missing info Roll Input structural failure modeling is incorrect.

[=475FG= Dawger]

At present, the introduction of aileron during high speed, high G flight will easily snap the wings off.

This behavior is incorrect.

The F-5E manual discusses this in some detail.

It is clear that at the published limits, roll input up to the SPRING STOP may be initiated. Above the published limit, rolls may be initiated using roll input LESS THAN FULL (To the Spring Stop).

 

Currently, high speed, high G roll inputs much less than to the SPRING STOP results in catastrophic wing failure.

Please correct this.

[=475FG= Dawger]

@BIGNEWY @NineLine Is this issue being looked at? It seems a very obvious error in the current F-5 modeling.

 

[cofcorpse]

Hi, could you attach a track showing a problem?

 

[=475FG= Dawger]

On 12/6/2021 at 1:09 AM, cofcorpse said:

Hi, could you attach a track showing a problem?

 

I will work on getting you one ASAP.

[=475FG= Dawger]

@cofcorpsePlease confirm you received my track relating to this issue.

[=475FG= Dawger]

The report linked below clearly indicates an actual F5E was static tested to ultimate load and DOES NOT experience any structural failure at 1.5 times the limit load (7.33)

https://apps.dtic.mil/sti/pdfs/ADA032403.pdf

So, from this report we know the F5E can sustain 1.5 times its limit load of 7.33 G (10.995g) without ANY structural failure, much less total wing failure. The only failure during the static testing was permanent buckling of the trailing edge spar during landing spin up, which was subsequently corrected by redesign.

Edited December 17, 2021 by =475FG= Dawger

[LowRider88]

On 12/17/2021 at 7:32 AM, =475FG= Dawger said:

The report linked below clearly indicates an actual F5E was static tested to ultimate load and DOES NOT experience any structural failure at 1.5 times the limit load (7.33)

https://apps.dtic.mil/sti/pdfs/ADA032403.pdf

So, from this report we know the F5E can sustain 1.5 times its limit load of 7.33 G (10.995g) without ANY structural failure, much less total wing failure. The only failure during the static testing was permanent buckling of the trailing edge spar during landing spin up, which was subsequently corrected by redesign.

 

How's many bugs are you going to open for the same non-issue?  Don't you think ED have bigger fish to fry?  Why didn't you add this to the original thread?  This is static test, to 1.5 * 7.33 G max, without additional aileron roll stress.  In your inflight G reading, 1.5 * 7.33 is your G meter reading for the fuselage only and not what the wing is stressed to during 1.5 * 7.33, plus roll stress.

ED, if you disregard physics and go with his logic, please also add code to kill the virtual pilot so we don't have crazy UFO flyers in the sim.  No human can dogfight at 1.5 * 7.33 + Roll stress.

[=475FG= Dawger]

As many as it takes until they get it right. 
 

I am unaware of any previous bug report regarding the current symmetrical G limits being too low. Feel free to point it out. 
 

FWIW, although closely related, symmetrical and asymmetrical limits are two different subjects for bug reports. 
 

And those each have sub-topics. As an example, the lower symmetrical G limits with external stores are not wing structural limits. They are pylon limits. The wing failure point should not be tied to those limits. Instead, pylon damage and subsequent effects should be modeled for over G with stores. This currently does not appear to be the case. 

[Basher54321]

Right - Here is where you are Dawger.

You have found an old document on the Internet.

You have spent a little time reading it.

Unfortunately you clearly have no understanding of what is written there and that is demonstrated in your various posts - you are not even close. But then you have no knowledge of this subject so not your fault.

My "opinion" as you put it is unfortunately for you more informed than you realize. There is a heck of a lot more to this however that is one can of worms I will not be opening because it will just confuse everyone even more.

 

If you can find the original USAF specs that Northrop had to build the aircraft to that might be useful - or if you can get hold of an actual F-5E structural engineer they would be the best source - anyone else seriously wouldn't have a clue.  My advice would be to pass information on without commenting on it.

cheers

[BIGNEWY]

merged threads, where did you attach the track replay?

thanks

[=475FG= Dawger]

21 minutes ago, Basher54321 said:

Right - Here is where you are Dawger.

You have found an old document on the Internet.

You have spent a little time reading it.

Unfortunately you clearly have no understanding of what is written there and that is demonstrated in your various posts - you are not even close. But then you have no knowledge of this subject so not your fault.

My "opinion" as you put it is unfortunately for you more informed than you realize. There is a heck of a lot more to this however that is one can of worms I will not be opening because it will just confuse everyone even more.

 

If you can find the original USAF specs that Northrop had to build the aircraft to that might be useful - or if you can get hold of an actual F-5E structural engineer they would be the best source - anyone else seriously wouldn't have a clue.  My advice would be to pass information on without commenting on it.

cheers

Of course, real world aircraft fatigue is complex subject.

If we were discussing the real world aircraft, that would matter.

We aren't

We are issued a factory fresh, fatigue free F-5 every sortie.

So the question before us is quite simple.

Would the factory fresh, zero airframe time, F-5 suffer catastrophic wing failure the first time it experienced 10.995 G?

The answer is quite obviously no, even without referencing an "old document on the internet".

Feel free that it should, indeed, suffer such a fate.

 

I did enjoy your riffing on the old "if you haven't flown it, you can't possibly have a clue" chestnut.

[Golo]

@=475FG= Dawger I just tested it for myself and your claims are BS. I was able to do full spring stop rolls under G and my wing were still attached after several tests. Ive tested pull out full stop spring rolls from over 450kias at 5-7g with no problems. I was obviously over limit g doing that, I even had it pegged at 10 after I was done and my wings were still OK. You must be doing something way worse with your F-5 or have some fails in DCS files. Track attached.

F-5 wing test.trk

[cofcorpse]

On 12/17/2021 at 3:22 PM, =475FG= Dawger said:

@cofcorpsePlease confirm you received my track relating to this issue.

I've received your track, thank you! But I didn't find anything suspicious in it. Could you record a simple and short track in singleplayer showing a problem and provide confirmation that it is wrong?

[dcsil2pilot]

I don't have the in-game track, but I do have my tacview from last night where my wings snap @ 6.4G because I started to roll during the turn.

I maintain a 6-7G turn looking for the bandit, find them behind me ready to shoot and begin to roll to get out of plane, poof! Wings pop right off. I attached pictures showing the telemetry data before and right as the wings snap though I doubt that will be helpful or what is needed.

 

A plane I have spent so much time learning and flying is no longer fun because they snap at the drop of a hat. I know it's extremely common, flying red I can get kills without even shooting because once you're behind them, they kill themselves with a single pull!

[=475FG= Dawger]

On 12/18/2021 at 1:23 PM, Golo said:

@=475FG= Dawger I just tested it for myself and your claims are BS. I was able to do full spring stop rolls under G and my wing were still attached after several tests. Ive tested pull out full stop spring rolls from over 450kias at 5-7g with no problems. I was obviously over limit g doing that, I even had it pegged at 10 after I was done and my wings were still OK. You must be doing something way worse with your F-5 or have some fails in DCS files. Track attached.

F-5 wing test.trk 2.23 MB · 2 downloads

Your testing methods are not quite up to the task. The aircraft needs to be at full internal fuel with tip stores for testing.

Here are the limitations to test against.

According to the limitations, you should be able to initiate a 3/4 stick input 180 degree roll at 0.95 IMN and 7.33 G and not be required to record a log entry (full internal fuel), much less snap the wings off. The current DCS F-5 will regularly shed its wings under those conditions.

[randomTOTEN]

16 minutes ago, =475FG= Dawger said:

you should be able to initiate a 3/4 stick input 180 degree roll at 0.95 IMN and 7.33 G and not be required to record a log entry (full internal fuel), much less snap the wings off.

I'm reading roll entry max G is +5.8?

Edited December 22, 2021 by randomTOTEN

[=475FG= Dawger]

1 minute ago, randomTOTEN said:

I'm reading roll entry max G is 5.8+?

 

It is a lot less black and white than that. The Roll Entry Maximum G is the maximum G where a 360 degree roll with the stick at the spring stop can be initiated WITHOUT exceeding the structural limits.

Further, the limitations section delineates when logbook entries are required. According to those limitations, one could initiate less than spring stop/less than 360 degrees rolls at the symmetrical G limit and not even be required to record a log book entry.

Reading between the lines, the real asymmetric G problems crop up with abrupt, full stop, 360 degree rolls. What this boils down to is that the current F-5E is a bit more delicate than it should be.

I am not implying it shouldn't break. There clearly should be a failure point. However, I think the asymmetrical failures are set far too low from my reading of the limitations. I do think the asymmetrical limits are driven by the symmetrical limit and I also think the symmetrical failure G is set a bit low at 11 g FOR A FIRST TIME OVER-G. Maybe bend the wing or twist it at that level but complete failure should be unlikely. Break on the second pull to high G or something a bit more realistic.

[randomTOTEN]

Yeah, that's not how I read it.

I quote: "NORMALLY, THE LOAD FACTOR INCREASES DURING A ROLL DEPENDING ON ANGLE-OF-ATTACK, ROLL RATE, ETC."

"ROLL ENTRY G LEVELS ARE ESTABLISHED BY DETERMINING THE G LEVEL AT WHICH A MAXIMUM RATE, 360 DEGREE ROLL (AILERON TO THE SPRING STOP) CAN BE INITIATED WITHOUT EXCEEDING THE MAXIMUM ALLOWABLE LOAD FACTOR. FOR EXAMPLE, AN AIRCRAFT WITH AN EMPTY CENTERLINE FUEL TANK MAY ENTER A MAXIMUM RATE ROLLING MANEUVER WITH 4.8 G ESTABLISHED AND BE ASSURED THAT 6.0 G WILL NOT BE EXCEEDED, PROVIDED NO AFT STICK IS APPLIED DURING THE MANEUVER."

"ROLLING MANEUVERS CAN BE INITIATED AT G LEVELS ABOVE THE ESTABLISHED ROLL ENTRY G IF LESS THAN A MAXIMUM RATE ROLL IS PERFORMED; HOWEVER SOME G INCREASE OCCURS DURING THE MANEUVER."

33 minutes ago, =475FG= Dawger said:

the real asymmetric G problems crop up with abrupt, full stop, 360 degree rolls

No. It reads to me that roll rate adds additional G. And the certification standard is set at 360 degree full deflection aileron rolls.

It's kind of a moot point. I just loaded the Caucasus Intercept Quickstart. The jet has about 2600lbs of fuel on board(above the quoted 2200lbs minimum condition) and two sidewinders. Exactly your test conditions.  I loaded the jet to 6 G (instrument), then put the aileron to the spring stop. I rolled through more than 360 degrees with this configuration and the jet held together just fine.

I suspect this might be a Multiplayer issue then.

You guys need to start posting tracks...

Edited December 22, 2021 by randomTOTEN

[Golo]

1 hour ago, =475FG= Dawger said:

Your testing methods are not quite up to the task. The aircraft needs to be at full internal fuel with tip stores for testing.

Here are the limitations to test against.

Like this?

Edit: I overstressed it past 10g and wing finally snapped (not shown in track), I still dont see anything wrong on my end with wing structure limits.

F()-5 wing test 2.trk

Edited December 22, 2021 by Golo

[fredclan]

lots of people are ripping the wings off, who cares why, it doesnt happen to other dcs aircraft with this frequency. either make all of them rip the wings off like the f5 if you claim its realistic, or fix the f5. 

[randomTOTEN]

33 minutes ago, fredclan said:

who cares why

that's exactly why it's happening

[=475FG= Dawger]

3 hours ago, randomTOTEN said:

Yeah, that's not how I read it.

I quote: "NORMALLY, THE LOAD FACTOR INCREASES DURING A ROLL DEPENDING ON ANGLE-OF-ATTACK, ROLL RATE, ETC."

"ROLL ENTRY G LEVELS ARE ESTABLISHED BY DETERMINING THE G LEVEL AT WHICH A MAXIMUM RATE, 360 DEGREE ROLL (AILERON TO THE SPRING STOP) CAN BE INITIATED WITHOUT EXCEEDING THE MAXIMUM ALLOWABLE LOAD FACTOR. FOR EXAMPLE, AN AIRCRAFT WITH AN EMPTY CENTERLINE FUEL TANK MAY ENTER A MAXIMUM RATE ROLLING MANEUVER WITH 4.8 G ESTABLISHED AND BE ASSURED THAT 6.0 G WILL NOT BE EXCEEDED, PROVIDED NO AFT STICK IS APPLIED DURING THE MANEUVER."

"ROLLING MANEUVERS CAN BE INITIATED AT G LEVELS ABOVE THE ESTABLISHED ROLL ENTRY G IF LESS THAN A MAXIMUM RATE ROLL IS PERFORMED; HOWEVER SOME G INCREASE OCCURS DURING THE MANEUVER."

No. It reads to me that roll rate adds additional G. And the certification standard is set at 360 degree full deflection aileron rolls.

It's kind of a moot point. I just loaded the Caucasus Intercept Quickstart. The jet has about 2600lbs of fuel on board(above the quoted 2200lbs minimum condition) and two sidewinders. Exactly your test conditions.  I loaded the jet to 6 G (instrument), then put the aileron to the spring stop. I rolled through more than 360 degrees with this configuration and the jet held together just fine.

I suspect this might be a Multiplayer issue then.

You guys need to start posting tracks...

 

The example (4.8 G max roll entry G with empty centerline fuel tank) is not actually a wing limit. Its the limit for the centerline pylon.

The relevant limits are 7.33 G symmetrical and 5.8 G roll entry (less than .95 IMN)

[fredclan]

On 12/22/2021 at 5:13 PM, randomTOTEN said:

that's exactly why it's happening

so the F5 is such a uniqe aircraft that a large number of people are ripping the wings off....why isnt this happening to the other aircraft?

[randomTOTEN]

58 minutes ago, fredclan said:

....why isnt this happening to the other aircraft?

Fly By Wire

they were ripping their wings off when they pulled the paddle (disabled the limiter) too...

EDIT: I have a tacview where a Viggen pulled an estimated 11 G on me in a merge. Clearly the limits for that aircraft should be looked at too. Regardless, you guys should not be putting your jets in a position where these become issues. Many users don't know the actual failure points of their modules, because those are set beyond the load limits in the manual. Because they respect those limits, they will spend years flying the F-5, and never snapping the wings once. They don't make it a policy to wreck their jets on every sortie.

Edited December 24, 2021 by randomTOTEN

[[40th SOC] Vapor]

Also, when the manual says "don't exceed 5.2 G with full lateral stick deflection," that does NOT mean you are free to yank 3/4 aileron deflection at 7.33 G.

The total load factor is a vector sum of the loads affecting the aircraft, and the ultimate load limit is not static; the airframe is better at handling some load combinations than others. Yes, you CAN enter some amount of roll at above the roll entry limit, but it's a sliding scale that will also be non-uniform. The manual gives you a number that has been tested to work under a specific set of conditions: constant aft stick, full lateral aileron, at 5.2G with 2,200+ lbs of fuel, or 5.4 G with less than 2,000 lbs of fuel. If you do that, but pull harder mid-roll, you exceed the total load limit. If you add rudder mid-roll, you exceed the load limit. If you do it abruptly even if only at 5G, you exceed the load limit (hence the AFTO entry).

At 7.33G, you have NO available roll. You are already maxing the jet out symmetrically. If you add an asymmetric component to that, some parts of the aircraft will exceed the load limit. 

Below 6.5G (or 7.33G if you have less than 2,200 lbs of fuel), you MIGHT have some amount of available roll, but that's not guaranteed. Asymmetric roll loads are complicated and their effects on the airframe are not uniform. All that you know for sure is the endpoints of the curve, because that's what they tested for the manual: at 5.2G you (just barely) have full roll input available, and that at 6.5G you have zero roll input available. Inducing roll at beyond 5.2 G is in the untested grey area: you know that you have less than full roll available, and probably that the farther above 5.2G you are, the less you have, but you do not know how much less. Nothing is guaranteed above 5.2G.