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.









Final Cowling pictures and internal Baffling


I have finished the fire wall forward. The Fiberfrax is installed, the latex primer is applied and the fuel and electrical wires have been run. The internal baffling is finished. I have some very thin countersunk Stainless steel washers that I am bonding to the surface at every fastener. This will reinforce the countersunk holes very cleanly.
L/H side
















My Friend Ed ttp://mmwauto.com/index.php/services.html  did the final paint on these parts. As you can see from the pictures the finish is excellent. He has a huge down draft paint booth. Its big enough to fit both of my wings and the fuselage. The paint by the way was Summit racing single stage Ureathane paint. http://www.summitracing.com/sitemap.aspx?ibanner=FD4
R/H side

Unfortunatly I had to cut away the blister for the tuned pipe. A 4 stroke version will have the full blisters, but it will be a new cowl. I'm looking at an all composite version in the LSA/Experimental class. Wood is really light, but it does take some time to work with. My new idea is to build most of the fuselage with flat sheets of 1/4" PVC foam core pre cured in a platten press with a layer of 120 fiberglass on each face. Preliminary sizing of the shear panels show this would be adequate for a fuselage. A structure built like this would not requite much final sanding and prep.
Completed baffles
This is the final design f the baffles. Not shown is another Baffle that seals off the back half of the side blister. There is only one place now for the air to flow and thats across the cylinder cooling fins.








looking aft at my messy shop
 Some more pictures















Tonight I am correcting a design problem I should have addressed when I first built the fwd turtledeck over the fuel tank. I'm making it removable. I'm buying some of Jim Weibes beautiful lightweight instruments, one of them is an electronic fuel gauge. I need to remove the tank so I can add the sender
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