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Annual Inspection - The Bakeng Deuce, Part 3: Strategy and Technologies
From Bits and Pieces Newsletter - September
By Bill Evans, President - EAA Chapter 266, EAA 794228
It is a reality that stripping an aircraft of all its panels and equipment has some risk involved. If you have wondered how aircraft become disassembled and derelict, this is one way. In contrast, our aircraft is in a returned-to-flight configuration every four hours. None of the parts are lost in four hours.
This is how she looks naked.
The fabric on the fuselage tail and empennage is in very good condition and so is the finish. If you walk in the door and turn on the hangar lights, its beauty just stops you. That says something about the aircraft. But as we shall see, there is another inside story and it’s not as shiny.
At this point we’ll turn to the fuselage interior. Aft of the pilots seat there is a large removable panel as well as two hand access panels. These are just 4 inches across, because the wooden fabric supports are 4 inches apart. Our hands are just a little larger. Thus, very long tools, forceps, mirrors, pliers, and vacuum hose are needed to clean and inspect. I had to find someone with much smaller hands to replace that trim tab cable fitting. Be on good terms with your kids; you may need their help with this.
How best to inspect inside the Bakeng Deuce tail?
We found it difficult to see and use a mirror to inspect inside the tail. But we are very fortunate to have a Pentax flex endoscope. It is about 6 feet long. The tip can be flexed 90 degrees in four directions and the light output is 300 watts. It would like a 600-watt lamp, but we fear the heat would melt the fibre-optic light cable. It hadn’t been used in a year, so some fiddling was required. Once we got the hang of it again, the inspection went quickly. This endoscope was bought at a flea market for $50; they are $4,300 new. Keep your eyes open.
The first two parts of this article included an introduction and discussion about the empennage. You can see that four more areas of similar size remain to be inspected. We mention this here to stress that it is very easy to have a good look around an aircraft and then sign off on the logbook. If Transport Canada (TC) finds that your inspection checklist is missing or incomplete, we can assure you they will be making enforcement noises against you. In part, this inspection took five days because the last inspection before the aircraft was sold did not.
We should also mention that if you submit an incomplete, undated, unsigned Condition and Conformity Inspection Report, you should know that TC now employs someone to read those reports. This is just to say inspect your aircraft to the checklist, and do the documentation and logbook entries properly. If you don’t know how, ask someone who does. Big Brother is watching and he can read.
The rear cockpit floor panels were removed. The amount of debris and small parts in the bilge also tells you something about housekeeping.
It is quite astonishing how much debris and lost hardware can collect under the floor panels in a year. We’d vacuum up the hardware and discard it, except for this: It’s very probable that some of those bits were installed on our aircraft, came loose, and fell into the bilge. So keep them for your own aircraft, because if your inspection is exhaustive, you’ll find out where many of them belong. You might also consider what it would take to keep them installed for the year ahead rather than in the bilge.
If you fly aerobatics, you really need to eliminate foreign objects from your aircraft.
Below the floor line, things are very tight – two control systems, elevator tab, static lines, wiring to the nav lights, perhaps a fuel line and fuel valve. Rear seat belts all pass through that space, too. Our Sonerai has the battery, two relays, and all the related wiring aft of the rear cockpit seat.
Thus our fuselage inspection focused on clearances, wear, fretting marks, and worn wiring insulation. Typically you want ¼-inch minimum clearance for all controls. Here we slowed down and examined each component separately. Are all the bolts and nuts in safety? Are the cotter pins and lock-wiring secure? It was at this point I had my first good look at the elevator trim hardware. Two turn-barrels were so short that the prescribed number of engaged threads (six) were not present. (This started our parts order list.) The turn-barrels also used the single-wire safety system, which we did not care for. Why not use the safety pins which slide down a slot in the turn-barrel?
The Deuce hardware is all World War II vintage AN – really! The turn-barrels don’t have slots. We prefer the twisted double-wire safety technique. Why? It’s simpler to do, quicker, and stronger and involves just one wire end to hide instead of four. One doesn’t find these lock-wires in disarray and puncturing one’s fingers all year long. We replaced the single-wire types wherever they are found.
The hardest work was using a toothbrush to loosen dirt beside the longerons so that it could be vacuumed out. It also took a long time; it’s been there a long time.
There are several pulleys at this location because the fuselage narrows enough to warrant pulleys. It is important to move the controls slowly. Do the pulleys turn on their bearings, or is the pivot bolt loose and turning with the inner race? Bolts will eventually wear through if they are allowed to run like this. Use a mirror to look inside the pulley groove. Has the cable worn slots into the pulley or worn away one side? Are the cables aligned or misaligned? Can you feel ratcheting as the control is slowly moved? It should be smooth. In this case, the rudder and elevator controls were good. We lubricated them with a little oil, wiped up the drops, and moved forward. Many owners rotate the pulleys annually so the pulley does not rotate over the same 90 degrees year after year.
The rear cockpit contains a side door with hinges and two latches. The fuel selector valve handle and extension rod are located here. We looked forward from the door and saw just a little blistered paint adjacent to the firewall. What would cause that? It turned out that the fuel selector valve is there, and when operated it leaked some fuel into the cockpit.
So we replaced the seal (the missing seal), tested the valve, and all was right. Right? Wrong! The fuel supply elbow also showed signs of fuel leakage. We removed the elbow, and the screen inside was completely clogged with debris. We cleaned the screen and sealed the elbow with the new Permatex fuel-resistant sealant, and all was well. Right?
Wrong again. The main fuel tank seemed to have about four stains along the edges of welds. It’s an aluminum tank. A little cleaning and a closer look showed four tiny cracks or fissures in otherwise good-looking welds. Out the tank came, and it went to the coded aerospace welder. EAA 266 is privileged to have such a welder among its members. His work is a true art form. Thanks to Mark Clement.
How do you TIG weld a fuel tank that has recently contained fuel? Flush it out with acetone. Blow it air dry or vacuum. Do not use compressed air to apply any pressure inside the tank. Ever! Cracked welds will result. Even 3 psi is too much. Then argon gas is used to flood the tank interior and the area to be welded. This is the inert gas part of TIG welding. The use of argon is about flow not pressure.
Engine controls: Throttle, mixture, carb heat, primer, and mag switches are all located here.
The aircraft received a maintenance check flight and ground run before the annual inspection began. During that run, the left or impulse coupled mag became intermittent. But it only became intermittent once the engine was warm. My co-owner went all through the airframe wiring with an ohm meter and contact cleaner. We removed the mag, opened the covers, and inspected everything. The points, condenser, and coil functioned perfectly. The plate that contacts the grounding lead was adjusted. When the impulse coupling was turned by hand, a blue spark appeared at each of the contacts in the cap in turn. Having exhausted the system, the mag was reinstalled, adjusted, and run several times. The engine starts on the first blade on that mag. The aircraft has completed its two-leg ferry flight and continues to function perfectly. This is Part 2 of Murphy’s Law: Mother Nature sides with the hidden flaw.
In next month’s issue, we’ll be using all our senses - eyes, nose, and especially ears - to look for trouble, and in this case, silence is golden.