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.









Cowling Baffles and engine installation

I continued working on the Baffles. I finally finished those up.
This shows the detail at the L/H cylinder. I used .020 7075-T6 aluminum sheet for all of these baffles. That's not a magic alloy, its what I had laying around. It does tend to crack pretty easy, but I guess that's what a stop drill is for.






















Support is where you find it!! I made a bracket that picked up one of the case bolts and used it to support the upper baffle. I used clip nuts here so the baffles could be removable.
























This shows the detail on the R/H cylinder. Note the cut outs for the exhaust. All around the edge of these baffle plates a blade of silicon rubber will be added. this will make a flexible seal between the baffle and the inside surface of the cowl.




















This picture shows the silicon seal added to the baffles. I needed to make a retainer plate for the silicon. This served two purposes. It clamped up the silicon seal and it created a stiffener that keeps the baffles from bending away. I made the retainer by bending some aluminum over a form block.
















This is the MDF Form block. note the bend relief cuts all along the edge near an outside curve.  When the metal is formed over it compresses along the edge and causes a wrinkle, the slits allow the metal to move and makes it much less prove to wrinkling.


















After I finished with the metal work, I made a template for the final trim of the cowl. There is a fly weight that is attached to the aft face of the prop flange that needs to have clearance to the cowl. The old trim was just a rough cut any way.




















finally I added countersunk washers to the main cowl fasteners. These will spread the fastener load out over a greater area and allow for a flush countersunk head. I covered the show face in tape and then sand blasted the back side. I countersunk the cowl fiberglass, sanded a small area under the washer and then bonded the washers to the fiberglass. I'm using a cleco with a small washer to clamp the washer during cure.
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