FWF: Spinner & Propeller. Spinner plate assembly.

The S-602-1 Spinner Plate and S-602B Doubler Ring are match drilled.

The center section of the Spinner Plate is removed via a combination of a multitude of holes made with a large unibit (left) and careful, though judicious, use of the Dremel (right), the latter of which was completed by my friend.  I attribute to "the 51% rule" that these parts aren't both pre-cut.

The parts are then primed with Napa 7220 and subsequently riveted together.

Panel: Airspeed indicator purchased.

I purchased my Winter 7 FMS 523 airspeed indicator.  It's a 360 degree, 2.25", 0-200 kts, zero up indicator.  I had them place the following markings.

• V_NE  200
• V_A   130
• V_FE  100
• V_X    70
• V_S1   62
• V_S0   51

A shot of the panel essentially complete.

Avionics: Nav/Strobe and landing/taxi lights circuit

Here are the posts pertaining to nav-strobe lights.

• 12-Aug-13, initial thoughts
• 17-Aug-13, lenses cut 
• 9-Sep-13, lights ordered
• 7-Jan-14, wiring completed
• 30-Apr-17, mounts fabricated 
• 16-May-18, first night flight

The navigation and strobe lights can be operated independently, as can the landing and taxi lights.  So there are four possible combinations to run them:

	Nav/Strobe	Landing/Taxi
1	Both off	Both off
2	Nav on. Strobe off.	Taxi on. Landing off.
3	Nav off. Strobe on.	Taxi off. Landing on.
4	Both on	Both on

I don't anticipate needing to use combination 3 (in red) for both sets of lights.  And, in the interest of consolidating panel space, I wish to control the remaining combinations, 1, 2 and 4 (in green), with only one switch for each light set.  An example of how to do that is shown below.

The diode is the key to this arrangement.  When the taxi light is selected, the diode prevents the landing light from being powered (option 2).  However, when the landing light is selected, the diode permits powering the taxi light (option 4).  In this way, one can select "off", "taxi" or "taxi+landing" with a single switch (or "off", "nav" or "nav+strobe").  The issue with using a diode is that its forward voltage drop causes heat generation when taxi+landing is selected.  This is especially an issue with a high current taxi light, like mine and a non-issue with the nav/strobe lights (due to their lower current demand).

Initially, I used a high current Schottky with a V_f  of 0.58 V (somehow I managed not to take a picture of that setup).  However, with the taxi light pulling 7.3 A when set to "high", that means the diode will create more than 4 W of heat.  And it sure did!  That was too much heat (again, this wasn't an issue with the nav/strobe lights since the navigation lights pulled only about 400 mA).

A more efficient approach would be to use a high-sided FET in a switching configuration, like shown below.  The PFET will only be switched on when its gate is effectively brought to ground.  This occurs when the landing light (or strobe) is powered on by the switch (not shown). When that happens, the NPN is switched on since V_BE>0.7 V.  With the transistor on, its V_CE is brought from +12 V to effectively ground.  With the FET's gate now at ground, V_GS is effectively -12 V, switching the FET on so that the +12 V at the source is now presented at the drain, where the taxi light is (or nav).  The taxi light (or nav) is then powered on with the landing light (or strobe).

Since R_DS for a FET is tiny (in my case, less than 0.004 Ohms!), there is a negligible amount of heat generated, even with more than 7 A being pulled through for a taxi light (which amounts to less than 30 mW of heat in the PFET).  Finally, a diode is placed to provide a path for the collapse of the magnetic field in case of any inductive reactance in the load (a.k.a., a flyback diode). 

With my planned approach determined, next I needed to design the circuit board appropriate for the OTTO K2 DPDT switch I planned to use (left).  I wanted my circuit board to plug in directly to the K2.  Here is a diagram I made to better show the K2's terminal connections (right).

My schematic is below.  It's a bit messy to present.  The K2 switch terminals are represented in the upper center.  Each K2 terminal needs a female tab so it can plug in to the switch.  In additional, each terminal needs a male tab to receive the wires (e.g., ground, power, landing and taxi or ground, power, nav and strobe).  The switch is DPDT, so that left and right lights can be on separate fuses (or wing and tail nav/strobes).  A single NPN transistor controls both the left and right PFETs.  In case the fuse blows on either side, the NPN is powered from both inputs, so a blown fuse will not result in the PFET changing its state and turning on or off a taxi light (and with 20 k-ohms between each powered input, neither side can power the other through that connection, should a fuse blow).  Finally, should the circuit fail, the lights are still controllable mechanically through the switch:  If a PFET remains off, then either lighting position can be selected, so either 'landing or taxi' or 'nav or strobe'.  If a PFET remains on then either 'taxi or landing+taxi' or 'nav or nav+strobe' can be selected.

Next I needed to design the circuit board so that I can just plug it in to the back of the K2 switch.  Using a micrometer and the K2 specs sheet, I mapped out the dimensions necessary.  Since space was limited due to the proximity of other switches on my panel (left), the board needed to be about the same width as the switch itself.  That criterion also necessitated using surface mount components.  The right image shows the board design.

Here are 3D rendered images of the board.

 

 

The boards were then manufactured.  The top image shows the front and back of the board (actually, the right board is an earlier revision, but it's similar enough to my final design).  The bottom images show the front (left) and back (right) after I soldered one up. The two red jumper wires were necessary since, when designing the board above, I ran out of room to lay down associated traces.  Lastly, the observant will notice that the PFETs are held down by LP4-3 rivets (hey, it's an airplane, right?).

And finally, here are two boards plugged in to the back of both my nav/strobe and landing light K2 switches.  After running the taxi+landing lights on for 15 minutes, the PFETs do not get noticeably warm (same for the nav/strobes, however they have much lower average current so it wasn't an issue).  Success!

As an aside, the wigwag line for my lights is active low.  Yet I wanted the panel switch to light up when wigwag was selected.  So I needed to use an independent rather than dependent light OTTO K1. To make sure the light turned on when wigwag was selected, I had to switch in the ground to the K1's light.  However, when the switch was off, the wigwag line would be connected to the ground of the K1's light.  Unfortunately, the wigwag line floated low enough to cause the OTTO K1 switch to illuminate slightly when wigwag was off (i.e., the landing light control line was sinking current from the switch's light).  Can't have that!  Hence the simple isolating Schottky diode on the switch.

In the above image, you can see that diode encased in a few layers of heat shrink tubing (it's the clear heat shrinked discrete on the ride side).  Below shows a representation of the circuit for the wigwag switch.  To ensure that wigwag line is pulled low enough when the switch is thrown, that diode I chose has a V_f of 450 mV.

For the curious, as in the case of when I designed my panel, I am a proponent of open-source software.  For schematic generation and board layout, I used KiCAD.  And there are a myriad of so-called "board houses" that manufacture circuit boards when provided with the CAD files for one's design.  Then it's just a matter of whipping out the soldering iron and affixing the components.

 

Parts list:

• Diode:  Kyocera AVX's SD1206S040S2R0
  
• PFET:  Infineon's IPP80P03P4L04AKSA2
• Quick Connect male:  Keystone Electronics' 4902
• Quick Connect female:  Keystone Electronics' 3528
• Resistor:  Panasonic's ERJ-8GEYJ103V
• Schottky diode:  On Semiconductor's 1N5817
• Transistor:  On Semiconductor's MMBT2222ALT1G
   

Avionics: Indicator lights circuit.

Update 6-Jun-25:  This circuit was updated.

 

I desperately wanted to have a "push-to-test" button for my stack of four indicator lights, only because it's cool.

Since the lights are all active low, that switch would need to apply ground to the cathode of each LED light (as the anode side of the LEDs would all be tied to +12 V).  However, it's poor form to also pull low each indicator output line from each instrument (they may not be designed to handle being pulled low when they're floating).  So one has to isolate the output lines when the switch pulls the lights low.  Below shows that simple circuit.

The lights are shown as LEDs in the above.  When the switch pulls the cathodes low, it does that through a stack of diodes that prevents the indicator output lines (coming in from the right) from being pulled low too.  This way the LEDs all turn on but the indicator output lines can float happily.

Next I needed to design the circuit board so that I could just solder it in directly to the back of the lights without additional connectors.  Since I knew the precise spacing I had on my panel that I designed, that was simple enough.  Using surface mount diodes kept the board's footprint small.

Here is the board soldered up.  You'll notice I have two "spare" boards in case I need to replace an indicator light (since that would require destroying the installed board to remove a light).

And here it is soldered to the back of the instrument panel lights.  It's unassuming and out-of-the-way.

Finally, here is what happens when you "Push-to-Test".

As an aside, I'll probably remove one of the TAWS indicators in favor of an oil pressure of EIS (engine information system) warning.  I may also remove the other TAWS indicator in favor of an "Alternator" light.

Update 15-Dec-16:  I changed the indicators as described above.  The TAWS indicators are now "Alt" and "Oil Press". 

For the curious, as in the case of when I designed my panel, I am a proponent of open-source software.  For schematic generation and board layout, I used KiCAD.  And there are a myriad of so-called "board houses" that manufacture circuit boards when provided with the CAD files for one's design.  Then it's just a matter of whipping out the soldering iron and affixing the components.

Brake fluid added.

The brake fluid was added tonight.  I used a Balkamp BK 7201013 1 pint oiler hand pump from Napa and Royco 782 hydraulic fluid with some 1/8" clear tubing from Lowe's.

It's a fairly simply process:  Puncture the can with a bottle opener, pour some of its "nectar of arrest" into the oiler, attach one end of the clear tubing to the can and the other to the zerk nut (bleeder valve in red in the below right image) of a brake.  Then unscrew the zerk nut with your fingers until it just comes loose.

Apply pressure to the oil can pumping handle and slowly continue to loosen the zerk nut until the pressure on the oil can handle diminishes.  At this point you're assured that the zerk nut is opened enough to pass fluid into the brake system but still not opened enough to pass the fluid out of the fitting.  However, I kept the zerk nut wrapped in paper towels since I couldn't prevent fluid from leaking.  Be weary of pumping air into the system.

Fluid will start to fill the system associated with the side of the airframe you're filling from. In my case, I filled from the left side first.  I continued filling until the master cylinder was about half full.

Then I filled the right side.

I didn't see any air bubbles in the system and the brake pedals were not spongy, suggesting no air in the system, which is frankly unbelievable.  However, after letting the system sit for several weeks, the air bubbles slowly worked their way up to the highest point in the tubes.  Apologies for the poor quality images, it was difficult to coax the camera to focus on the desired subject, however you can see an air bubble in each line as those lines feed into the fluid reservoir.

Before clearing these bubbles, a friend of mine helped me rock and push the pedals up and down through their full travel multiple times.  We were able to release even more air previously hidden in the master cylinders.  Then, I drained the fluid reservoir with a syringe and we slowly pushed in more fluid through the zerk nuts so that the air could pass into and out of the reservoir.

Currently, I see no air in the system, however it is apparently normal for more air to work out as the aircraft is flown.  In fact, when I visited Van's on 7-Aug-14, you can see in an image I took of their demonstrator, N214VA, they too had air.  Look closely at the very top center of the image.

After the rudder was attached, I verified the position of the rudder pedals as I put them as far forward as possible.  With the seats in and rudder on, that positioning worked great for me (the air bubble at the left cylinder was removed during the process outlined above).