N8ML 2013 Annual Inspection

N8ML is still in the hangar for her 2013 annual inspection, and tonight I had a chance to participate in the festivities and take some pictures! 🙂

We took the engine cowling off of her last Friday to do compression leak-down tests, and much more has been opened up and removed since then. At this point, she has no wheel fairings, wheels, fin fairing, or tail cone, and all of her inspection panels have been opened. Here’s what she looks like (that’s my mechanic, Pete Lindblom, behind the engine):


no modesty!


As part of this inspection, I had the Slick 4370 and 4373 magnetos overhauled. The mags are recommended for overhaul at 500 hours, and although her engine was running very strong, N8ML’s mags have 580 hours on them. Mag failures are rare, and there are two independent mags on the engine, but I’d prefer not to tempt fate. In this next picture, Pete is setting magnetos timing so the engine runs properly.


Pete adjusting magneto timing


I also opted to have the fuel tanks pulled so we could inspect the wing spars for corrosion and establish compliance with Piper Aircraft Service Bulletin SB-1006. The spars look excellent! I expected they would be okay because no corrosion was noted during the pre-purchase inspection, but now I know for sure. The tanks will be re-installed using structural stainless screw kits I purchased for the task.


tank pulled forward from rib bay


There was some surface rust on the stabilator trim arm bolts, so I purchased four new AN3-3A bolts (about $0.10 each) to replace them as a matter of preventive maintenance. Well, I think the maintenance guys were trying to impress me. They didn’t just replace the bolts – they removed the trim arm, shot it with glass beads to remove all of the old paint, repainted it with white polyurethane paint, and re-installed it with the new bolts. Aside from the finger print, the trim arm looks brand new! I wish now that I had taken a photo of it before they worked their magic. Anyway, color me impressed!


trim arm attached to anti-servo trim tab


In addition to cleaning up the trim arm, the guys also lubricated all of the hinges and the entire control column. The result is an unbelievably smooth flight control system unlike any I have ever felt before. Based on my experience, I had always assumed Cherokee pitch control was a little coarse. WOW was I ever misinformed!

The last two photos (below) aren’t all that spectacular – I am posting them mainly for my own reference. See, I have always wondered how, exactly, a Piper’s full-flying stabilator worked from a mechanical perspective. I’ve studied the manufacturer’s drawings and pictures, but it wasn’t until the tailcone was off and I could see the entire mechanism that it all made sense.

On the fuselage, there are two hinge points, one on either side of the aft bulkhead. On the stabilator, there are two hinge points engineered into the stabilator’s spar. The stabilator hinge points are affixed to the fuselage hinge points with pins – easy peasy. What you can’t see in this picure is the stabilator’s counterweight. The counterweight is affixed to a rod that extends into the fuselage from the front side of the stabilator spar. The counterweight is calibrated so the stabilator is balanced fore-and-aft right at its hinge point. This ensures the flight control responds to light control forces throughout its range of deflection.

The stabilator anti-servo trim tab is operated by a jack screw that is rotated in a fixed bearing (thus causing it to move up or down as it turns) using cables that run up to a control wheel between the pilot and co-pilot seats. The bottom of the jack screw is attached to the trip tab arm.

It all probably sounds somewhat complicated because of my inarticulate description, but when I looked at the mechanisms, I could not help but be impressed by their elegance and simplicity.


tail viewed from above


tail viewed from below


N8ML will start going back together tomorrow. When all is said and done, she will have:

  • New main gear tires
  • A new ELT battery
  • A new fire extinguisher
  • New engine and instrument air filters
  • New SCAT tubing and clamps
  • A new carburetor heat cable
  • Fresh oil and filter
  • A freshly dressed and painted propeller
  • Freshly overhauled magnetos
  • Freshly lubricated, rigged, and tensioned flight controls
  • A very proud and happy pilot/owner!

She should be all set and ready to fly Saturday morning after the avionics technician conducts a bi-annual inspection of her transponder to ensure it is broadcasting the proper four-digit codes.

Up to this point, the whole aircraft maintenance process has been a bit nerve-wracking, probably because I had no idea what to expect. I am nearly a week in now, and I think I am finally starting to figure out how to navigate the process. I hope this means I will be far better prepared to do this in 2014.

More to come!

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