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Q-talk 29 - Q2 CORROSION REPORT

I have recently purchased a 95% complete Q2. This aircraft was stored outdoors for seven years in New England weather; therefore, it is a good specimen for advanced corrosion evaluation. The airplane shows good workmanship, has never flown and the engine has only two hours on the tach. I am a mechanical engineer with aerospace experience.

Observations:

1) All five control surface end pivot bearings were seized. Each assembly was found to be per plans. No prior lubrication was found. Although the corrosion was not severe, the tight clearances between these parts filled with rust and aluminum oxide. The seizures were so tight that the threaded portion of the pivot bolts became the new bearings. After applying liquid wrench, a typical disassembly required backing off the retaining nut until it pulled the frozen pivot bolts out of the control surface bushings/reducers. In one case the aileron had to be cut back to make room for the wrench.

2) The elevator mid span bearings were tight but serviceable. Again, the limited radial clearance was filled with corrosion.

3) The steel torque tubes were seized to all five of the aluminum control surface reducers. This is a non-structural concern, but greatly increases the work required for control surface removal. Again, limited radial clearances combined with aluminum oxide buildup locked the parts together. A special tool was made which held two 3/16" dia pins (1/4" screws filed down in a drill press) in the holes of the aluminum reducers to hold them in place while the steel torque tubes were retracted in a twisting pulling fashion. (Call for sketch)

4) One aileron torque tube (steel) showed excessive pitting corrosion where it passes through the fuselage. It required replacement. Why this part showed more corrosion than the other torque tubes is unknown.

5) Water was found in the rudder torque tube/control fitting. This part is a natural water trap, not good. Corrosion was taking place in a water puddle behind the weld. After inspection, my part was found to be usable.

6) Water was found (about 1/2 cup!) puddled in one of the elevators. Water may be trapped in any of the control surface tubes and is believed to have aggravated some of the corrosion found in item 1.

7) Main wheel axle retaining rods and nuts were corroded. The rods were cleaned and the threads chased. They were reusable with new nuts and washers. An aluminum tiedown fitting attached to one side greatly accelerated the corrosion process on that side (galvanic corrosion).

8) Brake disks showed both uniform area corrosion and pitting. They are a little thin for machining; therefore after cleaning and sanding the surfaces, they were reluctantly reused. Final disposition will be performed at taxi testing (are replacements available?). Brake cylinders were quite free of corrosion both inside and out, however, mounting hardware required replacement.

9) Nylaflow brake lines were brittle and broken at the wheel cylinders where they are exposed to the sun.

10) The tail wheel assembly was a mass of frozen rust and required total replacement (a good idea anyway?).

11) All exterior nuts and bolts were corroded sufficiently for replacement.

RECOMMENDATIONS:

1) Inspect control hardware. Remove control surfaces, inspect and grease hinge points and clean torque tube/reducer corrosion. If this is performed prior to advanced corrosion, control surface removal is much easier. If no corrosion is found, inspection could be biannual otherwise inspect annually. I recommend a .002 to .005" diametric clearance on the 3/16 and 1/4" bearings with .004 to .008 on the larger phenolic bearings. Frequency of inspection should be adjusted for climate, storage and usage conditions. Also any change in control friction is cause for a teardown.

2) Drill a 1/8" dia. moisture vent in the underside at each end of elevator and aileron tubes (eight holes). This hole should be just inside of the reducer fittings. This recommendation is not flight-tested and may whistle. Try it on one tube first and let us know.

3) Drill a 1/8" dia. drain hole in the bottom of the rudder hinge/control fitting. Drill from the inside of the cup to push burrs out for removal with a file. This recommendation is considered safety related as welds can corrode unpredictably.

4) Check plastic brake lines (if so equipped) for brittleness where they are exposed to sunlight. Use dark paint to cover exposed plastic brake lines to prevent further deterioration from sunlight. Inspect regularly and pressure test during preflight. This recommendation is considered safety related.

COMMENT:

I have replaced the stock (steel) control surface pivot bearings with 1/4 x 1/4" shouldered bronze Oilite bearings. These bearings were re-machined for a press fit into the reducer fittings.

For your damage record, this craft broke a tailspring and a prop during low speed taxi trials. Uneven braking with the common master cylinder was blamed. Independent toe brakes are being installed.

From: Ed MacLeod 7/31/91 (508) 250-9092





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