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Autopilot sheer pin location?

TLYNCH

Well Known Member
With autopilot on, plane turns and descends. Was suggested by CFI that sheer pin needs replacement. Where is the servo located?
 
Well, if it's turning, the roll servo is probably in the wing. And if it's nosing down, the pitch servo is somewhere in the fuselage. Think you broke two shear pins?
 
Skyview / D180 or Garmin? Is the autopilot actually active on altitude and course or only "armed". Are you using simple or advanced modes (dynon)? If dynon, the install manual shows location of the sheer pins for each servo. The pitch servo is located beneath the pilot seat and roll servo is behind the baggage bulkhead.
 
My first question would be - -

Has it worked well at some point ? How long have you owned the plane ? Are you familiar with how it works ?
 
My D-180 autopilot has done the same thing on more than one occasion. It was always operator error. :) Sheepish smile. Either the auto pilot was not engaged even though I thought it was, or else the heading and altitude bugs were not set where they should have been.
 
The pitch servo is under the pilot's seat and the roll servo is just aft of the baggage bulkhead. Neither one is easy to access. Check them as a last resort.
 
Doubtful both shear pins are busted. You are an SLSA and so SkyView equipped. A good test would be to just push the "LEVEL" button. The aircraft should fly straight and level and you should be able to feel the servos working by a light touch on the stick.
 
I would try the level button first, but if that doesn't work, check the shear screws (not shear pins). On the servo control arm there is an off-center hole that holds a brass 6-32 screw with a narrow neck that is the weak link to shear. Each servo has 3 holes for shear screws. If you pull the center screw, the arm will come off and you can see if the shear screw is broken. If it has a nut with cotter pin, that's more difficult. In this case you can hold the barrell that the control arm attaches to and see if you can turn the arm independent of that. If so, then the shear pin is broken. Rotate the shaft until an open shear screw hole is visible (you'll need to get the head of the old one out of the hole first) and insert the new shear screw. You can get the shear screws from Dynon.

I have seen a lot of shear screws breaking in the last few years.
 
You don't have to fly to activate the LEVEL mode. Most autopilot modes are grayed out in the menus if the aircraft is outside of airspeed limits but you can turn on LEVEL with it parked in the hangar. You should be able to tell if the servos activate and center the stick. If that happens then your shear screws are OK.

Hitting the AP button in flight does not necessarily hold the aircraft straight and level, the default in expert mode is to hold current roll angle and VS.
 
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Well, if it's turning, the roll servo is probably in the wing. And if it's nosing down, the pitch servo is somewhere in the fuselage. Think you broke two shear pins?

I don't think the servo is mounted in the wing on the RV-12, check your manual for the proper location.

The Dynon EFIS (Both the D100/180 and the Skyview) has an AP test mode that you can run on the ground. Give that a try and you will find out pretty quickly if you have a broken sheer pin.

Order the sheer pin from Dynon, if needed. It will come with instructions and a new cotter pin. You will need to get some Loctite from your local auto parts place. The instructions will tell you which color to get.

To replace the pin, you remove the cotter pin on the servo arm and the castle nut. Do not remove the servo or the rod connecting it to the flight controls.

Remove the head of the old sheer pin, if it is still in there. (Mine fell out.)

Put some Loctite on the new pin, place the servo arm back on the servo, and screw it in an empty hole. (There are three and one is probably taken by the broken pin.) DO NOT tighten the pin. It should go in until it seats, that's all. If you tighten it, it will probably snap the first time the AP is engaged.

Put the washer, castle nut, and cotter pin back on.

With that done, you will need to calibrate your AP again. Check the Dynon manual for how to do that.

One other thing, I went through a few of the pins when I was a Beta tester for Dynon. Check with Dynon for the proper setup for your RV-12. With the correct setting (and installation. DO NOT over tighten the pin!), you shouldn't have any more issues.
 
Autopilot

Thank you all.....I have a lot of excellent suggestions and great advice. I'll get on it as soon as the outside temp gets above zero here!

Tim
 
Thank you Joe. Worked fine until this Fall. Had the plane now for 3 years. Maybe pilot error ? I push "level" and it turns.

Tim
 
Tony. I'll try "level" with the plane in the hanger with the motor off?

Thanks for the advice.
Tim
 
Bill, I don't see anyplace where the servos are located.
Great idea to find a "test mode" but I don't see rear either in the Skyview manual. Maybe in the RV manual?

Tim
 
Look in Chapter 10 of the Skyview Installation manual for AP Servo test mode and calibration instructions. The test mode will move the controls to the fore-aft/right-left limits, it the movement does not look correct you can recalibrate the servo-control position. You can also monitor the servo position feedback as you move the control stick, if the numbers change and the range is consistent the servo mechanical connection is most likely fine. The Dynon AP Inflight Tuning Guide might also be helpful.

John Salak
RV-12 N896HS
 
Bill, I don't see anyplace where the servos are located.
Great idea to find a "test mode" but I don't see rear either in the Skyview manual. Maybe in the RV manual?

Tim

The pitch servo is under the pilot seat pan. The roll servo is behind the baggage bulkhead. You can familiarize by looking at the plans section 44A.
http://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_44A.pdf
i-sg7x2dv-L.png


You say the aircraft turns when you press the "LEVEL" button? That doesn't sound good.

The Dynon SV Installation manual (http://dynonavionics.com/skyview-documentation.php) has all the procedures for installation, configuration, calibration and includes a test of the autopilot servos. That must be what Bill was referring to.
 
To test, hold button 7&8 together to enter setup. Scroll to the bottom to Hardware Calibration. There is an option in that list for auto pilot. Select test and run the test following the instructions on the screen. If that works, then the shear screws are probably fine. If not, then replace them. If it works, but not correctly, then another options in the list was Calibration, which you go to and follow the instructions on the screen to recalibrate.
 
Have you done any software updates since this fall? If it stopped working after a software update you may need to recalibrate it.;)
 
The pitch servo is under the pilot seat pan. The roll servo is behind the baggage bulkhead. You can familiarize by looking at the plans section 44A.
http://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_44A.pdf
i-sg7x2dv-L.png


You say the aircraft turns when you press the "LEVEL" button? That doesn't sound good.

The Dynon SV Installation manual (http://dynonavionics.com/skyview-documentation.php) has all the procedures for installation, configuration, calibration and includes a test of the autopilot servos. That must be what Bill was referring to.

The RV-12 Maint. Manual is another good resource for info need to repair and maintain the RV-12.
 
Autopilot

Thank you again.....As suggested I tried autopilot LEVEL flight while sitting in the hanger and it consistently pulls RIGHT until it starts chattering reaching limits.

Back home now but I'll go back to the hanger and do:
1. the test,
2. calibrate,
3. get sheer pins....
 
Thank you again.....As suggested I tried autopilot LEVEL flight while sitting in the hanger and it consistently pulls RIGHT until it starts chattering reaching limits.

Back home now but I'll go back to the hanger and do:
1. the test,
2. calibrate,
3. get sheer pins....

With that symptom it would need max one shear screw. It needs to be recalibrated. Depending on what it did in pitch, you probably don't even need one shear screw. Keep us posted.
 
Your post helped me Jesse on an unrelated problem. Years ago I had calibrated and tested my servos, all was well. The last time I ran a test, it went violently to the stops and chattered like it was trying to tear something up. I had not got back to trouble shooting it but your post made me think: Maybe it needs calibrating again for some reason. I re calibrated it and the test now shows it is working just fine. That was a load off my shoulders, thanks.

To test, hold button 7&8 together to enter setup. Scroll to the bottom to Hardware Calibration. There is an option in that list for auto pilot. Select test and run the test following the instructions on the screen. If that works, then the shear screws are probably fine. If not, then replace them. If it works, but not correctly, then another options in the list was Calibration, which you go to and follow the instructions on the screen to recalibrate.
 
Servos

Problem solved following Barry's advice. He could feel/hear the servos moving with the stick, so he knew the problem was not sheer pin. He loaded new software and ....it's fixed. !!! Thank you Barry!
 
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