Scott & Tanya Card RV9A build log (N4822C)

I finally got my GRT XM weather unit the other day. I spent a few hours getting it mounted in the plane. I’m having some problems getting it to activate that I’ll work on some more next time.
This GRT XM setup is cheesy to say the least. It is an aluminum GRT box with the WxWorx consumer hardware screwed to the top. It looks like they chose not to actually license the technology, but rather just resell the WxWorx receiver. This is what we accept for a low price. The WxWorx hardware clearly isn’t what I would call “aviation quality”. It is a big plastic box with an antenna connector, USB connector, and a normal consumer electronics barrel power connector. This whole setup weighs surely twice as much as it has to. Oh well, once I see radar on the displays, I won’t care.

 

  

  

  

  

  

  

 

This is mostly just a status report with pictures. The panel is back in. I used some stainless steel black oxide button head hex screws on the panel with some small plastic washers under them (from McMaster carr). I labeled all of the fuse positions. I soldered the wires on annunciator lamps and momentary switches for the AOA. I used some 1/2″ black silicone self fusing tape from McMaster to wrap those connections. I’m very happy with how that worked out. The pitot and static tubing is all connected behind the panel. Manifold pressure tubing to the sensor is installed. I also got the cabin heat control cable installed. I finalized all of the control stick nuts and bolts and installed the push tube from the controls to the elevator bellcrank. The fuel selector valve is now installed as well.

Now we’re riveting the rear top skins on the fuselage. I spent a couple of hours inside the aft fuselage last night on a board with Tanya inserting the rivets from the outside. Another couple of sessions and the aft riveting will be done. I’m starting to think about landing gear and wheels now.

 

  

  

  

  

  

  

  

  

  

  

  

 

Still at it. I’ve still been cleaning up and finalizing a bunch of wiring runs and details (anti-chaffing) in the center floor in prep for installing the rudder pedals. I also did even more trimming on center tunnel cover for the wire bundle transitions. I removed the instrument panel and got it painted. It looks pretty good. I sprayed it with basic rustoleum gray then baked it in front of a couple of space heaters. I glued the pitot tubing to the floor in a couple of places and secured it with adel clamps up the left side fuel vent line. Also, the parking brake cable is secured. Lastly, I got the pedals in place. That was quite a trick but possible. Now I’m just finishing up securing the brake hoses. Then I think the instrument panel will go back in for the “final” time. That should be exciting.

 

  

  

  

  

  

  

  

  

  

  

  

  

  

 

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.