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 installation

 I am using the MZ-34 from Leon Massa at Compact Radial Engines in Surrey BC Canada. This is a single cylinder 28 hp engine. This engine was originally designed in Italy by Zanzottera as a back pack powered Parachute engine. Leon has up dated the engine with Nikasil coatings and absolutely exquisite machining and internal compression releases.The engine comes with a pull starter and an electric starter as an option. I have eliminated both of these features on my prototype to save weight. I will need to redesign the wings to an all wood design to save enough weight to allow for an electric starter, more on that later!! 

The main reason I bought the MZ-34 is because of the mounting system. It uses 4 radial shear type mounts placed around the center line of the crank. This is similar to the mounting system of a Radial engine, but not quite as refined. It is however greatly improved over a flat bed mount like the Rotax 277.
 Years ago I worked for Ford Motor Company in the NVH lab (Noise, Vibration and Harshness) our job among other things was to isolate vibration and eliminate noise. One of the basic principals of vibration isolation is to convert the vibration into heat. This is accomplished in a rubber mount system by absorbing the vibration by shearing the rubber. In order for a rubber mount to work, the fuselage side of that mount must be held fixed in all 6 degrees of freedom. Any movement in any axis will result in vibration transmission. So far this is all theory on the Robin, because I have not yet started the engine. You can all drop by in a few months to see if I have to eat some Humble Crow Pie!!! But you have to start with a theory!!

  So here is a side view of the engine installation

Notice the 4 struts that connect from the longerons to the fire wall.  The fire wall is a structural foam and glass sandwich of 1/4" 4.5 lbs PVC foam and 120 style fiber glass. This will eventually be covered by a layer of Quartz Fiberfrax for a heat shield. The fire wall itself has a great deal of in plane stiffness in the inboard/outboard and up/down directions, this effectively accounts for 4 of the six degrees of freedom. The struts account for the stiffness in the fore/aft direction. There will be an out of plane vibration mode due to the angle of the struts, but that is again reacted by the in plane stiffness of the fire wall.

mounting locations

The engine was mounted in space per the layout of  the plans and the location of the 4 attach points were located. A hole saw was used to cut through the fwd face of the fire wall only. Glass inserts  using 1/4" commercial NEMA grade fiberglass plate were fabricated and bonded into place. A doubler of two ply's of 120 glass were laid up over the top of the inserts. 

core removed prior to insets installation

The engine was temporarily installed after this.

MZ 34 Engine  installed

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