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

[Esac_mirmidon]

So if you fly the Flanker over the structural limits and pull more Gs than permited for the speed and weight the frame can sustain it and breaks apart.

 

Whats the problem here?

 

The same as the Su-25, the Mustang, the Dora or the Kurfurst. And this last three without that nice russian grandmother voice nagging over.

 

I cant understand the problem.

Edited April 13, 2016 by Esac_mirmidon

[Ironhand]

So if you fly the Flanker over the structural limits and pull more Gs than permited for the speed and weight the frame can sustain it beaks apart.

 

Whats the problem here?

 

The same as the Su-25, the Mustang, the Dora or the Kurfurst. And this last three without that nice russian grandmother voice nagging over.

 

I cant understand the problem.

:)

 

"Problem" 1: Trying to get a handle on the actual parameters involved. With the right parameters, the wings will come off well before our Russian grandmother starts nagging.

 

"Problem" 2: Should our Russian grandmother be nagging in relationship to changes in weight and speed? Or not?

 

"Problem" 3: Learning to adjust our behavior to the new parameters.... For me the adjustment is to not pull in excess of 5 or so Gs while flying in the Mach 1+ range.

 

:)

[Esac_mirmidon]

But we have all the information and parameters needed in the real manual.

 

Its not aleatory or magic. If you keep the G values under the max permited as this manual shows i dont have any problem at all. Dont pull more than the value listed below 0.85. The same between 0.85 and mach 1 i think, and the same beyond that.

 

And take in count the ratio between weight and max Gs according the formula related. Thats all.

 

I've tested myself this values and i've never broke my Flanker.

 

Beyond yes. Below never.

 

You only need the G meter your weight and your speed. Nothing more.

[Ironhand]

But we have all the information and parameters needed in the real manual.

 

Its not aleatory or magic. If you keep the G values under the max permited as this manual shows i dont have any problem at all. Dont pull more than the value listed below 0.85. The same between 0.85 and mach 1 i think, and the same beyond that.

 

And take in count the ratio between weight and max Gs according the formula related. Thats all.

 

I've tested myself this values and i've never broke my Flanker.

 

Beyond yes. Below never.

 

You only need the G meter your weight and your speed. Nothing more.

That's all correct. And it's not a problem in the true sense of the word. I'm just curious about how much over the operational G values and according to what parameters things break. Think of it as an intellectual exercise. That and adjusting my flying to include keeping an eagle eye on the G meter as I turn.

[GGTharos]

Interesting theory about the F-15,

 

It's not a theory.

 

but strange because first of all the flanker was designed second and to take on the f-15 so I would think the Russians would design it with the characteristics of the 15 in mind (if they were fully known of course at the time) In fact when they build the first prototype the main engineer decided to scrap the project and go back to the drawing board because it could not match the known characteristics of the 15.

There's nothing strange here. People are probably just fighting outside of the flanker's preferred combat envelope and they're being impatient. They're trying to always evade missiles with max stick deflection. Even with pulling less g, the Su-27 has etter turn rates.

 

Why is it not likely that the F-15 will pull enough g's to bring it anywhere near to taking serious over-g damage? Is it because of the FBW limits? Or is it because it is a BVR fighter so it has no need?

No, the CAS won't stop you from deflecting the controls as much as you need, but there's a limit to how much pressure the hydraulics can produce to give you that deflection. The faster your indicated airspeed, the more resistance there is for the elevators.

 

Theoretically speaking wouldn't the flanker reduce it operational hours as well by pulling high G's but not necessarily break its wings, other wise you would pretty much have a fleet of planes that are useless if piolets break the g limits for a few secs. I think that the laws of physics apply to all the planes equally (with some adjustments of course for structural design).

But pilots are disciplined and they know their aircraft, so they will not do that. And yes, you can reduce the Su-27's life-span as well. That's what happens when you exceed the design g-limit, but not the breaking limit. Understand that physics apply equally to everything, yes, but a hummer isn't going to crumple like your car in a collision. Same physics, different design.

 

regarding the s keys and the 30g turns, well yea that is pretty ridiculous and would definetly do some damage.

Not 'some damage', it would disintegrate the aircraft. This is from the FC3 manual:

 

"In 1978, the second prototype designated T10-2 was completed though its life was brief. On 7 July, 1978, the fighter suffered a mid-air accident resulting in death of test pilot Yevgeny Solovyov. The crash was triggered by the plane's oscillation in the longitudinal plane at a supersonic speed, due to which it suffered an extremely high g-load and disintegrated in midair"

 

From what i remember from playing BMS the F-16 and even the mirage both have a FBW over ride switches for extreme situations, not sure if the 15 does or not, but it seems that it probably would have something similar as well, in which case it should be able to break a wing also IMHO ofcourse.

The F-15 doesn't limit you. And like I said before, it has demonstrated the ability to operate at beyond it's design limit in training and combat. The BAL at all weights seems to be 9g by the aircraft's documentation, so you're not really going to be able to break it.

The one F-15 that disintegrated in mid-air in a 3g (yes 3g, not 4, not 5, not 30) turn had defective longerons - they were manufactured thinner than they were supposed to, and the aircraft's useful lifespan was therefore so much shorter and it's g limits actually lower, so those airframes (a few f-15's had this defect and had to be removed from service) were easy to over-g and damage.

[SinusoidDelta]

There was another instance of an F-15 disintegrating when it exceeded 780 kts at 24,000ft.

 

See my post here: http://forums.eagle.ru/showpost.php?p=2646887&postcount=34

Edited April 13, 2016 by SinusoidDelta

[GGTharos]

Yep, but knowing that NASA has flown this thing to M2.7, and unofficially the USAF even faster, to me it sounds like a one-off. Then again, maybe they never reached that IAS.

 

The documented maximum speed for the eagle is 800kts and various SMEs had some ideas about what to do with the aircraft at that point.

[Esac_mirmidon]

Thats another story Ironhand.

 

And very interesting. Pushing beyond the limits the Flanker to find where are the structural limits under different speeds/weights/G could be very fun and important. Maybe testing it in the whole envelope could make us to find if there are any problem, trouble or bug in some maneuvers or some weird behaviour.

 

Until now i didnt find any strange, and i was pushing a lot of 9 G ( over the 8 max value indicated ) in a lot of weight-speed configurations without breaking anything. Yes we must be very careful with the G indicator all the time because if you pass the threeshold then the structural strenght is degraded and then you need less G to break it.

 

But is a very interesting research. For a Simulator.

 

Because in real life the pilot testing it would suffer a lot because so much G so much time. XDDDD

[JazonXD]

Had the same situation yesterday while trying to tear the wings off this butterfly. Half a wing snapped and had to land it. Jettisoning the weapons helped--also not my first thought, more like 3rd or 4th--after seeing what kind of control I had and figuring out where to try and put it her down. Getting them jettisoned was problematic because of the yawing forces involved--never could get the last one off. The aircraft did seem a bit easier to control after that, though.

Your chute opened and blow out because of the excessive landing speed. That's why the cannister was open but no chute was showing. It opened for me on the grass without a problem.

Ahh okay, interesting. I thought keeping the weight on the right side would be a decent idea, especially at lower speeds

Had same wing failure 2 days ago.

Managed to land. Taxi. Take Off again (for fun). Land again.

No worries.:D

 

haha, that's awesome! I remember doing that with the f15 back in 1.2 when the hydraulics allowed to be working even if one wing was torn off.

[Ironhand]

Thats another story Ironhand.

 

And very interesting. Pushing beyond the limits the Flanker to find where are the structural limits under different speeds/weights/G could be very fun and important. Maybe testing it in the whole envelope could make us to find if there are any problem, trouble or bug in some maneuvers or some weird behaviour.

 

Until now i didnt find any strange, and i was pushing a lot of 9 G ( over the 8 max value indicated ) in a lot of weight-speed configurations without breaking anything. Yes we must be very careful with the G indicator all the time because if you pass the threeshold then the structural strenght is degraded and then you need less G to break it....

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.

[GGTharos]

But also let's keep in mind that speed doesn't change your basic airframe's g limit.

 

What's really happening (IMHO) is that the nature of the load changes, and may actually be fluctuating due to turbulence, or turbulence may increase the g-loading on some parts of the aircraft.

 

At supersonic speeds, the nature of the airflow itself changes, and a hard, high-g turn may cause different types of airflows to be present at various parts of the aircraft - this means not different g-loading, but different pressure applied to different parts of the aircraft.

[SDsc0rch]

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.

 

that's what my understanding is

 

you have allowable load - then there is a safety factor/margin of 30%, and damage comes at 150% of allowable load

 

so its not like the SU is *instantly* disintegrating the moment you trip 1% over the allowable load ----- by the time it cracks up, you've exceeded max allowable load, you've exceeded the 30% safety factor - and you've gone 1.5x more G than the airframe is rated for

 

and ppl are surprised they are experiencing catastrophic failure!

 

good post iron

[Ironhand]

But also let's keep in mind that speed doesn't change your basic airframe's g limit.

No. But it does alter how many Gs are available be applied. (EDIT: And air pressure against the aircraft.)

 

What's really happening (IMHO) is that the nature of the load changes, and may actually be fluctuating due to turbulence, or turbulence may increase the g-loading on some parts of the aircraft.

 

At supersonic speeds, the nature of the airflow itself changes, and a hard, high-g turn may cause different types of airflows to be present at various parts of the aircraft - this means not different g-loading, but different pressure applied to different parts of the aircraft.

This is all true in real life. But if all of this was being tracked in the sim, I'd be very surprised. I'm guessing that the calculations being performed are much simpler than that. (And that's not to denigrate the programming, BTW. Simply why run 1000s of calculations when 5 or 6 might provide a reasonable facsimile?)

Edited April 13, 2016 by Ironhand

[Bushmanni]

Wings snapping off in simplified terms is a function of root bending moment, ie. force applied to the wing that causes it to bend and the highest bending moment occurs at the wingroot. This might not be the place where the wing snaps as there might be a relative weak point further along the wing span but it's the point of the highest bending torque. G-load on the other hand is a function of acceleration of the fuselage of the aircraft. Total aerodynamic force is responsible for the fuselage acceleration while root bending moment is only function of the forces acting on the wing. If the ratio between lift from body and wings changes, it will change the relationship between G and wing root bending moment like change in fuselage mass does.

 

Blade element theory calculates body lift and wing lift separately so there's no reason to assume that mach effects on G and wing breaking relationship couldn't be modeled.

[Esac_mirmidon]

But a factor of 1.5 threeshold is A LOT more.

 

We have a lot of space and room for not breaking if the factor is 1.5 or near that over the manual G limit. So it´s going to be our fault always if we break it.

 

And we are going to get used to fly at the best corner/turn speed for the Flanker, around 670 IAS. No more Fast and Furius 12 G at Mach 1. Just keep the Flanker in his best speed, at his best weight for combat and with multiple eyes over the G meter.

 

Easy....

 

XDDDDD

[Ironhand]

Wings snapping off in simplified terms is a function of root bending moment, ie. force applied to the wing that causes it to bend and the highest bending moment occurs at the wingroot. This might not be the place where the wing snaps as there might be a relative weak point further along the wing span but it's the point of the highest bending torque. G-load on the other hand is a function of acceleration of the fuselage of the aircraft. Total aerodynamic force is responsible for the fuselage acceleration while root bending moment is only function of the forces acting on the wing. If the ratio between lift from body and wings changes, it will change the relationship between G and wing root bending moment like change in fuselage mass does.

 

Blade element theory calculates body lift and wing lift separately so there's no reason to assume that mach effects on G and wing breaking relationship couldn't be modeled.

Good info. Thanks. :)

 

 

But a factor of 1.5 threeshold is A LOT more.

 

We have a lot of space and room for not breaking if the factor is 1.5 or near that over the manual G limit. So it´s going to be our fault always if we break it.

 

And we are going to get used to fly at the best corner/turn speed for the Flanker, around 670 IAS. No more Fast and Furius 12 G at Mach 1. Just keep the Flanker in his best speed, at his best weight for combat and with multiple eyes over the G meter.

First, keep in mind that my numbers are for a simple 120* roll, then pull type of maneuver (slice). The FCS is fully engaged. Also I'm not testing to see what happens subsequently. I was just doing some quick testing to see when the wings broke on the first over-G.

 

Unless you are using either the "S" key or "W" key, for most speeds, it is difficult to break the aircraft by significantly over G-ing. The exception occurs in the supersonic range. There you need to keep a very watchful eye on the G meter. Below those speeds you're not going fast enough to generate the required Gs in most cases.

 

I say "in most cases" because I can generate forces that will break a single wing--this may speak to Bushmanni's observations above. But that takes some radical maneuvering and still requires forces somewhat beyond 7 or 8 Gs.

Edited April 13, 2016 by Ironhand

[Esac_mirmidon]

Yes.

 

But the manual FORBIDES to override the FCS at any time. 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.

 

So it´s not inside the Operational Limits to fly without FCS.

 

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

 

People needs to get used to fly inside flight envelope. Thats all.

 

How far we can go? Thats the point of those interesting tests.

[Ironhand]

...

And also whats the point to turn supersonic at maximum G?...

Well...you do get your fastest, tightest turn at Max G for your airspeed... until the wings come off. And, then, you really slow down. :)

 

As long as you're below roughly M 1.25 and FCS is on, you can turn without looking at the G meter and simply be guided by your darkening vision as to when to ease off the stick. But above that number, that is no longer the case and you have to constantly eyeball the G-meter. Unfortunately, that is one of the few ways to know how many simulated Gs you're pulling while sitting at a computer.

 

Just this morning I lost my wings in exactly that situation. My coffeecup blocked my view of the G meter...

Edited April 13, 2016 by Ironhand

[DarkFire]

Just this morning I lost my wings in exactly that situation. My coffeecup blocked my view of the G meter...

 

We regret to inform you that your sons are dead because their vision was obscured by a caffeine administration receptacle (or in old-school British military parlance a "cup, coffee, drinking, for the use of") :lol:

 

Some really good information in the last few pages, thanks everyone for sharing, I've learned a lot :thumbup:

[Winston60]

......but a hummer isn't going to crumple like your car in a collision......

Funny alert!

 

Ahh... careful what you say about a Hummer crumpling..... :megalol:

 

[GGTharos]

I'm thinking of the military ones, but that's still pretty funny. Does this version even have a roll bar?

[Winston60]

I'm thinking of the military ones, but that's still pretty funny. Does this version even have a roll bar?

No it doesn't. The H2 Hummer's were a far cry from the military versions although still awkward, heavy, uneconomical and not really that robust. They had pickup truck frames and suspension instead of the independent suspensions of the military Vee's. The H3's were smaller, similarly made and equally hampered. The target consumers were the military wanna-be types and Rock Stars/Movie Stars. California Gov. Arnold Schwarzenegger had one during his time in office.

 

Such are the USA crash requirements. The "crumple zone" must dissipate the headon collision forces plus try to keep intrusion into the passenger compartment to a minimum. Also notice the left front door is open so evidently the driver exited. A car is completely totaled but the occupants probably survived. :doh:

[SinusoidDelta]

A roll bar? How's that going to help in a frontal offset crash? The H3 actually recieved a "poor" rating in side and frontal offset crash tests.

 

Everything changes in a dynamic impact. This I know very well, I do it for a living.

 

Edit: And a car that doesn't "crumple" in a crash will kill you.

Edited April 13, 2016 by SinusoidDelta

[Axion]

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.

[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?...

I would assume nothing in that regard. I hope it would be "repaired". But...