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.

IT'S HERE!!!!!

My Casler 1/2 VW just arrived. I just started unpacking it. Here are some pictures. I need to finish the Tiafun first however. 

my new Casler

 Thank You Scott!!!

Tiafun Cowl repair cont.


I got back from Brazil Thursday morning. After a day of nonstop sleep I got back to work on the cowl repair. I finished cleaning up the internal blister layup and blend sanded the new laminate into the existing laminate. 
inside ply's trimmed and blended
most structural glass repairs only need one inch per ply overlap to fully develop the tensile strength of the ply. In the case of the blister, this was a 6 ply repair with 3 structural plys on the inside and outside, each layer overlapping the existing laminate by 1 inch. This is truly overkill, but meets the requirement of restoring original capability, plus one ply. I will spray the inside of the cowl with a grey trunk paint and this damage will be completely hidden. The outside micro balloon and epoxy was completely cured when I got back from my trip. I rough sanded the micro with 100 grit sandpaper with my orbital DA sander. This reduced the high points and leveled most of the surface. There will always be slight pin holes left that will need to be filled with Pinhole filler or spot putty.

micro balloon blend sanded
This picture shows the micro balloon after it was rough blended with the DA. The surface is wave free but there are still small pin holes and very shallow applicator marks. I followed up with the DA by using a flexible rubber sanding block with 180 grit paper. This served to further level the surface. This cowl is very easy to blend out because there is severe contour. The hardest surface to make smooth, level and wave free is a flat surface. For that type of contour I will usually stop at this point and spay the surface with a sand able primer. A long sanding stick quickly shows high and low spots. I usually try to level the surface with a combination of sanding and spot putty fill. Spot putty is designed to adhere to primer paint.
catalyzed spot putty
This is my preferred spot putty. This is far superior to the Auto-Zone lacquer based products.  This material is catalyzed like auto body filler. Its ready for sanding in 10 minutes. The cycle time of your products makes all the difference in speeding up the repair. I could have used light weight auto body fill in place of the epoxy micro in the earlier step, but since I knew I would be in Brazil for 5 days, I knew the time didn't matter. Epoxy Micro is a very strong filler and is superior to Automotive bondo.

blended spot putty
 This is what the spot putty looked like after an initial rough sanding with 100 grit. I finished the feathering with 180 grit and there was hardly any left.

There was one other issue with this cowl and that was a corner Dzus fastener had pulled thru the cowl laminate. Normally I would look for an oversize repair fastener and enlarge the existing hole with a step drill or tapered reamer. I would then install a repair fastener. But that would require a crimp tool and a special set of repair washers. This fastener fit just fine but had no retention on the back side of the laminate. So I cleaned the metal with  rotary wire wheel and sand blasted the metal to a dull finish. I then mixed some T-88 structural epoxy adhesive with a small amount of chopped cotton fiber. I then bonded the Dzus fastener back in place and formed a fillet around the inside surface. This will stop the fastener from backing out.The main difference between structural epoxy adhesive and epoxy laminating resin is the addition of molecules of an elastomeric. This dramatically increases the peel strength of the adhesive and stops all tendency for  delamination

This lower cowl had been repaired previously after the original nose gear collapse. I have noticed that the door underwent extensive reconstruction and is over 1/2" thick in some places. The leading edge of the door sits below the existing contour and quite frankly looks terrible. I am thinking about blending the the existing contour to the door contour after I rework the door hinges to slightly lower it. The idea is to get a smooth surface when the climb door is closed for soaring. That will be the subject of the next entry in the blog. My friends at the airport have repositioned the Tiafun fuselage into a larger hanger where I will have full access to the engine. Since the plane skidded on its fwd engine mount, I am unsure of the actual condition of the metal engine mount. There is flaking paint on the mount and I suspect its just a bad paint job, but I will pull the engine and remove the mount so I can sand blast it and inspect the for cracks. Dan has already bought a new Saur fwd engine mount that fits like the original. I will prime the mount with zinc chromate and finish with a polyurethane top coat. The last thing you want to do is powder coat any aircraft parts.Powder coating is a plastic film that is fused to the metal in an oven. It doesn't not have any ability to act as a rust conversion coat and in a short period of time it will develop cracks and water will migrate.

Casler update and Tiafun Motorglider cowl repair

I guess I have more blog readers than I thought. Some of you folks cornered Scott Casler at Oshkosh last week and pushed him into starting the build on my Engine. Wont be long now!!

In the mean time, I finally finished a big side modification job and I was able to clear the decks and start on the repair of Dan Stofman's Tiafun Motorglider. 3 years ago when I went out to the SSA western workshop in Tehachapi CA, I met Dan who was a friend of Murry Rozansky, treasurer of the ESA and the guy who invited me to speak. While I was there a beautiful Tiafun Motorglider taxied up to the restaurant. Dan remarked that  was looking for that very plane. Two weeks later I was browsing the Chartis /AIG insurance salvage list and I found a Tiafun in Moriarty New Mexico. I called Dan and sent him the link. He threw a really low ridiculous bid against it and guess what?? He won. So Dan flew out to Texas and we grabbed my flat bed trailer and pick up truck and drove to New Mexico. The plane had made a hard landing in Grants New Mexico and collapsed the nose gear. The prop struck and she settled down on the front cowl. The plane was sent to a repair facility in Moriarty and Chartis paid around 50k to put a brand new Sauer 90 hp VW conversion engine and a brand new MT electric prop. The shop worked on the plane for two years. The original mechanic on the project quit and when the second finished the repairs, the plane was being taxied to the run up area and the nose gear collapsed again!!! The second Mechanic did not know that the rigging was incomplete.  Chartis got fed up with the whole affair and put it up for salvage. Enter my friend Dan!!

Dan and his new bird

It took us 8 hours to securely load and rig the plane and then another 13 hours back on the road to Midlothian

we had to add an 8 foot extension to the trailer
The primary damage to the plane was the prop, lower cowl, gear door and the actuator linkage. I sent the Prop back to MT in Miami and they rebuilt the whole prop. For $500 more we could have bought a new one. We figured the main components should be good, after all, the engine prop combination only has .8 hours total time!! I had a local IA inspect the engine run out and he found no signs of a bent crank. The blades were wood covered in Fiberglass, so they absorbed all of the impact damage and protected the engine.

The main damage to the cowl was the grinding down of a chin blister that once was used to streamline the original motor mount.

Ground down chin blister
The only other damage on the cowl was severe gel-coat cracking. I took the cowl out the the Airport and trial fitted it back to the fuselage. I wanted to check if I had any clearance issues with the Sauer engine mount.

clearance check
After looking at the new mount, I realized that the old blister was not really needed with the new engine. The cowl however has blend contour from the base loft to a blister surface. Rather than rework a much larger section, I decided to restore the original blister contour.
I started the process by cleaning up the blister opening.

Dotco motor with flapper wheel
 I cleaned out the opening using a sanding flapper wheel. I then went back to my old faithful technique of using floral urethane foam to shape the actual blister.

floral foam
 The opening was larger than the stock block size so I pre-fit two blocks together and very carefully bonded them along the very lower edge in the middle of the block. The idea is to locate the glue below your final contour so the glue doesn't interfere with the shaping.

5 minute epoxy
I like to use 5 minute wherever I can get away with it. I have no patience!! Both blocks were bonded to the exposed edge of the cowl. After it cured I carved the rough shape using a hacksaw blade.

Rough cuts
The plan here is to rough in a side view and plan view. I want to get within 1/2" of the final shape. The next step is to sand in a tangent edge. This edge will be tangent to the existing cowl contour. I use a sanding stick with 36 grit. No sense in wasting your time!!

side tangent sanding

edge tangent sanding
Now the magic happens with this process, the foam is used to sand the foam. This is why I paid careful attention to keep the glue line below contour. A block of scrap is used alternately on the left, then right side to sand the foam. The contour is constantly being transferred back and forth between the two pieces of foam. The result is almost perfectly wave free and a spherical surface.

front view after final sanding

side view after final sanding

See how pretty and easy this method is!! I have used this to build full size fuselage masters, repair Corvettes, Sailplanes and power boats. You will recall in the previous blog entry's I made my cowl. The next step was to sand back about one inch the existing gel coat.

1 inch of Gel Coat removed
The next step is to layup the fiberglass repair ply's. I like to used the old Burt Rutan Hexcel 7725 BID cloth. Its about 8 oz/yd sq and lays up about .010" per ply. I didn't bother to pre-fit these ply's, I just draped them over the foam and wet out the glass from the outside.I laid 3 bid ply's and one very thin final ply that will require very little final fill in its weave.

3 ply's of BID and one ply of fine cloth

The next day the laminate was fully cured thanks to living here in the Texas summer autoclave!!
I feather sanded the edges with my Dotco and 4 inch disk. This cut away the excess cloth and tapered the glass into the 1 inch area I removed the gel coat from/

feather sanded edges
The next step was to sand out the sever gel coat cracks. I decide to fill all of these deep cracks with a mixture of Microballoon and Epoxy. This makes for a very strong, but sand able filler surface. I let that final mixture cure overnight again. This however usually takes an extra day to cure to the hardness needed to fine sand without loading up the paper.

sanded gel coat cracks
Microballoon filler

The next day I flipped the cowl over and removed the old foam core. A wire wheel on the Dotco removes the foam in about 10 seconds. You could also sand blast it, but that's  bigger mess.

Dotco and Wire cup
And just like that, its gone!!!!

Foam be gone!!!
Again I sanded away the interior paint up to an inch away from the repair. I also taper sanded the main cowl into the inside of the blister. I then added three more internal structural ply's wetting them out without trimming.

internal repair ply.
 This is now up to date at this time. I am going to let everything cure up for the next week. I am leaving for a short business trip back to Brazil on Saturday. I will be back next Thursday and I will complete the rest of this repair and update the Blog in my next entry.

Still waiting for the Casler Engine

I have another 3 months to go before I get the engine. I wrote Scott Casler to make sure he didn't forget me.
I have asked a Woman who works with me at Triumph/Vought to help with the redesign of the wing and landing gear. Once Michelle has some preliminary drawings of the new wing I will post some. The new wing will be similar to the Woodstock wing and will look more like the original Fournier wing. The wing will be all wood and be a tapered design. There is a very significant weight savings due to a tapered wing. The big disadvantage of a tapered wing id poor stall characteristics. I am going to use two different low speed laminar airfoils chosen to have a constant coefficient of lift at the local Reynolds number. This will emulate a square Hershey bar wing with a tendency to stall in the root first. I do not want to mechanically twist or wash out the wing because it is really inefficient.

The landing gear will go back to a single wheel with out riggers. Again this is similar to the original RF4D and is very weight efficient.

Thats really all I have to report right now. Hopefully I will have some preliminary drawings to show in the near future. 

Casler 1/2 VW

Just a quick update, I have ordered a Scott Casler 1/2 VW engine. I'm tired of being in the engine manufacturing business. Unfortunatly Scott is so busy, I have to wait another 6 months for the engine. In the mean time, i am working on a complete redesign that will make the Robin look even more like her namesake the Fournier RF4D. I purchased a set of Woodstock plans and I intend to incorporate a similar wing. I will go back to the single mono wheel and will fix it for the ultralight version. I bought a N/C router a while back and my redesign will take advantage of this. Eventually I would like to sell an experimental and ultralight version powered by full and 1/2 VW engines. I will fly my current plane and incorporate all lessons learned.

Latest Update



I am sorry its been so long since Ihave done an update to the Blog. Events have conspired that demanded all of my time. I had to take an emergency leave from work to help my mother who unfortunatly was diagnosed with terminal cancer. I could write for weeks on the ins and outs of Hospice care!! My Mother unfortunatly passed away after 4 weeks. At least she wasn' in any pain thanks to the Angels in Nurses uniforms who work for Hospice at Henry Ford Hospital!! 

my poor old ma, God rest her soul!
This is a hoot!! This is a picture of my Ma 3 years ago at Halloween dressed as Jimmy Leyland the current Detroit Tigers manager, my ma was a huge Tigers fan and during the Funeral, the organist actually played "Take me out to the Ball Park" when we were walking her casket out of the church. She wouldn't have had it any other way!!! 

When I got back to Texas, I recieved notification of shipment of my new Router. That took a good two weeks of my time dealing with the shipping agents, customs and secondary shippers. But it was definitly worth it!!  I took a bit of a risk by ordering this router from China. I have had some quality problems, but thankfully all of the important stuff like Bearings, gears and servos came from Tiawan and Japan. My biggest issue turned out to be poor Chinese quality control on the wiring. Servo motors are very sensitive to noise and because of this they require good grounds and solid connections. The latter was the root of my early problems. I ended up soldering every crimped connection on the machine.
The proud owner and his new Router

The router is 4' x 8' x 19" it has a variable speed 7.35 hp spindle. I can machine wood, aluminum, plastic and steel with this. It took a while to get this up and running, but thanks to my Buddy Ed who is an electronics genius, we worked out all of the initial bugs. I plan on using the router for fabrication of a all wood airplane kits. On the side we are also using it to cut some beautiful laminated wood gun stocks. Here is a picture of a couple of test projects we cut using standard clip art from our 3d software files.

Cat and the Eagle
These projects were roughed out with a 1/4" ball nose cutter. after the rough cut the finish cut was done with a 1/16" ball nose cutter. The router took a pass every .007" Each piece took 1 hours to finish cut.

Back to the Robin!!!

I decided to swap out engines. The MZ 34 proved itsself to be an unreliable choice. The engine just would not cool. The vibration is terrible and because of the earlier problem of it dieseling and not shutting off, I decided it was unsafe. When I went to the SSA Western homebuilding convention in Tehachapi Ca, I was talked into swapping the engine for a Briggs and Stratton Vanguard V twin. I am in the process of adding that engine. Unfortunatly I am forced to leave the cylinders unfaired and in the breeze just like other aircraft that use the same engine. This in my opinion detracts greatly from the original lines of the Robin which was designed to emulate the Fournier RF4D. Consequently, I am drawing all of the final plans using a 1/2 VW or a modified Generac industrial engine. Both of these engine are opposed Boxer configurations.
 The first thing I needed to do to use the Vanguard was to strengthen the fwd fuselage to accept the higher shear loads. I decided that the simplest method for the modification would be to sheet the fwd section with plywood. I had to double up the fwd longerons so I could bolt new fittings for the new engine.

side truss with doublers
  This is a view of the fwd fuselage side truss . I designed the original truss so close to the existing loads, that I had to double up all of the members between the landing gear and the firewall. Also you can see the large plate doublers added to the fwd longerons to accept the mount fittings. Unfortunatly this meant that I had to uncover the whole fuselage!! That is not a bad thing actually, because I had a number of areas that were not well thought out regarding the final shape after covering. This will give me a chance to clean all of that up.

side sheeting

After the doublers were addded, I then sheeted the sides with 1/16" Finnish Birch plywood. The circular cutout is for access to the brake pedal adjustment screws.

I am stripping the engine of a great deal of its weight, just the steel shrouding alone adds 5 lbs. The flywheel is 15 lbs! I have debated inverting the engine and making a new ignition , But since this is going to be a one off design I have decided to just turn the flywheel down and use the stock ignition. I am driving the prop from the flywheel side and mounting the engine on the PTO side.

PTO of Vanguard
On this engine I am again designing a dynafocal mount system. To refresh everyones memory, a dynafocal mount is designed to theoretically support the engine at the exact center of gravity. The theory is that all vibration nodes are zero crossing in there amplitude when they pass through the center of gravity. Since there is zero displacement at this point if it were possible to attach here, there would be no induced vibration into the mount. Obviously this is impossible so the next best thing to do is focus the input axis of the rubber shock mounts through the center of gravity. To find this angle a process called tri-filing is used.

Trifiling process

I made up some small lugs with a small hole in them. I attached a length of welding rod through that small hole and then hung the engine from that rod. I then took an angle measurement and that determined the input angle to the center of gravity. I then designed the mount to these angles. The picture above shows 4 angles lugs that the engine mounts attach to.

This brings everyone up to date with my progress.

Now forf the bad news, as I write this I'm sitting in the Admirals club at DFW airport waiting for a flight to Brazil!!! My company Triumph Vought just won a contract to design the aft section of the new EMB 195 airliner. Yours truly is in charge of the Empannage!! I will be at Embraer for 4 weeks starting tomorrow. To all of the Brazillian blog followers, if you are around Sao Jose Dos Compos, please write me at : Planebuilder@yahoo.com.


Brake pedal installation

I'm sorry I'm so late in updating the blog. I have been very busy!! 6 months ago I agreed to take on a side job for a Gulfstream G3 Engine swap. I am designing a new engine installation for the Right side pylon. This plane will be a flying test bed for the manufacturer of the new engine. I have a hard deadline for complete release of the engineering drawing of Feb 9. Consequently I am slammed for time and the Robin has to take a back seat. That's the bad news, the good news is I have earned enough money to purchase a 4 x 8 x 19" 5 axis N/C router!!!! I am expecting delivery to Houston Texas in May. I can't tell you how excited I am to get this tool. Not only will it allow me to make an exquisite wood kit for the Robin, but it will also make possible my next project. I am going to design and build an all wood laminar flow single place high speed airplane powered by an industrial Suburu 40 hp engine. Speaking of industrial engines, I recieved my replacement engine for the MZ 34 I currently have on the Robin.

23 hp Vanguard Engine

When I get back on the project I will swap this engine for the MZ 34. Stripped down and using a forged billet flywheel this engine will weigh 64 lbs. That will put the prototype over the part 103 254 weight limit. However I anticipate that changes to the wing and landing gear will bring her back under 254 lbs. More on those changes later. I plan on mounting the prop on the flywheel directly. Research has shown that a direct drive should yeild 154 lbs of static thrust. By Mounting the prop on the flywheel side the airflow thru the cowl will be in the same direction as the engines design. I will also be able to mount the engine using the PTO mounting fasteners.

I have finished the new replacement landing gear installation. I fabricated a cover plate that can be removed to service the gear. 
new gear cover plate
 landing gear center cover.

The part 103 Robin will go back toi the original Fournier mono wheel. If a direct drive installation works, the prop clearance issues are such that I could use a non retractable gear. Saving even mode weight.

The existing rudder pedals were removed and modified to add toe brakes. This installation is very clean. Here are some pictures of the installation:
toe brakes

toe brake pedals were added to the existing rudder pedals, The toes brake position is adjustable. I will set the position after I get a chance to sit in the cockpit. The brakes are cble actuated and are modified Go Cart drum brakes.

break cable routing
there is enough relief loop in the brake cables to allow full rudder pedal adjustment.

rudder return pulley

I decided to update the Blog this evening because I received a question from a reader about the rudder return cable design. The main change I would make to this design is to raise the cable attach points to the end of the rudder pedals. This still works pretty good. I like this a lot better than the spring return I used to have. You will notice that the pulley bracket can swivel horizontally. The  fwd pivot hole is oversize and allows the pulley bracket to also rotate up and down. The threaded rod is also the cable tensioner.

 This is a better picture of the return mechanism.

Finally in December it was my privilege  to meet a blog reader from Sweden Dr Jörgen Åstrand. He is Fournier RF4 and Piper Cub Owner and possible a future neighbor here in Texas. It was sure nice meeting up here in Texas. Ironically he was also a reader of my Friend Ed Piper Cub Blog. Only at the last minute die we all realize that he was coming see us both during his vacation.

 Dr Jörgen Åstrand and myself.