Card Model to Stick-and-Tissue build

Discussion in 'Aircraft & Aviation' started by k5083, Apr 6, 2007.

  1. k5083

    k5083 Member

    I've been working on a project to convert paper models into balsa stick-and-tissue models. I was going to wait until the build was a little farther along before posting a thread, but the topics seems timely now with Paul's related and very interesting Ca-2 build thread,, so I'll go ahead.

    Interestingly, Paul and I are doing almost the opposite thing. Paul's project is to adapt a stick-and-tissue plan to be built out of paper; mine is to adapt a paper model to stick and tissue. But our goal is the same: we are both looking for lightweight models for either electric or rubber power.


    It started with a new toy that came out this year, one of the new micro r/c toy airplanes. It is called the Tyco SkyForce. See:


    These are profile models made out of flat sheets of roughly 2mm thick stiff foam, similar to meat-tray or picnic-plate foam ("depron"). They contain a 2-channel radio receiver, a li-poly battery, and two small geared motors placed on the trailing edge of the wing. Climbing and diving are controlled by changing the speed of both engines together; turning is accomplished by chaning their speed differentially. The same basic system is used in another popular line of toy planes called the Air Hogs Aero Ace. The advantage of the SkyForce system, for this application, is that rather than being built permanently into the airplane, the SkyForce hardware is modular and meant to be transferred from one airplane to another. After spending $40 for the starter kit with the hardware and 2 gliders, additional gliders can be purchased separately ($8 for a pack of 2) or you can easily design and make your own substitute; several plans are now available on the web.

    Here's what you get when you open the $40 starter kit (with a 15-inch ruler for scale): The hardware and pieces for two gliders with their clip-on attachments for the hardware. One looks a little like an Me 262 and the other is meant to resemble a flying boat adapted for firefighting.


    All very nice, but I prefer scale models with 3D fuselages rather than this profile stuff. Thus this project.


    Good question. There are lots of good plans and kits out there, either stick-and-tissue or foam, that could be used instead. Paul's CA-2 is a great example. And I'm building some of those, too. But I wanted to do a paper model because:

    1. I have a lot of paper models and thought it would be fun to try.

    2. Paper models cover a lot of subjects not easy to find in balsa or foam. Balsa kits exist for a lot of pre-1939 subjects and WWII aircraft, but not so many later types, especially multi-engine subjects and jets, which are harder to adapt to the rubber power that gave birth to these kits. And anyway I just happen to have a lot of paper models of subjects that I would have to buy balsa or foam kits/plans for.

    3. Paper models come with nicely decorated, ready made skins that can be inkjet-printed onto tissue and used to cover the model. That can also be done with stick and tissue, but it's time-consuming and may even require mapping the stick-and-tissue plans into Rhino or some CAD program to develop and unfold the tissue covering patterns. And then you have to color it and make sure it all aligns; it's almost as much work as designing a whole paper model. Even then it might not work, because a lot of stick-and-tissue plans call for the tissue to assume a compound curve, which it actually can do when you shrink it, but it's hard for CAD programs to unfold. More on this later.

    4. Paper models come with handy bits like patterns for spinners, cowlings, landing gear, canopies, and even cockpit interiors and radial engines that could be built straight from the kits and added to the stick-and-tissue model for scale detail; these are often not included, or not done as well, in small flying scale model plans and kits.

    NEXT: Getting started.
  2. k5083

    k5083 Member

    Getting Started


    Which paper model to adapt? Well, the easiest kind are the ones where the fuselage is essentially a square box with slab sides. A lot of WWI biplanes and other early aircraft fit into that category. For example, I think the new Fiddlers Green Boeing 40 would make a dynamite little stick and tissue model, and it's got good proportions for flying, too. Making one would simply be a matter of printing the paper model, building the sides out of balsa stick right over the model with appropriate reinforcing members, and adding cross members to make the box. Then cover with a tissue-printed copy of the model and voila. I do plan to do this, but for this initial foray I wanted more of a challenge; something with a circular section fuselage requiring bulkhead-and-stringer construction.

    The best paper models to adapt are the ones where the fuselage is designed as a relatively simple set of tubes with vertically aligned bulkheads. Examples would be anything by Marek, Nobi, the Israeli AFM series, and most of the older Maly, Fly Model, Modelcard, Modelik, Orlik, GPM, Answer, PMI, and Modelart series. That's a lot of possibilities! Generally, the Halinskis, with their more complex internal structure, would not work as well; neither would some of the newer GPMs, Answer-Modelarts, etc. for the same reason. On the other end of the scale, bulkheads are really needed for this, so they would need to be created in order to use, say, a Fiddlers Green or Betexa. Creating accurate bulkheads for these models is not actually that difficult, and for some of the unique subjects covered by FG probably worth it, but I'll save that for another time.

    From within the basic tube format I wanted an attractive, good-fitting model with enough room inside for the radio gear at the desired wingspan of about 14 inches. Since I intended from the get-go to post a build thread here, it would be a plus if it were free of charge and by a member of these forums. I settled on Nobi's freebie Sea Fury scaled up to 1/33. His criterion of "simple but beautiful" is exactly what this type of project calls for.


    The fuselage is really the only difficult part of these models. Wings and tail can either be cut from sheet foam to match the paper-model patterns or built up from balsa by laying ribs of whatever airfoil one chooses over them every inch-and-a-half or so. Because of the need to support the motors and to handle crash damage better, I knew I would be going with sheet foam wings. So I did the fuselage first because success or failure there would make or break the project.

    The bulkheads from the scaled-up paper model can be transferred directly to the balsa (or depron foam, which would also be fine for these pieces). The tricky part is figuring out how far apart the bulkheads should be and at what vertical offset they should be from each other. In a paper model, this information is encoded in the skins; when rolled into tubes, their shape dictates the spatial relationship between the bulkheads. But when joining the bulkheads with sticks of balsa, and using the skins only at the end, one must first establish the positions of the bulkheads based on measurements of the skins. The following schematic illustrates the what must be computed:


    Imagine that is a side view of a nose section of a fuselage pointing to the left, and that the two bold vertical lines are bulkheads seen edge-on. We need to know how far apart the bulkheads are (x), how far the rear bulkhead pokes above the front one (y) and how far it pokes below the front one (z). We don't know any of these values, but we do know A (the width of the skin at top center, usually right in the middle of the skin if it joins at the bottom) and B (the width of the skin at the bottom, generally where it joins). We also know y+z which is the measured difference between the heights of the two bulkheads. Thanks to Pythagoras we also know that:

    A^2 = x^2 + y^2 ("^2" means "squared")
    B^2 = x^2 + z^2

    and given measured values of A and B there is a unique ratio of y and z for which these can be true. Maybe somebody who took more algebra than I did could solve for x, y and z based on these equations, but I can't. I could, however, create a very simple Excel spreadsheet that can iteratively solve for x and z at any desired precision by entering a range of candidate values for y. Measuring the Sea Fury model parts, I triangulated them to an accuracy of about 0.5mm, which is about as accurately as I can measure, draw, or cut, then plotted the fuselage on a piece of paper. Then I laid 1/16 balsa strips along the edges to make a keel. (Probably should have used 1/16x1/8 for extra stiffness.):


    (The thicker-looking parts are the tape that I used for sticking them to the paper while gluing.) When that was dry, I cut notches at the top and bottom of each of the balsa copies of the kit bulkheads that I had made, and inserted them at the appropriate places along the keel. Very important here to make sure that the bulkheads are square with the keel when viewed from above.


    NEXT: Stringers and covering.
  3. paul a

    paul a Member

    Thank you for the plug. I like your idea too! I,ll be guled to this thread.and last wear did you get the cool toy!!!
  4. k5083

    k5083 Member

    Stringers and covering

    How many stringers are needed and at what positions is a judgment call for the modeler. The competing considerations are strength, lightness, and fidelity to the scale cross-section. Most models have one stringer that runs straight along the side, more or less along the thrust line, which is the first one added (on both sides) because it helps square up the fuselage. I did that first. Then, the question is whether you need 1, 2, 3, or even more additional stringers for each "quarter" of each bulkhead. For a model this size I decided to use 2, giving a total of 12 stringers roughly at the positions of numbers on a clock, except for the rearmost section which uses only 8 stringers because it is smaller and weight is most critical there (small scale flying models with no big motor up front are inherently tail heavy). So:


    You can see that in place of the side stringer in the second section of the fuselage, I substituted a foam insert with a hole cut in it. This would hold the clip for the radio receiver and battery in the finished model. At this point, I faced a "problem" -- once this model is fully built, the radio and battery will not be removable, and I was unwilling to commit them to this model yet because I was still flying them with the profile gliders that they came with. So, not wanting to lose my momentum with the build, I decided that this model will become a test glider and proof-of-concept experiment, and will not receive the radio gear. I may still tear it apart after completion and add the gear then.

    Another angle on the fuselage frame:


    Now on to the covering. I inkjet-printed Nobi's fuselage skins onto white gift-wrap tissue that had been glued to cardstock carrier sheets around the edges. This was the acid test of my bulkhead alignment spreadsheet because the skins will fit only if the positions of the bulkheads are right. Generally, they did. However, I found that I had to enlarge them slightly when printing to get them to fit. Not sure whether this is because my build is somehow oversize, because I didn't attach the tissue perfectly tight, or because the tissue shrinks a little when printed. Probably all three. Anyway, trial and error led to an enlargement ratio of 3-4% and the skins fit just fine. For now, I have left off the tissue at the back of the fuselage, where the horizontal stabilizer will have to be mounted and flight-adjusted before final covering, and from the nose section where I will add any ballast needed when the model is almost finished.

    First three pieces on. Some modelers use an underlayer to reduce that translucent effect of the tissue, but I consider it part of the charm of a stick-and-tissue model.


    Another angle.


    Now with the cowling piece added. The next step will be to build the front cowling rim, spinner, and canopy frame straight from the kit out of cardstock or paper and attach them to the completed fuselage.

  5. k5083

    k5083 Member

    The cool toy is available at Toys R Us and I think also Target. Not sure about Wal-Mart. Other toy stores may have it also.

    If you are willing to tear up an Air Hogs Aero Ace (or fly it until the airframe wears out), they would work just as well and are available a little cheaper and more often in stock at the same outlets. The drawback is that instead of the nice plastic clip-on modules of the SkyForce, you will have to break open the toys and pull out the naked Li-Poly cell and receiver (a small circuit board) to install in your model. Some would consider this a plus, because you'd lose the dead weight of the plastic clips and casing. I decided to spare myself the hassle this time around.

    BTW, if anyone likes the idea or is even awake at this point, I'd be happy to share my spreadsheet in the tools section. It's very small, under 30Kb.

  6. paul a

    paul a Member

    I was wondering if you made the wing removable would that solve the comment issue for the radio?
  7. k5083

    k5083 Member

    Yes, that could work, although for center of gravity purposes it is best to have the hardware as far forward as possible rather than over the wing. Also it would necessitate some redesign of the model. It might also be possible to build a hatch or some other kind of access into the nose.

    The trouble with all of this is that the extra structure adds weight. The motors being used here are geared versions of the same tiny motors that make your cell phone, PDA or pager vibrate, and the toys they originally come from are very light and have almost no drag (frontal area = just the edges of the flat foam sheets). This airframe will inevitably have a lot more drag than the original so I want to bring it in as close to the original toy's weight as possible so that it might actually fly!. I'm willing to lock the gear into the plane in exchange for keeping the structure simple.

  8. Ben Gal

    Ben Gal Member

    Fascinating stuff - where do you fly them and how far do they go. I have never done RC before?

  9. k5083

    k5083 Member

    You fly them at the local park, baseball diamond, soccer field, or schoolyard. They turn tight enough that you can fairly easily keep them on within a baseball infield if you want to. The current generation can stay airborne for about 10 minutes on a charge. The main constraint is that they can handle hardly any wind. Search for "air hogs" or "skyforce" on youtube and you can watch some fun videos of people flying them.
  10. yaniv

    yaniv Active Member


    lol i just think about making the P47 of jhon to 1 like this


    good luck my friend

    i will not stop to see th eprogres of your project
  11. rlwhitt

    rlwhitt Active Member

    These 2 projects (yours and the stick to card one) are really interesting! As for the Air Hogs, they are pretty easy to fly. I've made a couple different attempts at "real" R/C planes, and never really "got it". But the air hogs are just fun!
  12. k5083

    k5083 Member

    Work on these projects has been slowed lately by record rainfall in my area that diverted much of my attention last week to my flooded basement. However, recently I have squeezed out a little time to work on the Sea Fury. I now have the fuselage and tail done and assembled, and wings made and ready for fitting. The tissue covering could still use a little tightening.



    The tail is made of 2mm sheet depron with printed tissue covering. At the moment, the tailplane incidence is adjustable for flight trimming. The wing is 3mm zepron. (Zepron is different from depron but not in any relevant way; it was just what I had handy in this thickness.) The nose cap and spinner are of standard 60-lb. cardstock for strength and because more weight will be needed in the nose anyway. Any additional balancing weight will be carried inside the spinner. The canopy is 24-lb. typing paper.

    Weights are 6 grams for the fuselage and tail and 5.2 grams for the wings. By comparison, a single 8.5x11 sheet of 60-lb. cardstock weighs 10.5 grams. The glider that I am replacing with this model weighs 11.5 grams, so it is close to the original weight, which was my target.

    As a proof-of-concept model the project has already succeeded in proving that I can reverse-engineer a paper model mathematically to get the right bulkhead positions and render a reasonably light airframe in stick and tissue. After glide testing I may yet tear the model partially apart and install the motor and radio. Problem is I have not had time for flying lately, therefore no crashing, therefore I have no systems available to install.

    However the ongoing RC-paper threads are so interesting that after this I may switch gears and try to do an RC project like the other guys, using more paper in the construction.

  13. paul a

    paul a Member

    looks good .
  14. Gil

    Gil Active Member

    Nice Investigation


    You're providing us with a nice intro to doing something a bit more than building a display model using paper as the major medium. I've been following your progress and applaud your efforts. Be nice to see flying paper penetrate the Flying Aces...,

  15. newcomer

    newcomer Member

    what happened to the photos in this thread ?
  16. Amazyah

    Amazyah Senior Member

    This is one of a few threads which lost it's attachments in our last server move.:oops:
    Thank goodness it only happened to a very small percentage.

  17. sparrowhawk

    sparrowhawk Member

    Any chance to Upload the pictures again? Having built some Peanut Scale rubber powered models as a teenager and now an avid cardboard modeler, I would like to see this thread in full.

    Many thanks in advance,

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