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  #1  
Old 01-06-2017, 10:18 PM
TLYNCH TLYNCH is offline
 
Join Date: Apr 2013
Location: Mequon, WI
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Default Autopilot sheer pin location?

With autopilot on, plane turns and descends. Was suggested by CFI that sheer pin needs replacement. Where is the servo located?
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  #2  
Old 01-06-2017, 10:30 PM
BobTurner BobTurner is offline
 
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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?
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  #3  
Old 01-07-2017, 01:55 AM
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KALEWIS KALEWIS is offline
 
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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.
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  #4  
Old 01-07-2017, 06:06 AM
JBPILOT JBPILOT is offline
 
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Default 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 ?
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  #5  
Old 01-07-2017, 07:29 AM
Mich48041 Mich48041 is offline
 
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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.
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  #6  
Old 01-07-2017, 07:32 AM
Mich48041 Mich48041 is offline
 
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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.
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  #7  
Old 01-07-2017, 08:09 AM
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Tony_T Tony_T is offline
 
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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.
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  #8  
Old 01-07-2017, 08:53 AM
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Jesse Jesse is offline
 
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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.
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Old 01-07-2017, 09:04 AM
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Tony_T Tony_T is offline
 
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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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Last edited by Tony_T : 01-07-2017 at 09:08 AM.
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  #10  
Old 01-07-2017, 09:50 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by BobTurner View Post
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.
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