VLA sensitivity to wakes

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How sensitive are the VLA - An-225 and Ai-380-800 to wakes generated by conventional heavy aircraft like Bo-747, An-124 or Ai-340-600?

Does the large wing area of the VLA catch the vortices easily and make the VLA sensitive? Or does their large size enable them to ignore turbulent wakes and fly close behind the conventional heavies?

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Profile picture for user Bmused55

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How sensitive are the VLA - An-225 and Ai-380-800 to wakes generated by conventional heavy aircraft like Bo-747, An-124 or Ai-340-600?

Does the large wing area of the VLA catch the vortices easily and make the VLA sensitive? Or does their large size enable them to ignore turbulent wakes and fly close behind the conventional heavies?

Generaly, as I understand it, the larger the aircraft the less sensative it is to wake turbulence from another aircraft.
Its like driving a car past a truck, as you reach the front of the truck, the air its pushing aside hits you and can often cause you to swerve a little. Pass the same truck while driving anouther of similar size or larger and you don't feel a thing.

II guess it is more or less the same with aircraft. The Bigger you are, the less effect wake turbulence has. That is not to say the An225 or A380 won't feel it at all.

The real question is; What effect with the wake of an AN 225 or A380 have on current aircraft like the a320. 757 or 747 for example.

According to Flight Internation, ICAO are recommending an extra gap for spacing between an A380 and following traffic. They are recommended a minimum of 10 miles for approach seperation. This is in comparison to the 6mile seperation needed between a 747 and an A320 for example. This is going to cause some problems at busy airports like LAX or LHR who are going to end up loosing approach slots.

Here's the FI article I got my info from.... you can see a graphic of the seperation distances the ICAO are recommending, alongside a comparison of current distances.

http://www.flightinternational.com/Articles/2005/12/20/203708/A380+powers+on+through+flight-test.html

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14 years 6 months

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Generaly, as I understand it, the larger the aircraft the less sensative it is to wake turbulence from another aircraft.
Its like driving a car past a truck, as you reach the front of the truck, the air its pushing aside hits you and can often cause you to swerve a little. Pass the same truck while driving anouther of similar size or larger and you don't feel a thing.

II guess it is more or less the same with aircraft. The Bigger you are, the less effect wake turbulence has. That is not to say the An225 or A380 won't feel it at all.

The real question is; What effect with the wake of an AN 225 or A380 have on current aircraft like the a320. 757 or 747 for example.

According to Flight Internation, ICAO are recommending an extra gap for spacing between an A380 and following traffic. They are recommended a minimum of 10 miles for approach seperation. This is in comparison to the 6mile seperation needed between a 747 and an A320 for example. This is going to cause some problems at busy airports like LAX or LHR who are going to end up loosing approach slots.

Here's the FI article I got my info from.... you can see a graphic of the seperation distances the ICAO are recommending, alongside a comparison of current distances.

http://www.flightinternational.com/Articles/2005/12/20/203708/A380+powers+on+through+flight-test.html


I wonder how the An-225 does about the wake turbulence. Yes, there is only 1 frame but it has been flying for many years and undertakes commercial charters.

As for sizes, An-225 is the biggest landplane - wingspan 88,4 metres versus 79,8 metres for Ai-380. It also is the heaviest - MTOW 600 tons versus 560 tons of Ai-380-800Passenger. So, one could just look at the experience with An-225 in airport and cruise operations - then compare with Ai-380-800.

How close can An-225 or Ai-380-800 get behind another aircraft and how big airport slot is, in practice, needed for an An-225 visit?

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I wonder how the An-225 does about the wake turbulence. Yes, there is only 1 frame but it has been flying for many years and undertakes commercial charters.

As for sizes, An-225 is the biggest landplane - wingspan 88,4 metres versus 79,8 metres for Ai-380. It also is the heaviest - MTOW 600 tons versus 560 tons of Ai-380-800Passenger. So, one could just look at the experience with An-225 in airport and cruise operations - then compare with Ai-380-800.

How close can An-225 or Ai-380-800 get behind another aircraft and how big airport slot is, in practice, needed for an An-225 visit?


I'd imagine it would be roughly the same for the AN225 as it will be for the A380. Perhaps even a slightly larger seperation.

The only difference is, there is only one AN225, where as there will be hundreds of A380s. Oh boy... thats a lot of lost slots!

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The impact of a Wake Vortex Encounter is dependend on:
- aircraft's span
- inertia
- airspeed
- mass
The higher inertia will reduce the effects of rolling. The size will maybe result in encountering both vortices at the same time. Generally I think the effect is neglitible.

@Bmused55: Be aware about the preliminary status of the ICAO-recommendation. The seperation categories by ICAO are outdated and not appropriate at all. The understanding of wake vortex generation is limited. We will see a totally new approach developing over the next years. After being threatened by ICAO with the increased seperation, Airbus is doing research in order to prove that A380 will have only slightly increased vortex. Additionally, the A380's climb performance will enable it to clear the airspace faster than a B747.
This research was not conducted before because nobody was really interested. The (sorry to say it this hard) propaganda of Boeing, that A380 will nullify its slot-advantage, is embarassing for such an old company. I actually believe that they have no idea what kind of vortices their own aircraft produce.

Just to add: Category heavy starts at 136 tons (including everything from a A310 to a B747-400). A B757 is actually rated as "heavy", too, because it produces such strong vortices. Taking the ICAO-seperation as proven fact is scientificly not valid.

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The impact of a Wake Vortex Encounter is dependend on:
- aircraft's span
- inertia
- airspeed
- mass
The higher inertia will reduce the effects of rolling. The size will maybe result in encountering both vortices at the same time. Generally I think the effect is neglitible.

@Bmused55: Be aware about the preliminary status of the ICAO-recommendation. The seperation categories by ICAO are outdated and not appropriate at all. The understanding of wake vortex generation is limited. We will see a totally new approach developing over the next years. After being threatened by ICAO with the increased seperation, Airbus is doing research in order to prove that A380 will have only slightly increased vortex. Additionally, the A380's climb performance will enable it to clear the airspace faster than a B747.
This research was not conducted before because nobody was really interested. The (sorry to say it this hard) propaganda of Boeing, that A380 will nullify its slot-advantage, is embarassing for such an old company. I actually believe that they have no idea what kind of vortices their own aircraft produce.

Just to add: Category heavy starts at 136 tons (including everything from a A310 to a B747-400). A B757 is actually rated as "heavy", too, because it produces such strong vortices. Taking the ICAO-seperation as proven fact is scientificly not valid.


Has Boeing ever tried to prove that a B757 does not produce such strong vortices and is not heavy?

Also, how sensitive is a B757 to the wake vortices of B747? Or of another B757?

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Has Boeing ever tried to prove that a B757 does not produce such strong vortices and is not heavy?

Also, how sensitive is a B757 to the wake vortices of B747? Or of another B757?

Please define a scenario and "sensitivity". B757-pilots will surely not want to take of directly after a B747. Encounters are very frequent in today's business, some really getting close to "upset recovery"´. The best documented incident (AA587 in NY November 2001) was not really a big encounter.

Profile picture for user Bmused55

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The impact of a Wake Vortex Encounter is dependend on:
- aircraft's span
- inertia
- airspeed
- mass
The higher inertia will reduce the effects of rolling. The size will maybe result in encountering both vortices at the same time. Generally I think the effect is neglitible.

@Bmused55: Be aware about the preliminary status of the ICAO-recommendation. The seperation categories by ICAO are outdated and not appropriate at all. The understanding of wake vortex generation is limited. We will see a totally new approach developing over the next years. After being threatened by ICAO with the increased seperation, Airbus is doing research in order to prove that A380 will have only slightly increased vortex. Additionally, the A380's climb performance will enable it to clear the airspace faster than a B747.
This research was not conducted before because nobody was really interested. The (sorry to say it this hard) propaganda of Boeing, that A380 will nullify its slot-advantage, is embarassing for such an old company. I actually believe that they have no idea what kind of vortices their own aircraft produce.

Just to add: Category heavy starts at 136 tons (including everything from a A310 to a B747-400). A B757 is actually rated as "heavy", too, because it produces such strong vortices. Taking the ICAO-seperation as proven fact is scientificly not valid.


Of course ICAO recommendations are just that, recommendations.
I'm also aware that Airbus are contesting the seperation recommendations. We'll see how it pans out.
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Hmm, according to my friend ad CX, the controllers at WSSS are taking up ICAO's recommendations on the A380 seperation.

Also, he says the ICAO recommendations came from measurements and tests. What measurements and tests could these be? Perhaps something undertaking while the A380 is currently touring.

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Knowing ICAO reasonably well I doubt they have done anything on A380 testing that quickly ...

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Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707's and DC-8's who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn't only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739's as well but I could be mistaken. I know there was an attempt to get the 737NG's recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737's. I know the few times I've gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

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Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707's and DC-8's who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn't only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739's as well but I could be mistaken. I know there was an attempt to get the 737NG's recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737's. I know the few times I've gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

I actually concentrated more on the aircraft as rigid-body system. But you are right: A high-energy vortex may cause structural damage at large aircraft. Especially parts like vertical tail plane.

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I actually concentrated more on the aircraft as rigid-body system. But you are right: A high-energy vortex may cause structural damage at large aircraft. Especially parts like vertical tail plane.

As Airbus and American Airlines are painfully aware of! (although that was more the tail fin)
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As Airbus and American Airlines are painfully aware of! (although that was more the tail fin)

While in this case the vortex did not cause anything like strutural damage or aircraft upset. It just triggered the wild behaviour of the co-pilot.

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While in this case the vortex did not cause anything like strutural damage or aircraft upset. It just triggered the wild behaviour of the co-pilot.

Airbus say the pilot acted wildly, American say he did what he was trained to do.

So there is no way you or I can sayfor sure who is to blame. Personaly I say both parties have responsibility. Although to Airbus' credit, the tail didn't snap till around 130% designed max load.

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Airbus say the pilot acted wildly, American say he did what he was trained to do.

So there is no way you or I can sayfor sure who is to blame. Personaly I say both parties have responsibility. Although to Airbus' credit, the tail didn't snap till around 130% designed max load.

I would orientate myself on the official report of the NTSB that clearly states that
- the co-pilot was responsibly due to "excessive and unnecessary" rudder inputs
- the training of AA contributed to the accident
- the rudder control system contributed to the accident

The tail withstood 1.9 times the limit load, that is the maximum allowed load on vertical tail. The structure behaved exactly as Airbus predicted and NTSB stated that in the report. The rudder travel limiter was object heavy criticism by authorities and the reason why AA blamed Airbus as responsible. However, the limiter is not well designed and tricky to handle, but was certified.

Hence we can clearly conclude who is responsible.

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Hence we can clearly conclude who is responsible.

It's always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we've yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of "experts" judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.

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It's always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we've yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of "experts" judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.

I agree with you.
This is why American Airlines are bitterly defending their pilot.

Its because of all this, I reserve judgement on who or what was responsible.

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The NTSB is the responsible US authority and their findings on this terrible incident are available for all to see.

I presume that we can agree that their invesigations will have been far more thorough and authoritative than any of our speculations.

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The NTSB is the responsible US authority and their findings on this terrible incident are available for all to see.

I presume that we can agree that their invesigations will have been far more thorough and authoritative than any of our speculations.


Yes indeed we can.

However, the belief is still there that the blame cannot be shifted squarely on the pilots shoulders as Schorsch seems to beleive. We're airing different points of view on that, not disputing official investigative results.

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At least you can spell "investigative"........ :o