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DocLightning
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A380 Load Alleviation Function

Tue Aug 19, 2014 3:40 am

So I understand that the A380's ailerons have a load alleviation function. I understand that as a wingtip is deflected upwards the aileron will counter the movement to dump the lift and relieve the bending moment on the wing spar, improving fatigue life.

I wonder if anyone can shed a bit more light on exactly how they work. Why are three aileron panels necessary? Why do they move in different directions at different times?

Doesn't the A320 also have a LAF but only one aileron?
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RE: A380 Load Alleviation Function

Tue Aug 19, 2014 4:33 am

Quoting DocLightning (Thread starter):
Doesn't the A320 also have a LAF but only one aileron?

It does, as an option to increase MTOW. If you recall the thread, I experienced it recently and it felt (and looked like) like a giant was thrumming the wing like a ruler on a desk. Pihero provided some great info: Rhythmic Wing "flapping" Question (by Starlionblue Jun 1 2014 in Tech Ops)
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RE: A380 Load Alleviation Function

Tue Aug 19, 2014 5:55 pm

Quoting Starlionblue (Reply 1):
It does, as an option to increase MTOW. If you recall the thread,

Right. My question is why the three ailerons are used on the A380 but only the one on the A320. Wouldn't one single large aileron on the A380 be simpler (and lighter)?
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RE: A380 Load Alleviation Function

Tue Aug 19, 2014 6:39 pm

Quoting DocLightning (Reply 2):
My question is why the three ailerons are used on the A380 but only the one on the A320. Wouldn't one single large aileron on the A380 be simpler (and lighter)?

I was wondering that too. I came across the german wikipedia article about the XB-70 which had split elevons to "reduce drag, vortices and actuation forces".
What is puzzling me is that these three ailerons have a combined effect. For example one slightly up, one neutral and one slightly down would result in a combined neutral position as the effect of the upwards defelected and downwards defelected ailerons cancel each other out (right?) but you would still have the drag on both deflected ailerons.

like this:



could someone shed some light on how this is advantageous compared to one big control surface or even a split surface as we see it, but moving in sync?
 
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RE: A380 Load Alleviation Function

Tue Aug 19, 2014 9:29 pm

Quoting DocLightning (Thread starter):
Why do they move in different directions at different times?

See the "Valse Des Ailerons" discussion in the excellent article by Claude Lelaie in this issue of AB's "Safety First" magazine:
http://www.ukfsc.co.uk/files/Safety%...0First%20Mag%20-%20July%202012.pdf
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RE: A380 Load Alleviation Function

Wed Aug 20, 2014 7:49 pm

Quoting hivue (Reply 4):
See the "Valse Des Ailerons" discussion in the excellent article by Claude Lelaie in this issue of AB's "Safety First" magazine:

Ah! That explains it nicely!
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RE: A380 Load Alleviation Function

Wed Aug 20, 2014 10:32 pm

The B787 has the most-advance LAF because it is not only horizontal but vertical too.
 
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RE: A380 Load Alleviation Function

Fri Aug 22, 2014 5:36 am

Quoting Chamonix (Reply 6):
The B787 has the most-advance LAF because it is not only horizontal but vertical too.

I presume by Lelaie's reference to the "Valse de Rudder" in the linked article that the A380 is likewise equipped ....

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RE: A380 Load Alleviation Function

Fri Aug 22, 2014 6:26 am

Quoting Chamonix (Reply 6):

On the A330/A340 well before the 787
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RE: A380 Load Alleviation Function

Fri Aug 22, 2014 6:47 am

Related question. The linked article mentions load alleviation as a factor for both comfort and materials fatigue. If the load alleviation system were to fail in flight, what would be the consequences? Discomfort for pax? More fatigue on the wing spars and fuselage? Would the structure need inspection or is it ok as long as it is just one flight?

[Edited 2014-08-21 23:48:45]
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RE: A380 Load Alleviation Function

Fri Aug 22, 2014 5:44 pm

Quoting Starlionblue (Reply 9):
Related question. The linked article mentions load alleviation as a factor for both comfort and materials fatigue. If the load alleviation system were to fail in flight, what would be the consequences? Discomfort for pax? More fatigue on the wing spars and fuselage? Would the structure need inspection or is it ok as long as it is just one flight?

A failure of the LAF would probably require a failure of the FBW system, so I think the issues would be a lot greater than discomfort and fatigue, no?
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RE: A380 Load Alleviation Function

Sun Aug 24, 2014 7:17 am

The A320 LAF accumulators are being removed as unnecessary. Load alleviation is now a function of the SECS and particularlySEC#3. and the ELAC .
 
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RE: A380 Load Alleviation Function

Sun Aug 24, 2014 7:19 am

Quoting horstroad (Reply 3):
could someone shed some light on how this is advantageous compared to one big control surface or even a split surface as we see it, but moving in sync?

Multiple redundancy. Increased safety.
 
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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 3:07 am

Having few ailerons helps to control the aircraft more easily in high speed operations. One large aileron creates huge rolling movement for a small deflection in high speed and it will be difficult to control the aircraft. We can use the outboard aileron to control the aircraft at high speeds hence it creates more moment than other ailerons (less moment comparing to a one large aileron) located inboard to it.  

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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 6:55 am

Quoting skywalker92 (Reply 13):

Having few ailerons helps to control the aircraft more easily in high speed operations.

At higher speed it is more common to use spoilers for roll control rather than ailerons as the control loads generated are too high. On most current generation Boeing's the outer ailerons are locked out at high speed, and they use spoilers and maybe an inner aileron for roll control.
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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 12:57 pm

Quoting Chamonix (Reply 6):
The B787 has the most-advance LAF because it is not only horizontal but vertical too.

you mean it jiggles its bootie? ( to invite some shagging ...  
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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 3:48 pm

Quoting zeke (Reply 14):
At higher speed it is more common to use spoilers for roll control rather than ailerons as the control loads generated are too high. On most current generation Boeing's the outer ailerons are locked out at high speed, and they use spoilers and maybe an inner aileron for roll control.

You are are correct. I am mistaken   Even in the Airbus air crafts outer aileron locked at high speed. Does spoiler action is same for Airbus air crafts?

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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 3:58 pm

I am having another problem.  
Load Alleviation Function comes in to act when the difference between the pilot demanded load factor and aircraft current load factor is greater than 0.3. During a up gust load factor of the aircraft reduces ( as load factor = lift/weight) due to the support coming from the up gusting wind. There will be a difference generate and to bring that difference to zero aircraft it self deploy flaps and spoiler 4,5 to dump some lift. I hope it gives the explanation. Is it?

During an turbulence there might be wind going both up and down.How the Load Alleviation Functions during a down gust?
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RE: A380 Load Alleviation Function

Sun Jan 31, 2016 7:03 pm

Quoting zeke (Reply 14):
On most current generation Boeing's the outer ailerons are locked out at high speed, and they use spoilers and maybe an inner aileron for roll control.

Locked out outer ailerons are nothing new and are not specific to current generation aircraft.

The 707 and 727 had inboard and outboard ailerons. The outboard ailerons were locked out with the flaps up and were progressively introduced with increasing flap settings with a wonderfully simple mechanical system. The B747 and B767 also had locking outboard ailerons.

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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 7:21 am

Quoting skywalker92 (Reply 17):
During an turbulence there might be wind going both up and down.How the Load Alleviation Functions during a down gust?

I will give you a simplistic explanation which is not 100% technically correct of how Airbus implemented Load Alleviation Function in the the FBW, however it should provide you with the underlying concept.



In this diagram you can see a simplistic 2D spanwise lift distribution in dashed lines, and the lift distribution with LAF activated with the solid line. In response to a simplistic symmetrical gust, both ailerons move in the same direction to reduce the amount of lift being generated in the outboard part of the wing. This reduces the load (bending moment) at the wing root, hence a reduction of load.

Quoting boeingfixer (Reply 18):
The 707 and 727 had inboard and outboard ailerons. The outboard ailerons were locked out with the flaps up and were progressively introduced with increasing flap settings with a wonderfully simple mechanical system. The B747 and B767 also had locking outboard ailerons.

I am well aware of this, and it is my counter argument (as well as the rudder limiter) to people who claim that pilots on Boeing's have full control over the aircraft at all times when they claim incorrectly only Airbus FBW restricts pilots use of full control during flight.
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 8:53 am

Quoting zeke (Reply 19):
n response to a simplistic symmetrical gust, both ailerons move in the same direction to reduce the amount of lift being generated in the outboard part of the wing. This reduces the load (bending moment) at the wing root, hence a reduction of load.

It explains a lot
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 9:23 am

Quoting zeke (Reply 19):
I am well aware of this, and it is my counter argument (as well as the rudder limiter) to people who claim that pilots on Boeing's have full control over the aircraft at all times when they claim incorrectly only Airbus FBW restricts pilots use of full control during flight.

As you well know but won't concede Zeke, there's a big difference between flight controls on a Boeing that lock out with increasing airspeed and hard limits built into the flight control system on an AB that apply throughout the flight envelope.



In the Boeing, as with any aircraft increasing airspeed does not require the same amount of control deflection for the required response, it still leaves you with full, unrestricted control over the aircraft with no limits in any phase of flight.


This is not even close to the hard limits in place on the AB fbw products.
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 11:37 am

Quoting Max Q (Reply 21):
big difference between flight controls on a Boeing that lock out with increasing airspeed and hard limits built into the flight control system on an AB

From Dictionary.com

"lock" "any device or part for stopping temporarily the motion of a mechanism."

I will need to find an online north american dictionary which defines "lock" as "full, unrestricted control", have not found one yet.

Seems you are not the only north american that failed to understand the normal English use of the word lock. http://www.aopa.org/News-and-Video/A...fatal-takeoff-with-controls-locked
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 11:39 am

Quoting Max Q (Reply 21):

FBW is an integral part of the plane.
the planes are all designed in scope of system limiting actions
independent of it being a distinct hardware piece "rudder limiter" or
a rule in FBW programming.


That plane old Boeing PR stick isn't worth the ink needed to print it.
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 1:08 pm

Quoting zeke (Reply 19):
In this diagram you can see a simplistic 2D spanwise lift distribution in dashed lines, and the lift distribution with LAF activated with the solid line. In response to a simplistic symmetrical gust, both ailerons move in the same direction to reduce the amount of lift being generated in the outboard part of the wing. This reduces the load (bending moment) at the wing root, hence a reduction of load.

Why is the solid line higher than the dotted in the center? Is it only to separate both lines in that illustration or is there more lift when the outboard ailerons are deflected?

BTW: is that a Tristar and its "lift control mechanism" (don't know the right term) that IIRC can e.g. increase lift very fast in case of a go-around?

b.
 
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 1:12 pm

Quoting Max Q (Reply 21):
As you well know but won't concede Zeke, there's a big difference between flight controls on a Boeing that lock out with increasing airspeed and hard limits built into the flight control system on an AB that apply throughout the flight envelope.

Guys, please. That has been discussed at nauseum and your standpoints are well known.

No offense and freedom of speach and all that. But maybe consider an own thread for that.

b.
 
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 5:10 pm

Can any one explain me how this Load Alleviation Functions during a down gust.Increasing drag by control surfaces may further reduce the lift and in worst case a stall  Wow! .

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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 6:49 pm

Quoting Bambel (Reply 24):

Why is the solid line higher than the dotted in the center?

No, it illustrates an upward gust, which increases the AoA ( somehow) hence making the wing produce more lift.
The symetrical raise of the ailerons, in fact, reduce the local AoA, lower the lift produced at that place. In ideal conditions, the loss of lift due to the raised ailerons shouid just be equal (i.e counter) to the increased lift due to the gust.

Quoting Bambel (Reply 24):
is that a Tristar

It is a Tristar 500 the last of the queens and the only one with that set up

Quoting Bambel (Reply 24):
its "lift control mechanism"

yOYou're probably referring to the DLC - Direct lift control -.
No that feature is only available with landing flaps and involve using the spoilers as vertical path control ( not pitch).
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 7:01 pm

Quoting Pihero (Reply 27):
Quoting Bambel (Reply 24):
Why is the solid line higher than the dotted in the center?
No, it illustrates an upward gust, which increases the AoA ( somehow) hence making the wing produce more lift.

Another way to look at it: This is an "ideal" illustration, so the "area under the curves" needs to be the same for solid and dashed lines or the airplane will descend.
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RE: A380 Load Alleviation Function

Mon Feb 01, 2016 8:05 pm

Quoting Bambel (Reply 24):
Why is the solid line higher than the dotted in the center? Is it only to separate both lines in that illustration or is there more lift when the outboard ailerons are deflected?

When an aircraft encounters a gust, say of a normal value of 0.1g, the load (i.e lift) is around 10% higher. What the LAF is doing is moving that lift inboard by changing the span wise lift distribution. If you would take the centroid of the lift distribution by the distance from the longitudinal axis under normal 1g conditions, with LAF that centroid moved inboard, so the moment arm of the total lift distribution is reduced, which in turn reduces the amount of structure needed to carry that load. This results in a lighter wing, or using the same wing to carry higher loads.

Quoting Bambel (Reply 24):
BTW: is that a Tristar and its "lift control mechanism" (don't know the right term) that IIRC can e.g. increase lift very fast in case of a go-around?

Yes it is, it was used to visualize the concept. It was the clearest diagram I could find that I could use to explain the concept.
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 7:47 am

Quoting hivue (Reply 28):
Another way to look at it: This is an "ideal" illustration, so the "area under the curves" needs to be the same for solid and dashed lines or the airplane will descend.

Thanks, understood.

Quoting zeke (Reply 29):

When an aircraft encounters a gust, say of a normal value of 0.1g, the load (i.e lift) is around 10% higher. What the LAF is doing is moving that lift inboard by changing the span wise lift distribution. If you would take the centroid of the lift distribution by the distance from the longitudinal axis under normal 1g conditions, with LAF that centroid moved inboard, so the moment arm of the total lift distribution is reduced, which in turn reduces the amount of structure needed to carry that load. This results in a lighter wing, or using the same wing to carry higher loads.

So the advantage of load alleviation is a lighter structure? Compensating a gust by the elevator would mean a lot of forces going through the plane. The gust increases lift and you could force the plane down by the elevator. Load alleviation simpy reduces lift at the (outer) wing and avoids elevator usage?

thx
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 8:25 am

Quoting zeke (Reply 22):
From Dictionary.com

"lock" "any device or part for stopping temporarily the motion of a mechanism."

I will need to find an online north american dictionary which defines "lock" as "full, unrestricted control", have not found one yet.

Seems you are not the only north american that failed to understand the normal English use of the word lock. http://www.aopa.org/News-and-Video/A...fatal-takeoff-with-controls-locked

Interesting that you used to fly a Boeing with no hard limits yet still can't understand the concept. Locking out
or restricting movement of a flight control with higher airspeed still leaves you with full unrestricted control of the
aircraft and no hard limits unlike the AB.



Your understanding of English seems seriously flawed as is your understanding of the accident you provided a link
to, do you understand what a gust lock does ?



I'd suggest some time with a dictionary yourself, you could learn a lot.

[Edited 2016-02-02 00:26:28]

[Edited 2016-02-02 00:27:14]
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 11:48 am

Quoting Bambel (Reply 30):
So the advantage of load alleviation is a lighter structure?

That is one advantage, or to use the same structure to carry a higher load that what would otherwise be achievable. It also saves fuel as the trajectory path vector (velocity) changes are reduced, improves passenger comfort, and reduces pilot workload.

Quoting Bambel (Reply 30):
The gust increases lift and you could force the plane down by the elevator.

That will depend on the gust. Gusts by definition are almost instantaneous increases in load, where the elevator is used in cruise for longer term trajectory control. i.e. a significant gust could result in an almost instantaneous change of altitude by a couple of hundred feet, elevator control control would be used then over a period of a minute or two to restore the trajectory. Using elevator for instantaneous trajectory control in cruise will result in passenger injury. Do the math yourself, if an aircraft has a TAS of 475 kts, or 800 ft/sec horizontally, a 1 degree change in pitch results in what rate of climb in feet/min ?

There are a number of accident reports about where pilots were too aggressive in pitch control in cruise in response to a TCAS RA, resulting in passenger injuries as the pitch change put passengers heads through the cabin ceiling.

Quoting Bambel (Reply 30):
Load alleviation simply reduces lift at the (outer) wing and avoids elevator usage?

You will have to forgive me with the simplistic explanation I provided above that resulted in that summation, I did so to convey the major concept. The actual interaction is far more complex as lift is just one component that adds load to the wing, apart from the lift, there is the weight of the wing, the fuel load, and the engines that all contribute positively and negatively to the load distribution. Lift distributions are not 2D, they are 3D, LAF impacts on not only the spanwise lift distribution, also the chordwise.

You have grasped the major concept I was trying to explain with that statement.

Quoting Max Q (Reply 31):
do you understand what a gust lock does ?

It is this

Quoting Max Q (Reply 31):
Locking out or restricting movement of a flight control without full unrestricted control of the
aircraft and hard limits
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 3:19 pm

Quoting zeke (Reply 32):
ou will have to forgive me with the simplistic explanation I provided above that resulted in that summation, I did so to convey the major concept. The actual interaction is far more complex as lift is just one component that adds load to the wing, apart from the lift, there is the weight of the wing, the fuel load, and the engines that all contribute positively and negatively to the load distribution. Lift distributions are not 2D, they are 3D, LAF impacts on not only the spanwise lift distribution, also the chordwise.

I am thankfull for ever answered question! And of course i need simplified because i am only an amateur  

So, load alleviation is not only used to react to gusts, it is more a by-product. It is working during the whole flight. (static and dynamic reactions)

On the other hand, how do aircarft without such a concept react to gusts during approach? From your explanation, it's not the elevator?

thx again.
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 4:15 pm

Quoting zeke (Reply 32):
You will have to forgive me with the simplistic explanation I provided above that resulted in that summation, I did so to convey the major concept. The actual interaction is far more complex as lift is just one component that adds load to the wing, apart from the lift, there is the weight of the wing, the fuel load, and the engines that all contribute positively and negatively to the load distribution. Lift distributions are not 2D, they are 3D, LAF impacts on not only the spanwise lift distribution, also the chordwise.

So there is also a question of torsion on the wing box on the plane lateral axis… (and maybe many more   )
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 6:27 pm

Quoting Bambel (Reply 33):
So, load alleviation is not only used to react to gusts, it is more a by-product. It is working during the whole flight. (static and dynamic reactions)

That is correct, if you were to model it dynamically, it would be close to active air springs (air suspension) on a heavy vehicle, except in this case you have an air spring on each side of the wing as the gust can go either direction . The dampening response by the "ideal" air spring is non-linear.

Quoting Bambel (Reply 33):
On the other hand, how do aircarft without such a concept react to gusts during approach? From your explanation, it's not the elevator?

You have asked what I see to be a two part question, first being how does the structure handle the load, and then how does the aircraft recover after the gust.

Aircraft without LAF are deigned to meet the same certification gust envelope, and have traditionally done so by just making them stronger and heavier for that design case. Without LAF however, from the passenger perspective it will be like going over a speed bump on a road without modern suspension.

In normal flight an aircraft's inertia will continue on its current trajectory. If you were to place the aircraft in a control volume, and then suddenly translate that control volume up or down (which is the acceleration of the gust), that is similar to what the aircraft will experience.

After the control volume translation the aircraft is displaced vertically. The vertical translation will be seen by the autopilot feedback response loop as a difference between the target altitude and actual altitude, and it will command the aircraft back to the target altitude. There are gains in this loop so it is comfortable for the passengers.

Quoting Aircellist (Reply 34):
So there is also a question of torsion on the wing box on the plane lateral axis… (and maybe many more   )

That is correct, there will be torsion, as well as aeroelastic (i.e flutter) effects to consider. Reducing the outboard lift will also temporarily marginally increase the spanwise flow from the inner part of the wing outboard.
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RE: A380 Load Alleviation Function

Tue Feb 02, 2016 11:42 pm



Quoting zeke (Reply 35):
The dampening response by the "ideal" air spring is non-linear.

Hm, from what i can remember, an ideal spring is f=c*l (f=force, c=spring constant, l=length of deflection) which would result in a linear response. And also the ideal gas law P*V=n*R*T leads to a linear response of a "gas spring" (change V and keep everything else the same – like the car suspension you mentioned). Just courious...

Quoting zeke (Reply 35):
After the control volume translation the aircraft is displaced vertically. The vertical translation will be seen by the autopilot feedback response loop as a difference between the target altitude and actual altitude, and it will command the aircraft back to the target altitude. There are gains in this loop so it is comfortable for the passengers.

Thanks again. But a last question: which controll surfaces are used to counter gusts on a "traditional" plane? How is a plane "commanded" back to it's targeted altitude? Spoilers? Elevators? ...?

BTW: i guess i understand the very basic physic laws of why a plane flies and how it is controlled. But this topic is a very fascinating detail how all this is not only done, but done very optimised.

b.

[Edited 2016-02-02 15:42:43]
 
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RE: A380 Load Alleviation Function

Wed Feb 03, 2016 12:13 am

Quoting zeke (Reply 35):
Without LAF however, from the passenger perspective it will be like going over a speed bump on a road without modern suspension.

PS
Reading it again, i guess i understood more. Without load alleviation the plane simply does "react less" to a gust (or can't react better) and thus the feeling of a "bump" is pronounced. And to get back on trajectory a "traditional" plane "accepts" the bump and corrects a change of altitude by eg elevators but with a sufficient dampening to make it "comfortable" for the passengers.

b.
 
Max Q
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RE: A380 Load Alleviation Function

Wed Feb 03, 2016 5:50 am

Quoting zeke (Reply 32):
Quoting Max Q (Reply 31):
do you understand what a gust lock does ?

It is this

Quoting Max Q (Reply 31):
Locking out or restricting movement of a flight control without full unrestricted control of the
aircraft and hard limits

Interesting you would choose to edit my statement and then attempt to misquote me, the manner in which you have 'doctored my post' leaves it as nonsensical, rather like your attitude towards having full, unrestricted flight control and no hard limits in any phase of flight.


This is what I actually said:

Quoting Max Q (Reply 31):
Locking out
or restricting movement of a flight control with higher airspeed still leaves you with full unrestricted control of the
aircraft and no hard limits unlike the AB.

Incidentally, a gust lock is used to immobilize flight control surfaces and prevent damage caused by unintended, abrupt movement of said controls while the Aircraft is parked on the ground, this device can be activated by a device inside the cockpit, or on some aircraft with external locks.



They are not found on larger jet transports whose flight controls are immobilized with lack of hydraulic power.



Just as a reminder.
The best contribution to safety is a competent Pilot.


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zeke
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RE: A380 Load Alleviation Function

Wed Feb 03, 2016 9:09 am

Quoting Bambel (Reply 37):
Reading it again, i guess i understood more. Without load alleviation the plane simply does "react less" to a gust (or can't react better) and thus the feeling of a "bump" is pronounced.

Correct, think of a mountain bike with or without suspension and what the rider feels if they were to go over the same course.

Quoting Bambel (Reply 37):
And to get back on trajectory a "traditional" plane "accepts" the bump and corrects a change of altitude by eg elevators but with a sufficient dampening to make it "comfortable" for the passengers.

That is correct.

Quoting Max Q (Reply 38):
full, unrestricted flight control and no hard limits in any phase of flight

There not a single military or civil aircraft that does not have hard limits (i.e a maximum range of movement) in the flight control system, nor is there any aircraft that affords unrestricted control, even those with negative stability.

"Additionally, there may be misconceptions among transport pilots about the use of flight controls, how aircraft may be manoeuvred, and what are the structural load capabilities of transports. These misconceptions may be due to previous experience with other aircraft classes or configurations (e.g., tactical military aircraft, small General Aviation {GA} aircraft). Such misconceptions could lead transport pilots to attempt manoeuvres in unusual situations that could make the situation worse and introduce excessive risk. The issue is further compounded by the limitations in simulator fidelity that may cause pilots to assume some manoeuvres are feasible and repeatable"

from http://www.ifalpa.org/downloads/Leve...udder%20on%20Boeing%20aircraft.pdf
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Max Q
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RE: A380 Load Alleviation Function

Wed Feb 03, 2016 10:05 pm

Quoting zeke (Reply 39):
There not a single military or civil aircraft that does not have hard limits (i.e a maximum range of movement) in the flight control system, nor is there any aircraft that affords unrestricted control, even those with negative stability.

As usual you are dancing around the subject and avoiding the point (rather like you won't admit doctoring my previous post)



Maximum range of movement on a flight control is not remotely the same as the hard limits in the AB flight control system, which limit the Pilot in respect to angle of bank, pitch, airspeed, g etc.


These limits restrict the flight PATH not just the maximum range of movement on a flight control.
Not the same thing at all, as you know.
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boeingfixer
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RE: A380 Load Alleviation Function

Wed Feb 03, 2016 10:12 pm

Quoting zeke (Reply 19):
Quoting boeingfixer (Reply 18):
The 707 and 727 had inboard and outboard ailerons. The outboard ailerons were locked out with the flaps up and were progressively introduced with increasing flap settings with a wonderfully simple mechanical system. The B747 and B767 also had locking outboard ailerons.
Quoting zeke (Reply 19):
I am well aware of this, and it is my counter argument (as well as the rudder limiter) to people who claim that pilots on Boeing's have full control over the aircraft at all times when they claim incorrectly only Airbus FBW restricts pilots use of full control during flight.

Wow, how very convenient for you to turn my statement around and use it as fodder to fuel YOUR A vs B agenda. I could care a less about FBW limits as my reply was directly related to your statement about Boeing outer ailerons.

Since you are "well aware" I am presuming you have a complete understanding as to why outboard ailerons get locked out at higher airspeeds thus I will not get into the engineering and aerodynamics of this function. That being said, you wouldn't want your outboard ailerons working at high airspeeds. Care to elaborate on this as I don't appreciate my factual statements getting turned into self fulfilling arguments.

Regards,

John
Cheers, John YYC
 
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zeke
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RE: A380 Load Alleviation Function

Thu Feb 04, 2016 3:58 pm

Quoting boeingfixer (Reply 41):
I could care a less about FBW limits as my reply was directly related to your statement about Boeing outer ailerons.

They are related, manufacturers limit the range of control inputs to that design loads/range is not exceeded. That applies to any aircraft. Every Boeing aircraft you have worked on has limits in the flight control system that the pilot cannot override, they are there by design.

Quoting boeingfixer (Reply 41):
I am presuming you have a complete understanding as to why outboard ailerons get locked out at higher airspeeds

The main reason why Boeing on models up to and including the 777 locked out the outer ailerons at high speed was they had not developed the technology into their civil airframes to provide active load control for vertical gust response. There is structural advantages to add active control to achieve the requirements of FAR 25.341, however is adds significant complexity to mechanical systems, whereas it is much simpler to implement with FBW like on the Airbus FBW and the 787. I dont know why it was not used on the 777, however I would not be surprised to see it as a feature on the 777X.

On the C5, L-1011, 747-8 active control of the ailerons was added as an afterthought to fix some design issues. The B2 uses something similar on its elevons, and that aircraft would fail structurally without it. Due to its unique configuration, gust load response was the limiting design requirement that sized the wing.

On the A320/A330/A340/A350/A380 and 787 active load control by use of ailerons at high speed was incorporated in the early design phase allowing the manufacturers to have a wing that is not sized primarily by gust loads response.

Quoting boeingfixer (Reply 41):
That being said, you wouldn't want your outboard ailerons working at high airspeeds.

Many aircraft do use ailerons in high speed flight, including the 787. The control inputs are made without the pilot being aware much like a yaw damper.
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Max Q
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RE: A380 Load Alleviation Function

Fri Feb 05, 2016 2:09 am

Quoting zeke (Reply 42):
They are related, manufacturers limit the range of control inputs to that design loads/range is not exceeded. That applies to any aircraft. Every Boeing aircraft you have worked on has limits in the flight control system that the pilot cannot override, they are there by design.

Just to clarify, this is not the same as the hard limits built into the AB flight control system despite your attempt to portray
it as such.


Limiting the range of control on a flight control surface with increasing airspeed and / or configuration change has been
part of the design on Boeing, Lockheed and Douglas aircraft for years, you don't need to move a flight control surface as much at higher speeds as it is more effective with the increased airflow.


However this 'limiting' of the flight control surface is just that, it does not impede the pilots in any manner from having full, unlimited control of the aircraft flight PATH.


This is completely different from the AB set up that imposes hard limits on bank, airspeed, pitch, g, etc.

Quoting zeke (Reply 42):
Many aircraft do use ailerons in high speed flight, including the 787.
ALL aircraft, except those without any ailerons like the B52 use ailerons in high speed flight, supplemented by differential spoilers, the point you're missing or fail to comprehend is that OUTBOARD ailerons are normally locked out at high speed.

[Edited 2016-02-04 18:27:45]

[Edited 2016-02-04 18:29:27]
The best contribution to safety is a competent Pilot.


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zeke
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RE: A380 Load Alleviation Function

Fri Feb 05, 2016 7:45 am

Quoting Max Q (Reply 43):
Just to clarify, this is not the same as the hard limits built into the AB flight control system despite your attempt to portray it as such

It is exactly the same, the reason is to meet the design load requirements in FAR 25 or its EASA equivalent. Boeing and Airbus aircraft are designed to meet the same structural loads at the time of certification.

Quoting Max Q (Reply 43):
Limiting the range of control on a flight control surface with increasing airspeed and / or configuration change has been part of the design on Boeing,

I know, I have stated that above. All manufacturers limit the control of the aircraft to meet certification requirements. Pilots cannot override that.

Quoting Max Q (Reply 43):
you don't need to move a flight control surface as much at higher speeds as it is more effective with the increased airflow

That is not the reason why they are limited, it is so that design loads are not exceeded.

Quoting Max Q (Reply 43):
However this 'limiting' of the flight control surface is just that, it does not impede the pilots in any manner from having full, unlimited control of the aircraft flight PATH.

They do.

Quoting Max Q (Reply 43):
This is completely different from the AB set up that imposes hard limits on bank, airspeed, pitch, g, etc

Those limits are not set by Airbus, those limits are certification limits for any transport category aircraft. The g limits on your light twin are exactly the same an the A320 or the A380. Airbus will allow you to momentarily overspeed, more than enough that what you would even need for a safety case.

There has never been an accident that has stated that the certification limits in the flight control system contributed to an accident on an Airbus aircraft.

Read that paragraph I quoted from IFALPA about the misconceptions pilots with inferior knowledge. Thats why they publish those bulletins, there are pilots who still think they can make any control input or any maneuver the like in an airliner.

Quoting Max Q (Reply 43):
ALL aircraft, except those without any ailerons like the B52 use ailerons in high speed flight, supplemented by differential spoilers, the point you're missing or fail to comprehend is that OUTBOARD ailerons are normally locked out at high speed.

I read that paragraph before you edited, your corrections are still wrong.

Outboard ailerons are not locked out on the , L-1011, 747-8, 787, A320, A330, A340, A350, A380,. Thats how this thread started, LAF on the A380 uses the outboard ailerons.

With FBW, control surfaces now do not have a singular function, the inner aileron on the 777 is an interesting example of this, its use as as an aileron, a flap, and a brake.
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WIederling
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RE: A380 Load Alleviation Function

Fri Feb 05, 2016 8:36 am

Quoting zeke (Reply 44):
With FBW, control surfaces now do not have a singular function, the inner aileron on the 777 is an interesting example of this, its use as as an aileron, a flap, and a brake.

That is the core "Nice Thing TM" with FBW and envelope protection.
You can route pilot input overlayed with airframe requirements ( Load alleviation, high lift, lift destruction, Center of lift shift, lift distribution.. ) to all the surface available on the plane in a way that gives the proper results.
All this is cost effectively changeable via software and does not require further manipulations on hardware.

coming from electronics design this was available in 80ties via use of PLD, PLA, FPGA, (programmaable logic function hardware...) integrated circuits. Were you previously had to hardwire all logic you now could just route all input and output to a sufficiently complex programmable logic IC and then in a flexible process "think" functionality into the unit.

Quite the step at the time. Hardware was dumbed down to a "connection box". Easier to design and faster to prototype, produce and test and for space hardware much easier to qualify. One complex antifuse FPGA instead of a big IC dump.
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zeke
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RE: A380 Load Alleviation Function

Fri Feb 05, 2016 10:02 am

Quoting WIederling (Reply 45):
coming from electronics design this was available in 80ties via use of PLD, PLA, FPGA, (programmaable logic function hardware...) integrated circuits. Were you previously had to hardwire all logic you now could just route all input and output to a sufficiently complex programmable logic IC and then in a flexible process "think" functionality into the unit.

The other major advance which is also often overlooked is in the design of the actuators themselves. The advances Moog have achieved with their electronhydraulic, electromechaincal, electrohydrostatic, and backup electrohydraulic actuators are amazing. They now have smart electronic controllers embedded into the actual actuator that can monitor parallel actuators on the same control surface to provide seamless redundancy. This is one of the key advances that enabled the removal of a complete hydraulic circuit on the A380, and the adaptive lift control and ride control on the A350/787.

Developing advanced actuators provides control systems engineers with capabilities that were unheard of 10-20 years ago in civil aerospace.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
Max Q
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RE: A380 Load Alleviation Function

Sat Feb 06, 2016 4:34 am

Quoting zeke (Reply 44):
It is exactly the same, the reason is to meet the design load requirements in FAR 25 or its EASA equivalent. Boeing and Airbus aircraft are designed to meet the same structural loads at the time of certification.

It is not the same, it's misleading and incorrect to state otherwise, the AB has hard limits built into the flight control system that among other things prevent structural overload but this is not always desirable, in a Boeing, Douglas or Lockheed Aircraft you CAN overload the aircraft if you need to, you may bend it but if your input is necessary for the safety of the aircraft it will allow you to do so, unlike the AB.

Quoting zeke (Reply 44):
I know, I have stated that above. All manufacturers limit the control of the aircraft to meet certification requirements. Pilots cannot override that.

Correct, in an AB they certainly cannot, in a Boeing, Douglas or Lockheed Aircraft they can.

Quoting zeke (Reply 44):
That is not the reason why they are limited, it is so that design loads are not exceeded.

Correct however less movement is required at higher airspeed and loads on the airframe can still be exceeded if necessary on non AB aircraft.

Quoting zeke (Reply 44):
They do.

Limiting the range of a flight control surface does not place a hard limit of the flight path of a non AB aircraft, its not the same thing.

Quoting zeke (Reply 44):
Those limits are not set by Airbus, those limits are certification limits for any transport category aircraft. The g limits on your light twin are exactly the same an the A320 or the A380. Airbus will allow you to momentarily overspeed, more than enough that what you would even need for a safety case.

Those limits can be exceeded in all respects, airspeed, angle of bank, pitch, g, etc if necessary in all types but AB, a real advantage for Pilots that value having full control of their aircraft.

Quoting zeke (Reply 44):
There has never been an accident that has stated that the certification limits in the flight control system contributed to an accident on an Airbus aircraft.

There certainly has, the LH A320 fatal overrun in Warsaw is just one example.

Quoting zeke (Reply 44):
Read that paragraph I quoted from IFALPA about the misconceptions pilots with inferior knowledge. Thats why they publish those bulletins, there are pilots who still think they can make any control input or any maneuver the like in an airliner.

I don't make a habit of reading your 'quotes' especially when you doctor mine and other peoples and misquote them to try and make your (invalid) point !
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zeke
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RE: A380 Load Alleviation Function

Sat Feb 06, 2016 8:50 am

Quoting Max Q (Reply 47):
AB has hard limits built into the flight control system that among other things prevent structural overload but this is not always desirable

If it were "desirable", it would be a certification requirement.

Quoting Max Q (Reply 47):
Boeing, Douglas or Lockheed Aircraft you CAN overload the aircraft if you need to, you may bend it but if your input is necessary for the safety of the aircraft it will allow you to do so, unlike the AB.

A pilot can overload an Airbus.

Quoting Max Q (Reply 47):
Correct, in an AB they certainly cannot, in a Boeing, Douglas or Lockheed Aircraft they can.

No pilot can override the hard limits in the Airbus, Boeing, Douglas, or Lockheed flight control system.

Quoting Max Q (Reply 47):
loads on the airframe can still be exceeded if necessary on non AB aircraft.

Loads can be exceeded on any Boeing or Airbus aircraft, that is why IFALPA issued their briefings on the use of control surfaces around 2010 because there were many pilots with inferior knowledge that thought that it was not possible.

Quoting Max Q (Reply 47):
Limiting the range of a flight control surface does not place a hard limit of the flight path of a non AB aircraft, its not the same thing.

It does, you are way out of your depth here. Moving the flight control to the hard limit results a control response commensurate with the conditions at the time. Maximum control input may in fact produce undesired or unintentional control response. Pilots are taught this early in the flying training when the are shown the effect of using aileron with an impending stall. No control response is unlimited.

IFAPLA did tests on GPWS escape maneuvers and found that pilots are unable to control the aircraft flight path as effectively in non Airbus FBW aircraft, and resulted in less the optimum flight path as the pilots overshot the desired path to gain the maximum ground clearance. That was a canned exercise with pilots prepared for the upcoming test. Add the startle factor into the play, the results will be worse.

Quoting Max Q (Reply 47):
Those limits can be exceeded in all respects, airspeed, angle of bank, pitch, g, etc if necessary in all types but AB, a real advantage for Pilots that value having full control of their aircraft.

And all limits on an Airbus can been exceeded, most have at one time or another.
Quoting Max Q (Reply 47):
There certainly has, the LH A320 fatal overrun in Warsaw is just one example.


What part of the flight control system failed ? Can you select reverse and ground spoilers in flight on your light twin ?

What airliners dont use a air/ground logic in some form ?

So are you suggesting there have never been a fatal overrun in a Boeing ? What does your light twin have the AIR/GND SYS EICAS ? What reverse and spoilers will you get with the AIR/GND SYS inop ?

Quoting Max Q (Reply 47):
I don't make a habit of reading your 'quotes'

i.e. you totally ignore your professional body that explicitly contradicts your statements and explains the misconceptions that some pilots with inferior knowledge have. The reference link was provided.

They produce those documents because they are aware that some people in industry are teaching or stating incorrect information.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
michi
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RE: A380 Load Alleviation Function

Sat Feb 06, 2016 10:00 am

Quoting Max Q (Reply 47):
...in a Boeing, Douglas or Lockheed Aircraft you CAN overload the aircraft if you need to, you may bend it but if your input is necessary for the safety of the aircraft it will allow you to do so, unlike the AB.

What kind of situations do you have in mind?


I like the GPWS evasive maneuver for example. The GPWS calls "PULL UP". What will you do as a pilot?

- In a Boeing you will start pulling the yoke until you "feel" a good pull up maneuver. You think you can't pull more or you will not only bend but destroy the aircraft. There is no sensor in the aircraft or your body that tells you: "I am pulling 2.5g right now."
Unfortunately you seldomly apply that much back pressure on your yoke. 2g will feel like a lot! Studies have shown that a yoke pilot will normally pull less than 2.5g, as he assesses the force he feels to be greater than it is in reality.

-In an Airbus you simply pull back your sidestick. You will fly the evasive maneuver with 2.5g exactly. The chance of survival is better, as you will get the best performance out of the aircraft.


Your argument now would be: " I can overload my Boeing so I will get an even better performance out of my aircraft." This is correct, but does normally not work under the high workload, high stress GPWS situation with already failed sensors of your own which brought you in this near ground situation at first (might happen in an Airbus too, as it has nothing to do with the aircraft itself, but with the situational awareness of the pilot/crew).

I know, it feels wrong to be "isolated" of the aircraft envelope like in an airbus. Isolation always feels bad. But the airbus protection's kick in so damn late, you never want to be in a situation like this at all. You don't even come close to a protection in normal ops at all.

When you come close however, you might be stressed because something went wrong already!

Cheers,

Michi

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