Wednesday, May 25, 2005


Yellowbird's Attitude Problem

She's always had it, but I didn't notice it until a flight with Faithful Instructor George last year during which I logged about 45 minutes of simulated instrument time on the way home from Columbia County. It was the first time I had flown Yellowbird under the hood, and to my discredit, it was the first time that I had really paid attention to the instrument cross check. I noticed that with wings level according to the gyroscopic attitude indicator, she would slowly turn to the left. After a few minutes of puzzlement, I began to closely monitor the indications of the attitude indicator, heading indicator, and turn coordinator. I found that the turn coordinator gave me a better indication of wings-level attitude than the attitude indicator did. Sometimes all three instruments would agree, but at times the attitude indicator would appear to sag slightly to one side. It was barely discernible, and at times it appeared to indicate accurately, but my suspicions were aroused.

DisagreementDuring VFR flights, the variance wasn't critical, and sometimes I wondered if it wasn't merely an optical illusion. The Cardinal windshield is steeply raked, so I sometimes suspected that I was seeing the effect of some visual distortion, but a diligent cross check confirmed that something was amiss. Another disconcerting sign was a slight vibration of the instrument face while in flight it never showed signs of real instability, but I wasn't quite confident in its long-term health.

(Note how the turn coordinator indicates a slight turn to the left, while the attitude indicator shows a slight bank to the right.)

During last year's annual, I had the vacuum pump replaced, but it made no difference. A busy autumn of flying and a very lean winter gave me little time and incentive, respectively, to get her to the shop, but with imminent plans to begin training for my instrument rating, I took advantage of her time in the shop to have the attitude indicator replaced. My mechanic recommended a new Sigma Tek indicator, and since I had heard good things about them, I went along with his recommendation.

Much betterThe new indicator proved to be much more reliable. It was rock solid in flight and it agreed nicely with the turn coordinator and heading indicator. It did have two quirks that I hadn't seen in the old instrument. First, as the gyroscope spun up to speed after starting the engine, it would shimmy about for a few seconds before stabilizing. I had observed this on at least one other airplane, and I understand it to be normal behavior. Second, during engine runup prior to takeoff, the instrument face would vibrate noticeably at the runup power setting of 1800 RPM. This had me concerned, as I couldn't imagine that it would be good for the bearings, but no one I asked could offer any recommendations. I logged it among a few other questions I intended to ask of my mechanic the next time I spoke to him, and then forgot it.

Tuesday dawned gray and dreary, with a low, solid overcast. I was thrilled, since George and I had been waiting for such a day to fly an instrument lesson in actual instrument conditions. After briefing the KBAF VOR 2 approach, we started up and taxied down to the VOR test point in the runup area of runway 2. The VORs centered within a degree of the radial and I ran though the pre-takeoff checklist. We were picking up carburetor ice just sitting on the ramp at 1000 RPM, so I let her run up a little longer than usual with the carburetor heat on to warm things up. During runup, the attitude indicator showed its usual vibration, but while doing a final cockpit check after runup, I noticed that the attitude indicator had fallen. I had a good vacuum indication during runup, but the gyro had assumed the slightly off-kilter position that it normally displays before starting up. George and I sat there for a few minutes pondering this while the gyroscope slowly erected itself again. Sadly, we canceled IFR and taxied back to the tiedown. During taxi, the attitude indicator was erect and stable.

Before parking, I did another runup. Again, I noticed the normal sympathetic vibration, but after about 30 seconds, the gyro began slowly rolling to one side until it had assumed the position observed previously. After reducing power to 100 RPM, the gyro slowly erected again. Today, I did another runup and found that the vibration began at about 1300 RPM and was worst between 1700 and 1900 RPM. Above 1900, the vibration stopped immediately, and the attitude indicator was nice and stable.

I called my mechanic and described the problem, but such things don't generally benefit from long distance diagnoses. She'll have to go back to the shop, but not until the weather clears. Until then, I'm stuck on the ground watching the overcast roll by, no doubt just a few feet above decision height.

Attitude denudedAs for the old attitude indicator, it gave good service for thirty years. When pulled out of the panel it rattled with the unmistakable sound of something adrift inside. I decided that $55 was a reasonable price to pay to satisfy my curiosity and gain an unusual paperweight, so I paid my mechanic the core deposit and took it home. Eight screws later, I had it apart and found a small screw and nut rolling around inside the instrument case. It didn't take long to find that they belonged to a counterweight on the gimbals that holds the sealed gyroscope. The counterweight was normally held in place by two screws, but with one missing it sometimes slipped out of place slightly, rolling the whole thing a few degrees to one side.

It's fun to spin it up and watch the innards move aboutI replaced the errant screw and put everything back together. I plan on bringing it to work and perching it atop my computer monitor. When my boss tells me that I have a bad attitude, I'll point to my old gyro and cheerfully agree.

Saturday, May 21, 2005


A Brief Affair

When she was in the shop, Yellowbird shared the hangar with a recent friend. Jamie had his Skylane in for it's annual inspection, to be done by Yellowbird's mechanic. After the Danbury flyin, we had discussed possible plans for trading rides, but our schedules had yet to coincide to do so. Jamie's annual took a week longer to accomplish than the work done on Yellowbird, so I was in a good position to offer him a ride up to Turners Falls to bring his bird home. Sunday the first of May worked out for both of us, so plans were made.

Jamie pute Yellowbird through her pacesThe weather that morning was looking iffy, with scattered showers and low ceilings, but we decided to at least meet at the airport to feel things out. As it turned out, the weather decided to cooperate and we were treated to a rare day when the weather was actually better than forecasted. The ceiling lifted and the showers moved elsewhere, so we had flyable skies at least to Turners Falls and back. We fired up the Yellowbird and set forth. After departing Westfield, I let Jamie have the controls and he put Yellowbird through her paces during the brief trip.

On the ground at Turners Falls, Jamie spent some time with Bruce, his mechanic, discussing the work that had been done. I was hoping for a short trip around the pattern in the Skylane before we parted ways, but Jamie had planned out a decent cross country flight to Utica, NY, and back and he graciously invited me to join him. It was too good an opportunity to pass up.

Gloomy, but at least there's a horizonAt first, it seemed that our plans would finally be canceled by the weather. After departing Turners Falls, Jamie let me have the controls and we eyed the western sky. It didn't look promising. The clouds were low and dark, and we couldn't see a clear horizon between the higher terrain and the cloud base. Putting our Utica plans on hold, we headed south towards the practice area, but we kept a westward eye open just in case. Our case proved just, and we were soon rewarded with a clear view of Mt. Greylock. We turned west and resolved to go as far as the weather allowed.

Utica, inboundThe weather was apparently in a generous mood. The ceiling lilted to about 3,500 feet, and we had good VFR clearance as we passed to the north of Greylock. I still had the controls, while Jamie worked out the details of our journey on his GPS. I had never navigated by GPS, but I soon got the hang of monitoring his panel-mounted Garmin.

A tricky approachAs we proceeded westward, Jamie contacted Albany approach and received clearance through the Albany class C airspace. The clouds held, but the air was fairly turbulent, and it was with some relief that I handed the controls back to Jamie for our approach to Utica. It was an interesting approach, due to a healthy gusting crossword, but Jamie had a solid reign on his Cessna and he pulled off a perfectly respectable landing.

After the rainAn old aviation saying goes: "It's better to be on the ground wishing you were up in the air, than up in the air wishing you were on the ground". On the ground at Utica, we experienced that anew. The gusty winds heralded a good sized downpour, which began soon after we parked and walked to the FBO. Inside, Jamie checked the weather radar and called Flight Services for a briefing to evaluate our chances of returning home. Fortunately, the storm was merely a local shower, and as it moved away, we had a good forecast for our return flight. After refueling, we climbed aboard and prepared for departure.

Departing to beat the weatherJamie handled most of the return flight, leaving me to watch for traffic and enjoy the view. Climbing out from Utica, we got a good view of the rain as it moved off to the northeast.

Utica, outboundWe also got a nice view of downtown Utica, except for that darn wing strut.

Shelburne FallsAlbany was in no mood to handle us on the way back, so we diverted to the north to stay clear of their airspace. Jamie let me fly for a while, and I brought us back to the GPS direct route once we were clear of Albany. The weather improved as we progressed eastwards, with the cloud layer thinning considerably, but the air was still rough. For some reason, perhaps the unfamiliar experience of flying from the right seat, perhaps compounded by the Skylane's restricted visibility compared to a Cardinal, my stomach was not finding this to be a comfortable flight.

Clearer skies at Turners FallsAgain I was glad to let Jamie take over for our arrival back at Turners Falls. And for the first time since my flying life began, I was actually glad to be back on solid ground. I was a little more comfortable in Yellowbird's familiar cockpit, but I was unprepared for her behavior. Unfortunately, I had parked her where she had a perfect view of my departure and arrival in Jamie's Skylane. She saw everything, and she surely sensed the smell of an unfamiliar yoke when I took her controls again.

She knew I had been seeing another airplane. She was not happy, and she let me know. On approach to Westfield she shed one end of her carburetor heat duct. And when I pushed her back into her tiedown spot, I noticed oil leaking again from her cowling. Neither would prove to be expensive to fix, but I suspected that it would take more than a trip back to the shop to put me back in Yellowbird's favor.