FAQ for F-15 AFM Development

[Cmptohocah]

5 minutes ago, dundun92 said:

That is not a structural limit though, that was an operational limit on early F-15As because of the lack of an over G warning system (the beeping the pilot hears at high Gs in the F-15C in DCS). With that its 9G rated, but again this is not a structural/engineering limit, this is purely an operational limit. Same thing with the 6.5 G F-14 limit.

I understand, it was my oversight: so 9G instead of 7.33G.

[draconus]

2 hours ago, Cmptohocah said:

Don't all DCS pilots have same tolerances? I was not aware of the fact.

 

Not sure what "+1 for the Eagle's G-induced DM for the aircraft and stores." means.

Jet pilots in DCS might have the same G tolerance. Older props pilots are probably more affected due to not wearing G-suits. I'm just suggesting that since different nations use different suits for the pilots of different aircraft maybe they should have different G tolerance too. Consistency and equality smells like "MP balance" to me.

 

The note mentions CFTs and AG stores - isn't it for the Strike Eagle by any chance?

 

"+1 for the Eagle's G-induced DM for the aircraft and stores" means that I welcome implementation for the overload induced damage model for the Eagle and stores.

[Cmptohocah]

27 minutes ago, draconus said:

Jet pilots in DCS might have the same G tolerance. Older props pilots are probably more affected due to not wearing G-suits. I'm just suggesting that since different nations use different suits for the pilots of different aircraft maybe they should have different G tolerance too. Consistency and equality smells like "MP balance" to me.

Actually no, I don't care about MP Balance per se but I do care about the things you already mentioned. If you check my post on pilot-g tolerance I was the one to point out that F-16's pilot has no higher g-tolerance compared to others even though its cockpit ergonomics is superior to other fighters (reclined seat, static side stick with FBW, etc.). Dunno where would you get that idea, except of course the fact that I fly "Red" fighters exclusively. Or is it my avatar?

27 minutes ago, draconus said:

 

The note mentions CFTs and AG stores - isn't it for the Strike Eagle by any chance?

 

"+1 for the Eagle's G-induced DM for the aircraft and stores" means that I welcome implementation for the overload induced damage model for the Eagle and stores.

The manual that the chart was taken out is for F-15 A/B/C/D versions.

Edited September 22, 2021 by Cmptohocah

[GGTharos]

51 minutes ago, draconus said:

Jet pilots in DCS might have the same G tolerance. Older props pilots are probably more affected due to not wearing G-suits. I'm just suggesting that since different nations use different suits for the pilots of different aircraft maybe they should have different G tolerance too. Consistency and equality smells like "MP balance" to me.

 

The note mentions CFTs and AG stores - isn't it for the Strike Eagle by any chance?

 

"+1 for the Eagle's G-induced DM for the aircraft and stores" means that I welcome implementation for the overload induced damage model for the Eagle and stores.

 

These are the F-15A-D FAST packs, not the CFTs like the F-15Es.   The difference has to do with weapon stations etc.    I believe the USANG/USAF air sovereignty eagles will be mounting them now.  You lose a bunch of BFM performance but your flat dash intercept and loiter gets more efficient.

26 minutes ago, Cmptohocah said:

If you check my post on pilot-g tolerance I was the one to point out that F-16's pilot has no higher g-tolerance compared to others even though its cockpit ergonomics is superior to other fighters (reclined seat, static side stick with FBW, etc.).

 

IMHO the g-tolerance of the DCS pilot is too low generally.  The devil is really in the details but, if pilots had better tolerance then I'd be more partial towards fatigue systems, higher quality g-tolerance simulation etc.

 

I think while the F-16's ergonomics regarding g-tolerance are believed to be superior, realistically there is some question as to whether they really provide something better.   Anyway that's a huge discussion in and of its own and with its own science.  The current investments seem to be going into better g-suits rather than reclining seats.

[Lurker]

You are arguing over each other and neither side is actually getting to the point. Which I guess is par for the course for most interweb arguments

 

The essence can and should be summed up like this.

 

@Cmptohocah Do you accept the fact that the F15C has better structural stability than the Su27 and a faster available g-onset due to its FCS and design? Because that's what it comes down to. This is the point that @GGTharosand others are trying to make. The F15C is simply more structurally sound and can achieve a significantly faster onset of g forces. 

 

Unfortunately this is something that is unacceptable to those who for some reason always argue Red vs Blue in DCS World. Their argument is always, missiles should be balanced, radars should be balanced, airplanes should be balanced, and in this case particularly, the F15C should break at the same point that the Su27 breaks. 

 

Unless people specifically accept that two airframes can be different, in some cases very different and as a result behave differently and that Eagle Dynamics takes these points seriously then any argument of this kind is pointless. No one is going to change their mind, and no one will allow their mind to be changed. 

Edited September 23, 2021 by Lurker

[draconus]

5 minutes ago, Lurker said:

...and in this case particularly, the F15C should break at the same point that the Su27 breaks. 

You didn't read their answers, did you?

Edited September 23, 2021 by draconus

[Lurker]

2 minutes ago, draconus said:

You didn't read their answers, did you?

 

 

Their answers keep changing. First it's structural limits, then it's pilot limits, then it's.....oh whatever. Just balance the damn planes.

[Cmptohocah]

16 minutes ago, Lurker said:

You are arguing over each other and neither side is actually getting to the point. Which I guess is par for the course for most interweb arguments

 

The essence can and should be summed up like this.

 

@Cmptohocah Do you accept the fact that the F15C has better structural stability than the Su27 and a faster available g-onset due to its FCS and design? Because that's what it comes down to. This is the point that @GGTharosand others are trying to make. The F15C is simply more structurally sound and can achieve a significantly faster onset of g forces. 

 

Unfortunately this is something that is unacceptable to those who for some reason always argue Red vs Blue in DCS World. Their argument is always, missiles should be balanced, radars should be balanced, airplanes should be balanced, and in this case particularly, the F15C should break at the same point that the Su27 breaks. 

 

Unless people specifically accept that two airframes can be different, in some cases very different and as a result behave differently and that Eagle Dynamics takes these points seriously then any argument of this kind is pointless. No one is going to change their mind, and no one will allow their mind to be changed. 

 

Unfortunately this somehow escalated into Red vs Blue or Flanker vs Eagle, which was not intentional.
I mention the Flanker only 'cause I have manuals for it - that was the only reason.

 

Anyway the point was that for some reason only the Eagle out of all the contemporary fighters has the ability to create higher G loads in shorter amount of time. Not compered to Flanker only but to all of the flyable fighters. Again I don't have manuals for those, but only for Flanker/Fulcrum.

 

Your question is correct: I was challenging both the faster onset and the effects on it on the pilot. Then I found the video, which I shared, of a pilot sustaining 12G in a centrifuge, so I dropped that argument as it shows to be technically possible.

The only question remaining was: why is the Eagle superior in the onset rate to all other fighters? Answer was not satisfactory to me, as there was no documentation reference provided to back this up. Closest explanation was 'cause of the hydraulic system/control flight surfaces combo. I am simply asking for prof of this claim, or any evidence to back this up.

Was this onset calculated, simulated taken out of a manual, demonstrated in RL? This is all I am asking.

When it comes to comparing structural strength between to fighters: how would this be done? X compred to Y. What would be the reference?

 

[Lurker]

The F15C uses an electro mechanical FCS which is not a fly by wire system. AFAIK this is the main reason why it's possible to pull more Gs in the F15, and pull them quicker compared to the Su27, that and higher structural limits. During testing of the Su27 prototype during fly-by-wire testing, it was determined that with a high onset of G the plane would actually break it's "neck" In fact the entire cockpit separated from the rest of the fuselage. A test pilot died. Let me see if I can dig this up: Yes this was I think on the 23rd of December 1981. The name of the pilot was Aleksandar Komarov. I first heard about this in a documentary detailing the development of the Su27, one of the Red Wings documentaries. 

 

I think other than having classified engineering design docs, this is as close as you're going to get to a satisfactory answer. 

 

[HWasp]

I have just made a nice little track to demonstrate how stupid it can look, when an aircraft has absolutely no limitations simulated:

 

1. I broke the limit of 800 kts indicated by close to 30%, diving at 1030 kts indicated (and reaching M2.6 in the process)

2. At that point, way over Vne I displaced all controls to max deflection, resulting in a max G over 23(!!)

 

I mean, look at it. It looks really stupid doesn't it?

 

Why ruin a nice simulation allowing unserious things like this to happen?

F-1520G.trk

[HWasp]

So, the usual safety margin for strutural loads in aviation is 1.5x 

 

Without any specific research, I think a general over G damage system could work like this:

 

G value between 1,2 x limit G and 1,5 x limit G ----> dice roll for structural damage resulting in some asymmetry (like a gun hit to the wing, aircraft is still flyable, you can limp home with it)

G value between 1,5x limit G and lets say 1,6x -----> 100% damage, dice roll to loose a wing 

G value over that ---> 100% structural failure

 

Surviving an over G incident is not a F-15 specific thing, I know about MiG-29 surviving the same (airframe was bent, it did not fly again (I think that was also around 12 Gs))

 

I think we should agree, that having absolutely no limitation is a bad thing, and it should be fixed.

Edited September 23, 2021 by HWasp

[HWasp]

BTW it was mentioned here, that the MiG-29 has also no limitations, which is simply not true:

 

You'll loose your vertical stabilizers at those speeds, then the aircraft falls apart at 16G

 

 

 

So yes, the F-15 is the only UFO amongst the FC3 planes, that needs to be fixed, all the others have some limitations simulated at some level.

Edited September 23, 2021 by HWasp

[Lurker]

33 minutes ago, HWasp said:

 

I think we should agree, that having absolutely no limitation is a bad thing, and it should be fixed.

 

 

I don't think anyone disagrees with that. The problem is how should Eagle Dynamics determine that limit with regards to the F15C?

Edited September 23, 2021 by Lurker

[Snappy]

4 minutes ago, Lurker said:

 

I don't think anyone disagrees with that. The problem is how should Eagle Dynamics determine that limit with regards to the F15C?

 

How should ED determine the limits for any of their aircraft?

 

[HWasp]

3 minutes ago, Lurker said:

 

I don't think anyone disagrees with that. The problem is how should Eagle Dynamics determine that limit with regards to the F15C?

 

 

As I mentioned above, I think it should be a chance based thing between certain values (dice roll), and fixed damage above.

 

1,5 x limit G is the general rule, so I think if there is no accurate info otherwise, then take that into account. 

 

For the F-15, if they'd use values, that are close to what I have mentioned, then it would look like this when the actual aircraft limit is 9G

 

- between 11G and 13,5G you would get a dice roll for some damage, so if unlucky then you'd end up with some asymmetry (aircraft won't fly straight anymore, but you can rtb )

- between 13,5G and 14,5G, you'd get a 100% chance for some damage (the previous condition), and a dice roll for the wings falling off

- 14,5 G+ game over

 

If there are more accurate numbers from somewhere else, use that. (I mean from a structural test, and not some odd lucky flight incident )

This would be better than nothing.

 

Same thing for speed. 800kts indicated is already a crazy value, forces are extreme, and they grow exponentially. 

[draconus]

Example:
 

DamageG = math.random(11,13.5);

StructuralG = math.random(13.5,14.5);

if (aircraftG > DamageG) then

 aircraft_random_Gdamage();

 if (aircraftG > StructuralG) then

  aircraft_disintegrate();

 end;

end;

 

Edited September 23, 2021 by draconus

[Cmptohocah]

5 minutes ago, draconus said:

Example:
 

DamageG = math.random(11,13.5);

StructuralG = math.random(13.5,14.5);

if (aircraftG > DamageG) then

 aircraft_random_Gdamage();

 if (aircraftG > StructuralG) then

  aircraft_disintegrate();

 end;

end;

 

 

I don't know if this was supposed to ridicule or not, but I could not agree more with the code above.

BTW, MiG-29B has 9G limit as per the manual - absolute limit that is.

[GGTharos]

1 hour ago, Cmptohocah said:

I don't know if this was supposed to ridicule or not, but I could not agree more with the code above.

 

You shouldn't, because it's arbitrary and doesn't take gross weight or time into account.  I get why you like it, but you shouldn't, it doesn't even come close to corresponding to reality.

It's a good start of an idea of one, but not good all on its own.

 

1 hour ago, Cmptohocah said:

BTW, MiG-29B has 9G limit as per the manual - absolute limit that is.

 

That doesn't mean anything.   Look at the Su-27 manual, IIRC in there they have something that I think answers you question above (how do you determine the limits?):

 

Somewhere in that manual it is stated that the flanker's g-limiter is tuned to permit you a certain amount of g for a certain GW, and that number changes based on the GW.  While this doesn't completely answer your question it gives you the necessary hint because of how the limiter is tuned to prevent structural failure, or at least aging out of the aircraft.

 

To understand when/how the aircraft will actually fail you need to see documentation from either structural testing (Good luck with finding that, at least I've never seen it for a fighter) or from IRL experience with the aircraft.

 

When the aircraft has a 1.5 engineered over-g tolerance, it isn't just going to come apart or get damaged because you pulled 1.3x the g limit.  That's going to depend entirely on the airframe and how it's constructed, and there's no rule that says two aircraft have to act the same.  To give you a simple example, you could bend a carbon fiber wing all you want as long as it's under the ultimate load limit, but when you reach that limit it'll just snap.

This isn't the same for the aircraft we're talking about - ie. you could deform the fuselage - but that doesn't mean one aircraft will tolerate the overload the same way another will.

Edited September 23, 2021 by GGTharos

[draconus]

13 minutes ago, GGTharos said:

It's a good start of an idea of one, but not good all on its own.

That was its only intent as an example of the idea implementation, of course it does not take GW into account and many other values, but the random values are used to take into account that no airframes are the same and will snap at different G for sure.

Edited September 23, 2021 by draconus

[GGTharos]

^^^^

 

Yes I understood that, this is why you added the 'for example'

 

Random values don't take different airframes into account, you would have to manipulate distribution.  Unless you mean changing the values in the random value call then yes.

 

By my very naïve calculations, and going completely off of memory, the F-15 is rated at 9g at 38000lbs.   This would give it an ultimate load limit of about 12.2g at 42000lbs before the airframe starts bending which would approximately correspond with known over-g incidents and also indicate that the F-15 won't come apart at the 1.5 x g-limit but a bit later.  But it will bend and be unusable after landing.  Also, I'm not adverse to start damaging equipment at this point, ie. break the radar or HUD (I mean what else can you break on the FC3 eagle?) and accumulating airframe damage, which should be unrepairable in-game.

 

There are a lot of things that you can do in addition to this, like change the FM ... but this stuff is a lot of work as well, so damage accumulation should suffice until the aircraft is broken.

 

Now lets take a 'three bagger' ie. a 58000lbs eagle, which you're unlikely to encounter with full fuel but you never know:  That aircraft would start bending at 8.8-8.9g, and would break apart quickly.   That's not even taking into account pylon strength for holding the full fuel tanks.

Edited September 23, 2021 by GGTharos

[GGTharos]

3 hours ago, HWasp said:

BTW it was mentioned here, that the MiG-29 has also no limitations, which is simply not true:

 

You'll loose your vertical stabilizers at those speeds, then the aircraft falls apart at 16G

 

 

So yes, the F-15 is the only UFO amongst the FC3 planes, that needs to be fixed, all the others have some limitations simulated at some level.

 

Great, so the MiG-29 has UFO strength but the eagle is still at fault.  Did you have to work hard to get to this condition?  Could the MiG-29 still do those things that were complained about in the gif posted here without breaking?

 

I even directly wrote that the question isn't 'should there be a limitation' because no one says that.

Edited September 23, 2021 by GGTharos

[HWasp]

1 hour ago, GGTharos said:

 

Great, so the MiG-29 has UFO strength but the eagle is still at fault.  Did you have to work hard to get to this condition?  Could the MiG-29 still do those things that were complained about in the gif posted here without breaking?

 

I even directly wrote that the question isn't 'should there be a limitation' because no one says that.

 

 

What are you talking about? Either you or someone else wrote in this thread earlier, that the MiG-29 does not have any limitations simulated. That is not true, simple as that. The F-15 is the only one with this problem. ( I won't read this whole mess again to find it...)

 

MiG-29 and Su-27 limits may or may not be correct, BUT they are there and they pose a risk to anybody using the stick limiter override to get extra Gs. So even if the 29 were unrealisticly strong, still there is a good chance, that if you override the limiter at high speeds in a fight where you are concentrating on other things, you'll break it. That is a good thing even if the numbers were inaccurate, and the whole thing is simplified.

 

So what the hell are we arguing about? My point is, that I want the F-15 to have similiar simplified structural limitations, comparable to the other FC3 modules. (for speed and G as well)

[GGTharos]

1 hour ago, HWasp said:

What are you talking about? Either you or someone else wrote in this thread earlier, that the MiG-29 does not have any limitations simulated. That is not true, simple as that. The F-15 is the only one with this problem. ( I won't read this whole mess again to find it...)

 

Yes I did that, with the caveat 'maybe my knowledge on the subject is outdated' which is was

 

1 hour ago, HWasp said:

So what the hell are we arguing about? My point is, that I want the F-15 to have similiar simplified structural limitations, comparable to the other FC3 modules. (for speed and G as well)

 

I don't know if you read the whole thread but I'll try to boil it down - no names 'cause they're not needed and not important:

 

1) The complaint was made that the eagle won't break under g (true), while flankers do (this last part is only important for the sourcing of the complaint ... the complaint stands on its own anyway)

2) Then statements were made to the effect of how easily the eagle would break, because flankers break easily

3) Responses to 2 saying it really won't be that easy to break are then interpreted as it being ok to not have a DM or equating it with indestructibility

4) In all of this as well, statements regarding pilot g tolerance are made, further confusing the issue, but eventually that part is settled

5) Questions remain about f-15's g-onset time.

 

Anyway, as far as I personally am concerned, there's really not much do be discussed WRT the eagle, for me it's like this:

1) Do we need to implement a g-based DM?  Yes

2) Will it affect most dogfights?  F no.  As in it won't be anywhere near as harsh as some want it to be.  Will it surprise people who like to pull loads of g while heavy? Yes, as it ought to, and people who significantly over-g while not so heavy.  There are other issues, captured below (like you should not be able to reach more than 12.5 g on a eagle IMHO)

3) Do we need to implement a speed-based DM?  Yes

4) Control surfaces need to disintegrate when Vne is exceeded and they are deflected, so that DM is needed too.

 

And yes, other aircraft need this too. 

 

[nighthawk2174]

10 hours ago, Cmptohocah said:

Unfortunately this somehow escalated into Red vs Blue or Flanker vs Eagle, which was not intentional.
I mention the Flanker only 'cause I have manuals for it - that was the only reason.

 

Anyway the point was that for some reason only the Eagle out of all the contemporary fighters has the ability to create higher G loads in shorter amount of time. Not compered to Flanker only but to all of the flyable fighters. Again I don't have manuals for those, but only for Flanker/Fulcrum.

 

Your question is correct: I was challenging both the faster onset and the effects on it on the pilot. Then I found the video, which I shared, of a pilot sustaining 12G in a centrifuge, so I dropped that argument as it shows to be technically possible.

The only question remaining was: why is the Eagle superior in the onset rate to all other fighters? Answer was not satisfactory to me, as there was no documentation reference provided to back this up. Closest explanation was 'cause of the hydraulic system/control flight surfaces combo. I am simply asking for prof of this claim, or any evidence to back this up.

Was this onset calculated, simulated taken out of a manual, demonstrated in RL? This is all I am asking.

When it comes to comparing structural strength between to fighters: how would this be done? X compred to Y. What would be the reference?

 

The F15 CAS system manual is out there and it goes into a lot of detail.  As far as i'm aware the eagle's current pitch rate is correct.

[Hummingbird]

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.