Introduction - The Coz-E

This is the build log (and other relevant information) for my cozy-derived electric canard airplane.

You can effectively think of this as a Cozy Mark IV with the rear seats replaced with a large battery compartment and an electric motor.

Unlike my digital garden, which provides more generic knowledge and things I’ve gathered, this site is intended to scope down to the Coz-E.

Last updated: 2021-06-23 22:19:06 -0700

Build Log

This section is meant to describe the build log for the aircraft, and will roughly reflect the chapters in the Cozy Mark IV plans.

Because the sidebar will last chapters in alphabetical order, I’ll also list the build-order here.

Last updated: 2021-06-23 22:19:06 -0700

Materials Used

Fiberglass aircraft are made primarily of foam, fiberglass, and epoxy.

Epoxy

There’s a number of epoxy systems you can use with your aircraft. This is a link to presentation on the Dos and Don’ts of epoxy

I elected to go with the MGS 335 system, which seems to be fairly popular amongst the different builders.

The MGS 335 system should be mixed at a 100:38 ratio of resin:hardener by weight.

Microballoons

Microballoons (or microspheres) are used with already-mixed epoxy to create slurry, wet micro, and dry micro. Microballoons should be stored in a covered container with as low humidity as possible. I use a small dehumidifier to help with this. To dry out microballoons, bake them at 250° Fahrenheit, then sift them with a flour sifter to remove lumps.

As noted, you mix microballoons with epoxy in the following mixtures, by volume:

MaterialMicroballoons : Mixed Epoxy mixture, by volume
Slurry1:1
Wet Micro2-4:1 (sags or runs like thick honey)
Dry Micro~5:1 (enough microballoons to create a paste that does not sag or run)

Though, really, you’re supposed to add thee microballoons until the desired consistency is achieved.

Slurry/Micro Slurry

Slurry is mostly used to paint or squeegee over foams immediately before glass cloth is applied over them. Do not let the slurry dry before you apply the glass cloth. With urethane foam, use a full thick coat of slurry.

Wet Micro

Wet Micro is used to join foam blocks.

Dry Micro

Dry Micro is used to fill low spots and voids.

Flox

Flox is a mixture of epoxy and flocked cotton. There are two types of flox: standard and “wet”. Standard is epoxy mixed with just enough flocked cotton to make the mixture stand up, whereas wet flox uses less flocked cotton, and is mixed so that it’ll sag or run, similar to wet micro.

When using flox to bond a metal part, be sure to sand the metal dull with 220-grit sandpaper. Also paint pure epoxy (no flox) on the metal part prior to bonding with flox.

Last updated: 2021-09-03 19:22:16 -0700

Cozy Newsletter

Marc Zeitlin has all of the Cozy Newsletters available at cozybuilders.org. Here’s some of the more relevant information to the Coz-E build.

Note for builders of gas-powered Cozys: I have not included any of the tips related to the fuel and engine systems. This will be a fully-electric airplane, and so I have no reason to include those for my reference.

Builder Tips

In addition to some of the dedicated articles going in more depth on specific advice, here’s a sorted list of most of the advice given in the Cozy Newsletter.

General

  • Keep joints tight with “no joggles” to improve performance. (Cozy Newsletter #4)
  • Do not cut up the large-size drawings. Instead, trace templates onto another sheet of paper and save the original drawings intact. (Cozy Newsletter #12) (Personally, I take photos of the drawings with a ruler for scale, but that’s for archival purposes).
  • “NEVER allow yourself to be distracted while working on your airplane, such that you might not complete a task, and then forget to finish it later. We all have had the experience of visitors dropping in while we are working. Even if you have to be rude, finish the job before laying down your tools.” (Cozy Newsletter #24, The Canard Pusher #57)
  • Joints between all permanently installed parts should be taped. (Cozy Newsletter #24)
  • This one comes up in more than a few newsletters: Check your attach bolts. If more than 2 threads extend through the nut, add another washer. Don’t let the threads bottom out before the bolts are tight. (Cozy Newsletter #34)
  • Holes through bulkheads or instrument panel do not need to be glassed. (Cozy Newsletter #36)
  • Wherever possible, orient bolts either heads up or heads forward. (Cozy Newsletter #38)
  • “Extruded piano hinges MS20001-P6, P5, P4, etc. are all identical except for the width of the flange. It is easier just to order and stock the P6, and if the flange is wider than necessary, trim it on your band saw.”” (Cozy Newsletter #39)
  • Try using a light inside to identify holes that have been glassed over. (Eric Westland, Cozy Newsletter #39)
  • For bending aluminum, rule of thumb is that the bend radius should be no less than the thickness of the material. E.G. 1/16 inch thick aluminum can bend 90°, provided the radius is 1/16 inch or greater. Always bend aluminum across the grain, not with it. (Ray Goldsmith, Cozy Newsletter #39)
  • Always order a little extra material, especially in the beginning, so that you don’t run out of epoxy, cloth, micro, or flox before finishing a job. (Cozy Newsletter #69)
  • “all aluminum parts [should] be protected from corrosion by cleaning first with Alumiprep 33 or metal prep #79, and then soaking in Alodine 1201, which is a visible (golden brown) moisture barrier, greatly increasing resistance to corrosion. This also acts as an excellent surface to bond epoxy or paint. Even if you do not live near the coast, the airplane you are building could some day end up there.” (Cozy Newsletter #81)

Safety

  • Use nitrile gloves for your hand, with water-soluble barrier cream on the arms. Switch out the barrier cream early and often. (Cozy Newsletter #89)
    • This has evolved significantly, from the original advice, starting way back in #7: To protect your skin from epoxy, Nat heavily recommends water-soluble barrier creams. If you must use gloves, use nitrile gloves. Under no circumstances, use latex gloves.

Tools & Shop

  • Store and dispense glass cloth on a rack in a wall cabinet. Hinge the front of the cabinet so that it opens to form a table to lay out the cloth for cutting. Keep a clean pair of scissors there just for cutting clean cloth. (Cozy Newsletter #14)
  • Put a 2 inch overhang all around your work table. This makes clamping parts to the table much easier. (Cozy Newsletter #17)

Neil Clayton says the tool (s) he uses the most are sanding sticks he made himself. He says Home Depot paint dept gives away 2 sizes of paint stirrers; a 1”wide stick and a 2” wide version. Both have a nicely formed handle. I always grab a handful as I pass towards the check out. Then at Lowe’s I pick up some 12” x 18” sanding sheets (the kind used on those big floor sanders). Several grades are available. I use left over epoxy to glue the stirrers to the sheets and then split them into individual sanding tools with a razor blade when the epoxy has dried. One sheet yields about 10-15 sanding sticks of various sizes so they are cheap and disposable. Try it!

(Cozy Newsletter #78)

  • Get a Fein tool for trimming cured layups and electric scissors for cutting cloth and peel ply (and trimming wet layups) (Cozy Newsletter #82)

Antennae

  • Make sure the nav antenna misses the area in the bottom of the fuselage that will be cut out later for the nosewheel well. (Eric Westland, Cozy Newsletter #39)

Location

From Cozy Newsletter #34, with a discussion on where to place the antennas (For a Cozy 3).

  • Transponder: In the nose ahead of the rudder pedals with the probe extending through a 1/4” hole in the bottom of the fuselage.
  • Nav: Two good locations:
    1. Underneath the skin on the bottom of the canard, legs extending forward and offset to the radio side.
    2. Under the skin on the bottom of the fuselage, legs extending forward on either side of wheel well.
  • ADF: Use King electronic antenna and locate inside cockpit under right front seat.
  • Com: Located under skin of winglets, per plans.
  • FM and/or Marker Beacon: Under skin mid-wing.

GPS was not specifically called out, nor was VOR.

  • Be careful in laying out VOR antennas on the bottom of the fuselage to avoid future cut outs for the landing light and nose wheel. (Thomas Kennedy, Cozy Newsletter #55)

Here are the dimensions (each arm) Jim Weir has published for the following di-pole antennas:

  • Marker Beacon - 34.3 in.
  • FM Music Radio - 26.2 in.
  • VOR/LOC - 22.8 in.
  • VHF/COM - 20.3 in.
  • Amateur 2m - 17.7 in.
  • Glideslope - 7.5 in.

The COM is the only one that needs to be vertically oriented. All the rest should be horizontal. The VOR should be a V shape. Some say the marker beacon should be along the airplane centerline. I installed mine in the wing and it worked just fine. You should keep the tips of di-pole antennas away from metal, and away from each other, particularly transmitting antennas. I have used Jim’s measurements and they work well-better than most factory antennas. My GPS antenna is mounted in the nose, just under the inspection cover (pointed upward toward the satellites) and works well there. I like this location because the co-ax is very short. My transponder antenna is in the bottom of the nose, with the probe just sticking through the skin (pointed down toward the ground stations). You can make your own transponder antenna. It should be 2.65 inches long from the tip of the probe to the ground plane, and insulated from the ground plane. The ground plane can be made from .062 aluminum. It is about 8 inches in diameter (I lost my drawing). I have made my own from one of Jim’s kits, and also from scratch, and they work well. You attach the center conductor to the radiating rod, and the co-ax ground to the ground plane. You get a lot of satisfaction when you make your own antennas, they are all hidden, and they work better than the ones that cost mucho bucks!

(Cozy Newsletter #73)

Canard

Several Mark IV builders have advised us that their canards are slightly longer in cross section (chord) then shown on M-11, and when the lift tabs are in contact with the forward face of F-22, the trailing edge of the canard is 1/8 to 1/4” aft of the forward face of F-28, and that the alignment tabs cannot be built as shown. Should this also be the case with your canard, you may lay up additional plies of BID locally on the forward face of F-22 up to 1/8” thick, or remove up to 1/8” of the trailing edge of the canard locally at the tabs, or a combination of both.

(Cozy Newsletter #44)

Canard installation. Make sure you allow for at least 3/4” of horizontal travel for the canard so the incidence pins will not bind during installation or removal.

(Cozy Newsletter #50)

Some builders are still having trouble with the trailing edge of their canard being too low, such that the airfoil dips down and they have to mount the elevators lower than desired to get the required 15 degrees of trailing edge up travel. We suggest that you remove 1/16th inch (no more) from underneath the fishtail on the templates before cutting the foam cores, or from the foam after cutting to avoid this problem. We have made this suggestion to Feather Lite as well to do on their precut cores.

(Cozy Newsletter #53)

Canopy

On getting a smooth edge where the fiberglass contacts the canopy:

Builder Wayne Hicks said he made a paper pattern of the canopy deck, then laid up the 2 UND on plastic (and later the 2 BID), used the pattern and razor pizza cutter to make a nice, clean cut along the pattern lines. Then he laid the piece nice and neat up against the glass. There were absolutely no problems. No excess flox, no excess resin, no excess glass. Never had to use a dremel! If anything, all he had to do was cut one or two stray strands with a razor blade. He did this for both the outside and inside canopy deck layups, and highly recommends this technique.

(Wayne Hicks, Cozy Newsletter #70)

to avoid corrosion of the canopy hinge attach bolts. Saturate the bare wood in the holes through the longeron with epoxy to seal the wood fibers. Do this by dipping a cotton swab into epoxy and then inserting it into the hole. Alternatively, you can drill the hole slightly oversize, fill it with flox, and after cure, redrill it to the correct size.

(Nick Parkyn, Cozy Newsletter #83)

Contouring

  • Fill low spots before sanding surrounding areas down to contour. This keeps your low spots from turning into high spots. (Cozy Newsletter #22)

I found a method to make the final canard contour perfect per plans. I used the checking contour templates for the canard to cut out (hot wire) a block of styrofoam. Then I stuck a large piece of sandpaper to it and used it to give the canard a perfect contour over its entire length. The same thing worked fine for the elevators.

(Jean-Jacques Claus, Cozy Newsletter #85)

Cowlings

Cowlings should have extra layers of BID along all the edges to make them more rigid when they are removed from the airplane, and to provide more beef for the fasteners. This is shown in Figures 12 & 15, Chapter 23, but builders were not instructed to add them because the supplier (Featherlite) added them while the cowlings were still in the mold. In February 1999, when we inspected AeroCad cowlings, we noticed that they were not doing this. We asked them to add the extra layers while the cowlings were still in the mold. They agreed, and we approved their cowlings contingent upon their doing this.

(Cozy Newsletter #68)

Elevators

Your elevators should balance with the weights shown in the plans. If they do not, do not try to balance them by adding weight inboard. Instead, discard them and make new ones more carefully to make them lighter (you can probably re-use the torque tubes and other hardware). The mass balance called out for the elevator and the specification for balancing them applies only to an elevator fabricated with the same weight and stiffness as that which has successfully passed all the flutter testing. It is extremely important, and life-critical that the manufacturer or owner of each Cozy, or any plane for that matter, assure himself without a doubt, that the control surfaces are conformal to those which have passed flight tests and been shown to be flutter-free.

(Cozy Newsletter #24)

Elevator torque tube offsets (CZNC-12A for the Roncz canard). The drawing we submitted to Brock Mfg. stated that these offsets should be a slip-fit in the l” OD x .035” 2024 T3 torque tube. Brock Mfg. cannot guarantee a slip-fit because the tolerance on wall thickness for .035” 2024 T3 drawn tubing is +/-10 %. To prevent too loose a fit if the wall thickness is on the thin side, the specification for the offsets has been tightened to .930’ OD. If the wall is on the thick side, you will have to sand the offsets to obtain it slip-fit.

(Cozy Newsletter #50)

In the first edition Mark IV plans Chapter 11, p.7, we instructed builders to mount their elevators at zero degrees with jig L so that there was a .2 inch gap between the canard and the elevator. When some builders did this, they were not able to get 15 degrees trailing edge up of the elevators. So we changed the L jig (see p. M-18) to mount the elevators at 15 degrees trailing edge up and zero gap. Please note this on p. 7, Chapter 11, 1st paragraph and Figs. 17 & 18.

(Cozy Newsletter #68)

Epoxy

Starting with Cozy Newsletter #61, the MGS system is now recommended. Either the L335 or L285 system.

  • Save the foam scraps. Many parts can be made by gluing small pieces together with 5-minute epoxy. (Cozy Newsletter #5)
  • To conserve epoxy, mix microballoons with any excess into a very thick paste, and trowel that over your finished fiberglass parts. This will save you time when finishing. Rough the surface with 36 grit sandpaper first, though. (Cozy Newsletter #5)
  • Lava soap works great to remove epoxy from your hands. (Cozy Newsletter #35)
  • Use the bottom of 8 ounce mixing cups to make 5 minute epoxy (Cozy Newsletter #17)
  • Store near-empty bottles of 5 minute epoxy on their side. (Cozy Newsletter #28)
  • Mixing some flox with 5 minute epoxy will make a bit stronger joint and prevent it from running. (Cozy Newsletter #35)
  • Epoxy Resin should be clear and colorless (or a slight yellow). Hazy indicates crystallization, and the epoxy should not be used until it is heated and becomes clear again. (Cozy Newsletter #85)

Cozy builder Phillip Johnson, in the Pacific Northwest, protects his resin and hardener from exposure to air by putting a plastic bag over the top of his plastic containers in his dispenser after filling them, with the bag resting on top of the liquid surface and with enough slack so the bag will follow the surface down as material is used, and then putting the cover on the container.

Cozy Newsletter #54

Fiberglassing

  • Micro joints (which hold urethane blocks together) cause bumps when glass is laid over them. Undercut all joints with a dremel before shaping and before layup. Fill the undercuts with fresh micro just before the layup. (Cozy Newsletter #5)
  • To prevent air bubbles from coming back in after being worked out, cover the cure area with saran wrap (or any plastic wrap) and squeegee the air out. (Cozy Newsletter #5)
  • Cut the glass cloth ahead of the layup to the approximate size. Do this after the foam is vacuumed, but before applying any epoxy. Drape the cloth over the part, cut it to size, label it with a felt-tipped pen, roll it up and set it aside. (Cozy Newsletter #14)
  • To prevent UNI from unraveling when cutting it lengthwise, lay down a strip of masking tape and cut down the tape’s center. Scissor trim the masking tape off after the cloth has been wet in place. (Cozy Newsletter #14)
  • Use a sabre saw, not a band saw, to cut fiberglass. (Cozy Newsletter #17)
  • Use a rubber squeegee to spread epoxy on the glass. Take a 6 inch squeegee, and cut it in 2. Remove the epoxy after use. You can use a belt sander to remove any cured epoxy, but it’s less work to just clean it. (Cozy Newsletter #31)
    • It takes a couple of minutes for epoxy to soak in and wet out one or two layers of glass cloth. Rather than waiting for this to happen in a small area, use this time to spread epoxy over as wide an area as possible. Pour a ribbon of epoxy on the cloth and follow behind with the squeegee spreading it. Keep the pressure very light, so as to not disturb the cloth. After the cloth is wet out, you can increase the pressure of the squeegee to distribute it. You can pick up excess epoxy with your squeegee, wiping it off on the edge of your mixing cup. Conversely, you can apply a small amount of epoxy by dipping your squeegee into the mixing cup. If you practice these techniques, you will find that you can make lay ups much more quickly.
    • Do not waste time trying to get just the right amount of epoxy on the lower layers of a multi-ply layup. Actually, cloth wets out better from underneath and not as much air is trapped between layers. It is only on the last layer that you need to spend the time working on getting the air out an applying the optimum amount of epoxy.
    • Do not leave bristles from the throw-away brushes behind in your layups--they weaken it. You can pick them up with the tip of a brush.
  • Double check that you remove the peel ply. If you leave it in and glass over it, the part must be discarded and rebuilt. (Cozy Newsletter #37)
  • Instead of peel ply tape, get the 38 inch wide peel ply. Then, when you need tape, cut the peel ply to whatever width you need. (Eric Westland, Cozy Newsletter #39)
  • “Buy cheap 100% polyester (or Nylon) cloth (peel ply) by the bolt and cover all layups with it. First test a sample piece to make sure no additives are present that may cause removal to be difficult. I find that I do not need to add extra resin to wet out the polyester, just stipple and use a hair dryer. I make it a habit to strip the polyester the next day, so none is left by mistake. This eliminates the need for a lot of sanding, and dust breathing. All layups look and feel smoother.” (Steve Blank, Cozy Newsletter #46)
  • “We use peel ply extensively on all of our layups. Glass fibers act somewhat like a sponge, and can soak up extra resin. If a layup is resin-rich, it is not only too heavy, but it is weaker than a layup with just the right amount of resin. The peel ply seems to hold the fibers down more compactly, so they don’t soak up too much resin. Sort of a poor man’s vacuum bagging. If you use peel ply, you can make the layup a little wet, then lay down the peel ply, and with a squeegee and hair dryer, remove the excess epoxy (if the layup was really wet) or else free up almost enough epoxy to wet out the peel ply, and add epoxy as necessary to wet it out completely. The only thing you need to be careful of is that the layup underneath the peel ply isn’t so dry that it is porous, because then the compressive strength would suffer (buckling in compression). Synthetic fabrics with a straight weave (not knit), like nylon, polyester, or dacron, as long as they aren’t fuzzy, and don’t contain cotton or rayon, seem to work well. Sometimes you can find real bargains at fabric stores. But test a swatch first. Alexander Aeroplane lists peel ply at $2.25/yd. in 45” widths, which is quite reasonable.” (Cozy Newsletter #47)
  • “BID is always cut on the bias and overlapped l’ in every direction, but UND is overlapped only in the direction of the major fibers.” (Cozy Newsletter #50)
  • Whenever possible, use peel ply. As an extra precaution, sand the surface that the peel ply was on before applying the bond. (Cozy Newsletter #55)
  • A wet-on-wet layup usually results in the strongest bond between layers. To do this, wet out the first layer of glass, squeegee the air out, but leave an excess of epoxy and then lay down the next layer of cloth on top to soak up the excess. (Cozy Newsletter #55)
  • Do not glass over a cured, microed surface, if structural strength is required. (Cozy Newsletter #55)
  • Put flox in a bag and dispense it like cake frosting. (Dave West, Cozy Newsletter #62)
  • In tight corners where it’s hard to roughen up the surface with conventional sandpaper, try a carbide studded grout removal tool that has carbide deposited on the edge of a steel blade approx. 1” long attached to a handle with a slight “S” bent arm. (John Fritz, Cozy Newsletter #66)

Early in the game we learned that various fabrics sold in fabric stores work well as peel ply, and can sometimes be purchased at quite a low price. We learned that hard-weave (not fuzzy or stretch weaves) nylon, polyester and dacron work well. Watch out for cotton and rayon. Often there are roll ends tables where things are reduced for clearance. Once I was able to purchase nylon like is used in ski jackets for $.45/yd, and later wished I had bought the entire table. It is best to take a sample home first, use it on a wet layup, and make sure it peels off, before buying a whole bunch. Make sure you iron any wrinkles out of peel ply before using it. Otherwise they transfer to the layup.

(Cozy Newsletter #68)

  • A general rule is that whenever joining two or more intersecting surfaces together, they should always be floxed and taped, whether instructed to do so or not. (Cozy Newsletter #71)

    • A rule of thumb for estimating how much mixed epoxy you will need for any given layup is 1 oz of epoxy for every oz of cloth needed. This includes the micro layer. “For example, the bottom side of one Cozy MKIV wing will need 12 yards UNI (7 oz/yd. 38” width) or 84 oz. total. Epoxy weighs 9 lbs. (144 oz) per mixed gallon, so you will need 84 oz. mixed epoxy to wet out 12 yards of UNI.” (Cozy Newsletter #80)
  • Leave a little mixture of epoxy in the cup and check it for cure the following day. If it has cured correctly, a scratch on the surface will leave a white mark (Cozy Newsletter #81)

  • “[If] glass cloth wets out and becomes transparent, it is safe to use. If it stays white, throw it away.” (Gary Hunter, Cozy Newsletter #83)

  • “DO NOT USE glass that has become wet.” (Gary Hunter, Cozy Newsletter #83)

  • Take your time. Do not apply epoxy until you are 100% satisfied with the shape and integrity of the part. (Neal Johnson, Cozy Newsletter #84)

Tom McNeilly’s Vacuum-bagging technique

From the Cozy Newsletter #4, this describes a way to get very light layups using vacuum bagging. Later newsletters state that vacuum-bagging is generally not worth the effort, though.

Place the layup down as quickly as you can, cover it with perforated poly. Cover that with soft carpet underlayment foam, and cover that with regular poly. Tape down the edges, and pull a vacuum with a vacuum cleaner house between the layers. The vacuum should squeeze the excess epoxy out of the layup and into the soft foam. After cure, strip the coverings off, including epoxy. Tom claims this saved 6 lbs per wing.

Dealing with BID

  • You can create 2 inch wide BID cloth tape by rolling the BID cloth into 1 inch diameter rolls at 45° to the selvage edge. (Cozy Newsletter #4)
  • For installing BID into the corner tapes: Layup the BID you’ll need onto the foil. Squeegee it out to a good layup. Cut your tapes out of this layup, cutting through the glass and aluminum foil. Sand and paint a coat of epoxy onto the area to be laid up over, then use your fingers to bend the aluminum foil to form the tape into an angle to fit into the corner. Position it, then lightly squeegee or stipple it into place. Peel the aluminum foil off, stipple any remaining air bubbles out, peel ply the edges. (Cozy Newsletter #4)
  • Sand a slight recess (1/32 inch) into the foam on flat or curved surfaces where you’ll place BID overlap joints so overlaps won’t cause a bump in the finished surface. (Cozy Newsletter #5)

Finishing

  • Don’t use featherfill. It does not bond well with epoxy and will cause the paint job to delaminate in a year or two. (Cozy Newsletter #10)
  • Make sure to fill and finish paint the inside of the cowlings. (Cozy Newsletter #22)
  • Most silicones give off corrosive fumes, Dow Corning Silastic RTV 738 is a non-corrosive sealant, use it to secure the cover plates over the wing attach bolts. (Bruce Ibbotson, Cozy Newsletter #22)
  • Use Polyurethanes, not Enamels or Lacquers. Enamels and lacquers chip in heavy rain. (Vance Atkinson, Cozy Newsletter #23)
  • “It is not necessary to use a spray booth to paint an airplane and get a good finish. You can spray the finish coat in a garage or outside. After cure, wet sand with 1000 and then 1500 grit, and then buff with 3M Finess-it II. This will remove orange peel, overspray, dust, and other imperfections and result in a very flat surface with high sheen. This works well with Ditzler Deltron (acrylic urethane) which is the finish we recommend.” (Cozy Newsletter #41)
  • “We recommend use of a high-build epoxy primer. Cozy builder Nick Parkyn in Western Australia says that he has used the new System Three water reducible Epoxy Primer and Polyurethane paints and is impressed with the performance. We are not familiar with these products and have asked him for more information. We would welcome other builders input.” (Cozy Newsletter #41)
  • “Have you ever tried to pour paint from a full 1 gallon can and had it run down the side? Try this. Wrap a strip of masking tape (2- wide works the best) around the top of the can, and punch a hole in the groove around the rim. You should be able to pour without spilling, and the excess paint should drain through the hole back into the can. The hole will be sealed after the cover is reinstalled.” (Cozy Newsletter #41)

Mark IV builder Chuck Larson writes, “I’ve discovered a tip that works great for wet sanding the Sterling primer. I use a grouting trowel which is used for grouting ceramic tile. I bought mine years ago at Color Tile. It is 9” x 4”. It has a wooden handle attached to an aluminum plate which has dense rubber foam bonded to it. Wet or dry sandpaper will adhere to the foam rubber well enough to allow the sanding. It keeps the surface flat, and it is easy to remove and wash out the sandpaper”.

(Cozy Newsletter #44)

If you need to pour paint from a can without spilling and wasting a lot (paint is expensive!), first punch a hole in the trough around the rim to let paint drain back into the can. Then wrap some 2” tape around the rim of the can, extending up above the rim about 1-1/2”. Now you can pour the paint out of the can without it running down the side of the can, and any excess will drain back into the can.

(Cozy Newsletter #45)

  • If you use masking tape when painting, don’t leave it on a long time, and when you remove it, pull it back at 180° to itself, not 90°. (Cozy Newsletter #63)

I just completed painting the bottom of my plane. I’ve used the new poly fiber system. All water based. Very impressed. Pin holes are a total non-issue. Particularly when you use the Superfil instead of normal microballoons. Superfil is substantially better than micro. Trapped voids are rare. Sands easy, mixes easy. Areas where I used micro have more pinholes, but using the Smoothprime primer is highly effective at filling pinholes. It really does flow into holes. Must have low surface tension or something. I also elected to use their water based “topgloss” top coat (polyurethane). So far, I really like it, but I have yet to color sand and buff the paint, so the verdict is still out. I haven’t done adhesion tests yet. On my second coat (of three) of topgloss, I got too aggressive and had quite a few runs on corner radius. I elected to sand the entire coat before applying my last coat. Final coat looks good, although areas have a matte appearance (too lean). No runs. The top coat appearance is quite sensitive to spray quantity. More is better unless you develop runs. I had no problems with vertical surfaces. I learned that I don’t need to use finer than 120 grit when sanding micro or superfil. The primer fills all those scratches fully. I used a sanding stick only to achieve straightness, then I used an electric random orbit sander with 220 grit. I was willing to sand the primer completely off to achieve uniform appearance. I mixed paint and primers 1 cup at a time to avoid splatter. I’ve heard people describe sanding and painting as the worst part of the process, but I enjoy it. It’s great to see objects finally transformed into airplane like appearance. Just wanted you to know more about these new products. My superficial conclusions: Superfil micro replacement is way better. Smoothprime primer is way better. Topgloss top coat may not be better (lotta work)....we’ll see when I’m further along.

(Al Wick, Cozy Newsletter #67)

I put the drip lip on the front fuselage cover last night. Here is a hint for those who have yet to do this. The plans say to build up an 1/8 inch ledge with balsa or foam. I used a piece of 1” wide webbing (either climbing rope type webbing or load binding strap type webbing) with duct tape on top of it. The webbing will bend around the curve just right, and it is about the right size.

(Norm Muzzy, Cozy Newsletter #72)

  • Do not use polyurethane paint. Nat recommends a acrylic-urethane (PPG “Deltron” or “Concept”) (Cozy Newsletter #83)

Fuselage

  • If you have difficulty stickling the copper foil tape to the bottom of the fuselage, try heating it with a hair dryer and pressing down on it with a hard rubber roller. (Eric Westland, Cozy Newsletter #39)

Fuselage Sides

  • Put a 6” wide strip of wax paper between the masonite and the foam pieces where the edges butt together. This will make the eventual removal from the jigs MUCH easier. (Thomas Kennedy, Cozy Newsletter #49)
  • In assembling the bulkheads to the sides, forget the ropes to tighten the whole assembly. Use threaded rods and wing much more precise control. (Thomas Kennedy, Cozy Newsletter #49)
  • Buy a kiln-dried board (not construction grade) for your WL 0.0, and use bolts rather than nails to secure. This will allow precise placement and later shimming if required. (Thomas Kennedy, Cozy Newsletter #49)
  • I had very good results mounting my WL 0.0 board on my work table which was mounted to 4x4s glued to my garage floor. There is no such thing as a level garage floor. The work table becomes your level surface. (Thomas Kennedy, Cozy Newsletter #49)

Foam

  • Before cutting wing sections, clamp the styrofoam blocks and glue them using pour foam. This produces very thin joints that keep the styrofoam joined together while still allowing the hot wire to cut them without catching. (Tom McNeilly, Cozy Newsletter #4)
  • You can use a dremel tool with a router attachment to make the small depressions in foam as called out in the plans. (Cozy Newsletter #15)
  • Covering the edges of hot wire templates with copper foil tape makes them easier to use (Cozy Newsletter #38)
  • “The 2 lb./cu.ft. large cell blue styrofoam called for in the plans is called Styrofoam in the Aircraft Spruce catalog, Polystyrene in the Wicks catalog, and extruded Polystyrene in the Alexander catalog. Urethane foam may also be called Polyurethane foam.” (Cozy Newsletter #39)
  • Use a router to carve 1/8 inch and 1/16 inch relief cuts in the foam (e.g. in chapter 9, on the landing brake). Attach the router base to a 36 inch long board to make quick, smooth work of the cuts. (Eric Westland, Cozy Newsletter #39)
  • Try using double-sided tape on the forms to hold the foam down. Recommended the kind used on golf club grips or carpet tape. Should peel right off with little or no effect on the foam. (Mark Loy, Cozy Newsletter #64)

If you “screw-up” when cutting airfoils, and have a bad cut on one side (top or bottom), no need to throw it away and start over. Just slice the airfoil apart, and splice in a piece of styrofoam (like making a sandwich), and re-cut it. Don’t know how to make a sheet of styrofoam? Just clamp your hotwire saw 1⁄2 inch or so above your work bench, and slide your scrap chunks of styrofoam underneath, sorta like cutting boards from logs. The beauty of composite construction is its hard to spoil something so bad you can’t fix it.

(Cozy Newsletter #77)

Joints

For Structural reasons, all joints should be taped with 2 plies of BID 2’ wide (1” on each surface) cut on the bias (45 degrees) unless otherwise specified. After application, the tape should be peel-plied. One recommended way to accomplish this is to wet out 2 plies of BID on wax paper or Saran wrap, cut into strips, apply over joints, remove the wax paper or Saran wrap, cover with peel ply and wet out same. Wax paper should only be used with discretion. It should not be left in place while the epoxy cures, because wax will be left behind, and it should only be used on those joints which will not be later covered with additional layups.

(Cozy Newsletter #50)

Landing Gear

  • “If you wrap the gear leg first with 1/8” fiberfrax, and then with shiny aluminum, you will greatly reduce the heating by radiation.” (Cozy Newsletter #24)
  • “Provide a vent for hot air to escape from your wheel pants. Hot air rises and will be trapped inside the wheel pants unless you provide a vent, on the top, on the disc side, for it to escape.” (Cozy Newsletter #24)

In Chapter 9, p.2, it says that the [landing gear] strut should be cut at 8 degrees, but on p.3 it says 13 degrees. There has been some disagreement as to what is the correct angle, and it also depends on whether it is measured at the leading edge or trailing edge. The angle is not critical, so shoot for somewhere in between.

(Cozy Newsletter #68)

I thought it was in the plans, but maybe not. An easy way to make the fairing where the main gear strut enters the fuselage is to shape it with molding clay (Playdough), glass over with at least 2 layers of BID, attaching to both the strut and the fuselage. Then after cure, make a saw cut at least 1/8” wide halfway between the fuselage and strut, remove the strut, and dig out the clay. If the cut is wide enough and the inside of the fairing is empty, the strut can flex without cracking the fairing. This should be done when the fuselage is upside down with no weight on the gear. Then when you are flying, both halves of the fairing will be aligned for minimum drag.

(Cozy Newsletter #72)

Panel

  • Don’t cut holes for your panel until everything else is done, and you’ve put together the instrumentation. Build a mock panel first (Nat suggested 1/4 inch plywood. You can also use cardboard) to test it out. (Cozy Newsletter #5)

Spars

The 3 inch spar cap material presently being supplied is only 2-3/4 inches wide, but not to worry. If you pull out the cross threads as instructed for the canard, centerspar, and wings, and then squeegee after applying epoxy, the strands spread out to 3 inches, and you will be able to fill up the troughs with the maximum amount of glass they can hold.

(Cozy Newsletter #65)

Strakes

Bending 3/8 in. PVC is a universal problem. When I re-built my right strake, I made a scribing tool from a block of wood and a hacksaw blade. I made a saw cut in the wood and 5-minuted in the hacksaw blade so it protruded 1/4 in. I carefully scribed a number of cuts in the PVC where I wanted it to bend, then bent it into the frame and fastened it in the bent shape, and then microed and glassed the scribed surface. That worked better than anything else I have tried to date.

(Cozy Newsletter #10)

  • Postpone installing the center section spar and building the strakes until you have completed as much work inside the fuselage as possible. It is much easier to work inside the fuselage with it sitting on its side on saw horses. (Cozy Newsletter #35)

It is important for appearance that the strakes are straight (no bumps), and properly aligned with the wing. The wing should be installed on the center section spar when the strake is built, and a straight edge should be used to make sure that the leading edges of the ribs are aligned with the leading edge of the wing, and that all points on the rib airfoils align with the wing airfoil. Of course, you will need to make allowance (using spacers) for the 3/8” foam and several layers of glass skin which will be subsequently be laid over the ribs.

(Cozy Newsletter #44)

Strakes, Chapter 21, p.2. Please note that the fuel cell ends at Rib R-57. The empty space outboard is necessary as a buffer to prevent any fuel, liquid or vapors, from reaching the wing. An open drain at the low point would indicate any fuel leakage through R-57.

(Cozy Newsletter #64)

Keith Scull (England) didn’t want to pay the cost of shipping Featherlite’s leading edges all the way from California, and he didn’t like the idea of carving foam blocks, so he came up with an innovative alternative. He purchased some thin card stock from a local art supply store, wrapped it around the leading edge of the strake using the ribs as guides, trimmed it so it just fit into the recess provided for the leading edge layup, and taped it in place with 20 inch long strips of masking tape. Then he cut openings in the top so he could pour pour-foam into the empty space. The openings were 3 in. x 1/2 in. every 6 to 9 inches parallel to the strake leading edge. He poured the pour foam thru the slots, let it expand and cure, and then removed the masking tape and card stock. He said the result was a perfectly formed leading edge which required very little sanding to prepare if for the glass layup (see pictures). He said it sounds like a lot of work, but only took a couple of hours, and did a better job with less mess.

Keith said when he leak tested his strakes using an altimeter, the right strake had a very small leak (20 ft. in 3 hrs.). He couldn’t find it with soapy water. So he called in a local refrigeration man who filled the strake with R22 and used an electronic sniffer to locate the escaping gas. He found the leak. It was traveling along the score lines he had cut in the foam to bend it around the ribs, and escaping where the foam joined the fuselage. Apparently he hadn’t completely filled up these score lines with micro. The cure was quite simple. He drilled a very small hole thru the top skin into the score line at the tank rib and injected epoxy using the vacuum method described in the plans. To be doubly sure, he did this with every one of the score marks, and found three to be leaking. After filling with epoxy, the altimeter indicated no more leaks.

(Cozy Newsletter #68)

Wings

There is a discontinuity (dip) in the top surface of the wing at B.L. 67.5 (see Chap. 19, p. 10). This is intentional. You have not made a mistake!

(Cozy Newsletter #53)

when you attach the wings many times in the shop, don’t use the AN365 nuts over and over again, but instead get some fine thread nuts at the hardware store which are much easier to install and you don’t have to worry about them wearing out.

(John Epplin, Cozy Newsletter #73)

Unsorted

Jim White’s advice

From Cozy Newsletter #67, copied verbatim:

  1. Attach the wing before working on the stake and bondo a 1/4” or so thick template to the end of the main spar that matches the contour of the wing. This is needed so that the strake matches up to the leading edge.
  2. When cutting out the top and bottom PVC foam pieces, finish one (top or bottom). The top is the same as the bottom except it is 0.2” longer. All the angles are the same. Use the top or bottom strake as a template by simply shifting it up or down 0.2” accordingly. You might as well make all four top and bottom skins at once. GET THE FIRST ON RIGHT, OR YOU WILL HAVE 4 WRONG ONES.
  3. I placed blocks under the ends of the landing gear struts to level the airplane perfectly and give it a solid foundation. I supported the jig table with two saw horses, and four pieces of 2x4’s individually clamped to the saw horses. The jig table simply rests on the ends of the 2x4’s that are adjusted up or down.
  4. INSTALL THE RELEASE TAPE ON THE BACK OF THE JIG TABLE BEFORE ATTACHING IT TO THE MAIN SPAR.
  5. Use long clamps from the top of the spar to the jig table beneath to firmly attach the plane to the jig table, inboard and outboard on the spar. I did not use any bondo and the jig table never moved relative to the plane, even when getting in and out of it repeatedly to cut out the openings and tape the inside joints.
  6. I believe the strainer inspection hole in B33 is marked wrong in the plans. The inspection hole should start 6” from the spar, not 3”.
  7. For B33 bulkhead reference I clamped a straight edge to the canard bulkhead and strung a string back to a mark on the top of the spar. For the B57 bulkhead I simply used a plumb bob hung over the edge of the jig table at BL 57 and attached the other end to a mark at 57” from centerline on the spar.
  8. The B.L. dimensions are to the INBOARD face of the bulkhead. Carve the outboard to get the contours of the bulkheads to match the sweep of the strake. DO NOT CARVE THE INSIDE EDGES.
  9. String a line from the leading edge of the template you made in step 1 above to the fuselage using the leading edge of the bulkheads as a guide. This will ensure the leading edges of the wing and strake come together.
  10. 1 inch spacing is fine for the scoring of the bottom foam to bend around the ribs.
  11. On the top foam, 1/2 inch cuts minimize the flat spots which occur on the top of the curved part of the strake between the two bulkheads. Make the cuts just after the 1 ply layup has cured. If you can make the cuts while the fiberglass is hard but still pliable, you can bend it over the ribs and let it finally cure in its final shape.
  12. I fully trimmed the strake openings into the fuselage before putting the top on permanently. If you jig the top foam sufficiently, it will match up repeatedly to the same place on the fuselage.
  13. I wanted to make sure my upper skin was firmly attached to the ribs so I made a flange to go on the bulkheads instead of simply stacking flox on the bulheads. The flox method probably works just fine, but I have heard of some Cozys developing fuel leaks after time and thought this might minimize the possibility of this occurring. This modification added several days work to the process! When the top foam is all ready to flox to the bulkheads, I carefully marked the location of the bulkheads on the bottom of the top strake skin. I then turned the top foam over. You only need to do this for the interior fuel tank edges. Do not extend the flanges into the storage area. You can tape those areas like normal. Do the leading edge, but not the trailing edge along the main spar. On top of each bulkhead marking I put a wide layer of box sealing tape, followed by a layer of peel ply, one layer of bid tape 2” wide, and peel ply on the outer edges of the 2” bid tape. On this second layer of peel ply, DO NOT PUT THE PEEL PLY WHERE THE BULKHEAD OR RIB WILL SIT. Err on the cautious side when putting on this peel ply. You can always sand the area not peel plied, but it is difficult to remove peel ply between the flange and bulkhead. Place a thin layer of flox on the bulkheads and place the top on to cure. Let it fully cure for at least a day or the one layer of bid will sag after you pull the top back off. Pop the top off and remove all the peel ply. Glass the interior corner of the new flange with one layer of bid tape, let cure, trim with dremel, and “voila”, flanges that perfectly match your strake skin.
  14. When you place the top skin to the bulkheads and ribs, realize that it is a ton of work to tape all the inside edges. But doing the top skin placement and inside tapes in one sitting will save lots of sanding while upside down in the back of your airplane.

Owners Manual

Updates from Newsletter #52

From Cozy Newsletter #52:

Do not fly until you add the following information to the Takeoff performance section of the Owners Manual, and comply:

High Density Altitude Takeoffs

The combination of high aircraft gross weight and high density altitude represent significant dangers for takeoff obstacle clearance. Special care is required to avoid premature rotation, i.e., if liftoff is too slow, the aircraft will be on the back side of the power curve and may not climb. When operating heavy and high (say, within 100 lbs. of gross weight and above 5,000’ density altitude) do not fully rotate to liftoff attitude until your airspeed is within 5 kts. of the best rate of climb speed, for your specific weight and altitude (see climb charts). This will require more runway than a slower liftoff, but will assure the best capability to clear obstacles and continue a safe climb. Never attempt takeoff under conditions in which you cannot achieve best rate of climb speed while still on the available runway. If this ability is not clear at any point during takeoff_abort. Off-load weight or wait for a cooler time of day. Lift-off is possible as slow as the minimum lift-off speed, and can be successfully used at light weights and/or low altitudes to achieve a short ground roll. However, that technique will usually result in inadequate initial climb if used when heavy or high. Runway slope effects are minor when light or at low altitudes, but they become very significant when heavy/high. For example, a 1% uphill runway slope may add well over 1,000 feet to the distance required to clear an obstacle. Never take off uphill when your takeoff toll performance is marginal. Never continue a takeoff if crosswinds require you to brake so much that a safe liftoff is in doubt. Always use best power mixture for high altitude takeoff conditions. An over-gross weight takeoff that seems like an acceptable operation near sea level can be a real killer when hot and high. Never attempt a takeoff when over approved gross weight!

There may be considerable variance in takeoff capabilities from one homebuilt aircraft to another of the same type. Engine installed power and propeller efficiency at low speeds may be less than that for the prototype that provided the basis for the takeoff distance charts. Find a long runway and measure your takeoff capability at the weights you intend to fly. If your actual performance is less than the charts, correct the charts or improve your prop and/or engine.

Updates from Newsletter #56

From Cozy Newsletter #56.

Page 46, ENVELOPE EXPANSION: Add this:

Caution:

Before expanding your flight envelope, you should make sure your airplane has positive pitch stability; i.e., if you trim it for level flight and then either pull back on the stick or push it forward, upon release of the stick, it should return to level flight in no more than 3 oscillations.

Also, before expanding your flight envelope, you should double check that your canard is set at the right angle of incidence and/or your c.g. calculations are correct by comparing elevator position with the flight test data for our plans model shown below. If your elevator position differs by more than 1 degree, land and re-check your canard incidence using template “G”, and re-check weight & balance and c.g. calculation. Do not fly until you have determined the problem and corrected it.

Elevator position diagram

  • Page 19, Stall Characteristics, 2nd para.: After “shortening the canard span 6”, add “to a resultant tip to tip span of 151”.
  • Page 19, Stall Characteristics, 3rd para.: Instead of “plans”, substitute, “1st edition plans”. Page 19, Stall Characteristics, end of 3rd para.: Add, “This applies to builders with 1st edition plans. The canard span has already been reduced on 2nd edition plans to 151” tip to tip.
  • Page 25, under recommended entry speed for Stalls, after “Slow deceleration” add “from level flight only”.
  • Page 25: Delete “Accelerated Stalls” as an approved maneuver.
  • Page 33, Canard incidence: Delete “templates B & C” (a holdover from the 3-place Owners Manual), and change to “template G”.
  • Page 33, Canard incidence: Change tolerance from +_ .3 deg. to + .6 deg and - .0 deg.

Updates from Newsletter #64

  • Page 35, Main landing gear: Check wheel camber. When aircraft is empty, wheel camber should be between 2.5 to 3.0 degrees negative (bottom of wheel tilted in). Measure after pushing aircraft forward at least 5’, then aft 5’ and take average. Record in aircraft log book.
  • When checking for proper toe-in, wheel camber should increase slightly when pushing forward and decrease slightly when pushing aft.
  • Page 50, Annual inspection: Check wheel camber and toe in as prescribed on page 35 and record in aircraft log book.

Updates from Newsletter #65

  • Page 35, Main landing gear: Check wheel camber. When aircraft is empty, wheel camber should be between 2.5 to 3.0 degrees negative (bottom of wheel tilted in). Measure after pushing aircraft forward at least 5’, then aft 5’ and take average. Record in aircraft log book.
  • When checking for proper toe-in, wheel camber should increase slightly when pushing forward and decrease slightly when pushing aft.
  • Page 50, Annual inspection: Check wheel camber and toe in as prescribed on page 35 and record in aircraft log book.

Mark IV Part Weights

David Domeier (unfinished)

ItemWeight (lbs)
Center Section Spar48
Fuselage on gear (no canopy or strakes)242
Canard & elevators33
Right wing with winglet & aileron69
Left wing with winglet & aileron68
Turtle deck with glass12
----------------------------
Total472

As of Cozy Newsletter #50, this wasn’t all of the weights.

Paul Kuntz (unfinished)

ItemWeight (lbs)
F22 Bulkhead2.45
F2810.7 oz
Seat back5 lbs, 1.9 oz
Lower forward landing gear bulkhead1.4
Upper forward landing gear bulkhead0.7875
Aft landing gear bulkhead2.7
Lower firewall1 lbs, 14.5 oz
Center firewall10.2 oz
Upper firewall3 lbs, 7.8 oz

Flying advice

  • When filing for IFR, use the designator CZ-10. (Cozy Newsletter #36).
  • Keep a fire extinguisher in the plane.
  • When filing flight plans, the correct designator for the Coze 3 and 4 place aircraft is HKB (Cozy Newsletter #43)
  • As of Cozy Newsletter #51, use COZY as the designator when filing flight plans.

Flight Testing

  • One of the tips in Cozy Newsletter #51 suggests AC-90-89A, Amateur-Built Aircraft and Ultralight Flight Testing Handbook. The current version is AC-90-89B

Last updated: 2021-08-02 18:00:57 -0700

Canard Incidence vs. Pitch Stability

Copied verbatim from Cozy Newsletter #72. Make sure this is done early in flight testing:

The Cozy Mark IV is designed to have positive pitch stability and to be resistant to a main wing stall throughout its approved c.g. range. But for this to be true, the canard must be set at the correct angle of incidence. During your initial flight tests, you should determine whether your canard is set at the correct angle of incidence, and there is an easy way to do this safely in flight. If you notice on large drawing M- 18, there is a protractor which shows the full travel of the elevator from minus 15 degrees at full forward stick to plus 30 degrees at full aft stick, and there is a notation that at cruise, the elevator should be in trail, i.e. at zero degrees. In newsletter #56, page 5, there is a plot of elevator position as a function of c. g. and speed for our plans-built model, and on this plot, the zero elevator position occurs at a c.g. of 101 and 150 knots IAS. For several years now, we have been including a copy of this page with each Owner’s Manual. It also lists several changes for you to make to the Owner’s Manual. So, before you expand your flight envelope, and before you fly at slow speed and aft c.g., check your elevator position. It is perfectly safe to do this at a c.g. of 101 and 150 kts IAS, or even better, at a c.g. of 100 and 150 kts IAS, your elevator position should be at less than minus 1 degree, i.e. about 1/16th inch trailing edge down. If your canard is set at too low an angle of incidence, it is a dangerous condition. The indication will be that the trailing edge of the elevator will be too low in cruise. The symptoms will be difficulty in rotating, pitch instability, and a tendency to react too fast to back stick. And the result could well be a main wing stall.

Very recently two builders complained of pitch instability, and difficulty rotating. I went for a demo ride with one of the builders in his Mark IV. With both of us in the front seat (and estimated c.g. of 100), the elevator trailing edge was down almost 3/8 inch or 5 degrees. For comparison, we both went up in our plans-built Cozy and the trailing edge of the elevator was zero to 1/16th trailing edge down. We concluded that his canard was set at too low an angle of incidence. After a telephone discussion with the other builder, he sent me this e-mail: “Hi Nat, Thanks for your input the other day. I adjusted the canard incidence by 2 degrees. Did so by relocating the guide bushings that engage the alignment tabs, as we discussed. Had to slightly modify the canard cover, but it was really much less of a task than I’d envisioned. Bottom line is that the aircraft now flies lovely all the way out to the forward c.g. limit. The c.g. and weight envelope is fully expanded as well as all flutter testing and low speed/min speed tests. Cooling is pretty good though I’m still working on it. Will provide more soon. Regards, Rob”

This is an important matter. Make sure you check elevator position early in your flight test program.

Last updated: 2021-08-02 18:00:57 -0700

Cleaning Up Epoxy

From Cozy Newsletter #83. Very good information. The main takeaways are:

  • Use barrier cream, replace it regularly.
  • Minimize the use of organic solvents as much as possible.
  • Use cheap paint brushes you can throw away.
  • Wipe squeegees with a paper towel. Let remaining epoxy cure, then sand it off with a belt sander.
  • Scissors: Wipe with a paper towel, then scrape away epoxy with a straight edge razor.

In the handling of chemicals, we urge caution. Epoxy resin, by itself, is inert and nonreactive. But the hardener has active ingredients, which you can become allergic to if you are not careful. So we recommend the use of barrier creams on your hands which are water soluble (hydrophilic) which you can wash off with soap and water, but are not penetrated by organic materials (oleophobic). Now when it comes to cleaning mixed epoxy from hands and tools, a word of caution. It is best to try to hold the use of organic solvents to an absolute minimum. MEK (methyl ethyl ketone) is a very powerful organic solvent. It will certainly remove epoxy from your skin and tools, but it can be deadly! It can penetrate your skin, and inhaling the vapors can also cause damage to internal organs. Acetone is a cousin of MEK. It isn’t quite as bad, but can still cause damage. So it is best to avoid the use of solvents as much as possible. How do you do this? Use barrier cream on your hands, and try not to soak your hands in epoxy, and replace the barrier cream quite regularly. Wash it off with soap and water. You can use gloves, but not latex gloves, because they can also cause allergies.

When it comes to tools, for paint brushes, use a cheap variety that you can throw away. If you insist on using them more than once, washing with hot water (really hot) and soap works very well. You can store them in a large bottle with a little solvent for later use, or you can wrap them in plastic and put them in your freezer. With squeegees, wipe them with a paper towel. Rather than using solvents, let any remaining epoxy cure and then sand it off with your belt sander. With scissors, you can wipe them off, and periodically scrape any cured epoxy off with a straight edge razor. Builders report that apple cider vinegar cuts epoxy very well on hands or tools, but we have never tried this. Vinegar is acid, so it should be neutralized or flushed later.

Last updated: 2021-08-02 18:00:57 -0700

Main Landing Gear Strut

From the Cozy Newsletter #78:

The FeatherLite main landing gear strut for the Mark IV is halfway between that of the Long EZ and Defiant in span, chord, thickness, weight, cost, and load carrying ability. It is made of S-glass and very dense, with no voids. It has an excellent spring-constant, and will not deform or take a permanent spread after repeated loading to many gs, nor should it be necessary to “set” the gear after parking. In newsletter #64-6 we explained how to measure wheel camber and suggested checking it annually to determine that no permanent spreading of the strut has occurred. We have yet to hear of a FeatherLite Mark IV strut taking a permanent set.

The strut was purposely designed with a return curvature at both ends to reduce local bending loads. This also results in the wheels having a slight camber (bottoms closer together) of about 2.5 degrees when the Mark IV is empty or slightly loaded. As the loading is increased, the strut spreads and the wheels move outboard and become closer to vertical. As the loading is further increased, like in a high-g landing, the strut has been known to spread enough for the inside of the wheel pants to scrape the runway, and in very extreme cases, spread enough for the brake calipers to scrape the runway. But always the strut should return to its original shape after the load is relieved.

Tire wear is always the greatest at the instant the tire touches the runway, because wheel rotation is instantly accelerated from zero to about 70 knots. Because of the camber of the wheels, which is even greater when the airplane is in the air just before touchdown, the outboard tread receives the greatest wear. So when the outboard tread is nearly worn away, it is the accepted and recommended practice to reverse the tires (outboard to inboard) to even out the wear, similar to what you do with your automobiles when you rotate the tires. Before installation of the strut, you are instructed to wrap it with 8 crossing plies of UNI, to increase the torsional strength. This should eliminate or at least minimize any possibility of wheel shimmy. You should not substitute BID, Bi-Ax, or Tri- Ax cloth.

You are instructed to install the axles with a slight toe-in, about 1⁄4 degrees. This will provide the least rolling resistance in takeoff and landing, and least tire wear. When you think about it, the reason is simple. During takeoff, as the load is relieved from the wheels, the strut tries to come together, and toe-in helps it do that. When you land, the sudden load (unless you “grease it on”) spreads the strut and then as the load is relieved, the toe-in helps it come together.

Last updated: 2021-08-02 18:00:57 -0700

Peel Strength

From Cozy Newsletter #55.

The peel strength of a cured fiberglass matrix is the amount of force required to delaminate a layer of fiberglass from the layer below or the substrate below. It is the measure of the internal strength of the cured epoxy or its adhesion or mechanical bond to the substrate. It is a very important property, because the peel strength of the epoxy is literally what is holding your airplane together.

It should be obvious that when you are making a layup over a dry, previously cured surface, the peel strength will be either the strength of the mechanical bond, or else the internal strength of the epoxy, which ever is weaker. It is important, therefore, in making a wet layup over a dry surface to properly prepare the dry surface so the mechanical bond to the surface will not be the weakest link. There are two methods of preparing a fiberglass surface for the maximum strength mechanical bond. The first is to sand a previously cured fiberglass surface dull with 36 grit sandpaper. The disadvantage of this method is that if the surface is not absolutely flat, it is nearly impossible to remove all of the shine without sanding through some of the glass filaments, weakening the substrate . The second method is to squeegee peel ply over a fiberglass substrate before it cures, and strip it off after cure. The advantage of using peel ply is that the shiny surface (which might also be waxy) is stripped off with the peel ply, and the surface remaining is flat but fractured and rough. Sanding this surface is a wise, extra precaution to maximize the mechanical bond.

It is normally assumed that maximum peel strength is obtained by making a wet-on-wet layup, because then there is no mechanical bond involved. There may be an exception, or at least a reservation to this rule. We recently received a call from a builder in the state of Washington who said that he was using Epolite 2427 resin, and he noticed after glassing the inside of his fuselage sides, that the peel strength of the second layer was poor, and he could peel off the second layer rather easily. After discussing his technique with him, we think we know why this happened. Very often, first-time builders are too meticulous, and take a long time to squeegee each layer of glass to remove all of the excess epoxy before laying down the next layer of cloth. The fuselage sides have a lot of area so this could take quite a long time. If, as has been alleged, 2427 is more susceptible to contamination by humidity (and/or carbon dioxide) in the atmosphere, and it is exposed to the atmosphere for a long period of time before the next layer of glass is applied, there could be a contaminated surface between the two layers of glass which would reduce the internal strength of the epoxy at the worst possible location -- between the glass layers.

Experienced builders have learned that it is much faster, and results in better layups, to wet out the first layer of glass, squeegee the air out, but leave an excess of epoxy and then lay down the next layer of cloth on top to soak up the excess. This wets out the second layer faster, because the excess epoxy from underneath pushes the air out ahead of it. This saves much time, results in less air in the layup, requires less squeegeeing, and, if the epoxy is susceptible to contamination from the atmosphere, there is much less exposure to the atmosphere, and any contaminated surface epoxy does not end up being between two layers of glass. The same considerations apply also and argue for the use of peel ply over the top layer.

We have tested the peel strength of Epolite 2427, and haven’t found it to be any different from the several other epoxy systems we have used. It is true that we have low humidities in Arizona most of the year (not during the monsoon season, however), but it is also true we follow the procedure for faster and better layups recommended above.

Last updated: 2021-08-02 18:00:57 -0700

Post Curing of Epoxy Layups

From the Cozy Newsletter #61

All epoxy systems have a minimum and a maximum curing temperature. At the minimum curing temperature, for example, room temperature, an epoxy system achieves a good degree of curing, that is, over 80%, and produces a hard, shiny, tack free surface, with good properties, but the properties, including glass transition temperature, are not maximized. For both L335 and L285, the properties achieved from room temperature cures are quite acceptable for aircraft use. The glass transition temperature of L335 after a room temperature cure, would be about 130 deg. F (the glass transition temperature is the temperature at which the epoxy begins to soften and become rubbery). To obtain 100% of the available properties and maximum glass transition temperature requires either post curing or curing at the maximum curing temperature. For L335, the maximum curing temperature or post curing temperature would be about 160 deg. F and results in a glass transition temperature of about 185 deg. F. But to achieve maximum cure and glass transition temperature, the layup would have to be held at the maximum curing temperature for about 16 hours. For L285 the maximum curing or post curing temperature would be about 170 deg. F and result in a maximum glass transition temperature of about 240 deg. F. Again, it would have to be held at the high temperature for about 16 hours. So is it necessary to post cure your airplane? Actually, no. As either parts of your airplane or the entire airplane sit at temperatures above 70 deg. F, some post curing occurs. Even if your airplane sits outside in the sun, and the ambient temperature reaches 100 deg. F, it will do so gradually, and the post curing will proceed gradually so that glass transition temperature will always be considerably higher than ambient. The wings will not sag. Remember, you are going to paint your airplane white, and the surface temperature (only the top surface in the sun) will only get about 10 degrees higher than ambient. So on a 100 degree day, some post curing will already have occurred, so the glass transition temperature will already be higher than 130 deg. F and approaching the maximum of 185 deg. Now there is a possible exception to this rule. If you are going to paint your airplane black, or some other dark color, a fully post-cured L335 might not have a high enough glass transition temperature (185 deg. F might not be high enough). So, if you intend to paint your airplane black or some other dark color, you probably better use an epoxy like L285, and do some post curing before you park it out in the sun on a hot summer day. Remember, with an epoxy like L335, the glass transition temperature will always be higher than ambient and the epoxy will not soften unless or until the surface temperature reaches the maximum glass transition temperature, which in the case of L335 is about 185 deg. F. If you paint your airplane white, at least on the top, the surface should never reach this temperature even outside in Saudi Arabia in the summer. Even if you are not going to paint your airplane a dark color, but are willing to spend a little extra money on the best epoxy available, consider using L285. That would be our choice. If you do not understand, or have further questions, please contact us.

Last updated: 2021-08-02 18:00:57 -0700

Unapproved Design Changes

From Cozy Newsletter #59, copied verbatim.

We referred earlier to design changes which we haven’t approved, which we think are ill-advised, and which in some cases may even be dangerous. Here are design changes to avoid:

  1. Do not change the way the elevators are constructed or installed. The top surface of the elevators must be reflexed, as we show in the plans, as for example in the cross sections we show in Chapter 11, pages 5 & 6. If yours have not been built this way, scrap them and start over. A false rumor has been circulated that there is a “dead spot” in elevator response. This is not true if built according to plans, and we have proved it and can demonstrate it with our “plans-built” Cozy Mark IV. It has been reported that the same person circulating this rumor has a problem with pitch trim. This could be a symptom that there is something more seriously wrong with his airplane, if not the shape of his elevators, it could be that his canard is not set at the correct angle of incidence, and his airplane is unstable in pitch. Our flight tests apply only to a Mark IV built according to our plans. You should be aware that the fuselage is a lifting body, and the canard span and incidence needs to be adjusted for the amount of lift contributed by the fuselage. If you change the shape of the fuselage, either by making it wider, higher, or using a different canopy, or you change the angle of incidence on the main wing, there is only one way to determine whether you have a safe airplane, and that is to install a traveling 135 lb. weight, like we did, and go up to 11,000 ft. with a parachute, and determine whether the point of neutral stability is well aft of the aft c.g. limit, and whether the c.g. range is safe at the aft c.g. limit and at least 1.2 inches beyond.
  2. Do not limit elevator trailing edge up (nose down) travel to 11 degrees rather than the 15 degrees we specify. If you should ever remove your vortilons, or miscalculate your c.g., or set the canard at too low an angle of incidence, or change the fuselage, and do stall tests and find the main wing start to sink at the same time the airspeed starts to fall, you will want as much nose down authority as you can muster to keep from becoming a statistic. The plans say 15 degrees trailing edge up, and that is what you should have.
  3. Do not use “hard shelling” (Note: applying a mixture of micro to the foam, letting that cure, then applying glass). This results in a poorer bond between the fiberglass and the core. On airfoils, the top surface is usually in compression. A poorer bond means that the airfoil (canard or wing) skin can delaminate, buckle and fail sooner, that is, fail at a lower g-loading, than an airfoil built according to plans.
  4. Do not use “tri-ax” cloth. We are not aware of any static load testing that has been done with Cozy or Long EZ wings to prove that it has as much torsional, tensile, and compressive strength as the individual layups specified by Burt Rutan, and which we use. Furthermore, it is much harder to work with because it does not conform as well to curved surfaces and can cause air bubbles (poor lamination), and it has a tendency for one or more layers to wrinkle when squeegeed, which it is not possible to correct. Also, our plans call for one less layer of glass where the ailerons will be cut out. You can’t do that if you are using tri-ax. Ailerons covered with tri-ax cloth will not balance leading edge down, with the very likely possibility of “flutter” which can cause catastrophic failure of an airframe, unless you sand off at least one layer of glass, which is more work than if you had used the correct glass cloth layups in the first place.
  5. Do not increase the chord length of the ailerons. There is no possible justification for doing this. It not only makes it much more difficult to balance the ailerons, but it reduces the wing cross section at the point where the bending load is the greatest. In other words it weakens your wings both in drag and in bending loads.
  6. Do not increase the span of the ailerons. Our 3-place Cozy has excellent roll response. The Mark IV has even greater roll response because the 2 ft. greater wingspan puts the ailerons farther outboard which results in a greater roll moment, and also farther outboard of the downwash from the canard. There is no possible justification fo this change.
  7. Do not buy “fast build” wing kits where the foam cores have been cut for wider chord and greater span ailerons, and the “kink” in the trailing edge of the wing has been eliminated. The latter changes the angle of incidence of the airfoil, which makes it different from the airplane we have tested, and causes problems in fitting the cowlings.
  8. Do not eliminate the extra layups on the top of the wing which we show in Chapter 19, page 6, Fig. 32. These provide added strength to the wing where the bending and drag loads are the greatest.
  9. Do not increase the span of the rudders. They are even more effective on the Mark IV than on our 3-place because of the increased wingspan. Very little rudder input is required in flying a Mark IV. Furthermore, it was discovered on the Varieze that too much rudder authority could cause a Varieze to lose control. You wouldn’t want this to happen on base or on final.
  10. Do not leave the lower winglets off or make them smaller. We found in our very thorough aft c. g. flight test program that the lower winglets shown in our plans give you a 0.5” c.g. safety margin protection against a main wing stall. They also provide more roll stability at slow speeds and high angles of attack. Again, something that is important on base or on final.
  11. Do not eliminate the NACA scoop in the fuselage bottom and use arm pit scoops instead. The NACA scoop gives better cooling of the engine when parked nose down, and probably also in flight. Better cooling of the carburetor or throttle body means fewer problems (if any) with hot starts. Also, if you notice, the Cozy Mark IV is quite clean underneath. We believe this (and better cowling contour) contributes to the extra 20 mph we get as compared to another aircraft with arm pit scoops, fixed gear and the same horsepower.
  12. Do not cover the top of the canopy. The compliment we receive most often on the Cozy and Cozy Mark IV is its wonderful visibility. If we had gull-wing doors, we couldn’t have a full bubble, but with a side-hinged canopy it is a wonderful feature. Install the full bubble first. Then, if sun bothers you (it helps to keep you warm at high altitudes in the winter), you can always wear a baseball cap. Then, if you are still bothered by the sun, you could use cling-type plastic shades, which are moveable, over your head. If you really like reduced visibility, you can always paint part of the bubble. The latest pictures we have seen of the Velocity show that they removed most of the cover over the top of their canopy. We consider this to be a safety consideration.
  13. Do not hook your fuel tanks together. Having two separate tanks is a safety feature. If you lose one fuel cap with both tanks hooked together, all of your fuel will be siphoned out, and you will become a statistic.
  14. Do not eliminate the sumps under each tank. They make all of your fuel usable, and allow you to fly for a little while after the gauge shows empty. Although not recommended, you can run one tank completely dry, switch, and keep on trucking. We have done this (accidentally) twice in the last 12 years.
  15. Do not locate your fuel selector valve remotely. Experience with the Varieze was that the remote location of the fuel valve was the cause for more than one emergency landing.
  16. Do not buy components from custom shops without calling us first. Custom shops are in business to make money. They may use unskilled labor and take shortcuts, and sometimes their parts don’t fit or are unairworthy. They will probably claim their parts are better, but then ask you to sign a waiver relieving them of any product responsibility or liability, and will not guarantee the airworthiness of parts they supply. We have heard of some very bad experiences some builders have had with custom shops. If you are not willing to build the parts yourself per plans, you would be better advised to build a Velocity. The Swings have a pretty good record.
  17. Do not install retractable main gear. Our airplane was not designed for it. Most people agree the benefit (if any) isn’t worth the cost (and we aren’t just talking about dollars).
  18. Do not change the size or shape of the engine cowlings (in other words, use the cowlings we approved from Feather Lite). Our cowlings were contoured to have nice clean airflow back to the prop, to avoid a vacuum or reverse airflow at the prop. It was interesting to hear that one 4-place canard aircraft (we won’t mention the name), which has been highly advertised, and which has a very blunt rear end, has not yet been able to meet its performance goals of useful load and speed because it cannot generate enough thrust after becoming airborne. We suspect that it is because the prop is spinning in reverse airflow or a vacuum (you know, like behind a semi).

[A bunch of text to backup that unapproved design changes tend to have bad results]

Lastly, if you do not build your airplane according to plans, the Cozy Mark IV Owner’s Manual does not apply, and we ask that you not register or insure it as a Cozy Mark IV!


Which is why I’m not building a Cozy Mark IV, I’m building a Coz-E, which happens to be largely similar to the Mark IV, but is not the same airplane.

Last updated: 2021-08-07 08:24:43 -0700

How do you make Vortilons

From Cozy Newsletter #77:

A way that works well is to make a flat 3-ply 8 x 8 layup on a piece of plastic, and then cut out a pair of each of the 3 vortilons (see M-18). Then tape saran wrap on the leading edge of the wings at each of the 3 locations. Use a generous amount of saran. Then put down a 2-ply layup over each of the saran wraps on the leading edge of the wing. Make it generous, and use peel ply over the top. Sand the vortilons. After the leading edge layups have cured, remove the peel ply and 5- minute the vortilons to the leading edge layups, using the 67 degree template on M-18 to make sure they are at the right angle. After all are in place with the right alignment, micro the inside corners and tape both sides of the vortilons to the flanges with 2 plies of BID, and peel ply. After cure, remove the flange-vortilons from the leading edge, and trim the flanges to about 3⁄4” width each side of the vortilon. Paint them. After the wings are painted, stick them on with clear silicone. They will adhere without coming loose even after many head bumps. Put them on before you fly and never take them off!

Last updated: 2021-08-02 18:00:57 -0700

Resources and Inspiration

  • The unofficial cozy builders web site, run by Marc Zeitlin.
  • Cozy Girrrls makes and sells parts for the Cozy and other canards.
  • John Slade’s page on building his Cozy.
  • Phillip Johnson’s Kinda Kozy has a subaru engine, fully retractable gear (which makes the cozy look so much better, even with the retracts deployed, a front hinge canopy w/ gull wing passenger entrance.
  • Cozy Serenity has a really detailed, modern build log. Definitely standing on the shoulders of giants type deal.
  • Eureka CNC - this person built a CNC hot wire machine, and sells jigs that are CNC’d, or fully CNC’d out foam cores.

Finishing

Last updated: 2021-06-23 22:19:06 -0700

Shop Setup

Here’s how I set up my shop for this:

You’ll need a lot of workbench space. I designed my own 2’x4’ workbench, and plan to build 6 of them.

Additionally, you need a bunch of storage space. I built a cabinet to store fiberglass in, which has space underneath it

Future known work includes:

  • Box to store and heat epoxy.

Additionally, I also have some printouts of information good to have visible in the shop.

Last updated: 2021-09-03 19:22:16 -0700

Fiberglass Cabinet

Unlike the workbench, this is joined mostly with butt-joints. This doesn’t need to support a ton of weight, so butt joints held together with glue and screws is perfectly fine for this.

Bill of Materials

First, the actual materials and lengths needed to construct this. This is made primarily with 2x4 studs (which are actually 1.5 x 3.5 inches, because of course they are).

2x4 studs:

  • 2x 60” (for the backplate)

  • 2x 33.5” (for the front support)

  • 2x 30” (Giving extra depth for the fiberglass container)

  • 6x 48” (4 for the “rails” supporting the front and back of both the top surface and the bottom shelf, then 2 for the top part, covering the fiberglass container)

  • 6x 24” (the “ribs” of the top surface and the bottom shelf)

Plywood. half-inch or even quarter-inch is fine.

  • 2x 48” x 27” sheets (The shelves)
  • 1x 48” x 31” sheet

Extra:

  • Screws. I used 3 inch #8 screws for most of the frame. For securing the fiberglass container, you’ll want longer screws, 5 inches or so should work.
  • a single 48” x 24” (or so) sheet of whiteboard.
  • Bunch of wood glue.

Raw Materials

Because you won’t be able to find individual pieces cut to the exact size, these are examples of how you can obtain the required materials in the necessary lengths.

The “remaining material” assumes the cuts are made with a 1/8 inch blade saw blade.

Studs

  • 2x studs, cut to 60” and 33.5” (2.25” remainder)
  • 2x studs, cut to 48” and 30” (17.75” remainder)
  • 2x studs, cut to 48” and 48” (0 remainder - and it’s ok that one is going to be slightly short)
  • 2x studs, cut to 48”, 24”, and 24” (0 remainder. It’s ok for the short side to be on one of the 24” cuts)

In total, 8x 8’ studs.

Plywood

From a single 4’x8’ sheet, you can cut it length-wise into the sizes specified.

Plans

  1. Cut studs to lengths specified
  2. Create the rear-frame by joining via butt-joints the 60” studs, and 3 48” studs.
  3. Attach the studs for the fiberglass container
  4. Attach via butt-joints the “ribs” of the shelves to the rear-frame.
  5. Attach the front “legs” as well as the rib to the frame
  6. Attach the plywood to the back and the shelves.

Last updated: 2021-07-26 20:57:50 -0700

Printouts

Notes to print out and place in a visible place in the shop.

Here we have:

  • Materials is good info on making epoxy, with QR codes for the epoxy and glass bubbles MSDS.
  • Basic Layup Procedure is more-or-less a transcription of Chapter 3, page 19. I didn’t want to rip it out of the plans and hang it out on the wall.

Last updated: 2021-09-03 19:22:16 -0700

Basic Layup Procedure

  1. Preparation: Ply #9 or Gloves (Nitrile preferred) on hands, shop temperature 75° F ± 10 °.
  2. Cloth Cutting: Use the electric scissors.
  • Unless otherwise specified, cut at 45° to the fibers.
  1. Surface preparation:
  • Foam: Hot-wire-cut surface needs no preparation. Sand ledges or bumps even. Fill holes or gouges with dry micro immediately prior to layup. Vacuum up the dust.
  • Glass: Always sand to completely dull any cured glass surface with 36 or 60 grit sandpaper. Re-sand if it has been touched with greasy fingers.
  • Metal: Dull with 220 grit sandpaper.
  1. Mix Epoxy:
  • Mix for 2 minutes.
  • 80% stirring, 20% scraping sides and bottom.
  • Hot cup: Throw it away and mix more. A hot cup indicates exotherm.
  • Don’t use a brush to stir.
  • Micro Slurry: Approximately equal volume of mixed epoxy & glass bubbles.
  • Wet Micro: Add enough bubbles for a “thick honey” mix.
  • Dry Micro: Enough bubbles so it won’t run.
  • Wet Flox: Thick, but pourable mixture of mixed epoxy & flocked cotton.
  • Applying to surface:
    • Over foam: brush or squeegee on a thin micro slurry layer (urethane foam: Use a thick micro slurry layer).
    • Over glass: Brush on a coat of epoxy.
  1. Lay on cloth:
  • Pull edges to straighten wrinkles.
  • If working alone: Roll the cloth, then unroll it onto the surface.
  1. Wet Out:
  • Don’t slop on excess resin; Bring epoxy up with a vertical stab of the brush (This is stippling)
  • Start in center and work out to sides.
  • Most of the time in a layup is spent stippling. Stipple resin up from below, or, if required, down from above.
  • “Not wet, not white”.
  1. Squeegee:
  • If you have excess epoxy, squeegee it off to the side. Use squeegee with many light passes to move epoxy from wet areas to dry areas.
  1. Preliminary Contour Fill
  • Save sanding by troweling dry micro over low areas while the glass layup is still tacky.
  • This is done at trailing edges, spar caps, or over any low areas.
    • The low places are overfilled with micro, then sanded smooth after full cure.
  1. Knife Trim:
  • Razor-trim the edges at the “knife trim” stage, about 3-4 hours after the layup.
  • Alternatively: Wait until a full cure, then use the variable oscillating tool to knife trim.
  1. General Inspection:
  • Look for dry glass, excess epoxy, bubbles, and delamination before walking away from wet layup.
  1. Cleanup:
  • Remove gloves, or rinse ply #9 off with soap and water.
  • Epocleanse can also remove epoxy off unprotected skin areas.
  • Brushes: Rinse twice with MEK, and wash with soap and water. Throw away after 2-4 uses.

Last updated: 2021-09-03 19:22:16 -0700

Materials

MGS 335 Epoxy

The MGS 335 Epoxy should be mixed at a 100:38 resin:hardener ratio. This means the following:

Total EpoxyResinHardener
60 g (~2 oz)43.48 g16.52 g
120 g (~4 oz)86.96 g33.04 g
180 g (~6 oz)130.43 g49.57 g
240 g (~8 oz)173.91 g66.09 g

Don’t try to mix more than 8 ounces (~240 g) in a batch. If your layup requires more than 8 ounces, make multiple batches. Mix enough epoxy for a 1:1 ratio of epoxy to fiberglass by weight.

Slurry, Wet and Dry Micro

Mix the glass bubbles with already-mixed epoxy.

MaterialDesired ConsistencyRatio (Balloons:Epoxy) (by volume)
SlurryAlmost same as epoxy1:1
Wet MicroSags or runs like thick honey2-4:1
Dry MicroPaste that does not run or sag~5:1

Apply Dry Micro with a putty knife. Apply Wet Micro and Slurry with brushes.

Flox

As with Slurry and Micro, mix the flocked cotton with already-mixed epoxy.

MaterialDesired ConsistencyRatio (Cotton:Epoxy) (by volume)
FloxJust enough to make the mixture stand up~2:1
Wet FloxSag or Run

When using flox to bond a metal part, be sure to sand the metal dull with 220-grit sandpaper. Also paint pure epoxy (no flox) on the metal part prior to bonding with flox.

Safety

3M Glass Bubbles

Wear googles and dust mask when mixing!

3M Glass Bubbles Material Safety Data Sheet

Last updated: 2021-09-03 19:22:16 -0700

Workbench

CAD rendering of workbench

These are heavily inspired by the EAA Chapter 1000 Standardized Work Tables, only designed to to be 2 feet by 4 feet instead of 2 feet by 5 feet. A bunch of people in the cozy community prefer joining 6 tables of these size to ultimately create the plans-recommended 12 foot by 4 foot table for the wings and other large pieces. This is my take on that.

USDZ (AR Preview) Fusion 360 file.

Materials

This is made using 2x4 studs and plywood, held together using simple woodworking joints, with wood glue and screws to supplement.

  • 2” x 4” studs (which should actually measure 1.5” x 3.5”)
    • 2x 48” studs
    • 3x 24” studs
    • 4x 32” studs
    • 2x 37” studs
    • 3x 16” studs
  • Plywood
    • 1x 48” x 24” x 3/4” plywood “project board”.
    • 1x 34” x 16” x 1/2” plywood “project board”.

To minimize material needed to buy, you can buy 6x 8’ studs, and have the lumber yard cut them to size.

Instructions

First, we’re going to build the frame, then screw in the table and shelf tops.

  1. Top Frame
  • Cut half-laps into the 48” studs. These will have a depth of 1.75” (half the height of the studs). They should be 1.5” long (the width of the studs). Cut 2 of them 4” from the edges, then a third in the exact center of the 48” stud (starts 23.25” from either edge). Make these cuts all on the same side.
  • Cut rabbets into 3 of the 24” studs. These will be at the ends of the studs. As before, they’ll be 1.75” deep, and 1.5” long. Make these cuts all on the same side.
  • Join the 48” studs with the 24” studs you just cut into. The correct orientation for this is that the 24” will slot down into the 48” (so that, when weight is placed on the 24” studs, they’ll transfer that weight into the 48” studs)
  1. Legs
  • Cut rabbets and half-laps into the 32” studs. These will have a depth of 1.5”, and a length of 3.5”. The half-lap should be made on the other end (but same side) of the stud. The half-lap cut should be inset 4” from the end it’s cut on.
  • Join the rabbet from these studs into the inside corners of the 48” studs and the 24” studs of the top-frame.
  1. Bottom Shelf
  • Cut 3 half-laps into the 37” studs. All these should be 1.75” deep, and 1.5” long. 2 of them should be inset 1.5” from the ends, and the third should be in the dead center (starting 17.75” from the ends).
  • Cut 2 rabbets into the 16” studs. Similar to above, these should be 1.75” deep and 1.5” long.
  • Join the 37” studs into the legs from earlier, into the unused half-lap cuts near the bottom.
  • Join the 16” studs into the 27” studs.
  1. Surfaces
  • Screw the surfaces to their respective places (the 4’x2’ plywood sheet should screw into the top, the 34”x16” sheet should screw into the bottom).

Last updated: 2021-08-01 22:35:13 -0700