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.









Casler Engine mount build.

                           Finally Back on the Robin

I finally have cleared the decks to the point where I can get back on the Robin. It took 9 months to order and receive my new Casler 1/2 VW. Then I was named the lead engineer on the Embraer 190/175 Rudder/ Elevator program. That took a lot of my spare time and required quite a bit of travel to Brazil. That program is winding down and I started to have more time in the evening. In addition to the Robin, I have been redesigning the nose landing gear of a Tiafun Motor Glider and the fabrication of a new 1-26 sailplane Nose Cowl. All of the heavy work is finished so I set to work on the Robin. The first task was to locate the engine in its proper location relative to the center line of the fuselage and in the correct vertical position. My main criteria for the location was to have the old prop spinner contour blend into the existing fuselage contour. So I set up a three strap hanger from the overhead of my shop. I used three turnbuckles on each strap so I could fine tune the positions.




Casler hanging from ceiling
the thrust line was set 1 degree downward. I used a piece of long welding wire as a spline. once the curves blended from the cowl to the fuel tank fairing, I knew I had the correct vertical height. On this new cowl, the cheek cowls will be functional like the original Limbach installation in the Fourier RF4D. If you look carefully at this side view you can see the welding rod spline.


Welding rod Spline
Once I had the engine in position I added temporary wood trusses to keep the engine from moving. I used Hot Glue to temporarily attach them.


Temp braces
In this picture you can see round aluminum pucks that were fabricated to dummy up the rubber engine mount. Since I intended to build in place, I want to be able to tack weld the engine mount together. I am using a thru bolt style Lord Mount that was available thru WD Granger industrial Supply. This mount is inherently safe because there is a thru bolt that will keep everything in place should a rubber bushing fail. The  most common style of engine mount used on light engines have a section of rubber bonded between two plate with a threaded stud. These mounts require a safety strap should the rubber fail.


Lord Mount

 I mentioned this in my previous post from the original engine mount for the 2 stroke, but this is worth repeating . The basic principal of designing a proper engine mount is to ensure that on the airframe side of the rubber isolator, there exists a stiffness path for all 6 degrees of freedom. in order for an isolator to absorb engine vibration, it must convert the vibratory energy into heat. It can only do this when the vibration input node is being reacted by a stiff load path. Consequently, there will be a series of tubes that will supply the needed stiffness. The first being a square pattern that ties all 4 mount pads together.

corner mount pad

 I fabricated four corner mount pads. The two tangs extending outward are the weld pads for the trus. The corners are made of 3 pieces of 1/8" 4130 steel. I used a hole saw to cut two circular pads to be welded to the main base. The mounts require 3/8" of spacer per the mount spec. I have just finished fabricating the square backing and I will cover that in the next blog update. But before I sign off tonight I want to share a trick that an old machinist taught me 35 years ago when I was a safety crash test technician at Ford Motor Company in Dearborn Mich. There is a trick to drilling a large hole in thin material. I have what is known as a Deming Drills. Large diameter drills with a reduced shank. These drills will tend to chatter and elongate the hole when they are used. Except if you use the "Trick"

"The Trick"


use a small piece of cloth soaked in cutting oil. I like Tap Magic. Center the drill on the work piece and then place the folded rag between the drill and the work piece. Apply pressure with the drill press and then turn it on. The rag will stop all chattering and create a perfect started hole.

Until next update

Mark




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