Restoring the A-10D Mitchell Wing

SN# 275

By

Scott McCarthy

 Episode III

“The Pilot’s Cage”

 

            I had not planned on disassembling the entire pilot’s cage. The objective here was to be replacement of the right diagonal frame tube and the left engine support tube. Some type of flailing metal object had somehow battered both. I would learn later that a previous pilot had taken off without securing his shoulder straps. Another repair effort would be the removal of the main gear leg steel support sleeves. Designed to be sacrificial during a hard landing they had performed their role admirably. Replacing the sleeves would also correct the serious list to port that the plane had acquired due to the last landing. The gear legs themselves, miraculously, appeared to be still intact.

            The nose wheel assembly would be replaced too. The vertical pivot housing was cracked at the lower bearing surface.

I had also intended to repair the fiberglass pod and “podsterior”. The pod had a large square section removed when the previous owner attempted, unsuccessfully, to install a softpack ballistic parachute in the nose section. It had been put back with copious quantities of Bondo that gave the nose a curious lumpy profile and whole area repainted with red spray paint. The thin fiberglass had also collected a remarkable number of stress cracks in the gel-coat where it met the frame. The podsterior, wheel pants, wingtip shrouds and stabilator tips also had stress fractures and the same faded red gel-coat or hardware store spray paint.

            The pilot’s cage would also receive some custom touches. Since I would likely be operating off grass runways, the four-inch wheels would be replaced with six-inch Asuza units and the wheel pants would be left on the ground. The color of the fiberglass components would be changed from unstable, quickly fading red to a stable, high-visibility yellow. And finally, a custom aluminum instrument panel would replace the floppy black plastic panel that had been cable tied to the frame tubes. In the process I’d also replace the wiring and controls, including the articulated control stick hardware found wanting during the initial inspection.

            The question was: Where to begin? This was answered by yet another viewing of selected sections of the A-10 assembly video. The pod and podsterior had already been removed for inspection and the old instrument panel removed. This, I carefully disassembled noting electrical connections and plumbing for the air pressure operated instruments. The sensitive altimeter and airspeed indicator appeared to be in good shape, but being of a pessimistic nature I sent them off to the Aircraft Spruce avionics repair people in California for checkout and calibration. The panel also had an old-fashioned pellet variometer with what looked like an insulated peanut-can that acted as an accumulator. I hadn’t seen one of these since my early soaring days. I noted it’s plumbing and tried to make out the manufacturer’s name and city. All this information went in to my restoration notebook for further use later.

            Replacing the fuel tank was my next adventure. The old tank turned out to be a 3.5-gallon Rubbermaid waste oil collection container. It was held in place with a curious assortment of bungies and fuel soaked nylon cord creatively fixed to the seat frame. It rested on a short length of steel angle bolted to the spreader tube at the bottom rear of the seat. The fuel outlet grommet had leaked, which explained the large oily stains inside the podsterior and vibration had begun eroding the bottom of the tank where it rested against the edge of the steel angle. All in all, it was a clever installation, but one that would have to be replaced. The old tank, therefore, was relegated to the trash and the search for a replacement began.

            The final effort was to remove the engine to allow replacement of the twenty-year-old Lord engine mounts. In order to make this task easier and prevent any damage, I disassembled the two-bladed Ultra Prop and removed it from the hub. During the process I discovered that two of the pitch blocks were cracked. This prompted another command decision, to switch to a three-bladed prop configuration. Three blades would allow a reduction in pitch making for a quieter system. A quick call to the good folks at Ultra-Prop had the new hub components and a third blade on the way.

            The engine and mounting plate came off the frame with very little effort, although handling it was a bit awkward. Once in the garage, the old Bing carburetor and electric starter were removed to make it ready for shipment. I intended to have it torn down, inspected and rebuilt, if necessary. The following week it went by FEDEX Ground to Olenik Aviation in Ohio for the princely sum of $26.00.

            The fiberglass components did not leave the state. Boating being a major recreation in Rhode Island, it did not take long to locate an individual skilled in fiberglass repair. Gathering up all the pieces, they nested neatly in the bed of my small pickup and were delivered to Al Millington at his company, DELCO in Newport. At first sight, Al was taken aback at how remarkably thin the pod and podsterior actually were. “Not at all seaworthy, ya know. Should be thicker,” he remarked. I explained the concept of “ultralight” and that if fortune was in my corner none of it would ever touch seawater. Reluctantly he agreed to limit his enthusiasm and forgo the yacht quality hull. He also agreed to paint the exterior with a high quality automotive paint rather than go with gel-coat. I showed him a color chip of the yellow I was looking for and then headed back to the hanger.

            The naked pilot’s cage hanging beneath the stubby center wing section now resembled the fossil of some pre-historic bird. I considered this for a moment and then reached for the wrenches that would free the cage from the wing. Once free, I set about replacing the nose wheel assembly with the redesigned unit from the factory. Bad news, it didn’t fit. The clearance between the main support plates was an eighth of an inch too narrow. @#%#$! An e-mail to Iowa brought the disappointing news that the entire run was just like it. There weren’t likely to be any more made for quite some time. This left me with the option of either filing down the main frame tubes or bending the support plates. I chose to open the plates slightly with the assistance of a bench vise. Using some care and with the now customary frustration, it eventually fit.

            Next, the old rudder pedals came off along with the curious double axles that supported them. The replacement was a single axle system obtained from Ameriplanes that removed the need for the pilot to have one leg three inches longer than the other. The pre-drilled holes in the axle support brackets, of course, didn’t match up with the holes in the frame. Liberal application of a coarse tooth round file resulted in a reasonable fit.

            From here, I moved aft on the frame, replacing the AN hardware as I went. When I reached the down tubes at the front of the seat, I pulled out my notebook and found the reminder that, during inspection, I’d discovered the tubes’ lower ends had been crushed into ovals. The large extruded aluminum brackets had also been distorted and the seat attachment hardware twisted. Looking more closely now I found the ends of the Teleflex cable bracket had been distorted, as had the ends of the steel cross tube that supported the control stick. The mechanism by which this occurred was not something I wanted to consider outside of a nightmare. Therefore, I simply resolved to replace everything and retired to my catalogs to search for the needed raw materials. Fortunately, they were found and the credit card once again took the brunt of the order. I also made a new lower seat pan to replace the torn original and a new spreader tube at the lower rear of the seat assembly. The old one had somehow been turned to Swiss cheese with drilled holes of various sizes for purposes I could only guess at.

While waiting for the new parts, I decided that disassembling the entire cage was the most expedient way to do the inspection and, in the process, ran across more tubing to be replaced. I also decided to check out the fit of the new steel sleeves for the main gear. More disappointment, like the nose gear assembly, they didn’t fit either. The walls were too thick. They would not slide over the frame or gear leg tubes. This prompted another e-mail to Ameriplanes and was met with the news that these were the components used on the new A-10s. The best option available was to file a “few thousandths” off the frame and gear tube ends to make them fit. I was not happy with this and set about finding a source for 4130 steel tubing that would replicate the original sleeves. Taking some careful measurements off the old sleeves I went back to the now dog-eared aircraft supplier catalogs, and came up dry.  After another week of searching I finally gave in and started the careful, time-consuming process of filing. Two days and some nights later I had a perfect fit. And, as luck would have it, the following day I found a source for the original tubing. @$#%^, again! In a very black mood I whipped out the trusty plastic and ordered a length of steel tubing along with several lengths of thick walled aluminum tubing to replace the main frame tubes. Another three weeks passed and with some careful cutting and drilling, I had recreated the entire lower section of the pilot’s cage. At this point I pulled out the spare set of gear legs from the company and slipped them in place to mark them for drilling. Completely deadened to any hope of success with a factory part I discovered, to my dark humor, that the new legs were quite a bit different in shape compared to the old ones. Another e-mail to Iowa along with a digital photo solved the mystery. Yes indeed, these were the gear legs from a T-10. The next day found me at the Post Office under the eagle eye of the clerk who had noted my disgruntled attitude and frequent patronage of the parcel post line with an array of odd sized packages. “No Sir,” I replied. “I am not a terrorist. I am building an airplane in my garage!” It is indeed fortunate that the postmaster and I belong to the same gun club, as he was immediately able to vouch for my patriotism and sanity. Thus, the legs headed west with the next truck.

            Back in the garage, annoyed by yet another delay, I noted that the tubing left over from the main frame tube replacement was exactly the same as that for the gear legs. Hmmm, why not make my own gear legs? I had the material, but bending it to the required angle would present a problem. I needed professional assistance. The next weekend found me haunting the garage areas of several local muffler shops that offered to try bending the tubing. None, however, could make the bend without seriously kinking the aluminum. Then, by chance, I ran into a friend who recommended a shipyard in Newport. The welding shop supervisor, with bearded smile and a thick Australian accent, offered to “have a go” but didn’t have the right size bending dies. Unfortunate, but I was getting close. The yellow pages turned up a small company in North Dartmouth, MA, N.E. Pipe and Welding, which had the right stuff. The shop owner invited me to show up after hours and they would see what they could do. After half an hour of explanations, the hydraulic cylinders hummed and I walked away with two very good replica gear legs.

            When the steel tubing for the sleeves arrived I limbered up the recently acquired Harbor Freight chop saw and cut a new set of sleeves. A splash of paint and some drilling yielded near perfect replacements. Getting the legs in place at the proper 45 degree down angle was quite a challenge. This was accomplished using a set of steel car jack supports from my Triumph sports car days and a great deal of patience. Next came the main gear wheel axles. Wheels attached, they were inserted into the gear leg ends, but how to adjust their alignment was a mystery. A magazine article from my homebuilt aircraft friend solved this with the recommendation of adjustment to neutral or slightly toe-out. Armed with this knowledge I snapped a chalk line on the pavement beneath the centerline of the pilot’s cage and began twisting the axle assemblies until the wheel hubs were parallel with the line. The result was quite satisfactory.

            The controls were next. An e-mailed photo and a few measurements from a friend with an A-10 (Yes, by God, I wasn’t alone in owning one of these things) provided the information to recreate an original throttle lever. It worked quite well. The original brake lever that came with the plane, however, was quite a different matter. It’s unusual shape and small size was not conducive to easy use. Obviously, it had once been a bicycle part modified to fit the one-inch diameter down tube.

I began the search for a replacement at the local bike shops but was unable to find anything that would fit a one-inch diameter tube. Finally, one of the cycle mechanics asked how my handlebars could possibly be one-inch, unless I’d ripped them off a Harley motorcycle. A Harley? Hmmm…this called for a visit to my neighbor who just happened to be a professional Harley-Davidson mechanic and maker of custom competition motorcycles. Later that day I was walking homeward through the woods with an old clutch lever assembly from his junk bin. It fit like a charm, but unfortunately didn’t have enough throw to fully activate the nose brake. What to do? After some brainstorming, I came up with a modified lever design that might do the job. The problem was how to get it made. It would take some serious machine shop talent. As I pondered the situation, my wife made a rare appearance in the garage to advise me of a plumbing issue with one of the bathroom toilets. Noting that my interest was elsewhere and frustration level higher than usual, she enquired as to the latest A-10 crisis. I produced the Harley lever and explained the situation. “No problem”, she intoned. “The kids at school do that stuff all the time”.

“They do?”

“Yep. Call the shops department head. He might help you out. Now about that leak…?”

Two days later I was standing amid the whir and whine of the metal working tools of the Diman Regional Vocational Technical High School machine shop in Fall River, MA explaining my problem and proposed solution. The department head, always looking for real life training projects, agreed to see what could be done and handed it off to some of his more promising students. Having made parts for projects on NASA’s space shuttle and replacement hip joints for the elderly, they quickly determined that my solution was in need of, well… refinement, but they could straighten it out. A week went by and a beautifully crafted duplicate lever with an altered geometry appeared out of my wife’s briefcase. “Yes!” I cried, and disappeared into the garage. Another problem solved! Buoyed by this success I turned to the control stick.

The control stick assembly is a clever, articulated design that allows only the upper portion to move left and right, activating the stabilators on both wings. Unfortunately, when I disassembled the stick for inspection and to replace the hardware, I noted that the ball joints that attached the control rods to the upper portion of the stick were loose. Loose enough, I discovered, to pop off if a small amount of pressure was applied in the aft direction. Harking back to the assembly video, I remembered the factory tech assembling the control stick using rod end bearings instead of the ball joints. I decided to follow suit and ordered two bearings along with a set of dust seals. While waiting for the order to arrive I decided to remove the rest of the upper stick and examine the spot welds that held the short length of aluminum tubing in place that formed the bearing around which the upper stick rotated. To my surprise they were both cracked and the tube fell out into my hand. I immediately moved to the lower portion of the stick and examined the welds that held the cross tube in place. The cross tube formed the bearing which allowed the stick to move fore and aft for pitch control. Earlier designs had small spot welds that were prone to cracking, while the later ones were welded completely around. Luckily, mine was one of the later models and the welds were intact. Dealing with the upper bearing was now the problem. My first thought was to have the small tube welded back in place within the thin walled main stick. Doing so, however, was not very appealing. Replacement sounded like the way to go. So, I fired off an e-mail to Larry Smith at Ameriplanes to find out the cost of a new lower control stick. The answer was expensive and would involve a considerable wait, since there were none presently in stock. Okay, a redesign and repair was in my future.

After studying the stick and the gaping hole where the original bearing used to be, I decided to reinforce the upper portion of the lower stick with a steel sleeve and devised a bolt-on bearing assembly that did not require welding. It also raised the upper stick pivot point about a half an inch to make room for the added length of the rod end bearings. I was on the phone the following day ordering the steel tubing.

The steel tubing and the rod end bearings showed up at about the same time. The cutting, drilling and assembly went off very well resulting in a very rugged stick.  The next move was to install the custom stick grip to which I had added a palm rest, ala an old F-86 grip I’d once had as a kid. It looked good, very good. So good that I decided a test “flight” down the driveway was in order.

It took a while, and some vague promises about a car, but my teenaged daughters finally agreed to simulate the motive power of the Rotax 277 for an unspecified number of test runs. And, to my amazement, both the nose wheel steering and the brake worked. On the down side, I discovered that the old vinyl seat cover was falling apart at the seams. Not unusual for a piece almost twenty years old. So, I set out to have a replacement made.

The next weekend found me at Alan’s, a local upholstery shop that specialized in custom car and auto restoration work. Oddly enough it was not the first job he’d done for an Ultralight. In the corner of a collage of pictures, Alan, the owner, pointed to a photo of a Mini-Max with a Red Baron paint job. The seat and the canopy cover were “his”.

Success, however, was short lived. The following week a box arrived from Aircraft Spruce containing my airspeed indicator and altimeter. Both had large orange REJECT stickers attached. A call to California confirmed that neither was worth the effort or money to repair. Another setback.

            So, with another order in place for replacement instruments, I turned to the fuel system and the engine. Be sure to tune in next week for more frustration in Episode IV.

Episode III pictures

Bulletin from Scott  McCarthy

Episode I   Episode II   Episode IV   Episode V   Episode VI   Episode VII   Episode VIII   Episode IX   Episode X

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