Musings from the Combat Pits

Nekked Chicken
or: How to build a Sonic Chicken

By Buzz Wilson

This is an article about dissecting a chicken. Not just any chicken but Jeff Dawson's chicken, the one he calls his “Sonic Chicken.”

Dawson sells the Sonic Chicken ready-to-fly, and they're a great value. However, for those who are crazy like me and want to build their own, here's how to go about it.

When dissecting a chicken, the first thing you have to do is to remove the feathers. There are several ways to do this. Where I come from you throw the chicken into a pot of boiling water and then pluck the feathers. Where Jeff comes from you take it up in an airplane and throw it out at about 10,000 feet. It is not so much a plucking that occurs but a delaminating as the chicken tries to fly. When it hits the hot Texas soil, you get chicken fried steak. Sorry, no Texas toast.

With the feathers removed, you can start the dissection process. When I did this, I was amazed at what I found. There are enough parts in the innards that a stunt flyer would think that they had opened the centerfold of their favorite erotic magazine - Stunt News.

Here you see raw chicken.

Next is the chicken gutted and cleaned.

All you health freaks make sure you wash your hands - do not want you getting salmonella. Here is the hardware removed and setting by itself.

I decided to build 10 chickens - do not ask me why; at the time it seemed like a good idea. To cut the panels I used my computer-controlled foam cutter and cut 20 panels. The cutter has the capability to cut spar slots; however, I decided to wait for another project before exploring that option.

The wing consists of two foam panels. I used a router and taper tool to slot the spar slots.

The spars come from Aircraft Spruce and Specialty. Dry fit the spars to the panels. I find it is easier to knock down spar high points before you install them in the wing. Dawson installs them and places tape along the sides to protect the foam and uses a plane to bring the spars flush to the foam.

Taper the end of the spar at the tip. Mark on the wing the end of the spars and identify top and bottom spar, and inboard and out board wing panel.

The panels are notched for a nose block and drilled for a carbon tube. The first step is to drill the nose block for the carbon center tube. Once this is done, drill the mounting holes for the engine. I use a machinist vice to hold the block square. My mounts are set for two holes - 2-56. If your mounts are single hole 4-40, you can wait to drill. Check the fit of the tube in the nose block to make sure it is straight.

Next position the nose block and mark the center of the hole for the carbon tube in each of the wing panels. I built a simple jig to align the wing and the hole position. Rather than drilling, use a dowel that has a sharpened end.

Mark the dowel with the depth. The carbon tube is inserted into the block and placed against the side of the foam. If there is push back, insert the dowel, and clean up the hole. If there is no push back, then repeat the process for the second panel.

Assembly begins with measuring the nose block and cutting away half of the width of the block from each foam panel. Mark each panel and then using an index card and a fine point pen draw a line for the cut. The index card bends over the leading edge and provides a straight line.

Place the panel in a sleeve and carefully cut the foam for the mount. You can use a band saw or as I prefer, the disc sander. Place the carbon tube in the nose block and test fit the two panels. If you over cut the foam, correct the problem by gluing plywood to both sides of the mount.

The top of the panels behind the nose block are notched for a 1/8 inch lite ply triangular bellcrank platform. This platform rest on the nose block. The top spar rest on top of the platform. A 1/8 inch balsa triangular piece fits behind the spar and on top of the bellcrank platform. A simple tool is made using spar material and balsa to mark the top of the panels. Use a 1/4 inch scrap piece of balsa and mark the area on the foam to cut out for the bellcrank platform and filler.

Again dry fit the nose block, wing halves, bellcrank platform and spars - adjust as needed.

Mark the end of the panels; the outboard is 1/4 inch shorter than the inboard. Also mark on the inboard where the lead out tube will be positioned. Take and draw the wing tips on the wing cores. I made a simple tool the shape of the tip and attached spar material to both sides. This is inserted in the spar slot and the shape drawn on the blank. On the inboard panel the centerline is marked and a pilot hole is drilled for the lead-out guide.

Glue the nose block to the outboard panel. Again a simple tool makes this easy, using scrap spar material; a spacer is glued taking the depth to 1/4 inch. Two of these are made and center the nose block. Use wax paper to prevent gluing the jig to the nose block.

When this is dry, mark the center rib and notch for the bellcrank platform.

Dry fit and sand to fit the center rib flush to the top and bottom of the wing panel. Glue the center rib to the outboard panel.

Add a scrap piece of spar to fill the gap between the motor mount and the spar on the bottom of the wing.

With the wing assembled, remove it from the cradle. Mark on the 1/8 inch bellcrank platform the hole for the bellcrank. Place the outboard panel in a wing cradle and drill the hole for the bellcrank bolt. Take one of the triangular plywood reinforcers and glue it to the top surface. When dry, take a sharp object (I use an ice pick) and push through from the underside to the top. Open the hole to make sure the bellcrank bolt will fit. Next glue the bottom triangular piece in place. Again, take a sharp object and push through from the top to the underside and test fit that the bellcrank bolt fits.

It is now time to add the plywood sub spar. A simple tool is used to guide a saw blade to notch the foam for the sub spar.

It is glued in place. A change that I made from Dawson's build is I add balsa to fill the gap after the sub spar is in place.

Cut the wing tips to shape. Mark the centerline of the wing tip. On the inboard tip take a piece of small diameter music wire and carefully push it through the wing tip to the exit point you previously marked for the lead out guide. If you exit before or after your top mark, rethread the wire.

Once you have the wire in the correct location, take the lead out tube, thread it onto the wire, and cut the hole for the lead out guide. Use a piece of tube that is a smaller diameter than the lead out guide; sand the foam for the control line exit. Cut the fuel bladder compartment using a two-part template and a hot wire. The template is positioned and a hole pushed through. The wire for the hot wire cutter is threaded through and the hot wire connected to the cutter. The compartment is cut and the foam removed from the wing.

Next, carefully sand the wing tips to their final shape. Locate on each wing tip where the tip is 3/32 inch thick. Previously you marked the center of the rib at 3/32. Carefully cut the trailing edge to the final shape. Now the real work begins - sanding the wing to the final shape. I like to use the foam sanding pads beginning with a 220 grit and then working down to a fine grit. Any dings or low spots are filled using light drywall compound.

Carbon fiber is now applied to the trailing edge and wrapped around each tip. Glue is applied approximately one inch around the tip and the surplus carbon fiber cut away.

Take the 1/8 inch stab blank and mark the centerline. Next position the stab blank against the trailing edge and mark the location for the cutout. The stab should be 1-1/8 inch behind the center of the wing. Save the cutout, you will use this to make the stablets. Hold the stab in place using a good quality masking tape (I use blue painters tape). Check to make sure it is straight and glue the stab to the wing. Take and cut the stablets and follow the same process for the stab. Carefully remove the tape and glue where the tape was covering. Once the glue is dry, apply a second coat. If you did a poor job of cutting and have gaps, use lightweight balsa to fill the gap and CA and sand.

Recently I experienced a problem after a midair. The stab was damaged and I did not see it when I repaired the wing. When I tested the plane, it flew as if it had down elevator. Back in the shop, I reset the elevator but did not see the down stab. The next time I flew it I was flying for a place in a contest and had to hold full up just to keep it in the air. Back on the bench, I discovered a cracked stab, cracked plywood center, and loose attachment at the trailing edge. All contributed to the down stab. After repairing, the plane was back to its old self.

Place carbon fiber tow over the center rib, both top and bottom, and glue in place. Add the 1/64 plywood over the carbon fiber and glue in place. Hold the wood in place using masking tape.

Using the carbon fiber pre preg, add reinforcements to the top and bottom plywood over the center rib at spar and stab. Add pre preg reinforcements at the stablets. Foam safe CA is applied to the pre-preg reinforcements.

Slot the outboard wingtip and glue a 1/4 ounce weight.

Final sanding, filling, and shaping are done. The wing is now vacuumed to remove sanding dust.

The final step prior to covering is to add reinforcing strapping tape. The tape is cut in various widths. The way this is done is to measure the width on the tape and cut a slit at the width mark. Next pull the tape and it will tear at the width mark.

The top and bottom tape is put on in the center of the wing. Next the tape is wrapped around the trailing edge including approximately one inch on the stablet. Tape is then applied from the stablet past the center plywood. Tape is applied over the tip weight, and the end of the spars.

Foam can be painted. Krylon makes a paint that you can apply to foam if you do not get overly aggressive. Water based acrylic paints can be applied with out damaging the foam. I also used a fiberglass pigment that I diluted with alcohol and added color to a foam wing. Keep in mind that paint adds weight.

The covering process begins with the fuel bladder compartment. The sides and end are covered using FasCal or clear packing tape. The top and bottom are covered using two pieces of fascal. A large piece about one inch greater than the compartment and a piece the size of the compartment. The smaller of the pieces is attached to the larger. The results are a non tacky surface. These are now attached to the top and bottom of the compartment. An alternative is to use a non tacky covering. I use Ultracote Lite to cover the access bladder compartment. Once the plane is covered, reinforcing tape is added to the top and bottom of the bladder compartment. Using a Dremel the bladder access hole is cut and the bladder drain hole cut.

A word about covering. Dawson likes to use a half-mil FasCal. We put together an order and I have 1000 feet. This is different from the FasCal that I used for years. The backing is not paper, but appears to be the same as the covering with the adhesive. This stuff is like flypaper and takes some getting used to. To separate the backing from the covering, use two pieces of tape. Place one piece on each side and pull. This will separate the backing from the covering. You do this at root for both the leading edge and trailing edge. Lay the covering on the wing, mark and trim away excess, but leave enough to work with. Next, you take masking tape and attach the covering to the root. Make sure everything lays out smooth.

Now pull on the tape at the leading edge and trailing edge.

The stab is made from 1/8 inch balsa. Use 1/64 plywood to reinforce the elevator top and bottom.

Take the stab and elevator and pre punch the hinge holes and elevator bolt location. Make sure you identify inboard and outboard on each piece.

The elevator is sewn to the stab. Dawson uses a 20 pound test fishing line. I prefer unwaxed dental floss.

An exhaust slot is cut using the Dremel. I use a small drum sander bit to rough cut the hole and then a tapered bit to final shape the hole.

A mixture of 30 Minute epoxy and alcohol is put on the hole to seal around the covering. This is filled with a high temperature RTV.

Bellcranks are made from 1/8 inch thick Kydex. Apply masking tape to the Kydex and draw outline of Bellcrank.

Cut the blank and drill holes. Use a bandsaw to cut the slits.

Once the elevator is on, the bellcrank tube is cut and glued in place. The length of the tube is critical. Take the tube and dry fit with the bellcrank assembly and push rod. You want the tube to stop the push rod. Use 5-minute epoxy to glue the tube in place. Once this is dry then assemble the bellcrank assembly with the push rod and mark the elevator for the control horn bolt and drill the hole in the elevator.

The bolt must be a full thread 4-40. On the bottom side, place a washer against the bolt head, on the top side use a blind nut. Use CA glue to hold the assembly in place. Take the 3/32” Dubro E/Z Adjust Horn Bracket (PN 557) and thread onto the bolt. Next, insert the E/Z Connector (Dubro P/N 605), put the push rod through, and attach the assembly to the horn bracket. A 1/8” cotter pin is used as a push rod guide.

A chicken in every pot, these are tough. Here is a photo of one that Don McKay used for several seasons. He pimped it out at the Portland contest this year, where I rescued it. Since then, I have used it to bash with Robert Smith, who on more than one occasion has tried to Robertize it but with not much success.

The following pictures show the results of a midair.

A hole was punched in the wing and the stabilizer destroyed. The damaged foam was cut out and a piece patched into the wing. The stabilizer area is cleaned up and a new one glued in place.

The old elevator is sewn on and the plane covered. In its next flight it mated with Gene Pape's chicken with Gene cutting it from the under side and the prop going thru to the top surface. A little tape and it flew the rest of the contest. Back on the bench, foam safe CA was put in the holes and light weight drywall compound applied, sanded and recovered. The light colored areas are where the plane has been repaired.

These are tough birds.

At some point in the future, I will draw up a set of plans.

Look out here comes a flock of the chickens.

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This page was upated Nov. 10, 2011