Scott & Tanya Card RV9A build log (N4822C)

I’m working on completing the remaining unswitched audio input signals into the audio panel from the AOA, EFIS, and EIS. I tested the AOA signal for the first time. I decided it was a bit too loud. There is a very small POT on the CPU board for the AOA that adjusts the output gain. So, I opened up the case and adjusted it. There is currently no audio output from the EFIS but the wire is there and there is a note in the documentation that it may be used in future software releases and that its output gain will be adjustable in the settings menu. So I will be connecting it to the audio panel. There is also an audio out from the EIS that sounds an intermittent tone when a warning limit is exceeded. I tested it out but decided that the tone was just too annoying in addition to the flashing big red light. I won’t be attaching the EIS audio out.

 

  

  

 

I took a few minutes to improve the stability of the wire exits from the connector shells on the autopilot pitch servo and the magnetometer. The wires were a little loose in the shell exits so I added some silicone tape to make them a nice snug fit. I sure wish I had allowed about another inch of clearance behind the magnetometer for the connector, but it will be fine. It doesn’t rub. As you can see, I’m using a bunch of stick-on cable tie anchors. I’ll keep a close eye on them to see how they hold up. The plan for when they let go is to put a dab of “shoe-goo” on them, and they’ll be good to go. I actually already did this on some of the ones that are a bit harder to get to.

I also did some electrical load testing and am prepared to post my results. Builders (including myself) like nothing more than real measurements as opposed to calculations.

First up, I’ll report my EFIS AUX battery test. This battery is a 5Ah gel cell battery mounted next to the AHRS that is wired to an aux switch position on my EFIS power switch. It drives DU1,2,3, the AHRS and magnetometer when selected (DU 3 can be disconnected separately for max conservation).
I started with the battery at 13.2V with its charging circuit disconnected. I powered up only all of the EFIS equipment as described above. The battery status at runtime is as follows:

11.6V @ 35min.
11.5V @ 40min.
11.2V @ 47min.
9.2V @ 55min. (began rebooting. Voltage too low)

I think that is very cool data. It will run even longer than that if the charging circuit is left connected to the main battery. So, worse case of electrical failure, provided that the EFIS, AHRS, and magnetometer are still ok, we have at least 45 minutes of completely disconnected power for attitude, air data, direction, and even navigation with the internal GPS in DU2. Even if the aux battery isn’t fully charged for some reason, there is still plenty of time to get on the ground. I’m very happy with this setup.

Next up are my load results for all of my panel equipment. I have a digital variable power supply that can put out 20A that is connected exactly how the alternator(s) will be. This allows me to select a voltage input into the aircraft electrical system and read the current output on the power supply. This is fun for measuring real load of stuff in its installed state with all the busses, wires, and switches in between. Not to mention minimum operational voltages.
I set the power supply to 13.4V and left the main battery contactor open (main batt disconnected). Then I turned on everything that is currently installed in the panel. The whole panel draws 8.3A (with the A/P active). Then I began turning off equipment and noting the current difference as follows:

TruTrak A/P with pitch servo on 1.3A
GTX330 Transponder 1A
SL40 .4A
PMA8000B Audio Panel .3A
GNS430 GPS1/Nav/Com 2A
GRT EFIS DU3 1A
GRT EFIS DU1,2,AHRS 2.2A
GRT EIS .1A

This is all critical stuff to know and have tested before the wheels leave the ground. It is neat to see all of the hard work in electrical design and calculation come together to match the calculated design within a few tenths of an amp.

 

  

  

 

The #1 phillips 12″ long screw driver that I ordered arrived. That is exciting because I got a bit frustrated with manipulating the radio tray back plane screws when I installed them. There are a bunch of them way back there at the back of the radios that are a real pain to turn with your hand inside of the tray.

Avionics wiring has been the name of the game for quite some time but the end is clearly in sight. I took a couple more days off of real work to get this stuff shook out. I made all of the connections to all of the EFIS display units and EIS (minus the engine instrumentation). That is easy to say, but this was a couple of very long days of routing wires and connector termination. I slowly powered up the displays one at a time, one full connector at a time. With all of the wires run and everything powered up, the really fun part is configuring each piece of equipment to talk to the others. I used some non-standard serial port definitions so almost nothing was communicating until I made some config adjustments. Speaking of serial ports, there are some implications that don’t become obvious until you get well down the path of serial port planning:
- Anything that you plug into the modular expansion port of each display unit consumes serial port #1 input and output. So that is no longer available for other stuff. I have the ARINC 429 interface in the modular port of DU1 and the internal GPS (vfr) in the modular port of DU2.
- The XM Weather module must use serial port #2 into all displays (that you want to display weather on) and out of one display. Note that serial port 2 is usually (default) used for AHRS I/O. So if you’re planning on WX (which I am), the AHRS must be moved to another port.
- You can configure the input and output of each serial port separately so you can have serial A input from on piece of equipment and serial A output from a different piece of equipment. The catch is that the baud rate setting for any given serial port applies to both the input and output. This leads to the next observation.
- Obviously, each piece of equipment requires a specific baud rate setting if communication is going to be successful. The catch here is that this is either not documented at all or requires some very deep study of the documentation to find it. The GRT EFIS documentation says absolutely nothing about what the required baud rates are for the inter-display serial link or the serial link to the AHRS. Through experimentation, I found that 14.4 works for the display link and 19.2 works for the AHRS. Most other stuff (GNS430, 330 xpndr, SL40, EIS) is 9600 if I remember correctly. So, if you’re going to mix serial in and out on the same port, you need to be sure that both pieces of equipment need the same baud rate. This caught me and I needed to open up a connector and move a couple of pins (ports) around.

Also, similar (I guess) to a baud rate, the ARINC 429 interface has a speed setting of High or Low for both Tx and Rx. Once again, different equipment requires different rates. I found that the TruTrak Digitrack II autopilot requires a Low ARINC 429 input rate. This is documented by TruTrak. I spent another couple of hours verifying operational power failure modes. I measured the voltage drop across my power diodes and made sure such things correlated with other instrumentation. I measured the Amp load of each piece of equipment as it is installed and that of the whole system. It is nice to take an actual measurement as opposed to calculating from an equipment spec. I found that my full up panel, with everything turned on, draws about 7.5 amps. I’m quite happy with that. I also tested my EFIS 5 amp auxiliary battery circuit for the first time and verified that the power diode in it’s charging circuit (from the main Bat. buss) is indeed doing it’s job. I still need to test just how long I can run the EFIS displays, AHRS, and magnetometer solely off of the aux battery with everything else disconnected. This would be the worst case scenario if the rest of the electrical system died.

I did get some compact flash memory installed in DU2 to support the terrain database. That is pretty cool. I made a pretty little label for the back of the unit to show that it is in there. Tanya says I’ve had just about enough fun pushing buttons and it is time to get back to building. I agree.

In other news, I got checked out in a Diamond DA-40 with a G1000 panel. I spent about 3.5 hours with the check pilot in the plane and he ran me through all of the cool whiz-bang stuff it can do. Tanya was in the back seat for both flights to soak up the same instruction. We flew it almost full time on the autopilot coupled to a nav flight plan. We even had the autopilot fly some approach procedures. Very cool stuff. This thing is definitely not one of the standard rental junkers.

Time to get back to productive building. The things that I’m thinking about are:
- prettying up wire bundles (always)
- wire the audio inputs from the AOA, EIS, and EFIS into the audio panel.
- do a final cleanup of the rear fuselage and rivet on the aft top skins.
- rivet and paint the panel
- install the rudder pedals and brake lines
- landing gear
- engine mount …

 

  

  

  

  

  

  

  

  

  

  

  

 

I’m still plumbing the EFIS displays. I haven’t applied power to them yet. I’m getting close. With a tipup canopy, everybody sees all of the wires behind the panel whenever the canopy is open. This is adding to the time and care taken in how the wire bundles look.

I received my Grand Rapids EFIS stuff on Friday. Great fun. On Thursday I dove into working out the control sticks which took me almost three days to complete.

Installing the control sticks started with a careful consideration of how long they should be. One problem with making a final decision on this is the fact that the final control stops aren’t installed without the elevator and ailerons. The main concern is the forward stick position clearance of the instrument panel and controls. I chose to simply trim the sticks to clear the bottom of the instrument panel, even though I don’t think they will get that far forward once the elevator is installed with the stops. As far as engine control interference, once again, I don’t think the stick will get that far with the aileron stops. We’ll just have to see much later at final assembly. Anyway, I went ahead and trimmed the sticks like I said and moved forward. It is a little bit of a gamble but the worst that could happen is to have to trim a little more (then with all of the wires in them) later.

Moving on to other considerations, I decided that the right side stick will not be removable because the passenger will almost always be Tanya (I’m not afraid of commitment to a plan :), and she will be a pilot just as much as me. I think we’re going to be flying this thing almost as much from the right seat. So, I drilled the right stick and put an AN3 bolt through it. This then allows for full controls in the stick grip. I drilled for a small grommet at the base of the sticks for the grip wires to pass through and used some expandable sleeve to protect the wires. I’m using RAC 307 grips on both sides with the two aux momentary switches being com1 flip-flop and autopilot disconnect (control wheel steering). Soldering all of the wires to the grip switches was a fun exercise. I love my new super-duper whiz-bang production soldering iron. It makes this kind of stuff so easy and repeatable with precisely controlled heat. The stick grips are all wired up and completely assembled. I also spent some time working with the aileron trim spring assembly. I concluded that this could only be a temporary setup that will need major adjustment in the linkage when the aileron stops are installed.

I kind of did a build sprint to complete the stick grips so I could move on to the EFIS wiring. The first thing I did was drill the holes for mounting the AHRS up front and the magnetometer in back. The paper templates that I made long ago as place holders and built around were perfect. Then I drug out all of the wires for the three EFIS displays, the EIS, and AHRS and began to identify what was what and the wires that I wasn’t going to use and could be removed. This took me a couple of hours. I got the harness thinned out quite a bit, mainly because I already have a lot of the interconnects in the plane hooked up to the radios. While I was doing the heavy thinking, Tanya came out and volunteered to pull wires. I happily set her up to pull all of the long wires from the AHRS to the magnetometer which she did with great skill. I decided to punch a 3/4″ hole on the left and right sides of the sub-panel to put a snap bushing that will pass all of the EFIS and EIS wires. With the wiring routing figured out now I’m pulling all these wires and terminating them into their 25pin D-sub connectors (9 connectors in all).