This is my entry for the $75 Build Contest and my scheme is to take the Titan toy glider "build-over" plug and construct a variation of the XP-55 Ascender. I have a small collection of Titan glider toy RC conversion pictures collected off the internet and pictures of XP-55 Ascender look alikes. Most of the look alikes are art, but some are models made from plastic, wood, or foam. If I look about for a bit, I can probably find some paper scale models and more fantasy aircraft models, or art. There are computer games like Crimson Skies by MS that took aircraft from the 1920-1950's with various changes and made them into aircraft for air pirates. Some of the changes made it difficult to figure out which aircraft the variant was modeled from. Many of the models were based on experimental aircraft designs.
My plan is to do the same sort of thing, but it may not be so hard to figure out the aircraft my variant is modeled from. What is different is the use of a build-over plug made from a Titan glider toy fuselage. I got the idea, generally speaking, after watching a master modeler of free flight models use a foam plug to help shape thin strips of balsa wood he had covered in wood glue. The balsa wood strips were very, very thin and once wetted with the slightly thinned wood glue, they would bend around the foam plug. He would wrap the strips around the foam plug at least three times to make a laminated rib. Later he would add strips of wood between the laminated ribs to capture the shape of the foam plug. He ended up with a strong, lightweight balsa wood "bird cage" he could cover in tissue paper.
The balsa wood "bird cage" was cut in half so the foam plug could be removed, glued back together, and covered in tissue paper to make the free flight model that was rubber band powered. I am doing the same sort of thing, but instead of balsa wood, I am using rings from recycled foam drinking cups. I also use the $1 foam sheets from the poster board sold by the Dollar Tree store (paper removed). Since I can buy fan fold foam (Blu-core and other options) for less than $1 a sheet from time to time, I use it when a thicker, softer foam board offers an advantage. When making foam fuselage or wing ribs, I find the foam drinking cup material superior to other options. The building process is a little different in some ways, but generally still very old school with ribs and stringers covered with sheeting, but in this case the skin of the fuselage, or wing is thin foam board, rather than balsa, or thin plywood.
Hopefully I have described the basic details enough and others might see the advantages to the process. The basic detail to notice is foam drink cups are about as free a source of building material as one can get. Most are used once and thrown away. I have been keeping mine for a while now and have the family members give me theirs when they are done with them. I did a little dumpster diving, or trash picking at first, but ended up with so many in a large cardboard box within a month, I stopped, and have only collected from the family to keep my surplus supplies peaked. At first I only collected the largest foam cups, but have since collected all sizes available. The smaller the foam cup, the thinner the foam, and the more flexible. A useful set of characteristics for the tail area of a fuselage, or wing tip. One exception to flexible foam cup is the thin foam coffee cups. They are very stiff, and useful when you want to stiffen a rib, or skin area. Enough for now.
$75 Build Contest - Making the picture attachments larger
If you are having trouble reading the comments included with the picture, use the page "customize and control display" option at the top, right corner. The last picture has very light yellow printed comments, which are very difficult to read in the default display size. You may want to enlarge the display 200%, or more so it is easier to read the comments. I must remember to use a better contrasting color so the comments aren't so hard to read. I have more information about using foam drinking cups as a source of rings for ribs and foam sheet material for fuselage and wing skins in my RC Groups blog. I also have a few video in my Youtube channel. I am Tsavah in both also.
I am still pondering options while I am getting the stringers mounted and preparing to put a foam skin on the fuselage. I do plan to fix the canard wings, once I determine the degree of incidence, if any. This first one will be with elevons to keep things simple, or this is my plan at this stage in the build. In the next few days I hope to take some pictures before I put the skin on just in case some might want to see what a build-over process looks like. In short, the foam plug made from the Titan fuselage is inside, foam rings (fuselage ribs) are wrapped around it, held in place by friction and straight pins, and the thin, round stringers from a bamboo room divider run from front to rear. I am thinking I will run a lot of these lightweight wood stringers even though it will make the fuselage a tad heavier than it needs to be. The stringer wood is either some sort of long, thin bamboo, or fruit wood like someone said it probably is. All I know for sure is the room divider is sold as a bamboo room curtain, the very thin, round wood runs horizontally, and they are very long.
In my RC Groups thread one builder/pilot showed me a picture of a scratch build he had been working on for a while using a KFm wing. Not the straight cut edges most use for the KFm layers, but very curvy. In the background he had a large balsa wood looking wing on the table. Might be the reason he hadn't finished the XP-55 foamie. His XP-55 looked to be a smaller sized park flyer compared to what I have started. His build is looking good, but may be a tad boxy when finished. I have seen others do their foamie builds in the same manner. They cut out two profiles of the fuselage, space them apart as desired, and mount the wings. After installing the electronics and RC gear, they glue on the top and bottom of the fuselage, which often makes a very square fuselage box that looks like a thicker, or wider version of a profile build. Some curve the fuselage sides a little to have a less boxy fuselage design and installed bulkheads to help maintain the slight curve. Others cut the fuselage sides wider than would be for a profile and curve the sides before mounting the wings. Bulkheads inside help hold the shape of the fuselage sides to give a rounded appearance and provide support for any shelves installed to mount the RC gear and electronics. There is another scheme that works well also, but it is primarily a thicker spin on a profile build.
The thicker spin on the profile build uses a layering scheme of thick foam. Many have access to 1/2" (or thicker) x 4'x 8' sheets of house insulation foam board, so they draw out a profile of the fuselage from a side view (common). Sometimes they start with two layers, but if they do the rudder will be made from much thinner and stiffer foam board and mounted between the (center) layers. The other layers are matching cut-outs that are a profile minus what would be sanded away to mirror a top, or bottom view of the fuselage. A few add matching layers (one for the right side, and one for the left side) to the profile fuselage until the fuselage is as thick as a scale one would be. Normally the fuselage is only thick enough to hide the RC gear and electronics inside, where cut-outs have been made for the parts and to provide adequate airflow. One has to remember air has to pass through the foam fuselage or stuff will overheat. The thick profile building scheme does require a lot of sanding, so it is necessary to invest in good quality dust masks, a foam dust clean up kit, power sanding tools, and a variety of hand sanding, or shaping devices. Wondering if Watt Flyers has a thread about this foamie build method? Enough for now.
Thanks for the encouragement. I plan to get busy on the new build-over plug to fit the changes I made so I can get serious about the thin foam skin. Looked about and came up with some 1/2" scrap house insulation foam board pieces. Two pieces are pink and one is blue, which will add some color to the new plug. In the back of my mind the Japanese cartoon Sky Crawlers is having a great deal of influence. You can see some clips from the movie and might even be able to watch the full movie in Youtube. The canopy looks very Me-109, and the fuselage contours look more like a clone of the A7W1 Shinden. Another favorite WW2 pusher design I have liked for a very long time. I should see if I can find a link.
This link is some air combat cuts from the movie and there are more like it in Youtube of various parts of the movie. Notice the aircraft are highly modified fantasy versions of various aircraft designs, most of which are from WW2. The theme of the movie is how people can be controlled to accept a constant state of war. Sort of reminds me of what others have said is the condition of the world and why.
Thought I should take some pictures and share what I have done so far. Since I needed a new build-over plug for the modified Titan glider toy air frame, this is what I came up with. I have already said a little about how I might use this new build-over plug in the future, but generally speaking, any new air frame I might make over the new build-over plug would look slightly different. Of course I could add more foam strips to the build-over plug to make radical changes to the contours. The first primary change would be to add more support for more rib rings. I was sparing with the rib rings since I will be using the double thin foam skin construction scheme.
On a side note, you can use this method to construct any aircraft fuselage real or imagined. If scale is your objective, the plug has to be thin enough to allow the foam rib rings and skin to keep the scale dimensions. You can also use this process to make a replacement section of a fuselage if you have crashed a purchased RC aircraft and would only need enough build-over plug to replace the section that was damaged, which is often the nose area. A build-over plug that is more like the Titan plug I made provides the option to make very thin rib rings (one thickness of foam drink cup, or sheet foam) with one layer of thin foam skin. You would want more rib rings at 2"-3" (on center) spacing and (ribs are usually 1/2" wide) either make the fuselage as a top and bottom half, or left and right half, and install strips of foam between the rib rings before application of the foam skin, or after the skin glue has cured.
The foam strips between the rib rings would transfer the stress from the motor, landing gear, control surfaces, and wings to other parts of the air frame and skin. Otherwise stress cracks and fatigue damage is likely to appear after a few flights. The concept is to build super lightweight and float about rather than speed demon through the flight. The primary stiffness of the air frame will be the glue, which is why I like urethane glue so much and it is very lightweight if applied sparingly. The foaming action of the urethane glue can be cleaned up before the glue has set with alcohol on a piece of cloth rag or paper towel, but it is best to learn how to use less glue. I apply a very thin coating of glue to both surfaces, mist the parts with water, and apply pressure to the joint until the glue has set. If any glue is around the joint, it will feel stiff to the touch, but with a slight flex still obvious. Once cured the flex is gone. You can experience this by placing a drop of urethane glue on wax paper, mist it, mix the water in a little, and press on the spot of glue after about 14 minutes. Keep testing the flex of the glue every 10 minutes. When the flex of the spot of glue is gone, the glue has cured. This is also a good way to know your glue joint made at the same time has set and it is safe to move on to the next gluing task.
Removed the rubber bands yesterday after letting the glue cure over-night on the new build-over plug and was looking at the fuselage framework. I didn't like the way the "hump" foam rib ring looked after I had cut it in half so the front and rear fuselage parts could be slid off the Titan build-over plug. First- the two halves of the foam ring were very thin. Second- they flexed easily, and third- felt flimsy. I removed both halves of the hump foam ring and have been making a new hump foam ring on the new build-over plug. It is wider than 1/2", but only two layers of foam thick.
The first layer of the new hump ring is poster board foam core (paper removed) from the Dollar Tree store, and the second is from a large foam cup I recycled. I cut a wide strip from the poster board, cut it to the length needed to make a tight ring to fit the plug, and glued the edges together. It takes more than a few dry fittings to ensure a good fit, cutting and sanding the edges as needed. Once I am satisfied the ring fits over the build-over plug firmly, but not impossible to remove later, I put a small piece of wax paper between the glue joint and the build-over plug. Otherwise it is likely the ring will be glued to the build-over plug as the wide rubber bands constrict the joint closed.
Note: it is best to roughly sand the foam rings surface before application of the urethane glue to make a lamination. If you don't sand the surfaces before gluing them together, there is a risk the glue won't get a good bite on either surface of the foam rings. I had one foam ring come apart and I am pretty sure I had applied urethane glue between them since one surface was harder than normal. If you apply urethane glue thin enough, you will get a great bond with no glue foaming out of the joint. That is the objective when building a lightweight foam model airplane. Besides, a 4 oz. bottle of urethane glue should last more than a few months and have enough glue for three or four park flyer sized airplane projects. Once you get the hang of how to use urethane glue with foam, the small weight gain is easy to dismiss.
I hope to post more pictures of the new build-over plug with the fuselage framework on it before I apply the foam skin so some of the details are easy to see. I am currently debating with myself if I should apply a recycled foam drink cup skin, or use foam sheet. I have $Tree poster board with the foam core and fan fold foam. The fan fold foam on hand is either blue (Dow product), or pink (Corning product). The blue is softer than the pink enough to suggest it is best as the skinning foam. All three foam types, as well as others, cold roll just fine, and each is bonded very well with urethane glue. I suppose it comes down to application and cost. Not much cost in any of the choices since the most expensive is the $Tree poster board sheets at $1 plus tax each.
Oh, before I forget - here is the link to how to cold roll thin foam sheets, but there are a few details I need to add to the video at some point. The basic process is well displayed, as far as I can tell. If you want more information or instructions, let me know.
I came across a useful video on Youtube that goes well with one of the video I made - making foam cones. In the video below she is making cones using poster board, or heavy card stock, but the same process can be used with thin foam sheet to make cones. In the RC airplane world, we would glue the edges together rather than overlap them. We can also glue more than one sheet of foam together so a shallow cone could be made and cold roll it if the glue joint isn't brittle or stiff. As long as the roller is long enough and overlaps the edges of the foam board (hands), and the firm foam rubber cushion is bigger than the foam piece, it should cold roll just fine without damaging the material. Keep the thin sheet plastic the foam board normally comes with on the outside while you do the cold rolling. It will protect the outer surface of the foam board and can be removed later after all the assembly work has been completed and it is time to apply some paint, or other coloring scheme.
Another note is she used a string pulled tight, but I would recommend a dowel rod, or nice piece of 1" x 1" stock with straight grain. Popular wood is a good one, or oak if you can get a piece that is longer than 3' for the shallow cones one might want to make that are almost a cylinder. Shallow cones need a radius (arc) of 5', or a bit more. I may need to make a demonstration video about this. Many aircraft fuselage designs are shallow cones for the back section, and a slightly sharper cone for the front half. This is true of propeller designs as well as jet designs. There are sections of many fuselage designs that either are a cylinder, or almost a cylinder. There is an old school method used by sheet metal workers to make all sorts of cone shapes, some of which are used to make a funnel. At the moment I cannot remember what the method is called, but it can come in handy if you want to make a fuselage in sections and join the sections together later with alignment devices to ensure no twists or warps. I will try to remember to post a link to a video, or two that shows the process. I haven't made a video for RC airplane construction using the method yet, but hope to in the future. It is a very useful thing to know, especially if you want to build large, yet super lightweight for extra low wing loading. A necessary combination of requirements for a larger, slow flying, and graceful RC aircraft model.
Have a few more show and tell pictures to add to this build thread. Hopefully the pictures contain enough details to communicate what I am doing. I was sure others were making foam fuselages in this manner, but I haven't been able to find evidence to support the theory. Maybe this is a unique way to make a foam model airplane and keep the project very lightweight and strong using thin foam from foam drink cups or sheet foam. Until next time ...
Useful tools; wire mesh pencil can, mini wire trash can, plastic storage containers, tall drink cups, and etc. OK, so you are thinking; "What the heck?" Not long ago I was shopping and looking at office supplies. I saw an office trash can made of wire mesh. The mesh had a small diamond pattern, was stiff, and I started thinking; "Hey, what a nice tool for a thin foam workshop!" I wasn't thinking about trash collecting, but rather the fact heat would transfer through the wire mesh easily and the fact the small trash can was made of thin metal. It looked to be around 2.5 to 3 gallon size. A bit bigger than anything I was currently working on as a RC aircraft model fuselage frame, but still useful. I knew I could wrap thin foam board around it and set it inside a small box to hold the heat in and heat form 1/4", or 6 mm thick foam board. All I need is a way to heat up the box and it's contents to 110 - 120 degrees F. Once the foam was fully warmed to temperature and allowed to cool off, the foam would retain the shape of the metal trash can. If you are wondering why anyone would want to make a copy of a metal trash can in foam, allow me to explain.
I'm not making a copy of a small office trash can, I am capturing the contours, the angle, which happens to be a shallow cone. Of course I have already shown how easily thin foam can be cold rolled to make a tube, or cone shape, so this might seem redundant, and a more expensive way to do the same thing - shape foam sheet. There is one unusual characteristic heat forming give to fan fold foam (FFF) and most other foams commonly used by folks making RC aircraft models - stiffness. For some reason thermo formed insulation foam is stiffer than how it comes from the store. For example, if you feel Blu-core FFF (Dow Product) is too soft and flexible, take a strip that is around 3" wide and 18" long and place it on wax paper and a sheet pan, or sheet metal. Carefully set your house oven for 100 degrees F and ensure the temperature is at, or near the target temperature range. If the oven is too hot there is a risk the foam will melt and could even catch fire, making a terrible smell, and toxic fumes. If the foam isn't overheated and doesn't warp (sign it is too hot), after 5 minutes of baking, open the oven door and let it cool after you turn the heat off. While you are waiting for the foam to cool off (takes around 10 minutes), cut another test strip of the same type of foam for comparison.
Place both test strips side by side on the edge of a table, allowing at least 12" of foam to hang off. If the heated strip isn't twisted or warped, both should hang off the table just fine, but the unbaked strip will probably show a slight curve towards the floor. It won't be noticeable easily until you place a dime on the end of the strip. Place a dime on the end of each strip to see which one is stiffer of the two. I used soup cans on the other end so the strips would stay put on the table and provide a counter weight for each strip. Keep adding coins of equal weight to each foam test strip and notice how the baked strip has gained stiffness and can support more weight before the coins slip off, or the strip bends, causing a crease in the foam strip. This is why some folks wanting thin foam wings with an airfoil curve have made undercambered sheet wings using a forming jig and either their kitchen oven, or a hot box. I plan to do the same thing for my current xP-55t build. The design is a canard build, but I want to test a thin sheet wing with a slight undercamber and two KFm steps.
I also will want quicker ways to make fuselage rib rings, which means I need build-over jigs to make larger diameter foam rings. The fuselage I am making at the moment is a larger diameter than the original Titan toy glider fuselage, but I am on a slow march to bigger. I also want to build lighter and that means I want a way to stiffen a thin foam shell that saves weight and resists damage from stress and minor unplanned landings. As I have stated before, some of my objectives are to build lightweight, larger, and quicker so I can have RC model airplanes that fly slow and graceful. I can always add weight to test the airframe, wings, control surfaces, and over-all design, or provide better wind penetration. For now, I will go with slightly larger and simple design concepts. After all, half this month has passed already and this thing needs to be flown by the end of next month so I can build another with changes if need be. I do want to test other wing configurations, so I will need to include a way to be able to exchange wings and have an adjustable canard wing.
I am sure I said something about a Youtube video I had seen that inspired the build-over plug concept I use to make a model airplane fuselage. The video inspired me to convert a Titan foam glider toy into my first build-over plug and try out a few ideas. Since the early experiments I came to believe a profile fuselage of any aircraft design real, or imagined would make it much easier to make a thin, lightweight foam fuselage shell quickly. I will post the Youtube video link I found inspiring and I suspect others will also be inspired in the same way. I am thinking if others adopt the foam plug idea, there is no telling what might come from the construction method as we share ideas and projects. Notice the way he forms the foam plug isn't all that different than what folks do when they use soft wood to carve out an airplane model.
If you haven't shaped foam before in a method many use to shape soft wood, the video below should provide a good show and tell. In this video he is keeping the process simple and showing the first stage one can use to get towards the desired shape, which will be very rounded when finished. For more details check out his other video. No doubt there are other video showing folks craving on soft wood, but might be tough to find modelers making an airplane fuselage.
That is odd. For some reason the video won't play. I suppose that means if you want to see it you will have to note the title and plug it into the search option after entering the Youtube site.
Have another video of the unfinished fuselage and some notes about the details. Best get started on the rest of the thin foam skin work and wing so I can get started on the glide tests. In the mean time, I will distract myself with a bit more War Thunder while it is still under Beta testing.
Before I forget, I did a weight check of the empty fuselage shell after removing the build-over plug and the postal scale said it weighed 94 kg, or 3.4 oz. (Do those weights match). The build-over plug weighed 70 kg, or 2.4 oz. I am thinking a "less foam" plug could be used as the framework and get skinned in thin foam if I go bigger. The result should still be lightweight enough to fly as a RC floater. I would likely start with a box, or tube, or a series of tubes that fit one into the others made from thin sheet foam, or a series of recycled foam drink cups. A few foam rib rings would be placed between the skin and internal structure for stiffness. I can see how this would work in my mind.
If I started with the 1/2" insulation foam board, the model would be significantly bigger and would likely be a shaped squarish tube. I cannot cold roll 1/2" insulation board, so I have to either go squarish, or six sided that tapers as it needs to for the fuselage design. Very do-able, but I don't know a great deal about bigger than medium sized RC parkflyers. I would also need advice and bigger servos and such.