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.









Engine cowl part 8 (Mold).

Well I finally got back to work on my poor Robin!!  This work stuff keeps getting in the way!! I had originally been scheduled to travel to Charleston South Carolina for 3 weeks. I am (or was) an MRB engineer specializing on the Boeing 787. My company (Triumph/Vought Aerosystems) designed the aft portion of the 787. They call these sections 47 and 48. 47 is the last pressurized section and 48 is the first unpressurized section. during the design I was the lead engineer for all metal structure in section 48. Separating the sections is a huge composite pressure dome ironically built and designed by EADS the parent company of Airbus. I went to Charleston to help with an issue relating to some detail parts. I was working with a young woman MRB engineer on this same project. We were a day into the job when she got up from my desk and excused herself for a few minutes. She walked around the corner past a partition. I did not see her, but I hear a sound that sounded exactly like someone smashing a pumpkin. The next thing I heard were shouts for an ambulance and when I stood up, I saw her face down on the floor. She had had a mini maul seizure and fell directly and unprotected on to the concrete floor. The poor thing fractured her skull and had to have immediate emergency surgery to stop internal bleeding. Because of this unfortunate incident, I agreed to extend my trip an extra week to cover for Tracy.

Anyway, once I got back I started immediately on the lower  cowl mold. before I left I had the plaster all prepared and waxed in preparation for the fiberglass tool. The surface of the plaster was sprayed with a mixture of 50/50 shellac and alcohol. This mixture will soak into the surface and seal the porous surface of the plaster. after the shellac was applied, I put 7 coats of Carnuba mold release wax. machined buffed between each coat. The final release agent is a product called Partall 10. This is a polyvinyl acetate water soluble film. because it is water soluble and hygroscopic (absorbs moisture) it is applied no more than 24 hours before the application of gel coat.
gel coat gun
This is my newest toy, this is a commercial gel coat gun. The plastic cup is replaceable and is used to mix the gel coat and hardener. It clamps up to the handle assembly and dispenses gel coat through a huge nozzle (.080" dia.) The gun is held upright when it not spraying. Because the cup is disposable, clean up is a snap, although I am reusing my cup.







lower Master with Gel Coat
This is what the master looks like coated with Gel Coat. The gel coat is laid on really heavy, I shoot a surface that is almost too thick to not run. I like a thick gel coat surface because it allows a lot of clean up sanding in areas off the tool surface.










fiberglass mat
After the Gel coat is shot, you wait about 30 minutes until its very tacky. at this point raw resin is brushed onto the surface to ensure a good bond between the gel coat and the fiberglass and mat. I pre cut the mat into9' x 9" squares. The mat is set into the raw resin and then allowed to soak up. additional resin in brushed into the mat and allowed to soak up. I usually work in sections while the mat is soaking up resin. Non direction uni roving mat is a product produced in sheets. They use a starch binder that will dissolve eventually in the laminating resin. after the mat has wetted out, a mat roller is used to drive out the air bubbles.
another view of the curing mold

















After resin cures, the mold is released. Becaue the Partall 10 is water soluable, a small crease is created with a plastic wedge and then water is sprayed into the mold. its just a mater of minutes before the Partall dissolves and the mold releases
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