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G-limiter allows gross over-g on the airframe


Rissala
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The FCS fails to limit Gs to safe levels when there are sudden movements. The over-g possible can be as high as 25% over max. (max G ~10g)
With oscillations, it can be even higher. (~13g)

The effect is pronounced with low A/C weight and oscillations. This should not be possible as the FCS should protect the airframe's 7.5G limit.
It is possible to completely break the wing off without ever pulling on the G-override.

(In the track and the 2 videos, the g-override "paddle" was never pulled once.)

 

g limiter.trk


Edited by Rissala
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1 hour ago, Rissala said:

The over-g possible can be as high as 25% over max. (max G ~10g)
With oscillations, it can be even higher. (~13g)

The effect is pronounced with low A/C weight and oscillations. This should not be possible as the FCS should protect the airframe's 7.5G limit.

it increases maximum g by 33%. in case of clean jet (7.5g max), increase to 10g is correct.

source: natops


Edited by dorianR666

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5 minutes ago, dorianR666 said:

it increases maximum g by 33%. in case of clean jet (7.5g max), increase to 10g is correct.

source: natops

That's only when the paddle switch is in effect, the OP is referring to standard FCS limits without using the G-limit override (specifically mentions the paddle was not used).


Edited by Tholozor

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19 minutes ago, Tholozor said:

That's only when the paddle switch is in effect, the OP is referring to standard FCS limits without using the G-limit override (specifically mentions the paddle was not used).

 

ah youre right, my bad

i cant read

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54 minutes ago, Hulkbust44 said:

Correct, you can out-run the limiter with sudden movements. This is documented in the NFM as well as other sources, and pilots have said the same thing.

Yes. That is why I said "gross over-g", not "slight over-g".
A casual 10g over-g when just pulling hard should not be possible.
Not even talking about the 13 max g with oscillations.

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1 hour ago, Rissala said:

...The effect is pronounced with low A/C weight and oscillations. This should not be possible as the FCS should protect the airframe's 7.5G limit...

As far as I have seen, you made very abrupt stick movements. Some confirmation that these are acceptable and won't lead to any over-G would be very helpful.

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On 4/12/2022 at 10:03 PM, cofcorpse said:

As far as I have seen, you made very abrupt stick movements. Some confirmation that these are acceptable and won't lead to any over-G would be very helpful.

I am not a real life combat pilot, nor do I have access to any hard evidence. (see "hard" evidence down below)

That being said, the second video (posted here) pretty much underlines the issue in the best way.
The stick movement here is fast, but smooth and uniform. That should not in my opinion lead to 10g pulled. It seems way too easy to over-g the airframe. In addition, the oscillations when the maneuver is taking place seem unnatural. In other words, it feels springy.
If we consider real-life combat training for example, it should be very alarming if many flights could exceed the g-limits on the airframe that easily.

The reason why I brought this up is because I get frequent significant over-gs on a lot of flights in DCS despite practically never pulling the g-limit-override "paddle".
This is something that the finely tuned FCS should be able to deal with.

The other video (not in this reply) was me deliberately doing oscillations and trying to break the airframe with unexpected success. There the "springy" behaviour is more clear.
A real life F/A-18 pilot told me (long ago) that "snapping the wings is impossible" as all maeuvers are automatically controlled by the flight computer.


 

 


Edited by Rissala
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It's a known fact that pulling too fast will outpace the FCS's ability to limit the G. That's why IRL pilots are trained to not pull too fast.

Having said that, snapping the wings during these excursions is likely a bit too far, as you said. Probably due to the interim damage model we currently have on hornet. Once we get a proper DM then I hope we will start seeing things like specific control failures, wing fold issues, etc etc at these G excursions. And not just binary broken or not.

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IRL pilots have also confirmed that the G-limiter in DCS is much worse than the real.

It should be possible to over-g, it should definitely NOT be as easy as it is in DCS.

In close connection with this report, the G-limiter in DCS also doesn't allow the aircraft to achieve the G-limit in the FCS page (i.e. will cap sustained G at 7.1g when the FCS page states 7.2g) under many different conditions.

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On 4/14/2022 at 1:00 PM, Swift. said:

It's a known fact that pulling too fast will outpace the FCS's ability to limit the G. That's why IRL pilots are trained to not pull too fast.

Having said that, snapping the wings during these excursions is likely a bit too far, as you said. Probably due to the interim damage model we currently have on hornet. Once we get a proper DM then I hope we will start seeing things like specific control failures, wing fold issues, etc etc at these G excursions. And not just binary broken or not.

Do you think that a 2.5g overload is possible with just pulling the stick fast? Seems like a lot to me.
IMO, 1g overload would seem more realistic and acceptable if you do pull too fast on the stick. 2.5g can already compromise the airframe.
And that said, even with slower imputs, the limit can still be very easily exceeded by 0.5 or more.


Edited by Rissala
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39 minutes ago, Rissala said:

Do you think that a 2.5g overload is possible with just pulling the stick fast? Seems like a lot to me.
IMO, 1g overload would seem more realistic and acceptable if you do pull too fast on the stick. 2.5g can already compromise the airframe.
And that said, even with slower imputs, the limit can still be very easily exceeded by 0.5 or more.

 

Not sure tbh, I imagine its not a regime of flight that's known much about. Especially if pilots are being trained specifically to avoid it. 

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In the "A" in general terms in Subsonic flight the g limiter was pretty good. A  random snatch to full backstick might result in a minor overstress to say 8G (setting a 811 code for maintenance) but you could rely on the limiter to protect you, pulling to the limit was pretty normal.  In the transonic region it was still meant to protect with the "G Bucket" incorporated in the loop.

In earlier fighters "Transonic Tuck" was a huge player. In simple terms the instant you come subsonic the C of P moves rapidly forward so with the surfaces deflected you get an instant increase in moment arm and Bang overstress.

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On 4/15/2022 at 4:40 PM, Figaro9 said:

Watch this. https://www.youtube.com/watch?v=a-gPWlODKCY

01:21:58 10.5g on a Hornet

It is operator technique, you can’t blame the aircraft.

 

I am aware of transonic effects on the moment coefficient of an aircraft/foil.
However, I do not see how the situation described in the podcast represents this situation. He said he was "riding the limiter" through the transsonic region when that happened. I was maneuvering at M .8 with a sudden pull back. Also, the situation described in the podcast cannot be replicated in DCS. (g limiter works ok in this regard)

Also, don't you think that this is a bit of an anecdote, especially when it is mentioned that "maybe it was one of those early ones" and "I don't know if you can still do that".


Edited by Rissala
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He started the pull at 1.1M according to his recall in the interview. So riding the limiter through the transonic range.

Looking at an early version Flight manual circa 1986. is the following comment.

"Before 8.3PROM there is an over-G potential associated with abrupt longitudinal stick inputs at high subsonic speed where transient G overshoot of 1g or 2G may occur ........CAUTION Before 8.3PROM above 400Knots, avoid abrupt longitudinal stick movement which can cause large G overshoot"

8.3PROM came in around 1985, G limiter as I recall came in with 8.3PROM


Edited by IvanK
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14 hours ago, IvanK said:

He started the pull at 1.1M according to his recall in the interview. So riding the limiter through the transonic range.

Looking at an early version Flight manual circa 1986. is the following comment.

"Before 8.3PROM there is an over-G potential associated with abrupt longitudinal stick inputs at high subsonic speed where transient G overshoot of 1g or 2G may occur ........CAUTION Before 8.3PROM above 400Knots, avoid abrupt longitudinal stick movement which can cause large G overshoot"

8.3PROM came in around 1985, G limiter as I recall came in with 8.3PROM

 

So it is a non-factor in our Hornet. Excellent research.

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I think this is correct as is, I am not seeing any evidence it should be any different for our hornet. If you pull to fast you will override the FCS

thanks

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On 4/20/2022 at 11:15 PM, BIGNEWY said:

I think this is correct as is, I am not seeing any evidence it should be any different for our hornet. If you pull to fast you will override the FCS

thanks

 

On 4/17/2022 at 12:52 AM, IvanK said:

He started the pull at 1.1M according to his recall in the interview. So riding the limiter through the transonic range.

Looking at an early version Flight manual circa 1986. is the following comment.

"Before 8.3PROM there is an over-G potential associated with abrupt longitudinal stick inputs at high subsonic speed where transient G overshoot of 1g or 2G may occur ........CAUTION Before 8.3PROM above 400Knots, avoid abrupt longitudinal stick movement which can cause large G overshoot"

8.3PROM came in around 1985, G limiter as I recall came in with 8.3PROM

 

The evidence is right here @BIGNEWY?? We just proved it in this thread.

Quote

"Before 8.3PROM there is an over-G potential associated with abrupt longitudinal stick inputs at high subsonic speed where transient G overshoot of 1g or 2G may occur ........CAUTION Before 8.3PROM above 400Knots, avoid abrupt longitudinal stick movement which can cause large G overshoot"

But crucially:

Quote

8.3PROM came in around 1985, G limiter as I recall came in with 8.3PROM

And as stated in the evidence, the issue is there "Before 8.3PROM".
So if our Hornet is really supposed to represent a C variant in 2005, the issue of over-g in transsonic flight envelope was fixed 20 years before the DCS variant...
But as seen in the videos and tracks above, there is still gross +2.5g over-g easily achieved at  M .80.
(Additionally the manual states a "G overshoot of 1g or 2G", so a 2.5G overshoot is at very the top end).

Therefore, "correct-as-is" is not the correct verdict for this report. Let me know if you need more explanation.
 

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In the next Open Beta update, we will be releasing a further improvement to the Viper FLCS. After which, our team will be doing a full review of the Hornet flight model and flight control system. The G-limiter will be included in this review.

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Just now, BIGNEWY said:

In the next Open Beta update, we will be releasing a further improvement to the Viper FLCS. After which, our team will be doing a full review of the Hornet flight model and flight control system. The G-limiter will be included in this review.

Thank you 👏
Appreciate it

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