Airplane is Fixed!
I flew to New Market to visit Shenandoah Avionics Monday to replace the D.G. (aka directional gyroscope or heading indicator). Finally, after a very long backorder, it had come in from Aircraft Spruce. (For symmetry’s sake, there should be a New Market Avionics in Shenandoah airport.)
It was a nice flight down there in the morning. I keep overestimating my airspeed though, I got there later than I’d planned. I pulled up to the unmarked hangar in the middle of the field (the airport owner doesn’t let Shenandoah Avionics put up a sign for some odd reason) and stopped.
When I went inside, the hangar was full, so we’d be working outside today. No problem, it was a pleasant morning. The mechanic and I got started, I removed the panel and loosened the existing DG’s mounting screws. He did the upside-down work from under the panel and dismounted the old one. We found out pretty quickly how it failed. They’d not seen this failure before where the instrument fittings broke. Usually the vanes on the gyro break off apparently.
So, I get to take the old one home to disassemble it. The owner suggested I cut away the case and make a teaching instrument out of it as the rotor was probably in good shape. Sounds like a good idea!
We checked the air and vacuum hoses to see if they were too tight, but they had the right amount of play in them. Sometimes things fail and we won’t be able to figure out why. This is one of those cases. Not all answers are worth the effort.
While the mechanic reached the new instrument up from the bottom, I pulled it into place from the panel and mounted it. Naturally, the mounting screws were different between the two instruments, so we had to put a new hole to the left bottom. The old instrument had the third mounting screw on the right bottom. The nice thing about standards is that there’s so many to choose from.
This new DG has a heading bug. We also wanted an internal light, but I couldn’t find one in our price range that had both. (To have both would have almost doubled the price.) So, the bug was it. My IFR instructors will be pleased, and it will be a lot easier for us owner-pilots when flying too. But the knob for the bug also meant another new hole.
The new DG was finally installed (here shown on my flight home, I’m using the bug). We tested it, but it didn’t work. So, check the hoses!
The vacuum-powered gyroscopes work by a vacuum pump pulling filtered air through the gyro housing, which directs that air by vanes on the gyro that spin it up to around 5000 revs/min. The little gauge to the right of the new instrument shows the vacuum pressure. (By the way, the new turn coordinator is to the left, we replaced that after my first IFR lesson in the plane.)
Each manufacturer labels the hose connections in the back of the instrument a bit differently. This, naturally, is subject to misunderstanding. Which is what happened. The filtered air intake was connected to the vacuum and vice versa. Once that was fixed, all was good. We taxied around in a circle and it worked. The mechanic was chagrined but I wasn’t concerned though. Mistakes happen, we’re human. It’s the unchecked and uncaught mistakes that worry me. We were checking and double-checking here.
By now it was the middle of the day and I had a bumpy flight home, not as peaceful as the morning’s flight. The winds were from the north everywhere else around here, but due to the particular pattern of hills around New Market, this airport’s winds were from the south. So, takeoff to the south, give extra space to the hill just off the runway on climbout (easy enough) and turn north, then east to home.
Done. Now I can finish my IFR, and the other owner-pilots can do their flying as needed with the DG working again.