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It’s been a very busy few weeks. I did two weeks of Global Express avionics update flight testing in Wichita in early April. Then there was a crazy week and half in the office writing up the test results and putting out a bunch of different fires. Then Terry and I did a week of vacation in the Orlando area. We had a wonderful week down there. We spent a day at Epcot, a day at the Kennedy Space Center, and a day zip lining at Florida Eco Safaris. We also visited friends at the Spruce Creek Fly-In community for a day. Spruce Creek looks like a wonderful place to spend the winters, but I doubt we would enjoy summers there - too hot. We got home on Friday.

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Great news - I finally got the radio working again!

Saturday I spent most of the day at the hangar. First, I figured out where my cockpit brake leak is - both master cylinders are leaking where the sliding shaft comes out of them. I’ll order some new O-rings to fix that. I had replaced the original Buna-N O-rings with Viton ones that were compatible with automotive fluids, but I eventually decided to use a synthetic aviation fluid which would have been compatible with the original O-rings. The new O-rings were supposed to be compatible with the aviation fluid too, but I’ll switch back to the ones that Matco recommends as Buna-N is slightly softer than Viton, and that may make it better at sealing.

I pulled the cowling to do an engine inspection and to top up the brake fluid. I reinstalled the wheel pants and put the front seat back in. Then I did a short test flight, hoping to find that the radio was working. I could hear it in my handheld COM when I transmitted, but it was very broken. I was hoping that the high power transmitter was overpowering the handheld COM’s receiver at close range in the hangar, and that things would be fine when I was talking to stations a bit further away. But once I got flying I found that the radio was still not transmitting. :(

Late Sunday morning I attacked the problem from scratch. The intercom and COM 2 were working, so I knew that the wiring up to the intercom box was good. I used an ohmmeter to recheck the wiring from the intercom to COM 1, and everything was perfect. I tried bypassing the intercom, but that made no difference in the quality of reception on the handheld COM. I checked the resistance in the power and ground connections, and found that one of the power connections had a slightly high resistance between the radio tray and the fuse block. I cleaned the connection at the fuse block, which brought the resistance back down to a very low value. And, suddenly the handheld COM was picking up the transmissions loud and clear.

I pulled the aircraft out of the hangar and went flying. The radio appears to be working perfectly. Finally! I am so happy :)

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Yesterday when I went flying to do the radio check the wind was blowing a bit harder than forecast, and it was straight across the runway. There is no anemometer at Smiths Falls, so I am not really sure what the wind speed was. The wind sock was blowing straight out. Ottawa, the closest airport with a weather report, was calling gusts to 33 kt, but I’m sure it wasn’t blowing quite that hard at Smiths Falls.

The take-off was a non-event. The hardest part about the landings was getting the aircraft onto the runway due to the gusts and turbulence as the wind tumbled over the hangar line. My first touch and go was an embarrassing bounce and go. The second one did multiple hops before it settled onto the runway, but the third one was much tidier. After that I decided I was ready for the full stop, which went very well. There was lots of aileron and rudder left, so I’m sure the ultimate crosswind limit is quite a bit more than whatever this wind was - it had to be more than 20 kt, but I’ll claim a demonstrated crosswind of 20 kt for now.

Andy W., a local RV-8 builder, happened to be at the airport while I was doing the circuits, and he took these photos - Thanks Andy.

 

 

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I was contacted by Barry A., a local ham radio operator, a few days ago. Barry had taken an interest in my RV-8 project years ago, and he happened to check my blog and see that I was having radio problems. He offered to bring a bunch of his gear to the hangar to check out the COM antenna.

Saturday morning I removed the front seat and floor yet again, and fixed the problem of the COM 1 antenna coax connector hitting the doubler at the antenna mount. I removed the antenna, and enlarged the hole where the connector comes through the floor to make room for the connector. My current theory is that the original radio problem was due to the coax connector working itself loose at the antenna - it was found to be loose last weekend when I went under the floor. During my initial troubleshooting, I managed to create a wring issue when I replaced a questionable intercom connector. So I was dealing with two problems, one of my own making.

Saturday afternoon Barry came by. First he checked the antenna Standing Wave Ratio (SWR). The SWR was about 1.3 at 127 MHz, and 2 to 2.1 at 118 and 136 MHz. The antenna impedance was about 41 ω, a bit lower than the ideal 50 ω. The return loss was about 15 dB. The aft tip of the antenna is a few inches from the lower surface of the flaps when the flaps are down. I raised the flaps, and he checked again - the return loss improved 2 to 3 dB. Next he checked the transmitter power - it was cranking out a bit more than 10W (the spec is 10W). Bottom line - I don’t understand the significance of all the numbers, but Barry says the antenna and coax between the radio and the antenna are both in good shape.

Out of curiosity, I also had him check the COM 2 antenna, which is a Bob Archer internal wing tip antenna. I expected that it would be less optimized than the Comant external antenna, but the Archer antenna produced numbers that were slightly better. Its SWR was 1.3 at 126 MHz, increasing to about 2 at the upper and lower ends of the frequency range. The impedance was about 54 Ω, not too far off the ideal 50 Ω. The return loss was about 16 dB. He also offered to check out the NAV antenna, which is another Bob Archer internal wingtip antenna, but it proved to be too hard to get to the connector on the back of the GNS 430.

I really appreciated Barry taking the time to help me. Thanks Barry!

After Barry left I reinstalled the floor, then spent some time reworking wiring harness position to gain a bit more slack at the intercom connector. I rechecked all wiring, then tried some transmissions, listening for the speaker output from the ICOM A6 portable VHF COM I bought last week. I could hear the audio, but it was a bit broken. This is a bit improvement over earlier tests where nothing was heard at all. I suspect the audio may have been broken because the high power transmitter was overpowering the ICOM receiver at such short range (it is not at all uncommon to read reports of aircraft in close formation who are unable to communicate with each other due to this problem).

I need to check out a brake leak before I fly again and I ran out of time to do that this weekend. I hope to get a test flight off next weekend, and I think there is a chance the radio problem is solved. But, I won’t know for sure until I fly and can do some radio checks with stations a long way away.

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I did a bunch more troubleshooting this weekend. I found that the intercom failure was due to a bad connection I made when I replaced one of the connectors at the intercom. I fixed that yesterday, and now the intercom and the MicroAir 760 (COM 2) are working again. But the GNS 430 (COM 1) is still dead.

I confirmed good connections from the front seat mic jack all the way to the GNS 430, with the intercom ON and OFF. The PTT connection at the GNS 430 rack is pulled to ground when I press the PTT switch. I reconfirmed good power and ground connections at the COM pins at the 430 rack.

Today I removed the front seat and the floor so I could get at the antenna. I confirmed continuity from the antenna connection at the rack to the antenna, and no shorts between the coax centre conductor and ground. I found the coax connector loose at the antenna - it was not fully turned until it locked. I found that the end of the coax connector would hit the doubler on the inside of the skin slightly before the connector was locked. I was able to get the connector to lock using a pair of pliers, but I realize now that what I probably should have done instead was enlarge the hole where the antenna’s coax connector comes in from the outside so it was larger than the coax connector diameter. I’ll do that next time I’m back at the hangar.

I went flying this afternoon to do another radio check. No one would talk to me on either radio, which really bummed me out. After landing, I saw that Alfio and Shirley’s RV-9A was parked on the ramp, so I went down to the club house hoping to get them to man the club house radio while I did a radio check (the Smiths Falls Flying Club has no permanent staff, so there is usually no one at the radio). But, they started up and taxied out before I got there. I found Fred, a local C-172 pilot, in the club house who had landed just before I went flying. He had heard me on the radio, so that suggested that COM 2 at least was working. He offered to man the radio while I did a radio check, which confirmed that COM 2 was working but there were no signs of life from COM 1, not even carrier. Hmm.

I’ve ordered an ICOM A-6 handheld COM, which should greatly help in the troubleshooting. I also ordered some coax cable and connectors so I can temporarily hook up the GNS 430 to the COM 2 antenna. That should help determine whether the problem is the antenna or wiring. I also look at hooking up a way so that I could hook up the handheld COM to the COM 1 antenna when needed in flight.

I also made another adjustment on the prop coarse pitch stop, and now have clearly gone too far, as the rpm increases to 2800 rpm as I get to VNE. I’ll set it about half way between the two previous settings and check it again.

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I tested my GNS 430W in another aircraft today, and the radio check was perfect. Thanks Dave! So a GNS 430 failure is ruled out. On the one hand it would have been good to know where the failure was, but I’m happy it must be something a lot cheaper than a 430 repair. I didn’t try his 430 in my aircraft, just in case I have some wiring issue that could damage his unit. I didn’t relish spending gas money to repair someone else’s avionics.

The intercom harness was quite tight after I had replaced one of the connectors on the weekend to correct an intermittent fault, so I loosened up some Adel clamps and repositioned the harness so it wasn’t under tension at the connector. I inspected all the pins in the connector, and they seemed to be properly seated.

I then rechecked the mic audio hi and lo between the intercom and GNS 430 rack, and they were fine. I reconfirmed good power and grounds at the 430 rack. I measured the resistance between the ground pins and aircraft ground as less than 0.5 ohm. The resistance between the power pins and the fuse bus was also less than 0.5 ohm.

I confirmed the centre pin in the COM coax connector at the back of the rack wasn’t shorted to ground.

I redid the GNS 430W rack engagement check from the Installation Manual. The results were identical to what they were when I first installed it - 4 turns of the Allen key from power on to fully seated. The minimum allowable value is three turns, so I am OK there.

I unplugged the COM coax at the back of the 430 and plugged in the coax for COM 2, which was working on the weekend. A radio check did not work, but I also noted that I was no longer hearing sidetone when transmitting, nor was I hearing myself when talking in the intercom. I tried my other headset, but no difference. Something has changed here, as the intercom was working on the weekend.

At this point, more confused than before, I stopped and came home.

Next visit to the hangar, I am going to check continuity between the headset jacks and the intercom. I’ll also check intercom power and ground, but its lights were lit up, so they must be OK.

I’m wondering if maybe the intercom box has died. Maybe the COM 1 outputs died first, and now the intercom portion has died too. I’ll make up a test plug that connects to the two intercom connectors and directly ties the headset earphone, mic and PTT lines to COM 1, bypassing the intercom completely.

I also got an e-mail from from another builder saying that he had a bad GPS antenna connection that had somehow killed his COM TX. I don’t understand that one, but I learned a long time ago to not try and tell someone that what he just saw couldn’t possibly have happened. Next time I’m at the hangar I’ll unplug the GPS antenna and see if that makes any difference.

I think my next chance to attack this problem is late Thursday afternoon.