Between the restorer and I we have two airplanes which are out of the required annual inspections: the Bonanza needs engine work before doing its inspection and the Cub went out at the end of August.
As the Cub is in good shape, the restorer felt it would take several days to get its inspection completed.
Airframe and Powerplant mechanics, known as A&P’s, can perform 100-hour inspections on airplanes for hire. The annual inspection required for certificated aircraft is the same inspection as a 100-hour with the addition of an Airworthiness Directive (AD) search, this inspection can be completed by an A&P who also holds an Inspection Authorization, known as an IA.
The restorer holds both credentials and as such can perform the inspections on our airplanes.
Taking advantage of the day off, the restorer and I head to the airport on Labor Day to start the Cub annual.
Day 1: Engine Inspection
Just before leaving the house, the restorer looked at the airframe log for the Cub to note the amount of time on the airplane from the previous year and calculated from his logbook how much time it had flown over the previous year.
35.5 hours is not a lot for an airplane, but certainly more than most small privately owned airplanes fly in a year.
Arriving at the hangar, the restorer laid out moving blankets on the floor and pulled a cart holding his toolbox and a clipboard armed with a checklist from the manufacturer indicating which areas needed to be checked at what intervals.
Opening his toolbox, small boxes are pulled out and laid on the cart. We remove the fasteners holding the engine cowling on and place them in the small boxes then lay the cowling on the moving blankets.
Looking at the checklist in more detail, it covered several similar types of aircraft produced by Piper Aircraft at the time as well as inspection intervals in some columns. The restorer mentioned he had bought a similar checklist while we were at Oshkosh for the Bonanza as it is a useful tool for the regular inspection.
While I was looking at the checklist, the restorer moved the top park plugs for visual inspection sitting them in a tray with holes for each of the 8 spark plugs which are appropriate for a 4-cylinder engine.
The restorer next turned on the air compressor and pulled out a device with two gauges on it which would hook up to both the air compressor and to each cylinder to check for efficiency – a compression check.
Compression Check
One of the restorer’s airport sons along with a mutual friend came in at just the right time – to assist with the check. The restorer had indicated two people were necessary to complete the check safely as one holds and uses the device to register the pressure difference between the air compressor and the cylinder while the other moves the prop to advance the piston within the cylinder as needed.
Hooking an air hose onto the engine where the top spark plug would have been, the other end of the device is connected to the air compressor. The first gauge indicates the pressure coming from the compressor – 80 PSI, and the second gauge indicates what pressure is in the cylinder at the top of the compression stroke – as close to 80 as possible.
When cylinders get older, compression may not be as good. Air can seep around rings, the intake and/or exhaust valves on the cylinder which could indicate a problem.
Of the four cylinders, the lowest compression was 72. Well within tolerances.
When I was learning how to fly, instructors would bring students in to see work being done on aircraft in order to understand systems more thoroughly. Seeing what goes on underneath the cowling has been rare, mostly it has been hearing in passing about compression checks and engine work without the process being explained.
Seeing the process being done and the restorer talking about what occurs at each step of the inspection – why he is looking at various items filled in the mental map between what a pilot is expected to know as part of their training and what an owner or caretaker understands as necessary to keep an airplane flying.
As engine items can be the most disruptive, the restorer wanted to tackle that first. When cylinders were done for the Bonanza earlier this year, it took almost a month. If the Cub were to need engine work the restorer would likely do the work himself as not many engine shops still work on the smaller Continental engines.
The restorer’s airport friends left after the compression check was done.
Magneto Timing
The restorer put away the compression gauge and brought a box with lights back to the airplane in order to check the engine magneto timing.
Gesturing to the propellor flange, the restorer asked me to look for numbers along the edge – those indicated the positions where magneto firing would take place while the piston was moving through the number one cylinder. Firing should take place when the piston is at a specified position on the compression stroke. On this engine, the magnetos should fire at positions 28 and 30 degrees before the top center.
Close but not at the same time.
The box is then hooked up to the magnetos to register the timing with a light which indicates when it fires while the engine is running.
Proper magneto timing prevents both conditions which could damage the engine.
More areas are being filled in within my mental map!
The last area to go over for the day was an inspection of the spark plugs. Looking at the overall condition of the spark plugs, the restorer was looking for damage along the top of the plug from use and any carbon or lead deposits within the plug itself.
Shining a bright light down the spark plug, deposits would be readily apparent. Anything that is within the plug needs to be removed.
Pulling out a circular tool that looked like a small half-apple corer, the restorer inserted it into the plug and then moved it around to dislodge any deposits. He then turned the plug upside down and gently tapped on the side to remove any deposits.
As we clean up and put everything away, the restorer pulls out his borescopes as they need to be tested before the next workday to make sure they are indeed operational as he will use them to inspect the exhaust system.
Day 2: Visual Inspection of Engine Compartment
After getting the borescopes up and running with the restorer’s new phone and tablet, we were back to make more progress on the Cub annual.
Prior to jumping in with the borescopes, the restorer pulls out a strong flashlight and an inspection mirror to look at the structure around the engine for any damage. He indicated that getting comfortable with the inspection mirror took time during his practical training – the mechanic who mentored him often said “See what is there, not what you want to see.”
That’s apt for life as well as maintenance.
While the restorer continued to inspect with the mirror, I sprayed a lubricant on hinges that attach ailerons, elevator, and rudder along with the cables and pulleys that provide movement between the control stick and the control surfaces themselves.
Once done with the lubricant, the restorer had me in the cabin pulling out the carburetor heat and mixture control knobs so he could inspect and lube the cables as necessary.
The restorer then pulled out the borescope and tablet to inspect the inside of the muffler. The interior inspection was completed by pushing a borescope up the exhaust tube to look for any debris or damage. He then opened up the muffler housing itself to look inside there with the borescope.
The AD which requires this inspection was released in 1984 and the restorer had taken the muffler and exhaust apart to visually comply with the inspection items many times before obtaining the diagnostic tool about 10 years ago.
He is still able to visually inspect all necessary areas but does not have to dismantle as much in order to do so.
The last area we tackled for the day was cleaning the air filter. The restorer has a Supplemental Type Certificate or STC for a reusable air filter on the Cub. It is removed as part of the annual and rinsed off before being allowed to dry.
Day 3: Wings and Tail Inspections
Visual inspections of the wings and tail were on deck for the day.
Over the previous year, the restorer had flown about 35 hours in the Cub, prior to that he had recovered one wing due to some damage.
He had restored the airplane completely in 2013, rebuilding areas that needed attention as well as cleaning and maintenance. Since that time, the airplane has flown 300 hours.
It received new fabric as part of the restoration and was completely recovered.
The clipped-wing Cub is capable of light aerobatics, and in a past life has flown in air shows.
The inspection plates that need to be removed are difficult to remove as they need to stand up to larger air loads. The restorer removed the covers while I worked on the removal of farings around the door and wing root.
Fabric condition is examined for any holes or other signs of damage.
Once everything was removed for the left wing, the restorer pulled out his flashlight and mirror to look inside.
It took longer to take the plates and farings than to do the inspection.
We repeated the same process with the right wing before heading to the tail.
Inspection plates on the tail were removed revealing the jackscrew which moves the horizontal stabilizer up and down to trim the airplane.
Once again lubricant was brought out to spray over the screw. The restorer had me rotating the trim crank inside the cabin so he could spray all necessary areas on the jackscrew.
The restorer then brought out a jack and grease gun to service the tailwheel.
Placing the jack underneath the tail just in front of the tailwheel, the restorer lifted the Cub until the weight was off of the tailwheel.
The restorer explained tailwheel servicing isn’t done as often as it should be as the mechanism that controls the direction of the airplane while operating on the ground; if it malfunctions the airplane is difficult to control on the ground.
Removing a cover similar in size to an air stem valve cover, the restorer explained we would be using a grease gun to service the tailwheel.
New grease is pumped into the orifice pushing old grease out which is wiped up with a shop towel.
Each process was straightforward but took time to accomplish.
As airplanes go, Piper Cubs are older technology but still require time and attention to stay airworthy.
Mechanics trained today do not gain experience with fabric, small engines like the Cubs, or tailwheels, it is getting tougher to find A&P/ IA’s qualified and willing to work on older airplanes.
Day 4: Landing Gear Inspection and Servicing
It was the Sunday of the Waco Fly-in at Troy, OH (1WF) and many of our friends had gone over to the event over the past several days. The restorer and I both wanted to go appreciate the airplanes and were hoping to do so after finishing the physical inspections.
The last areas to be inspected and serviced were the landing gear.
The restorer’s Cub has wheel pants that cover the wheels and have to be removed to inspect the tires, wheel assembly, and brakes.
The wheel pant is removed, then moving blankets are placed on either side of the right gear, the restorer positions the jack just above the wheel assembly using wood blocks to provide a bit more stability while raising just enough to get off of the ground.
Once elevated, the restorer gets comfortable laying on the moving blanket with pliers and wire cutters to remove a cotter pin that keeps the wheel assembly together.
Focusing his attention to the inside of the wheel hub, pliers are used to bend the bottom of the cotter pin straight down. Once satisfied both sides of the pin will clear, the restorer gripped the top of the cotter pin with the pliers to pull it out.
A brake caliper is set to one side.
The wheel assembly is removed from the landing gear axle and placed on the moving blanket. A screwdriver is then used to remove a ring from the inside of the wheel.
Bearings and washers that were held in place below the ring are pulled out for further inspection.
The wheel is turned over and another ring is removed revealing another set of washers and bearings which are also removed for inspection.
A tray with parts cleaner is placed close to the brake pad and the parts still on the airplane are brushed with cleaner. The brake pad itself is sprayed with brake cleaner.
The round bushings are placed in the tray and cleaner is used to remove the old lubricant from the small surfaces.
Once clean and dry, the restorer repacks the bearings with new grease, reassembles the wheel, and places it back on to the airplane.
Pulling out a tray of cotter pins, the restorer pulls one out and bends several places before attempting to insert into the hole in the axle and mount tube.
As the hole is small and it is impossible to see inside the assembly the pin has to go through before coming out the other side, it is a matter of both skill and trial and error.
The restorer indicated some days it happens on the first try while others like today seem to take forever.
While the restorer is bending the third or fourth cotter pin, an airport friend stops by to say hello. He had flown over the field in Troy just before stopping by and said no airplanes were left.
After a deep breath and a short break, the restorer was able to get the cotter pin through and the wheel back onto the airplane.
As time has a way of flying when we least realize it, we decided it was time to take a break and get something to eat.
The short break worked wonders and the restorer got the left wheel done with fewer issues.
After reattaching the left wheel he cleaned the underside of the airplane and we got the spark plugs and cowling reinstalled onto the airplane.
While there was still some daylight left, we pulled the Cub out of the hangar and did a preflight before taking a short flight to enjoy what was left of the beautiful day.
As we were taking the first flight after maintenance, the restorer wanted to make clear our plan if there were any problems.
Before starting the engine, the restorer indicated if there were any issues after takeoff before an altitude of 400 feet above the ground, he would make a slight turn to land on a service road adjacent to the airport. Otherwise, we should be able to return to the airport if there were any engine issues above that point.
Takeoff and climbout were no issue, still having a plan to address ahead of time is a wise call.
The late afternoon sun called for making turns around a friends farm close by before flying over a maze and closed up pools on the way back to the airport for a landing.
After shutting down, we used a wet microfiber cloth to wipe the leading edges of the wings, elevator, and rudder down removing the bugs still out.
Putting the Cub away, we headed home to finish the paperwork.