Page 268)，Plus the 150% design safety factor，+10.995G.
So it is correct that F5E pulls about 11g without break up. The structural damage should be consistent across the speed range.

Why?  At 800KIAS you're risking speed alone destroying control surfaces or tipping stabs off.  Add a little load (after all it is loads, not g, and loads are different when transonic/supersonic) and you ensure that things will start coming apart.

[Northwind]

Sorry,Just noticed this,At 0.95 to 2.0 IMN,SYM (G): +6.5, -3.0 (T.O.1F-5E-1 Page 268).
Is this an OPERATING LIMITATION for transonic pitch-up? I don't know.

Edited November 2, 2021 by Northwind

[GGTharos]

Likely more than just that.   G limitations for transonic flight are usually even lower than the supersonic one.

[Machalot]

6 hours ago, Snappy said:

Well for the purporse of this discussion I would say this makes no real practical difference. Because in the end G is G. You are talking about the indicated/measured G by the accelerometer which may differ slightly with speed. But this is about the actual G force on the airframe and the point at which it makes it come apart. And this actual G force limit at which damage occurs should be more or less constant under ideal conditions, which we have in the sim.

I will admit I didn't write my post very well since I was using my phone.  I also had a sentence in there about how increased speed increases Mach and dynamic pressure, which changes the pressure distribution on the skin and structure.  That's how you can eventually destroy an airframe in level flight at 1 g.  The Nz accelerometer doesn't measure axial G's at all (which would only be part of the story), nor does it measure bending and shear stresses on the wing roots and control surfaces.

Anyway, @GGTharos said it better.

Edited November 2, 2021 by Machalot

[PetRock]

So was this an attempt at trying to integrate maneuvering speed load limits? Will this get fixed or at the very least, streamlined in the near future, or will this be left "as is" for the foreseeable future?

I don't think anyone has an issue with a load limit being imposed, just that it is consistent, not only with the known reference documents that we have access to, but also physics to the limit of what we have in the DCS engine.

@NineLine@BIGNEWY

[NineLine]

We are looking at wing damage right now, such as the F-16 for example, some wing breaks happen too easy and are too exaggerated. 

I think across the board sometimes wing breaks were used in cases where you cant really show or model issues, the push of realism will hopefully show better representations of over G and the effects.

For this report, I dunno. I am not sure we can expect the fighter not to suffer something bad in the given examples. Whether it would be catastrophic, or how bad it would be is another thing. Part of it is the more basic DM as well as how wings pop off instead of bend and tear as well.

[Schmidtfire]

I think it is really strange that we can rip the wings off at all.

It doesn't make any sense, since it would take a Hulk to pull that kinds of G's that result in catastrophic failure. And even if it would be physically possible, there would be major audio and visual feedback that the eyes are about to pop out of your head. Not saying these over G effects should be removed. But loosing your wings should not be something to worry about in a dogfight either. Has it ever happened in real life that a jet fighter pilot has pulled his wings off during a fight?  

Edited November 3, 2021 by Schmidtfire

[GGTharos]

1 hour ago, Schmidtfire said:

Has it ever happened in real life that a jet fighter pilot has pulled his wings off during a fight?

Given that they don't pull 10g+ in a dogfight ... no?   These dogfights in DCS are done at 500-600kts, for whatever reason.  IRL a merge might indeed happen that way but the fighters are usually prepared and have chosen a speed to merge at which is typically much lower.  Your chances of breaking wings or other things diminish rapidly when this happens.

[FoxAlfa]

Pull 10+ G is bad, mkay? 

Jokes aside, I find current Over G modeling quite acceptable, you really need to do something stupid in heavy plane to break the wings.

And yes, although in RL there would be probably a set things that would go wrong before wing brake (like INS, Radar, control surfaces jamming)

if a RL madman kept going breaking up the plane would be quite possible.  

From things that could be improved is maybe sound could telegraph more what is going on... like frame banding sounds or such. 

[GGTharos]

What's missing now is overspeed damage.  I see plenty of examples of people exceeding Vne and to my knowledge this condition is far less forgiving than over-g.

[FoxAlfa]

21 minutes ago, GGTharos said:

What's missing now is overspeed damage.  I see plenty of examples of people exceeding Vne and to my knowledge this condition is far less forgiving than over-g.

Completely agree, also store pylon jamming and such

Edited November 4, 2021 by FoxAlfa

[GGTharos]

Store pylons jamming I think won't show up on FC3 any time soon, but over-g and over-speed can be relatively easy to implement across all modules as the damage types caused by these are already modeled in some way.

[=475FG= Dawger]

The new G limits are horrible. Making the F-5 unplayable in PvP. Event today saw 50% of F-5 losses to wing failures. 

 

[GGTharos]

So how many Gs are being applied to break those wings?