Notes About Making the Fiberglass Windshield Fairing

Source: 2026 Issue 1 Beartracks, David Kragnes

Finally got to windshield install. Thought I might have some tips.
I have built 3 boats, don’t ask why I spent time on something that doesn’t fly, so when I got to the lay up of the windshield faring I thought I might have some worthwhile tips. The plans lay out good advice for prep of the windshield and cowling.
I have used System Three so my thoughts focus on that type of epoxy. I believe West Systems behaves much the same. Once you have the windshield in place and the area taped and waxed, mix up about 1/5 cup of epoxy, the bottom 1/3 of an empty beverage can is the perfect mixing cup, plan ahead you don’t want to have to stop the process to empty more mixing cups, have the cut cloth strips and a 1 inch stiff bristle brush ready. Wear rubber disposable gloves.
You don’t need to make a big mess. Lightly paint epoxy down the center of the area, press the first layer of dry cloth on the damp surface then use the stiff brush to stipple, dab a little at a time, epoxy into the cloth only wetting till it is clear. You want to see the weave. Remember the cloth is the strength so keep it as dry as you can and have the cloth turn clear. Now in a 70ish degree shop wait 2 hours. You can save the brush in a can soaking in MEK.
Mix the next batch and repeat. Inside a day the epoxy will bond and letting it set a little will make the next layer easier. If you catch it just as it is firm but tacky, shop temperature will dictate the time. the next layer will stick nicely in place for you to stipple. Dry is good but cloth should go clear with no bubbles underneath, again being in the right time frame makes it easier as you can push down a bump if it is cottage cheese or so consistency. Start early in a day and this will all time out nicely.
When you are happy with the number of layers again give it a couple hours. Now since you have been a good craftsman the last layer looks like you can see the weave, as you start sanding you don’t want the first thing cut to be the cloth (reducing strength), so mix a little epoxy with thickener, micro balloons or wood flour, till you have thin peanut butter, and paint a nice smooth finish on the surface. This will give a nice layer to do less sanding on.

Beartracks 2026 Issue 1 – Technical Q&A with Bob

Technical Q&A With Bob
Builder Matthew Brennan asks about Bob’s use of aramid composite floorboards in his latest plane, instead of aluminum. Matthew says, “Curious if the Kevlar floorboards “sound” any different than aluminum when in flight. Is “drumming” reduced?”
Bob says, “I wear ear plugs when I fly and it’s hard to tell for sure due to all of the rest of the noise, but the composite floorboards should help dampen some of the noise.”

Builder Collin McDonald noticed some ambiguity about the hardware to use when securing the round tailwheel spring to the fuselage, and made a post on the forum to seek clarity. Should those be AN5 or AN6 bolts?
Bob says, “We’ve used 5/16 and we’ve used 3/8 bolts there, and we’ve never had any problems with those bolts. We’ve used 5/16 on the lighter planes and 3/8 on the heavier planes.” Bob has used 5/16 bolts there on his own planes, and adds, “That stinger is hardened steel. It’s a really big job to drill those out. You don’t want to have to do that.”

Making Bending Dies to Bend a Radius to Fit Around a Tube

Source: 2025 Q4 Beartracks, George Huntington
MAKING BENDING DIES TO BEND A RADIUS TO FIT AROUND A TUBE: This trick is great for matching a bend radius to a tube, such as aluminum panels that might be installed under the cabin doors and wrapping around the longerons. First, find a thick tube whose inside diameter matches the outside radius you want.
-use the procedure from the this tip to get a straight line on each side off the tube, then cut the tube in half lengthwise. Clean up the edges and cover them with masking tape, so as not to mark the aluminum sheet when bending.
-now using a tube that fits into the half tube with some clearance for the sheet aluminum you are using, place it into a vise or use “C” clamps to form the sheet aluminum into a nice radius. This works good for the elevator cable attach access at the tail, and the kick panel at the entrance. It also makes a nice large radius like I used for my gear fairings.

Duplicating Fitted Tube Ends with Paper Templates

Source: 2025 Q4 Beartracks, George Huntington
DUPLICATING FITTED TUBE ENDS: For example, if you have fit a tube for one side of the fuselage, and want to make a second tube for the other side:
-Stick a small piece of 2-sided tape place between the two tubes at each end, then wrap masking tape around both tubes near the ends (leave a space for marking). This helps to hold the 2 pieces of tubing secure without either one turning.

-Next take a new box cutter blade and using the back side, draw it across the sides of the tube. This makes a perfect straight line down the tubes, as you just remove the manufacturing scale. Be careful not to press too hard, as you only want a nice fine line. A small fine file works good for this step also.
-While the two tubes are taped together, the other side can be marked also, giving you a nice center line on both sides. This can be useful in drilling a straight hole, by drilling from each side.
-Take a piece of paper and wrap it around both ends of the fitted tube, slightly overhanging the coped ends. Tape the paper to itself, but not too tight as you’ll want to slide it off of one tube and onto the new one. You can also use a rubber band to hold the paper in place while still being able to move it around.
– Use a half round file on each end of the tube to remove the excess paper from the fitted ends. The file is cutting the paper where it is rubbing the paper between the tube end and the file. When done, the paper will have the exact shape of the fitted tube.
-Next take a sharp pencil and mark the other end of the paper, corresponding to the center line that you scribed on the tube. Measure and record the distance between the 2 pieces of paper, or the total length of the tube.
–Slide each paper off of that first tube, and onto the next tube you want to cut to fit. Set the length and align the pencil marks with the scribe mark along the length of the tube. Using a felt marker, trace the paper’s outline on the ends of the tube. Now the tube can be trimmed to make a duplicate tube.
If you want to make the same tube but mirror it for the opposite side of the fuselage, untape the paper templates and roll them up opposite way around the tube, making sure you can still see the pencil marks for the centerline. Install them as above, mark and cut the tube. Now you have made a left and right tube.

Weight Savings with Composite Floorboards and Door Skins

Source: 2025 Q4 Beartracks, Bob Barrows
I have made and installed lighter weight door skins and floor sheets. Instead of using aluminum, I used carbon fiber and Kevlar. For the floor, use Kevlar layup, to about the same thickness as the aluminum call out. For the door skins, use carbon fiber about .025 thick, 2-3 layers. Lay up by using a sheet of .032 aluminum, about 2” larger all around than the panel needed. Apply three coats of wax to the face. Apply epoxy resin, lay first layer of cloth on wet resin, then apply a little more resin. Apply the next layer of cloth and poke it with a stiff brush until the cloth is a little wet from the underlying resin. Scrape the extra resin off to the sides with a plastic Bondo spreader. These panels will be about 1/2 the weight of aluminum.
I use the West System resins, selecting the slower variant (206) if I’m going to be working in hot temperatures, or the faster variant (205) for colder temperatures. A good starting point for these materials is Aircraft Spruce Part Number 01-01665 for the Aramid (Kevlar), or Part Number 01-01232 for the carbon fiber.
The West Systems epoxies are sold in various kit combinations starting with Part Number 01-08100 through 01-08400, depending on the size of the can and the hardener type.

The photo below shows the Kevlar hinge on the mouse door. This is a scrap piece of the same material in the floorboards. I start with a rectangle, then bend it in a brake to about 90 degrees. This breaks the plastic resin but the Kevlar fibers remain. It has a natural spring-back action and is good use for what would otherwise be waste.

Thermoforming a Custom Skylight

Source: 2025Q2 Beartracks, Paul Gyger
When considering a skylight for my Bearhawk 4-Place, I had the usual difficulties and decisions, all mentioned in various threads of the Bearhawk forum. I remember reading somewhere that shaping the skylight proved difficult, mostly because the Bearhawk has 2 contours, one for the shape of the wing, and another perpendicular to the wing for the “Bearhawk bump”. This bump is required due to the elevator trim wheel, and if it is to be removed requires significant modifications to both the trim wheel and the stringer supports. Somewhere in the vast history of the forums I read about the process of thermoforming plastic, and so my long journey began to form a plastic skylight that followed the natural shape of an original Bearhawk 4-Place. The driving force of the experiment was that if the plastic was contoured it might solve two problems. First it would keep the original shape and avoid rethinking the trim wheel, and second I imagined that shaping the plastic would lend strength to it while reducing stresses from forcing it around curves. Time will tell.
Like so many of these side projects or modifications, if one sat down and responsibly made an estimate of the time and resources required for these fanciful substitutions, no one in their right mind would even consider them. Somewhat providentially some of us are not burdened with accurate assessments of how long things will really take to perfect, or how much material we will burn through in the process. It was in that spirit that I set out to first make a form, then make an oven, and then thermoform my skylight.
Thermoforming plastic can happen in a number of ways; vacuum molds and pressure molds both with weights and with air pressure. In the case of the Bearhawk a relatively simple drape type mold would suffice, basically just a copy of the natural shape of the surface in question. I accomplished this with plywood ribs that were held in place with a light frame that could then be removed and transferred to a base sheet of MDF. The voids between the ribs were then filled with whatever wood scraps were lying around the shop. The one exception to this is where the curves were only in one direction, say the center portion of the skylight. I was able to use a flexible plywood product meant for going around curves. Two examples of this product are Flexyply and Wigglewood.
The form was then covered with an old, mostly cotton bed sheet to prevent scratches in the final product:

When using a drape type mold, some consideration must be given to how the material will be held down and made to conform to the mold. This doesn’t seem like a big deal until you actually try to form a part and realize that some parts of the skylight are stretching and some are contracting, and even though things are quite flexible and pliable, it still requires a significant amount of persuasion. When planning a drape type mold having proper generous edges that extend past the actual part dimensions is highly recommended, as well as having some type of nesting area or starting point where the hot plastic can be locked into place as weights and clamps are applied. A little extra time on the mold will go a long way in making a repeatable part.

While plastic can be thermoformed with local heat application such as a heat gun, infrared, or torch, using an oven to thoroughly heat the entire part is essential. Plastic that is heated locally tends to get a wavy look that is very difficult to assuage. So the building of an oven is really inevitable, and anyone that is embarking upon this process must include this in their “time and resources” balance sheet. The design of such an oven is relatively simple, a large structure that is able to withstand heat and is insulated in some fashion. I used scrap metal to make a frame, I covered that with scrap sheet metal, and then insulated that. My heat source was two stove top burners sourced from Amazon for $30, a thermocouple and temp control unit. Now there is one design feature of the oven that is critical, it must allow the piece of plastic to stand vertically. Adapting a horizontal oven, ie the local pizzeria’s oven won’t work. There is a bit of an art to fine tuning things as far as placement of the burners and the thermocouple etc. I found that burners at the bottom worked best, with a piece of sheet metal separating the burners and the plastic. I did have a significant temperature difference between my oven floor and the top, around 10° C. I think this could be mitigated with a fan to circulate the air but I had success without. I used two metal tubes to clamp my plastic at the top, which allowed it to hang unimpeded. I won’t step into the debate of Lexan vs Plexiglass, but I will say that Lexan (polycarbonate) was significantly harder to work with. This is probably due to poor oven design, poor temp variation control, and inexperience on my part. Both of my attempts at making this part from polycarbonate failed. Lexan must be heated to a higher temperature, which exacerbates problems with oven design as a temp differential will be greater with an oven that is working harder. Another problem with Lexan is even though it’s hotter when forming, it cools faster, necessitating a fast transfer from the oven to the mold. After I built my oven I had some scrap acrylic that I used as a practice piece to test the oven and get a feel for things. This acrylic proved much easier to work with. It requires less heating (145°C vs 175°C for Lexan) , it cools slower, and it just seems to be much easier to work with for an amateur. Lexan also requires a drying phase to get the moisture out which is really quite long- for my piece it was 6 hours. Acrylic can be heated to temp without this drying time.

Eventually the time comes, the mold has been made, the oven is at temperature, and the plastic is ready. Nothing left to do but get everyone in the house fitted with welding gloves or oven mitts and bake some parts. I found that after about 25 min in the oven with a temp set to 145°C my plastic was just the right blend of pliable and able to take shape, without it being too molten. When a piece of acrylic is heated it will first bend or rise, this is a natural occurrence and it means that your plastic is not yet at temperature. A little more heat, or just a little more time baking and that curve or rise will settle down and the whole piece will be perfectly flexible. Going much past this temperature isn’t a great idea as it opens you up to deforming wherever weights or clamps are applied. It is a sweet spot, I found mine at 145°C.
Small deviations in adherence to the mold shape can be touched up later with judicious use of a heat gun. Great care must be taken as this local heating can give a distorted look. I had a couple small areas that raised up a bit as they cooled, but I was able to use the heat gun and get them proper.
In the end my acrylic skylight was a success. I have a part that follows both contours of my frame almost exactly. My skylight is under no stress from bending, actually quite the opposite it has added strength from the bending reinforcement. The view through the acrylic is almost perfect, I did end up with a few slight waves but they aren’t really noticeable unless you suffer from the OCD only a fellow builder will be racked with. Ultimately I decided to make two skylights and keep one on the shelf for the inevitable replacement required down the road.

Carbon Fiber Door Construction Using 3D-Printed Joints

Source: 2025Q2 Beartracks, Matt Clark
I wanted one-piece gull-wing style doors similar to what Virgil did on his BH5. I considered welding the window and door sections together or building from scratch out of steel, aluminum, or carbon fiber. I wanted to use square tubing to make attaching the plexiglass and sealing the edges easier. I’m better with composites than I am with TIG but my initial problem with the carbon fiber idea was how to make the corners strong.
When looking at carbon fiber tubing online I found some manufacturers sold corner inserts at normal angles like 45 and 90 to make strong epoxied joints. So, I figured I could 3D print corner inserts like those at whatever angles I needed and then wrap the corners with another layer of carbon fiber to make a very strong joint. I used 3/4 square 0.045 wall thickness CF tubing (Dragonplate from Allred co.) and 3D printed corner inserts using ASA-CF filament. The ASA is good with epoxy and the CF infusion makes it stiff and dimensionally stable. I created a 3D model in Solidworks for the corner insert and printed a few (many!) prototypes in cheap PLA or PETG. The top two corners are the easiest because those 3 pieces (top, upper front, and rear) are in the same plane. I measured each corner angle and printed those top 2 prototypes first. I had to print a few versions to get the angles just right. To get the angles perfect on the CF tubes I cut with an abrasive wheel and then sanded to fit.
1. Prototype Corner Insert:

2. Checking Fit

3. Fits Good

Once I was happy with the fit, I printed the corners out of the ASA-CF. I had to adjust the dimensions of the CAD drawings to get the ASA-CF part to fit snugly compared to the PLA or PETG. I epoxied those top 2 corners in place by clamping them into the door openings with approximately a 3/16 gap all around.
Top 3 Pieces and Hinges Tacked:

With those 2 corners secure I next worked on the hinges using 3/8” long sections of 3/16”ID stainless tubing on either side of the fuselage hinge tube very similar to the window hinge design. The stainless barrels were epoxy tacked in place. I used a clear 3/16 PETG plastic rod through all the stainless to keep them aligned during the glue up. I did have to adjust the hinges on the frame to provide more standoff to clear the square tubing and reinforcement CF (two photos below). I cut the outer welds, bent the barrels down slightly and then re-welded. I used a 3/16 solid brass rod through both hinges to keep them aligned while adjusting.
Hinge Outer Welds Cut:

Hinges Adjusted and Welded:

Once the SS hinge pieces were tacked in place on the top CF tube, I used epoxy with micro bubble filler to smooth the hinges out before wrapping them with carbon fiber.

7. Micro filler epoxy:

8. Sanded Smooth and Painted:

9. Unwrapping Hinges:

To wrap the hinges, I used 3 wraps of 3k carbon fiber, peel ply, and flow material. I then tightly wrapped the whole joint with electrical tape working from the middle out and let it set for the whole curing process under a heat blanket. The electrical tape wrap is a good way squeeze the excess resin out into the peel ply and flow material for a part that is difficult to vacuum bag. And the vinyl tape doesn’t stick to epoxy. The lower doors are a little more complicated as the front lower piece is curved and creates a compound angle at the 2 lower joints. For the curved lower pieces I clecoed a piece of .025 aluminum to the lower front door former and used that to trace the curve onto a piece of ¾” MDF. I cut kerfs into the inside of that piece without cutting through the 4th wall and bent it around the MDF form to glue the kerfs shut. Then I wrapped and vacuum bagged those pieces.

10. Lower front piece bent around form. The cuts are on the gold lines through only 3 walls:

11. Vacuum bagged lower pieces:

The lower corners have to allow for a slight twist to allow the square tube to be parallel and flush to the bottom former, so one leg of the bottom corner inserts is round to allow the bottom tube to be on a slightly different plane than the lower front. The round section isn’t as strong because it’s less surface area to epoxy, but that lower front corner will get a lot more reinforcement to mount the door handles there.

12. Final corner inserts for the lower 3 joints in ASA-CF:

13. Epoxy for lower corners

Once I had it all aligned perfectly in the door opening, I epoxied all the corners with the doors clamped into the openings just like I had done the top three pieces.

14. Curing in place within door formers:

15. Corners reinforced:

After the inserts cured, I reinforced each corner with an external wrap of carbon fiber using the same technique as the hinges, with the electrical tape compression. Once I figure out where exactly to mount the gas strut to the front upper tube, I’ll add 1 more wrap from the front hinge all the way to the gas strut attachment. To seal the front, bottom, and rear edges I’ll wet layup carbon and Kevlar around the edges just like Virgil did. Those pieces will extend ½” inside the frame to provide the lip for securing the window pane. This will also strengthen and stiffen the whole assemblies. To seal the top, weatherstrip will get squeezed between the top tube of the door and the fuselage tube as it closes. The lower front corners will get reinforced further to mount the door handles which will be the same as Virgil’s with the Z linkage to pin the front and rear. I’m planning to use a single pane of 3/32 Lexan for the windows. My door frames weigh 0lb 13oz compared to 4lb 14oz for the steel frames. Yes, there is more weight to add with the handles, windows, seals etc, but all those things get added to the steel frames too.

Winter 2024 Update from Bob Barrows – Companion Progress

Source: 2024Q4 Beartracks
Bob’s Bearhawk Companion is looking more and more like an airplane. During our October visit, the weight was 1010 pounds, as pictured. In November, Bob broke some bones in his foot, and that has limited his shop hours. Thankfully the cast was removed a few days ago and in the coming weeks he can rebuild strength and spend more time in the shop. He is currently working on the exhaust and baffling. I asked whether he used a kit for baffling, and he said no. He enjoys the challenge of making a custom baffling set for each installation, and is also somewhat particular about how he wants it to turn out. He says, “When you already have an airplane to fly, it doesn’t matter that it takes a little longer.” He enjoys building things and likes the rewarding feedback that comes from consistent input to a project. There is fun and a sense of accomplishment in seeing it come together. The new Companion has several interesting features including Kevlar composite floorboards. Their translucence is displayed with the belly pan removed. The door skins are carbon fiber, and the mouse door hinge is a strip of Kevlar layup.

Summer 2024 Updates from Bob Barrows

Source: 2024 Q2 Beartracks
Work continues on Bob’s Companion project. As of press time he did a preliminary installation of the wings and has mostly completed the cowling. There is a mock-up engine that has no cylinders in place, and he has validated alignment and positioning of the engine, and is quite pleased with the kit’s conformation to the plans. The ailerons, flaps, rudder are covered, and the elevators and horizontal stabilizer are in progress. With the mock-up engine in place, the weight was 767 pounds. Bob feels like he is on track to meet the target empty weight of 1050 pounds. This build uses carbon fiber door panels instead of aluminum. Bob says it saves a little weight, and he’s pleased with how the carbon panels flex, drill, and otherwise behave much like aluminum would. To make them, he starts with a flat sheet of aluminum. He says you can also bend the aluminum if you want the part to also be bent. He applies lots of wax to the aluminum, draws out an outline of the rough shape of the panel, and paints resin onto the panel. Then he lays 2-3 layers of carbon onto the panel, and the next day, it’s ready for cutting to shape and installing. He made similar floor boards out of Kevlar, and figures those are 2/3 to 1/2 the weight of aluminum in the same application.
Bob and Diana recently flew the Patrol to Pence Springs, West Virginia for a get-together that included around 30 airplanes. They have a nice long grass strip there. Diana’s improved mobility and health are great news. She’s always eager to ride along whenever Bob flies. He says he alternates between flying his Patrol and LSA, just to keep both active, and enjoys both equally.
He has not been working much on his electric Ultralight project. It is still pending a new motor controller to up the motor output from 230 to 300 amps. Bob did design and build a new full-castering tailwheel for it, to improve taxi handling. The new tailwheel doesn’t attach to the rudder for steering but is easier to maneuver than the original skid. Bob says back when he flew his RV3 the tailwheel could either be swiveling or steerable, so he usually left the chains off and allowed it to swivel so that he could turn around more readily at the end of the runway.
Bob has been working on a solution for the Brake master cylinders that uses an EDM (electrical discharge machining) machine to make very precise fluid passageways inside of the bore. The EDM machine is well-suited for this kind of work and yields very smooth and precise shapes down inside the bore, based on the shape of a custom electrode.
Save the date for Bob’s Picnic on 10/19/2024 at VA04!

Cabin Organization with MOLLE

Source: 2024 Q2 Beartracks, Tyler Williams
I like clean organized spaces. Well, at least I do in my airplane and in my kitchen. My truck, on the other hand, is a complete mess…always. It looks like I live in it, which sometimes I do. But not a lot goes on inside the truck that forces me to be meticulous about it being clean and organized. I sit, hold the wheel, throw the snacks in the center console and turn on some good tunes. My kitchen is a different story. My chef’s knife is sharp, my spices are stocked and I am a stickler for “mis en place.” When everything is in its place, I can work efficiently and get into a flow to create, improvise and make great food.
Operating the airplane is a similar experience for me. I like everything in its place, the plane prepped and my mind sharp for the task at hand. Flying a plane, at least the way I do it, involves much more than road tripping in the truck. I don’t just get in, hold the wheel and follow the line on the map. From the preflight, to the engine management, to flying the terrain and improvising the route around weather and airspace, to chatting with ATC and jotting down instructions, there’s always something to do. An organized cockpit helps keep the mind free for the important things, and I don’t like anything flopping around loose. When flying far, I need water, a bag of snacks, sometimes a pen and paper, sometimes I need my flashlight, I’ve got my InReach on and I like to plug in my phone for music. I keep a lot of stuff in the back of the airplane too and it all needs a secure place to rest. From the basic things like a screwdriver, fuel tester and a small flashlight that get used every preflight, to the just-in-case tool kit, spare fasteners, tubes and patches, to control locks, tie downs, travel chocks and a first aid kit, I like to have what I need, when I need it. You can usually find help anywhere in the lower 48, but it sure is nice to have what you need to handle things, in flight and on the ground.
When I finished the Bearhawk and started venturing across state lines, I kept all the tool kits and spares in a duffel bag in the baggage area. But, digging through a bag of stuff to find what you can be annoying at best. For the cockpit items, I initially used the side pockets installed by my feet and the seat back pockets to stow checklists, small items, snacks and water bottles. But we travel as a family often and I like to keep those seat back pockets clear for my kids to stow their drawing paper, books, cards and such. My side pocket is best kept minimal so I can get my checklist or writing pad without fumbling around down there while trying to fly and my wife likes to have her side available for her magazine or book.
I got some inspiration from some nice overland camper trucks that used the MOLLE (Modular Lightweight Load-carrying Equipment) system to organize gear and tools. I saw seat-back MOLLE panels with small pouches and also some nice tailgate MOLLE panels for easy access to tools, even when the truck is loaded with gear. That seemed like the perfect solution for my plane. Our doors are all recessed slightly from the interior so there’s a little space there that can be used to hang a MOLLE panel and install some organizers.
I made mine out of PVC coated Cordura nylon. I found some basic dimensions for the standard laser-cut Molle grid, drew it out on the fabric and simply melted the slits with a soldering iron. Mine are 1.12” wide slits, spaced ¼” apart horizontally and 1” apart vertically. I probably don’t have the exact military spec, but it was easy to lay out and fits all the attachments well. Someone more digital savvy could do the layout on a computer and have the fabric laser cut for a faster and more precise, factory looking result. I installed snaps in the door frames and fabric and snapped on the panels. They are lightweight and work great. Up front, I have my water bottle holder, sunglasses, pen, charge cord pouch, a place to keep my phone and snacks and my fire extinguisher secured on the door for easy access and still have all the elbow room I need. The passenger door has a panel as well with the same drink holder and stuff pouches and my wife loves it. The big panel on the aft baggage door stores my first aid kit, gust locks, travel chocks, extra quart of oil and funnel, preflight tools, hanging luggage scale, spare fuel cap, pitot cover, etc. etc. You can certainly stuff all these things under the back seat and that works just fine. But it sure is nice when the plane is fully loaded to be able to just pop the baggage door open and grab what you need.