The Aileron Bay Project.

Started: 11/11/1980
Finished: In Progress

One of the Comet's pioneering features was the use of hydraulic-only actuators for all of the primary flight controls (ailerons, elevators, and rudder). In other words, the Comet was a fly-by-hydraulics aircraft with no direct linkage between these surfaces and the cockpit's yokes and rudder pedals. Although hydraulic flight controls had been used for a time in military aircraft, the Comet was the first civil transport to have them.

This was very brave engineering for a design concept that was essentially complete in 1946. Hatfield engineers tell me that the major motivation for doing this was the hydraulic system's natural damping of control surface flutter.

There were many special details, including totally new seal designs, and extensive redundancy to avoid loss of control due to hydraulic failure. For instance, the aileron control bay features servodyne cylinders massively sized for the few pounds of force they have to deliver to the ailerons, plus there are no less than six levels of system redundancy, all of which would have to fail before the pilot lost control of the ailerons.

Incidentally, I have not been able to find any record of hull loss or accident due to hydraulic failure. The early systems in the MK 1 tended to leak and be messy, but with reasonable attention, they did not fail. Given the historic significance of this feature, we decided that the aileron control bay should be an important part of the display. Although it was in truly terrible shape, all of the parts had to be removed and restored to static display standards. The plan was to completely rework all of the components and re-install them to achieve a 'like new' appearance.

We gained first access to the area during the general removal of most of the aircraft's floorboards, including the compartment just aft of the wing center section. This was done soon after the beginning of restoration, in mid 1996. Work on the bay itself began in September 1999 with removal of the bay's floor support structure.


Our crew then removed the compartment's smaller components. Badly corroded items included:

1. The cabin pressure control system
2. Hydraulic reservoir and associated plumbing
3. Servodyne control and feedback cables, including those for the ailerons, the rudder, and the elevators.
4. Complex (and very foul) cable tensioner assemblies
5. Backup electrical motor driven hydraulic pump assembly
6. Autopilot control input actuator

The very advanced corrosion we found made removal of the two major servodyne assemblies extremely difficult. After literally days of trying, we could not break free the units, which have large magnesium casting frames, from the pressure hull-mating surface. After much twisting, prying, jacking, and general brute force effort, we were still not able to free them.

We eventually found that the magnesium frames had become so corroded that they had become forcibly imbedded in the surrounding airframe. The only recourse was to painstakingly work a broken off hacksaw blade around the castings to free them. When the mass of magnesium oxide had been severed, the assemblies slipped right off. After initial cleanup, the corrosion damage was very evident.

After removal, subassemblies were carefully photographed to make a record of their original condition, assembly details, and the correct type of finish. Each component from this bay has been given a thorough and time-consuming restoration. For instance, the servodyne assemblies had to be completely disassembled into more than a hundred separate parts.

Each part was then cleaned and repaired as needed, then pickled (Aluminum parts were Alodyned; Magnesium and steel parts received other chemical preparation. Next, the parts were primed and painted. At the end of this process, the finished parts were given a careful final color coat to reproduce the original appearance.

After what seemed like eons, we finally have a completed aileron bay