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Do Aircraft Controls Have To Be "calibrated"?  
User currently offlineJamesbuk From United Kingdom, joined May 2005, 3968 posts, RR: 4
Posted (8 years 1 month 1 week 2 days 6 hours ago) and read 5823 times:

Hi guys and girls,

As most people know, when you use any controlled for computers the have to be calibrated every so often, which involves moving all its Axis. Do aircraft have to do this? is it done automatically? I understand if so this would only be in the modern day FBW aircraft as they are connected to computers then to the control surfaces.

So any ideas?

Rgds --James--


You cant have your cake and eat it... What the hells the point in having it then!!!
20 replies: All unread, jump to last
 
User currently offlinePilotpip From United States of America, joined Sep 2003, 3152 posts, RR: 10
Reply 1, posted (8 years 1 month 1 week 2 days 4 hours ago) and read 5798 times:

Aircraft with cable-actuated controls will need to be "rigged" from time to time. As they age, the cables will stretch, get dust and contaminates on pulleys and whatnot. For FBW aircraft, I'm sure that aging hydraulic actuators would have the same effect.

Not really along the same lines, but when you replace a control surface, you have to make sure it is properly balanced as well.



DMI
User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 2, posted (8 years 1 month 1 week 2 days 4 hours ago) and read 5788 times:

Quoting Jamesbuk (Thread starter):
So any ideas?

Just last week i was involved in a rigging of the outer and inner ailerons of a B747 that was pulling to the left by a fair margin. (Almost like the tracking on a car). Adjustments were made to the Actuator and we hope that the corrections made will solve the problem.

I'll dig the job card out and post up the procedure, i wasnt actually involved in the adjustments, simply the set up...



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 3, posted (8 years 1 month 1 week 2 days 3 hours ago) and read 5772 times:

Quoting Pilotpip (Reply 1):
Aircraft with cable-actuated controls will need to be "rigged" from time to time.



Quoting Kaddyuk (Reply 2):
Just last week i was involved in a rigging of the outer and inner ailerons of a B747 that was pulling to the left by a fair margin.

The B747 has a mechanically actuated flight control system. This means that there are cables running from the control column / wheel to the servo-valves on the actuators. These cables will pass over a myriad of pulleys, levers, bell-cranks and other assorted mechanical devices.

Rigging of mechanically actuated flight control systems often entails the use of rigging devices to hold the control surface and control column / wheel in the neutral positions. The cables are then adjusted such that rig pins can be fitted in several of the mechanical devices over which the cable passes. Once this is achieved, the cables are tightened to the correct tension. Once this is done, much testing and adjustment is performed to ensure that the control surface is moving in the correct manner with respect to the control column / wheel.

I remember being involved in the rigging of the lateral control system of a B747SP. This task took the best part of a week. Not only did the ailerons have to be rigged, but the spoiler system as well. Once this was done, the spoilers and ailerons had to be rigged together. On the B747, the spoilers are mixed in with the ailerons to give additional lateral control.



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineJamesbuk From United Kingdom, joined May 2005, 3968 posts, RR: 4
Reply 4, posted (8 years 1 month 1 week 2 days 3 hours ago) and read 5766 times:

Quoting JetMech (Reply 3):

Wow! Sounds like a VERY big job there!.
Also thanks Kaddyuk and Pilot pip for the answers also

Rgds --James--



You cant have your cake and eat it... What the hells the point in having it then!!!
User currently offlineATCT From United States of America, joined Mar 2001, 2345 posts, RR: 38
Reply 5, posted (8 years 1 month 1 week 2 days 1 hour ago) and read 5727 times:

Yea on the Cub (J-3) we re-rig it every time we recove the fabric. If it seems to fly one way or another, we either adjust the trim tabs (on the rudder) or if its actually banking, then re-rigging is necessary. We also grease the pulleys every time we get. Keeps her flying smooth.

ATCT



"The way to get started is to quit talking and begin doing." - Walt Disney
User currently offlinePilotpip From United States of America, joined Sep 2003, 3152 posts, RR: 10
Reply 6, posted (8 years 1 month 1 week 1 day 19 hours ago) and read 5666 times:

Jetmech, or anybody else that can answer:

On larger aircraft, the cables have a compensator designed into them to take up the slack for temperature changes correct? Is this something in addition to the turnbuckles or part of them?



DMI
User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 7, posted (8 years 1 month 1 week 1 day 18 hours ago) and read 5657 times:

Mostly its Rigging & Adjusting of Tension.
regds
MEL



Think of the brighter side!
User currently offlineDALMD88 From United States of America, joined Jul 2000, 2614 posts, RR: 14
Reply 8, posted (8 years 1 month 1 week 1 day 13 hours ago) and read 5611 times:

I've never worked on a FBW aircraft but I would suspect on power up the computers would do a cross check cal. A full check would most likely be required anytime a componet in the system would be changed. They may also call out a checkout during some of the letter checks.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 9, posted (8 years 1 month 1 week 1 day 13 hours ago) and read 5604 times:

What about inertial nav systems? Don't they require a few minutes to power up and calibrate? I have even heard about "calibration points", places on the apron with exactly known positions that are used to calibrate inertial nav.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 10, posted (8 years 1 month 1 week 1 day 11 hours ago) and read 5580 times:

Quoting Pilotpip (Reply 6):
On larger aircraft, the cables have a compensator designed into them to take up the slack for temperature changes correct?

I do remember seeing such a device whilst looking up at the bottom of the cockpit floor from the main deck of a B747. This device was basically two segments of a pulley that were spring loaded. IIRC, this device was used for the rudder control cables. I presume that the compensator kept an adequate tension on the control cables despite changes in temperature and the subsequent changes in fuselage and control cable length  Confused .

The bottom of this compensator device had rigging marks on it. I never did rig the rudder control cables, but I presume that the compensator and the other mechanical rudder control components had rig pins inserted to assure the correct orientation of these components in relation to one another. I presume turnbuckles were then adjusted such that the compensator tension springs were preloaded to the correct amount for the temperature at the time of rigging.

Quoting Starlionblue (Reply 9):
What about inertial nav systems? Don't they require a few minutes to power up and calibrate?

On an Airbus A330 / A340, the Air Data Inertial Reference Units (ADIRU's) will be aligned by the crew when they arrive at the aircraft. They will enter the co-ordinates of the parking bay into the ADIRU's, which then take about 7 minutes to align.

At the end of each flight, the drift (nm/hr) of each of the three ADIRU's can be accessed and printed out. I this drift is outside a certain limit, that ADIRU will need to be replaced. In other words, the ADIRU is " calibrated" daily when the crew aligns the system before flight. If the ADIRU drifts out of limits, I presume it will be removed and calibrated in a proper sense in the workshop.

I am under the impression that the navigation system of the Airbus uses GPS, with the ADIRU as a backup  Confused . Anyway, I will try to look up the MM for both of these items to confirm.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently onlinePihero From France, joined Jan 2005, 4670 posts, RR: 77
Reply 11, posted (8 years 1 month 1 week 1 day 7 hours ago) and read 5523 times:
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Quoting JetMech (Reply 10):
On an Airbus A330 / A340, the Air Data Inertial Reference Units (ADIRU's) will be aligned by the crew when they arrive at the aircraft. They will enter the co-ordinates of the parking bay into the ADIRU's, which then take about 7 minutes to align.

In order to avoid typing errors, once you have initialised the flight - origin, destination -the system would present the official airport coordinates for you to accept as an "align" position. The actual position will be entered automatically as the takeoff runway coordinates upon selecting takeoff thrust. A shift of xxx meters needs to be set on the performance page if you start from an intersection and not the threshold.

Quoting JetMech (Reply 10):
I am under the impression that the navigation system of the Airbus uses GPS, with the ADIRU as a backup . Anyway, I will try to look up the MM for both of these items to confirm.

It is a bit more complicated as with GPS stations available, the GPS position is mixed wth the IRS to provide the flight management with a hybrid position called GPIRS Pos. The factoring of the data gives some priority to the GPS Pos.
Thus the ADIRS position is "updated" permanently by the GPS. If for some reason, one loses the GPS, then the ADIRS begin their mixing+monitoring act as they will then be left to drift at their own rate, with or without DME environment.



Contrail designer
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 12, posted (8 years 1 month 1 week 13 hours ago) and read 5432 times:

G'day Pihero, thanks for the information  Smile ! It certainly made the process much clearer, but I still have a few questions.

Quoting Pihero (Reply 11):
In order to avoid typing errors, once you have initialised the flight - origin, destination -the system would present the official airport coordinates for you to accept as an "align" position.

Is this done as a matter of standard procedure? I would thus presume that the displayed parking bay co-ordinates are to check the data in the aircraft's computer?

Quoting Pihero (Reply 11):
The actual position will be entered automatically as the takeoff runway coordinates upon selecting takeoff thrust.

Does this automatic co-ordinate acceptance mechanism work for take offs performed from the FLX/MCT detent?

I'm a bit confused about the ADIRU drift. If GPS is available, is this used to remove the drift from the ADIRU's, or are they allowed to drift regardless  Confused . From this sentence;

Quoting Pihero (Reply 11):
It is a bit more complicated as with GPS stations available, the GPS position is mixed with the IRS to provide the flight management with a hybrid position called GPIRS Pos. The factoring of the data gives some priority to the GPS Pos.

It sounds like the ADIRU's are allowed to drift even if GPS is available. The position signal the aircraft uses in this situation seems to be a mix of the ADIRU signal with drift and the GPS signal (GPIRS Pos); with a heavier weighting going to the GPS signal. From this sentence;

Quoting Pihero (Reply 11):
Thus the ADIRS position is "updated" permanently by the GPS. If for some reason, one loses the GPS, then the ADIRS begin their mixing+monitoring act as they will then be left to drift at their own rate

It sounds like the ADIRU's are continually updated by the GPS signal when available, the ADIRU's only being allowed to drift when GPS signals cannot be received  Confused .

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14139 posts, RR: 63
Reply 13, posted (8 years 1 month 1 week 11 hours ago) and read 5415 times:

Quoting Pilotpip (Reply 6):
Jetmech, or anybody else that can answer:

On larger aircraft, the cables have a compensator designed into them to take up the slack for temperature changes correct? Is this something in addition to the turnbuckles or part of them?

The MD-11 (and DC-10) use compensators in their aileron system (located in the R/H and L/H main wheel well. They look actually like split pulleys with a spring in the middle, which keeps the cables at a constant tension.
The B737 (Jurassic, Classic and NG) use pulleys attached to springs in their aileron cable runs (just O/B of the ailerons in the wing) to keep the aileron cables at the correct tension. The other cable runs are less sensitive to temperature changes because for most of their length they are running inside the airconditioned fuselage and are therefore not that much exposed to extreme temperature changes.

Jan


User currently onlinePihero From France, joined Jan 2005, 4670 posts, RR: 77
Reply 14, posted (8 years 1 month 1 week 8 hours ago) and read 5389 times:
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Quoting JetMech (Reply 12):
Is this done as a matter of standard procedure? I would thus presume that the displayed parking bay co-ordinates are to check the data in the aircraft's computer?

Yes. Airport charts also display parking coordinates.

Quoting JetMech (Reply 12):
Does this automatic co-ordinate acceptance mechanism work for take offs performed from the FLX/MCT detent?

Yes.

Quoting JetMech (Reply 12):
It sounds like the ADIRU's are continually updated by the GPS signal when available, the ADIRU's only being allowed to drift when GPS signals cannot be received

Basically, each ADIRU drifts all the time, but the architecture is such that the GPS position is forced into each ADIRU. The difference between IRS position and the GPS are kept in each ADIRU memory as a "bias". When GPS signals are lost, then each ADIRU will slowly annul its own "bias" - within 8 minutes IIRC- and use afterwards its own computed position. The 3 IRS infos are then collected as "mixed IRS" position by the FMGS and updated by the two DME receivers.
The system built-in redundancy is quite impressive.

Regards.



Contrail designer
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 15, posted (8 years 1 month 1 week 4 hours ago) and read 5360 times:

Thanks again Pihero  bigthumbsup  ! Just one more question;

Quoting Pihero (Reply 14):
updated by the two DME receivers.

Is the updated position from DME forced into the ADIRU's ? I am not exactly sure how a DME works or how they are laid out, but if you could triangulate off two different DME's (beacons?), would it be possible to use this position to "realign" the ADIRU's? Would this practice be desirable?

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlinePilotpip From United States of America, joined Sep 2003, 3152 posts, RR: 10
Reply 16, posted (8 years 1 month 1 week 2 hours ago) and read 5333 times:

Thanks all, I've really enjoyed reading this one. Lots of good explanations!


DMI
User currently onlinePihero From France, joined Jan 2005, 4670 posts, RR: 77
Reply 17, posted (8 years 1 month 6 days 13 hours ago) and read 5283 times:
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Quoting JetMech (Reply 15):
s the updated position from DME forced into the ADIRU's ? I am not exactly sure how a DME works or how they are laid out, but if you could triangulate off two different DME's (beacons?), would it be possible to use this position to "realign" the ADIRU's? Would this practice be desirable?

On a modern airliner, the DMEs data are a direct input to the FMGS in order to generate an FMS position. A DME is just a "distance - to a ground transmitter -measuring equipment", therefore, without a bearing information, one's position is on a hemisphere centered on that station, the radius of which is the displayed distance. If one combines two distances from two stations, then the intersection of the two hemispheres provides an accurate position (the system takes into account both the aircraft's altitude and the station elevation from a data base in order to compute a ground circle from the "slant" range.
In the old days (not very long ago),and IIRC, it started with the Carousel IV, one could force DME data into the IRS. It was an awkward procedure as one was required to input the DME station elevation, make sure that the tuned station was correct...and after a transatlantic flight the update could be quite violent ! Ah ! the good old days !



Contrail designer
User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 18, posted (8 years 1 month 6 days 10 hours ago) and read 5263 times:

Quoting Pihero (Reply 17):
Carousel IV

Thanks again Pihero  bigthumbsup  ! I take it that the Carousel IV is an electro-mechanical INS set-up with accelerometers mounted on a gimballed platform which is controlled by rate gyros and electric motors  Confused .



JetMech split the back of his pants. He can feel the wind in his hair.
User currently onlinePihero From France, joined Jan 2005, 4670 posts, RR: 77
Reply 19, posted (8 years 1 month 5 days 15 hours ago) and read 5202 times:
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Quoting JetMech (Reply 18):
I take it that the Carousel IV is an electro-mechanical INS set-up with accelerometers mounted on a gimballed platform which is controlled by rate gyros and electric motors

That's a nice way to present it !
Yes, it was second generation INS, with the DME update as a very useful feature.
Here are some pictures to show you what we had to pit up with : As each INS drove its own autopilot (INS1-->AP A and INS2--> AP B, INS 3 acting as both spare and majority voter, and INSs by definition drifting each at its own rate, in oceanic / polar airspace, the different INSs positions could be visualised on the pilots' FDs. See the FD bars ,
1/- F/O as PF , :

View Large View Medium
Click here for bigger photo!

Photo © Luca Baroncelli




2/- F/O as PF, and the drift must have been so great that the captain has switched his FD off :

View Large View Medium
Click here for bigger photo!

Photo © Marlo Plate - Iberian Spotters



3/-Capt as PF ; the INS model is unknown to me :

View Large View Medium
Click here for bigger photo!

Photo © Juan Pablo Marini



Upon reaching a DME environment, the AP will make a drastic course change in order to regain its track and both FDs should re-center.

Regards.



Contrail designer
User currently offlineDC8FriendShip From United States of America, joined Apr 2005, 243 posts, RR: 2
Reply 20, posted (8 years 1 month 2 days 6 hours ago) and read 4974 times:

Quoting JetMech (Reply 3):
The cables are then adjusted such that rig pins can be fitted in several of the mechanical devices over which the cable passes



Quoting JetMech (Reply 3):
Once this is done, much testing and adjustment is performed to ensure that the control surface is moving in the correct manner with respect to the control column / wheel

If your rig pins all fit then the controls should move exactly as they are suppossed to. should'nt require any adjustment.

Quoting Pilotpip (Reply 6):
On larger aircraft, the cables have a compensator designed into them to take up the slack for temperature changes correct? Is this something in addition to the turnbuckles or part of them?

The compensator is in addition to turnbuckles, as described above. turnbuckles are only used to set the tension to it's correct value, and if the cable is compensated, adjust the conpensator to the present temperature range.



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