3- the Overhead

Translation by Christian Girardet


 

The overhead, also known as “Upper Panel” in French airplanes, includes 12 working panels and 3 blank panels. The yellow panels on the plan are the most important for us and will be the first to be installed.

 

In this chapter, you will find a description of the overhead structure, of its components as well as of the wood support holding it.

 

The paragraphs are following the logical order of building the overhead, with sometimes some back and forth on the same topic.

 

 The V.U. have been cut to their precise outer dimension and checked for squareness.

 

Lay the V.U. panels on the floor and before drilling them, make their aluminum support : L shape aluminum profile for the outside and T shape aluminum profile for the 2 inner rails.

 

If your V.U. panels come from different suppliers, you must wait to have received all of them before starting the overhead frame: differences in dimensions can create havoc.

 


Aluminium frame

 You will need 5 meters of L aluminum profile (15mm x 15 mm) and 2.5 meters of T profile (20mm x 20mm).

The number of cuts in the L profile can be reduced to a minimum by bending the profile at each of the overhead corner. Even then you will not be able to build the whole overhead outside frame with only one 2.5 meter length, unless you build the front and the back overhead sections separately.

 

Precise measurements and markings are essential and remember that each bend will “use up” a bit of the profile length. Start with the front side (2 bends). The side section will require a “V” cut in the profile done with a saw. The other sides will be cut to the length measured when we put the V.U. on the floor, keeping a 2mm spacing between panels plus 2 mm for each end. The panels will be screwed on the profiles using 3mm screws with washer and nut. The removal of a V.U. panel cannot therefore be done just externally but will require the overhead to swivel and therefore some hinges will have to be installed. This setting with hinges will be extremely useful when wiring the overhead or for maintenance operations.

 

The precise location of the 2 T rails will be found by placing the V.U. panels on the L profile frame: check for squareness and make a mark.

 

Even with the T rails installed, the whole frame will remain quite flexible once finished. The rigidity will be provided by the V.U. panels themselves. Keep in mind that the whole overhead will weigh close to 10 kg (22 lbs). It is highly recommended to reinforce each of the bent corners with an aluminum piece (2mm) under the horizontal part of the L frame, and to screw this piece with two 3mm screws. The rigidity will be greatly improved. Another approach to building this frame would be to use steel and welding: no rigidity concern there!

 

An exact reproduction of the real Airbus Overhead will require to set the 2 lateral sections of the overhead at a 5 degree angle with the central section. This brings in much complexity to the assembly, requires adjustments to the wood frame as the L profile rails will not be parallel to the wood frame any more. I did not follow this route.

 

Now the frame is completed and we have to drill the holes for the screws in the V.U. panels to attach them to our overhead frame.


Of slots and screws…

All the screws holes should be drilled at 5 mm from the edge. Still it is wise to check for each V.U. panel that with a hole made there, one will be able to put a corresponding nut under the profile and that there will room to tighten with a socket. As mistakes were possible at that stage we decided to first build the frame and then drill the V.U. panels

 

Each screw is at the center of a half-circle slot. Cutting these slots without heating up the Plexi turned out to be impossible with a router, regardless of the router bit I used. The only solution which turned out to be practical is the following:

Put some masking tape where the cuts will be made. With a Vernier caliper set at 5mm, trace a mark parallel to the edge of the panel. We will drill 12mm slots which therefore will not be exactly tangent to the panel edge. Repeat at the other end of the panel, but be careful, some V.U. panels actually have a slot right in the middle.

 

 -  Use a Dremel (set at 5,000 rpm) with a small round bit to mark the center of the hole (this is more prudent this way than to use a punch and a hammer…)

 

 - On a press drill, drill a centering hole though the panel with a 3mm drill.

 

 - Take a 12 mm boring spade bit, like the one on the picture.

 

Two panel variants are possible: either a 6mm thick panel or two stacked 3mm panels. For the 3mm Plexi (like those made by Opencockpit or Cockpitsonic), drill with the spade bit only half way down, flip the panel and finish the hole. Use some water to prevent heat while drilling. Though the bit will not bite as well because of the water lubrication, the Plexi will not heat up and you will get a very clean cut. If you push too hard, steam will be produced well before the Plexi reaches its fusion temperature, giving you a good warning to ease off a bit.

 

For the thick panels variant (6mm) set the press drill depth so that the bit will not go deeper than half the panel thickness. Once the drill bit is well centered in the 3mm pilot hole, it will cut the slot only halfway through the panel thickness. The remaining portion of the pilot hole will be used for screwing the panel onto the overhead frame.

 

In both cases, we now have a 12mm hole tangent to the edge of the panel: it has to be turned into a slot…

 

For the thin panels (3mm), it can easily be done with a file, holding the panel with a vice.

 

For the thicker panels (6mm) this is more difficult as one cannot use the file and the Dremel router bits skip or slide too easily. All that is left is the Dremel rotary filing stone (10mm). Running at 5,000 rpm with a Dremel 400, it did not cause the Plexi to melt and opening the hole into a slot was after all quite easy. No need for water here.

One can even round up the corners as on actual Airbus V.U. panels.

 

These slots as well as the sides of the panels will be painted with 2 layers of RAL 7011 to avoid backlight leaks.

 

The blank panels can be made of particle board and the slots cuts will follow the same process. You will likely need to prime the sides slightly before painting.

 

 

 

To simulate Dzus fasteners holding the panels to the frame, take some plastic tube 5 mm x 6 mm. Enlarge the center hole to 5.5 mm, cut the tube in 3mm long pieces with a cutter knife. Place a 3 mm screw into our 3 mm long plastic tube part, glue the screw in the tube with some type of superglue. Paint with blue-grey RAL 7011. If the head screw is pushed a little bit into the tube, the result will look pretty close to the original Dzus.


Of round holes and square holes…

The files to drill the holes of the V.U. panels can be found in the downloadable drawings listing , in chapter 2 "making the panels". To drill the holes, I printed an inverse drawing of each V.U. on a transparent adhesive sheet A4 format. After placing the sheet on the panel and having drilled the holes, remove the sheet, adhesive traces can be removed with solvent.

 

If they are not already on the drawing, trace the diagonals of the square holes to find the center. With a small round Dremel bit mark the center of the holes at the intersection of the diagonals. Drill the holes with a 3mm bit, not larger.

 

Round holes are usually easy to drill. Still, remember that regular metal drill bits are really not the type of bit needed to drill through Plexiglas. If not careful, you will end up with a hole looking like the one on the following picture:

 

If you chose not to adapt your drill bit, drill at slow speed one side of the Plexi and then on other side. The cut will be clean (hole #2)

 

 

 

Note that with thick Plexiglas panels (5mm thick and above) you may not be able to tighten the nut on the screw threads. In that case make your through hole at the right diameter and then with a large bit, drill half way through to make space for the nut (see hole #3 on the picture). Drill wide enough that you will be able to use a socket wrench to tighten the nut. This is particularly the case with rotary switches.

 

Korry switches square holes, as well as rectangular holes for some other components, are a bit more tedious to make. Make a centering 3mm hole at the intersection of the diagonals. Using a 18mm spade bit drill make a round hole, drilling half way through one side, flip the panel and finish the hole from the other side. Secure the panel into a vise; make sure the jaws are protected so that they don’t scratch the Plexi. Using a medium square file (not a fine file) enlarge the hole to the mark/lines on the drawing. Dry fit the component and finish with a fine file. The rough-in can be done suing a special Dremel bit for plastic/Plexi.

 

This method can be used for all V.U. panels.

 

Drill and tap the holes for the Korry screws and other components such as DB connectors.

 

The overhead can now be attached to the wooden frame.

 


Notes:

 

 

1- As mentioned earlier, the panel base color will change a lot depending on the printer and the paper you use and there will be trials and errors before you get the right RAL 7011… Photoshop and other similar software will enable you to adjust the various components of the color…

 

2- This part about the overhead was written before CNC machines became more widespread and found their way into hobby applications. These machines will cut the panels and engrave them with great accuracy: a dream come true! The French Air Cockpit forum hosts a whole section dedicated to CNCs.


Windshield center post:

 Time to move to the windshield center post which also forms the front support for the overhead. The French term is “gallows”, so “center post” it will be!

 

The post is attached to the F and G boards of the CEN block (15 mm particle board) with 2 steel brackets (40mm x 40mm x 40mm). These brackets are permanently fixed to the post (wood screws 4mm x 30mm) but can be unfastened on the F and G boards (5mm x 30mm metal screws).

center post drawing
center post drawing

 

 

 The post 2 sections can be glued together with a simple butt joint re-enforced with 2 steel plates in each side of the post. Even better would be to use a finger joint (bridle joint or open tenon joint): it is cleaner and stronger. You should not have to push hard to put together the joint together.

 

 

 

 

 

 

 Glue, drill two holes for wood dowels (10mm). Use strong wood glue.

 

 


Overhead wooden frame:

Four pieces of wood (100 mm wide) are listed in the Excel “Débit du bois” sheet. The OVH 7 to 9 pieces can be cut from one piece, accounting for the angle cuts at the corners. The assembly will start with the 3 front pieces of the overhead frame. After planning and sanding, glue these 3 pieces with strong wood glue.

 

The other sides and the piece separating the front and the back overhead are simpler. After gluing, re-enforce with 40x40x40mm steel brackets. Each bracket requires six 5x15 metal screws. These brackets are located 15mm front the top of the overhead sides and not in the middle of the 100mm wide side pieces. Use a carpenter square during the whole process to check that all parts are square with each other as well as perfectly vertical to your workbench surface.

 

Do not forget to make a hole for the cables/wires between the front and the rear part of the overhead as well as 2 notches (either in the front or the back side of the overhead depending on the location of your computer) for the wire bundle to exit the overhead.

Once the glue is perfectly cured, reinforce the connection between the faces with four 20x200mm steel bands, bent to the appropriate angle and screwed with 5x15 metal screws. At this point the whole contraption is already quite sturdy.

 

It will be even stronger with the addition of the large 43x43mm section piece of wood which will support the whole overhead. This piece will be set at the top of the center post (cut to the appropriate angle) and screwed in. Its initial length will be 1.90 meter to start and will be adjusted as needed. At the wall side, the overhead will be attached to one of the 43x43mm steps of the “ladder”.

 

Our 43x43mm wood rail is connected to the overhead using three 40x40x40mm brackets with 5x15  metal screws at the top of the boards in the front, rear and center of the overhead. Proper alignment and centering are keys to avoid seeing your overhead box take a diamond shape while being screwed to the wood rail. Check that everything is aligned and straight with a carpenter square. To attach the steel brackets to the wood rail first use some 4x20  wood screws without driving them in too deep. When all is fixed, put the whole overhead wood frame contraption on the cockpit (without the V.U. panels : it will save some weight !).


The wall “ladder”:

We will call this part “the ladder” (though it looks more like some rugby goal posts). It is made of 2 vertical 43x43mm wood rails (2,40 meter long) connected together with 2 cross-pieces of same cross-section. The first cross-piece is attached directly to the floor. The second is attached higher to the ladder, with its lower face at 1,755 meter from the floor.

 

These 4 pieces can be butt glued (with some 40x40x40mm steel brackets for added strength) or better, with a half lap joint and two 10mm wood dowels at each connection.

 

The ladder width should be at a minimum 800mm wide and 950mm at maximum. Make sure you select perfectly straight pieces of wood: long wood pieces as these often show some warping.

 

The bottom cross-piece is attached to the floor. To allow this, drill the CPT and FO floors and install some 6x80mm TF bolts (with their head embedded into the lower side of the floor). These screws are spaced every 60cm. The cross-piece will be drilled with corresponding 7mm diameter holes for the screws to go through. Use large washers and Nylstop nuts for fastening. This cross-piece will also keep the center floors in place and prevent them from moving.

 

The top cross-piece will support the rear of the Overhead frame.

 

A practical trick for easy removal is to connect the Overhead frame to the upper cross piece on the ladder using 2 slip hinges. With this type of hinges, it is very easy to disconnect the overhead from the ladder just with a lateral push. In case you have an aluminum frame for the rear Overhead V.U. panels, make sure the screws heads holding the slip hinges on the overhead wood frame are place inside the frame: the bolt nuts will not be visible as they will be facing the wall.

 

Putting the overhead in place is very simple: install the center post and the ladder, lift the overhead wood frame, connect it to the hinges on the ladder, put the overhead large wood rail on the top of the center post and screw it with two 6x60 screws.

 

The ladder could be screwed into the wall, but this is not really needed: once it is in place, the whole ensemble is quite rigid by itself. No plan for the ladder: the design is quite obvious…

 


Back to the overhead frame:

Once the ladder is secured vertically, slide the overhead into the slip hinges and lower the ensemble until the overhead rail touches the center post. If everything is square, it will land right on top of it. Let the rail descend on one side of the center post by pulling it laterally, until the lower edge of the overhead frame front stands at 1,325mm from the floor. Check that the overhead is parallel to the glare-shield. If everything is right, the front face of the overhead frame should be at 1,145mm from the wall and at 855mm from the front of the cockpit. Hold the rail in this relative position to the center post with a clamp. Mark the cut lines on the rail and the post.

 

Parallelism check of Overhead and Glare-shield:

 

 

Everything can now be taken apart. Cut the center post precisely, take the rail off the frame (temporary 4x20mm screws), cut the rail and paint everything. Put the rail temporarily back on the overhead wood frame, re-install the center post in its definitive place securing it with the four 40x40x40mm steel brackets.

 

 

Using two 200x16mm perforated steel bars (perf bars), mark the center for two 6.5 mm holes on the overhead rail. Remove one more time the rail from the overhead box, and with a press drill, make 2 perfectly perpendicular 6.5mm holes in the rail. Use some 6x60 metal screws to fasten the perf bars to the rail. The rail is then finally re-attached to the overhead –this time, definitively- with some 4x30mm screws. Make sure to taper the holes in the perf bars so that the 4x30 screws heads are mounted flush. Slide the overhead back on to the slip hinges.

 

With the two 6x60 screws holding the perf bars, align the rail at top of the center post, and screw the perf bars to the post with 4x30 wood screws. From now on, the two perf bars cannot be removed from the center post: for assembly, just slide the rail between them and tighten with the two 6x60 screws with their washers and Nylstop nuts.

 

 

With the ladder and the CEN block attached to the floor, the whole system is quite rigid front to back. Laterally, the overhead wood frame has a few mm of play as well as some play in torsion. The overhead can be left as such and the slight flexing is not a problem when pressing a Korry switch. This gives us a cockpit with an open structure, without windshield. All in all, this makes the construction so much easier.

 

At this stage, here is an overall view of the cockpit:

Another picture, slightly edited for clarity (the room is actually quite a mess…)
Another picture, slightly edited for clarity (the room is actually quite a mess…)

 

Now, take the overhead down one more to install the V.U. aluminum frame


Assembly of the 2 overhead V.U. panels.

We have used the term “overhead” in the singular form all along. It comprises actually 2 sections: the front overhead and the rear overhead.

 

The rear overhead can be equipped either with a picture of the breaker panel, with a non- functional panel replica or to be completely true to the real thing, with actual breakers. This is up to you.

 

The front and rear aluminum frames are set on hinges for easier access.

 

 In the close position, the frames are locked with by pins.


V.U. panels back-lighting

This is for the front overhead only. Each of its sections is closed at the top with a “lid”: this is a 3mm particle board resting on a series of 10x10mm rails. The 2 lids are installed by sliding one side under the overhead rail, slightly angled toward the back; the other end is then slightly bent upward, to enable it to rest on the series of 10x10mm rails. The slight warping is what keeps them into position. The steel brackets, holding the overhead rail to the overhead wooden frame do not protrude, and there is no risk to scratch these lids.

 

The inside of each lid is painted white, the outside, like everything else on the overhead is a very dark blue.

 

The V.U. panels’ back-lighting is installed on the lid, and not on each individual V.U. panel. The latter would have required using an additional Plexi sheet. I have used white LEDs ribbons available at that time, from Hong-Kong. These bands comprise 60 to 300 LEDs each and can be split in lengths of multiple of 3 LEDs.

 

These are placed as best as possible parallel to the overhead width, under the text or symbols to be retro-lit. Keep in mind that Korry switches will cast a shadow onto the back of the V.U. panels. The LEDs will run on 12 Volts DC. This system provides a very homogeneous light, without any “light spot” on the V.U. panels. The rear overhead is not back lit.

 

The light of these LEDs is white with blue overtones, quite far from the actual orange light of the A320. One solution would be to use 2 gelatin colored filters, one yellow and one red, covering all of the overhead LEDs. One issue with this is that 3 of the V.U. panels have green lines engraved needing a green light. Red/orange light on the laser color printed green of these panels is quite ugly…I chose to use white LEDs for the whole Overhead and, on the back of the black and white flashed film of the V.U. panels, I put a coat of transparent yellow paint used by stain glass window hobbyists. This paint can be found in any art supplies or Hobby store. Practically, one thick coat will be enough. For the green lines of those 3 V.U. panels, use the green version of that paint. The result is very transparent; the paint does not get dissolved by the contact glue we used to put the films on the Plexi panels. This approach will work similarly with all other panels in the cockpit, including the pedestal and the glare-shield, though these do not have any orange text.

 

For the detailed description of the making of the transparent films to apply to the V.U. panels, refer to chapter 2 “ panel building ”.