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Inconsistent in-flight flap extension

G

Glen P

Active Member
I have a -7 with about 60 hours on it. The flap behaviour today has me scratching my head. I thought I had a flap failure in flight but after looking at the uploaded flight data on Savvy, I see that
- the first in-flight extension (and subsequent retraction) was normal
- the second in-flight extension went to about 88% of normal. Retraction normal.
- the third extension went to about 5% of normal. This is what I identified as a failure.

After landing, powering down and powering up, the flaps worked normally through several cycles on the ground. I wanted to believe that the power cycle had solved the problem so I went for another quick flight. On that flight, the flaps extended to about 12% of normal. Post-flight they again worked fine on the ground.

The flaps are controlled by an Advanced ACM.

Any ideas?

BTW, the flap actuators from Van's are $695 and on back order so that won't be my preferred option.
 
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One possibility

Have a VERY close look at the bell-crank to torque tube weld.

A hair line crack can be almost not detectable when everything is relaxed on the ground in the hangar. With an air load in flight , with a partially failed weld the torque tube can rotate like a torsion spring. The actuator can be operating normal with a full stroke, but the flaps not.

Your description of the last flight are classic symptoms of a mostly failed weld.
In the hangar with no air load on the flaps they will go all the way down and back up .

If the weld is OK and the tube beside the weld, then do a search for issues with your model of actuator and over ride clutch.
 
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Needless to say, continued flight with a potential future asymmetry problem would be a worry for me.
 
F1R said:
Have a VERY close look at the bell-crank to torque tube weld.

A hair line crack can be almost not detectable when everything is relaxed on the ground in the hangar. With an air load in flight , with a partially failed weld the torque tube can rotate like a torsion spring. The actuator can be operating normal with a full stroke, but the flaps not.

Your description of the last flight are classic symptoms of a mostly failed weld.
In the hangar with no air load on the flaps they will go all the way down and back up .

If the weld is OK and the tube beside the weld, then do a search for issues with your model of actuator and over ride clutch.
Click to expand...

While this is possible, I think that the fact the OP got the data download makes me suspect a setup or faulty limit switch issue.
If the displacement sensor is on the same arm as the flap motor (the standard setup) then if the weld had failed, the indicator would be indicating a greater flap displacement than the actual flaps.

Can the OP confirm that what he saw out the window correlated with the flap position indicator?

Over the years some of the flap motors have been hit and miss. My 7 needed a replacement at about 7y. I never really looked into why it died.
 
Sounds like the flap motor is not getting a lot of amps. It is a DC motor and the amount of current required to move it will vary based upon the load placed upon that motor doing it's work. On the ground, it doesn't take a lot of current to get the motor to move the flaps. With the plane moving 100 Mph through the air, the motor has to work much harder to overcome that force pushing back on the flaps and therefore will be trying to draw more current. Due to the flap design, it progressively gets more resistance from neutral to full flap and therefore progressively requires more current to move it.

I don't know what an Advanced ACM is but might start there. If it has PWM capabilities or s/w based amperage control, it could be a config issue. Otherwise, start looking for wiring issues that increase resistance and thereby reduce the current that can flow on those wires.

It could also be a failing motor, but to me, the symptoms point upstream from the motor. A common promblem with these is grease migrating from the linear worm gear up to the motor. Once there it can get in the brushes and this creates a lot of resistance and could display similar symptoms. This can be fixed by disassembly and cleaning. Typically it just stops working when this happens, but I can see a case where it starts with the symptoms you describe.

Larry
 
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Advanced Flight Systems Control Module

If this is the device you have then there is a possibility that you are in a step deployment procedure.

For example in my similar system I have a momentary switch that I can hold down for full flap deployment or use a momentary command to get 10 degrees, then another momentary gets me 20 degrees, the third gets full flaps.
 
wawrzynskivp said:
If this is the device you have then there is a possibility that you are in a step deployment procedure.

For example in my similar system I have a momentary switch that I can hold down for full flap deployment or use a momentary command to get 10 degrees, then another momentary gets me 20 degrees, the third gets full flaps.
Click to expand...

Yes, I have it set up to give half flaps from the first push and full flaps from the second.
 
Further on this. On extension, introducing resistance to flap movement causes a grinding noise from the the actuator. Removing the actuator now for further investigation.
 
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