Robin Ultralight: MZ 34 Initial Run Up

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.

Well I finally started the engine!!!!!!!! My theory of engine mounting was correct!!! The vibration was absolutely minimal. This is so much less than a 277 Rotax!! Once the engine is running above 1400 rpm, which is only 598 prop rpm, the engine smoothed right out. I am spending the rest of the week end breaking in the engine. Next week end could be the first taxi test. I am uploading a video The theory was explained in this blog post http://www.blogger.com/blogger.g?blogID=25566109025005725#editor/target=post;postID=7281790481309410657

My Friend Yuki has a 277 mounted in a FP303, and the vibration is so bad, his instruments are failing. This thing is really running smooth. so later in the day I added the cowl. I was getting worried that the engine would not cool properly because of the cowl baffling. So my Buddy Ed and I installed the cowl and spinner and ran her up. The engine definitely cooled better, but the cowl is seeing high temps after shut down. Some of the paint near the exhaust pipe started to blister. I need to add header wrap to the pipe, and aluminum foil insulation to the inner surface of the cowl, and a heat shield between the exhaust and the fabric. Sounds like tomorrows job.

I added the foil and header wrap. Should be smooth sailing this week end. i plan on running the engine in for 5 hours before I attempt to fly. I bet my neighbors will be thrilled!!!

insulation

I used 3m automotive trim adhesive to bond the insulation. Aircraft Spruce sell this product.

header wrap installed

this should take care of the need for a thermal barrier against the fabric. There is a lot of air flowing there and during the run up there weren't any issues.

and finally here is a video of the second run up with the cowl in place. I'm pretty proud how well centered the spinner is

3 comments:

Unknown said...: I'm very interested in this project. It has just about everything I've been looking for in a project. Please keep the blog rolling. I can't wait to see what is next. When do you think you will have plans available?; May 15, 2012 at 4:07 PM
Unknown said...: PS. I can seem to open the link on your theory.; May 15, 2012 at 4:47 PM
Mark Calder said...: Dave, thanks for the comments, I hope to have everything ready for the 2013 Lakeland airshow. I am going to rebuild the wing center section and the build a brand new wing. This wing was made by using Vacuum Resin Infusion, that is well beyond the average builder and does not lend itself to a plans built plane. I also am redesigning the horizontal and elevator attach. I started flying German sailplanes after I designed the Robin and I now fully appreciate the need to under 10 minute field assembly. The wings by the way will be all wood.; May 17, 2012 at 7:18 PM