VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   Safety (https://vansairforce.net/community/forumdisplay.php?f=100)
-   -   RV-9 with Dynon AP servo beta test (https://vansairforce.net/community/showthread.php?t=112807)

gereed75 05-07-2014 01:50 PM

Bill. The link between the servo and the control attachment must be lengthened so that the servo arm is operating between 10:00 and 2:00. It can not operate between 8:00 and 10:00 as your set up currently does.

With current set up, when the servo is at about 9:30 your controls will be locked!!!! It is only by pure luck that this has apparently only happened this one time.

N941WR 05-07-2014 02:07 PM

Quote:

Originally Posted by gereed75 (Post 877883)
Bill. The link between the servo and the control attachment must be lengthened so that the servo arm is operating between 10:00 and 2:00. It can not operate between 8:00 and 10:00 as your set up currently does.

With current set up, when the servo is at about 9:30 your controls will be locked!!!! It is only by pure luck that this has apparently only happened this one time.

Are you talking about the 2nd picture I posted? If so, you are correct, and as I stated, that is the position it was in when it jammed, after the AP bent the plate doing a self-test on the ground. Prior to the AP bending the plate, it could not go over center and I flew that way for four or five years without any issues. In fact, I had just inspected that servo two weeks prior during my condition inspection and found nothing amiss.

krw5927 05-07-2014 02:20 PM

Quote:

Originally Posted by Toobuilder (Post 877869)
Bill,

While similar, the execution between your pictures and the drawing provided have some subtle, yet important differences. Without seeing the actual dimensions of the two, the spacers are much shorter and larger diameter on the Tru Trak drawing, and the rod end is on the inside of the servo arm. Both contribute heavily toward increasing stiffness of the system.

While Bill's installation does not match the TruTrak drawing linked, his setup does appear to conform to the RV9 roll servo installation drawing from Dynon which uses a 7/8" spacer.

Dynon Instructions

Apparently Dynon installation uses a longer bolt and spacer than TruTrak, and installs the rod-end bushing on the opposite side of the servo arm. I too have the Dynon installation. This is a solid argument for installing the rotation-limiter brackets. I'll be doing so ASAP.

N941WR 05-07-2014 02:32 PM

Time to admit something?
 
Quote:

Originally Posted by krw5927 (Post 877888)
While Bill's installation does not match the TruTrak drawing linked, his setup does appear to conform to the RV9 roll servo installation drawing from Dynon which uses a 7/8" spacer.

Dynon Instructions

Apparently Dynon installation uses a longer bolt and spacer than TruTrak, and installs the rod-end bushing on the opposite side of the servo arm. I too have the Dynon installation. This is a solid argument for installing the rotation-limiter brackets. I'll be doing so ASAP.

I was on the Dynon Beta team for their autopilot and was the person who helped them come up with the RV-9 installation. Thus, I?m not sure if their directions follow my installation, or if my installation follows their directions.

Either way, I will try installing that rod per the Tru Trak recommendation this evening and report back.

I don?t recall why I put that longer bolt in there, there very well might be an interference problem when putting the push rod on the other side of the servo arm or it could be that I simply messed up. Either way, I will report back after I get a chance to pull it apart.

gereed75 05-07-2014 02:44 PM

Bill glad you read the last post before "fixing" and flying again. This is not about the length of the spacer at the attach point. Yes good practice would dictate re arranging the actuation arm to shorten that spacer.... But the most important point is to get the length of the actuation arm correct so that the geometry of the setup is correct

My reccomendation is to disassemble your current setup. Set your controls at the midpoint of travel. Then set the servo arm at 12:00 or 90 degrees to the actuation arm. Then make an actuation arm the correct length to maintain that geometry. Bolt it all together and check that the servo arm only moves throught 10:00 to 2:00 or so AND NEVER COMES CLOSE TO 9:00 while moving the controls through full range of motion

gereed75 05-07-2014 03:00 PM

Bill. The AP servo can not bend the tab. It was the center locked geometry and you pushing the stick that supplied the force to bend that mount tab. Think of a piston at exactly T D C. You can push it down with lots of force but it will not go down until it rolls past T D C. Your servo rod was "at TDC" and there is enough friction in a powered up servo that you can not get it past TDC. Result - locked control

N941WR 05-07-2014 03:05 PM

Quote:

Originally Posted by gereed75 (Post 877895)
...My reccomendation is to set your controls at the midpoint of travel. Then set the servo arm at 12:00 or 90 degrees to the actuation arm. Then make an actuation arm the correct length to maintain that geometry. Bolt it all together and check that the servo arm only moves throught 10:00 to 2:00 or so AND NEVER COMES CLOSE TO 9:00.

That's exactly how it has been is set up since its installation, only I based it on the bell crank movement and not the aileron being centered, IIRC. It has been a long time since I installed that thing.

N941WR 05-07-2014 03:08 PM

Quote:

Originally Posted by gereed75 (Post 877898)
Bill. The AP servo can not bend the tab. It was the center locked geometry and you pushing the stick that supplied the force to bend that mount tab. Think of a piston at exactly T D C. You can push it down with lots of force but it will not go down until it rolls past T D C. Your servo rod was "at TDC" and there is enough friction in a powered up servo that you can not get it past TDC. Result - locked control

You are wrong on this point, it was the servo, in test mode, that bent the tab. Simple as that and allowed it to go over center. Once the tab was straightened, and reinstalled, it could not go over center.

Toobuilder 05-07-2014 03:29 PM

Quote:

Originally Posted by gereed75 (Post 877895)
... This is not about the length of the spacer at the attach point. Yes good practice would dictate re arranging the actuation arm to shorten that spacer.... But the most important point is to get the length of the actuation arm correct so that the geometry of the setup is correct...

Yes, the over center geometry is the most critical aspect here, but it's more than "good practice" to address the length and diameter of the spacer. All issues are conspiring to cause safety issues in this case. This installation can be improved dramatically with a little effort.

N941WR 05-07-2014 07:05 PM

Quote:

Originally Posted by Toobuilder (Post 877869)
Bill,

While similar, the execution between your pictures and the drawing provided have some subtle, yet important differences. Without seeing the actual dimensions of the two, the spacers are much shorter and larger diameter on the Tru Trak drawing, and the rod end is on the inside of the servo arm. Both contribute heavily toward increasing stiffness of the system.

OK...

I just returned from the airport. It is as I feared, there is not enough room on the roll servo to move the bearing to the top of the arm. This leaves me with three options:

1) Make a push rod that bends up. This could allow flex in the tube.
2) Add a doubler to the existing plate. This will require longer bolts.
3) Make a new plate with tabs bent up to stiffen it. This requires me to buy some 4130 and is probably the route I will go.


All times are GMT -6. The time now is 01:57 AM.