Demistifying Eagle damage model

First I urge everyone to leave emotions away from this topic. This thread aims for engineer’s point of view using extensive knowledge of physics and aerodynamics as tools of explanation. Let me be clear, my standpoint around Eagle design and performance is described as pure appreciation of engineer masterpiece and respect given to its design team that made hell of a job by creating Eagle as is. Some Eagle users pushed its performance margin a little bit too far.

That "famous" IAF Eagle one wing landing is, based from my knowledge, experience and common sense, pure fiction in act of propaganda. There are many reasons that proved this claim to have good standing ground. Here are some rock-solid facts:

-jet fuel is highly flammable liquid that is specially designed to maintain stable combustion process in combustion chamber inside jet engine. It is selected for a reason and most important one is rapid flame propagation, or high burn speed that is around 20m/s. By using special technique of slowing down the airstream in combustion chamber, stable combustion is maintained inside chamber but outside of that zone, fuel disperses fast and slows down enough to ignite and burn.

-pilot claimed that he was not aware of scale of damage after midair collision as fuel spray was continuously hiding his view. Pilot had a wingman on disposal who was also unable to determine the scale of damage. This is extremely unreal scenario as fuel from exposed tanks cannot form such wide spray zone in high velocity airstream. Damaged tank would empty its content in a matter of seconds regarding scale of damage and starboard opening.

-motion of debris and fallen of wing body would very likely act as high velocity impact objects further damaging fuselage and potentially control surfaces aft of the damage zone, respectively starboard rudder fin and ailerons, reducing control surface effectiveness and possibly more hydraulic/electric actuator systems damage that would lead to total unrecoverable dive spin. There is no visible damage on tail control surfaces.

-as soon as pilot would engage afterburner, leaking plane would lit in fireball as fumes and spray that would occasionally enter engine exhaust nozzle path, ignite and spread its flame to source - remaining fuel in fuel tanks. This would lead to entangled fireball around airframe that would lead to skin meltdown and rapid damage propagation. That plane would be doomed instantly.

-pilot claimed that he was able to maintain level flight without one wing using afterburners. I already explained impact of afterburner heat and flame effect on spraying jet fuel before. Level flight in case of extremely high aerodynamic imbalance due to complete missing wing is absolutely impossible, Plane would have to roll to that remaining wing and match its lift center axis with plane remaining body axis parallel to gravity vector. Focus is on level flight. To this day, no wind tunnel test has been committed to prove this claim to be true, as matter of fact plane manufacturer engineers neglected that possibility as impossible. Logical explanation is that due to high roll momentum that plane would be impossible to balance with remaining control surfaces that had no enough authority to fight asymmetric lift/drag generated by single remaining wing. Claiming this premise true is out of engineer’s scope as there must be a larger portion of wing remaining to counter roll momentum.

-pilot claimed that he was able to land safely without one wing. I already explained that plane should be tilted sideways along roll axis and that would mean that high-speed touchdown would be committed on starboard wheel first. Released friction heat amount would be tremendous knowing that landing speed was already high by scale factor of 2. Scale factor of 2 doesn’t mean double centrifugal stress on tire as acceleration force is square product of angular velocity of wheel, but exponential propagation of tensile force inside tire. That high safety margin is uneconomical as all elements of airplane tend in reduction of unnecessary weight. Tires are no exception. This case tire would break apart exposing aluminum rim to runway and highly possible ignition as rubber and aluminum are used as propulsion in SpaceX project rocket engine. Drag generated by broken lit rim would increase already high drag on starboard side of plane that would make it sideslip and roll on missing wing side leading to possible crash and fatality. Tire manufacturer touchdown limit is half of landing speed pilot said to have landed on, further ultimate stress limit would give tire ¾ of that speed life. All above is fatal for tire.

Godspeed.

May i ask if are you an engineer?

Yes, structural engineer in marine design office. FEA and CFD are my fields.

Thanks.

I am an aeronautical engineering. And I find most of your statement lack any rigorous analysis and are just anecdotal in nature. You make no quantitative assessment, you just to conclusions with very little analysis of the physics of the problem. ( However, I don't say that all your conclusion are wrong). I will try to write a developed answer tomorrow

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First I urge everyone to leave emotions away from this topic.

You should have left yours away :)

That "famous" IAF Eagle one wing landing is, based from my knowledge, experience and common sense, pure fiction in act of propaganda.

Your analysis is also very poor. First off, you weren't there. None of us were, and your 'engineering insights' are rather useless here. The pilots saw what they did, to call the whole thing a lie because you don't want to believe it is silly.

By posting logical states above I urge everyone interested in this topic to reconsider posting unproved and irrational claims made by IAF pilot that completely neglects logic and common sense of all engineers around the world. Probably used as propaganda tool in specific combat environment, false claim in purpose of helping IAF raise war survival rate can be justified in that environment but everything above is just not tolerable by common sense.

Perhaps you'd like to claim that NASA is lying also:

https://www.nasa.gov/centers/dryden/pdf/88798main_srfcs.pdf

The most affected by this false case are real hardcore sim-fans as damage modeling schematic applied in simulators like DCS is based on forgery. By posting all above I also urge DCS damage model designers to fix this historical error and make it real as possible - approved by engineers.

Just the landing speed thing alone is something you're proven wrong on. There's a video of an F-15 landing at 300kts, HUD view. That eagle was on fire and the high speed was maintained to keep the fire from spreading.

There's another incident where an eagle lost part of a wing (he dumped the fuel tank while accelerating through transonic, it came up and ate part of one wing - about a meter of it IIRC) ... nowhere near as dramatic, but that pilot went of to shoot down a MiG-23 he was chasing, and he found out that part was missing when the boomie told him during air refueling. There are photos of this, but I don't have them handy. The pilot was 'Muddy' Watrus IIRC.

You may be an engineer, but you're obviously out of your depth here.

Tharos, are you an engineer?

PS: I believe more to NACA then NASA. Lets stick to this case first.

Nope, I'm on the math side.

Why would I believe you over an agency who's flown their F-15 to limits that you'll never even get close to?

Why would I believe you over an agency who actually drives and contributes to a bunch of the NACA stuff?

Why would ED's aerodynamicists believe you over their own knowledge?

Tharos, are you an engineer?

 

PS: I believe more to NACA then NASA. Lets stick to this case first.

Let ED believe common sense first, never myths. Documentary on this case is made by HC and not supported by single NASA/MD wind tunnel test nor HPC CFD analysis, even raw calculation or any scientist claims. Nothing, just pilot talk and few pictures, and the rest is history.

If one wants to, go step by step over my statements and destroy each one you want by science facts, freely using math. I explained this case's weak points (and there are lot of them) on the most simple way for more people to understand this case. Lets talk about each one posted initially?

Let ED believe common sense first, never myths. Documentary on this case is made by HC and not supported by single NASA/MD wind tunnel test nor HPC CFD analysis, even raw calculation or any scientist claims. Nothing, just pilot talk and few pictures, and the rest is history.

Not necessary. The incident itself is history.

If one wants to, go step by step over my statements and destroy each one you want by science facts, freely using math. I explained this case's weak points (and there are lot of them) on the most simple way for more people to understand this case. Lets talk about each one posted initially?

The picture of the aircraft itself and the loss of the other aircraft in the collision don't exactly help in making your case either.

I don't think you understand - the ED guys are quite smart, and actually have experts in the specific field of aerodynamics. The F-15C FM is heavily validated and very close to the real thing - in fact, I'm not sure you'll get closer for DACT between an eagle and a flanker in any other simulator ... or even closer to their actual flying characteristics.

Seriously, why do you want to talk about this? There's no point. The incident is real, documented, it happened. If it really had been false, it would have been falsified already. Pilots will quickly tell you 'yeah that didn't happen'. These kinds of stories rarely last.

History channel actually made case "historical". Can you explain why you find my high speed landing explanation false by describing actions and forces acting on plane in that exact moment? What about XB70 case?

Do you see any traces of A4 embedded in F15 wing root?

History channel actually made case "historical". Can you explain why you find my high speed landing explanation false by describing actions and forces acting on plane in that exact moment? What about XB70 case?

How are they the same? Different aircraft. F-15 had already absorbed lessors from XB70 and other aircraft.

Here's an eagle landing at 250kts (5:20):

Another training collision (or perhaps very near miss - no eagles were lost in the making of this tape):

First: do you see any traces of A4 embedded in F15 wing root?

But ok, I'll go with some of your points:

- Jet fuel is NOT highly flammable. The vapors are.

- I don't recall there being a wingman but I could be wrong, not really a big deal in this case.

- Yes, that wing's fuel would have been gone very quickly, as well as that hydaulic circuit, but guess what ... lots more where that came from :)

- The debris didn't damage anything else. Period. There's nothing to prove here, there's no requirement for the debris to hit anything at all. You've got zero math on this one, since we don't even really know the geometry of the collision.

- The fuel may have been quite gone by the time the AB was used, and besides, vortices can keep it out of the way as well.

There are certainly some sources which are obviously a false re-telling of the pilot's story (IMHO, or the pilot himself was half-joking), for example:

http://www.uss-bennington.org/phz-nowing-f15.html

He says 'no warning lights' but that can't be - he'd have lost a hydraulic system connected to that wing, as well, he said that he had to reconnect the controls - well if your CAS pops off, that's a warning light. Specifically, you don't get to DISCONNECT the controls, nor does the aircraft do so at any time - it will disable the CAS which helps fly the aircraft - think of it kind of like the flanker's FBW.

And now I'll quote the NASA paper, which delivers a lot more detail about the incident:

Though curious about the whole affair, the engineers had no data for such extensive damage, and so they placed an F-15 wind tunnel model in MDC’s high-speed wind tunnel, sawing off successive sections of the right wing between tests. In the end, calculations done by controls engineers discovered that the margin to maintain controllable flight for this extent of wing damage was only ±20 knots and ±20 degree angle of attack variation from trim. The engineers were amazed that the IAF pilot found and maintained this very narrow margin of control. And the revelation that there was a stable flight condition for such serious damage triggered a much higher interest in reconfigurable controls technology.

I'll point out that this very incident sparked the reconfigurable controls research. There is no doubt that there was a tremendous amount of skill displayed here on the part of the pilot, as well as tremendous luck present for the particular circumstances of this flight.

Your argument, however, it kinda cooked :D

I am an aeronautical engineering. And I find most of your statement lack any rigorous analysis and are just anecdotal in nature. You make no quantitative assessment, you just to conclusions with very little analysis of the physics of the problem. ( However, I don't say that all your conclusion are wrong). I will try to write a developed answer tomorrow

Yep, exactly

We do like a good discussion here jackmckay, you certainly like your drama post tho.

Yes, structural engineer in marine design office. FEA and CFD are my fields.

There are many experts here and some highly in there specific field, you need a little more data and analysis to go head to head with NASA. Otherwise it does look anecdotal and just fluff to have a days of our lives tv show episode on the next how many pages.

I do hope lucky-hendrix comes back with an analysis on this and doesn't think his just wasting his time, I could see that he might.;)

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The engineers were amazed that the IAF pilot found and maintained this very narrow margin of control.

If they find out that every DCS F15C pilot can found and maintain this very narrow margin of control they would commit a collective suicide.

No, they'd just point and laugh at you.

If they find out that every DCS F15C pilot can found and maintain this very narrow margin of control they would commit a collective suicide.

May I ask what is the point of this thread?

I think the main complaint has to do with the eagle's damage model in all of its forms.

There are some problems:

- G-loading DM is not implemented

- Sometimes FM performance does not match the visual DM, especially in MP.

Some might want to add the whole about tanking missiles recently, but this isn't an eagle problem. It just manifests with the eagle the most.

"Jet fuel is NOT highly flammable. The vapors are."

In fully developed turbulent flow fuel droplets tend to disperse in a mist - its trivial. High speed airflow can only delay full dispersion of fuel.

keywords: turbulent eddies, vortex street, multiphase flow phases, droplets dispersion ..

study example: http://homepages.abdn.ac.uk/jderksen/pages/pbl/aichej61p2618.pdf

pictures in post: F111 dumped fuel ignited by afterburner. mig29 midair collision - what happened next? observe fuel (obviously not in liquid phase) ignite after entering afterburner path 4.5 seconds later.

fuel/air mixture combustion is stable inside combustion chamber and does not damage internal cambers of engine - because they are designed to do so by default, material used - HS titanium alloys, HS steel alloys, ceramics..

outside of engine close to airframe skin - meltdown, strength weakening - structural failure.

Pilot/wingman couldn't see the extent of damage because mist hide complete wing - that's the greatest lie I ever heard. like it was smoking parked and not in high velocity airstream.

NASA - one word: Grasshopper (or Falcon 9). Where is NASA now? No more Von Braun and German scientists to make some progress.. it looks they stayed frozen in 60s. I don't take them serious really.

That F15 that couldn't stop on runway threshold - tires still in one peace, hmm? no reverse thrust or parachute?

IAF one didn't have one wing so he should land with much greater roll angle to maintain direction - port side tire says: wiiiiiii-kaboom-spark-wooshh and then goes roll pirouette.. pilot is in heaven (or hell).

PS: I believe that midair could actually happen but with much lesser extent of damage, then ground crew scissored the rest to make repairs easier, and then some idiot said: hey we could make some story, there are few aeronautic engineers in world, most people are idiots, we can sell them that story, and to the enemies too.. rest is history (channel).

F15s didn’t have thrust reversers and relied on arresting hooks for emergency landings. Get your facts straight on the basics first.

Why would increased roll deflection cause tyre damage if the plane touched down normally? After that control is mainly retained by rudder anyway.

Also tires don’t go boom with anti skid brakes, they might deflate if brake temperature exceeds a point due to fusible plugs.

That F15 that couldn't stop on runway threshold - tires still in one peace, hmm? no reverse thrust or parachute?

Yes he landed on a relatively short runway and no emergency measures were erected (cables for the hook, and arresting net at the end).

IAF one didn't have one wing so he should land with much greater roll angle to maintain direction - port side tire says: wiiiiiii-kaboom-spark-wooshh and then goes roll pirouette.. pilot is in heaven (or hell).

You can fantasize all you want - this happened, and you've literally got nothing going here other than shouting 'conspiracy' and 'propaganda', like 9/11 truthers.

Its not the F-15C landing with one wing thats a bother, Whats a bother is the damage model in DCS and the fact it takes 3+ missiles to bring it down its a tank, Bad net code can get you away with also flying about in flames as we found out yesterday in a private server, Just flying like a ghost shooting missiles and bringing planes down. DCS will never replicate actual real life.

This thread is nothing but funny. :)

F-15 is a very tough plane, that's for sure.

But IMHO it's clear how the F-15 has issues with damage model in DCS. Something that ED/BST needs to look at.

Almost everything has problems with the dm now. Mig21s stroll around happily after 3 missile hits all the time. Patience people...

Demistifying Eagle damage model

Nothing but funny? Can you say that while onboard of an airliner, cruiser ship or a car thats been designed by actual engineer? Is that funny? Funny how your life is tailored by engineers that takes care for rest to stay alive and safe? That the gratitude for all hard work and effort? All that is funny to some. Next time use horseride or foot for traveling great distances. To me as an engineer is funny level of naiveness of manny people that can't counter any claim state from post start with any hard argument. Core: if pilot kicked afterburner, plane would lit in fireball 4.5 seconds later - rock solid state. That whole story is undoubtly fake. One emotionaly damaged user can only battle this post by adding tags on author itself but having no real argument to logically counter any claim of posts itself from initial claims. That's sad. Saddest thing is that ED dm coders got persuaded that this full crippled landing is actually possible further hardening eagle damake model. Such irrational attitude is not acceptible in sim worls, maybe only in fantasy game enviroment.

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