correct as is F-15C Structual wing surface failure.

[=475FG= Dawger]

9 hours ago, cofcorpse said:

A lot of words and no exact information. I'm sorry, we can't do anything without information. 

"approach the design ultimate limit load (1.5 times the limit load)" - you can approach 1.5x design limit many times, but you can't exceed it in current implementation. 

"he force required to reach the static strength limit of metals is MUCH greater than the fatigue strength limit." - How much greater? Again, no information.

"The design ultimate limit load is the FATIGUE strength limit load not the static strength of the structure." - Could you proof that? 

"Modeling the static failure of the wing at the ultimate limit load is incorrect." -Why?

I don't think I can compress the technical information required to completely explain aircraft structural engineering into one post.

I suspect that you are in some way responsible, at least in part, for this state of affairs and are attempting to save face. 

No aircraft manufacturer publishes catastrophic static failure data. There are a lot of reasons for that. One of the biggest reasons is that destructive testing is very expensive and wasteful but even when it is done, the results are not included in easily accessible publications.

All you can do is read what is available and make inferences.

As an example, the F5 Fatigue Structural Integrity Program report is publicly available

It very plainly states that the test subject was static loaded to 1.5 times the limit load with only one failure, a permanent buckling of the trailing edge spar structure. This failure was corrected and retested to ultimate load. Note they define a permanent deformation as the only "failure". One can infer that the F-5 can withstand 1.5 times the limit load a single time without suffering permanent damage to the structure. This very obviously means that the static strength exceeds the 1.5 times the limit load. How much? Who knows but it is somewhere north of that figure. Given the longevity of the F-5 in service and the fact that Northrop F5 program successfully completed 4 lifetimes of testing on the test subject (16,000 hours).

Yet, in DCS we have an F-5 that will snap its wings at at 1.5 times the limit load of 7.33. 

The DCS F-15C also has the same limit load of 7.33 and will snap its wings at 11 G, just like the F-5.

We know the F-15 doesn't break its wings at 11 G in the real world. We have living examples of crew who have exceeded that threshold and do not recall losing the wings. 

Yet your response is, unless I present proof positive to the contrary, catastrophic failure at 1.5 times the limit load is here to stay.

Such proof, should it exist, is not going to be something I would waste my time trying to locate. Life is too short and I am almost positive it would not change anything.

So with that, I shall bow out.

ED will do what they will do with regard to this. 

[cofcorpse]

7 hours ago, =475FG= Dawger said:

The DCS F-15C also has the same limit load of 7.33 and will snap its wings at 11 G, just like the F-5.

You are incorrect. Limit load for DCS F-15 is 9G.

[stefasaki]

18 hours ago, cofcorpse said:

Completely unusable. How did you get this value, 18G?

Please turn down the passive aggressiveness, I was not attacking you in any way.  I just gave an example about fatigue in aluminum, the main material for fighter jets. I just stated the fact that if something breaks at X force after about 10^5 cycles then it should break at 2X at the first cycle (18 is the double of 9 and forces on the airframe scale linearly with g's if the weight and configuration is the same).

 

@Spurts

Yes I was implying 10 cycles per hour, seemed reasonable for a fighter jet... I guess it depends on what we agree a cycle is. My comment was merely there to put numbers about fatigue stresses, it is not directly related to any aircraft but it applies well to a wing spar for instance. If we were to consider 10^4 cycles then the ultimate strength should be about 30% lower than the original.

Edited January 26, 2022 by stefasaki

[=475FG= Dawger]

4 hours ago, cofcorpse said:

You are incorrect. Limit load for DCS F-15 is 9G.

Thank you for helping me demonstrate that your only concern here is “winning”, not actually modeling realistic behavior with regard to aircraft structural integrity.

It validates my decision to let this issue go.

However, I do have one final request.

You demand from me conclusive proof that the wing does not fail at 1.5 times the design limit load.

I shall do the same. I demand conclusive proof that the wing DOES fail catastrophically the very first time it is subjected to 1.5 times the design limit load.

Video evidence is preferred but official documents will be acceptable. 
 

Cheers!
 

[grafspee]

I watched  F-15 pilot interview, he claimed that he pulled 12g and plane was fine. 

[draconus]

So, 13,5G failure is wrong but "somewhere north" is acceptable? Or do you want 18G? Just pick a value and defend why is it correct. Teaching devs about structural strenght will get you nowhere.

[GGTharos]

1 hour ago, grafspee said:

I watched  F-15 pilot interview, he claimed that he pulled 12g and plane was fine. 

And another pulled 12.5 and was not fine.  Aircraft have been written off for over-g damage.  Not a lot of them, because there aren't that many incidents.   In DCS, there are plenty of incidents.

[grafspee]

14 minutes ago, GGTharos said:

And another pulled 12.5 and was not fine.  Aircraft have been written off for over-g damage.  Not a lot of them, because there aren't that many incidents.   In DCS, there are plenty of incidents.

In DCS pulling over 12G is much much easier then IRL  Probably this is why we have more incidences in DCS

[Ironhand]

13 minutes ago, GGTharos said:

And another pulled 12.5 and was not fine.  Aircraft have been written off for over-g damage.  Not a lot of them, because there aren't that many incidents.   In DCS, there are plenty of incidents.

You don’t understand. We want the correct structural modeling without modeling the requisite training and discipline to fly these things.

[grafspee]

2 years ago i flew F-15C in DCS a lot and i can't recall that i even once snapped wing, and i was pulling as much as i could sometimes so i assume that something have changed ? 

And if F-15 snaps wings at 11G than it is pity.

Edited January 26, 2022 by grafspee

[razo+r]

9 minutes ago, grafspee said:

2 years ago i flew F-15C in DCS a lot and i can't recall that i even once snapped wing, and i was pulling as much as i could sometimes so i assume that something have changed ? 

And if F-15 snaps wings at 11G than it is pity.

 

I'm pretty sure snapping wings has been introduced "very" recently. 2 years ago, you could not snap your wings because it most likely wasn't implemented back then.

[Cab]

With regard to wings breaking in game, my impression has been it was to limit jets like the F-15 from over-performing rather than mimic reality. Afterall, even with the current "structural limitations" a skilled DCS F-15 player can routinely maneuver at 13g's and 40 degrees AOA, and that is well beyond the F-15's real-life capabilities.

[grafspee]

1 minute ago, Cab said:

With regard to wings breaking in game, my impression has been it was to limit jets like the F-15 from over-performing rather than mimic reality. Afterall, even with the current "structural limitations" a skilled DCS F-15 player can routinely maneuver at 13g's and 40 degrees AOA, and that is well beyond the F-15's real-life capabilities.

40 degrees of AOA are you sure ?

[Cab]

1 minute ago, grafspee said:

40 degrees of AOA are you sure ?

Yes, I have seen it spike to that on both the Info Bar and Tacview.

It isn't common, but the "superstars" on the Dogfight servers have achieved that.

[HWasp]

OVER G OVER G OVER G

OVER G OVER G OVER G

Oh no! I can't pull 13 Gs casually, all the time anymore, what a tragedy.

[GGTharos]

2 hours ago, Cab said:

40 degrees AOA, and that is well beyond the F-15's real-life capabilities.

No it isn't.  There are incident reports regarding F-15s exceeding that number.

[Cab]

22 minutes ago, GGTharos said:

No it isn't.  There are incident reports regarding F-15s exceeding that number.

Has it been done? Sure. Can it do it regularly without departing flight? I don't think so.

I think you'd be hard pressed to find RL pilots saying that was within the normal operational flight envelope.

Regardless, there is no way the DCS F-15 performance capabilities on BFM servers reflects reality.

[dundun92]

14 minutes ago, Cab said:

Regardless, there is no way the DCS F-15 performance capabilities on BFM servers reflects reality.

based on what? That 40° of AoA "feels" too high to you?

[Cab]

5 minutes ago, dundun92 said:

based on what? That 40° of AoA "feels" too high to you?

First, my question to you is, have you really watched the DCS F-15's being flown by the competent players on the dogfight servers?

To answer your question, no, it goes beyond just AOA. But yes, it is just my subjective opinion, based on what I believe to be a good working knowledge of how real jets fly, that the DCS F-15 BFM performance is not realistic.

However, I am willingly to be persuaded otherwise by someone with actual experience. Someone who has either flown the F-15 or against it.

[GGTharos]

39 minutes ago, Cab said:

Has it been done? Sure. Can it do it regularly without departing flight? I don't think so.

It happened during a regularly practiced defensive maneuver which included high AoA flight.   Why do you believe the eagle would depart?  There are definitely reasons for it, but why do you believe it would have to?

39 minutes ago, Cab said:

I think you'd be hard pressed to find RL pilots saying that was within the normal operational flight envelope.

Regardless, there is no way the DCS F-15 performance capabilities on BFM servers reflects reality.

There's no way DCS anything reflects reality, it's just close to it.

[Cab]

10 minutes ago, GGTharos said:

It happened during a regularly practiced defensive maneuver which included high AoA flight.   Why do you believe the eagle would depart?  There are definitely reasons for it, but why do you believe it would have to?

There's no way DCS anything reflects reality, it's just close to it.

Sorry, other than my admittedly subjective assertions above, I really don’t have anything else to add here.

I’ll patiently wait for a real Eagle Driver to weigh in. 

[=475FG= Dawger]

10 hours ago, GGTharos said:

No it isn't.  There are incident reports regarding F-15s exceeding that number.

Some of the confusion here seems to stem from what the AoA displayed in the F-15 actually is telling you. 

AoA is not displayed in degrees. It is displayed in dimensionless units. In the F-15 40 units AoA is equal to 30 degrees.

Here is an interesting wing rock thesis. https://apps.dtic.mil/sti/pdfs/ADA256613.pdf
 

If you bother to read it, you will discover that the F-15 in this particular flight test program achieved a maximum of 30 degrees AoA (40 units) in the pullup test and this was slightly lower than what was achieved in the turning and 1 g stall testing.

One can safely assume the maximum AoA is slightly more than 30 degrees or 40 units from this publicly available source.

[GGTharos]

5 minutes ago, =475FG= Dawger said:

Some of the confusion here seems to stem from what the AoA displayed in the F-15 actually is telling you. 

AoA is not displayed in degrees. It is displayed in dimensionless units. In the F-15 40 units AoA is equal to 30 degrees.

Here is an interesting wing rock thesis. https://apps.dtic.mil/sti/pdfs/ADA256613.pdf

If you bother to read it, you will discover that the F-15 in this particular flight test program achieved a maximum of 30 degrees AoA (40 units) in the pullup test and this was slightly lower than what was achieved in the turning and 1 g stall testing.

One can safely assume the maximum AoA is slightly more than 30 degrees or 40 units from this publicly available source.

Yep, the incident in question stated 54CPUs.

[cofcorpse]

21 hours ago, stefasaki said:

Please turn down the passive aggressiveness, I was not attacking you in any way. 

I'm sorry, it really came out rude. All I wanted to say is that unfortunately not enough evidence has been provided that the current implementation is wrong.

[Hazardpro]

This topic has also come up on the Hornet board and I'll contribute my 2c here like I did there, as an aerospace engineer. The way these aircraft fail in DCS by regularly and predictably ripping their wings off in high G maneuvers really is not realistic at all. But frankly, I think realistic damage modeling of this kind is probably beyond the scope of what's reasonable to expect in a flight sim. I don't really expect ED to do sophisticated structural and material analysis of every element of our virtual airframes every time I go out of limits with it because it's a game and not a professional design product. So I suppose it's an acceptable DCS-ism for me.