correct as-is Concerns about G-Onset and Damage to wings

[ElvisDaKang]

I was honkin it around pretty good when the wings decided to say ""FCK IT"". That said - they didnt use to be so flimsy. Enough people are talking about it now  in YT vids etc etc now so we will see where it goes. 

[Sarge55]

“Honking it around pretty good” is that technical term?

I wonder how many G’s that is?

[Esac_mirmidon]

29 minutes ago, Sarge55 said:

“Honking it around pretty good” is that technical term?

I wonder how many G’s that is?

1.5 times a regular  sneeze

[LowRider88]

If the wings are ripping off during rolls while under 10 G, that seems plausible to me.  If you have never heard about that happening in real life, it may be because 10 Gs is quite high for a human to endure.  Doesn't 10 Gs kill a human?  The human would at least black out way before then and not even have the congitive ability to roll the plane.

People claim the MiG-19 lawn darts into the ground during dives due to the compressibility effect, I.e. It does not have an efficient supersonic wing, I.e the wings are too thick.

If the F-5 with its weak engines is able to go supersonic, that is because it is aero dynamically efficient, I.e a thinner wing.

Its thin wings are not as short span as the F-104. So wouldn't they be weaker than both a MiG-19 and F-104?

We can't have everything.  There are design trade offs.

Please, no more UFO behaviour in DCS.  Doing a scissor fight at 10Gs in a plane built in the 70s seems quite absurd.

Just because some find it difficult to look down at a G meter in flight, does not mean rules of physics should be tweaked.

To fly within G limits is easy, just control your speed and be careful of maneuvers.  Real pilots had to do that or else the plane would kill them.

[MiG21bisFishbedL]

2 hours ago, LowRider88 said:

 Doesn't 10 Gs kill a human?  The human would at least black out way before then and not even have the congitive ability to roll the plane.

 

It's not that simple, just for clarification. Most fighter jocks train to withstand 9 with the help of G suits, but I've seen records and evidence of people sustaining more than 10. The dudes in the Red Bull series subject themselves to 10+ on a somewhat regular basis, but it isn't a sustained figure. It's really the time spent at that G that's important and DCS has always been pretty fiddly on that one.

Edited December 11, 2021 by MiG21bisFishbedL

[LowRider88]

Well according to Scientific American:

"We experience higher or lower g forces when we are rapidly changing speeds or directions. Normal humans can withstand no more than 9 g's, and even that for only a few seconds. When undergoing an acceleration of 9 g's, your body feels nine times heavier than usual, blood rushes to the feet, and the heart can't pump hard enough to bring this heavier blood to the brain. Your vision narrows to a tunnel, then goes black. If the acceleration doesn't decrease, you will pass out and finally die. The Air Force's F-16 can produce more g's than the human body can survive. We're forced to limit the acceleration of planes and spacecraft to a level humans can survive."

It might help if you provide sources for your claims.

What ever the case with supposed acrobatic pilots, who some how don't get their brains torn out of their skulls and thrown into their chest from 10 times their body weight forcing it there, the F-5E wings are still weak.

We have the nice Belsimtek 3D animations of the wings wobbling when firing a missile.  You think those wobbly things won't sheer off under 10 G stress?  Someone should post documented evidence that the F-5E was designed to sustain 10Gs long enough to complete a roll.

 

[LowRider88]

Just an additional note.

If the G meter says 10 Gs, that is most likely coming from an instrument installed somewhere on the fuselage of the F-5, and not the wings.  So even before rolling, the violent pitch up the silly pilot invoked is already causing the 10G, just from pitching, which is well over design limitations.

10Gs is the plane flying at transonic or supersonic speed and then the pilot uses the elevators and wings to force it to go in another direction.  The inertia wants it to go forward, so the wings have to turn the plane by taking a huge mass of airflow crushing it at extreme angle of attack, at 10 times the weight of the plane.

Add to that the rolling movement, and one of those wings is stressed far beyond what the fuselage G meter is indicating.  That wing is gone.  Once that one goes the other will follow in short order.

[MiG21bisFishbedL]

9 hours ago, LowRider88 said:

Well according to Scientific American:

"We experience higher or lower g forces when we are rapidly changing speeds or directions. Normal humans can withstand no more than 9 g's, and even that for only a few seconds. When undergoing an acceleration of 9 g's, your body feels nine times heavier than usual, blood rushes to the feet, and the heart can't pump hard enough to bring this heavier blood to the brain. Your vision narrows to a tunnel, then goes black. If the acceleration doesn't decrease, you will pass out and finally die. The Air Force's F-16 can produce more g's than the human body can survive. We're forced to limit the acceleration of planes and spacecraft to a level humans can survive."

It might help if you provide sources for your claims.

What ever the case with supposed acrobatic pilots, who some how don't get their brains torn out of their skulls and thrown into their chest from 10 times their body weight forcing it there, the F-5E wings are still weak.

We have the nice Belsimtek 3D animations of the wings wobbling when firing a missile.  You think those wobbly things won't sheer off under 10 G stress?  Someone should post documented evidence that the F-5E was designed to sustain 10Gs long enough to complete a roll.

 

I don't recall disagreeing with your notions about the F-5's wings? Like, at all, in my post? Just clarifying that the time spent at G and physical conditioning also matter. 

And DCS has always modeled G forces in a pretty basic manner. But sure, tilt at windmills.

Indeed, max safe structural G in the F-5 is a touch over 7, 7.3 positive and 3.9 negative Gs. You can go past that, but you're risking structural damage.

Edited December 12, 2021 by MiG21bisFishbedL

[Machalot]

The stresses that destroy a wing during heavy g are primarily caused by lift, which creates both a bending stress and a shear stress at the wing root. If you are pulling a certain number of g's that puts you near but under the limit, the wings should survive.  But if you then apply roll input, the aileron deflection causes one of the wings to generate even more lift, increasing the bending and shear stresses and possibly exceeding the limits.  That may explain why roll input under high g is breaking things.

Edited December 14, 2021 by Machalot

[=475FG= Dawger]

 

This certainly does not seem to indicate that minor aileron input will rip the wings off. As I said to my wingman earlier today, if the pilot is afraid of the airplane, it is no longer a fighter.

[Quid]

On 12/15/2021 at 1:34 AM, =475FG= Dawger said:

 

This certainly does not seem to indicate that minor aileron input will rip the wings off. As I said to my wingman earlier today, if the pilot is afraid of the airplane, it is no longer a fighter.

Without a track file showing how much "g" you're loading, or what your control inputs were at the time it's hard to assess, but like all aircraft, the F-5E's rolling limits are lower than its symmetrical limits.  Since you're quoting the manual, I assume you have access to it.  Read the "In-flight carriage & sequencing limitations" section, which has all of the g-limits including symmetrical and asymmetrical for the F-5E and F by configuration.  You're over-stressing the jet if you pull more than +5.8g or -1g with wingtip rails/Sidewinders and otherwise clean.  If you have more than 2200lbs of fuel at 0.95-2.0IMN, you've got +5.2/-1g as your asymmetrical envelope.  I don't know if the F-5 is modeled against different limits or not, but it's something to bear in mind.  Right now, it sounds like several aircraft are too sensitive to overstress and it is being worked on.  I flew the F-5 a few times about two weeks ago and could not pull the wings off in symmetrical pulls without ordnance (guns only).  I did manage to remove them in a rolling defense at high speed.  I'd wait to see how/if ED tweaks the overstress model in the coming patches.

[LowRider88]

On 12/15/2021 at 2:34 AM, =475FG= Dawger said:

 

This certainly does not seem to indicate that minor aileron input will rip the wings off. As I said to my wingman earlier today, if the pilot is afraid of the airplane, it is no longer a fighter.

How does it not?  It says Roll G Entry should be less than Max G limit.  If max G is about 7, roll G should be less than that.  People here are rolling at 10 G.  That is not minor aileron at all.

The Roll G Entry Guideline acts as a warning.  If you say you should not be afraid of the plane because it is a fighter, then you are just ignoring the rule.  It's the same as a gun owner getting killed by his/her own guns for being laxed with safety guidelines.  The fighter is still a fighter.  The fighter pilot is still a fighter pilot (and perhaps a better one) if he is afraid, because that is being aware.

Whether or not we are afraid of the plane doesn't change the rules of physics.

Edited December 16, 2021 by LowRider88

[Baaz]

I've probably got more seat time in an F-5 than any other bird aside from helos.  I've never experienced the wings just ripping off.  I guess I'm doing something wrong... or right, depending on your perspective.  When I'm listening to the pilot sucking in oxygen and the plane starts buffeting, I know I'm pulling a lot of G's, and ease off on the stick.  Simple as that.  No need to look at G-meters, airspeed or anything.  Learn to keep your head out of the cockpit and just listen to what the pilot and plane is telling you.  Never have to worry about stalling when you do this also, as she'll pretty much be between 300-400 knots easily.

[=475FG= Dawger]

4 hours ago, LowRider88 said:

How does it not?  It says Roll G Entry should be less than Max G limit.  If max G is about 7, roll G should be less than that.  People here are rolling at 10 G.  That is not minor aileron at all.

The Roll G Entry Guideline acts as a warning.  If you say you should not be afraid of the plane because it is a fighter, then you are just ignoring the rule.  It's the same as a gun owner getting killed by his/her own guns for being laxed with safety guidelines.  The fighter is still a fighter.  The fighter pilot is still a fighter pilot (and perhaps a better one) if he is afraid, because that is being aware.

Whether or not we are afraid of the plane doesn't change the rules of physics.

 

A careful reading is required.

The Roll Entry G limit is the limit where EXCEEDING the aileron spring stop will over G the aircraft for its current configuration.

The aileron spring stop in the real airplane is a physical stop that the pilot can push through by applying extra force.

In DCS the spring stop is mapped to a button and you cannot exceed the spring stop without pushing the button.

So, essentially all rolls in the DCS F-5 are executed at the spring stop or less.

The limitation for the clean airplane reads as follows:

So that means you can slam the stick to the spring stop at 5 G, roll the aircraft 360 degrees and only be required to make a log book entry (probably generating an inspection).

This also means that you could push the stick to the spring stop at 7.33 G ( the clean G limit) and not be required to make a log entry if the roll was less than 360 degrees.

Any roll above 5 G using less than spring stop deflection does not even require a form entry

Nearly all rolls in combat are less than 360 degrees.

If the aircraft was likely to lose its wings when rolling at high G, I think they would require more than a log entry

Quote

"Dear Logbook, Today I rolled the aircraft at 7 G and the wings snapped off. Please re-install them at your earliest convenience"

There is nothing in the manual indicating that the pilot needed to be extremely vigilant in this regard. The very long time in hard service of these aircraft indicates no structural issues. Metal fatigue is cumulative and were the F-5/T-38 wing structures as delicate as they now are in DCS the aircraft would have been long retired.

Given the limitations information in the manual and the long service history of this aircraft, the current wing failure modeling is very suspect.

 

 

Edited December 16, 2021 by =475FG= Dawger
typo

[LowRider88]

27 minutes ago, =475FG= Dawger said:

A careful reading is required.

The Roll Entry G limit is the limit where EXCEEDING the aileron spring stop will over G the aircraft for its current configuration.

The aileron spring stop in the real airplane is a physical stop that the pilot can push through by applying extra force.

In DCS the spring stop is mapped to a button and you cannot exceed the spring stop without pushing the button.

So, essentially all rolls in the DCS F-5 are executed at the spring stop or less.

The limitation for the clean airplane reads as follows:

So that means you can slam the stick to the spring stop at 5 G, roll the aircraft 360 degrees and only be required to make a log book entry (probably generating an inspection).

This also means that you could push the stick to the spring stop at 7.33 G ( the clean G limit) and not be required to make a log entry if the roll was less than 360 degrees.

Any roll above 5 G using less than spring stop deflection does not even require a form entry

Nearly all rolls in combat are less than 360 degrees.

If the aircraft was likely to lose its wings when rolling at high G, I think they would require more than a log entry

There is nothing in the manual indicating that the pilot needed to be extremely vigilant in this regard. The very long time in hard service of these aircraft indicates no structural issues. Metal fatigue is cumulative and were the F-5/T-38 wing structures as delicate as they now are in DCS the aircraft would have been long retired.

Given the limitations information in the manual and the long service history of this aircraft, the current wing failure modeling is very suspect.

 

 

 

Not sure why you are requesting a more careful read.  According to HWASP's post on the first page, the wings rip off at 10G.  You post here does not address that.

[Snappy]

I think the problem is , many people on various modules in DCS have simply becoming used to habitually over- G-ing their aircraft to exploit performance gains and now that overstressing, even beyond additional buffer results in structural damage (surprise, surprise..)the pitchforks come out.

They complain about it being unrealistic, but I think people have unrealistic ideas of how aircraft are operated in reality

Edited December 17, 2021 by Snappy

[=475FG= Dawger]

4 hours ago, Snappy said:

I think the problem is , many people on various modules in DCS have simply becoming used to habitually over- G-ing their aircraft to exploit performance gains and now that overstressing, even beyond additional buffer results in structural damage (surprise, surprise..)the pitchforks come out.

They complain about it being unrealistic, but I think people have unrealistic ideas of how aircraft are operated in reality

 

Folks who operate them in reality disagree with you.

[Snappy]

1 hour ago, =475FG= Dawger said:

Folks who operate them in reality disagree with you.

Oh, so it’s normal operating procedure to exceed the aircraft G-Limit ,plus the safety buffer ? Sorry but you will have to provide some evidence or source for such a bold statement if you want to be taken seriously.

Edited December 17, 2021 by Snappy

[=475FG= Dawger]

22 minutes ago, Snappy said:

Oh, so it’s normal operating procedure to exceed the aircraft G-Limit ,plus safety buffer ? Sorry but you have to provide some evidence or source for such a bold statement.

The following information 

is from this

And clearly indicates the USAF planned for 40+ 9+G excursions every 1000 flight hours during air to air combat sorties.

Here is the rest of the section on how this chart was derived. 

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

 

 

Edited December 17, 2021 by =475FG= Dawger
additional information

[=475FG= Dawger]

And the F-5E wing experienced NO structural failures of any sort when subjected to 1.5 times 7.33 in static testing. It experienced one structural deformation in the trailing edge spar during landing spin up testing at limit load.

 

 

Edited December 17, 2021 by =475FG= Dawger

[Bananabrai]

Take the G numbers with a grain of salt for the following report, I rember that off of my sometimes nor very reliable brain...:

We (2 friends and I) did some BFM training on tuesday and where using the F-5 with the official EFM diagrams:
- up to the max lift speed (385 KIAS according to real docs) at 15.000ft, we pulled the merge with roughly 6 to 7G
- then we tested/maintained/fought at max sustained rate (0.7M) at around 3G most of the rime and for the angle/1-circle (0.55M) around 2.5G.

The real diagrams showed that (if I remember correctly), at 15k ft and 0.7M (max sustained rate), should be around 3.5G, so in DCS we have seen lower numbers (max reheat) 

None of our planes wings snaped during these ~20 dogfights.

[Snappy]

On 12/17/2021 at 1:48 PM, =475FG= Dawger said:

The following information 

is from this

And clearly indicates the USAF planned for 40+ 9+G excursions every 1000 flight hours during air to air combat sorties.

Here is the rest of the section on how this chart was derived. 

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

 

 

 

This is a fatigue integrity program, it has almost nothing to do with normal operating procedures  and what limits the pilots were expected to respect. Otherwise you could drop the whole G- limitation chapter from the FCOM and replace it with , "pull as much as you want , just keep it below 40x +9G occurences/1000hrs" 

Still even then ,on average that would be only one +9G occurence during every 25 flight hours. If you assume a 2.5h sortie length, (which is very optimistic, given that most DCS flights on popular cold war servers are a lot shorter) , that would translate into one 9G event ( assumed ) per every 10 flights. That alone should tell you a lot on what the USAF  really assumed how its Pilots performed & behaved in regards to taking limitiations seriously.

On a shorter sortie , like in DCS, you would have to perform even more flights while still only ever doing a single over-G to +9G, otherwise you're already outside the USAF fatigue profile. Do you really think this is what happens in online servers?

Again, in reality you have a  +7.33G RL symmetric limit in the best config, plus a roll entry G-Limit of 5.2G , depending on how much aileron you put in and how many degrees you roll.

This is what you should aim for, even in combat . Sure, you can exceed it by chance , adrenaline or to survive and you can also do that in DCs , to a point which is still generous in my opinion.

Are you really complaining about the edge case, that you want to be able to pull the full 7.33x1.5 = 10.995G  all the time without any damage?

Even the fatigue integrity programm you quoted does only account for up to +9G (wonder why?) . You can do that in DCS, so what the issue? 

Edited January 27, 2022 by Snappy

[LowRider88]

4 hours ago, =475FG= Dawger said:

The following information 

is from this

And clearly indicates the USAF planned for 40+ 9+G excursions every 1000 flight hours during air to air combat sorties.

Here is the rest of the section on how this chart was derived. 

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

 

 

 

Your charts here do not show 10G.  Because 10 Gs will kill a pilot.

[LowRider88]

3 hours ago, =475FG= Dawger said:

And the F-5E wing experienced NO structural failures of any sort when subjected to 1.5 times 7.33 in static testing. It experienced one structural deformation in the trailing edge spar during landing spin up testing at limit load.

 

 

 

This was a static test done with jigs on the ground and not in the air.  Because overstressing the plane in the air at 10 Gs will kill a pilot.

The test stressed the wings to the first sign of weakness, then they stop.  In the air, a silly pilot who overstressed the 1970s plane does not have fly by wire reflexes to correct this all the while blacking out and dying from 10Gs.

As I mention d above, 10Gs on the G meter is fuselage overload.  Add rolling and the wing is even higher.

[=475FG= Dawger]

1 hour ago, Snappy said:

This is a fatigue integrity program, it has almost nothing to do with normal operating procedures  and what limits the pilots where expected to respect. Otherwise you could drop the whole G- limitation chapter from the FCOM and replace it with , "pull as much as you want , just keep it below 40x +9G occurences/1000hrs" 

Still even then ,on average that would be only one +9G occurence during every 25 flight hours. If you assume a 2.5h sortie length, (which is very optimistic, given that most DCS flights on popular cold war servers are a lot shorter) , that would translate into one 9G event ( assumed ) per every 10 flights. That alone should tell you a lot on what the USAF  really assumed how its Pilots performed & behaved in regards to taking limitiations seriously.

On a shorter sortie , like in DCS, you would have to perform even more flights while still only ever doing a single over-G to +9G, otherwise you're already outside the USAF fatigue profile. Do you really think this is what happens in online servers?

Again, in reality you have a  +7.33G RL symmetric limit in the best config, plus a roll entry G-Limit of 5.2G , depending on how much aileron you put in and how many degrees you roll.

This is what you should aim for, even in combat . Sure, you can exceed it by chance , adrenaline or to survive and you can also do that in DCs , to a point which is still generous in my opinion.

Are you really complaining about the edge case, that you want to be able to pull the full 7.33x1.5 = 10.995G  all the time without any damage?

Even the fatigue integrity programm you quoted does only account for up to +9G (wonder why?) . You can do that in DCS, so what the issue? 

 

You  are trying very hard to justify the wings breaking at 11G or breaking at something less than 11G with any roll input contrary to available evidence.

Its pretty obvious they will not break at 11 G, especially the first time 11 G is achieved. 

They tested the equivalent of 4 aircraft lifetimes (16,000 hours)without issue up to the ultimate limit.

The DCS F-5 wing breaks at 11 G the first time you reach it, which is demonstrably wrong.

The DCS F-5 will shed its wings with very minor roll inputs above 7 G, also demonstrably wrong.

For more information on how the Mission Phase Maneuver Spectra requirements were determined, you should refer to MIL-A-8860 and MIL-A-8866. I imagine they were developed via survey of actual sorties and the 9 G cutoff likely has more to do with the limitations of the recording accelerometers installed in line aircraft than anything else.

40 minutes ago, LowRider88 said:

This was a static test done with jigs on the ground and not in the air.  Because overstressing the plane in the air at 10 Gs will kill a pilot.

The test stressed the wings to the first sign of weakness, then they stop.  In the air, a silly pilot who overstressed the 1970s plane does not have fly by wire reflexes to correct this all the while blacking out and dying from 10Gs.

As I mention d above, 10Gs on the G meter is fuselage overload.  Add rolling and the wing is even higher.