Robin Ultralight

Welcome to my Robin Blog.

It was suggested to me that I start a Blog on my ultralight project the "Robin". I have been working on this project for 4 years. On one of my first days at Vought aircraft, a stress man and future friend named Kenny Andersen walked up to me and said, "Aren't you the Mark Calder that designed the Wren Ultralight" Why yes I am I said. "well what have you done lately?" That was the genesis of the Robin design. The first 2.5 have been spent in the design phase. Actual construction started 1.5 years ago and has actually progressed smoothly. There have been a number of changes from the onset, but for the most part it is following my original concept. I will eventually sell plans for the Robin and make available all molded parts, fittings and welded assemblies. The Robin is designed to FAA part 103 and as such requires no pilots license to fly, although I think its a good idea to actually learn how to fly!! The actual name "Robin" was my Daughter Jamie's idea, I asked her to name the design based on my "cute little bird" theme (Wren)

Every good aircraft design has a "Mission" in mind before the actual design is started. A good designer will refer back to this mission every time a design decision must be made. Good design after all is just a series of good design decisions. On my first Ultralight design the Wren, the mission was to design a high performance low powered aircraft. The reduction of drag was the prime concern. I had been flying powered Hang gliders prior to this and because of this experience, I placed a high priority on climb performance. While most designers chose bigger engines, I chose lower drag and high aspect ratio (low span loading) wings. The Wren could out climb conventional Ultralight with up to 65 hp. The Robin follows this philosophy, but tries to improve on the performance of the Wren. Ultralight are not built by "rich" people, they offer an inexpensive means to enjoy one of the greatest experiences of my life, low speed soaring and flying.

Design Concept

The cost of an aircraft is directly proportional to its weight. , if low drag can be achieved then lighter and cheaper engines can be used. The Robin expands on the design mission of the Wren by using a longer span (40') wing and using a low speed laminar flow airfoil, (Wortmann FX 170) The leading edge of the wing on the prototype is molded fiber glass. The spar has been placed at 33% of the wing chord because the chosen airfoil is laminar over the first 32%. The aft covering is light weight Dacron Fabric. The leading edge of this fabric is purposely pinked and placed at the 32% chord point to facilitate laminar transition and elimination of separation bubbles. The main difference between the original design of the Robin and the current final design is the elimination of the single mono wheel retractable landing gear. Part 103 does not allow for a retractable landing gear. Which is really unfortunate because I spent a long time designing a really neat mechanism!!

In the course of the 4 years I have worked on the Robin, the structural design concept has evolved radically. Originally I was going to draw on the design of the Wren and use essential the same construction concepts. The original design of the Wren was heavily influenced by my Friend Steve Wood's Sky Pup design. I lived in Wichita Kansas and worked at Cessna Aircraft along with Steve. I watched his progress on the Pup and was very impressed with his concepts. I adapted the concept of using Styrofoam sheeting as the shear panels for the fuselage and the wing ribs. I did not however use the foam for the shear webs of the wing as Steve did. I originally wanted to build the fuselage of the Robin in a similar manner. Weight and the desire to not use foam for the basic structure due to the danger of fuel leaking eventually drove me to a all wood fuselage design. The wings were designed to take advantage of the Graphlite carbon pultruded material pioneered for the experimental aircraft by Jim Marske. I was familiar with this product from my experience at Bell Helicopter where it was considered in the construction of the V-22 wing.

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!!

Welcome to my Robin Blog.

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