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.









Squawk list burn down

I had a week off from work due to the 4th of July holiday, a few vacation days and a summons to appear for a Grand Jury!! I didn't get picked for the Grand Jury, but it sure wasted 1/2 a working day!! All of This means I got to work on my Robin for long uninterrupted periods. My original plan was to assemble the airplane at Midway Airport near Midlothian Texas, but cooling problems, traced to a bad head design, and carburetor leakage side tracked me from all of the small final jobs. The MZ 34 cooling issue was first on my plate, I discovered a few weeks ago that the head was retaining too much heat and when I tried to shut her down, she continued to run in diesel mode. This turned out to be a poorly designed head, why I had to pay for a new head, is beyond me and making me consider my choice of engine, but non the less, I received a new redesigned head from Compact radial engines and when I installed it, It seems to have solved the heating problem.
MZ 34 with new head
The new head has about 40% more cooling fin area, it does however completely screw up my old baffling system. I have not run the new head with a baffling system yet, or the cowl. If I have to, I will do the first flight without a cowl. The engine is cooling very well and it seems I may have to rethink my cowl design. I will however try to run it first with the baffle on to see how it behaves. After I got the engine running with the new head, I discovered that the carb was leaking gas when it was shut down. In addition, the engine was not running very smooth and it was almost impossible to warm start. I started doing some online research and came across a very good web site http://www.aerocorsair.com/index.htm. They also make a good engine!!! Anyway, I determined that the problem was probably an incorrectly set pop off pressure on the main float needle. The web site has a very good step by step troubleshooting guide and for this project I invested in an automotive cooling system tester. The web page shows how to modify this so you can set the pop off pressure. The Tillotson HR carb should have held 8 psi indefinitely. But when I tested it, it started leaking at 3 psi, this obviously was the root of my problem. when I applied the pressure tester to the fuel inlet as I mentioned, it immediately bled down to 3 psi. I then disassembled the pump housing and inspected the gaskets. Nothing seemed amiss. I then applied pressure to an alternate port and I noticed fuel leaking past the needle seat. When I pulled the needle seat out, I noticed a mangled copper gasket. It appeared that the gasket wasn't fully seated before the needle seat was installed. Of course I didn't have a new needle seat copper gasket in the rebuild kit, so I made one by hammering flat and then annealing a section of copper tubing. once I trimmed it and installed it, the carb held 8 psi and "popped off" ay 11 psi just like it should. I then ran the engine for another 45 minutes and almost finished with the ground break in.

Another nagging issue with the design, was the final design of the seat. All along I knew I needed to build a head rest, but I didn't think it would be a big deal. My friend Ed came over and we shot a series of  pictures with mocked up head supports. It became apparent that by just supporting the head, the pilot would be choked, because his upper shoulders were not supported. I decided to modify the seat to add the upper support. This was quite easy because of the way the seat was made.  sanded off a 4 inch wide section of the inner skin and exposed the foam core. I made two patterns out of Styrofoam and then clamped the seat the form blocks. I then lain up another ply of 8 oz fiberglass over the core. 

bonding supports
  The next step was to build a support from the roll over cage to the back of the seat. This part has to be substantial, as it will see heavy compression load in the event of a crash. I made the support and side ribs from .032 aluminum sheet.
upper seat support












I need to rebuild the triangular rib and adjust the flat pattern slightly. But this shows the support clearly. I will build a light weigh aluminum head rest on top of this. That will support the head cushion. The white color by the way, is protective plastic that will come off eventually.









Another project was to do the final rig of the ailerons and cut a cable exit slit in the wing.
Right wing and aileron





This is a picture of the right wing, the left wing was already finished.











Where the wing interfaces with the fuselage, there are slits that needed to be cut in the fuselage skin for the leading edge attach fitting and the aileron cables. I located the areas, added fabric doublers and then added felt seals.

Felt exit seals






I will touch up the paint after I am done adding the seals.










Leading edge felt seal




Before a doubler is added, the old paint is removed with a solvent wipe with MEK. It works quite well!!











I am continuing work on the seat support and head rest. Nest week I should have the final engine run with the cowl and baffle, hopefully this is all I will need to do before the first taxi test.
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