Precise Speed Brakes sensor

[N131MA]

I have Precise Speed Brakes in my M20S. The brakes extend and retract very well.

Some flight hours ago I got this issue:

• After using the brakes, the amber annunciation light in the cockpit would not go off, despite the brakes retracted completely. Even after extending / retracting the brakes a couple of times the light stays on. Only after resetting the brakes (pull/push in circuit breaker) the light goes off.
• As soon as the master is switched on, the speed brake motor in the right wing starts working (I can hear the electric motor noise).

Precise Flight's technical support indicated a defective retract sensor in the right wing brake as potential root cause. The sync control units "thinks" the right brake is still extended and continues running the retraction motor. I will have a look at the brake later this week.

Did anyone have the same issue? Any recommendation on where the retract sensor is located and/or where to get a replacement?

[rgpilot]

The service from Precise Flight is excellent. I have a few Moonies with speed brakes over the years and they do need occasional service. I have always sent them to Precise Flight.

[M20S Driver]

19 hours ago, N131MA said:

I have Precise Speed Brakes in my M20S. The brakes extend and retract very well.

Some flight hours ago I got this issue:

• After using the brakes, the amber annunciation light in the cockpit would not go off, despite the brakes retracted completely. Even after extending / retracting the brakes a couple of times the light stays on. Only after resetting the brakes (pull/push in circuit breaker) the light goes off.
• As soon as the master is switched on, the speed brake motor in the right wing starts working (I can hear the electric motor noise).

Precise Flight's technical support indicated a defective retract sensor in the right wing brake as potential root cause. The sync control units "thinks" the right brake is still extended and continues running the retraction motor. I will have a look at the brake later this week.

Did anyone have the same issue? Any recommendation on where the retract sensor is located and/or where to get a replacement?

The one on my plane has a micro switch that is adjustable.  It is a very simple mechanism so once it is removed, you can see the sensors and the rotary adjustment with set screws.  My switches activate within 5-10 deg inside of full extension or full retraction.

[Jeff_S]

Ditto on the good service provided by Precise Flight. I was having an issue last year with one brake that wouldn't stay in the up position, so as a safety feature they both would close. What I learned is that when you're dealing with these speed brakes, the fault could be in either of the two wing controllers or the main sensor unit in the belly, so it's best just to pull all three of them so PF can do a complete diagnostic. My A/P had built some aluminum inserts he put in while the brakes were out so I could keep flying. I've heard others say duct tape is a workable solution but I'm not sure about that. At any rate, PF got the brakes fixed and turned around within a week so the only reason I needed the inserts was so I could fly home, and then fly up to have the brakes reinstalled.

[carusoam]

Expect a maintenance visit in the 1500 - 2000 flight hours on the speed brakes.  The clutches have a tendency to wear.

is it time to send them in for clutches, and review the other operations while in there?

here is how to ask the source...

https://www.preciseflight.com/general-aviation/shop/speedbrakes/products/speedbrakes-mooney/#qa-contact-us

Best regards,

-a-

 

[Mark89114]

I had similar problem and my mechanic and myself adjusted the micro switch.  I take exception to something with such a poor service life and the dollars to rebuild.  Let's pretend each flight over the 1500 hours is 1 hour, so 1500 flights, what is the cycle time, 5 seconds?  Over the 1500 hours flight time that is only 2 hours of use age, let's double that for the preflight check, so a total of 4 hours of cycling.  Once extended, nothing is going on except for the clutch holding speedbrake.  The clutch in my car probably handles 100 times the torque, in a much hotter environment and is used order of magnitude higher.  Rant off.  

[N131MA]

Precise Flight service is indeed great. I got more guidance on how to diagnose the problem:

1. Recycle the speedbrakes (up and down) and check whether the motor in the wing still runs with the brake retracted. If recycling makes the motor stop: Control box defect. If recycling has no impact: Step 2
2. Adjust the cams (position of the brakes when pulled in). Precise Flight sent me instructions. If this fails: Step 3
3. Defective retract sensor. Send the brakes to Precise Flight for service.

Step 1 did not work in my case. I'll try step 2 this weekend. Keep you posted.

[carusoam]

Mark89,

Do the same math for the landing gear no-back-spring-clutch.  You will calculate the same angry feeling without the ability to test the gear before departure. 

Fortunately, you can operate the plane in a normal fashion with only half the speed brakes deployed.

Best regards,

-a-

[M20S Driver]

On June 22, 2016 at 6:28 AM, N131MA said:

Precise Flight service is indeed great. I got more guidance on how to diagnose the problem:

1. Recycle the speedbrakes (up and down) and check whether the motor in the wing still runs with the brake retracted. If recycling makes the motor stop: Control box defect. If recycling has no impact: Step 2
2. Adjust the cams (position of the brakes when pulled in). Precise Flight sent me instructions. If this fails: Step 3
3. Defective retract sensor. Send the brakes to Precise Flight for service.

Step 1 did not work in my case. I'll try step 2 this weekend. Keep you posted.

Did the procedure work?  Do you mind sharing the procedure?

[N131MA]

Sorry for the late reply....

Yes, the adjustment procedure fixed the problem

1. 1Remove SpeedBrake from wing.

   2.      While looking at the top of the SpeedBrake you see a set screw in the slot on the forward side of the SpeedBrake.

   3.      Loosen the set screw and move the cam slightly inboard, the motor should stop running (see Cam Adjustment drawing 1).

   4.      Adjust cam so the motor shuts off ½ inch from the top of the SpeedBrake (see Cam Adjustment drawing 2).

 

[N131MA]

and here are the two drawings.

The procedure took not more than 30min!

 

cam adjustment 1.pdf

cam adjustment 2.pdf

[M20S Driver]

1 hour ago, N131MA said:

and here are the two drawings.

The procedure took not more than 30min!

 

cam adjustment 1.pdf

cam adjustment 2.pdf

Thanks for the follow up.  I have the 100 series and the set up is basically the same. I also learned from Precise Flight that the up setting has to have 1/4 of an inch of overlap between the two plates.

Driver