I had stated I had a few goals; 4 channel, 8-ounce flying weight or AUW, to have a landing gear, big wheels, ailerons and be able to fly some basic aerobatics. My basic construction is foam board, carbon fiber rod, and a basswood stick.
I want to talk about the foam board I am using. There are a few "aircraft" type foam sheets out there available to buy. Depron is the name most are familiar with. Midwest Balsa made some called Cellfoam88 but have since discontinued as well as few others made varieties. It is all essentially a cell foam that is unskinned meaning it does not have a paper skin on it like poster board. Kit manufactures laser cut it for really nice fitting kit parts. Most construction of these planes uses very small diameter carbon rod or tube that is CA(super glue) glued to the foam to stiffen it up and make some pretty rigid airframes. Unlike balsa wood planes the foam planes can be pretty easy to repair.
Just to clarify the foam I am referring to is a sheet, injection type styrofoam is also used for RC planes. The sheet foam renders a "profile" type plane although it can be paneled like thin balsa sheet to make full dimensional fuselages and airfoils. Some of the "aircraft " type foam sheet is sorta expensive in my opinion, it typically comes in 1, 3, 5mm thicknesses.
What I am using is really cheap, in fact, $1 for a 2'x3' sheet. It is Dollar store poster board that has a paper on it. I run some warm water in the bath and soak a sheet for a few minutes and the paper skin peels right off both sides. Now it is near or the same weight of the expensive "aircraft" foam sheets.
Now you have some sheets of foam ready to cut up into parts, the laser cutter is awesome but a box of sharp razor blades and a good straight edge you can make some cool planes. Don't waste your time with a hobby knife unless you want to swap the blade out every few minutes, as soon as the foam starts to stagger or pile up while cutting the blade is shot. Foam kills blades fast.
At this point, I want to point to some places you can download and print off a tiled PDF to tape together and cut out for templates to make your own plane. Everything from high wing trainers to Jets can be made for RC out of foam sheet.
There are many types of glue you can use to join foam and join the carbon rod to the foam. Just always consider weight, which means first use as little glue as you need to make it join no more. Second, choose a glue that is lightweight and that would be CA glue or what many know as super glue. NOW a word of WARNING some CA glues will MELT the foam. That is good for styrene but no good for foam. So I can list a few I know have worked for me but Always Always take a scrap of foam and test it. If you are familiar with CA glue might know there are 'Foam Safe' CA glues and something called an Accelerator. Agin the foam safe I have melted some foam so test it. Accelerators for CA glue speed up the curing process and I hate using them. In my experience, the Accelerator crystallizes the exposed glue and makes the joint very brittle. So with all that said Test that glue, have patience and go get some education on CA glues. BSI Industries or Bob Smith are the kings of Epoxy and CA glue, in fact, you might have purchased some and didn't know it. Hobby Town USA, Tower Hobbies and a ton of others market the BSI glue on their own as well BSI labeled bottles. As a business, you can buy their product with your store's name on them like it your house brand glue. They have a good section of what glue to use for what and good videos on using their different products. The other brand I like is ZAP makers of Zap a Gap and others. I use the regular medium consistency CA glue on this and other foam without fail.
When sourcing the carbon fiber rod in most hobby shops, kite stores carry some selection. It is easily found online too. I try to use a diameter that is roughly 25-35% of the thickness of foam I am using, bigger, I feel is just extra weight. If in some cases I do use larger diameter I try to use tubing instead of a rod for the weight savings. Truth is when you drive an RC plane into the ground a few thousands of an inch would not have saved the plane from total destruction. Every now and then the ground just jumps up and its back to the workbench.
The other supplies needed for foam RC planes are clear scotch or similar tape. This used to hinge control surfaces as well as seal them from air breaking through the hinge point. Look for the thinnest lightest tape possible, I have found some cheap packing tape is terrible for shipping boxes but great for RC planes.
Low temp hot glue is very handy to fix servos and other radio gear to the planes and can be peeled off later and reuse the electronics, just don't use too much it is heavy.
Now back to building...
I got creative looking around for some wheels for this plane an ended up taking some condiment cups and trimming them, adding a circle of foam to fill and for more rigidity. I then cut the tube from a mixing pipette and used it as the bearing to ride on the music wire axle. I set some weight on the plane to simulate it fully built and loaded and I think they will work just fine.
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| They are really rigid for what they are made of. |
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| The wheel will ride on the lip of plastic |
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| A small piece of shrink tubing on the axle end holds the wheel on, these can easily be painted |
Next, I cut and attached my tail section to the fuselages. I glue foam to carbon rod onto both surfaces to not only stiffen up the foam but it provides a nice round to round surface to rotate against as the surface is moved. Then the clear tape is used as the hinge I re-designed the rudder section I needed clearance for elevator throw and wanted a bigger one to have a bit more if I can get this to knife edge in flight.
I found a sole tail lightweight tail wheel I had and in the end, I might need to ditch it for something lighter yet but I went ahead and made this a steerable tail. Glued the carbon rod into an aluminum tube which ended up going through the wood stick at end of the fuselage and another small piece of music wire glues inside of the bottom of the aluminum tube to bend and hold the wheel.
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| CA glue carbon rod into the aluminum tube |
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| I bevel sand the ends of each piece of foam where I attached the carbon rod. This keeps the edge of foam from hindering or limiting throw. |
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| Tubing passes through the wooden section making it like a bearing block |
Note the triangular plastic piece sticking out of the rudder and elevator, these are called "control horns" I had some laying around but here are 2 types available from many hobby shops and online.
As you can see EFlite are pretty proud of their products, I am a big fan of Dubro hardware products, Type 3 would be my choice since they have more holes, which governs your mechanical leverage in conjunction with the horn on the servo. A push rod runs between them.
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| The pivot hole of the horn needs to be right over hinge of surface or you will not have equal throw both ways. |
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| Starting to look like something that should fly |
I did a weigh in so far and knowing what my radio gear weighs this is looking like it is going to meet my weight goal.
I have set the top where the wing will set and the Incidence it will have. and yet decide how I will mount the servo and linkage for the ailerons.
I will have more to update on the build but that will be in next post. Thanks to all following along I hope to be out to fly next weekend and I will be filming the flight.
- Hobby Dude
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