Sunday, 28 March 2010

A new Battery Box

Mid February and the fuselage frame had one coat of epoxy primer applied. I would have liked to get to the stage of painting the acrylic top coat but have decided to wait until the warmer summer months as it will be easier to apply with the warmer, dryer weather. In the mean time I managed to give the frame a second epoxy coat, spray up some of the tail surfaces and start to fit out the cockpit area. This will be a first fit process allowing me to construct a new interior, fit it and make sure everything works before I finally top coat the fuselage. The sort of items that new working on are the new instrument panel, seats, baggage sling, parcel shelf, harnesses, stringers, trim system etc ... the list is endless.

To begin, I fitted the new floorboards and bulkhead forward of the seat. This is where the new battery box will be sited (previously it was under the seat sling which was difficult to access when changing batteries). I spent some time pondering various designs of battery box, most of which were prototyped in card prior to settling on the final design.

One of the earlier box designs; looks OK but how do you lift the batteries out?

The final criteria for the battery box was:
  • Should be lightweight.
  • Should be simple to construct.
  • Should protect the batteries and wiring from accidental damage from pilot & passenger.
  • Should take up minimal space in the cockpit.
  • Batteries should be easily replaced.
  • Machine screws/anchor nuts should be used to secure the battery box.

The final design consists of a simple tray made from aluminium angle which will be secured to the floorboards with machine screws. The underside of the floorboards will have an aluminium plate, with anchor nuts riveted on, bonded to the floor. The two batteries will sit in the tray and be enclosed by an aluminium cover fixed to the floor and bulkhead in a similar fashion to the tray.

The tray and cover sit over the centre join of the floorboards and will help secure them as there is no fuselage framework at this point to support the floor.

The tray will take two 12V, 7Ah batteries. The corners were simply cut at 45 degrees with a band saw.

The cover was marked out on a single sheet of 0.032 NS4 aluminium (equivalent to 5251 H22) using a fine permanent marker (not pencil), remembering to add between 1/16" and 1/8" for the bends. All fixing holes were pre-drilled prior to bending. The sheet was guillotined and the main bends made on a sheet metal folder. Some of the bends had to be done by hand later.

Two photo's showing the cover in place prior to final riveting

Inside the cover, two pieces of angle have been riveted in place. These clamp the batteries down preventing the positive/negative terminals from touching the case itself.

Wiring will pass through the bulkhead and be routed to the instrument panel along the port cockpit side. I have not made up the fixing plates yet but they should be ready to fix in place within the next week. After that the cover and tray will be painted.

The next task will be the construction of the parcel shelf. This should be fairly straightforward, I hope.