Burnelli CBY-3 Restoration Diary

June 2017 update on the restoration of the Burnelli CBY-3 "Loadmaster" from restoration Crew Chief, Harry Newman.

"Field Expedient Repairs"

When the CBY-3 restoration began our restoration crew was faced with several generic issues with the aircraft's overall condition including preexisting structural damage, widespread pockets of corrosion and wear and tear from the time it was in service - often operating out of rough airstrips. All of these conditions proved to be challenges for our crew. The majority of the structural issues have been resolved and work continues on addressing the remaining corrosion pockets - several of which will be described later in this narrative.

The "wear and tear" issues - of which there are many - presented our crew with decisions about which issues should be restored and which should be left as they were found since they represent an important aspect of the CBY-3's operational history. Adding to this history has been the ongoing discovery of numerous "field expedient repairs," which our crew has dubbed "FERs."

Some examples of FERs are numerous sheet-metal patches that are evident on the underside of the CBY-3's fuselage. We believe these resulted from rough field operations in South America and Canada during the 1950's. As we removed some of the patches we found many punctures and gashes to the hull - most likely resulting from foreign object debris on the landing strips. Additionally, portions of the lower surfaces are pockmarked with numerous small dents, also consistent with gravel and stones from unimproved fields.

Since the CBY-3 fuselage was not pressurized these patches were adequate. However, we have also found examples where the structural integrity could have been compromised such as severed floor "stringers" where patches were bolted in place to span the damage.

Faced with hull punctures and tears while operating in very remote areas, the CBY-3 crews and mechanics apparently used whatever materials were available to cope with the damage and return the aircraft to operation, perhaps with the intent to make permanent repairs at a later date.

Since it is not our intent to return the CBY-3 to flying condition, our approach during this restoration has been to preserve many of the FERs in situ, while repairing or replacing those where the aircraft's structural integrity is impacted. Where a FER is located on a skin panel that requires replacement due to widespread corrosion, the FER will not be preserved or reproduced. In one instance a FER was found where a long piece of steel angle-iron was bolted in place to span a damaged area along an aluminum structural channel in the floor substructure. Over time this repair disintegrated and separated at a bulkhead joint, possibly the result of dissimilar metal (galvanic) corrosion. In this case the damage compromised the structural integrity of the fuselage. The FER was removed by volunteer Don Durner who then made the repairs using appropriate techniques and materials, thereby restoring structural integrity.

Preserving FERs While Ensuring Structural Integrity

This is a photo of a section of the cargo bay floor under-structure at the junction of the number 3 bulkhead on the starboard side of the CBY-3. Several examples of "field expedient repairs" (FERs) are evident that date back to the aircraft's period of operation. A simple patch had been riveted in place on the lower horizontal stringer to mend a crack. A similar patch was installed on the next stringer, and a piece of steel angle-iron had been installed in the corner channel to replace a damaged section that had been removed. In this case the two stringer FERs will be preserved in place as part of the CBY-3's history, but the corroded channel FER needed to be repaired since it compromised the structural integrity of the fuselage. We elected to address this issue by replacing the field repair with new materials to restore structural integrity. The finished work is apparent in the photo below.

Ongoing Corrosion Ameliorization

Some of the most challenging repairs to the CBY-3 involve addressing the nemesis of older aircraft - corrosion. Each such area requires a customized solution that involves excising the affected area and designing, fabricating and installing replacement components. Solutions to each of the impacted areas have been formulated and great progress has been made addressing these issues.

A pocket of extensive corrosion was evident on the CBY-3's external top surface where the heater bay dome meets the fuselage. The corrosion had spread to the underlying structure, so parts had to be fabricated from scratch. Bob Upson has taken on this task and it is nearing completion. Bob has experience in such work, having built and flown his own aerobatic aircraft.

The topside heater bay dome where the combustion heater's exhaust pipe exits the aircraft. Extensive repairs were made to the underlying structure and skin before adding the plates (shiny areas) which, in actual practice would protect the skin from the heater's exhaust. They have yet to be permanently attached and the exhaust port and cover have yet to be installed.
Volunteer Bob Upson making repairs to the heater bay dome on the CBY's top surface

This photo is of the heater bay which is located in the cockpit dome behind the pilots. At the floor of the bay is an extreme example of exfoliation corrosion. The products of this type of corrosion forces the material to move away from the body, so these products occupy a greater volume than the volume of the parent metal, thus causing the metal to exfoliate or delaminate. In this case the area of exfoliation occupies 7 times the original parent aluminum plate.

The same area after the heater had been removed and the corroded sections had been excised by volunteers Tom Palshaw and Wayne Dow. This process also involved milling the center cross-structure to arrest the spread of corrosion. Tom and Wayne are now designing and fabricating replacement sections. When that is completed we will begin the reinstallation of the large combustion heater.

Right Accessory Bay

Now that the corrosion issues in the right accessory bay have been addressed the area is being prepped and primed before the new structural components can be installed. As noted in the previous updates, all of the electrical junction boxes, racks, cabling, tubing and other components were removed from the bay, restored and set aside for reinstallation.

Storage rack containing all of the restored components which will soon be reinstalled in the right accessory bay

Cockpit and Rudder Pedals

The restoration of the cockpit has advanced to the point where a number of components can be reinstalled, including the rudder pedals. Much remains to be done in the cockpit but a turning point has been reached as reassembly of the area begins after 12 months of preparatory work by volunteer John Smith. The photo at the right shows the newly restored and installed rudder pedal assembly. (The plywood flooring is temporary and will eventually be replaced.)

Right Wing

The restoration of the wings continues in stages. After the right wing's lower surface had received a primer coat it was turned over on the workbenches so the top surface could be prepared. Numerous repairs were completed and it is ready to be primed. Originally there were two hard points in the top surface that once housed hardware for installing lifting eyes. These lifting points were compromised and could not be used. We decided to install modified lifting points to assist us in installing the wings in the future. Our machinists, Sandy Brown and Henry Bachand designed and fabricated new hardware which was then installed by Doug Davis. This required removing small sections of the wing skin in order to remove the old hardware and to inspect the stability of the underlying structure. Once the new hardware was installed we did a test lift of the 1600 pound wing, hoisting it several inches off the workbenches. This also enabled us to accurately determine the center of gravity of the wing and to devise a plan for future installation on the aircraft. New covers for the modified lifting points were then fabricated and installed. When the right wing top surface is primed it will be put into storage until such time it is mated to the CBY-3 fuselage.

Next we plan to bring the left wing back into restoration to repeat the procedure of preparing the top surface and installing modified lifting hard points.

Sheet Metal replacement - Lower Fuselage

As mentioned earlier in this narrative, the lower surfaces of the fuselage have sustained a lot of damage over time which necessitates replacement of a number of sheet metal panels and numerous repairs to others. The panels to be replaced have been identified and are being removed and replaced one at a time to ensure the integrity of the CBY-3s monocoque construction, where the skin carries the load forces on the aircraft. Replacing one panel at a time minimizes the chances that the fuselage will become distorted as panels are removed.

This is view of a section of the lower aft fuselage showing the type of preexisting damage to the CBY-3's skin. The open area to the left is the rear landing gear wheel well. The orange markings depict areas to be repaired or replaced and the blue tape marks the existing seams and rivet lines.

This is a view of the same section at a different angle - from the aft looking forward at the underside of the fuselage. Here the rear wheel well is seen at the top. The severely damaged sheet metal panel has been carefully de-riveted and removed, and the replacement panel has been temporarily mounted in place after repairs to the understructure were made. The many hundreds of rivet holes are then precisely located and drilled in the new panel. It will soon be permanently riveted in place allowing the next panel to be removed.

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