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.

Fiberglass cowl mock up

I just completed the lay up and fitting of the fiberglass mock up cowls, spinner and spinner backing plate. I decided to make some scrap fiberglass parts first so I could set the final trim lines and locate the attach fasteners. I used fiberglass because i could see thru it and measure from the edge of the mating structure underneath the cowl. The final parts will be 2 ply's of 7 oz Graphite cloth. I don't want to scrap those parts!! the material is $32/yd compared to $4.90/yd for glass.

scrap parts
As you can see from this picture.The cowling is translucent and the sub structure was visible. All in all the cowling fit very well. Even so, I will still not drill mating holes in the lower graphite cowl. I will match drill those holes from the upper cowl. The cowl will be fastened with countersunk screws into a nut plate riveted to the lower cowl.

view looking aft
this is a good view of the asymmetrical cowling. i chose to do this because I will flow the air over the single cylinder. The inlet will have some foam blocks added to the inlet lip that will act as a flow diffuser.  The idea is to slow the air down before it turns the corner. Heat added when it flows across the head will recover the pressure loss. its very critical that this cowl be fully sealed. a series of aluminum and silicon baffle plates need to be fabricates. as does an aluminum heat shield for the exhaust. The next step will be to cut out the out let around the tuned pipe.

another view without the spinner

The cowl will be pretty light. The final parts should weigh in at just over a pound.

graphite backing plate

This is the graphite spinner backing plate. although I only used 3 ply's of 7 oz graphite, it is half the weight of the 7 ply fiberglass mock up, yet it is at least 10 times stiffer. I will wet sand the resin line that is visible. this is the joint between the two mold half's. I will chuck this part in my lathe in the 3 jaw chuck to register the center, This will be a check to see if I located the center true enough in the mold.

On another unrelated note, I am now back in Design at my company Triumph/Vought. I am working on a manned/unmanned program based on the Berkut Home built. We are designing a larger version. I had the pleasure last week of meeting Dave Ronnenberg, the designer and builder of the Berkut. I was invited late this week to come out to Santa Monica and fly the Berkut by Dave. I'm sure we will also talk about some structural issues!!!I leave tomorrow morning for Santa Monica via San Diego. My friend Mike and Neal La France are going to pick me up at the Santa Monica airport in a Luscombe Sedan  and fly us back to Gillespie field in San Diego. Neal and Mike are old friends from my early Wichita days. its been years since I have seen them.

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