Su27 Wing Thing

[jackmckay]

Darkfire, thank you for doing actual tests in game. I appreciate that regarding of outcome. :thumbup:

 

Other important issue regarding damage model of A side top class fighter in DCS is lack of same feature implemented on B side top class fighter as ostensibly equivalent opponent. That should be at least minimum fair enough to keep people not giving up of DCS experience because of this situation. :bye_2:

 

From my point of knowledge in aerospace design philosophy I can state next: Sukhoi utilizes blended fuselage wing concept also known as blended body in not so radical phase though. Anyway lift force fraction generated by fuselage is quite large and there is no actual accessible data proving amount of overall lift fraction generated by fuselage itself. This means that we do not know how stressed wings actually are in tight turns without testing that at least virtually. I mentioned early that Sukhoi philosophy regarding plane operational demands implements minimal field maintenance and that means higher safety standard than western counterparts. I said previously that by my personal experience in mechanical engineering Russian aerospace FOS is around 2.5 in global but depending on structure element it could be as high as 5. Pure example of wing strength of Su-27 is executing Cobra maneuver at 500+km/h in AoA of 90deg. This same maneuver stresses the wing extreme high up to the limit of elastic deformation and this maneuver could be done without permanent damage to plane's structure repeatedly.

 

Wing failure expected by accumulating stress is kind of resistance to fatigue test and should be properly done by continuous high load cycles during prolonged period of time but since in DCS we take fresh factory rolled planes every time it is very unlikely that new plane will develop lower fatigue resistance.

 

Overloading structure up to point of wing break should always befall after 12G because this G-load is G-LOC limit for even the best and the most G-resistant pilots. It's very hard to break the wing of a modern fighter and first one to break is the pilot itself. If some people don't know how planes fly they should just imagine giant vacuum cleaner on top of plane's upper surface and that means that plane actually hangs on low pressure air bubble that is controlled by airspeed. It there are no extreme differences in pressure gradient on top surface regions of plane lift surfaces there could be no high shear stress generated load on plane structure and everything is in fine balance and compensating various types of loads, even rotational inertia and inertial couplings of various components that have resistance to directional vector change, because everything is rigidly tested and every behavior is predicted.

 

Flight manuals are written for pilots to protect pilots from damaging own health primarily, then for long operational use and safety of structure itself as is inspected by maintenance crew on ground. No air force in world will ever allow top fighter of that performance as Su-27 to ever enter it's operational service with design feature of brittle wings before breaking the pilot first in any circumstances. That just won't pass for this type of airplane.

 

... I'll keep digging for actual test data of Su-27 family wing to find exact point of wing break... :pilotfly:

 

Edited November 1, 2016 by jackmckay

[Falcon_S]

That "BIG" story (ED story) about Su27 wing is based on only ONE case from test flight (at 51:05s):

 

 

(Did you see how they with smile talk about that: - "shaking, turned and continued to fly...")

 

Experts in this video says G-limit is 9 units and no one said that 9+ mean disaster for Su27.

 

Why DCS Su27 is fragile and what DCS simulate with that i don`t know but this is to far from reality.

 

As jackmckay said -

Flight manuals are written for pilots to protect pilots from damaging own health primarily, then for long operational use and safety of structure itself as is inspected by maintenance crew on ground. No air force in world will ever allow top fighter of that performance as Su-27 to ever enter it's operational service with design feature of brittle wings before breaking the pilot first in any circumstances. That just won't pass for this this of airplane.

...but because numbers in that manual DCS Su27 is only for ballet. :doh:

 

If it was not sad it would be funny.

[amazingme]

When you pull the Gs and use rudder then the magic happens..

[GGTharos]

That "BIG" story (ED story) about Su27 wing is based on only ONE case from test flight (at 51:05s):

 

It's based on the safe g-limit formula provided in the real flanker manual, actually.

 

Experts in this video says G-limit is 9 units and no one said that 9+ mean disaster for Su27.

 

Why DCS Su27 is fragile and what DCS simulate with that i don`t know but this is to far from reality.

 

It isn't fragile. The g limit chart is listed for a specific combat weight. If you exceed this weight, naturally the g limit will be lower.

 

As jackmckay said -

...but because numbers in that manual DCS Su27 is only for ballet. :doh:

 

If it was not sad it would be funny.

 

You're funny. You can calculate the g-limit yourself.

1.5x this limit is (AFAIK) the breaking point, if you're not applying lateral acceleration - less if you are.

 

The most vulnerable phase of flight is between M0.85M and M1.3, and people just LOVE to yank-and-bank at those speeds. In other words, it's your own fault.

 

The safe g limit in this region is 139/GW in metric tonnes.

[mvsgas]

GGTharos,

 

[DarkFire]

I'm still in the process of gathering data for what will as scientific a test as I can manage, but some early indications are:

 

1. Loads applied slowly are survivable, up to and including full stick pitch deflection condition.

 

2. Under any conditions (within the Mach 'danger zone') your AOA limiter will save you, provided it's given time to engage and do it's thing.

 

3. Gradual application of G-loads are safe. Shock loading the airframe is not safe. Compound loads (pitch & roll components) are less safe.

 

4. The 'safety factor' appears to have increased to roughly 1.5 - 1.7 (!!) though the safety factor itself appears to be weight dependant.

 

Full test results to come in the next few days.

Edited November 1, 2016 by DarkFire

[Pocket Sized]

As an aside, I had the control position monitor turned on and as G went above ~8, the AOA limiter chased around the control column position. The effect of this was to create a sort of pitch oscillation which, at maximum amplitude, added about an extra G to the airframe load value. It may well be the case that the AOA limiter is actually to blame for causing airframe damage when carrying out high-G manoeuvres right at the edge of the airframe capability.

 

That's a stick pusher. They're usually used for AoA limiting (flanker, F-104, SR-71, etc) but I see no reason it couldn't be used as a G limiter.

 

If you apply G slowly the stick pusher will save you in my experience.

 

Or you can use muscle memory and pull near the limit then slowly proceed to brush against the stick pusher.

 

Edit: Sniped while typing

Edited November 1, 2016 by Pocket Sized

[ShuRugal]

1.5x this limit is (AFAIK) the breaking point, if you're not applying lateral acceleration - less if you are.

 

Do you have any data on that point? This seems to be the major contention here. Based on what Falcon was saying, it would seem that the norm for Russian aircraft is a safety factor of 2.5.

 

Considering that the Su-27 is less than 10% larger than the F-15, but has fully 25% more empty weight, it stands to reason that some of this extra weight would be in structural reinforcement, which itself stands in line with the general Russian principal of over-overengineering things.

 

Is there any data to suggest that the safety factor for the Su-27 really is so low as 1.5?

[GGTharos]

Do you have any data on that point? This seems to be the major contention here. Based on what Falcon was saying, it would seem that the norm for Russian aircraft is a safety factor of 2.5.

 

And I'm the Pope.

 

Sorry for the smart-aleck retort, but seriously - what kind of BS is this? No one of us actually knows what the safety factor is, and comparing to a tiny, lightweight little sports plane is utterly inappropriate. I'd expect an engineer to understand how load-bearing capacity scales vs. mass.

 

So, the industry standard of 1.33 and 1.5 is used, AFAIK.

 

Considering that the Su-27 is less than 10% larger than the F-15, but has fully 25% more empty weight, it stands to reason that some of this extra weight would be in structural reinforcement, which itself stands in line with the general Russian principal of over-overengineering things.

 

No, it doesn't stand to reason, and your principle is made-up. Russian aircraft were designed to be built by relatively unskilled labor, and maintained by the same. They slowly got themselves out of this, but that's for much more modern air-frames.

 

Russian airframes are not magical ;)

 

Is there any data to suggest that the safety factor for the Su-27 really is so low as 1.5?

 

What do you mean low? It's an industry standard.

[Ironhand]

I'm still in the process of gathering data for what will as scientific a test as I can manage, but some early indications are:

 

1. Loads applied slowly are survivable, up to and including full stick pitch deflection condition.

 

2. Under any conditions (within the Mach 'danger zone') your AOA limiter will save you, provided it's given time to engage and do it's thing.

 

3. Gradual application of G-loads are safe. Shock loading the airframe is not safe. Compound loads (pitch & roll components) are less safe.

 

4. The 'safety factor' appears to have increased to roughly 1.5 - 1.7 (!!) though the safety factor itself appears to be weight dependant.

 

Full test results to come in the next few days.

IIRC, when I tested this way back when (it's actually in a chart buried in a thread kicking around here somewhere), the Flanker was surviving Mach 1.0 G loadings of 1.8 times the operational max G allowed. And this was for the heavier gross weights, not the 21,400 Kg standard. I remember being surprised by that given the assumed 1.5x.

 

EDIT: Found it: G Chart. Darkfire, don't know if you have any previous baseline figures of your own to work from. If not, these might help...or not.

Edited November 1, 2016 by Ironhand

[*Rage*]

From the Russian side..

 

Су-27 доделывается. В следующем патче уже видите новую САУ и ограничитель на ручке.

А вообще, если мы будем до бесконечности допиливать один модуль мы просто умрем с голоду. Делать симуляторы далеко не тоже самое что нефть продавать.

 

Su-27 gradually completed. The next patch is already seeing new ACS and stop on the handle.

And in general, if we endlessly dopilivat one module we just die of hunger. Making Simulation is not the same as selling the oil..

 

Could be interesting:)...

[Veritech]

From the Russian side..

 

 

 

 

 

Could be interesting:)...

 

How old is that post Rage?

[pr1malr8ge]

 

Considering that the Su-27 is less than 10% larger than the F-15, but has fully 25% more empty weight, it stands to reason that some of this extra weight would be in structural reinforcement, which itself stands in line with the general Russian principal of over-overengineering things.

 

 

There is a reason for the extra weight and it's not because of reinforcements due to over engineering. It's because RU design philosophy is to make it as cheap as possible. Thus they do not use or keep to the minimal use of exotic metals [i.e. TI]. Thus they have to use more of the heavier materials to get the same structural integrity.

[DarkFire]

IIRC, when I tested this way back when (it's actually in a chart buried in a thread kicking around here somewhere), the Flanker was surviving Mach 1.0 G loadings of 1.8 times the operational max G allowed. And this was for the heavier gross weights, not the 21,400 Kg standard. I remember being surprised by that given the assumed 1.5x.

 

EDIT: Found it: G Chart. Darkfire, don't know if you have any previous baseline figures of your own to work from. If not, these might help...or not.

 

Thanks for the link to your chart, I'd been trying to find it to compare with my figures. :thumbup:

 

So far (I'm working my way down from 29,720Kg) my figures for the safety factor are slightly higher than the ones you got, but the difference is small enough that it could easily be within the uncertainty range. For example, at an all-up weight of 29,720 Kg (full AAM & ECM load with 100% fuel & gunpad) I was able to survive up to 8.6G load applied slowly, but the wings broke at 7.4G when applied quickly, e.g. an instant hard turn. My calculated theoretical maximum G was 4.68 so using the 7.4G break point I got a safety factor of 1.58. This particular test was run at 1.075M and 2,100m altitude at the point of airframe failure.

 

Edited to add: I'd remembered your chart incorrectly. For some reason I'd imagined that the safety factor is a constant and somewhere between 1.4 and 1.5. Faulty memory on my part.

Edited November 1, 2016 by DarkFire

[GGTharos]

Could it be that some sort of a bending or shearing moment is simulated?

Or perhaps the sensors did not have time to catch up to the actual g, but I imagine you verified this one through external views.

[Ironhand]

Thanks for the link to your chart, I'd been trying to find it to compare with my figures. :thumbup:

 

So far (I'm working my way down from 29,720Kg) my figures for the safety factor are slightly higher than the ones you got, but the difference is small enough that it could easily be within the uncertainty range. For example, at an all-up weight of 29,720 Kg (full AAM & ECM load with 100% fuel & gunpad) I was able to survive up to 8.6G load applied slowly, but the wings broke at 7.4G when applied quickly, e.g. an instant hard turn. My calculated theoretical maximum G was 4.68 so using the 7.4G break point I got a safety factor of 1.58. This particular test was run at 1.075M and 2,100m altitude at the point of airframe failure.

 

Edited to add: I'd remembered your chart incorrectly. For some reason I'd imagined that the safety factor is a constant and somewhere between 1.4 and 1.5. Faulty memory on my part.

I'll look around and see if I was smart enough to save some of the trials as TRKs. If so, running them could be quite illustrative, since the trial be flown exactly the same way.

[ShuRugal]

It's an industry standard.

 

yes, it is an industry standard. "An", not "The Only".

 

Sorry for the smart-aleck retort

:surprise:

Either I've died, or PT this morning was worse than usual and I'm <still> hallucinating.

:suspect:

[Pocket Sized]

How old is that post Rage?

 

Click the little red icon on the quote ;)

 

It was posted on October 28, 2016

[DarkFire]

Could it be that some sort of a bending or shearing moment is simulated?

Or perhaps the sensors did not have time to catch up to the actual g, but I imagine you verified this one through external views.

 

Ah yes, should have made this clear. I recorded the G levels by monitoring the point of destruction using the F2 view and watching a track file at 1/16th speed. I'm running each test twice to help reduce any anomalous errors.

[Fri13]

 

It isn't fragile. The g limit chart is listed for a specific combat weight. If you exceed this weight, naturally the g limit will be lower.

 

But G-limits changes based the weight.

More weight = higher G-forces with same speed and turn.

Less weight = higher G-forces with same speed and turn.

 

At least this is the reason why a swallows or hawks can pull far tighter turns than any human made device, because their weight is so small that they don't experience same G-forces. If a swallow or a hawk would weight more compared their sizes, speed and turn radius, they would die instantly what they can do now.

 

 

So I would expect that the G-force meter and limiter kicks same way in at the same limits, regardless the weight or speed because G-meter measures actual G-forces aircraft is under, and then G-limiter kicks in at given values. Wrong?

 

As I don't understand why Soviets put Su-27 out with a computer to control limits, but didn't put G-limiter functional to deny pilot from doing deadly maneuvers.

As in videos I have heard pilots to say that it becomes only dangerous when limiters are disabled as nothing is denying pilot to do unfit maneuvers.

[Fri13]

No, it doesn't stand to reason, and your principle is made-up. Russian aircraft were designed to be built by relatively unskilled labor, and maintained by the same. They slowly got themselves out of this, but that's for much more modern air-frames.

 

Russian airframes are not magical ;)

 

I would say they are magical if they can be built by unskilled labor and maintained by unskilled labor (and some would even say, fly by unskilled pilots aka Korean War) and still operate and survive. :music_whistling:

[GGTharos]

Relatively unskilled, not unskilled.

 

I would say they are magical if they can be built by unskilled labor and maintained by unskilled labor (and some would even say, fly by unskilled pilots aka Korean War) and still operate and survive. :music_whistling:

[GGTharos]

So I would expect that the G-force meter and limiter kicks same way in at the same limits, regardless the weight or speed because G-meter measures actual G-forces aircraft is under, and then G-limiter kicks in at given values. Wrong?

 

I don't think there's an actual g-limiter in this particular aircraft.

 

As I don't understand why Soviets put Su-27 out with a computer to control limits, but didn't put G-limiter functional to deny pilot from doing deadly maneuvers.

 

It's not the first aircraft without a g-limiter. Pilots plan a lot of stuff, including the GW they'll be at when they expect to enter combat.

 

As in videos I have heard pilots to say that it becomes only dangerous when limiters are disabled as nothing is denying pilot to do unfit maneuvers.

 

The Su-27S as modeled has an AoA limiter. It's a soft limiter, you can pull through it in the real aircraft as well.

 

If you want to pinpoint problems, here they are, as I see them:

 

1) Real pilots can feel the stick shaker, you cannot

2) Real pilots can feel the g (and so know how much they're pulling), you do not.

3) Real pilots train to fight in a specific way.

[GGTharos]

You can reach for as many straws as you like, and pick as many nits as you like ... if you believe that these fighters have a 2.5 safety limit, I have a bridge to sell you :)

 

yes, it is an industry standard. "An", not "The Only".

[DarkFire]

As I don't understand why Soviets put Su-27 out with a computer to control limits, but didn't put G-limiter functional to deny pilot from doing deadly maneuvers.

As in videos I have heard pilots to say that it becomes only dangerous when limiters are disabled as nothing is denying pilot to do unfit maneuvers.

 

As far as I'm aware the purpose was to give the Su-27, which is aerodynamically naturally unstable, the same pilot handling properties as a conventionally stable aircraft. I guess they could have designed the ACS to 'trim for 1G' in a similar way (as I understand it) to the flight control system on the F-15. I can only surmise that the intent of the designers was to make flying the Su-27 more familiar to pilots who begin their training on conventionally stable aircraft.

 

Again my understanding is that the intent of the designers was specifically not to design the Su-27 to have care free handling. This also goes for the MiG-29. The theory was that while it's completely possible for the pilot to carry out manoeuvres that are suicidal or that lead to destruction of the aircraft, it allows very highly trained and experienced pilots to be able to get more out of such an aircraft than the same pilot would be able to do in an aircraft that imposes artificial limits on pilot input commands.

 

Of course, this relies on the pilot being sufficiently skilled to know when he or she is at the limits of the capability of the aircraft, and how to avoid exceeding them.

 

I'm not saying that this approach is better than the care-free handling design paradigm, indeed modern Su-27 variants (Su-30MKi, Su-35 etc.) also have the same sort of fly-by-wire system that modern western types have, to some extent, but these were the reasons why the Su-27 control system was designed in the way we see it in DCS.