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.









More Cowl. Cowl mold.

I cannot believe how many Russian subscribers I now have!!!  Welcome!
On Saturday I swapped labor with my friend Michelle. She needed a new Radiator installed in her Subaru, I needed help doing the lay up on the cowl mold. Michelle used to work for me at Triumph Vought. I was her lead engineer on the Embraer 190.195/175 Rudder and Elevator Program. We both were the first two people assigned to that program. We spent quite a few months together in San Jose Dos Compos Brazil. The home of Embraer and Santos Dumont, the early Brazilian aviation pioneer. Michelle and I did all of the preliminary design and lay out of these control surfaces. I met Michelle when we were both studying to get our Pilots license. I am quite satisfied with my private Pilots license, but Michelle had a much higher calling than me. She wants to be a Mission Pilot for MAF or JAARS. In order to do this she needs a commercial pilots license and an A&P license. She needs tail dragger time and about 500 hours. So at my suggestion she bought a damaged 1946 Taylorcraft and has been working this past year on its restoration. Michelle is one ambitious woman!!


Michelle
This is right at the start of the cowl lay up. We had just finished swapping out her radiator. It was over 100 degrees on Saturday so we started early so we could be in the shade of the shop.


















The tool had been previously prepped for the Gel coat with a coat of Partall 10 PVA release agent. This is a water soluble release agent, and like I have mentioned before, I have never had a part stick when I used PVA






ready for mixing
Michelle's main task was to keep me supplied with mixed resin. Because of the heat, I cannot mix a large batch. It would quickly go into an exothermic reaction and turn to jelly. The mold required 4 28 oz. cups of resin and one 28 oz. cup of gel coat. Gel coat is polyester resin mixed with Calcium Sulfate. This creates a thixotropic mixture that has superior surface hardness. I have a special gun that is designed to shoot gel coat.














shooting Gel Coat


here you can see me and the gel coat gun. I have a fan blowing all the overspray out the main door. the idea here is to get an even but thick coat. Its not too critical if the gel coat starts to run, the surface of the tool is already covered.






















initial layer
Once the Gel Coat started to tack off to the point it was about 3/4 cured, I wiped a Bondo filler radius all along the corner between the master and the header board. The following layers of mat and fiberglass cannot lay up into a sharp inside corner. This step is required to ensure that the gel coat has adequate support and will not crack. The first layer down on the fresh gel coat was a five 1.5 oz. layer of cloth. I cut a yard of cloth up into small 6" x 6" squares so they would be easier to handle. I like to use a ply of thin fiberglass against a gel coat surface. this again ensures that the gel coat surface is being supported. After the initial layer is added, I follow up with fiberglass mat. The mat has been held together with a starch binder, before you can move the fibers around, the mat needs to be wetted out. I like to have resin on the surface that will draw up into the mat, but I usually brush on additional and let it absorb the resin. once its wetted out, the mat is rolled with lay up roller to move the fiber and eliminate air bubbles. The rollers work very well.


Finished
I added 3 layers in total. It only takes about 2 hours before the tool is completely cured. I have modified my plan slightly. I was going to release this mold and then move the boards 3 inches to the opposite side, but when I tried to release the tool, the master started to crack on the good side. rather than risk any damage to the master, I have decided to lay up the next tool to abut this one.














opposite side ready to go
I removed the tooling boards and shot the surface with PVA. Its all ready to go. I need to get a helper to do this side. I will update the Blog when I finish the other side.

Posted by

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)