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.









Canopy Latch, and Windshield.

Well I am finally finished with the canopy. This is one of the last jobs I needed to complete before I start covering her.  On Saturday I was joined by Jay Swindle, Jay is a local Texan and one of my earliest Blog followers. We worked together all Saturday afternoon completing the canopy latch. Since my last blog update, I installed the Engine Primer pump. There is a small fuel port on the reed valve housing that is designed to accept an external primer. This is convenient because of the closed cowling of the engine. I decide to mount the primer on the L/H inboard longeron. To avoid removing any area in the  longeron I decided to mount the Primer on a 3/4" plywood stand off block, that block in turn was bonded to the the longeron with T-88 adhesive.

Fuel primer


The primer bracket was made from .063" 2024-T3 sheet. I bent this part on  a combination sheet metal shear, roller and brake. I bought this tool years ago when the price of steel was low. I paid one dollar a pound for this 350 lb tool.









Multi- Function brake/shear/roller

This is a view of my combination tool. in my plans drawings there is a line on every flat pattern that signifies the center line of the bend. That center line is directly in the middle of the upper radius plate. I usually measure back from one edge and offset that dimension for the width of the "V" groove. A machine square is used to square it to the face of the "V" groove. The flat patterns also account for the stretch that the part will under go when it is formed. I learned this skill by drawing flat patterns by hand on the 747 section 41 fatigue redesign program. I believe I drew over 5000 patterns. After that many, the process kind of sticks with you.
Primer Bracket and Uni Bit
One more word about the Primer bracket, and that is the process of drilling a large diameter hole in thin sheet metal. The best method I have found so far is the Step drill or Uni Bit. At $38 bucks for one bit, its a bit pricy, but well worth the price. As you can see the hole it drilled was very clean.









Canopy Centering clip

I needed 4 of these, canopy centering clips. when the canopy rotates to the closed position, these clips will center the canopy so the latch pin aligns













L/H canopy latch

Here is what I ended up with for the canopy latch. I had a design already drawn, but it was way too complicated and I didn't feel like building it. I wanted something simpler. Jay and I were brainstorming on this and we decided to take a ride to Midway Airport and see how the Germans did it on their sailplanes. What I ended up with is kind of a hybrid between the Schweitzer 1-26 and the Grob 103. There is a fwd and aft detent plate at the front of the latch handle and an adjustable home made eye bolt as the rear latch.

rear canopy latch detail
I took a 1/4" bolt and then made a lug out of 1/8' 4130 steel. I brazed the two together. I purposely made the rear post adjustable vertically to allow for adjustment to the center line of the latch pin. The latch rod by the way is 3/8 hydraulic truck brake line. I cut off a 5/16" bolt and put a 15 degree taper on the end of it. That was then brazed into the latch tube.








Canopy installed
Then it was on to the next big job, final installation of the canopy windshield. I attached the canopy with 200 Avex Countersunk pop rivets. The outside of the canopy was touch countersunk to accept the head of the rivet. The canopy installed very cleanly. There is a protective plastic covering still on the outside of the canopy. I will keep it that way until just before first flight. 








Another view of the canopy
This shows the reason for the yarmulke, the wind shield is flat wrapped with a single curvature. All compound contour is confined to the yarmulke. It also doubles as a sun shield. I'm pretty pleased at the way this came out
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