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VP-X: G3X PFD recycle after short in cowl flap

M

maus92

Well Known Member
I had an *interesting* issue on my way home from 5A1 on Sunday. Just prior to entering the Appalachians, I got an "VPX Fault" Crew Alerting System indication, then the PFD went black, then thankfully recycled and stayed on (*OR* it could have been the PFD going black, recycling, then coming back with the "VPX Fault" CAS.) Once I settled down, I checked the VPX page on the MFD, and saw that the (ASA) cowl flap had short circuited, and would not reset. The rest of the flight was uneventful (except for the declining ceiling as I crossed the mountains.)

Yesterday, I removed the cowl flap and discovered that the bolt that connects the actuator to the flap crank / lever was missing. The actuator had fallen flush with the inside of the flap, then the piston had jammed itself into the bracket that connects the crank to the flap door. Luckily for me, the good people at Anti Splat Aero are sending me a new actuator free of charge. What probably happened is that when I replaced the actuator earlier this year (another story, and not the fault of ASA,) I either misapplied the Loctite on the nut, didn't use the correct formulation, or neglected to do it at all. The Loctite is ESSENTIAL, as I discovered.

What concerns me is the recycling of the PFD after the short circuit. I would have thought that the VP-X would have isolated the the cowl flap short from the G3X PFD, thus protecting it from a spike / recycle. In my system design, the MFD is the only display that is connected to the IBBS, and it remained on. I *think* it remained set up as the MFD while the PFD was recycling. The other devices connected to the IBBS are the GSU, the GEA, and the GTX, which is slightly different than the recommendation of both GDUs. I have the GTX on the IBBS because of the airspace I typically fly in, but I am reconsidering my design to switch the backup battery to the PFD from the GTX.

Anyway, comments are appreciated.
 
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I can't make any connection between the cowl flap and the PFD in the VP-X...I am curious how you are running the cowl flap through the VP-X though.

Was there a fault present on the VP-X page for the PFD?
 
Allan's cowl flaps use linear actuators. If I recall correctly you shouldn't connect these loads to the VPX.

Chad, am I correct?

Could this have something to do with it?

:confused: CJ
 
Correct...and that's why I'm curious about it.

Section 4.12 in the install manual-

4.12 Electric Motor Considerations
The VP-X is designed to drive the flap and trim motors with special
circuits designed for that application. The VP-X can power smaller
motors like avionics fans or defrost fans.
Do NOT use the VP-X regular power circuits to provide power to
medium or large electric motors like gear extension/retract motors
(including canard nose gear) or hydraulic pumps. This also applies to
motors in linear actuators that may bind at the end of their travel. Those
motors should be wired directly to the main power bus outside of the
VP-X
 
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Why should we not connect these to the VP-X? Mine has been for several years with no problems. (The power lead only. I switch the direction of the cowl flaps with an external switch)

There is nothing special about the actuators, they are just very small DC motors with limit switches built into them. They run till extended and run till retracted...if they are installed properly, they will shut off at the end of their travel all by themselves. They are normally low current consumers.
 
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cjensen said:
I can't make any connection between the cowl flap and the PFD in the VP-X...I am curious how you are running the cowl flap through the VP-X though.

Was there a fault present on the VP-X page for the PFD?
Click to expand...

The switch for the flaps is wired per ASA diagram, excluding the indicator LED. The VP-X supplies power to the switch using a dedicated pin, which is programmed to be available when the master is on, and set to 1A. The switch (DPDT) wiring (outside of the VP-X) reverses the direction of the actuator.

I had a CAS alert on the PFD "VPX Fault," and on the MFD, the Cowl Flap was red X'ed, with a note "Short Circuit." It would not reset.

Also, during the ground test yesterday prior to removing the cowl flap, cycling the flap switch caused a reboot of the PFD. I *think* the inflight G3X reboot was also incidental with activating the cowl flap switch to close the flap.

I removed (actually had to pry off) the actuator from the flap. It was in its (almost) retracted position, which I think opens the flap. I applied power to it, and it extended, but would not retract, which is why it's being replaced. I have pix of the jammed actuator still installed in the cowl flap assembly, but tinypic was uncooperative today.

I can wire the circuit totally outside of the VP-X, or create an aux bus using the VP-X. Would the aux bus be OK?
 
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Brantel said:
Why should we not connect these to the VP-X?

...They run till extended and run till retracted...if they are installed properly, they will shut off at the end of their travel all by themselves. They are normally low current consumers.
Click to expand...

If installed properly is the key here. They are fairly easy to not install properly and then the tendency is to bind and twist.
 
maus92 said:
I can wire the circuit totally outside of the VP-X, or create an aux bus using the VP-X. Would the aux bus be OK?
Click to expand...

This would be my recommendation based on the installation manual for the VP-X, to wire outside of the VP-X. An aux bus using the VP-X just creates more connections and points of failure.

The PFD cycling during this is puzzling me though. Can you send me your configuration through email?
 
cjensen said:
This would be my recommendation based on the installation manual for the VP-X, to wire outside of the VP-X. An aux bus using the VP-X just creates more connections and points of failure.

The PFD cycling during this is puzzling me though. Can you send me your configuration through email?
Click to expand...

I'll be back at the hanger tomorrow, and I'll download from the computer I keep there for configuring stuff.

C.
 
Today is pretty dreary, so instead of going out to the hanger and wishing I could be flying, I'll write a dreary update:

I've been having email conversations with Garmin and VP/Ballard this week to try to get to the root cause of the PFD EFIS recycling. This is what we know so far:

- The actuator on the cowl flap disconnected from the lever arm on the cowl flap assembly. The actuator piston then jammed against the lever attach bracket during extension, which caused a fault. The VP-X Pro disconnected the circuit, and displayed a non-resetable "Short Circuit" fault on the MFD GDU VP-X page. At the time of the fault, the Garmin PFD GDU experienced an un-commanded reboot, but returned to normal operation.

- The cowl flap failure was caused by improper installation of a replacement actuator. (This time I made sure to use a threadlocker, IC-LOC Blue in this case.)

- Anti Splat Aero replaced the Actuonix L16-S actuator free of charge, a ~$70-$100 part depending on source. Exemplary customer service.

- Chad J. from VP/Ballard examined the VP-X configuration, but did not find any issues with the setup. Chad previously referenced a section of the VP-X Installation Manual that recommended against providing power to medium or large electric motors through the VP-X. The L16-S actuator (also used in RC aircraft and Arduino projects) has a small .5A electric motor with limit switches. It is probable that the actuator jammed while the piston arm was in motion between the areas where the limit switches normally operate, causing the fault.

- G3X Expert / Field Service Engineer Jonathan C. asked me to download the GarminError.xml file from the affected GDU. Garmin Engineering examined it and determined that the: "shutdowns are related to power interruption." Note that there were at least two GDU reboots / shutdowns - I had replicated the event on the ground when diagnosing the problem.

- The airplane is equipped with a TCW IBBS 12v-3ah backup battery system installed per VP-X Option 2. This method does not use the pass-through circuits, and backup power is wired to the secondary power inputs on both GDU460s (PFD & MFD,) the GEA24 (engine instrumentation,) and the GSU25 (ADAHRS.) The backup power is applied when the main bus voltage drops below 11v.

I've tested the IBBS, and it does provide backup power to the configured devices when there is no main bus power. It appears that the "Short Circuit" did not cause the main bus power to drop below 11v because all (as far as I can tell) other devices on the aircraft were unaffected, and no backup power was supplied to the GDU that rebooted, according to the .xml file supplied to Garmin for analysis.

Garmin recommended installation of the GAD27 Electronic Adapter Unit that provides a collection of services and connections. The reasoning was that the GAD27 includes circuitry that ensures that the GDUs remain powered during voltage drops (usually during starting.) I would consider installing it if I thought this would solve the root cause of the issue, but the GAD27 includes a number of duplicative functions already served by the VP-X.

Extrapolating, what *seems* to have happened was a momentary loss of power on the VP-X circuit that supplies main bus power to the PFD GDU when the cowl flap circuit faulted. Alternately, there was a momentary loss of power on all the circuits, but that particular GDU is more sensitive to power issues than other devices (I find this scenario less likely considering the IBBS did not kick in.) My understanding of the VP-X design is that it isolates circuits from one another, and that a fault on one should not affect another. I am going to check if the cowl flap and PFD GDU circuits are on separate internal busses (the VP-X Pro has two internal (logical?) busses, but I'm not sure that makes a difference.) The VP-X has a dedicated EFIS power circuit that is used for the display that is connected to the VP-X serial port. In my case this is the MFD GDU that remained up during the event. I'm not sure if this is significant or not.

There is an alternate method to wire the IBBS to covered devices using pass-throughs. A pass-through is normally used when a device only has one power input. The Garmin devices have 2 power inputs, so using pass-throughs is not necessary. However, the IBBS Install manual diagrams an optional wiring method that uses the pass-throughs to supply power to the Power 2 inputs of the Garmin devices. Theoretically, using the pass-throughs would provide another circuit to provide main bus power to the covered devices. Perhaps I can move some VP-X pins so that the covered devices were supplied by separate busses. IDK. I need help logic-ing this out.

Sorry for the long post, but I'm basically on hold here waiting to see if the two vendors can move this issue forward (or hope it goes away.) I've repaired the cowl flap, and I have no problem flying it VFR. If this was an IFR aircraft - which at some point it will be - I would not be so cavalier with an issue that could potential lose a display unit at the most inopportune time.
 
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cjensen said:
This would be my recommendation based on the installation manual for the VP-X, to wire outside of the VP-X. An aux bus using the VP-X just creates more connections and points of failure.
Click to expand...

Am I reading this correctly in that things with tiny motors (oil damper valve, cowl flaps, ram air, etc.. shouldnt get their power through the VPX? I'm a ways out but I was going to wire these off the VPX so I could see if current was being pulled to verify operation.
 
AviatorJ said:
Am I reading this correctly in that things with tiny motors (oil damper valve, cowl flaps, ram air, etc.. shouldnt get their power through the VPX? I'm a ways out but I was going to wire these off the VPX so I could see if current was being pulled to verify operation.
Click to expand...

You can use a power lead, but it would require another switch as Brian mentioned. If it's a low draw linear actuator, just be very careful about installing it correctly for the end points.
 
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