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CARST
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Alignment of Pitot Tubes...

Wed Dec 27, 2017 12:06 pm

Hello everyone, I just saw a photo in the top 5 on the a.net index page by Ms. Rychkovskaia, link: http://www.airliners.net/photo/Airbus/Airbus-A350-941/4755913/L

I saved the photo and highlited the positions of the pitot tubes, here it is:

Image

So you can guess what my question is: Aren't all these pitot tubes not aligned inthe wrong way? They seem to look backwards. And from every other picture I've ever seen the pitot tubes were always facing forwards, here are some examples I found by a quick Google search:

Image

Image

Image

Image

Image

Image

So is there something wrong with the A350? Have these tubes been turned around while being on the ground for a longer time? What's the deal? Some new design?
 
Woodreau
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 12:58 pm

Those are not all pitot tubes.

https://goo.gl/images/vS3nP6

The top two on the left are multifunction sensors combining the functions of the pitot tube/AOA sensor and the TAT probe.
The bottom on the left is an ice probe

The 3 on the top of the nose under the windows are side slip angle sensors (like AOA but on the side or like a glider yaw string)

The single circle in the right is a multifunction sensor (pitot AOA TAT)

And the two circled on the right the top is an AOA sensor and the bottom one is an ice detector.
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CARST
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 1:06 pm

Woodreau wrote:
Those are not all pitot tubes.

https://goo.gl/images/vS3nP6

The top two on the left are multifunction sensors combining the functions of the pitot tube/AOA sensor and the TAT probe.
The bottom on the left is an ice probe

The 3 on the top of the nose under the windows are side slip angle sensors (like AOA but on the side or like a glider yaw string)

The single circle in the right is a multifunction sensor (pitot AOA TAT)

And the two circled on the right the top is an AOA sensor and the bottom one is an ice detector.


Hi Woodreau, thanks for the explanation. But I see not one of these sensors on the A350 to be aligned forward. Is that the normal case on this airplane?
 
Woodreau
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 1:10 pm

I am not rated in the 350 just a peanut gallery a.netter like you. But it appears that Airbus went with a multi sensor probe versus a traditional pitot tube, so since the multifunction probe includes a AOA sensor, it would have to be shaped like an AOA vane. And would be free to turn to align with the relative wind. I imagine the pitot part would be a hole somewhere in the sensor. You’d probably have to google a detailed image of the 350 multifunction sensor to see.

Starlionblue should be along shortly to explain further.

Actually google a350 multifunction sensor and one of the first images that results is a close up and you clearly see your pitot tube that you’re wanting to see.

Old a.net thread about the a350 probes
viewtopic.php?t=772023
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CALTECH
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 6:39 pm

Image

1) Ice detector
2) Multi-function probe 1
3) Static port
4) TAT probe
5) Side-slip vane
6) Pitot probe
7) Angle-of-attack vane
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CALTECH
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 6:50 pm

Image
The gun is a precious Symbol of Freedom
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Those who believe otherwise are consumed by an ideology
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hivue
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 8:31 pm

CALTECH wrote:

1) Ice detector
2) Multi-function probe 1
3) Static port
4) TAT probe
5) Side-slip vane
6) Pitot probe
7) Angle-of-attack vane


Why only one pitot and 3 multi-function probes?

Also, a question I asked on this forum years ago when the A350 was entering flight testing is why the arrangement of all these probes so neatly around the nose? I don't recall seeing that on any other airplane. Everything is usually scattered around the fuselage. It's so striking (especially the static ports placed at the nose along with everything else in a nice circle) that there must be a reason for Airbus to have done it that way.

Also also, does anyone else see that the spell checker used by anet does not recognize "pitot" as correct spelling? :)
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Re: Alignment of Pitot Tubes...

Wed Dec 27, 2017 8:37 pm

Why the need for 3 side slip vanes? Is side slip really that big of a potential hazard on the A350? Is it needed for computer calibration? I don't think I have heard of a specific side slip detector before much less 3 of them.
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Re: Alignment of Pitot Tubes...

Thu Dec 28, 2017 1:08 am

I guess only an A350 has sideslip sensors. Would these be called beta sensors?
 
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CALTECH
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Re: Alignment of Pitot Tubes...

Thu Dec 28, 2017 7:20 am

hivue wrote:
CALTECH wrote:

1) Ice detector
2) Multi-function probe 1
3) Static port
4) TAT probe
5) Side-slip vane
6) Pitot probe
7) Angle-of-attack vane


Why only one pitot and 3 multi-function probes?



The description of what each probe is might not even be completely correct in that post

https://www.pprune.org/tech-log/514721- ... ign-2.html
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Horstroad
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Re: Alignment of Pitot Tubes...

Thu Dec 28, 2017 9:21 am

So the A350 has
8 static ports
2 ice detection sensors
4 pitot probes
5 TAT probes
4 AoA sensors and 3 side slip sensors

They really care about redundancy.

Does "the aircraft" (an airbus thinks for itself, right?) have its own set of instruments? There are three sets of static ports, MFP and side slip sensors, one each for captain, F/O and the computers? and then there are the backup/standby instruments on top of that.

The amount of TAT/OAT probes really surprises me though. Other aircraft have only one.
 
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zeke
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Re: Alignment of Pitot Tubes...

Thu Dec 28, 2017 9:34 am

CARST wrote:

So you can guess what my question is: Aren't all these pitot tubes not aligned in the wrong way? They seem to look backwards.

So is there something wrong with the A350? Have these tubes been turned around while being on the ground for a longer time? What's the deal? Some new design?


I covered some of this is another recent tech ops thread viewtopic.php?f=5&t=1381367

Basically your eyes are playing tricks on you, the pitot tubes part of the multi function probes are aligned withthe normal airflow, it is the Angle of Attack part of the multi function probe that rotates with the airstream, Often that looks like it points up as the pivot point is at the front, and the vane is at the back. However if there is a breeze, I have seen them flip the other direction as they will rotate with airflow.

The A350 has three identical Air Data/Inertial Reference Units (ADIRU), each ADIRU has an Air Data Part, and an Inertial Reference part. The Air Data part has the input of a multi function probe (MFP), a side slip angle (SSA) probe, and two integrated static probes (ISP). As there are 3 identical ADIRUs with its own independent sensors so you need 3 MFPs, 6 ISPs, and 3 SSA probes. On top of that there is a backup Integrated Standby Instrument System (ISIS) that has its own air data sensors, a pitot tube and two static ports.

The MFP provides angle of attack (AOA), total air temperature (TAT) and total pressure (ie pitot tube). Inside the nose gear bay there is the OAT probes, only two of these, they are only used on the ground and takeoff and landing (basically when the gear doors are open). Below the sensors on each side is an ice detector similar to what you see on the A330.

On the left side of the aircraft there is an additional convention AOA probe which is used by each flight control computers are a raw data AOA, this is different to the AOA presented by the ADIRUs, it can be used to compare values.

As a further backup the air data computers on the engines can be used in place of the normal air data system.

The test airframes had two additional TAT probes under the pilot windows in line with the SSAs, these are not on production aircraft.


CARST wrote:
But I see not one of these sensors on the A350 to be aligned forward. Is that the normal case on this airplane?


The sensors will align to the free stream direction as the airspeed increases. On other Airbus FBW aircraft you will see the AOA sensors at different angles at the gate.

CALTECH wrote:
Image

1) Ice detector
2) Multi-function probe 1
3) Static port
4) TAT probe
5) Side-slip vane
6) Pitot probe
7) Angle-of-attack vane


1) Ice detector - correct basically the same as the A330
2) Multi-function probe (AOA, TAT, Pitot) - correct
3) Static port - standby static ports for ISIS, normal ones are further back, 3 on each side
4) TAT probe - correct not on production aircraft
5) Side Slip Probe
6) Standby Pitot probe for ISIS
7) 4th Angle-of-attack vane

CALTECH wrote:
Image


You can make out the AOA vane at the back (only this part rotates), the pitot tube, and the square TAT inlet under the pitot in that photo
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CARST
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Re: Alignment of Pitot Tubes...

Thu Dec 28, 2017 9:34 am

zeke wrote:
CARST wrote:

So you can guess what my question is: Aren't all these pitot tubes not aligned in the wrong way? They seem to look backwards.

So is there something wrong with the A350? Have these tubes been turned around while being on the ground for a longer time? What's the deal? Some new design?


I covered some of this is another recent tech ops thread viewtopic.php?f=5&t=1381367

Basically your eyes are playing tricks on you, the pitot tubes part of the multi function probes are aligned withthe normal airflow, it is the Angle of Attack part of the multi function probe that rotates with the airstream, Often that looks like it points up as the pivot point is at the front, and the vane is at the back. However if there is a breeze, I have seen them flip the other direction as they will rotate with airflow.

The A350 has three identical Air Data/Inertial Reference Units (ADIRU), each ADIRU has an Air Data Part, and an Inertial Reference part. The Air Data part has the input of a multi function probe (MFP), a side slip angle (SSA) probe, and two integrated static probes (ISP). As there are 3 identical ADIRUs with its own independent sensors so you need 3 MFPs, 6 ISPs, and 3 SSA probes. On top of that there is a backup Integrated Standby Instrument System (ISIS) that has its own air data sensors, a pitot tube and two static ports.

The MFP provides angle of attack (AOA), total air temperature (TAT) and total pressure (ie pitot tube). Inside the nose gear bay there is the OAT probes, only two of these, they are only used on the ground and takeoff and landing (basically when the gear doors are open). Below the sensors on each side is an ice detector similar to what you see on the A330.

On the left side of the aircraft there is an additional convention AOA probe which is used by each flight control computers are a raw data AOA, this is different to the AOA presented by the ADIRUs, it can be used to compare values.

As a further backup the air data computers on the engines can be used in place of the normal air data system.

The test airframes had two additional TAT probes under the pilot windows in line with the SSAs, these are not on production aircraft.


CARST wrote:
But I see not one of these sensors on the A350 to be aligned forward. Is that the normal case on this airplane?


The sensors will align to the free stream direction as the airspeed increases. On other Airbus FBW aircraft you will see the AOA sensors at different angles at the gate.

CALTECH wrote:
Image

1) Ice detector
2) Multi-function probe 1
3) Static port
4) TAT probe
5) Side-slip vane
6) Pitot probe
7) Angle-of-attack vane


1) Ice detector - correct basically the same as the A330
2) Multi-function probe (AOA, TAT, Pitot) - correct
3) Static port - standby static ports for ISIS, normal ones are further back, 3 on each side
4) TAT probe - correct not on production aircraft
5) Side Slip Probe
6) Standby Pitot probe for ISIS
7) 4th Angle-of-attack vane

CALTECH wrote:
Image


You can make out the AOA vane at the back (only this part rotates), the pitot tube, and the square TAT inlet under the pitot in that photo


Very interesting. Thanks for the explanation. I never realised the tubes/probes could rotate or even change their angle.


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Starlionblue
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Re: Alignment of Pitot Tubes...

Fri Dec 29, 2017 2:12 am

I remember the first time seeing the front of an A350. "What the heck is all that stuff?"

Side note: The 350 air data architecture has ridiculous redundancy. You'd have to lose 5 levels of stuff including the engine air data sensors to lose everything.

CARST wrote:
Very interesting. Thanks for the explanation. I never realised the tubes/probes could rotate or even change their angle.

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As mentioned, the movement is a necessity of the integrated AoA sensing. (Then again, if you want to nitpick there are non-moving AoA sensors out there.)

Woodreau wrote:
Starlionblue should be along shortly to explain further.



Yeah, sorry I was flying. But you seem fine without me. ;)
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Starlionblue
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Re: Alignment of Pitot Tubes...

Sat Dec 30, 2017 2:52 am

I'll add to this topic that on the 330 the AoA vanes are much further back. If you look at this picture you can see the problem with the location. Right in the area where cargo loaders and catering trucks operate. I assume this is one of the reasons why they were moved forward on the 380 and 350.

Image
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jetmech
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Re: Alignment of Pitot Tubes...

Sat Dec 30, 2017 9:56 pm

Starlionblue wrote:
Then again, if you want to nitpick there are non-moving AoA sensors out there.)

The B2 bomber has such a system. If I understand it correctly, there are 24 PTU's (Port Transducer Units) that provide attitude (side-slip and pitch), altitude and airspeed data.

http://www.glennpew.com/Special/B2Facts.pdf

Starlionblue wrote:
I'll add to this topic that on the 330 the AoA vanes are much further back. If you look at this picture you can see the problem with the location. Right in the area where cargo loaders and catering trucks operate. I assume this is one of the reasons why they were moved forward on the 380 and 350.

They also ended up underneath and very close to the bottom of air-bridges. Because of this, we held a spare AOA sensor at each outstation as it was a no-go item if damaged.

CARST wrote:
Very interesting. Thanks for the explanation. I never realised the tubes/probes could rotate or even change their angle.

More detail here on A350 systems if you're interested. Page 289 talks about the probes.

http://www.smartcockpit.com/docs/a350-9 ... pilots.pdf

Regards, JetMech
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kalvado
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Re: Alignment of Pitot Tubes...

Sun Dec 31, 2017 1:08 am

Starlionblue wrote:
Side note: The 350 air data architecture has ridiculous redundancy. You'd have to lose 5 levels of stuff including the engine air data sensors to lose everything.

Could it be that A330 crash over Atlantic in 2009 was still a hot topic when 350 was designed?
 
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Starlionblue
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Re: Alignment of Pitot Tubes...

Sun Dec 31, 2017 2:55 am

kalvado wrote:
Starlionblue wrote:
Side note: The 350 air data architecture has ridiculous redundancy. You'd have to lose 5 levels of stuff including the engine air data sensors to lose everything.

Could it be that A330 crash over Atlantic in 2009 was still a hot topic when 350 was designed?


I'm sure that was a consideration. The automatic source air data source switching on the 350 makes losing one or more systems transparent to the pilot. (Aside from the warnings, of course.)

In general, many of the 350 systems are more conceptually simple and "straighforwardly redundant" than the 330 systems. For example there are two identical hydraulic systems instead of the three non-identical ones on the 330. The electrical system is easier to get your head around. The fuel system is no longer designed by a lunatic like on the 330.
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