29 November 2017

Avionics: Intercom output level for recording.

I picked up a fancy GoPro Fusion (marketing video below) to use with my aircraft.  It's a full 360 degree camera, in both xy- and xz-planes.  I also picked up the GoPro HERO 6 Black, GoPro HERO5 Session  and GoPro Session.  The Fusion and HERO6 Black will be placed under the canopy.  The HERO5 Session will be placed on the tail and the Session will be placed on the wing.


I would also like to record the intercom audio on the HERO6 Black.  This is why I wired in panel-mounted jacks, on the lower right of my panel, for audio input and output (Music 1 In and Out in the image below), figuring I would use the latter for a video camera.  For the Music 1 Out jack, I used the GMA-240's Passenger Headset Audio Out pins (40 and 41 on J2401). 


Because the output level from the GMA-240 is for a headset and can exceed ±4V (depending on load impedance) it can't be connected directly to the GoPro.  This is because the GoPro's audio input level requires "line level" (i.e., about ±1V) and has a 8k-Ohm input impedance in line input mode (2.2k-Ohm for mic and 47k-Ohm for powered mic).

By placing a 47k-Ohm resistor in series with the left and right audio lines into the jacks, the GoPro can accept output from the GMA-240 through the jack.  This occurs since this simple voltage divider network reduces the magnitude of the audio voltage into the GoPro to about 14.5% of GMA-240's output.


When I originally put in the panel-mounted audio jacks, I used Molex connectors on them figuring that I would need to replace the jacks in the future due to potentially many connect/disconnect cycles.  Turns these Molex connectors were ideal for accommodating the 47k-Ohm resistors in a little jumper cable.

The image below shows the back of the panel on the right side (looking aft).  The two Music 1 In and Out jacks are shown on the left of the image.  The bottom jack is the Music 1 input.  The top jack is the Music 1 Out jack which is the audio from the GMA-240's Passenger Headset Audio Out.  You can see a small Molex-plugged jumper cable with the 47k-Ohm resistors placed between the Molex connectors from the jack and from the GMA-240. 


When plugged in to the GoPro, the audio from the intercom is clear and unsaturated.  Should I ever need to, I can simply remove the jumper cable with resistors and return the jack to its headset-level output.

20 November 2017

Maintenance: Propeller governor leak.

My prop governor was leaking a tiny drip of oil every few days.  This was prior to my running the engine.  I have Hartzell's S-1-79 governor.  I removed the governor head (model 102889 Rev. 6) and found the below.  You can see that the o-ring apparently was pinched when installed.  I spoke to a Hartzell A&P and he thought it happened during assembly at the plant and was the first time he'd seen this.


The o-ring part number is  C-3317-035 with a 2016 list price of $2.70.  The replacement part was covered under warranty.


The damaged ring on the left and the new ring on the right.


When replacing the ring, I learned that it's important to lubricate it with oil and to stretch it in place not roll it.  It's trivial to reinstall.  The 9/32" hex cap head screws must be torqued to 21-25 in-lbs per the manual (HC-SL-61-277 Rev. 3 D(1)(b)g).

Then I needed to be sure the speeder compress spring sits properly when reassembling.  Left image is of course incorrect, whilst the right is correct.


09 November 2017

First Flight Prep: FAA Inspection. I can fly.

On 7-Nov-17, three FAA Aviation Safety Inspectors came to my hangar and completed their inspection of my aircraft, paper work and builder's log files, images and videos.  As of 9-Nov-17 my aircraft is legally permitted to fly. 


The FAA no longer provides "pink slips".  The airworthiness certificate is now provided on 8.5"x11" card stock and is part of the operating limitations.  This is FAA Form 8130-7 (11/2016).  It is a four page document, which includes a description of the approved flight test area (including permitted airports of use), that must remain in the aircraft during operations per CFR §91.203(b).  The certificate shown above is cropped from that document.

The official logbook entries are below.


And I can legally perform my own maintenance.  They put my model as RV-14/A rather than RV-14A.  When I pointed this out to one of the inspectors, he said "we're going to let that slide for now."


Soon these seats will be occupied.


Following placement of the top cowl half, this bad boy is ready to go.


The next posts will detail first and subsequent flight experiences.