Step 12.3, Designing the panel

It turns out that making the instrument panel is not such a hard thing to do, but there are a few questions that must be answered first.  Probably the most important question from a monetary point of view is whether or not the panel will be IFR certified (Instrument Flight Rules).  The cost of an IFR panel is largely dictated by the FAA requirement that the GPS and or VOR  and or localizer receivers be certified to operate within the national air traffic system.  This alone can easily add $10K to the cost of the full featured Visual Flight Rules panel.

With that in mind, it looks like I'll be doing a VFR panel, but what exactly does this mean?  A panel equipped for VFR flight means the aircraft is instrumented for flight under Visual Flight Rules. Basically, the aircraft can be operated only under clear weather conditions. This does not seem to be such a large impediment to me, since I don't have a burning desire to fly in inclement weather nor am I certified to do so.

Next question, how will the panel be in instrumented, that is, what style of instruments to choose?

The most basic choice is between a Glass panel or a panel with steam gauges.  Despite the confusing name, a glass panel is not actually made of glass.  It simply refers generically to an instrument panel that displays its data on some kind of screen, usually an LCD like a computer monitor.  Likewise, steam gauges do not actually measure steam pressure.  The term 'steam gauge' refers, in a somewhat derogatory fashion, to the round dials that traditionally adorn the aircraft instrument panel.

One of the big advantages of a glass panel is that all or most of the instruments are displayed on a single screen.  This can simplify the panel and reduce weight.  It also permits new functionality to be added to the display without having to physically change the panel.  On the other hand, one big advantage to the steam gauge approach is that if the power should go off, the steam gauges won't know it -- they don't need power to operate.

Alas, I chose the glass panel approach because it is the more modern way, and it offers the most flexibility going forward.  Still, I'm not entirely comfortable with the little problem of power or the accidental loss of of it, so I will be adding a separate ASI (AirSpeed Indicator) and altimeter, both steam gauges.  

Deciding the location and number of switches and their function was the hard part for me.  Since I had already decided the number of displays I wanted (2) and the brand that I would be using, Garmin, a lot the functionality has already been decided for me.  What remains mostly reduces to turning on or off lights or avionics.  To get started, I made a list of the things I thought I might like to control:

• Master power / Alternator field enable
• Engine start / mag select -- key switch
• Auxiliary fuel pump
• Avionics master
• Autopilot Enable
• Control Column passenger enable
• Strobe light
• Navigation lights
• Taxi light
• Landing light
• flaps
• pitch trim
• roll trim
• Wig Wag enable
• Pitot heat
• Seat heat
• Dome light

To arrange the switches I followed the idea that the switches should be placed in roughly the order they might be used in a typical flight, left to right.  This order makes about as much sense as any other, with the added advantage that this order will utterly befuddle any Hebrew, or Chinese plane robbers :)

With all that settled, I then laid out the panel using online software from frontpanelexpress.com. Their software allows one to import the panel outline, which I downloaded from Van's in dxf format. This way I could be sure that the panel would fit properly.  I was also able to get some pre-made 'macros' (FrontPanel express terminology) for some of the switches and instruments online.  One RV7 builder in particular, Brian Chesteen, was very helpful.  After that it's just a matter of placing the components, or rather, the cut-outs for them.  There is a lot of measuring involved to get the sizes of the switches and other components properly specified.  A fair amount of guessing is required.  Like how much clearance is needed over here or how much to allow for powder coat over there.  And so it goes...

When the design is finished, the front panel express application totals up the machine time it will take to cut the panel and how many tool changes are required.  It then gives you the bad news, which of course is the price. 

This is the point where I returned to the design to try and reduce the number of tool changes, as well as reducing the sizes and the number of labels as well.  After a few iterations, I got the price down some and simplified the panel a bit.  Both of which are good things.  It is a simple matter to place the order right from the application.  All they really need is your credit card and shipping address. Everything else is specified in the application while you design the panel. The cost of the panel includes infilled engraved labels which are done by the CNC router along with all of the other machining.  Sending this work out probably saved me a month of work.

And the finished panel?  Glad you asked:

My next task is to begin attaching the instruments to the panel.  A bit of filing was necessary here and there. but there were no show-stoppers.  I made adjustments to the design file, so if I ever need to order another it should be perfect.

Bracketry to hold the radio stack.

AML34 switches by Honeywell.  Custom engraved caps by engravers.net

Once all of the switches are in, there is still a lot of wiring to do on the back side.

And here is the nearly completed panel being test fit.

Very briefly, the two LCD screens on the left half of the panel will display the flight data and moving map, respectively.  In the center are the backup ASI and altimeter. To the right is the radio stack containing (top to bottom) the auto pilot panel, the audio panel, and two GTR-200 COM radios.  The big hole to the right of the radio stack is the glove compartment.  Finally, across the bottom are the aforementioned switches.

A cover plate below the second radio allows room for future expansion.  The radio stack was sized to allow a GTN-650 NAV/COM/GPS radio to replace one of the GTR-200 radios + cover plate.  This will convert the panel to a fully certified IFR panel.  The panel is ready -- I'm just waiting to win the lottery now.  And if the lottery doesn't pan out I still have a long lost relative from Nigeria that died and left me a pile of cash.  I just need to pay some expediting fees and...

The one item on the panel that was not previously mentioned is the annunciator panel. It's the row of 6 colored switches located just above the second LCD display.   That will be the subject of an upcoming post.