First Condition Inspection Status Update – Crankshaft Seal Leak and Battery Overheat Mitigation

Source: 2025Q2 Beartracks, Paul Minelga
Last month I did my first condition inspection. It’s hard to believe it has been a year since I got my Airworthiness Certificate! As the months went by, I kept a running squawk list of items that needed attention, but weren’t safety of flight items. In addition to all the inspection items normally done on an “annual”, I took care of the items on the list and did a deep dive into the entire aircraft, from one wing tip to the other, nose to tail. I even cut open the EFII boost pump fuel filter (FF-2 Pre-filter) to see if there was anything in there as it’s a sealed unit. I found nothing inside, completely clean except for a tiny fleck or two. It was $48 for a replacement, but now at least I know what it looks like on the inside.
One thing that was a bit of a concern to me was the nose of the engine always seemed like it was just a bit wet. Nothing that I would consider a leak, but a tiny bit oil was coming from somewhere. I was doing the inspection in the hangar I did the initial assembly in. The mechanic that helped me along the way through the years suggested that I pull the prop to have a look at the nose seal around the crankshaft. He called it the “Lycoming runny nose”, as from his experience they are susceptible to weeping from that crankshaft seal. But, with only about 43 hours on the engine it shouldn’t be wet up there. At the time he was painting a customer’s aircraft wings and had time in-between coats to lend a hand, so we pulled the prop. The seal was intact. But, he could place a pick that had a 90 deg bend at the tip onto the seal and rotate within the bore! It was pretty unusual as the bore the seal rests in needs a sealant applied before the rubber seal is pushed into place. We were sure that we had done this on assembly, but the evidence suggests otherwise! The old seal was removed, bore was thoroughly cleaned, sealant applied and a new seal was pushed into place. After the post-inspection run-up we had a good look at the nose, and the dry case proved we had found the culprit.
I did install a K&P S15 permanent oil filter in place of the normal Tempest oil filter. I’ll report on that and how it works out in the future.
One embarrassing find was the elevator trim cable turnbuckles weren’t safety wired! On my BH they are inside the back of the fuselage, in front of the horizontal stab. I don’t even know how many people looked the airplane over in the previous 12 months and everyone had missed it. I’m not proud of the find, but I’m glad it was found and taken care of. I pride myself on being anal-retentive on such things, but such a simple thing being overlooked is pretty scary. Anyway, lesson learned and I hope as others look at their builds when they are getting ready to fly to triple-check everything.
Another discovery was the bottom of my EarthX ETX900 battery case had melted! I never had any issue with the battery and it performed great. I shared these pictures with EarthX tech support, along with pictures of my installation. They said it was probably too hot against the firewall and that caused the case plastic to sag where it wasn’t supported. They said to send it back and they would check it out. I did, and after evaluation they said the battery checked out fine. They would put the components in a new case and send it back. I got it back and it looked suspiciously like a new battery, at no charge! It does get hot at the firewall and I do remember when I was breaking in the engine, it ran pretty hot under the cowl. On one day last summer, after refueling on one of the engine break-in flights, I did get a battery temp warning light indication. That may have been the time when it happened, I don’t know. But it wasn’t easy to spot and the folks at EarthX were amazing to deal with. At their suggestion I fabricated a heat shield box for it, covered with Thermo-Tec 13575 aluminized heat barrier. I’ll fly with it for a bit and see what happens and determine if it is effective in preventing any thermal deformation of the battery case. If it isn’t enough. I’ll probably install a blast tube for extra cooling.
The last thing I did was install an AV-MAG magnetometer in the right wingtip for my AV-30s. The headings on both units are worthless without it. The installation went relatively well, but it took some doing. We had to use the wiring for the nav light to pull the magnetometer shielded wire and some lacing tape through the wing, and then used the lacing tape to pull the nav light wire back through. Moral of the story, maybe when the wing is open, leave a string or something in the wire path to help someone thread something through in the future. After the installation, I had to go out to the compass rose and calibrate both units at 30 degree increments. Since there were no lines connecting the painted compass arrows, it was impossible to get it accurately on centerline. I ran to the local hardware store and got some lime green paracord. I used a couple of heavy things to hold each end in place on the painted compass rose while I wrestled the BH into position. It was a royal PITA to do by myself. The wind was blowing and it was cold, but I did get it done.
If you are building, don’t give in, don’t give up. It’s worth it!

Electrical Systems Part 3: Execution

Source: 2023 Q2 Beartracks, Jared Yates
This is the third and final entry in a series about Bearhawk electric systems. The first two covered design and materials, and this one is about bringing it all together, starting with tools. I’ll tell you about some of my favorites, and hope you’ll tell me if you have any that I’ve left out.

This handy kit from stein gets things started. Top from left to right: Blue-handled wire stripper, red packaged dies for the ratchet crimper (teal, lower left). The cyan handled flush cutters in the middle on the right are positioned under the less-desirable insertion and removal tools, and above the d-sub crimper. Left of the dsub crimper is a molex crimper, which will probably also work with Weatherpack pins.

Many of the wire-related tools are shaped like pliers. First, we have the flush-cutting side cutters, such as the Yard Store SKU 50195 or Stein Air SKU SAT-006. These are not strong, so don’t use them for anything harder than copper wire, and anything much bigger than 18-gauge is pushing it. They are cheap and I consider them to be consumable. They also work great for zip ties, because you can make a nice clean cut that won’t later remove skin if you are working in the area. My next most-used tool is a nice wire stripper. The Ideal Stripmaster series comes with various dies, such as the P/N 45-097 which covers 16-26 gauge. I use one designed for 10-20 gauge wire, and one designed for 20-30. In my case the plastic coated handles are different colors, but if they weren’t I’d probably paint one so that I could know which was which from a distance. Dies are also available for coax and other applications.
Next up is a ratcheting crimper with interchangeable dies, such as the Klein Tools 3005CR. There are several different variations on this style of crimper. One set of dies works with the color-coded PIDG terminals. I also have a set of dies for coax cables and one for automotive spark plug terminals. This last set comes in handy if you are making up an ignition harness for the P-Mags.
Another well-used tool is also a ratcheting crimper, but one whose dies crimp from four directions. This one is made for d-sub pins. As-delivered, the depth stop is set for standard density pins and sockets. I prefer to start by inserting the stripped wire into the pin, then I rotate the wire to ensure that all strands made it into the connector, then insert the connector into the crimper and crimp. You can procure a different type of machined brass stop that will automatically set the depth for high density pins, or if you don’t mind living dangerously, you can just not insert the HD pins fully to the stop. Insert them until the brass end is even with the outer edge of the die, and crimp. With all of the ratcheting crimpers, be sure to conduct a sturdy pull test once the connector is crimped, to ensure that the wire won’t come out. You might also need a crimper to handle big wires, such as the Stein Air SAT-002. On our first plane I soldered these sizes of connector instead of crimping, but the crimping is much faster.

Speaking of pins, you’ll need some way of removing d-sub pins from their housings. The extraction tools range from fragile plastic, to nickel-plated, to fancy brass tools with the replaceable tips (TE Connectivity 91285-1). The nice one is around $30 from places like Jameco and I wish I had learned about it sooner, because it works so much better than the other alternatives. In the photo above you can see that it comes with a little allen wrench and several tips. The green dot tip works with HD d-sub pins and the red dot tip works with standard pins. If you are wiring a whole panel it may be worth buying some extras of these, because while they seem to be the best, they are still consumable. All of the tips and the allen wrench fit into a hole in the handle, under the red cap.

I also get good utility from a device called a wire spoon (photo left). It allows for adding a single wire to a bundle, and works great for helping get wires through a grommet at the firewall or a bulkhead.

There are several ways to pass through the firewall, with my favorite being a welded stainless part and some fire sleeve. Some folks on the Aeroelectric list talk about finding bathroom fixtures (grab bars) to make these pass-throughs out of, but you can buy airplane-specific versions from the usual suppliers. I used ACS Part# 09-00978. If you’ll be wrapping the wires with fire sleeve inside the stainless tube, be sure to order an oversized tube to allow space for all of that. If you don’t have room or desire to use such a pass through, you can also make or purchase stainless steel shields for the grommets. Details in the Tony Bingelis books show how to use a socket (like from a ratchet set) and a block of wood to form them. Pre-made two-piece shields such as Part# 61-300 from ACS will likely present a better value unless you are just looking for something to do. I always use some type if shield at the firewall, because in the event of a fire in flight, those grommets will be gone in seconds, and you’ll have an unacceptably large hole in the firewall. I also seal the shield, wire, and grommet interfaces with 3M Fire Barrier 2000 caulk. One 11-ounce tube is enough for a few airplanes.

Having the tools ready is important, but there’s no progress without a definitive plan for which wires to connect. My favorite way to keep track of the wiring plan is with a computer spreadsheet. You can achieve similar results with a pencil and paper, but the spreadsheet allows for easy editing, color coding, and cloud storage. If my whole plan was on a physical piece of paper I’d be scared of losing it. I used Microsoft Excel but the no-cost Google Sheets works about the same. At the bottom of each workbook there are tabs for the sheets within the workbook. Each avionics device gets a tab, such as the audio panel, radio, Skyview, etc. I color-code the background of each tab. In my case Garmin is pink, the audio panel is tan, the Icom radio is blue, and the Skyview is gray. I make up a little table with three columns and as many rows as the connector housing has. The first column is the pin number. The second column is a description, and the third column is the destination. I color-code the background fill for the pin number yellow until the wire is done, then I change the fill to green. This helps ensure that all of the wires are done as the project comes to a close.

In the example to the above, each Skyview component has its own table, with the left and right screens being on the left side, the EMS being in the third column. In this case purple pin numbers are not intended to be connected. Use whatever colors you like, or not! If it helps to make a spreadsheet, then do it, and if not, do what works for you. Just be sure to save it, it will come in handy later if you ever need to change or troubleshoot connections. The second and third columns are filled with the color of the wire insulation.
Wire by wire, the harness will begin to come together. I’ve become especially fond of spiral wrap for this early stage. I get the cheap stuff and cut out short 3-4 inch lengths. If I space these every foot or so, it helps hold the bundle together until it’s complete. The final securing is a matter of preference. I’ve tried methods including periodic zip ties (least favorite), wax lacing cord (lightest weight), and higher-quality Fire-Resistant Polyethylene Spiral Wrap. I feel like it is worth the weight penalty to use the spiral wrap, due to the extra protection it affords the wires and ease of making changes in the future. At the moment Skycraft Surplus has some of the good stuff in stock. I use the 1/4’ and 1/2” diameters.
The most important thing about the execution phase of the wiring is to work carefully and with good craftsmanship. I hate having to chase down and troubleshoot an intermittent problem that turns out to be of my own making, either by performing a poor crimp, or connecting something wrong. Pull-test each crimp, check for good strain relief, check and double check pin placement in connector bodies before you apply power to expensive parts.

Electric Systems Part 2 – Materials

Source: 2022 Q4 Beartracks, Jared Yates
In the last issue, the first part of this series discussed electric system design. This installment covers materials, and just as with the last part, this will be an intentional over-simplification of the concepts in the AeroElectric Connection book by Bob Nuckolls. Sometimes it feels like there are too many ways to get the job done, so I’ll describe the way I prefer, which is certainly not the only right way.
Wire
Perhaps the first material required for an electric system is wires. For wires smaller than 8 gauge, I only use MIL-W-22759-16a wire, for a few reasons. First and foremost, if the wire overheats, I’m comfortable with how the insulation is going to behave. Second, I especially like how thin the insulation is, yielding a smaller overall wire size for a particular gauge. Also, I feel good about the quality control during manufacturing. Many of the wires that I see on eBay and Amazon are copper clad vs solid copper, and insulated with who-knows-what. The preferred wire is readily available in all sorts of colors and is usually around 21 cents per foot in 22 gauge. In my first wiring job I purchased a big roll of wire with white insulation, and that works fine, but since then I value and appreciate different colors. Sometimes a device comes with wires pre-attached, and in those cases the only option is to use what it comes with. I try to switch over to the preferred wire as close as possible to the device, minimizing the length of the unknown wire. Speaking of gauge, I follow Bob’s preference to use no wires smaller than 22 gauge, for mechanical durability and ease of working.
For the large wire needs, typically the one that grounds the engine to the airframe, and goes between the battery and starter, I prefer welding wire. It is often in a 4 gauge or 2 gauge size. It’s locally available from the same place you get welding gases in black, and with a little ecommerce you can find it in other colors too. It is mechanically very robust. As Bob says, it’s designed to be driven over by dump trucks. It’s also very flexible, a trait made possible by its very fine strands. The larger sizes of MIL-W-22759 -16a are certainly fine too but they are much less bendable, which can be a problem on shorter runs.
You’ll want to craft some means of wire identification. Wire insulation color can be a start, but in the years after initial installation, I’ve surprised myself by how much I forget about what goes to what. I have to leave myself notes and for wires that means labels. I’ve had good results with using 1/8”-1/4” clear heat shrink tubing. I write the label on card stock with a fine-point sharpie, cut that tiny piece of card stock off of the larger sheet, and shrink it under the clear tubing. I used larger tubing to label the Faston connectors where they joined the fuse panel, along with the amps required for the corresponding fuse.

For wires less than 16 gauge, 1/8” tubing worked well. In the case of a ground wire, I’d label the end that attached to the grounding point (forest of tabs) as to which device the wire belonged to (GPS, radio, etc) and the black insulation let me know that the wire was a ground at the device end. For wires with white insulation, I label each end with details about what the other end is connected to.
Here is a larger example, just disregard the loose nut at the starter contactor:

For my most recent project I tried a DYMO Rhino 5200 Label Printer. It makes the usual peel and stick labels which are great for instrument panel placards, but it can also print on heat shrink tubing. They sell the heat shrink tubing based on its width when smashed flat and ready to print, so a 1/8” tubing is much smaller than a 1/8” diameter. Here is a photo of the result, as compared to the handwritten version above.

What about shielded wire? Use shielded wire for the audio system. For stereo audio, you’ll need to have shielded cable with three insulated 22-gauge conductors (left, right, and low/ground, MIL-C-27500). The microphone jack will require two conductors. Ground the shield at the audio panel/intercom end and “float” the shield at the jack end. That means just cut it off and don’t connect it to anything. Be sure to isolate the audio system jacks from the airframe, which will require some insulating washers with shoulders.
Magneto p-leads need to be crafted from shielded wire, and in that case the center conductor goes to one terminal on the mag switch, and the shield goes to the other. When the mag is selected “off”, the circuit iscompleted between the center conductor and the shield. In this case the shield is doing double duty of taming the noisy magneto signal while also being half of the circuit. In the audio system, the shield is usually not a conductor. Shielding does mitigate specific kinds of undesirable noise, but it’s not a cure-all for noisy signals and using shielded wire when it isn’t necessary is going to add cost, build hours, and frustration for no gain.
Grounding
To a beginner the ground conductors may seem less glamorous than the supply wires, but electric things can’t work without a complete circuit. The ground conductor is just as important as the positive wire, and if you have very many devices, the grounds will be numerous. A great way to keep them organized is with what Bob calls a “forest of tabs.” This is a brass assembly with several quarter-inch brass tabs,
which make for easy attachment with Faston connectors. You can purchase these tab arrays from Stein or B&C. You can also create one by soldering on rows of pre-made brass tabs (photo right). One advantage of the latter option is that you can create custom shapes and arrangements. Add a dozen extra tabs for future expansion.
It is a crucial safety matter to have the engine reliably grounded to the airframe. This is best accomplished with a large conductor, in the realm of 2-4 gauge. This is a good application for the welding wire. Install the cable as soon as you have mounted the engine, just to keep from forgetting to do it. An engine that doesn’t have an intentional ground will have an unintentional ground, which may be a control cable or worse. I’ve found it useful to install two tab arrays, one on each side of the firewall, back to back. I used two AN-4 bolts that go through a tab array, through the firewall, through the other tab array, then through the eye terminal on the airframe side of the engine grounding cable. That provides a tidy and singular grounding point. There are many ways to get the job done, but I like to keep the soft copper layer out of any structurally critical bolts like the ones that hold the engine mount to the fuselage. The main takeaway is to take grounds seriously and keep them centralized to make life easier.
Circuit Protection
I use ATC blade fuses for circuit protection, except for the alternator field which requires a breaker. I elected to use a breaker for the p-mags so that I can pull the breaker during mag checks to verify the internal generators. This function could be obtained with a switch instead, in which case the pmag could be protected by a fuse. I subscribe to the philosophy that I’m not going to troubleshoot fuses in flight, so I don’t make them accessible. This is another reason that I prefer the p-mag to have a breaker. If the engine isn’t running in flight I might make an exception for troubleshooting, and using an accessible breaker opens up that option. I prefer the Klixon 7277 breakers because of their small form factor, and the breaker can be pulled to open if desired. They are around half the size of a similar Potter and Brumfield breaker. Keep in mind that the circuit protection is there for the wire, not for the device. AC43.13 has a chart to help decide on which size wire to use with a device, and that is of course the definitive source– but here’s a shortcut. If the device doesn’t need more than 5 amps, use a 5-amp fuse and 22-gauge wire. This will be almost everything in the airplane. The most correct answer will get into acceptable voltage drop based on the length of the wire and acceptable voltage drop. But in our airplanes, I haven’t found a case yet where I needed to increase the wire size bigger than 22 for a 5A fuse. Some devices may require more current, with corresponding larger fuses and larger wires. For example, if you are using incandescent position lights, they will likely need a 10A fuse and 18-gauge
wire. Surely you’ll want to switch to LED-based lights. These days they don’t cost much more initially, and they will likely save money by having no bulbs to replace. I used a 7.5A fuse and a 20-gauge wire for the starter contactor.
Shorthand Wire Sizes:
5A Fuse – 22 Gauge Wire
7.5A Fuse – 20 Gauge Wire
10A Fuse – 18 Gauge Wire
15A Fuse – 16 Gauge Wire
Often, small avionics devices will call for very minimal draw. An intercom might only need the services of a single amp fuse. It would be acceptable to use a 1A fuse in that case, but I still prefer to use a 5A fuse. If for some reason I need a replacement, even the worst local auto parts store will have a 5A ATC fuse, but the best store might not carry a 1A fuse. If it is acceptable risk, you might consider combining such small devices onto a single fuse. The risk is that if one device were to have some sort of internal short and open the fuse, the other devices on that circuit would also be inoperative. For example, panel-powered ANR headsets might pair just fine with the intercom. Losing one of those might as well mean losing the other. Some otherwise minor devices may warrant their own separate circuit, such as the dome light. If you’ll be flying at night, a dome light can be a very useful thing to have, perhaps even on a battery bus.
Connectors
In any vehicle electrical system, connections are often the weak link. Material selection can help mitigate this vulnerability. Whenever possible, I use crimp-on connectors and incorporate a strain relief. These fall into the a few main categories: AMP PIDG terminals, d-sub pins, and Weatherpack connectors. The PIDG terminals are made by AMP TE Connectivity and are color-coded to correspond to the wire sizes they fit The red ones cover 22-18 gauge which covers just about all of our Bearhawk uses unless more than one wire is going into the terminal. Stein and other places sell a handy variety kit, or you can make a list and just order what you need. Be sure to spring for the genuine AMP brand parts, because they have the nice integrated strain relief that supports the insulated part of the wire on the way out. I go through a few of the ring terminals but lots of the quarter inch Faston tabs (PN 8-640903-1) and butt splices (PN320559). You’ll also use a few of the larger ring terminals that go on welding wire. Purchase these based on the wire gauge and also the diameter of the hole. For example, the engine grounding wire might use two ring terminals with quarter inch holes for 2-gauge wire. They are available from Stein and also from the local welding store. D-sub pins are popular in avionics. They come in two main flavors, standard and high density. These little pins require a back-shell assembly for strain relief. The usual suppliers carry male and female standard pins. I haven’t yet encountered an application for female high density pins. They are available from Stein and B&C or if you want to try and hunt them down from non-aviation suppliers, search for those conforming to MIL-C-39029 for the standard size. It is possible to use solder-cup d-sub connectors, but it’s harder to swap around wires if you ever need to. D-sub pins can also make a very nice compact connector on their own, if you have a single wire that needs an occasional disconnect. Crimp on the pins, plug them together, then cover with snug heat shrink tubing. The end result is smaller than a butt splice and removable if you sacrifice the heat shrink tubing.
The final main category of connectors comes in applications like the wing tip lights. If you remove the wingtips as you probably should for condition inspections, you’ll want a way to disconnect the lights. Same with cowling-mounted landing lights. My first solution for these situations was the nylon-body Molex connectors. You purchase the housings with the desired number of conductors, then purchase male and female pins suitable for the wire gauge to be crimped. They have a built-in strain relief at the pin, but I’ve come to prefer the Delphi Weatherpack connectors (photo right). I get them from places like Amazon and eBay, and have had good results with both the genuine Delphi parts and the knockoffs. The pins are crimped onto the wire and also onto a little rubber seal.
This provides environmental protection extra strain relief. The seals and pins are gauge-dependent, and it takes a little digging sometimes to get the right parts for 22-gauge wires, because most non-aircraft applications are using larger wires. You can mix and match different gauges in the same housing, and housings are available in flat arrangements or in more compact arrangements. I like the flat ones for the
wing root area and the others for cases where the connector might need to pass through a hole.

Switches
There are several style choices available for switches, but I prefer the little silver ones called “bat” handles. The switches available from Stein and B&C are typically Carling F-series (such as the 2FB53-78/TABS). That line of switches is available with a broad variety of terminal options, but the quarter inch fast-on tabs are my favorite. These switches are reasonably priced by airplane standards, and will likely last as long as the airplane does. Some circuits will use a plain old single-pole on-off switch. Sometimes you’ll want a three-position switch. For example, on our blue airplane I used a three position switch for the forward-facing light: off, blink, and on. The switches come in just about any configuration you might need. You’ll also need push-to-talk switches for the control sticks. Most audio
systems will require a normally-open momentary push button. I prefer one with a snap-action for good tactile feel, and I look for a switch that is environmentally sealed to protect from sweaty pilot hands. (For example, see Digikey PN CKN4010-ND).
This gives some basics for one option to equip your electrical system. The next part will cover execution, which includes planning, tools, and craftsmanship. Do you have a better way to get things done? Get in touch so we can add a follow-up article.

Control Stick Push-to-Talk Switch Detail

Source: 2022 Q3 Beartracks
Need a place to mount the push to talk switch on your control stick? Here’s one way to do it with things you probably already have, like a scrap piece of aluminum, a drill, and a grinding wheel. Start by drilling the center hole where the switch will go. For the switch I used the C&K Product Number 8121SHCGE but any number of switches would work fine. The next step was to trace a circle with the diameter of the control stick onto the aluminum, then rough-cut the aluminum to that line. I ran a bolt through the switch hole, added some spacers from leftover baffle material, and chucked the bolt into a drill.
With the drill turning, I used a bench grinding wheel (also turning) to remove material from both at the same time, until the aluminum was just the right diameter. Add in a 7/8” standard-size bicycle grip (bonus points for sparkles) and you’re good to go. Unfortunately this installation precludes tassels in the bicycle grip but life is full of hard choices.

Electric Systems Part 1

Source: 2022 Q3 Beartracks Jared Yates
Going back to the 1900s when I was a 60-hour instrument student, I remember taking off on a training flight in a Cessna 172RG at night. Each student had a 2-hour slot, 5 days per week, and mine was 5-7pm. The Cutlass has an electrically-driven hydraulic pump with a major current draw during gear retraction. Shortly after gear retraction, the low voltage light came on, and until then, I didn’t realize how much I didn’t know about the electrical system on that plane, or any others. Obviously a red light was indicating a problem, but I didn’t have any plan for what to do about it. The instructor had me cycle the alternator half of the split red switch, resetting the alternator, and the light went out, so we continued the flight. Sometimes we get lucky with lessons like these, that don’t cost us much in the way of tuition.
When it came time to tackle the electric work on our first Bearhawk, I knew I wanted to build a robust system that I understood fully. That led me to reading the Aeroelectric Connection book by Bob Nuckolls, and joining the corresponding email list hosted by Matronics. These have both been a great resource over the years, but by design, these aren’t usually “recipe” resources that give step by step, actionable
instructions. Rather than try to write about everything you might want to know about electricity, I thought I’d attempt to make a Bearhawk-specific addendum in a short series of articles, to help make more specific observations that apply to our type of airplanes. If you are the type of reader that wants to know every detail, I can relate! Start with the Aeroelectric Connection book, and come back here for a few highlights, which by then you’ll judge as over-simplified.
There are at least three main considerations when it comes to your Bearhawk’s electircal system, or any other system. Those are the design, the materials, and the execution. Deficiencies in any one of the three will cause problems, maybe later or maybe right away. It’s important to be intentional about each of these steps if you want to have a safe and reliable airplane. All three are important, but let’s take them one at a time, starting with design. Surely you’ve had the experience of telling a non-flying person that you are building an airplane, to have them assume you are also designing the airplane? Designing and building an airframe are absolutely two different skill sets, but that might not be obvious for someone who hasn’t tried it yet. The electric system on your airplane is the same way. It needs to be thoughtfully designed, and I knew early on that I didn’t have the skills or experience to do that. Thankfully Bob Nuckolls has provided some
architecture” plans in his book. Ten years ago when I was wiring our first plane I used his drawing labeled Z13/8, and when we got our second plane and it was time to reconsider its wiring, I went back to the book to see if that was still the best drawing to use. Since then, the philosophy has changed slightly, and there is a new architecture called Z101B. This drawing replaces the others with updated thinking. It is modular, with the intent being that we can decide to use certain parts, and leave out certain parts, as the mission dictates. It’s color-coded, so pull up a copy let’s talk about it.
If you are going to have a charging system (alternator), the black ink represents the “pretty sure you’re going to want these” items. If your build is more like Bob Barrows’ first Bearhawk with no starter, alternator, or battery, you might want to skip this article. There have been a few Bearhawks with “total loss” systems that use a battery without an onboard charging system. If you’ll be going in that direction, the design is much simpler, but you can still start with the black portions of this diagram. Just leave out the starter contactor and route the b-lead to the battery contactor. It’s important to note that Z101B has some wire sizes noted, but these aren’t guaranteed to be correct, because the length of the wire and the size of the load may dictate a larger gauge. In our plane, I didn’t find any cases where I needed to enlarge any compared to the drawing. Just as we decide on which airplane to build based on how much we want to haul, we need to have a plan a the beginning of the electrical design for how much load the system will need to support. Make a chart with each item you intend to install, which bus it will be on, and how many amps it will need in operation. The kinds of things that tend to drive wire size increases are the hungry devices like resistive heaters (seat warmers, heated pitot tubes) rather than the low-draw LED lights and modern avionics. If you have trouble with these steps, there are lots of good resources on the Aeroelectric list and in the book.
Starting on the right side of the page, we can see the starter and alternator. This drawing uses an external alternator regulator like the B&C, which is mounted on the cold side of the firewall. Early in the process, I drew a line in the diagram to show where the firewall would be (photo below). In my case, the battery was on the aft side of the firewall, so there was a large wire going from the starter contactor, aft through the firewall, then to the master/battery contactor, which was as close as possible to the battery. In this arrangement, the alternator B wire (the output coming from the alternator) was all forward of the firewall. The small 20-gauge alternator field wire and the 18 -gauge “push to start” wire also pass through the firewall.

On both our blue and red planes, I found it convenient to make a small aluminum panel to mount just outboard of the front right seat occupant’s right knee. There are tabs on the kits in that area, and .032 aluminum with a flange here and there was plenty stiff in 805TB, our first plane.

For 303AP (the second plane/rewiring) there was already a piece of aluminum in that spot for the altitude encoder that we were removing, so I reused that piece which looked to be about twice as thick.

The main bus is a plastic automotive fuse block which I attached to that panel, and the battery is mounted on the cold side of the firewall, just forward of the right front seater’s knees. That allowed me to also put the battery bus, a smaller fuse block, on the same panel. The ground bus is a brass “forest of tabs” mounted through the top center engine mount bolt. There are some tabs on each side of the firewall, and that center engine mount bolt is a nice sturdy place to attach the large ground cable that connects the engine to the airframe. The black “DC Power Master” switch is a three-position progressive switch, with the middle position being battery on, and the upper position being battery and alternator on. This creates a function just like that red Cessna split switch with slightly different pilot action of course. On our blue airplane I didn’t even bother with an alternator switch, just pulling the field circuit breaker if I needed to have the master on without the alternator. When I wanted to sit in the plane and spend time tinkering with avionics, I would pull the alternator field breaker to reduce its rather substantial draw on the battery. While I used fuses for almost all of the circuits, the alternator fields must be on a breaker, because of the way the overvoltage protection works. The three-position switch is more elegant, but its two main downsides are that it is possible to forget to move the switch all the way up during power-up, and that it isn’t readily
available except from Stein and B&C. The first concern is mitigated by the must-have low voltage warning, which flashes any time the master is on with the system voltage at “battery only” levels. The second drawback is mitigated by not being such a tight wad, these are airplanes after all.
That covers most of the important pieces from Z101B in black ink. The color sections are optional modules. In our second airplane, we don’t yet have any need for a second alternator. Our first plane only had electric instruments, so I used the small SD-8 alternator on the vacuum pad, in addition to the primary belt-driven alternator. If you are building a strictly VFR airplane as most of us are, you might be happy with just the pad-driven alternator as your primary. If we ever create a more electrically-important instrument panel, we’ll go back and add in the red sections. I did save a spot on the instrument panel, marked with a tiny punch, for where we can put the “aux alt” switch, an additional warning LED, and a field breaker. The aux alt switch, like the master, is a three-position progressive switch.
The green and blue sections are the brownout bus. Some folks have electronics that they want to keep powered during the big voltage drop that happens while the engine is cranking. These parts of the system provide for that option, but I didn’t use them. With a system like the Dynon Skyview, each screen gets its own backup battery, and those little batteries will keep the screen alive during engine start. Our
second plane has simple analog engine instruments that don’t have any boot-up time, so there’s no need for the brownout bus. If for some reason you do see a need for it, you’ll want to make sure you have room on your distribution panel for another fuse block, another relay, and the optional brownout booster. Keep in mind all of these features add weight and complexity, and perhaps very little gain.
The purple section is the engine bus, and I did incorporate those parts. The engine bus itself is another small fuse block on the right side panel by the others. For me, this bus earns its keep as a load-shedding bus. If we are flying along and the alternator quits alternating, I can move the purple switch up, turn off the master, and save a little energy. The things on the main bus will be shed, and the master contactor itself will stop drawing the usual amp it uses just to hold itself open. In normal mode with the master on, the purple engine bus is powered by a short wire that goes from the right side of the battery contactor to the diode bridge. If the master contactor is off, this circuit goes cold, but by actuating the purple switch, the engine bus can be powered through the relay, which is powered by the “fat wire tie point.” In my case, that was the left side of the master contactor. The diode keeps current from flowing backwards on the normal path, and while the form factor is a diode bridge, it’s just using one of the diodes in my case. The bridge is an easy to mount and durable package. Converting these conceptual plans into a physical system is not trivial. I started by printing a hard copy of the diagram, and as I completed each wire, I traced its depiction with a highlighter. Just as none of our ribs are “born formed”, none of our planes are born with wires. While it can seem like a lot, start with one, and keep working, and before long you’ll run out of wires to install. But don’t start installing just yet, until you read about materials and craftsmanship in the upcoming issues. Also keep in mind that the installation I describe here is just one way to get it done, perhaps not the best way, but it works so far. If you’d like to know more about the why and how of Z101B and how it fails during various scenarios, head on over to the Aeroelectric list to follow the discussions that followed its development.

Wing Wiring General Discussion

Regardless of what you’re wiring, you have to give some consideration as to where the wires are going to be routed, how best to protect them, and how to guarantee the reliability of the connections.
Your best source of detailed information on wiring is the Aeroelectric Connection book by Bob Nuckolls. Another good source is the Tony Bingelis series of books. If you’ll be hiring out the wiring of your panel, ask the panel builder about what provisions you need to make in the wing before you close it up. There are far too many details and caveats for us to go into here. However, we will throw out some rules of thumb:
1. Don’t use cheap crimping or stripping tools. Good ones will make the job go smoother and more reliably with less chance of over, or under, crimping.
2. Use name brand components, even the little ones, like butt connectors and terminals. There’s a lot of cheap stuff on the market and you don’t want to nickel and dime an airplane project.
There is NOTHING more aggravating than trying to trouble shoot a bad connection.
3. Always anchor a wire with an Adel clamp a few inches from where it connects to the unit. This cuts down on vibration fatigue at the terminals
4. For long runs like nav lights to wing root, run it through a piece of flexible conduit like the clear plastic tubing found at the hardware store and Adel clamp it to every other rib. To thread wire through the conduit, use compressed air to blow a string through the tubing as a messenger line. Then, when pulling bundles through, always include one extra thin wire as an in-place messenger line, just in case you want to run another wire through later.
While you are working on the wing, here are some possible electrical gadgets to consider:
Pitot Tube (if heated)
Lights (position lights, strobe, landing, taxi)
Magnetic Field Sensor (if you have decided on an avionics package that uses one)
Temperature Sensor
Autopilot Servo (if you decide to put one in the wing instead of the cabin)
Aux Tank Pumps
Fuel Quantity Systems (other than the sight gauges)
Antennas

Also consider the pneumatic lines, which may include pitot, AOA, and/or static, depending on your installation.

EarthX ETX900 Lithium Battery in a Lycoming O-540 Bearhawk

Source: 2017 Q1 Beartracks, Tyson Sawyer

I had long desired weight savings of replacing my Odyssey PC680 AGM (Absorbed Glass Mat/Lead-Acid) battery with a light weight Lithium Battery. This would save nearly 10 pounds over the already light weight Odyssey. I was, however, mindful of the risks of lithium batteries. Lithium Iron Phosphate(LiFePO4) is my chemistry of choice for its high current capacity and thermal stability. This is not the same lithium chemistry used in laptops, Boeing airliners, or Samsung phones. Most lithium batteries offered as replacements for 12V, lead-acid starter batteries are Lithium Iron Phosphate. More information on the different lithium chemistries can be found here: http://batteryuniversity.com/learn/article/types_of_lithium_ion
LiFePO4 batteries still have a couple of weaknesses. If excessively discharged, your multi-hundred dollar battery is junk. They need periodic balancing of their cells. Also, though far more robust than other lithium chemistries, they still have limits. Some LiFePO4 batteries I had seen, such as AeroVoltz, required occasional balancing with a special charger and had no ability to disconnect and protect themselves if needed. There are many stories of AeroVoltz batteries being turned to junk from over discharge while trying to start a difficult engine. EarthX was the first affordable LiFePO4 battery I found that had a built-in battery management system (BMS) that balanced the cells and protected the battery. When a friend offered testimonial of how well the EarthX ETX900 was working in his C-180, I ordered one. Here is a link to their website.
The first test was to try starting the engine by disconnecting the on-board battery and using jumper cables to start the engine. This failed. Not enough power was getting to the starter. I noticed that the voltage drop was much more than expected for a lithium battery and suspect that my jumper cables were the problem. After finding
a better set of jumper cables, starting was successful, though a little labored. EarthX batteries are rated to 140F maximum and are not recommended for installation on the engine side of the firewall. My plan was to install it on the cabin side of the firewall. The effort to do this turned out to be much more than expected. To research just how hot the engine side was, I installed some “non-reversible temperature labels” (http://www.omega.com/pptst/TL-10.html). These indicate the highest temperature seen by the label in 5F increments. I installed several on the battery box with the existing PC680 battery and tested them during a Halloween week kayak trip from New Hampshire to Georgia with 80 degree F temps in Georgia. The first indicator on these is 105 degrees F, and it never “triggered”. Seeing this, I changed my plan and installed the EarthX battery in the existing location. Some minor tweaks to the existing box were needed as the dimensions are not identical to the old Odyssey.
The biggest difference is that the EarthX is not as wide. EarthX provided some stick-on foam spacers to solve this.
This also left some space on one side of the battery that let me lower a Bluetooth temperature sensor (from http://www.weatherhawk.com/myblue-t) into the box and monitor temperature in the box while in flight without the need to run any wires from the engine compartment to the cabin.
With the battery installed in the aircraft, without the long jumper cables, starting was clearly snappier than with the Odyssey. Voltage while cranking was also a couple of volts higher. I have had one case of pulling the plane out of a 40F hangar into roughly 0F conditions and having it sit for a little while.
By the time I was ready to start, the carburetor was cold and the air being fed into the engine was very cold. I didn’t give it enough fuel and ended up cranking it quite a bit. On one long crank, the BMS kicked me out for a short time. One of its protection policies is to limit cranking time. After a short wait (it seemed like less than a minute), the battery came back on line and I cranked some more. I don’t know the limits of this battery, but it was clearly cranking strong when the engine finally had enough fuel to start.
One concern with lithium batteries is that they won’t put out much power when cold. The procedure to deal with this is to pull some power from the battery. Its internal resistance will cause the battery to warm up.
Generally, people will either hit the starter for a short pull, or turn on their landing lights for a bit and then shut everything off and wait a minute while the heat in the battery spreads.
Because my battery is in the engine compartment and I don’t start my engine when cold soaked, I haven’t yet needed to test this strategy.
I have found that I see the highest temperatures on the Bluetooth thermometer when running on the ground and during climb out. In the originally installed configuration, I have seen temperatures as high as 132F. During cruise, temperatures were normally not much over 100F. I have yet to explain why the temperature labels have never indicated above 105F while I have seen up to 132F with the Bluetooth thermometer. Either way, 132F is too high given that summer is still to come. It is note worthy that Odyssey lists 113F as the maximum operating temperature for the plastic case version of the PC680. The Battery University web page lists the thermal runway temperature of LiFePO4 as 518F, and classifies the battery as “Very safe even if fully charged”.

The battery was removed and the box modified to include a cooling jacket. It draws air from the rear engine baffle, through a 1 inch SCAT tube, to a partial jacket that covers the lower front face and bottom surface of the battery box. The cool air is introduced at the top of the jacket, flows down the front face, across the bottom and exits at the rear bottom of the box. I figured that these two surfaces were most directly facing the exhaust pipes and introducing the most heat. I have one day of ski flying with this configuration. Temperatures while idling and taxiing on the ground and during climb out are down substantially. Generally well below 100F. While doing multiple back-to back takeoffs that included high powered taxiing through heavy snow, I was able to get temps nearly to 105F. This is a much harder test case than I had done previously.
However, my testing and data collection is ad-hoc at best, so no final conclusions are being drawn yet. I am planning to do some more testing with the temperature labels and placing the Bluetooth thermometer in different locations. I want to get a better picture of what is happening with temperatures and try to understand why I am getting such different readings with the two sensing methods. I will also do long term monitoring as the seasonal temperatures continue to rise. Mounting this battery in the engine compartment is still in question, it may need to be moved. Outside of that, the EarthX ETX900’s performance has been outstanding.
It is about the cheapest 10 pounds you can remove from your airplane without removing a “feature”.

Adjustable Wing Light Mount

Source: 2017 Q1 Beartracks, Mark Richardson
I’m mostly scratch-building an IFR capable 4 place Bearhawk (using a lot of used avionics bought off of the Vans Air Force forums!). I’ve been wondering for some time now how I was going to mount landing and taxi lights on the aircraft. There are examples of nose bowl mounts as well as wing mounts, but I hadn’t seen anything that I liked or that didn’t weigh too much. When I built my RV-8 15 years ago I got a kit from Duckworks that fit in between two leading edge ribs. It was lightweight, adjustable, and kept the lamp close enough to the leading edge that you got a decent amount of illumination out of it.

Now, 15 years ago, the kit came with a super cheap, 55W automotive halogen light. The light it produces is a bit anemic, so I decided I decided to go with PAR36 4.5″ LED landing and taxi lights from AeroLites this time. They are super bright, cheap (for LEDs), and only draw a couple of amps total.
This is what I came up with. The mount itself consists of a mount plate, two side angles, and two lamp holder tabs, all out of .032 2024T3 . I was a little worried about the thickness of the plate material, but the distance between leading edge ribs is only 7″, so I don’t think there will be any issues with flexing of the plate.
To the right is a rough drawing showing the approximate sizes of the pieces in the picture on the left.
Once everything was primed, I riveted it together. The side angle pieces with the slot get riveted to the back of the plate using AN426AD3-3 rivets. The lamp clamps get held on with K1000-08 nutplates and AN515-898 screws.
For mounting, I figured out the movement limits of the upper side angles where the set screw was going to go by placing the mount in the wing. I pivoted the assembly by hand until it seemed right, then marked the limits on the ribs themselves. This showed me where I had to flatten the lightening hole flange so I could pivot the mount. I drilled a #40 hole through the side angles AND ribs at the point where the light mount could be, with a range of 0 degrees (straight ahead) through lots of down angle if I need to adjust it that way.
This hole is near the end of the slot in the drawing (right). I then drilled the bottom pivot holes (again, using a #40 drill) and inserted clecos. This allowed me to now rotate the whole mount while marking the track for the set screw with a Sharpie through the RIBS onto the side angles. Yes, I did that backwards at first and had a Homer moment…. I dismantled everything, cut the set screw slot in the side angles with a Dremel, and installed K1000-08 nutplates on the ribs for the pivot screws and the set screws. I then remounted everything and I now have a landing/taxi light mount that I can adjust for elevation easily after assembly.

Strut Fairing With Taxi/Landing Light

Source: 2016 Q2 Beartracks, Larry Sullivan

I wired my Bearhawk N460K (first flight, May 2015) for an AeroLED Micro-Sun landing light to be placed at the right wing strut. This required a single 20-guage shielded wire from the panel to the top of the strut. This Spring I finally decided to mount it. I really had not thought out the mounting details at all.
I originally had planned to make a fiberglass strut fairing and incorporate the light into that but as I worked with foam to try to create a mold it became clear it would be very difficult. I would have to cut it to be able to take it off and on. Making adjustment to the direction of the light would be difficult and the whole thing would be bulky and heavy.
There was a PA-12 Super Cub in my hanger and one day while I was struggling with the foam mold I looked over and saw that it had an aluminum fairing in the same location. They were much smaller since it has two struts on each side but I thought perhaps I could rig something up similarly for my Bearhawk.
I removed the PA12 fairing, which was held on with three small screws, and laid it out on my table. I then began to copy the same shape to fit my larger strut. I made a number of cardboard templates and began to refine the size and shape. Once I had one that fit well I began to play with the light placement so that it would fit inside. I was able to make an adjustable bracket for the light, and mount it with two bolts and a backing plate to the lower wing surface just inside the strut attachment point so that it did not touch the fairing. My wire came through the skin just behind the strut, again, well within the fairing.

I practiced some taxiing with the light mounted and it seems to light across the nose and forward enough to be effective for taxiing. Once the position of the light was established, I then cut a hole in the fairing and mounted some 0.016” Lexan with small screws and a backing plate.
Overall, I’m very pleased with the finished product. I don’t know if I’ve gained any cruise speed, but I haven’t lost any and they look great. I’m not sure it would really be enough to land in a non-lighted field. I might run a wire to the left wing next year!

Forming a Landing Light Lens in the Wingtip

Source: 2016 Q2 Beartracks, Mike Swain
Disclaimer: Making these lenses brought me to an emotional low in my build. I really struggled to get a lens I was happy with and I was tempted to give up. I know ya’ll like a challenge, so here is how I did it.
First, I needed the shape of the lens. To know how big I wanted, I made some cutouts of poster board to represent the size of my landing light and nav/strobe. I used these to determine how far back to go so I would end up with enough mounting area for the lights. Once I had this I drew the cut lines on the wingtip. Keep in mind your position lights (red & green) are supposed to be visible 110 degrees.

Once I had the wingtip marked up with a fine sharpie (photo above), I used a Dremel cutoff wheel to carefully cut the lines, but I left small uncut areas in the corners so the piece we want to remove stays securely in place for the next step, which is making the lens mounting flanges. I’ll be saving this cutout piece to build the form for the lens.
I marked parallel lines to the cut lines on the inside of the wingtip, 3/4″ inside and 1.25″ outside. The idea is to have 1/2″ flanges after trimming and the 1.25 overlap outside gives good bonding area to the inside of the wingtip. I cleaned the area inside the cut lines with air then wiped with solvent to clean any dust from cutting. Next I used clear packing tape to cover the entire area inside the cut lines, this will prevent the fiberglass from bonding to the piece inside the cut lines (photo below).

I now cut some fiberglass cloth so it would span the lines marked previously. It should protrude about 3/4 inch into the area where the lens will be and 1.25 outside the line where it will bond to the wingtip. I ended up using 4 pieces to go all the way around, I found it easier to work with multiple pieces. Once I had the glass cloth shapes cut, I made 6 more of each shape for a total of 7 layers. I scuffed up the area outside the cut line where there is no tape (careful not to move or mess up the tape) then cleaned with some alcohol. For the flanges, I wet out the cloth on a piece of parchment paper then put it in place, lining it up with the lines previously marked.

Once your flanges have cured, you can carefully cut the rest of the lens area out. Be careful not to cut beyond the thickness of the wingtip, you don’t want to get into your new flanges. Once you’ve removed the material you should be able to work the piece free since the cloth will not bond to the packing tape underneath. Be careful not to damage the cutout, as it will be the form for your lens. Now you can trim the flanges back to .5 inches.
You’ve now got a wingtip with a big hole.

You now need to form the 4 “walls” that provide mounting surface for the lights and finish out the space. I used heavy card stock, tape, and trial and error till I got the walls laid out. I stole some of my kids play-dough and used it as a form to transfer some of the complex curves onto the cardstock where the walls meet the wingtip. I then covered the cardstock in clear packaging tape so the wall layup will not bond. I taped the 4 cardstock pieces carefully in place from the outside, these will now be the forms for the fiberglass.

I used some thickened epoxy (left) to create filets all around the interior of the wingtip along the backside of the cardstock where it meets the wingtip. This is so the fiberglass does not make sharp 90 degree bend. I then put 5 layers of cloth with about a 1″ overlap to get a good bond. Once the layup is dry, you should be able to easily remove the card stock (below).

I used 1/16″ mirror Plexiglas to cover the walls, so I simply lightly sanded the walls after I removed the cardstock. If you plan to paint, you might need to spend some more time and filler to get a nice smooth surface.
Forming the Lens
I thermoformed my lens from .093 Lexan (Polycarbonate) using my shop vac as a source for vacuum, so first step was to build a vacuum box. I used some 3/4 MDF I had laying around and built a box 14″x22″x3″. Why that size? From what I could gather online, you want roughly 30% more material than your form to allow for stretching, etc. It was an educated guess. It turned out well to have the top frame fit in the oven well (more later). I cut a piece of pegboard to fit inside. I then glued and brad nailed some pieces of wood around the inside of the box so the pegboard would sit flush with the top. I also glued a couple piece of wood to support the pegboard in the center. Cut a whole in the middle of the box to fit your vacuum hose. Now line the top perimeter of the box with weather stripping to provide a good seal.
You need some sort of frame to hold the Lexan. I used some 1×2 pieces cut to the same size as my box. I used my Kreg jig to make a quick square frame. I then cut 4 identical pieces and match drilled .25 holes towards the outside of the frame, 2 on each side to be used and secured with screws and wingnuts. It was a pretty crude frame and you might do better, the idea is to be able to hold the piece of Lexan securely and form and maintain an air tight seal against the vacuum box. Mine was essentially a clamp between 2 pieces of wood. I lined the portion of the frame where the Lexan sits with some thin .0625 weather stripping.

The cutout from the wingtip will be the form for the lens. This need to be reinforced since you will be pulling a good vacuum down over top of it, you want it to maintain it’s shape and it needs to be elevated slightly when it sits on your vacuum box. This is due to the Lexan being in a frame and not necessarily flush to the vacuum box. I used my card stock to mock up templates for some wooden supports I cut from scrap lumber which I epoxied into the cutout (clay version, shown right). It sits on the box open side down with what is the edge of the wingtip pointing straight up.
Once you have reinforced the form, you want to make sure the surface is perfect. Any imperfection will show in the lens. Use filler and sand if needed.
When you are ready to form, the first step is to “dry” the Lexan. Load a piece of Lexan in your frame and put it in the oven at 180 for 5+ hours. You can get steam bubbles if you skip this drying step. My frame was a perfect width where it would rest on the same supports used for holding the oven racks. Otherwise you will need to support the frame somehow in the middle of the oven. You don’t want anything below as the Lexan will sag when you raise it to forming temperature.
Make sure everything is in place before starting the forming step, because it happens fast. Vacuum box, vacuum on, helper, gloves to handle the hot frame, etc. I coated my form in petroleum jelly, I read somewhere it helps. When I was ready to form, I removed the frame and Lexan and bumped the oven temp up to 350. Once it reached 350, I put the frame back in. You have to keep a close eye on things because you are watching the sag of the Lexan as the indicator of temp. I found that once the middle of the Lexan was about 2.5″ below the frame it was ready. I had my vacuum box on the floor next to the oven. Open the door, pull out the frame and immediately push evenly down over your form. You have to eyeball things a bit, but your frame needs to come down and land on the weatherstripping around the perimeter of the forming box to make a good seal. Once the seal is made the Lexan will draw down. Rather than pulling a hard vacuum, I found that I got a better part by pulling the vacuum hose out of the hole as soon as the Lexan forms around the part and holding it close to the hole, acting like a partial vacuum, otherwise the Lexan would wrap around the under side of the part which makes it hard to get out. You have to be very quick as it happens very fast. It might be better to have a helper. Another approach would be to build a solid support for the part so the Lexan cant pull under. Pop the form out as soon as it cools enough to handle but hasn’t fully hardened. It’s easier when it’s still hot but solid.
Here is a video of the actual forming.
If you get the Lexan too hot, it tends to “print” easier, and it looks wavy and shows imperfections in the form easier. I found there is a very small sweet spot at 2.5″ inches of sag. Too cold or too slow from oven to form and it will be too stiff to properly form. Also, I had better results with the polycarbonate I ordered from Amazon, which turned out to be Bayer Makralon. The brand from Home Depot and Lowes I did not have much luck with. I also tried Plexiglas but found that it was very brittle and would crack easy when I tried to trim it. Keep in mind it smells up the house pretty good too, not to mention using the food oven for heating plastic may not be the best idea. My kitchen closes off from the rest of the house and I opened a window with a fan blowing out.
I pulled the formed part out of the frame and rough cut the excess material. Then I carefully marked the rough trim line by placing the lens in place. I then carefully final trimmed with my pneumatic 1/2″x24″ mini belt sander and a lot of trial fitting. I radiused the inside corners and sanded the edge with 220 grit when I was happy with the fit.
My lens shrunk slightly, so I ended up using some quick fair compound in the flange to get a perfect looking fit. Also, where I radiused the corners of my lens the cut in the wingtips are square, again I used some putty to make everything perfect.
Once you’re happy with the fit, you can drill the lens to the flange. I drilled and clecoed #40 first, then went back and opened them up for #6 screws and riveted on plate nuts using soft flush rivets. I originally planned to use countersunk screws, but I didn’t have good edge distance on a couple of holes and I read Lexan can crack if countersunk screws are used. I settled on some low head (.063) socket head screws (Mcmaster Carr P/N 90666A002). You can now mount your lights and add any trim. I trimmed the interior area where the lights mount in .0625 mirrored Plexiglas. I used adhesive caulk to hold it on. It was a long process but it was fun and I learned a lot.