Shitty shitty shimmy

What wasn’t visible from two thousand feet above was just how rough the washboard forest road really was. Not the clean, flat, smooth ribbon of dirt it appeared to be when the engine failed; instead it was petrified ocean surf. Long chains of small ridges and shallow valleys, all closely placed, laid out lengthwise like dismembered and abandoned treads of a gigantic broken-down bulldozer. Still, the first few seconds after I touched down were smooth and relief flooded my soul. Everything was going to be OK. Then… Bam! The plane lurched once, then all hell broke loose. She was gripped by a grand mal seizure. Powerful, racking vibrations shook her stem to stern and wingtip to wingtip. The securely locked doors flung open, a blast of cold air flooding the cockpit. A geyser of fuel ejected from the header tank. Doused the windshield. I frantically pushed the yoke in, pulled it out, rocked it side to side. Stomped on the brake. No dice. In my mind’s eye I could see rivets popping from the skin and flying through the air in all directions. My flightpad holder separated from the dash and crashed to the floor. Then the seismic vibrations cleanly decapitated the bobble-headed dog figurine that lives on the glare shield.

Well, OK. We don’t really have a bobble-headed dog figurine on our glare shield. But if we had had one, it would have lost its head. The vibrations were that bad.

61UgeCH58jL._SL1005_

Image: Amazon.com

Oh. And I wasn’t really making an emergency landing on a forest road, either. It just felt  like it. I was actually making a garden-variety landing on Runway 17 at Albuquerque’s Double Eagle II Airport, a perfectly respectable stretch of concreate. The washboard wasn’t on the ground.

It was in my plane.

It’s called “shimmy,” and this bout of shimmy was so bad it actually stalled the engine before subsiding in a quivering rollout, leaving me high and dry and motionless in the middle of the runway at a busy urban airport. Tower… we have a problem.

Clearly, I couldn’t put off dealing with this any longer. No more deferments. In aviation circles, putting off a repair is often called “owner-deferred maintenance.” It happens all the time, because no owner can afford to fix all the things that are wrong with any airplane at any given moment. Of course, you’re required by law to fix any safety-related items, but beyond those, there’s always a long list of optional repairs to little squawks that vary from barely noticeable, to mildly annoying, to seriously aggravating. These squawks tend to get worse over time, like an evolving species.

And my nose wheel shimmy had evolved from barely noticeable, to mildly annoying, to seriously aggravating. In fact, it occurred to me—as I sat smack dab in the middle of the runway trying to restart my engine with the tower ordering the planes behind me to go around—that my nose wheel shimmy problem had now risen to the level of a safety issue.

Why had I put off dealing with it for so long? Partly money. But mostly because there’s no easy fix, as there’s no clear cause. In ‘Coupes, shimmy originates either in the nose gear or in the control mast, or both. It’s largely caused by worn bearings and bushings that result in a system of components designed to fit tightly together not fitting so tightly together, allowing oscillating vibrations to build up. Sometimes it can be one part, but usually it’s a little bit of wear on a bunch of components. Tracking down the smoking gun(s) is a looooooong exercise in trial and error. Oh, and some of these parts require serious disassembly of the airplane to reach. Luckily, in our case, the bulk of the evidence suggested that our problems originated in the easier to reach nose strut, rather than in the cockpit control mast, which requires actually removing the center fuel tank to reach.

So what’s the big deal? Why not just replace the strut instead of messing with it, you say? I wanted to, believe you me, but there’s a problem. While we Ercoupe custodians (you can’t really “own” a plane that’s older than you and which will outlive you) are thrice blessed that Univair still holds the type certificate, and not only has an extensive inventory of new old stock, but can actually make many of the parts we need, they don’t carry or produce every part that makes up the planes, and the nose strut is a good example of this. Univair doesn’t have any complete assemblies, nor do they even have all of the components that might be needed to fix one.

This leaves the Ercoupe custodian in need of a nose gear repair in the role of Dr. Frankenstein. And like Dr. F, the custodian often needs the services of a good grave robber. Dead airplane parts are brought back to life using a combination of new parts, serviceable used parts removed from airplane corpses, and in some cases modified or re-manufactured parts.

So I think you can see why, ostrich-like, I just buried my head in the sand, even though I knew trouble was brewing. And in my defense, I was preoccupied with bigger troubles. But now that the rest of the plane seems to be largely working again (knock on aluminum) it’s clear to me that I missed a golden opportunity to deal with the shimmy, as you’ll soon see.

I’ll save you the Odyssey and the Iliad and just go straight to the cliff notes: In the process of trying to figure out our options, I learned late in the process that the outfit that rebuilt my wing tanks also rebuilds nose struts. I’m 70% thrilled. Why only 70%? Because that nose strut lay on the floor of my mechanic’s hangar for four months during the engine mount and forward skin replacement repairs. Had I known earlier, we could have had it done while the component was already off the plane, saving both money and flight time. Here, having just gotten the plane back after many months of not flying, it’s once again laid up for repairs and I’m at serious risk of becoming an alcoholic.

Still, I’m happy that someone with a good rep, who really understands these systems, is on the case. But meanwhile, having already missed out on the Georgia race—maybe a lucky thing or I might be broken down far from home—I’ll now miss the Spaceport’s open house and no doubt at least the next race, possibly the next two, costing me yet another season, depending on how long this takes.

Tess is back in Santa Fe once again, where I accused my mechanic of having an affair with my airplane, nose strutless and the strut is en route to the rebuilder. How long this repair will take depends on what they find when they tear it down.

Only then will we know how many graves they’ll have to rob to get my girl back in the air again, and landing as smoothly as she flies.

 

Weighty options

I let go of the yoke. One heart beat… Two heart beats…

The horizon rises in the windshield. Slowly at first, then faster. Up. Up. Up. Faster and faster still. The whisper of the wind turns into a roar. Then a howl. Twin tails rising high into the air, Tess nose-dives toward the earth like a Stuka dive bomber.

stuka

The wind resistance tugs at the prop, red-lining the tachometer.  The vertical speed indictor shows 800 feet per minute down… 900 feet per minute… 1,000 feet… 1,200… The airspeed indictor snaps to the yellow line. I lose my nerve. My hand back on the yoke, I pull back. Gently. Firmly. The horizon, now above my head, slowly slides across the roof of the canopy, down the windshield, below the nose. We are straight and level again.

I turn to Lisa, who’s sitting calmly in the right seat, pencil poised over her knee board. “Well,” I say, “that wasn’t encouraging.” Clearly the new trim is not working right.

So much for a trouble-free return to service.

We return to the field, land, and my mechanics make an adjustment. Back to the designated practice area. Back up to 8,500 feet. Again, the Stuka dive.

stuka

We return to the field a second time, land, and my mechanics make another adjustment. Back to the designated practice area. Back up to 8,500 feet. Again, the Stuka dive.

stuka

On the third try, we’ve run out of trim. It’s deployed 45 degrees into the slipstream, and still the elevator can’t hold the plane in level hands-off flight. Something is seriously amiss. Tessie has become mysteriously nose-heavy. Like our engine mystery of two summers ago, there’s no satisfactory and satisfying answer as to why this is so. But cause aside, we need a solution. And one solution to a nose-heavy airplane is to simply add some weight to the other end. And as the tail is much farther behind the center of gravity—that magic balancing point an aircraft in flight rests on and rotates around—than the nose is forward of the center of gravity, a little weight should go a long way.

Or so we thought.

Funny how many of the things we think  should work simply don’t with this stubborn little airplane.

I won’t bore you with all the details of the testing plan. Or with the details of the flights, one after another, after another, after another, after another. For most of a day. But we started by securing one-pound bags of “Sea Pearls” in Tessie’s tail. The bags are designed for scuba diver belts. They are small, flat, full of tiny lead shot, and surprisingly heavy for their size.

IMG_1947

Based on the weight and balance sheets, it shouldn’t have taken too many bags to get Tessie to fly right. The weights were placed 180 inches behind Tess’s center of gravity. One hundred and eighty inches is a loooooong lever with which to raise the nose. Or so we all thought.

But it was not the case. Seventy-five dollars’ worth of Sea Pearls later, I still had a plane the Luftwaffe would have been proud to deploy. With the maximum amount of added weight that my maintenance team felt was safe, we still couldn’t fly level. Oh, sure. It was better. The dives were slower. Less aggressive with each bag of Sea Pearls. But anything like level flight with neutral trim eluded us.

It was time for Plan B. Which was four washers installed along the bolts that secure Tess’s tail to her fuselage. Yep. We shimmed her tail. Then I went up to test fly.

No more Stuka.

But were the weights still needed? There was only one way to find out. Take some out, test fly, and see how many, if any, were needed with the shimming of the tail feathers. Again, I won’t bore you with the details of the flights. One after another, after another, after…

But in end, there were no Sea Pearls in Tessie’s tail and she flew true.

In fact, she’s never flown better.

Now, if we can just figure out why her brand-new attitude indictor is spinning like a top, and why her compass points the wrong way…

 

Not quite ready for prime time

35 miles per hour…

40 miles per hour…

45 miles per hour…

Oil pressure good. Engine cylinder and exhaust temps coming up, but in range.

50 miles per hour…

55 miles per hour…

We’re at the top of the green arc. Tessie should be able to fly.

60 miles per hour…

65 miles per hour…

The control tower zips past on my left as we barrel down the runway.

70 miles per hour…

75 miles per hour…

We’re still glued to the runway, speeding down the blacktop like a dragster without the slightest hint that the plane is ever going to fly. Ahead, the band of lights marking the end of the runway is fast approaching.

I smile ear-to-ear.

Yes! This is the way it should be! Properly rigged, with the main landing gear appropriately sprightly, holding the twin tails the designated height off the tarmac, the ‘Coupe’s wing has zero angle of attack on the ground. In other words, if you want the plane to fly, you need to pull the nose up.

Of course, I don’t want to fly. Not yet anyway. Flying will come later. After all, Tessie’s wings haven’t seen the light of day in many months, and I’ve learned from experience that rather than assume that everything will be all right when a shop declares that an airplane is fixed and ready to go, you should assume that nothingwill be right following maintenance.

IMG_0501

And these last few months of maintenance were like no other maintenance Tess has ever seen.

Parts of her that haven’t been seen by human eyes since she was built in 1947 were exposed to the light of day again as the very skin and bones of her nose were removed and replaced, her engine sitting for months on a pair of sawhorses. Her engine, naturally, is back on, sitting in a new engine mount. But every hose, cable, and wire was disconnected and then re-connected—and that means there’s no end of potential trouble.

So this time I decided to take a stepwise approach to returning to the air. First, I taxied lazily around the ramp, spinning slow motion doughnuts at low RPM, assuring myself that the complex control interlinkages were functioning. Going straight forward the ailerons were flat and the control yokes straight and true to the beckoning horizon. In a turn, one alerion flipped skyward and the other pointed to the earth, as the yin-yang of aerodynamics commands. Looking back over my shoulder I could watch the twin rudders flip left then right as I danced across the tarmac.

Naturally, given my hard-earned distrust of this particular aircraft engine, I kept one eye on the oil pressure gauge the whole time, but all was well.

Next, I asked the tower for a high-speed taxi test: Basically, to run down their runway as fast as possible without lifting off. This puts more air over the control surfaces, lets the engine run at higher power, and hopefully—while you’re still safely on the ground—shakes loose anything that might fall off. It’s as close to a test flight as you can come without actually flying. Which I didn’t want to do. Yet.

Which is a good thing, because, right now, I’m running out of runway.

I slide the crystal art deco throttle handle back, down to the base of the throttle quad, tap the brakes, and exit the runway.

My high-speed taxi test is complete. Next will come the flying.

But that’s a Plane Tale for another day.