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Flaps

Started by Hardy Heinlin, Sun, 19 Jun 2011 22:24

Hardy Heinlin

Good evening,

as we all know, the flap control operates in two modes:

- Primary mode (fast)
- Secondary mode (slow)

Basically. Ignoring the fine print.

This is probably the case also on aircraft other than the 744. Or similar, at least.

Has anybody ever flown the following scenario in the simulator or real life?

Flaps are in transit in primary mode (fast). Suddenly a fault occurs on one wing on which the affected flap group changes to secondary mode (slow). To provide symmetric air flow, the other good wing will also switch to secondary mode; however, not before it has completed the current transit. In other words, the rest of the transit time will be flown in an asymmetric configuration.

The intensity of this effect certainly depends on the phase of flap operation. Some phases take long, others fast. If we take the worst case, how much of aileron counter force might be required for the compensation?

Not an easy question, I know :-)

By the way, I thought flap groups are mechanically linked between the wings. But the manuals speak of faults on one wing, while having different processes on the other wing.


Cheers,

|-|ardy

dutch57

Goodevening Hardy,

B744 flaps nice subject i try to share,,

Te flaps have 2 modes of operation and one alternate

primary hydraulic(normal mode) and primairy electric(secundairy mode)

alternate is pure electric operation.

you have inb flaps, coupled to one flapdrive both sides of the wing are operated simutainasly by torque tubes.

and the outb flaps have their own flap drive with torque tubes

normal mode is hyd system 1 for inb and system 4 for outb.

if for a reason hyd is not availeble the flaps switch to primairy electric mode and continue driven by the electric motor on the flap drive.
And the flaps follow the flap handle position via the flap control units.

If a set of flaps have a position disagree you get a message eicas flap disagree and the flap motion is stopped hyd and electrically.

Same goes for the Le flaps, only they have pneumatic power as primairy and electric as secondary primairy.
Also they work in unison, if  in a group one set fails first it goed to single drive electric than le flaps multi drive to tell the pilots that all Le flaps are in primary electric mode.

Le flaps and Te flaps operate seperatly, one can be in electric mode the other in its normal mode.

alternate mode is a different ballgame , than to switch to alternate and bypass the flap control units and use a switch on the pilots panel with limit switches on the flap drives

Hardy this is a very simple way to explain hope you get the idea, if you like a more detailed vieuw please let me know.
Sincerly Bob

Hardy Heinlin

#2
Hi Bob,

thanks!

I just re-read my manuals; one thing I recalled not quite completely. The complete sentence: "Opposite trailing edge flaps are mechanically connected to maintain symmetry".

I conclude: Opposite leading edge flaps are not connected.

So my scenario can work only with LE flap failures.

Anyway, back to that scenario:

All LE flaps start to move in primary mode. While in transit, a fault occurs: All LE flaps on the left wing switch to secondary mode while all LE flaps on the right wing will complete their "movement" before switching to secondary mode. This is "due to the rapid rate of primary mode flap movement", they say.

My question is: Is this short-term asymmetry noticable? Perhaps even dangerous?


Thanks,

|-|ardy

Avi

QuoteIf a set of flaps have a position disagree you get a message eicas flap disagree and the flap motion is stopped hyd and electrically.

Are you sure about it?
As far as I know (unfortunately I don't have time right now to open my books and verify it) if the FCU detects position disagreement (one TE torque tube broke for example), it stops both Flaps Power Packages (since a single flaps input actuator commands both of them) but the FCU can command electrically the "healthy" FPP to the commanded position. Since this FPP drives the outboard or inboard TE flaps, there is no asymmetric movement problem.

Cheers,
Avi Adin
LLBG

Avi

Here is something I found:

QuoteIf a trailing edge asymmetry is detected, primary mode operation is immediately shut down for the asymmetric group and the FCUs do not use secondary mode.

I know there is a bypass valve inside the FPP which closes in a case of asymmetric movement (or when selecting ALTN).
Is it possible that one FPP is "shutdown" and the other continues to work normally (in primary mode)?
I don't see any reason to shutdown the group that has no problem with.
Avi Adin
LLBG

John H Watson

#5
Avi is correct, according to AMM 27-51-00 page 7 (or thereabouts).

The control of TE flap "groups" is independent, whatever "groups" mean. I suspect inboards and outboards are classified as "groups". You can't have independent control of, say, the left inboard flap mechanism.

i.e.  the inboards can run in Primary Electric, whilst the outboards can run in Primary Hydraulic.

Alternate flaps is a different matter.

Rgds
JHW

John H Watson

P.S. There is no real asymmetry protection for LE flaps. If there was a danger in having asymmetry, Boeing would have provided protection.

The LE flaps are divided into control groups. Group A and Group B. If a sub-group fails to extend within a certain time frame, the whole group (A or B) is switched to electric (from pneumatic). However, the time frames are far too long to protect against asymmetry. One subgroup will be completely extended by the time the FCU realises there is a problem with another sub-group.

dutch57

Avi John,

If the FCU`s detect a flap asymetry in the flap system depending what is senses, inb outb flaps pos diagree or difference between lh side flaps inb or outb and rh side inb outb.

If there is a difference between inb and outb flaps it will try to switch to primairy electric on the set which is failing hydraulicly. if than no movement the fcu`s shut down the flaps by means of closing the bypass vlv`s and arming the altn mode for direct electric drive.

However if there is a difference between for instance lh outb flaps and rh outb flaps (broken torque tube failing pos xmtr) it will shut down the complete Te flap system prim hyd and prim electric and disable the Te altn mode aswell.

Boeing does not want that inb flaps and outb flaps move indipendent from eachother, because when inb flaps are used the aircraft has a strong pitch up movement, this is noticeble even in normal operation when selecting landing flaps settings of 20 and beyond.

dutch57

Hardy avi john,

Yes Le flaps are divided into 2 sets , group-a and group-b , group-b are the ones between tip and outb engines and group-a are the others.

If during extension a le drive unit fails , the unit it self will revert to primairy electric, the time for the fcu`s to react to this failure is about 10second.

pneumatic operation for Le edge flaps is about 5 seconds from retract to extend and visa versa.

primairy electrig operation for the Le edge flaps is between 90 and 120 seconds and this is noticeble in the cockpit.

The flap display wil expand and wil show in amber the unit which is in electric operation. when reaching its selected position the display will returns to normal indication.

When during an approach this Le fail happens and the plane is close to the runway or busy airport it wil declare missed approach and leave the circuit in order to obtain the desired Le setting.

John H Watson

Bob, the AMM says

"If no movement with a group of flaps under hydraulic power is detected, the FCU automatically switches to primary electric for that group of flaps"

This appears to disagree with what you are saying here.

QuoteBoeing does not want that inb flaps and outb flaps move independent from each other, because when inb flaps are used the aircraft has a strong pitch up movement, this is noticeble even in normal operation when selecting landing flaps settings of 20 and beyond.

Can you confirm this in real life by putting only, say #4 hydraulics on?

Quotepneumatic operation for Le edge flaps is about 5 seconds from retract to extend and visa versa.

primary electrig operation for the Le edge flaps is between 90 and 120 seconds and this is noticeble in the cockpit.

The AMM quotes approximately 10 seconds and 75~100 seconds respectively.

I think it's time to get out my stopwatch  :mrgreen:

Rgds
JHW

Avi

QuoteHowever if there is a difference between for instance lh outb flaps and rh outb flaps (broken torque tube failing pos xmtr) it will shut down the complete Te flap system prim hyd and prim electric and disable the Te altn mode aswell.
How can the system disable the alternate mode?
When you select ALTN you basically override the FCUs. In this case you control directly the electrical motors in the FPP.
The pilots must not use ALTN in case of a FLAPS DRIVE message but they can (if they insist damage the aircraft).


A question about the time it takes LE to extend / retract in secondary mode.
Is it possible that on the ground it is the same time for extension and retraction but in flight it will take longer to extend (because of resistance of air flow) but faster to retract (the air flow push them back in and "helps" the electrical motors)?

Thanks.
Avi Adin
LLBG

John H Watson

QuoteHow can the system disable the alternate mode?

A broken torque tube will certainly disable one side. How about a jammed torque tube causing both sides to fail? Or do they have a shear point in the middle?

Rgds
JHW.

dutch57

Quote"If no movement with a group of flaps under hydraulic power is detected, the FCU automatically switches to primary electric for that group of flaps"

Yes john that is right,, you can have one set primairy electric and the other primary hyddraulic, and we simulate this when testing the different flap modes of operation.

QuoteHowever if there is a difference between for instance lh outb flaps and rh outb flaps (broken torque tube failing pos xmtr) it will shut down the complete Te flap system prim hyd and prim electric and disable the Te altn mode aswell.

Boeing does not want that inb flaps and outb flaps move indipendent from eachother, because when inb flaps are used the aircraft has a strong pitch up movement, this is noticeble even in normal operation when selecting landing flaps settings of 20 and beyond.

But the quote to mention to comment on is what will happen when there is a flap asymetry or diagree detected by the fcu`s see my initial remark above.

dutch57

Avi,

With a flap asymetry (broken torgue tube or failed indication) the 3 fcu`s internal logic will set an elec disable relay for inb and outb flaps,

When you now arm the Flaps with altn arm switch system wil not arm.

extend and retract time are the same on ground and in the air this is because of the gear reductions in the Le-drive unit.

Avi

#14
We may need to define first what "the system" is.
I thought that "the system" is the FCU and it can't disable the alternate mode (or it can :) ).
If "the system" is a broken torque tube then it does "disable" everything including ALTN since nothing can drive the effected flap.
Avi Adin
LLBG

dutch57

John ,

torgue tubes,

each flap drive unit has an output shaft, with left and right the torque tubes to the transmission assy`s which in their turn drive the ballscrew actuators.

There a no shear pionts in the torque tubes, only one shear point and that is inside the flap drive unit between the gear train(pos switches/rvdt`s) and hyd/elec tric motor gearbox

Pls note gearbox is just a name to glarify,

Bob

John H Watson

Thanks, Bob.

Re Asymmetry protection. A quote from the AMM:

"Each FCU[Flap Control Unit] will disable its control outputs if it determines that a flap asymmetry condition exists. The FCU's will disable their control and failure protection functions when the alternate system is engaged, but will continue to provide position information for flight deck displays and user systems"

According to the AMM, Avi is correct. Of course, the manuals have been known to be wrong from time to time  :mrgreen:  

Rgds
JHW

Avi

Bob and John,

Do you know what the power sources of the bypass valves inside the FPPs are (what drives them open or close)?

Thanks,
Avi Adin
LLBG

dutch57

Avi,
Having a quick glance at my SSM, electrical power for the bypass vlv, comes from TE Flap elec  cont inb  28v dc bus-3 located P6 panel

and outb is 28v dc bus-4 also on the P6 panel

Bob

Blake H

Hi Hardy and all,

I am reading handling the big jet at the moment and using Aerowinx to test some theories.

I know as a pilot having a trailing edge flap failure you will have a higher pitch for a given speed as the centre of pressure moves aft when the trailing edge flap is deployed. From memory from a previous book the centre of pressure moves forward when the leading edge flap is extended. Which requires a down pitch attitude. From my A320 sim experience I can't remember the exact pitch attitude during trailing edge flap failure as it wasn't on my mind during sim session. Can someone share light on this. I would like to know if Aerowinx simulator is or isn't demonstration what the 744 aircraft would do in reality as the pitch doesn't change for an all trailing edge failure.