Robin Ultralight

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planebuilder

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I put together this blog Robin Ultralight I am covering everything from fabrication to design for my new ultralight the "Robin" Thisd is a wood/graphite design. Its a loose copy of the Fournier RF4D motor glider. I am using a MZ 34 2 stroke. There is discussion of the wing design, engine installation, fuselage fabrication and a unique master model molding technique. A lot of this has been covered in previous posts, so I decided to tie it all together. I am working on an update to the new composite tail spring. I will have that entered some time later today.
 

planebuilder

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If you guys havent stopped by recently, I have updated the Blog to show the development of the cowling master model and the fabrication of the molds. The blog runs about 2 weeks behind my actual progress. I will be updating the blog soon to show the remainder of the master construction process.

Robin Ultralight


Mark
 

topspeed100

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Mark !

I enjoy this a lot.

Tell me would you say my design ( 15 hp plane ) really can be made into 110 lbs ? I see yours is 230 lbs empty.

I need to get mine under 155.5 lbs in order to fly it locally under "Part 103" kinda rule. Each pound under 155.5 will be more range.
 

cluttonfred

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Great stuff! Your design and approach remind me a little of two French designs that might interest you and make useful points of reference on performance.

1) Michel Barry's MAG-01 here and here

2) Michel Colomban's Luciole here and here

I admire your dedication in getting your cowling and spinner just right--I don't think I'd have anywhere near enough patience.

Cheers and please do keep sharing your progress,

Matthew
 

planebuilder

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As in everything, we learn as we go. I have identified 26 pounds of excessive weight in the wings. In the design of the prototype I used .125" dia carbon pultruded rods for the spar caps. Because there is a natural void that occurs when you bunch these rods together, this actually amounts to 5 additional lbs of resin per wing!!! Fiberglass is also not very weight efficient. Because of this, I have redesigned my wing to use .057" thick carbon flats and shear webs and leading edges from Birch Plywood. Plywood is very weight efficient for a shear web. The main reason is that the density is low and the equivalent section required to resist shear is far thicker than that of fiberglass. This leads to increased buckling resistance. The other area i have redesigned is the actual attach joint for the wing. I am using a blade and fork design similar to the beautiful ASW 20 design. I have also redesigned the horizontal attach. All controls are also automatic connect when the wing and horizontal is assembled. I just finished the cowl master models last night and will be making the molds shortly. All of this will be detailed on the blog.
 

Vigilant1

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Mark,
Thanks for the blog on your Robin design and the prototype construction. It's very well done and I am learning a lot. Tons of "here's a smart way to do this" tips.
First the Wren, now the Robin--maybe next an LSA with similar emphasis on weight control and safety? You could do all the drag reduction the FAA has precluded you from doing in your Part 103 designs, and the increased weight limit would open all kinds of reliable powerplant options. Apply the use of mixed materials to produce an efficient and economical ship. Keep the folding wing and the emphasis on practicality and there would be a lot of interest.
 
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planebuilder

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on the Ailerons I am using back to back paddles, similar to the Europa, Stits Playboy and Grumman Tracker. At the Horizontal, I have a fixed yoke that captures the elevator horn.
 

planebuilder

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You are reading my mind!!! My next project is to build a proper N/C router so I can cut full size foam master models. I have a number of ideas for a inexpensive laminar flow wing. I am a big believer in the Mike Arnold School of design; I would very much like to build a 2 place AR-5 with a reliable 4 stroke engine. My goal is 200 mph cruise on 100 hp for two people. I have been getting set up to make composites, I have built a curing oven, I have a cutting table and a complete fiberglass tool shop. The missing piece is the N/C router. I have quite a bit of interest in the Robin, I'm sure the plans will be the deal of the century when I am finished. It would be nice to make some extra cash so I could keep designing new planes.
 

Vigilant1

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You are reading my mind!!! My next project is to build a proper N/C router so I can cut full size foam master models. I have a number of ideas for a inexpensive laminar flow wing. I am a big believer in the Mike Arnold School of design; I would very much like to build a 2 place AR-5 with a reliable 4 stroke engine. My goal is 200 mph cruise on 100 hp for two people.
Will you try to meet the 53 MPH (clean) LSA stall speed criteria? Stay below the 140 MPH at sea level limit by achieving the 200 MPH at much higher altitude and having builders fit a climb prop for registration as an LSA and a cruise prop for E-AB? Maybe builders who want 200 MPH can fit a 100 HP engine, those who want an LSA can use a 2000cc+ VW-derived motor and still get a very efficient airplane that might do 170 MPH at 8500' MSL? Or, are you thinking about only E-AB, no LSA? Either way, it would be a really interesting project.
 
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planebuilder

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Will you try to meet the 53 MPH (clean) LSA stall speed criteria? Stay below the 140 MPH at sea level limit by achieving the 200 MPH at much higher altitude and having builders fit a climb prop for registration as an LSA and a cruise prop for E-AB? Maybe builders who want 200 MPH can fit a 100 HP engine, those who want an LSA can use a 2000cc+ VW-derived motor and still get a very efficient airplane that might do 170 MPH at 8500' MSL? Or, are you thinking about only E-AB, no LSA? Either way, it would be a really interesting project.
To be honest, I'm getting tired of being restricted by regulations. I want to go fast!!!! and I want to do it efficiently. The LSA and ultralight regulations are too limiting. Its possible that a derated version could be made with fixed gear, but that will not be my primary design criteria. The Robin is my Swan song in the ultralight arena.

When I was the president of Chapter 88 in Wichita Kansas, I was the first person to contact Mike Arnold after he broke the C1A0 record. I asked him to come to Wichita and show the rest of us how he did it. He is a very modest genius, his intuition about all forms of drag is remarkable. I bought all of his tapes and have studied all of his references. I do believe he understands how to go fast!!!

I want to travel from point A to Point B at 200 MPH cruise. This is why the next plane is called the A2B. I have been designing it on and off for 3 years. laminar flow is the key. that said, a few years ago I conducted a laminar flow study funded by the State of Kansas and NASA, I have this theory about laminar flow that I believe is revolutionary. I will be experimenting with this idea on the Robin, and incorporating it on the A2B. One of the reasons I designed the Robin was to have a low speed platform in which to experiment. The size of my devices are directly proportional to airspeed, They are economically producible at slow speed, but they get progressively expensive the faster you go.
 

Vigilant1

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To be honest, I'm getting tired of being restricted by regulations. I want to go fast!!!! and I want to do it efficiently. The LSA and ultralight regulations are too limiting. Its possible that a derated version could be made with fixed gear, but that will not be my primary design criteria. The Robin is my Swan song in the ultralight arena.
Well, I can understand the desire to break free of the regs. Still, don't forget all us folks in the "mass market." If you can do 200 MPH with two aboard and a stall speed the same as the AR-5, then a derated version (fixed gear, 80 HP) might easily qualify as an LSA. The only problem my pea-brain can see is that the "speedster" might need to minimize wing area to achieve the speeds you want, which might make it hard for the "derated" version to achieve low stall and acceptable climb rates.

Anyway--thanks again for the Robin blog, and keep us informed as your plans for the A2B come together. (FWIW--sorry to see you abandon the bird names, this new plane could have been the "Swift". I don't think you'd get much hassle from Globe, Temco, or whoever owns the name now)
 
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planebuilder

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LOL, A2B is the working name. Every great design always had a theme. Spectral figures for Mc Donnell Douglas (Phantom, Vodoo...) Cats for Grumman, Tomcat, Wildcat, Hellcat, Bearcat.... I will not break the chain and change the theme. I guess Im stuck with cute little bird names!!! Believe it or not, the working name for the Robin was "El cheapo". I will ask my daughter to name the new fast one, its sort of tradition. 80 hp will keep it slow, fixed gear can be made to work at both speeds, just look at Mike Arnold's AR-5. If you have never seen his tapes, they are really worth buying, Also try to find the old German Hoerner design manuals. The A2B will have wing flaps. 52 MPH is a good landing speed to shoot for. I do not want to sacrifice low speed safety for high speed performance. This is where efficiency comes into play. A clean laminar flow plane should be able to have a high speed ratio.
 

autoreply

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on the Ailerons I am using back to back paddles, similar to the Europa, Stits Playboy and Grumman Tracker. At the Horizontal, I have a fixed yoke that captures the elevator horn.
I'm not sure I follow you (hard to find pictures of those aircraft). Do you maybe have pictures of it?
I personally am a big admirer of the way SH solved it. The Discus, Ventus and so on are hinged on the elevator actuator and a single pin in the front. Very simple, very reliable.

For my own design (the flaperons) I'm still doubting about a torsional coupling, mainly with record to flutter and wear out of the control feel.
I have a number of ideas for a inexpensive laminar flow wing. [...]My goal is 200 mph cruise on 100 hp for two people.
Ha, another one. I'm going for roughly the same on my current design :)
 

planebuilder

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The horizontal, would be similar. I intend to load the leading edge spar with two shear pins , the rear spar will also have two shear pins and a single bolt locks it in place. I do not want to drive the elevator in the same manner as the ASW 20, this would require that the elevators be seperated. I adapted my current design with very little modification. Re: Paddles, I dont have any pictures with me now, but I do believe I have some pictures at home in a copy of the Europa manual. I also modeled the mechinism in 3D and did a kinematic study with it. Those files are home also. I will dig somthing up this weekend and post a picture. The way the paddle concept works is there are two back to back paddles that share a common pivot axis. one Paddle is attached to the fuselage, the other is in the root rib of the wing. When the wing is inserted into the two shear pins and the spar joint is made, the two paddles are automatically placed back to back. The paddle in the fuselage is driven by a 4 bar linkage. This in turn drives the wing paddle. The wing paddle is attached to a cable return system to the aileron. A push rod system could also work. This system is used in the outboard wing of the Grumman Tracker. This is the automatic connect/disconnect for the ailerons that mates and demates when the wing is folded onboard the Aircraft carrier. Aileron Controls using a torque tube scare me, I know it has been done, but to avoid flutter, the tubes need to be really stiff (heavy)
 

planebuilder

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If you guys get a chance, take a look at my blog today. Robin Ultralight
I just updated it with the plaster master splash process. this is why I want an N/C router!!! That will be my next project when I finish the Robin and the plans. This is an old process that was once the industry standard in the aircraft and Automotive business. Its starting to become a lost and dying art!!!
 
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