Electrical System

Mounting the strobe

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The best place for the strobe is on top of the fin. Getting the wiring up through the fin will be difficult since I’ve already covered the fin. Looks like I need to make a 3 foot drill bit.

I got a 1/4 steel rod and sharpened the end to a point on the sander.

Tip of homemade drill bit
Tip of homemade drill bit

Then I used a dremel with a cut off wheel and made two groves 180° apart.

Homemade three foot drill bit
Homemade three foot drill bit

It’s a little slow but works well.

The hard part was getting the angle just right to drill right down the center of the nose ribs. To assist with this I made a small guide block, similar to the guide block used to drill the axle hole in the landing gear.
Once the hole was drilled the wires were routed through the nose of the fin. A hole was drilled in the bottom of the strobe and the strobe base mounted into the fin.
Terminal ends were added to the wire and connected to the strobe.

Connecting wires inside the strobe base
Connecting wires inside the strobe base

With the fin mounted the wires were connected and the strobe tested.

LED strobe
LED strobe

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Strobe

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In the quest for an affordable strobe I found many suggestions. Some people have used fire alarm strobes, I considered this.

Others just say buy one so I looked into that. The Microavionics MM030 strobe is about $150 and has a xenon flash strobe powered with 20 joules and weighs about 9.5oz. Not really sure how tall or wide it is.

The cheapest pre-made strobe I found is the Skysports Bright Star Strobe avaliable from Aircraft Spruce. It has dual xenon flash tubes using 8 joules, weighs “under 5oz” and is 2.75″ wide and 4″ tall.

In my opinion the Skysports strobe is not bright enough. Sure it meets the need for twilight flying but 99% of my flying will be on sunny days. The main reason I want a strobe is to make my slow small airplane more visible to other faster approaching aircraft, this is especially important when taking off and landing.

I also wanted to avoid a xenon flash tube, the high voltage can cause radio interference. Sure properly grounded it should not be an issue but this is a wood airplane. 

After looking I found a nice LED light that fits the bill. It weighs 7oz so it’s lighter than the MM030 but heavier than the Skysports. At 5.5″ tall and 2.75″ wide it has the same footprint as the Skysports just 1.5″ taller. Most importantly it is very bright. It also ended up being the cheapest at $40.49 with free shipping.

LED strobe
LED strobe

Unexpectedly this LED light did cause RF interference with the radio. Each time it flashed you could hear a hiss on the radio. Adding a ferrite core to the power wires resolved this problem. The core was salvaged from an old VGA cable and fits nicely inside the bottom of the light.

I’ll cover mounting it in a future post.

Fuel Sender Wires

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Time to route the fuel level sensor wires. The first thing I did was mount the wings and locate a location to drill a hole for the wires. After drilling the hole I added a grommet.

After locating the hole I determined how much wire needs to protrude from the fuselage so they can be easily disconnected after removing the wing.

The sensor outputs need routed to the fuel selector switch so I decided to make some splices near the sender switch to accommodate this. I routed the left fuel sensor wire down the left fuselage side, across the floor and up the right side and through the grommet. On the right side near the fuel selector switch I spliced in the fuel selector and right side sender wires.

The red and black (power and ground) are spliced to the right side sender so both senders get power. The white wires from each sender are spliced to the wire going to the selector switch, right to red and left to black. The white wire from the dash and to the selector were spliced.

Terminal ends were added, the resulting harness looks pretty good.

Behind the dash the black is connected to ground, red to power and white to the green EIS Aux input.

ADS-B in for $20

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ADS-B ( Automatic Dependant Surveillance Broadcast ) provides much needed information to pilots and air traffic controllers. ATC can see the location, speed and direction of any aircraft equipped with ADS-B out. Pilots can see other aircraft with ADS-B out and get updated information such as weather and temporary flight restrictions. Historically getting access to this data required expensive avionics but recently a few low cost solutions have appeared.

With some specialized software European USB TV tuners can pickup the ADS-B signals and thanks to mass production such devices can be purchased for under $20. I purchased a tuner that comes with an external antenna from Amazon.

NooElec SDR
NooElec SDR

Using a USB OTG cable I connected the tuner to my tablet.

USB OTG with charge cable
USB OTG with charge cable

I already had Avare installed and setup so I only needed to install ADSB Receiver Pro on my tablet. Now when using Avare I can see other aircraft and weather data.

Blue dots represent other aircraft
Blue dots represent other aircraft

If you need more detailed directions to get this setup head over to the site that made this possible: http://hiz.ch/index.php/home/adsb-receiver

The FAA has mandated that aircraft flying in nearly all controlled airspace must be equipped​ with ADS-B out by Jan 1st 2020. I hope this mandate helps drive some competition in the market and bring down prices of ADS-B out transponders. In the meantime at least I can pickup ADS-B in with little investment.

Started the Electrical Wiring

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Running all of the electrical wiring is a larger task than I anticipated. Figuring out what needs connected to where is easy enough, doing so in a nice tidy, serviceable and long lasting way is what’s hard.

I secured the battery with a battery hold down strap. I had to shorten it significantly and heat weld part of it since I don’t have a sewing machine. A piece of foam is placed under the battery to keep it from sliding around.

Battery hold down strap
Battery hold down strap

I added a ground controlled relay for the master power. When the matter switch is off no power enters the cockpit and nothing electrical is energized. For those unfamiliar with airplanes, the engine ignition system​ is independent from the electrical system so the master switch will not turn off the engine nor prevent it from starting. The ignition is controlled with the keyed switch, more on that later.

Master relay
Master relay

Installed a diode across the starter solenoid. This reduces arcing across the starter switch contacts. Also, ACS service bulletin sb92-01  applies to my ignition switch and requires the installation of the diode. To protect the diode I put it in a small tube and covered it with black heat shrink. 

Starter solenoid
Starter solenoid

The regulator was mounted to the other side of the fuselage and it’s wire run through wire clamps on the engine just like the EGT and CHT probes.

All of the circuit breakers are on the dashboard so most of the power distribution happens there.

A small ground buss provides a convenient place to connect ground wires.

The keyed switch serves a few functions. When the key is removed the engine magnetos are disabled so the engine will not start, without this simply bumping the propeller could start the engine. The key also has a momentary start position to activate the electric starter, just like a car. It has a run position wherever both magnetos are allowed to operate and a left & right position where you can select the right or left magneto to ensure both are working before taking off.

ACS ignition switch
ACS ignition switch

Still have some other items that need wired, strobe, fuel pump, USB chargers and the radio. I’ll discuss that in a future post.

Wiring Engine Information System

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The EIS monitors the cylinder head temp, exhaust gas temp, RPM, battery voltage and air temperature. Each item can have limits set so if something is out of the ordinary the warning light on the dash will illuminate.

The cylinder head temperature probes sit between the sparkplugs and head. I ran the wires through the fins and up the side of the engine where they are held in place with a clamp. The exhaust gas temperature probe wire is also held by this same clip.

Cylinder head temperature probe wires run through fins
Cylinder head temperature probe wires run through fins
EGT and CGT probe wire secured with wire clamp
EGT and CGT probe wire secured with wire clamp

The probe wire then run to the front of the engine where another wire clamp was added.

EGT and CHT wires routed over starter
EGT and CHT wires routed over starter

The EIS harness terminates in from of the battery where the probes are connected. I kept the pair of wires for the second exhaust gas probe in the harness even tho I’m not using them. Maybe some day this airplane is updated to two cylinder and then they are needed.

EGT and CGT connected to EIS harness
EGT and CGT connected to EIS harness

The grey  tachometer wire goes to the other side of the engine and connects to the lighting coil. I spliced an extra connector into the voltage regulator wires to connect the tach input. Still need to put an end on the grey tach wire.

Lighting coil & tach connection
Lighting coil & tach connection

The EIS uses a single DB-25 connector for all the wires. I took the connector apart and removed all of the unused wires by pushing the pins out with needle nose pliers. A few of the wires exit the EIS harness just behind the connector such as power, ground, fuel sender and warning light.

EIS connector
EIS connector

The violet wire runs through the harness to the warning light with the other side of the warning light is connected to power. I made sure that the dash is easily removed by disconnecting wires as opposed to having to cut wires to remove it.

EIS warning light
EIS warning light

The last item to connect is the green wire to the fuel level sending units from the gas tanks. When it gets a little warmer I’ll roll her outside, mount the wings and tanks and then work on routing the fuel sensor wires. I’m not exactly sure where everything ends up so not much I can do with that for now.

Radio Interface for Phone/Tablet

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The MicroAvionics MM005 powered radio interface required a little extra effort to get working good with my tablet and phone. My Note 5 did not like the phone adapter, apparently the 1k Ohm resister across the microphone was insufficient to make the Note think a microphone was connected. This was not a huge problem since I planned on making my own cable anyway.

My Nexus 7 ( 2nd gen 2013) microphone input did not like the high level output by the MM005 from the phone or the AUX OUT port. The level was so high that it caused lots of clipping resulting in some horrible sounding recordings. My Note 5 did not seem to care and recorded well from both ports. The cable I made for the Nexus 7 included an additional resister to convert the line level output of the MM005 to microphone level. Maybe not the best way to deal with this but was certainly the easiest. The resisters fit inside the audio connector ends resulting in a nice clean looking cable. 


The other end of the cable goes to a dash mounted 3.5mm TRRS / USB port.
A short audio cable connects the tablet. 

To power the phone and tablet I used a ZeroLemon USB charger. I picked this particular model because it did not cause RF interference with the radio. Every other charger I tried caused tons of RF noise when tuned to around 132Mhz, the closest airport to me is CMH on 132.7 so it was only by chance that I even noticed this problem. I did take the charger apart so I could hard wire the power, I did not want to rely on it staying plugged into a cigarette lighter.

Not decided how our where I will mount this adapter but I’m thinking of just drilling a couple holes and using a zip tie. 

Fuel Gauge

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Started working on the electrical wiring and discovered that the EIS 2000 I have only supports a single fuel level input. They sell the EIS 2000 as a two or four stroke model when in reality it does not matter if you have a two or four stroke the difference between the two models is features not engine type. When I build the next airplane I think I will build my own EIS or use the flybox.

So the Grand Rapids folks suggested using a switch so I can select what tank level I want to monitor. After thinking about this for some time I decided this is the best option but that it needs to be implemented carefully. Imagine monitoring the full tank but running the engine from the empty tank. That could result in a bad day. 

In designing this I decided the goals should be as follows: 

  1. The position of the tank selector valve dictates what fuel tank is monitored by the EIS
  2. If the fuel selector valve is in the off position then the EIS should see an empty tank triggering the warning 

The typical inexpensive fuel selector valve is not suitable for triggering some electrical switches. I ended up purchasing a WSM 006-600 jet ski fuel valve on Amazon.com and a couple of 2750017 micro switches from the local RadioShack. 

Fuel valve and micro switches
Fuel valve and micro switches

Using a file I put a flat spot on the knob that was parallel to the flat side of the D hole in the knob. The location of the flat spot is important so if you have a different valve you might need to change the location.

Fuel valve knob modified with notch
Fuel valve knob modified with notch

When the knob is installed on the valve the flat spot should line up with a micro switch roller only when the valve is turned to the left or right tank. This will require the switches to be mounted 180° from one another. I used OnShape.com to make a drawing that I printed out in reverse on toner transfer paper. This will provide accurate centers for the holes and the labels for the valve. 

Putting the switches to their marked locations on the toner transfer paper you can get an idea of how this will work. 

Arrangement of micro switches
Arrangement of micro switches

I varnished a piece of plywood, sanded it smooth and applied the toner transfer. Then the parts were cut out and drilled. A smaller valve support plate needs to be 5/8″ away from the panel so the notch in the knob is just below the plywood. 

Micro switch actuated by notch
Micro switch actuated by notch

On the outside, for asthetics I used 1/4″ X 3/4″ pine. A 1/8″ notch was cut into the outside piece and the valve support set into the notch. The inboard side used a small piece of 1/4″ X 5/8″ pine. Alignment is important so I glued this together with the valve and knob installed to keep everything indexed.

Fuel valve support
Fuel valve support

Once the epoxy cured the switches were mounted using #3 screws and the valve installed. 

Fuel valve, switches and wiring
Fuel valve, switches and wiring
Fuel selector knob and labeled panel
Fuel selector knob and labeled panel

The electrical wiring did take a little bit of planning. I wanted to make sure that should there ever be a malfunction that only a single fuel level sensor would be connected to the EIS. Here is the wiring diagram that does this: 
http://schematics.com/embed/fuel-sender-selector-46440/full

Before takeoff simply turning the valve to all three positions will confirm if the system is functioning properly.

I think this turned out well, looks pretty good mounted on the fuselage side. 

Fuel tank selector valve
Fuel tank selector valve

Toner Transfer

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I’m still not happy with the dash so time for the fourth iteration. This time I designed it in CAD using OnShape.com, including all of the labels. To fabricate it and apply labels I thought using a tuner transfer method might be nice.

First the wood was vanished and sanded smooth. I only had A4 size toner transfer paper so I had to print multiple pages to cover the whole dash. PosteRazor was very helpful in printing the pages, just don’t forget to mirror your CAD image before printing.

Starting with the center bottom page I taped it to the board and used the wife’s iron to transfer the toner. To align the next page I pushed T-pins into various reference points.

Pins to mark index locations
Pins to mark index locations

Those same reference points were poked through the paper.

Pins to mark index locations
Pins to mark index locations

Then using the holes the next page was aligned using multiple reference points.

Aligning the transfer paper
Aligning the transfer paper

Then the page was tapped in place and toner transferred with the iron. This process was repeated until the whole dash was completed. The nice thing is if you mess up just sand off the mistake and try again!

Since all the holes were marked with toner it was really easy to cut out all of the holes precisely where I wanted then.

Toner transfer also marked hole locations
Toner transfer also marked hole locations

I might want to add some more text or switches before I complete the airplane so for now I am leaving off the final coat of varnish. But once completed I plan to add a couple of coats to help protect the toner from abrasion.

Preview of final dash
Preview of final dash

I recently started working on the electrical wiring and quickly discovered that most 12v USB phone chargers emit RF interference like crazy. When tuned to around 132Mhz the interference makes reception impossible. Anyone know of a decent priced charger that does not emit tons of RF?

Electrical Wiring

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With the fuselage nearing completion it will soon be time to do all the electrical wiring. I used schematics.com to create my wiring diagram. 

Still a work in progress but here it is:
http://www.schematics.com/embed/minimax-27727