FAQ for F-15 AFM Development

[Cmptohocah]

11 hours ago, Hummingbird said:

The F-15 has a very high G-onset rate because it has no FLCS AoA/G-limiter restricting stab movements, it's the same with the F-14, F-5 etc, they can also achieve the same very high onset rates because of this. 

Can they pull 12+G without breaking in DCS? The Tomcat and the F-5 I mean. I don't own them, hence the question.

[draconus]

1 hour ago, Cmptohocah said:

Can they pull 12+G without breaking in DCS? The Tomcat and the F-5 I mean. I don't own them, hence the question.

Tomcat can spike to 12G momentarily. Very risky to repeat the stunt.

[Hummingbird]

2 hours ago, Cmptohocah said:

Can they pull 12+G without breaking in DCS? The Tomcat and the F-5 I mean. I don't own them, hence the question.

 

That doesn't have anything to do with G-onset, but yes the F-14 can, and did in reality as well. 

[GGTharos]

5 hours ago, Cmptohocah said:

Can they pull 12+G without breaking in DCS? The Tomcat and the F-5 I mean. I don't own them, hence the question.

 

I don't know if the F-5 can reach 12g at all, but I have definitely seen it survive a very enthusiastic 10g turn into superior bandits...the airframe was destroyed soon after because the GLOCd pilot was well .. GLOCd and flying less than 1000' off the ground.

[Cmptohocah]

Looks like the structural limit for the Eagle A/B/C is 9G - same as the Fulcrum.

This is for clean config, with external stores it goes down to 8.6G.

[GGTharos]

+30% before damage occurs and +50% for reaching the ultimate load (things break right away).

[Cmptohocah]

Ex. fighter pilot talking about over stressing the aircraft in flight.
Basic gist of it: once you over-stress the airframe, the fight's over.
 

Timestamp: 33:26

[GGTharos]

Fun IRL fact:  Pilot overstressed the airframe (12g) and then blew up some miG-25's.   So the gist of it isn't quite the gist of it.

[Cab]

2 minutes ago, GGTharos said:

Fun IRL fact:  Pilot overstressed the airframe (12g) and then blew up some miG-25's.   So the gist of it isn't quite the gist of it.

Well, to be fair he did say, "even if you won the fight...".

No doubt the 12g jet was down for whatever period of time after that flight.

[GGTharos]

I'm sure it was, 12g is nothing to sneeze at.

[Cab]

17 minutes ago, GGTharos said:

I'm sure it was, 12g is nothing to sneeze at.

Right. And that was the gist of what they were all saying. Once you over-g the jet, even if you win the life or death engagement, the aircraft is down and not available for an unknown duration of time. No one is saying is doesn't happen, just that there are consequences afterward whether it's done in error (panic, excitement, etc) or intentionally to save the aircraft. 

But in DCS people over-g as a matter of routine. The DCS F-15 and F-14 are 13g jets; the DCS F-18 is an 11g jet; and even the humble DCS F-5 is a 10g jet. Then they tell themselves and everyone listening that that is the way it's REALLY done in ACTUAL combat. In actuality though, that attitude has more in common with the Fast and Furious movies than it does with real life aviation.

[GGTharos]

29 minutes ago, Cab said:

But in DCS people over-g as a matter of routine. The DCS F-15 and F-14 are 13g jets; the DCS F-18 is an 11g jet; and even the humble DCS F-5 is a 10g jet. Then they tell themselves and everyone listening that that is the way it's REALLY done in ACTUAL combat. In actuality though, that attitude has more in common with the Fast and Furious movies than it does with real life aviation.

People also casually kamikaze themselves as a matter of routine in the game...because it's a game, so 

[Cmptohocah]

2 hours ago, GGTharos said:

People also casually kamikaze themselves as a matter of routine in the game...because it's a game, so 

But wait. These people flew professionally in real life almost all of the Blue modern jets we have in DCS: F-15, F-16, F-14 and F/A-18 and some of them were with high ranks. They are saying exactly the same thing that the manuals are saying and this is clearly not what happens in the sim. It's not fair to take things out of context like that, we need to look at a bigger picture. Think of a paper clip, once you over stress it and bend it, it will not snap off straight away, but after that you can't really deform it much without failure. It's a simplified example, I know, but it paints the picture.

Sure you can pull 12G's, but after that you should be toast as any additional loading increases the risk of catastrophic failure dramatically. This is how it should be in DCS too. What do we have instead? We basically have unlimited strength of the material, so you are free to exceed the G limit by how many times you wish. This is just for the structural failure, but there are other parts of the aircraft system that have G limits also. One of them being stores and their respective rails. What about asymmetrical loads?

 

[Cab]

3 hours ago, GGTharos said:

People also casually kamikaze themselves as a matter of routine in the game...because it's a game, so 

Oh, I very much agree. I just try to fight the aircraft as they are in DCS, not as they’re “supposed to be” in real life.

But the point of the video was not how DCS aircraft maneuver in game. Rather it was addressing the constant parade of people with zero experience making claims about the appropriateness of over stressing jets that just aren’t true. 

Edited October 22, 2021 by Cab
Added additional info

[GGTharos]

7 minutes ago, Cmptohocah said:

Sure you can pull 12G's, but after that you should be toast as any additional loading increases the risk of catastrophic failure dramatically.

Not actually a fact as shown in real life combat.   We know it reduces airframe life, and the amount of trouble caused depends on how long the loads were applied for as well.

7 minutes ago, Cmptohocah said:

This is how it should be in DCS too. What do we have instead? We basically have unlimited strength of the material, so you are free to exceed the G limit by how many times you wish.

So you have a problem with an airframe capable of experiencing 12g without self-destructing under certain GWs, is that what you're saying?

7 minutes ago, Cmptohocah said:

This is just for the structural failure, but there are other parts of the aircraft system that have G limits also. One of them being stores and their respective rails. What about asymmetrical loads?

What about them?  Do you know how to model them, which ones to model and how?  Which aircraft in DCS has it modeled?  FC3 ones obviously do not since they don't have a whole lot of systems simulation to play with.

Please don't tell me that I'm taking things out of context - the fact that IRL pilots aren't going out of their way to test limits, while game pilots do is just that, a fact.  This is well and truly in context; virtual pilots will always get a new plane, so they'll pull more g, they'll never die really so they'll stay heads on to hit you with their own missile even when they know they're going to eat the one that's coming at them.

The airframes are capable up to a limit, the limit was implemented, so what are you really arguing about now?  Are we talking about DCS, or are you talking about IRL aircraft?  Or is this still some sort of veiled complaint that the flanker can't get up to eagle style g-shennanigans?

[Cmptohocah]

1 hour ago, GGTharos said:

Not actually a fact as shown in real life combat.   We know it reduces airframe life, and the amount of trouble caused depends on how long the loads were applied for as well.

So repetitive max-g of around 133% limit was demonstrated IRL combat?

1 hour ago, GGTharos said:

So you have a problem with an airframe capable of experiencing 12g without self-destructing under certain GWs, is that what you're saying?

Nope, I am just saying that once you hit the over-g it should be more prone to structural failure. Like 12G and then 5G, just an example. Not endless pulls of 12G without any consequences.

1 hour ago, GGTharos said:

What about them?  Do you know how to model them, which ones to model and how?  Which aircraft in DCS has it modeled?  FC3 ones obviously do not since they don't have a whole lot of systems simulation to play with.

You have these limits in the F-15 manual.

1 hour ago, GGTharos said:

Please don't tell me that I'm taking things out of context - the fact that IRL pilots aren't going out of their way to test limits, while game pilots do is just that, a fact.  This is well and truly in context; virtual pilots will always get a new plane, so they'll pull more g, they'll never die really so they'll stay heads on to hit you with their own missile even when they know they're going to eat the one that's coming at them.

I am pretty sure that RL pilots don't over stress the new planes either. Also I am not talking about fatigue here, but exceeding the material strength (yield point), or plastic deformation of it to be more precise. 

1 hour ago, GGTharos said:

The airframes are capable up to a limit, the limit was implemented, so what are you really arguing about now?  Are we talking about DCS, or are you talking about IRL aircraft?  Or is this still some sort of veiled complaint that the flanker can't get up to eagle style g-shennanigans?

I spent like 3 posts explaining that this has nothing with the Flanker.

IRL you just don't over stress the air frame, period. No one does it and bad things will happen if you do.
Unlike DCS where, everyone does it and nothing happens. Pretty simple.

Just a question regarding the RL examples you are using: there was a report of a Israeli F-15 landing with most of its wing missing. Does that mean if I take off an Eagle's wing in DCS it should still be flying?

Edited October 22, 2021 by Cmptohocah

[GGTharos]

1 hour ago, Cmptohocah said:

Nope, I am just saying that once you hit the over-g it should be more prone to structural failure. Like 12G and then 5G, just an example.

That's not what happens with the aircraft.

1 hour ago, Cmptohocah said:

Not endless pulls of 12G without any consequences.

And now they won't be able to.

1 hour ago, Cmptohocah said:

You have these limits in the F-15 manual.

Do we really have to go over this again?

1 hour ago, Cmptohocah said:

I am pretty sure that RL pilots don't over stress the new planes either. Also I am not talking about fatigue here, but exceeding the material strength (yield point), or plastic deformation of it to be more precise. 

We'll have every virtual pilot who does this come by your office for the appropriate dress-down then.

 

1 hour ago, Cmptohocah said:

IRL you just don't over stress the air frame, period.

IRL you also brief for hours before you fly.

 

1 hour ago, Cmptohocah said:

Unlike DCS where, everyone does it and nothing happens. Pretty simple.

And nothing will ever happen, which is why we'll send them to you for a dressing-down.

1 hour ago, Cmptohocah said:

Just a question regarding the RL examples you are using: there was a report of a Israeli F-15 landing with most of its wing missing. Does that mean if I take off an Eagle's wing in DCS it should still be flying?

 

Yep.  And it does, but you might have a hard time.  But really not relevant here.

[nighthawk2174]

4 hours ago, Cab said:

Oh, I very much agree. I just try to fight the aircraft as they are in DCS, not as they’re “supposed to be” in real life.

But the point of the video was not how DCS aircraft maneuver in game. Rather it was addressing the constant parade of people with zero experience making claims about the appropriateness of over stressing jets that just aren’t true. 

 

The F15 episode of the FPP has two pilots who have both brought the eagle up to over 10g.  Both of them talk about doing that, and others who have and they talk about it in a way that indicates it is not a rare occurrence.  Just because you go to high G does not mean the airframe falls apart that's not how this works, which is why some of ED's recent changes are not really accurate (again exceptions do apply).  Safety margins are a thing, they are hammered into an engineer from day 1 of their classes and its often a 50% safety margin from designed load till you get more permanent deformation.  This can and will vary from aircraft to aircraft, but the eagle has shown that it is a strong design and there are a plethora of times where significant overloads were achieved and sustained in flight.  Even with weapons and fuel tanks on the aircraft.  IRL there are consequences on frame life and that is something worth worrying about in peace time hence why pilots are chewed out for unnecessarily over-g'ing.  However taking a few years off the frame life when in combat is well worth brining the frame back and accomplishing your task.  Such maneuvers irl are limited by the fact that it's really only possible to pull that many g's once in a flight.  The physical effort of doing so is so extreme that doing it over and over again is not possible.  Without significant recover time between.  If a more realistic G-system was implemented you'd really only get one good pull at that G before not being able to do that again before nearly snapping to black out.

[Cab]

4 hours ago, nighthawk2174 said:

The F15 episode of the FPP has two pilots who have both brought the eagle up to over 10g.  Both of them talk about doing that, and others who have and they talk about it in a way that indicates it is not a rare occurrence.  Just because you go to high G does not mean the airframe falls apart that's not how this works, which is why some of ED's recent changes are not really accurate (again exceptions do apply).  Safety margins are a thing, they are hammered into an engineer from day 1 of their classes and its often a 50% safety margin from designed load till you get more permanent deformation.  This can and will vary from aircraft to aircraft, but the eagle has shown that it is a strong design and there are a plethora of times where significant overloads were achieved and sustained in flight.  Even with weapons and fuel tanks on the aircraft.  IRL there are consequences on frame life and that is something worth worrying about in peace time hence why pilots are chewed out for unnecessarily over-g'ing.  However taking a few years off the frame life when in combat is well worth brining the frame back and accomplishing your task.  Such maneuvers irl are limited by the fact that it's really only possible to pull that many g's once in a flight.  The physical effort of doing so is so extreme that doing it over and over again is not possible.  Without significant recover time between.  If a more realistic G-system was implemented you'd really only get one good pull at that G before not being able to do that again before nearly snapping to black out.

I don't know what's so hard about this. Of course pilots over-g aircraft and no RL fighter pilots are saying otherwise. Especially in older jets that don't have built in limiters. In fact, it was probably because is was not uncommon that motivated the idea of including g-limiters when the technology became available. 

BTW thanks for making my point. Since you like FPP, why don’t you write Jello and ask him? 

 

Edited October 23, 2021 by Cab
Grammar

[cofcorpse]

8 hours ago, Cmptohocah said:

Nope, I am just saying that once you hit the over-g it should be more prone to structural failure. Like 12G and then 5G, just an example. Not endless pulls of 12G without any consequences.

It is how it works now. Have you tried?

[Schmidtfire]

I have read interviews of F-14 going 12G's without a scratch. Checked over by Grumman engineers afterwards. The RIO ended up in hospital att the sudden break,
but the jet was fine. Not saying that stuff on F-15 won't break att high G forces, but Im sure it can take a good beating without falling to pieces.
 

[Njinsa]

15 hours ago, Cab said:

o one is saying is doesn't happen, just that there are consequences afterward whether it's done in error (panic, excitement, etc) or intentionally to save the aircraft. 

Well, if anything, this discussion could help one to understand why western built planes do have quite a bit higher number of service life hours.

With no attempt to get into Red vs Blue, I'll just quote the words of IAF pilot, Zivi Nedivi who managed to land a single wing unit (F-15D #957) and amazed his buddy flying the F-16 at that time:

'Can I transfer to F15s ?'

Any similarities to the topic in focus is strictly a coincidence.

Edited October 23, 2021 by Njinsa

[Cmptohocah]

3 hours ago, cofcorpse said:

It is how it works now. Have you tried?

Nope I have not tried it. Was there some update in the meanwhile?
The entire discussion was based of a GIF provided some posts ago, where a DCS Eagle did 3 sets of -4G to above 12G pulls without any issues.

 

3 hours ago, Cab said:

I don't know what's so hard about this. Of course pilots over-g aircraft and no RL fighter pilots are saying otherwise...

Have a look at the video I posted. Three ex. navy/air force pilot literally saying the opposite.

[Hummingbird]

12 minutes ago, Cmptohocah said:

Have a look at the video I posted. Three ex. navy/air force pilot literally saying the opposite.

There are so many well documented and easy to find cases of extreme G excursions, without resulting damage, that I really don't understand why you keep insisting on arguing over it? 

As has been mentioned there's usually a 50% buffer between design load limit and ultimate load limit - and in some cases even more (e.g. F14 which shared the same ULL as the F15). 

That doesn't mean the F15 shouldn't have structural over G damage modelled though, ofcourse it should. But it's such a strong airframe that reaching the ULL will require pretty extreme carelessnes unless rather heavily laden. 

Edited October 23, 2021 by Hummingbird

[Cab]

58 minutes ago, Cmptohocah said:

Have a look at the video I posted. Three ex. navy/air force pilot literally saying the opposite.

Saying, what? That pilot’s don’t over-g aircraft? Because the whole point of that excerpt is explaining one of the consequences when it does happen. 
 

Think about it. There are detailed maintenance procedures in place for when a jet is over stressed. If it didn’t happen, there wouldn’t be any such procedures. 
 

The point of that video discussion is not that pilot don’t over-g jets. In fact it probably could be said that most pilots have done it to a degree. The discussion in the video is that pilots don’t do it as part of their gameplan going into a fight. But combat, even in  training, is stressful, exciting, scary, etc, so it does happen from time to time. Especially if one finds himself in a critical situation where he and the jet may be destroyed.