It wasn’t long after takeoff that I noticed that my ammeter showed a steady discharge of 3 or 4 amps. The ammeter reads charging current going to the battery, and so it ought to show 10 or 15 amps at first, gradually diminishing as the battery regains the energy it expended during start-up and taxi. The system voltage was steady at 24 — not the 28 it should have been.
Maybe a voltage regulator problem? I tried switching the hydraulic pump, which draws a lot of power, on and off, and then toggled the master switch, hoping to jolt the system back to life. Nothing.
Luckily, this did not happen at night in IMC, although that would have made a better story. It was a cloudless June day, and I was flying to Paso Robles, California, 55 minutes away, for Antique Aero’s annual barbecue and fly-/drive-/tow-in. No weather, no pressure. What to do? I could be frugal with amps; on a trip like this, I could even shut down the electrical system completely. I could always get a cart start at Paso if it came to that. But when everybody’s busy having a good time at the barbecue, they don’t want to have to trundle out the start cart.
So, after 20 minutes of waffling, I turned back toward home.
I took off the cowling and checked the security of all the wire connections. No problems there. So I made an appointment with Able Air, the maintenance shop at the other end of the field, and a few days later, taxied over for a diagnostic check.
The mechanic climbed into the plane. I showed him how the breaker panel was hinged; you could take out two screws and it would drop open to expose all the bus wiring. He liked that. I wished that I had an instrument problem as well; then I could have shown him how the instrument panel also swings out, giving access to its own back side and to the wilderness of wires and hoses behind it. But, though praise is sweet, I guess one problem is enough.
He started the engine. There was no DC coming from the alternator, he noted, and no AC either. AC would have meant a faulty diode; the complete absence of DC was a little more puzzling.
He shut down, climbed out and began poking around behind the engine.
“Here it is.”
He had me grab the alternator and shake it. To my amazement, the whole back end of the case was loose. The bolts holding the two halves together were in place, the safety wire was intact, and yet the alternator was coming apart. What was embarrassing about it was that when I had checked the wiring a few days before, I hadn’t noticed anything amiss. I had never thought to twist and shake the alternator case. I guess that’s why they invented A&Ps.
“Vibration,” he said. “You can never tell with vibration. It can destroy anything.”
I felt offended. As if I would have an engine that vibrated! I assured him that the engine ran very smoothly. Unusually smoothly, really. Admirably smoothly!
“Not something you would feel, necessarily. When did you last have your prop balanced?”
Hmm. “Forty years ago,” I murmured, trying to be inaudible and easily misunderstood.
“I recommend doing it every 500 hours,” he said.
I began to reflect on times in the past year or two that I had thought I sensed a subtle, intermittent shudder behind the engine’s steady hum. Could that have been the alternator at some stage of self-destruction?
I pulled the alternator and took it to Aero Accessories at Van Nuys, where I had bought it six years earlier. A couple of days later, there was a message on my cellphone. I needed a new drive gear coupling; mine couldn’t maintain the required torque. Part number 635796 — Aircraft Spruce had them. “They’re kind of steep.”
The gadget in question, whose purpose is to damp torsional vibrations and to shear gracefully in the event that the alternator seizes up, is an unprepossessing little thing; three or four would fit comfortably in the palm of your hand. Continental wants $1,500 for a new one. Aircraft Spruce will sell you a rebuilt one for $575. They’re quite a bit cheaper on eBay, but you don’t know what you’re getting.
Luckily, Able Air happened to have one. I took theirs.
My curiosity piqued by the matter of my long overdue prop balancing, I dug into my old records from the original Melmoth and found two reports. The first, dated July 12, 1974, over the signature of Jim Chadwick, whose name is synonymous with rotor balancing in the helicopter world, recorded measurements taken both on the ground and in flight. Adding some washers to the outside of the spinner bulkhead had reduced the magnitude of the one-per-rev vibration by 75 percent, but Chadwick confessed bafflement about what could be producing ½-per-rev, 1½-per-rev and 3½-per-rev vibrations.
Five years later, Sandy Friezner conducted a different type of analysis, sort of a tuning-fork procedure involving the natural frequencies of the propeller blades themselves, and concluded that the prop “looks good for your operating range.” I had forgotten about this test, which disclosed essentially that all of the resonant frequencies of the propeller blades were below 1,950 or above 3,000 rpm. (The yellow segments on some tachometers reflect this type of analysis.)
I was glad to be reminded of it, though, because I sometimes crank the rpm down to 1,900, and I probably shouldn’t go lower than 2,100 or so.
Did any of this have anything to do with the alternator falling apart?
I don’t think there’s any way to know. The technician at Aero Accessories said they see this kind of failure maybe once a year, and have no idea what causes it.
Smarting from the cost of this misadventure, which came close to a thousand dollars not including the prop balancing, I wrote in my blog that I was not really in the airplane-owner demographic, and that my flying career would probably last only as long as not too many parts of my plane break at once.
A friend, himself an airplane owner — he has a sailplane, though, so he has not so much to fear from Continental or Lycoming — wrote back:
“Few of us are really in the aircraft-owner demographic. We just do it anyway. Those who are in the owner demographic probably don’t own the plane. Their company does. It’s a tax thing.”
So is that the trick? I need to incorporate? Melmoth Maintenance LLC?
