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OmniAtlas

I can't stall the Airbus

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Running the Airbus 320 here - when speed drops, and the aircraft is out of its speed envelopes (and whatever 'law' the aircraft is now operating in) autothrust/a floor will automatically kicks in. No matter how high I pitch the aircraft, the plane just does not want to stall...talk about thinking on its own :)

 

Is there a way to disable the autothrust?

 

FYI -- I am reading the Airfrance report now; fascinated by how complex and completely different the aircraft operates compared to the Boeings.

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To disable alpha floor the easiest way is to switch FAC 1+2 on the overhead and revert to alternate law

 

FAC 1 is on the left side and FAC2 is on the right of the overhead..

 

You could also hold down the instinctive push buttons on the thrust levers, you have to hold them for 15 seconds then the auto thrust will be permanently disabled.

 

All depends if it's modelled or not in your addon, it's not in the wilco or AXE

 

Regards

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Ah ok. Will check out the overhead.

 

I haven't read the full report yet.

 

Wasn't N1 at 50% when the aircraft went down?

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Ah ok. Will check out the overhead.

 

I haven't read the full report yet.

 

Wasn't N1 at 50% when the aircraft went down?

 

It gets a bit deeper then that.

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Can't stall the Airbus? Easy solution - ask any Air France pilot... ^_^

:LMAO:

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How does an aircraft (not only an airbus) know it is about to stall?

 

Are there parameters (angle of attack, rate of descent/climb, speed) that are computed into the plane and when it reaches outside these flight envelope it signals a stall alarm?

 

How about similar GA aircraft? I know weight will play a role in the calculations, but we don't have a CDU on board; are the parameters simply 'hard-wired'?

 

Thanks.

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To disable alpha floor the easiest way is to switch FAC 1+2 on the overhead and revert to alternate law

 

FAC 1 is on the left side and FAC2 is on the right of the overhead..

 

You could also hold down the instinctive push buttons on the thrust levers, you have to hold them for 15 seconds then the auto thrust will be permanently disabled.

 

All depends if it's modelled or not in your addon, it's not in the wilco or AXE

 

Regards

 

I disabled FAC1 and FAC2 on the overhead but A/Thr still kicks in when my speed drops too low. Still can't stall.

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That should have disabled your protections and put you in alt law, you should have also lost the speed trend on the PFD along with limitations like Vls, green dot, S speeds, Alpha max etc

 

If your flying an IAE variant you could try switching to N1 mode (right side overhead) near the manual start switches, that will also disable alpha floor. Are you flying the wilco or Aerosoft bus? As mentioned it is not modelled in those addons.

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How does an aircraft (not only an airbus) know it is about to stall?

 

Are there parameters (angle of attack, rate of descent/climb, speed) that are computed into the plane and when it reaches outside these flight envelope it signals a stall alarm?

 

How about similar GA aircraft? I know weight will play a role in the calculations, but we don't have a CDU on board; are the parameters simply 'hard-wired'?

 

Thanks.

 

The stick shacker A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke (the "stick") of an aircraft to warn the pilot of an imminent stall. WIKI

 

 

You will get a stall alarm too.

 

Is the fly by wire in the airplane help to stop the plane stall?

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The stick shacker A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke (the "stick") of an aircraft to warn the pilot of an imminent stall. WIKI

 

 

You will get a stall alarm too.

 

Is the fly by wire in the airplane help to stop the plane stall?

 

I know theres a stick shaker on the airbuses and boeings because they may not 'buffet'. My question is how do the systems *know* you are about to enter a stall.

 

When the systems know, then they activate the stick shaker.

 

 

If your flying an IAE variant you could try switching to N1 mode (right side overhead) near the manual start switches, that will also disable alpha floor. Are you flying the wilco or Aerosoft bus? As mentioned it is not modelled in those addons.

 

Aerosoft. Sorry missed your last sentence.

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When the systems know, then they activate the stick shaker.

 

A stick pusher is a device installed in some fixed-wing aircraft to prevent the aircraft from entering an aerodynamic stall. Some large fixed-wing aircraft display poor post-stall handling characteristics or are vulnerable to deep stall. To prevent such an aircraft approaching the stall the aircraft designer may install a hydraulic or electro-mechanical device that pushes forward on the elevator control system whenever the aircraft’s angle of attack reaches the pre-determined value, and then ceases to push when the angle of attack falls sufficiently. A system for this purpose is known as a stick pusher.

The safety requirements applicable to fixed-wing aircraft in the transport category, and also to many military aircraft, are very demanding in the area of pre-stall handling qualities and stall recovery. Some of these aircraft are unable to comply with these safety requirements relying solely on the natural aerodynamic qualities of the aircraft. In order to comply with the requirements aircraft designers may install a system that will constantly monitor the critical parameters and will automatically activate to reduce the angle of attack when necessary to avoid a stall. The critical parameters include the angle of attack, airspeed, wing flap setting and load factor. Action by the pilot is not required to recognise the problem or react to it.

Aircraft designers who install stick pushers recognise that there is the risk that a stick pusher may activate erroneously when not required to do so. The designer must make provision for the flight crew to deal with unwanted activation of a stick pusher. In some aircraft equipped with stick pushers, the stick pusher can be overpowered by the pilot. In other aircraft, the stick pusher system can be manually disabled by the pilot.

Stick pushers should not be confused with stick shakers. A stick shaker is a stall warning device whereas a stick pusher is a stall avoidance device.

 

WIKI

 

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My question is how do the systems *know* you are about to enter a stall.

 

The systems, at least on the Airbus series, calculate VS1G from angle of attack, speed/Mach, altitude, thrust and CG. Using equations for lift, you can then deduce the VS1G (stall) speed.

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When the systems know, then they activate the stick shaker.

 

In order to comply with the requirements aircraft designers may install a system that will constantly monitor the critical parameters and will automatically activate to reduce the angle of attack when necessary to avoid a stall. The critical parameters include the angle of attack, airspeed, wing flap setting and load factor. Action by the pilot is not required to recognise the problem or react to it.

 

 

Yes, this is what I'm looking for. So there is an equation depending on these values.

 

Found the equation -- V = sqrt[ 2W / (rho*S*Cl,max)]

 

http://www.ehow.com/how_5029873_calculate-stall-speed.html (dunno if ehow is accurate!)

 

The systems, at least on the Airbus series, calculate VS1G from angle of attack, speed/Mach, altitude, thrust and CG. Using equations for lift, you can then deduce the VS1G (stall) speed.

 

How about in GA aircraft that don't have computers to calculate values? Do they just assume certain values such as weight? CG of course will change depending on TRIM.

 

I might be talking out of my &@($*, I don't know anything about flying and FSX is just a hobby. :)

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You really don't need weight to determine a stall point.

 

All wings have a finite lift capability and it's directly tied to the wing's angle of attack. A stall vane is usually found on larger aircraft and a stall horn (if you look at it, it's a tube that has air pass through it) on most small GA aircraft that have stall warning systems.

 

These systems are what indicate a stall is about to happen. It's a mechanical device that's being used, not a computer that's dumber than a box of rocks.

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Yes, this is what I'm looking for. So there is an equation depending on these values.

 

Found the equation -- V = sqrt[ 2W / (rho*S*Cl,max)]

 

http://www.ehow.com/how_5029873_calculate-stall-speed.html (dunno if ehow is accurate!)

 

How about in GA aircraft that don't have computers to calculate values? Do they just assume certain values such as weight? CG of course will change depending on TRIM.

 

I might be talking out of my &@($*, I don't know anything about flying and FSX is just a hobby. :)

 

A wing stalls when it exceeds its critical angle of attack, period. It has nothing to do with speed or weight. (At least in the realm of GA flight, at high altitude and high Mach numbers the compressiblity of air starts playing a role).

 

The thing with stall speed is the following:

To keep an aircraft flying level you need the lift to equal the weight.

Lift depends on speed and angle of attack (and other things, but that's not important for this argument).

If you reduce speed you will lose lift, which you can compensate by increasing the angle of attack.

The maximum lift a wing can produce is at the critical angle of attack, just before it stalls.

The slower you fly, the closer your angle of attack needs to be to the critical angle in order to keep your lift equal to the weight.

At a certain minimum speed your angle of attack will equal the critical angle.

If you reduce speed further, one of two things can happen: (1) you keep the AoA constant, your lift is no longer equal to your weight and you start to descend.

(2) you increase the AoA further and stall the wing (at which point your lift is still not equal to your weight and you start to descend).

Stall speed is the slowest speed at which you can fly and still have a lift equal to your weight, which is achieved by maintaining your wing at the critical angle of attack. Unlike the critical AoA, the stall speed does depend on the plane's weight, as shown in your equation.

 

GA planes have a system that measures the angle of attack and acts (alarm, stick pusher, whatever) if the AoA gets too close to the critical angle.

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GA planes have a system that measures the angle of attack and acts (alarm, stick pusher, whatever) if the AoA gets too close to the critical angle.

 

Hi, thanks for the explanation. Is the system the stall vane warpd mentioned above? Found this picture --

 

Stall+Vane.JPG

 

So air has to be entering into this vane system to determine if you're at the stall warning point?

Couldn't you be at a high speed but still be at the critical angle, and therefore you are not at a risk of stalling?

 

Or is this where speed does play a role in addition to the AoA?

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Hi, thanks for the explanation. Is the system the stall vane warpd mentioned above? Found this picture --

 

Stall+Vane.JPG

 

So air has to be entering into this vane system to determine if you're at the stall warning point?

Couldn't you be at a high speed but still be at the critical angle, and therefore you are not at a risk of stalling?

 

Or is this where speed does play a role in addition to the AoA?

 

I'm not quite sure how that system works, but I would assume it needs to be in contact with the airflow somewhere to be able to measure the AoA.

 

You can indeed be at high speed at the critical angle of attack, and if you are you will still stall. You stall when you exceed the critical angle of attack, regardless of your speed. During normal flight it's unlikely to happen however, because if you are near the critical angle at high speed your lift will be much larger than your weight, so you will have a huge upwards acceleration. The most likely situation this would happen is if you're flying at high speed and suddenly yank the stick back. You definitely can stall the plane like that, as anyone who's flown in IL-2 Sturmovik on high realism settings will have found out.

 

At high speed (more than 100 m/s or 200 knots) you start noticing the effects of air being compressible, and if I remember correctly this can affect the critical AoA at which the wing stalls, but compressible aerodynamics was a while ago, I'm a structures and materials guy now.

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I'm not quite sure how that system works, but I would assume it needs to be in contact with the airflow somewhere to be able to measure the AoA.

 

You can indeed be at high speed at the critical angle of attack, and if you are you will still stall. You stall when you exceed the critical angle of attack, regardless of your speed.

 

Hi John, but isn't your critical angle of attack a variable depending on your speed? Its not a constant value?

 

I'll try some high speed angle of attacks tonight. Thanks.

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Stall speed is not a constant value.

 

As example, when you bank an aircraft... the speed you stall at climbs because you're translating some of the lift from the wings in the lateral direction. Since flight is a balance of forces, something has to 'give'. In a turn aircraft tend to have a nose-up attitude which reduces the amount of angle of attack left for the wing before reaching the critical angle of attack. Combine that with the reduction in lift to offset the weight... and *poof!* (<-- magic happens here!) the stall speed increases in value.

 

FYI, the stall speed equation referenced above is only valid for level flight.

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Hi John, but isn't your critical angle of attack a variable depending on your speed? Its not a constant value?

 

I'll try some high speed angle of attacks tonight. Thanks.

 

I'm not sure about the compressible range (speeds above 100 m/s), but in the incompressible speed range the critical angle of attack is always a fixed value that does not depend on speed, only on the shape of your wing. If it wasn't constant the equation you gave above wouldn't work, as C_L_max would not be constant either.

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