Su27 Wing Thing

[Veritech]

In MP you occasionally have some 0.5-3 second freezes that the simulation engine extrapolates over and somehow it reads the stick inputs during the freeze. So you can unintentionally pull the stick past the G limit while the game is frozen and when the freeze is over you suddenly have a wingless plane.

 

Same thing happened to me.

[jackmckay]

Just passing through... I guess I don't understand this fascination with AoA. Max AoA has nothing to do with whether or not your wings tear off. It has everything to do with whether or not the wing stalls and you fall out of the sky like a rock with your wings still attached.

 

In speed range from minimum to maximum, AoA is proportional value to the speed. This value is so important for the airplane that it has its own measurement device attached to the pitot tube(or somewhere in clean and uninterrupted air stream), actually it's second most important value after speed value.

On low speeds AoA limitation tells pilot when his wings should experience stall or boundary layer separation but contrary on high speeds AoA tells pilot the structural limit of his planes wings or when his wings will overload and disintegrate if made lightweight on trade with structural strength.

Every airfoil or wing profile is tested in wing tunnel to find its behavior on speed and AoA ranges and is selected to the new design by optimal performance. The best designs heave high AoA capabilities and so that's the case with Su-27 but its more aerodynamic question other than structural which is question of most importance on supersonic designs which is Su27 fighter plane. It's supersonic fighter not Piper Cub. That's why aerodynamic engineers are fascinated by AoA value. And pilots ar fascinated by this number because oh high speed this number tells you when to expect structural failure.

Edited October 10, 2016 by jackmckay

[jackmckay]

^this^

 

Its been said before, but AoA isn't G. Its also important to note that the faster you go, the greater the attainable G at lower AoA; if you're standing on stall speed, maximum AoA equates to 1G. If you're at corner, maximum AoA equates to your airframe G load rating. And if you're faster, maximum AoA is higher than what the aircraft can withstand.

 

So in your newest example, jackmckay- what was the G?

 

 

On my latest pre your post first 'G' is actually 1G or g or gravity acceleration value, second 'G limit' is force because it is combined with mass, second Newton's law (F=m*a). Force on area is pressure, pressure challenges structural elements elastic region of Yang's modulus charts and when pressure further increases first occurs plastic deformation or f.ex. twisted/bent airplane and if pressure continues to increase after exiting plastic region structural break occurs.

 

On my previous post I explained the importance of AoA charts and mandatory limitations for airplane safe operation. On high supersonic speeds AoA safe range decreases that's why Su-27 have this limit for Mach 2 on 8 deg and at Mach 1 limit on 18 deg positive G turn. I was around 10 deg AoA when structural failure occurred at Mach 1.25 .

Edited October 10, 2016 by jackmckay

[jackmckay]

I think it is possible to export telemetry data - isn't that exactly how Tacview creates ACMI files, via Lua export of telemetry?

 

That's true but acmi files are low resolution variant of telemetry. In my .acmi file my G's were around 3 and in actual .trk file it was around 9 at which wing failure occurred.

 

Mother of all my question to ED/DCS regarding this topis is:

 

If I was close to structural strength of my wings, at high G value, why my pilot didn't experience any signs of blackout tunneling? Suhkoi wings could have been made stronger if there would be no pilot flying it inside who is very accurate Over-G instrument by the way.

Edited October 10, 2016 by jackmckay

[Ktulu2]

You get ~5s of oxygen reserve in your brain before starting to get tunelling vision or any other G effects. So if you did a small G-spike, you wont get affected by it.

[GGTharos]

Plenty of aircraft are out there that you can break easily with over-g. Almost any air-liner fits the bill for example, and there's no lack of bombers that could suffer from this either when loaded down.

 

How about the MiG-25? It's maximum safe load factor is 5 ... if we were to assume structural failure at 1.5x, that's 7.5g.

 

As for why you didn't get black-out, here's the reason, as Ktulu2 pointed out:

 

 

If I was close to structural strength of my wings, at high G value, why my pilot didn't experience any signs of blackout tunneling? Suhkoi wings could have been made stronger if there would be no pilot flying it inside who is very accurate Over-G instrument by the way.

[lunaticfringe]

On my latest pre your post first 'G' is actually 1G or g or gravity acceleration value, second 'G limit' is force because it is combined with mass, second Newton's law (F=m*a). Force on area is pressure, pressure challenges structural elements elastic region of Yang's modulus charts and when pressure further increases first occurs plastic deformation or f.ex. twisted/bent airplane and if pressure continues to increase after exiting plastic region structural break occurs.

 

On my previous post I explained the importance of AoA charts and mandatory limitations for airplane safe operation. On high supersonic speeds AoA safe range decreases that's why Su-27 have this limit for Mach 2 on 8 deg and at Mach 1 limit on 18 deg positive G turn. I was around 10 deg AoA when structural failure occurred at Mach 1.25 .

 

I asked you what the *G* was at the point of breakage. Not a bunch of things I already know.

 

You should try answering the question that's asked.

[jackmckay]

I asked you what the *G* was at the point of breakage. Not a bunch of things I already know.

 

You should try answering the question that's asked.

 

You should read my posts from beginning.

 

I'm answering this specially for you:

3.9G

Edited October 11, 2016 by jackmckay

[GGTharos]

The G at the point of breakage was 8.5+. Right from the track.

[lunaticfringe]

The G at the point of breakage was 8.5+. Right from the track.

 

That's gonna leave a mark.

[jackmckay]

DCS miscalculated G's.

 

Then, redo it (brake the wings) with same conditions (3 times) and paste tracks here.

 

I'll withdraw my statements about everything I said and praise the DCS for the rest of my life.

[jackmckay]

Plenty of aircraft are out there that you can break easily with over-g. Almost any air-liner fits the bill for example, and there's no lack of bombers that could suffer from this either when loaded down.

 

How about the MiG-25? It's maximum safe load factor is 5 ... if we were to assume structural failure at 1.5x, that's 7.5g.

 

Well, Su27 is high G supersonic fighter, top of the shelf, designed for 8+G constant load, combine it with safety factor of 1.5 and you get 12G structural failure red zone. Its wings are not made of Swiss cheese.

[probad]

if you really gave a damn about this you'd do some actual learning about aerodynamics and material science and then you wouldn't need people to patiently explain it to you over and over.

Edited October 12, 2016 by probad

[mvsgas]

Well, Su27 is high G supersonic fighter, top of the shelf, designed for 8+G constant load, combine it with safety factor of 1.5 and you get 12G structural failure red zone. Its wings are not made of Swiss cheese.

 

:doh:

https://docs.google.com/viewer?url=http%3A%2F%2Fcdn.akamai.steamstatic.com%2Fsteam%2Fapps%2F250310%2Fmanuals%2FDCS_Su-27_Flight_Manual_EN.pdf

 

https://forums.eagle.ru/showthread.php?t=164429&page=2

 

Using these few resources or information we can learn a few things

If you look around you can find many more sources, but for now, a little example to try to explain my point (maximum "G" depend on many factors including but not limited to weight and speed);

So at mach .85< to ≤ 1.25 no more than 139000kg or 7g ( whichever is higher).

Empty around 17,400 + 8 tons of fuel plus 2544kg of missiles= ~ 27,988.

At this weigh and this speed maximum g would be around 4.9 so....not sure about your 12g theory.

 

I think we all need to read a lot more and move on.

Edited October 12, 2016 by mvsgas

[lunaticfringe]

DCS miscalculated G's.

 

Everybody else is wrong- run with that.

 

Then, redo it (brake the wings) with same conditions (3 times) and paste tracks here.

 

I'll withdraw my statements about everything I said and praise the DCS for the rest of my life.

 

That's not how this works- that's not how any of this works.

 

Stall is a function of AoA, not speed; nor is it dependent on G. The relationship between the two is that maximum aerodynamic load available to the wing is attained at maximum AoA.

 

An AoA limiter is invoked to preclude stall, not G. Mach is dependent on speed and altitude, as is G; the higher the altitude, the lower the available G for a given Mach due to lower density. Subsequently, an AoA limiter set to preclude high altitude departure (as is the Su-27's, being an interceptor) isn't going to save you from overstressing the aircraft at 23,000 feet, because your available G is too damned high- you will break off the wings well before they stall.

 

If you knew the mathematical relationship between minimum stall speed for a given weight and available G at a higher speed, you'd grasp this concept- it's blatantly obvious. You don't, so you're not. And that's why this garbage about DCS calculating G incorrectly is nothing more than hand waving by someone who doesn't know what they're talking about.

Edited October 12, 2016 by lunaticfringe

[GGTharos]

There may be an issue still though - the G was increasing despite the stick having been moved forward.

 

So, the question here is what caused that?

 

The G and wing breakage is correct. The AoA is fine, too.

 

The only remaining issue is the increase in G. Is it an FM issue, is it a real aircraft issue, was it, as someone mentioned, a game freeze where the game continued interpreting the input incorrectly? (but then, why did it record the input correctly? :P )

[lunaticfringe]

There might be. But it has absolutely nothing to do with the preceeding three pages of jazz hands.

[jackmckay]

I opened this topic referring to ED. Who's ED stuff here?

Stronger argument goes to people actually flying Su-27 in DCS, so you that fly only F15 quit spitting fire, its a matter of physics and coding not balls or politics.

 

I'm actually mechanical engineer, CDF analyst, structural engineer, graphical designer and programmer. I belong to the group of people that design stuff and write manuals not just read them. My area of interest is fluid-structure interaction, marine application specific and I'm good at that. I design floating objects, internal combustion engines and aircraft, and all kind of stuff. And I actually speak 4 languages so I probably speak yours too. Do you speak mine?

 

Conclusion: No one yet can repeat failure in same conditions so its an anomaly in DCS engine. Period. Its a BUG.

[lunaticfringe]

I opened this topic referring to ED. Who's ED stuff here?

Stronger argument goes to people actually flying Su-27 in DCS, so you that fly only F15 quit spitting fire, its a matter of physics and coding not balls or politics.

 

Physics:

 

Aircraft as configured gives AoA and G warnings at approximately 110 knots indicated preceeding stall. Mark the aircraft as stalled at that point. Knots true for 23,950' is roughly 160 knots.

 

Available G = [speed/Vs]^2

 

Mach 1.26 at 23,950 ~ 830 knots.

830/160: 5.18.

5.18^2: 26.8 G at Max AoA.

 

Baseline maximum AoA on the Flanker is what, 24 at M0.5? That's the pure performance of what the wing generates, not where the limiter is set, or what the airframe can withstand. Those latter two values descend as speed goes up.

 

The wing in the given configuration is making roughly 1.1 G for unit of AoA; this is the reason for the all but perfectly linear growth observed on both your gauges and mine between AoA and G. Look at your gauges as shown- the math above proofs out.

 

And that's why when you put the needle at 9+ AoA, your wings come off- because you have completely overloaded the aircraft. Last recorded G is in fact 9.2 on the needle.

 

I'm actually mechanical engineer, CDF analyst, structural engineer, graphical designer and programmer. I belong to the group of people that design stuff and write manuals not just read them. My area of interest is fluid-structure interaction, marine application specific and I'm good at that. I design floating objects, internal combustion engines and aircraft, and all kind of stuff. And I actually speak 4 languages so I probably speak yours too. Do you speak mine?

 

Nice CV you have there; I design simulations as a trade, and currently have one undergoing review for course usage at the USAFA.

 

Subsequently, since you want to roll out your background in building planes, I find it interesting that you immediately chose to claim ED calculates G incorrectly, when the most basic amount of math used to design those planes you say you're involved in engineering would prove that the simulation model was patently correct here, and your aircraft came apart exactly like it should have- to the stated Sukhoi numbers for the given weight and Mach.

 

Conclusion: No one yet can repeat failure in same conditions so its an anomaly in DCS engine. Period. Its a BUG.

 

Five times in 1.5 Beta, sloppy or clean. Three more in 2.0 Alpha, just to confirm uniform performance. Angle of Attack remains roughly 1:1 with G in this situation as it should, and both rip the wings off right around 10 units AoA- exactly like they should.

 

It's not a bug. It's you.

Flanker Test 15beta.zip

Flanker Test 20alpha.zip

Edited October 13, 2016 by lunaticfringe

[Ktulu2]

Hmm, where does that available g formula come from?

Don't wanna discredit what you said or anything, just am curious, as the units do not match (none vs 9.8m/s²)

[lunaticfringe]

The equation used to calculate available G at a given speed is derived from stall speed from a given bank angle.

 

VsΦ = Vs√n

 

Vs = stall speed at 1.0G wings level flight

VsΦ = stall speed at the given bank angle

n = load factor for the given bank angle

 

All you're doing is skipping the bank angle choice, because it's arbitrary so long as you have the minimum airspeed to do it. Instead, you're performing the equation to find the required speed for a given G- Vs times the square root of the desired G.

 

Proof? See the attached EM. Want more? Look at your normal bank angle chart.

[jackmckay]

[jackmckay]

@lunaticfringe you entered every maneuver with aprox. 10% higher speed. My IAS was around 950, yours is above 1050. Energy vs speed has exponential growth. You pulled your stick 90% to max, I pulled 50% to 60% released.

[lunaticfringe]

Oh Christ, that's funny. Right there on my notepad, and I didn't use the conversion I'd already done.

 

Mach 1.26 at 23,950 = 758 knots

Indicated Vs at 23,950 = 110 knots

Converted Vs at 23,950 = 160 knots

758/160 = 4.7375

4.7375^2 = 22.44 G Available

22.44 G/24 AoA units = 0.935 G per AoA

 

Ratio is 0.935 G to 1 unit of AoA. 10 AoA will still kill it.

 

Even genteel pulls in tests 4 and 5 immediately following roll, it dies. And it carries the same indicated G you had when it blows: 9.2.

 

Track 7b is interesting. Pull 6-8 units of AoA, and no pop. The maneuver is completed, and a pair of horizontal turns using the AoA gauge.

 

First turn- roll, wait, pull. An excursion to 10G is noted, but no pop. If there's fatigue modelling, this likely took it to the limit, and the only thing that saved it was the onset of induced drag- which is being offset in your descending track by speed gained through loss of altitude.

Second turn- roll, pull. Excursion to 10+G is noted, pop.

 

There's inertial coupling in there.

Flanker Test 15bbeta.zip

Edited October 13, 2016 by lunaticfringe

[Ironhand]

In speed range from minimum to maximum, AoA is proportional value to the speed. This value is so important for the airplane that it has its own measurement device attached to the pitot tube(or somewhere in clean and uninterrupted air stream), actually it's second most important value after speed value.

On low speeds AoA limitation tells pilot when his wings should experience stall or boundary layer separation but contrary on high speeds AoA tells pilot the structural limit of his planes wings or when his wings will overload and disintegrate if made lightweight on trade with structural strength.

Every airfoil or wing profile is tested in wing tunnel to find its behavior on speed and AoA ranges and is selected to the new design by optimal performance. The best designs heave high AoA capabilities and so that's the case with Su-27 but its more aerodynamic question other than structural which is question of most importance on supersonic designs which is Su27 fighter plane. It's supersonic fighter not Piper Cub. That's why aerodynamic engineers are fascinated by AoA value. And pilots ar fascinated by this number because oh high speed this number tells you when to expect structural failure.

FWIW, after all is said and done, the table you quoted in Your Post and to which I was responding is found in the Operating Limitations section of the Flanker manual and is filed under Stability and Controllability. It's referencing stalling the wing, not structural limitations.