Fuselage Fabric and Cable Fairlead

This has been a very productive week end, and as I write this, its still not over. I'm taking a break to let the last base coat dry on the fwd fairing and the canopy. When I finish writing this entry I will paint the first color coat on the fuselage. On Saturday morning I started the process of building a master model of a small streamlines blister that will hide the rudder cable exit fair lead. The whole process took exactly 1 hour, from the time I started until I was able to lay up the first blister. I started the weekend by finishing the turtle deck and the Vert. fin covering. Both of the projects were very simple and straightforward. Before I painted the base coat on the Turtle Deck my Buddy Ed was at again with my I phone camera, He took this picture from the rear near the horizontal attach.

Second Chantz Ballistic Chute

 This will be the last time this is visible.

Tail lowered so I could access the top of the turtledeck

While I am finishing out this plane, my Buddy Ed is painting a newly recovered wing of a Citabria. He was telling me that the complete weight of a traditional fabric covering for a plane like a Cub can be as high as 60 lbs. My plane is equivalent in area to a J3 Cub, and so far I estimate the complete fabric and finish weight is about 8 lbs.

Me and Boo

Other than Ed, Boo is my only friend who comes and visits when I'm working. I'm starting to get excited, I actually see the light at the end of the tunnel. The number of final jobs can now be counted on one hand. I installed my new tachometer this afternoon and revised all of the wiring. That was one of the last nagging projects I needed to address. From now on every time I install a rudder, aileron or elevator, it will be with final hardware.

Robin and Boo man!

The Lines of the Robin are really evident in this view. The fabric is literally the planes skin, and that can leave nothing to the imagination. I have received quite a few compliments on the lines of the Robin, but its really Rene Fournier who should receive credit. I tried to stay as true to his original design lines as possible.

Rudder cable fair lead lug

This is a picture of the rudder cable fair lead lug. A 3/4" nylon split Piper style cable fair lead installs here. I couldn't spend all of the effort to streamline the Robin just to leave 2 square inches of exposed frontal area. So on Saturday I started the process of making a master model and mold for a lightweight fiberglass blister that will fair this and be bonded to the fabric.

Blister loft

The project started by laying out a simple 3x body of revolution. Since the lug is 1" tall and 1.9" wide, a 3x after body was laid out with simple conic curves. Two copies of the plot were made.

Loft glued to a floral foam block

Since the blister is half as tall as it is wide I cut one pattern in half and then glued them to a block of Urethane floral foam block. The leading edges were aligned with each other.

After cutting on the band saw

It was off to the band saw with the foam. first the side profile was cut and then the center was left in the excess block which was used as a cradle while the plan view profile was cut. In terms of lofting this block represents the max half breadth and the inboard profile. All that is left is to use a small bit of the foam as a sanding block and round off the corners. You work both sides evenly because as the sanding block werars it transfers the contour to the block. By switching left to right, you get an equal shape

foam block positioned on my tooling plate

I used a small dab of bondo to adhere the foam to the tooling plate. The plate is well seasoned with hundreds of coats of wax already applied over the years.

Foam with one layer of fiberglass applied

I used Polyester resin and a single layer of 1.5 oz fiberglass. The surface needs to be sealed and a final finish needs to be applied.

Bondo added

After thee resin cured, a sweep coat of Bondo was added. I usually thin the Bondo with MEK prior to mixing it. Any way, a layer was added and the the Bondo was sanded. Don't screw around with fine paper at this point. The first coat was worked down with 80 grit. After a nice and level surface is achieved, I swept in a 1/2" fillet radius of Bondo between the table and the block. 180 grit paper was then used to further level the surface. A final sweep coat of Bondo was then added and 320 sand paper was used to smooth it out. 5 coats of Carnuba mold wax was then added

Gel Coat applied

I didn't want to get my Gel Coat gun dirty, so I just poured catalyzed Gel coat on over the form. Kind of looks like a rotten egg doesn't it?

The Gel Coat is allowed to tack off and when its about the consistency of firm rubber, more resin is poured over and layers of roving mat are added to reinforce the Gel Coat.

Mat being added

Now it looks lime some primordial animal!!! The thickness of the Gel Coat and fiberglass all but assured this would cure with heat due to the exothermic reaction of the resin. The heat actually melted the mold wax and the blob just popped off the tooling plate.

Mold

This is the mold when it was released. I trimmed the edges up and then sanded the Gel Coat with first 320 dry and then 400 wet sand paper. The smoother you make the mold the easier it will be to release the final part. So far up to this point I had spent about one hour. I was now ready to lay up the first blister.

Two types of Fiberglass

Now this is a lesson learned. I am now laying up a fine surface cloth before I lay a heavier structural ply. With contact wet lay up, the laminate is very porous and the final finish is prone to pin holing. So I now use a light weight fiber (1.5 oz) surface ply and then I follow with one ply of 8 OZ Rutan style BID fabric. Epoxy is always used for fly away parts. Polyester resin is not very dimensionally stable and will eventually warp.

Blister Temporally installed

This is what it will look like. There will be an 1/8 " slot cut in the after body and I will slip the cable thimble and shackle thru it. The blister will be cocked to align with the cable. I will bond it on with fabric cement.

Shoulder harness, ballistic chute and fuselage fabric.

I made good progress this Easter holiday. I started the installation of the seat and shoulder harness system. Because of the reclined position of the pilot, I realized that I need to add two crotch straps because the pilot would submarine under the lap belt. I bought my shoulder harness and seat belt from Aircraft Spruce. I need to find a source of the following shoulder harness fitting.

Davis Manufacturing Shoulder Harness fitting

For some reason I cannot get in contact with anyone at Davis Aircraft who made the original harness. If I have to I will buy a second shoulder harness and cut them down to make the crotch straps, but I would prefer to find the fittings and make up my own. I have a local Master Rigger who could sew up the webbing. But based on the response I am receiving form Davis, I will use another manufactures harness.  Anyway, if anyone has any Ideas I would appreciate an email.

planebuilder@yahoo.com


I laid out the parachute risers. The need to route around the main spar and around the landing gear. These are the hardest points on the Plane. The riser straps lengths are designed such that after they deploy, they will come to a point 12 feet in the air above the CG. 

main spar riser web instal

 I installed the riser strap with a liberal amount of fabric adhesive. The fabric will bond over the straps and then an opening will be pierced and then wrapped into the opening, further retaining the riser straps. This is an area I will revisit when I finalize the Robin Plans. There has got to be a cleaner way to attach the riser straps





 

Riser strap routing

I attached the Straps to the fabric standoffs.  The are non structural and sit outside of the longerons. The straps route over the longerons right next to a truss gusset. This particular gusset was increased in thickness to match the strap thickness. this way strap routing will be partially hidden.Notice that the risers route aft of the roll over structure. Everything that has fabric would be history if I ever have to pull the deployment lever.

bottom covering

 the covering of the fuselage starts with the bottom panel. Each successive panel will lap over the previous panel. All lap joints will face downward and be reinforced with a 2 inch pinked tape.

Side panel being installed

side panel was added after the bottom. Extra reinforcements were added at the wing carry thru and the the landing gear. This fabric shrinks very well with an Iron set at 260 degrees. One trick I learned watching the Stewart Video is to immediately wipe off the excess Eko bond right after application. This way a thick bond line is eliminated and a much cleaner fabric job is done.

Left side front view

The lower tape was also added. The fabric is coming out really nice and clean, I definitely learned some lessons from covering the rest of the plane.

Ballistic Parachute installation

I received my refurbished ballistic parachute from John Dunham at Second Chantz parachutes earlier in the week. http://www.secondchantz.com/. They did a fantastic job of reworking my 19 year old used parachute. I called John and asked if they had found a new case to repackage the chute. He informed me that this was the original case, but it had been thoroughly cleaned. The big delay was waiting for the sub contractor to fabricate the unique riser straps that the Robin will require.The deployment sequence had to be carefully thought out. The riser straps will rip away anything in their way. They need to be routed outside of the longerons and designed such that after deployment, the plane is supported by 4 straps that come to a point 12 feet in the air. The plane needs to sit level such that the main gear will be the first thing to strike the ground. All thought of saving secondary structure like the fabric and the fairings is ignored. A ballistic chute deployment is a serious action that is only contemplated when your life is in danger. Years ago, in my Hang gliding days when I was single, I participated in the Owens Valley Classic Cross country Hang Gliding race. This was run by my late friend Don Partridge. Don had a rule that all participants had to have a deployable parachute. This was in the days before ballistic chutes were ever designed. I launched that day from a turn out in a road 6500 feet above the floor of Death Valley. Truth be told, I had no business flying a hang glider at noon in Owens Valley. Every thing went smoothly until I hit the first freight train (thermal). I was pitched up violently 90 degrees. My audio vario pegged at 2000 fpm plus. I was barely ably to maintain control of my kite (Seagull 11 Meter) . I was tumbled end over end at least three times. Once I stabilized in a level flight attitude, I got hit by a monster thermal that bent both wing tips up at least 4 feet until each of them snapped. I then tumbled over and over at around 11, 000 feet of altitude. I cant tell you what I was thinking at this point, because it was all animal instinct. I do not recall my life flashing in front of me, but Hell after earlier Hang Gliding mishaps, it would have been a rerun any way!!. Finally I saw an open stretch of blue sky and I was able to deploy my hand held parachute. I was successful ( or I wouldn't be writing this) and the chute blossomed above me. From the time I deployed the chute until I landed on the ground, it was almost 1.5 hours. I was hit over and over by one thermal after an other. My flight profile took me from as low as 8000 Agl to over 14000 Agl. I drifted east away from Highway 395, my best estimate was about 20 miles. The only reason I was able to land, was because the sun had begun to set. I ended up drifting over a section of the ground that was in a shadow of the mountain west of me. Another requirement of the Cross Country Classic was the carrying of survival rations and water. This undoubtedly save my life the following day. I landed so late that I I decided I could not walk out at that hour. I made a very comfortable tent out of my wrecked 11 Meter. I rolled up in the Parachute and actually had a very restful night. The next day I started around 4 am and followed my shadow east. The sun was rising behind me and I knew that if I headed due west I would eventually intersect highway 395. This I did 4 hour later. I was at Highway 395 for no more than 5 minutes when a California Highway Patrol Car stopped and asked if I was Mark Calder? He informed me that 3 people had died the day before and that I was the last person missing!
Because of that experience, I am a firm believer in Ballistic parachutes.

The Robin has been designed from the onset for a Ballistic Parachute.

Riser straps

These are the riser straps that still need to be installed. They are made with shock resistant Nylon webbing. There are two sizes, one is designed to loop around the the main spar, the other is designed to loop around the landing gear. Each strap has a sewn in  loop that is stronger than the base web.

beginning the installation

I will take blind luck over careful planning any day of the week!! The chute will just barely fit under the roll over spreader bar with less than 1/8th of an inch clearance. If the wood intercostals were attached, it could not fit. The Chute is designed to mount to my roll over structure. I had an idea as to the dimensions of the chute but I was really guessing when I designed the roll over structure.!!

Business end

This is the business end of the chute. don't stare too long or you might not get a Second Chantz!! The mortar/rocket will shoot out between the roll over struts. The wood fabric fairing will be history if this lanyard is ever pulled. The riser straps will attach to a steel D ring on the R/H side of the package. The risers will rout around the outside of the roll over strut and outside of the longerons.

Deployment handle

 The deployment T handle is mounted forward of the stick and attached to the landing gear carry through. I debated where I should put this handle and my Friend Dan had a really good point, what if a left handed pilot flies the Robin, or I break my right arm. This way its centrally located. it will sit below the seat cushion.






 

Seat Belt  routing

 Once the chute was positioned, I could route the shoulder harness belts. They are designed to pass through the roll over cage and sit above the spreader bar. This way they are at the correct angle and will not cause the spine to be loaded in compression.

 

 The rest of the covered surfaces have been completed and final paint has been applied. The red color is spot putty that is filling pin holes in the fiberglass.

As I finish the paint, I am wrapping the surfaces in plastic. I have some kind of insect that loves to crap on  finished paint!! I'm tired of fighting with them, so I am wrapping everything as I finish.

Left wing about to be painted, Right wing wrapped

The right wing is fully painted. So far I have used less that one additional gallon of finish paint. I am a true believer I the Latex pint finish method. This is definitely the lightest way to cover an airplane!!