VPX and power to trim motors and AP servos

[david.perl]

Hi there and Merry Christmas

Im installing a VPX Pro and wondered if the power to the trim motors and AP servos once leaving the VPX should also run through a CB in case the VP goes haywire?

thxs

David

[Mark Dickens]

Just run the power connection through a switch so you can cut the power manually if you want. Keep in mind that a CB is there to protect the wire, so it IMO wouldn't make sense to use one of them for this purpose.

[Taildrgr]

I ran the AP VPX power wire through a 5A pullable breaker.

The VPX has built in runaway trim software so I did not do anything different there. I have read that it is not impossible to fly the plane manually with full trim deflection.

I also put my GTN-650 nav and comm on a backup power source using the "B" method in the VPX manual. My Dynon screens also have the backup battery. So I can power the VPX off and still have pretty much a full panel for an hour.

[penguin]

David,

I would bear in mind that the VP-X is a potential single point failure, so anything that you would like to be operational after such a failure (such as trim and autopilot) should have a secondary power supply that does not involve the VP-X. If you are planning to use the trim or flap control functions in the VP-X you may like to contact the LAA first. I believe they have recently insisted a builder re-wire his flaps when he had used the VP-X speed protection function.

Pete

[Brantel]

Just for the sake of keeping it simple....

Sure, the VP-X is a single point of failure. So are about a thousand or more other things in these airplanes.

How many people wire up 2 completely independent switched power/control sources to their flaps and trim?

The only thing I backed up were items absolutely critical for safe termination of the flight.

Most people should be able to land without flaps, trim and autopilots.

As far as I know, there has never been a reported complete failure of any of VP's electronic circuit breaker boxes. The VP-X even has dual processors and internal buses to help prevent such a failure.

Just food for thought.

[Jackm]

I agree with Brian. Just finished complete panel, aircraft wiring and setup. The capabilities of VPX is somewhat ingenious. It saves many connection points and aux relays, timers, diodes, resistors ect. Wiring in the flaps and trim simplified the electrical system. The technology used in the VPX is so much superior to any basic switch, circuit breaker and buss system. My worry as fair as single point failures are things like master disconnect relay, alternators, ect. After setup of the VPX and display access on the efis, I firmly believe VPX users with identify a electrical problem far before users of the conventional system. VPX will display information for each circuit and monitor the system as a complete system and display on efis ( Advanced in our case) Example in our case, when test fuel pump under full pressure, I was able to determine the pump was drawing 5.2amps rather than the 4.1amps according to pump specs, After running pump for over 2 minutes the efis warned of a problem and tripped the circuit. On takeoff, this would have happened shortly after wheels up. If I had a circuit breaker, I may not have identified this with out testing each circuit with a ammeter. My point is, this is some pretty cool technology we have available and I like it!

[RV7Guy]

I agree with Brian and Jack on this. It is frustrating to always hear the "single point of failure" argument. As Brian pointed out there are hundreds of SPOF in our planes, including the engine and pilot. The latter taking the lead

On my first 7 I had an auto pilot disconnect and a trim cut switch. Never had a problem. On the new 7 with VP-X I will also have an AP disconnect on the stick and a trim disconnect separate from the VP-X.

My EFIS systems will have the battery back up too. Failure of our fantastic modern electronics is very low. If it were an issue, we would hear about it as it happened. Can't even recall someone having an issue recently, yet many are **** bent on adding unnecessary redundancy that adds weight and complexity. Remember the KISS principle.

[david.perl]

Thanks all for the responses. I cant answer for Peter but i suspect he was pointing out that our uber conservative LAA in the UK who govern what we can and cant do don't yet approve of electronic technology unlike steam gauges, NDB's, whisky compasses and the like. Im surprised were allowed to use internal combustion engines without a steam generator as backup as these too might fail. It sounds self defeating to have to rewire the flaps as if no is VPX used there is still a SPOF as a faulty flap switch on my Cessna demonstrated.

Sometimes the LAA exasperate me.

Christmas rant over.

Merry Christmas all. David

[MCA]

Originally Posted by penguin

David,

I would bear in mind that the VP-X is a potential single point failure, so anything that you would like to be operational after such a failure (such as trim and autopilot) should have a secondary power supply that does not involve the VP-X. If you are planning to use the trim or flap control functions in the VP-X you may like to contact the LAA first. I believe they have recently insisted a builder re-wire his flaps when he had used the VP-X speed protection function.

Pete

Peter - I'd be interested to talk with this person and better understand the circumstances. We have not heard from him directly.

BTW, the flap speed protection function can be turned on or off, so if that is an issue for the LAA the user can simply turn that feature off.

Again, we haven't heard from either this user or the LAA - can you send me his contact off-line if you have it?