Flaps stuck down

[Joe Larussa]

For the second time in seven years of owning this 77 M20J I selected full flaps on landing. Well they decided not to come back up. Quick Google search suggested to choose flaps up and gently tap the flaps to come up. To my surprise it worked, so home I went. Limit switches replaced 16 years ago. No evidence that flap motor has ever been overhauled. Mechanic comes by and of course working perfectly. Any clues on why a love tap would make them come up? Thoughts?

[MatthiasArnold]

Had the same thing happening app. 2.5years ago and exactly this procedure worked great!

[hubcap]

Mine did that last year. I replaced the motor.

[PT20J]

Switches and relays do wear out. I have zero tolerance for electrical components - if one acts up once, I replace it. Especially something as inexpensive  as a microswitch.

[Joe Larussa]

So what is it about bumping the flap that makes it go up?

[Justin Schmidt]

Also, check for any binding of the flaps.

[Tom 4536]

On 7/5/2023 at 7:59 PM, Joe Larussa said:

For the second time in seven years of owning this 77 M20J I selected full flaps on landing. Well they decided not to come back up. Quick Google search suggested to choose flaps up and gently tap the flaps to come up. To my surprise it worked, so home I went. Limit switches replaced 16 years ago. No evidence that flap motor has ever been overhauled. Mechanic comes by and of course working perfectly. Any clues on why a love tap would make them come up? Thoughts?

My flaps stuck down during slow flight on two flight reviews but both times would retract after I landed. My MSC said I need to exercise the switches on the ground by lowering the flaps a few degrees, then raising them and repeat the process 10 times. The problem seemed to be resolved. During my next annual he sprayed the switches.

[A64Pilot]

On 7/6/2023 at 6:54 PM, Joe Larussa said:

So what is it about bumping the flap that makes it go up?

Likely it just shakes things a little, like sometimes tapping the solenoid on a starter makes one work. Both the contacts and likely the limit switch have a burnt or dirty contact. If you could get to it likely tapping the switch would work better with just a light tap.

Personally I’m in the camp that says use contact cleaner to get home or if you’re feeling lucky until the new switches / relays come in. I’ve just not had good luck with cleaning switches or relay contacts / ignition points etc working well over time, and tapping or rapidly turning off and on doesn’t always work.

Contact cleaner helped me diagnose my gear switch, so I’m not against it, just my experience is it’s a temporary fix.

What struck me about the post was that @Joe Larussa almost never uses full flaps, why not? Yes I know it will land and takeoff fine with no flaps, but it lands “better” with full flaps. Better being defined as slower requiring less runway and braking and at a more level attitude than with 1/2 or no flap.

Edited July 7, 2023 by A64Pilot

[Joe Larussa]

1 hour ago, A64Pilot said:

Likely it just shakes things a little, like sometimes tapping the solenoid on a starter makes one work. Both the contacts and likely the limit switch have a burnt or dirty contact. If you could get to it likely tapping the switch would work better with just a light tap.

Personally I’m in the camp that says use contact cleaner to get home or if you’re feeling lucky until the new switches / relays come in. I’ve just not had good luck with cleaning switches or relay contacts / ignition points etc working well over time, and tapping or rapidly turning off and on doesn’t always work.

Contact cleaner helped me diagnose my gear switch, so I’m not against it, just my experience is it’s a temporary fix.

What struck me about the post was that @Joe Larussa almost never uses full flaps, why not? Yes I know it will land and takeoff fine with no flaps, but it lands “better” with full flaps. Better being defined as slower requiring less runway and braking and at a more level attitude than with 1/2 or no flap.

The reason I pretty much never use full flaps is for several reasons. On doing instrument approach’s I always use 10 degrees, and if I need to go missed I’m already configured. Same goes for having to do a go around. 

[PT20J]

If you think about how the flaps are wired, it's hard to see how jiggling could help. Taking the original system without takeoff preset, when you put the flaps down the flap switch closes a circuit the runs through the down limit switch to the down relay. When the flaps reach the down position the down limit switch opens the circuit removing power to the motor. If you next put the switch in the up position and the flaps don't move, the fault must be in the switch, the up limit switch or the up relay. None of these are in contact with the flap mechanism when it is in the down position. So, it's probably the vibration from climbing out of the cockpit and walking down the wingwalk that has a much to do with it as wiggling the flaps. The system with a takeoff preset is only slightly more complicated with two more microswitches for the takeoff position limits, but the idea is the same.

Mooney didn't use hermetically sealed microswitches for the limit switches because they are in an area that is not very exposed to the elements. The biggest risk to them is someone hitting them with lube while lubricating stuff in the belly. The relays are probably more likely to fail than the microswitches because they carry more current.

Skip

[Bartman]

My experience with flaps stuck down was after landing, but resolved during taxi back to the hangar.  Having been a Mooneyspace member for years I immediately knew what the problem was.  I personally cleaned the limit switches and have no problems for the 5 years afterwards. Assuming it was not the flap motor or something else in the circuit, I knew the two potential solutions.  

1- My simple ongoing solution includes preventive cleaning at every annual inspection.

2- If it ever happens again the limit switches get replaced.

[EricJ]

The switches can be unobtainium, so finding some to keep in inventory for replacement is a good idea rather than waiting until you need one.   They turn up on ebay or elsewhere once in a while for less insane money than the usual vendors.

[skykrawler]

The flap motor circuit runs on a 5 amp circuit breaker and voltage passes through the control switch and then to the back.  I don't see any relays in the circuit diagram.  The motor has an input for each direction of turn which is from the switch up front - through a limit switch - and then to the motor.    When the jackscrew drives to the limit (say down), the limit switch STOPS the motor by interrupting the circuit.

When you select the opposite direction (say up) the jackscrew drives away from the down limit switch which goes normally closed allowing drive in the down direction again.  If the cherry switch actuator (little red nub sticking out) sticks and the switch is not released the circuit is not re-enabled.   It could be dirty contacts within the switch that don't re-enable the circuit when they go normally closes.   Thus, all this spraying of contact cleaner.

Its a pretty simple system.

 

[PT20J]

My 28V plane has relays -- perhaps the 12V ones do not. The switches don't really get dirty. What happens is that the arcing from breaking an inductive load eventually penetrates the plating on the contacts and then the base metal oxidizes. Many switches are designed to open and close with a mechanical wiping action to help clean the contacts if the switch is exercised often enough. But, these switches don't get used often enough for there to be much wiping. 

[lamarwilson]

5 hours ago, skykrawler said:

The flap motor circuit runs on a 5 amp circuit breaker and voltage passes through the control switch and then to the back.  I don't see any relays in the circuit diagram.  The motor has an input for each direction of turn which is from the switch up front - through a limit switch - and then to the motor.    When the jackscrew drives to the limit (say down), the limit switch STOPS the motor by interrupting the circuit.

When you select the opposite direction (say up) the jackscrew drives away from the down limit switch which goes normally closed allowing drive in the down direction again.  If the cherry switch actuator (little red nub sticking out) sticks and the switch is not released the circuit is not re-enabled.   It could be dirty contacts within the switch that don't re-enable the circuit when they go normally closes.   Thus, all this spraying of contact cleaner.

Its a pretty simple system.

 

My 70F wing flaps electrical schematic shows a wiring configuration that closely matches this description. 

Today during a preflight I discovered my wing flaps were stuck in the up position.   I searched this users group and found a suggestion that seems to work.  That was to thump on the baggage compartment floor.  It worked.  I must have “two-blocked” the actuator in the up position on my last flight/taxi.   I couldn’t find the post afterwards to that him.  So, Sir, Thank you!!

[Bigdaddie]

This happened to me also.  Cleaned the up limit microswitch and all was well.  I subsequently changed the microswitch.