Friday, June 01, 2007

Avionics Upgrade - Part 8

The initial harness is fabricated, I've received most of the parts, we're ready to begin the reassembly process!

Reassembling the main panel sections is basically the reverse of removing them. The parts were only painted, not modified, so they should fit right in. I start with the Circuit breaker panel after I have installed all of the new circuit breakers required for the installation. It is much easier to do it now than after the panel is installed.

The trick to this install is to be slow and careful. It is important that every circuit breaker is properly identified and in the proper location. It could be disastrous if it isn't.

After the CB panel is mounted, the next step is to slide in the avionics tray. This is a process that must be approached with extreme caution. The new wire harness has to be carefully merged into the existing aircraft wiring while many of the wires in the airplane need to be connected to the panel (e.g. power, ground, intercom jacks, etc). Rushing at this step can snap wires and cause a troubleshooting nightmare when the systems are powered.

The key to this step is to lace the wires through the bundle keeping them as straight as possible. Initially use only a few wire ties keeping them loose. If you miss a wire it can easily be slipped through a loose wire tie. You also want to keep some slack in the wire so the tray can be pulled forward; however, you do not want the length to be much more than a few inches more than you need. Surplus wire will make it difficult to push the tray all the way to the back for final mounting and the extra wire can also get caught up in moving parts such as the control yoke assembly behind the panel.

After the tray is somewhat secure and the power, ground, antennas and other key wiring is connected you'll want to do the initial system checkout and interoperability checkout. It is much easier to find out now that a component is not working than after it is fully installed in the plane. There are two ways to do this with the GNS430. One, is to have GPS reception and see if it will intercept it. The second, is to put the unit into test mode. On the GNS430W this is accomplished by grounding a pin in the main connector. Note: If you install the test mode wiring, it must be completely removed before completing the installation. You cannot tie it back and leave it. Don't forget this step. You do not want a unit to go into test mode in flight.

When the systems are checked out and all is working, the main avionics rack can be slid all the way in and mounted. At this point the loose wire should be tied back and the copilot side should be very close to airworthy condition. I also mounted the filler pieces to do a final validation that everything will fit properly. NOTE: I temporarily labeled the circuit breakers and completed a through checkout. I also tested the communication systems (Transmit, Receive and GPS interference) on the KX165 and GNS430. This is the last easy opportunity to correct wiring or system problems!

The steps to install the pilot panel is fairly straight- forward. You mount the panels and then the switches. I then installed the JPI Engine Monitor in its new location using a 3" to 2 1/2" step down hole converter purchased from Aircraft Spruce.

At this point, all of the main panel pieces and avionics are installed. It's time to do another very, very thorough checkout of the systems. This is a good time to validate that the aircraft lighting, gauges, temp probes, GPS, XM weather, etc. are functioning properly. Again I carefully validate the circuit breakers. Any discrepancy must be addressed. An aircraft cannot be released back in service if there is even the remote question in your mind that something isn't right. Never ever compromise the safety of your passengers and innocent people on the ground. There is zero room for error when installing something that is critical to the operation of the airplane.

Control Yoke & Main Instrument Assembly
We are on the home stretch. The main pilot instruments are mounted by first installing the pitot and static lines and mounting the instruments connected to them (airspeed, altimeter, blind encoder and VSI), then mount the HSI and Flight director. After all systems are in we can mount the control yokes. NOTE: I generally mount the yokes last since they are typically in the way of everything.

After the yokes are mounted and all of the switches are soldered it's time to do a ground test of the autopilot. This is a fairly easy test that is well documented in the autopilot install manual. The key is to make sure that when the GPS, heading bug, etc. say to turn left the autopilot and the flight director indicates a turn to the left. NOTE: You can feel and see the yokes turn. Just make sure and hold them. If the AP disconnects the controls will neutralize and fall hard potentially causing damage that may not be initially noticeable. It is also important at the autopilot test stage that the switches are functionally checked. Trim up/dn should turn the trim wheel in the proper direction, the AP disconnect switch should disconnect the AP, the CWS switch should let you make fine control movements with some servo resistance without disconnecting the AP, etc.

Installing Wood Accents
Installing the wood accent panels is probably the most enjoyable part of the project. At this point we know that we are very, very close to flying the plane! The panels go on easy, but you have to be very careful. The parts are very fragile until they are mounted. I designed the panels for 36G so that the instrument screw holes, CB mounting nuts, etc. hold the wood onto the panel. This would likely be how the manufacturer would do it; however, it is very, very easy to over tighten and destroy a part. Patience is the key to this step. Be careful. If something doesn't fit, don't force it. Use a step drill bit to enlarge a hole if necessary.

Alright, we're getting close to flying! The avionics and components are mounted, the initial checkouts are complete, all placards are in the proper location, and the aircraft is now in a condition that it may be moved.

Next we'll get the plane outside of the hangar and do a real checkout, we'll complete the paperwork and if all goes according to plan we'll get 36G in the air!

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