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.









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.

















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