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Old 04-26-2018, 08:27 PM   #1
jackmckay
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Exclamation 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.

Last edited by jackmckay; 07-04-2018 at 01:19 AM.
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Old 04-26-2018, 08:40 PM   #2
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May i ask if are you an engineer?
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Old 04-26-2018, 09:17 PM   #3
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Yes, structural engineer in marine design office. FEA and CFD are my fields.
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Old 04-26-2018, 09:31 PM   #4
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Thanks.
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Old 04-26-2018, 09:36 PM   #5
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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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Old 04-26-2018, 10:30 PM   #6
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Quote:
Originally Posted by jackmckay View Post
First I urge everyone to leave emotions away from this topic.
You should have left yours away

Quote:
That "famous" IAF Eagle one wing landing is, based from my knowledge, experience and common sense, pure fiction in act of propaganda.
Unfortunately for you, it is a very well documented incident. It's truly poor form of you to try and call it 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.


Quote:
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.
I urge to stop posting silliness that goes against documentation and testimony by multiple engineers from McDonell Douglass, not just the IAF pilot. In addition, you're forgetting the other aircraft in the accident.

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

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

Quote:
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.
They aren't going to based on what you said. Joke's on you - you need to provide real proof of falsification.
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.
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Last edited by GGTharos; 04-26-2018 at 10:46 PM.
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Old 04-26-2018, 10:34 PM   #7
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Tharos, are you an engineer?

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

Last edited by jackmckay; 04-26-2018 at 10:40 PM.
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Old 04-26-2018, 11:07 PM   #8
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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?

Quote:
Originally Posted by jackmckay View Post
Tharos, are you an engineer?

PS: I believe more to NACA then NASA. Lets stick to this case first.
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Old 04-26-2018, 11:39 PM   #9
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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?
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Old 04-27-2018, 12:05 AM   #10
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Quote:
Originally Posted by jackmckay View Post
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.

Quote:
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?
There is no need to go over your statements. Some are readily falsifiable, for example your high speed landing conjecture.
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.
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Last edited by GGTharos; 04-27-2018 at 12:12 AM.
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