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.









Heating problems

I have been running up the engine. So far I have 45 minutes on it. A number of problems have reared their head. The wiring has to be re done. I need to eliminate the quick disconnect plug. The tach pick up wire needs to be rerouted away from all of the other leads. The tach is not reading properly. The pick up is inducing a signal into the adjacent wires, which in turn are inducing a second signal into the tach pick up lead. The CHT lead broke because there was not enough strain relief, the EGT never worked. I need to disconnect the instrument panel from the canopy, yet it still needs to pivot away when the canopy is raised. I'm going to make a secondary pivot for the Instrument panel. That should solve the problem and allow hard wiring direct to the panel and eliminate the disconnect plug. The second problem which is much more serious is excessive hear build up on the reduction drive mount. That in turn is conducting the heat to the back of the spinner backing plate. The spinner backing plate is room temp cured graphite epoxy laminate. As soon as it gets above 175 degrees, the plate gets soft and the spinner starts to wobble. I plan on solving this by three methods, I will post cure the spinner plate in the oven at 300 degrees. Hopefully that will raise the T/G (Temperature of gel) to near the hub temp. Next I will place a fiberfrax or Mica insulator between the hub and the spinner backing plate. Third I am going to drill some vent holes in the backing plate and in the inlet baffle. to direct some of the input cooling air toward the mount. There is no secondary air flowing in the rest of the cowl, this is causing high internal temps. Hopefully the internal duct I am ding to add will help this. It will take very little flow to solve this problem. Because of this, I decided to tear down the engine compartment and install a .012 aluminum heat shield over the top of the firewall fiberfrax insulation.
 
Existing baffle wearing thru the FiberFrax
 The actual engine head temp is running cool, it seems to peak around 425 degrees. The spec allow the head to see 500 degrees. Because of this, I should be able to redirect some cooling air toward the reduction drive mount.











New Aluminum heat shield
I am in the process of finishing the engine re installation. I should have this finished tomorrow.

Finally I have a third problem that is also equally serious. My Fiberglass fuel tank is starting to deteriorate. I attribute this to the ethanol that is in modern fuels. I never had this problem 25 years ago on my Wren. I also do not like the design of the fuel pick up on this tank. Another glaring error I made was the lack of a tank sump for the fuel pick up. I also need a fuel shut off valve. The tank head pressure is overcoming the reed valves in the pumper carb, causing the engine to flood while sitting. The other problem I discovered, was that the fuel filter and line needs to be routed on the inlet side of the intake plenum.The fuel was cooking off when the engine was shut off causing a vapor lock and making starting hot very hard. I started laying up a new tank and I bought a special fuel tank epoxy coating designed to protect against the ethanol in the gasoline.  Anyway, better to find all of this out on the ground then of first flight!!!
















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