NOTE: This page is a work in progress and not yet fully complete.
The Forward (FWD) and Aft (AFT) overhead is probably THE crown jewel in a 737 cockpit. As the name implies, it is situated above the pilot’s heads. It is used to control and manage vital systems of the aircraft such as the fuel system, hydraulic control system, pressurization systems, electrical systems, and air conditioning/heating among others.
While primarily used during startup and shutdown, and of course emergencies, it otherwise goes largely untouched. Still, it is a critical piece of hardware that you’ll eventually want and need in your cockpit if you want to accurately simulate real-world ops. And you’ll probably agree it’s one of the coolest parts of the 737 cockpit.
Here is a photo from a real 737-800 I took while visiting a maintenance hangar:
I liken the overhead to a modern pinball machine. There are many, many indicators that light up and lots of switches that trigger based on various events. It’s all very complicated behind the scenes, but it’s a pleasure to look at and play with!
So what are the options for building an Overhead?
While the overhead is extremely important, when you’re first building your sim this is probably something you’re going to have to live without for a while because it can be expensive to acquire. But when you’re ready, which route should you go?
Depending on your desire for realism, your skill-level with building things, and your budget you have many options available for overheads in your simulator. Some options include:
- Using a virtual overhead, that is a monitor that you hang above you that displays a “virtual” overhead. Many static trainers at the airlines are built with virtual panels to cut down on cost but still keep things accurate. You’ll want a large touchscreen to make sure the switches and knobs are functional to the touch. This is probably one of the simplest, if not cheapest methods to recreate the overhead.
- Creating a scale printed/laminated overhead picture mounted to a backboard, and replacing the printed switches and knobs with real ones. This is a little more complex because now you need to wire everything together and connect to interface boards. But you don’t have to replicate every switch and dial, at least not at first, just the ones you feel are most important to you. Then add more as you get more comfortable.
- Building your own frame and adding individual simulated acrylic panels from reputable vendors and mounting/wiring them a little at a time. This definitely more expensive and complicated since you’ll now have to buy the panels in addition to the hardware and interface boards and wire it all up. Don’t forget you’ll eventually need gauges and backlighting!
- Buying a plug-and-play overhead. This is the most easy to implement, but most expensive option. Looking back, maybe I should have gone this route!
What path did I choose?
I chose the option to build my own overhead. My requirements were that I wanted a fully functional overhead that looked and operated accurately, at the cheapest cost. Isn’t that what we all want? I looked at the plug-and-play options and couldn’t swallow the cost, so I thought I could save money doing it myself (in reality, when I was done I didn’t really save much…more later).
I knew it would be a challenge, but boy was it ever! Not only is building your an overhead a VERY time-consuming and tedious process, but I didn’t know what I really needed, what parts were best for what I wanted to do, where would I get it all, and in the end, how would I put it all together. There was no instruction manual.
So I watched lots of YouTube videos, looked at other simmers web sites, talked to others who have gone down this path, etc. I researched them all. That certainly helped prepare me, but in the end each build is unique and there still were plenty of headaches and re-dos. With patience and time, however, it all eventually came together.
Here are a couple of shots of my overhead as of November, 2017. It probably took around 8-10 weeks to get to this point from scratch.
How did I do it?
I honestly didn’t know where to begin. I knew I first needed to build a frame. But how big should it be? What should it be made of? How would it work? Then I had to fill it with switches and knobs. Then wire it all. And finally back-light it all. There was a lot to do.
I started out buying an overhead panel and hardware set from CockpitSimParts out of the UK. Unfortunately, at the time I purchased them they were 5mm thick instead of the real 6mm thick, and had acrylic back panels instead of metal which can be a problem for heavy use, but for the money they were well worth the cost.
I laid out those panels on a large piece of cardboard, arranged them in the proper order, then traced around the perimeter with a pencil and marked all the mounting holes. This gave me the outer frame design and the location of all the screw holes the panels would mount to.
I decided I wanted this to be an enclosed box that would allow me to easily transport the overhead as a single, self-contained unit but it would have the ability to swing down the panels so I could easily do maintenance or upgrades if I needed to. I didn’t want to have to remove the entire heavy overhead each time I had to fix something.
So I first started framing the swing-down top, using the drawing I had made earlier as a guide. I laid out a wood frame that would be strong, but not interfere with the internal components, and kept test-fitting the panels as I went to make sure everything lined up right and adjusted as necessary for clearances needed.
NOTE: If I had the metal-working tools/skills, I would have made it out of aluminum instead for a much better strength to weight ratio, and allowing me to have thinner frame walls reducing clearance issues. Something to think about for your build.
Once that was complete, I started building the lower portion of the box, estimating about how high the box needed to be based on the clearance I had available with my FlightDeck Solutions cockpit shell. I also included a “hump” in the middle of the box to accommodate the cross-brace in the FDS cockpit shell, which unfortunately reduced internal space a bit. That cross-brace is only necessary if you plan to ever use the FDS overhead mounting frame, but I chose to leave it for strength. It is at this point I also test-fitted the box into my cockpit shell to determine the proper mounting location, drill the mounting holes, and test general fitment.
Lastly, I added some piano hinges at the rear of the box to allow the top part of the frame (where the panels mount to) to swing down, and added some simple locking catch-latches at the front to keep the box closed when in use, but easily unlatch if I wanted to swing it down. I ran into some issues with that which I’ll talk about later. I then sealed the box with wood primer, and painted the box with white latex paint inside (for reflecting light when I added back-lighting) and Iron Grey latex paint on the outside to match the Boeing dark grey color of the cockpit.
You can see the progression in the photo gallery at the bottom of this page.
Adding The Panels
So now I started assembling the CockpitSimParts panels I purchased. Again, I chose a complete CockpitSimParts panel set due to their general accuracy compared to others on the market, and the very reasonable cost. It also ensured I had one standard panel set to work with rather than a mix of various panels that may or may not be sized consistently. It’s up to you to make the best choice that works for you.
NOTE: You can buy overhead panels from almost anyone these days, both in kit form and plug-and-play. Just do your research to make sure they are of a quality, durability, and accuracy that meet your needs. Also keep in mind not all vendors accurately size their panels or the location of the mounting holes per the real aircraft, so whoever you decide to go with make sure all the panels are consistently matched in size or you'll run into spacing and mounting issues.
I had to solder a LOT of LEDs to mini printed circuit boards (PCBs) included in the kit, mounting the PCBs to the light boxes, and gluing the various indicator light plates on to the light boxes. It’s quite tedious as there are a LOT of lightboxes to assemble! I was also disappointed to later find the Amber colors of the CockpitSimParts panel LEDs to be too yellow, so I ordered a whole set of new correctly-colored LEDs from FDS along with some new PCB’s from PCFlights.com.
I also added the switches and potentiometers included in the CockpitSimParts hardware kit, then mounted the panels to the overhead frame using the included wood screws and plastic sleeves. The real aircraft uses DZUS screws and DZUS rails to mount the panels to, but obviously my frame is all wood so wood screws would have to do. You can’t tell, though, and unless you plan on moving your panels around later, DZUS rails are really an unnecessary and more costly novelty.
Wiring the Panels
Wiring the panels is probably the longest and most tedious part of the whole project. You need a LOT of wire. I recommend the following:
- Use 22 or 24 Gauge wire for all your internal wiring\
- Use 16 Gauge wire for any main power wire (22 or 24 Gauge wire is not enough to handle a long power run to feed all the components in your overhead under load).
- I color-coded my wires to ease identification. You can, of course, use any colors you want. This is just what I chose:
- I used industry standard Yellow wire for 12V power
- I used industry standard Red wire for 5V power
- I used industry standard Black wire for Ground
- I chose white for switches
- I chose purple for potentiometers.
- I also used Red for light indicators (since they generally run off 5V).
In order to know how to wire everything, you need to know what the interface boards you will be connecting to will require. Here are the interface boards I used in my build:
- FlightDeck Solutions SYS4X – My primary switch and LED controller. Components are connected in groups of 8 with one common ground. Pretty straightforward and uses less Black ground wire. Dual brightness LEDS are a little extra effort but is possible. I chose the Phidgets LED card for dual brightness LEDs.
- Phidgets LED card – Used for all the blue dual brightness LEDs. Each indicator is individually wired with a positive and negative wire so more wire is used. But I love the no brainer dual brightness configuration.
- Phidgets Relay card – Used to operate the magnetic start switches I bought from Anders Sim Parts.
- PoKeys 57E – Ethernet card that handles 7 Segment displays as well as switches and LEDs. Very versatile.
- Small LCD screen and video board I used for the ELEC panel. This is a little different than most do, with seven segment displays. I wanted the dot-matrix style numbers to look correct so I decided to use a TFT LCD and I just display the Prosim ELEC panel display on it.
Since the FDS board is the main board in my overhead, I started wiring it first to all my switches, LEDs, rotary switches, and potentiometers.
NOTE: The FDS SYS4X doesn't have enough inputs/outputs to cover ever single thing in a completely fitted out overhead which is why I also added a PoKeys 57E and Phidgets card.
I mounted my FDS board in my overhead box in a centralized location that would not provide interference with the opening and closing of the box. Then, I started routing wire from the board to each of the LEDs, taking into account that the box will be closed so there has to be enough slack and room for the wire bundles to fold when the box is closed.
Once I figured out where I wanted to route my wiring, I ran 8 red wires from the first FDS board LED output connectors to the positive pin of each PCB of a group of 8 LEDs. It doesn’t matter which of the overhead LEDs you choose to group, but I chose to wire the LEDs so that they are in close groups to keep the wiring a little neater and organized. I then daisy-chained a ground wire from ground pin on the first LED to the ground on each next LED and finally to the common ground of the first FDS board LED connector. I continued to repeat this grouping until all the LEDs were wired.
After each group of LEDs is connected, I would load up Prosim and make sure each LED you just connected can be controlled by Prosim when you go to identify LEDs. Prosim has a quick way of identifying LEDs by allowing you to “Find” an LED by activating the find function which lights up each LED and you progressively rule out all the LEDs until you get to the one you want. When you run this test, the new LEDs you just hooked up should all light up. If they don’t, you have a wiring issue you should resolve before moving to the next grouping.
Like the LEDs, I ran 8 white wires from the first FDS board’s switch input connector to the appropriate pin for each of the first 8 switches (or 6 or 7 switches depending on if the switch is a two-way or three-way switch). Again, it doesn’t matter which switches you run the wires to, but again, I chose to wire each group of 8 switches such that the switches are close to each other to keep the wire bundles neat and organized. And like the LEDs, I then daisy-chained a ground wire from ground pin on the first switch to the ground on each next switch and finally to the common ground of that connector on the FDS board. I continued to repeat this grouping until all the switches were wired.
After each grouping you should verify in Prosim that the switches are being recognized. Like the LEDs, Prosim has a quick way to identify a switch or rotary. In Prosim’s configuration, when you move a switch, you should see it immediately identified by Prosim. If not, then you have a wiring problem that should be fixed before moving on.
Rotary switches are a bit more challenging. Rotary switches are wired and behave similarly to regular toggle switches, but their wiring is a bit more complex. You wire them the same way you’d wire a normal switch, connecting a purple wire (in my case) from each applicable pin on a rotary switch to a grouping of 8 inputs on the FDS board. Which pins you should use and how they are identified in Prosim is a bit of trial and error. Sometimes a bit frustrating.
How you are going to power the Overhead is something you need to be thinking of early. Make sure you have a common ground, and ideally a single power supply. A CPU power supply converted for Overhead use is perfect because it’ll give you both 12V and 5V along with a common ground. There are, of course, other options but I found this the easiest way to power everything.
I finally settled on he following power configuration which allows me to control various overhead systems with relays so that they get power when they’re supposed to get power. It works quite effectively.
I used a several power distribution bars, one for 12V, another for 5V, and another for Ground. This gave me a central place within the overhead to connect always-on power to. From there, I was able to power the interface boards and also send power to the Phidgets relay card to power back-lighting, starter solenoids, and 7-segment pressurization displays.
One thing to note. After I finished building mine I found out that the long power run I made from the CPU power supply to the overhead was not using adequately heavy wire and the Overhead was “browning” out on me, particularly when back-lighting was full and I kicked in the starter solenoids. This resulted in enough of a power drain to shut down the relays powering the back-lighting and solenoids, and killing power to some of the interface cards. So make sure the power feed into your Overhead uses sufficiently heavy wire to handle the load when everything is on. I would suggest no less than 16 gauge wire. Once I replaced the 22 gauge power feed wire with 16 gauge the issue went away.
For all the wiring internal to the Overhead, I used 22 gauge wire. The short runs and generally low draw of the individual components means a thinner wire can be used. 24 gauge wire would probably work ok too, but the copper strands of wire are almost too thin to solder well. 22 gauge is a good balance of solder-ability and flexibility in the wire without being too bulky.
In my case, as in most simulated panels, the Overhead panels are white acrylic painted gray and the lettering laser etched out. This allows the back side of the panels to be lit and that light shines through the white plastic and out through the laser etched areas. While it may sound easy, when you are cramming a bunch of stuff into an overhead and then try to light it evenly, you have wires, boards, etc blocking the even distribution of light and you end up with a mix of inconsistent lighting.
The real aircraft uses a similar but much higher quality material and small aircraft bulbs are actually inserted into cutouts within the backing so the light scatters more effectively and consistently. FlightDeck Solutions makes their panels like that and that makes back lighting WAY easier.
I did the best I could by putting as many 12V warm white LED strips throughout the interior of the overhead box as I could, hoping to light it well enough that it reduces the inconsistent lighting. That is also why I painted the interior white to help reflect light internally. And that is also why my wiring is channeled into bundles as much as possible to reduce the blockage of light to the back sides of the panels.
While my method works, it’s not as good as I would like with some areas still brighter than others. Unfortunately, as long as I’m using panels that require the entire back side to be lit, I’m going to have this problem.
As you can see by looking at my Overhead interior, it’s not always easy to put lighting exactly where you want it. For example, the large FDS SYS4X interface board takes up a huge area that I cannot light with LED strips. So that area is much darker than, say, the front of the Overhead where there are less obstructions.
All this to say when planning out your overhead build make sure you take your back lighting into consideration from the start if you’re not using FDS-style panels..
The End Result
Once everything is wired up and working, pat yourself on the back. This isn’t easy and you’ve accomplished something pretty amazing!
Just to give you an idea of what mine looks like in its completed state, here you go:
Plan Ahead and Things to Avoid/Think About
It is hard to plan for everything and know what you’re going to need, especially if you’ve never wired an Overhead before. But try to do as much planning as you can in advance.
Some things to think about:
- What kind of FRAME are you going to use?
- You can opt to buy pre-made metal painted frames from many of the popular sim vendors. FlightDeck Solutions, for example, makes frames that are DZUS compliant, meaning they use the real-world mounting rails so you can move their panels or even real panels around anywhere in their overhead frame and they’ll mount properly. Others have fixed position holes for specific panels, meaning you’ll likely have to buy their panels to guarantee a fit. If you go with a pre-made frame, it’s best to stick with that vendors panels to guarantee a perfect fit.
- You can build your own frame. This is a lot more time consuming. You’ll need to research the proper dimensions, figure out where the panels will go and ensure they mount without interference from frame components, make sure it’s strong enough to hold the heavy weight of overhead components, and determine best access for future maintenance.
- What materials to use? Keep in mind a fully loaded overhead is VERY heavy, and if your frame isn’t strong enough it may bow under the weight, or even crack/break. I chose to use birch wood square dowels and plywood because it was cheaper and relatively strong. It worked out fine, but I might give more thought to its design in advance if I ever do it again. If you can, I would highly suggest building out of metal (aluminum would be my choice). The strength to weight will be much better and you won’t require nearly as thick a material.
- Is the frame going to be open or enclosed? You need to think about where you’re going to mount all the electronic boards. With an open frame you’ll likely have to stick them on the roof of your cockpit shell, if you have one. If you don’t have a shell, you’ll have to work out where you’ll be mounting those. I opted for a fully enclosed panel so I could easily mount everything inside the overhead “box” and if I need to pull it down for maintenance, I can remove it all as one piece. This has challenges as well, including ventilation, tighter space to work in and route wiring and such, depth issues (too deep and it may not fit your shell properly), etc.
- How are you going to access internal components? The real aircraft has a swing-down overhead, allowing you to get behind the panel pretty easily. I chose to mimic this idea by adding some piano hinges at the rear of my overhead box, and some locking clasps at the front. This allows me to easily swing down the panels to get behind them and fix or modify as needed without taking the whole thing down. Given how heavy it is, that’s not something you want to do if you can avoid it. If you have an open-style overhead frame, you still need to get behind it to perform maintenance. FlightDeck Solutions’ frame, for example, swings down like the real aircraft for maintenance. But it is an open design so you need to mount the interface boards somewhere else and ensure your wiring can accommodate the opening and closing of the overhead.
- What kind of panels are you going to use?
- There are many individual panels on the 737 overhead. Many sim vendors sell them, either as partial or complete kits, or plug and play. Some plug and play panels require proprietary boards to plug into. Some use wire harnesses, others use ribbon cables. Keep in mind that wiring can get very complex so the easiest solution is best.
- Switches, Rotaries and Potentiometers
- The 737 overhead has a variety of switches and potentiometers (see my diagram below). Some switches are two position, some are three. Some are two position with one position being momentary. Some are locking switches that require you to pull out the switch stalk to move it to a different position. It all depends on how real you want to get.
- You have several types of poentiometers. Some are just freely rotational like the AC temperature dials. Others are multi position potentiometers having 3 or more selectable positions.
- Keep in mind the more you add the heavier the overhead will get.
Related Site Content:
- Wet Compass and More 3D Printed Parts
- 737 Overhead Power Distribution Rewiring
- Progress Update – April 12, 2018
- Progress Update – March 14, 2018
- The Sismo GIC, ISDU, and Finally Getting it All to Work (Not Quite Perfect but Close)
- Getting to Know the Sismo IRS Display Unit (ISDU)
- Sismo Soluciones IRS Display Unit (ISDU)