Sunday, August 19, 2007

How to build your own RC airplane

Following in the steps of my father and my grandfather, and with a little inspiration from my friend and colleague Paul René, I decided to build my own radio controlled airplane. RC airplanes have always been a hobby, and I've been flying them since I was twelve, but I never built my own, from scratch. This weekend I went for it, and of course I documented the whole ordeal with photos and this blog article.

Best to start with the simplest possible solution, right? I went for a small, lightweight plane with 2D body and wings. In other words, no difficult wing profiles and bodies full of ribs and rods. That doesn't mean the plane is a trainer, far from it. It can do anything from inverted loops to vertical hovering, and is not easy to fly.

Step 1 - Get the RC know-how
If you're new to the area of RC airplanes you should definitively read a bit about the fundamentals of aerodynamics and RC modeling. The Laredo RC club has a beautiful site, but for some damned reason the page can't be reached from most networks in Norway. That's why I ended up creating a mirror of the Laredo RC site. I'll probably get sued for that, but until then check out all the pages under training. These pages are worth their weight in gold for the RC rookie, and for the expert too.

If you don't have an RC radio already, you can start by buying a simple ready-to-fly model first. Something like the Sapac Wilga will do nicely. When you've crashed it, or gotten bored you can use the electronics from that plane in your self made plane. If you're completely new to RC flying, start by acquiring a simulator and flying on your computer. It'll save you many planes. Trust me. Believe it or not there are free simulators out there. All you need is a dummy transmitter like the eSky USB controller for your PC.

Step 2 - Blueprints
There are plenty of great sites on the internet where people are constantly publishing new RC airplane designs. RCgroups and 3-view drawings are such places. The plans are usually published as PDF documents that you can print out and then tape together. The alternative is to create your own drawings. One way is to get a hold of profile and bird's eye view photographs (called 3 view images) of your favorite plane, and then create the drawings yourself using Google's Sketchup. Import the photo and sketch around the edges of the plane. Then hide the photo, scale your drawing to the size you want your model, and print it in tiled mode. The program is originally designed do 3D drawings, but it works perfectly fine for 2D. Just follow some of the tutorials to get a feel for the interface.

In my case I took pictures of my Multiplex Acromaster. It's a plane I'm very fond of, and that I've even used for filming my neighbourhood from above. I sized it to half it's original size, and called it the MiniMaster. The drawings are available from my site. You can download a one-pager version and a 10 page tiled version in real scale.

Step 3 - RC electronics, tools and materials
Motors, RC electronics and building materials have come a looong way since my father started building his first planes. Fuel engines have been substituted by brushless electric motors. Large and heavy servos have been substituted by tiny coreless servos weighing less than 7 grams, and the batteries are extremely light and effective Lithium Polymer (LiPo) batteries. The specs for my MiniMaster v2 are as follow:

While my father built most of his planes from balsa wood reinforced with pine, the materials of choice today are foams (such as depron) reinforced with carbon. This new technology means that the planes weigh a fraction of what they used to, and they require much less place to fly. So while my father had to go into the countryside to find an appropriate flying spot, I fly in the park a 100 meters down the road from my apartment in Oslo.

If you have to buy a motor, electronic speed controller or batteries, make sure to get the right specifications. I recommend using MotoCalc, a program that allows you to enter the specifications of your plane and whatever parts you have, and it will tell what you need to get. AXI Motors also have a simple online motor sizing service on their site.

Make sure you have the right tools and materials before the next step. Apart from a set of small screwdrivers and pliers, a cutting knife and scalpel are necessary. Good metal rulers are useful for measuring and guiding while cutting the materials. Depron comes in 3mm and 6mm sheets of approximately 120x80cm. It can be bought in hobby shops, but it seems they are also used under tiles. Paul René pointed me to a tile shop, where we found sheets for half the price. Carbon rods of any dimension can be bought in a hobby shop.

Step 4 - Creating the parts and gluing it all together

Now it's time to use the drawings you've made to help you cut out the parts in depron. Depending on the size and the power of the motor you're planning on using you can build your plane out of 3mm or 6mm depron. 6mm is strongly recommended for most planes. Gluing two 3mm depron sheets together gives you extra strength and the opportunity to hide a carbon rod between the layers. For even more strength you can glue incredibly light sheets of carbon in between the layers of depron.

Depron can be glued with CA (cyano acrylat), popularly known as Superglue, but it eats into the depron material, so use it very carefully. A kicker to get the CA glue hard almost instantaneously simplifies the building process, but the chemical reaction is exothermic, and the heated glue may eat into the material even faster. A lighter glue may be more appropriate for gluing layers of depron. Another possibility is using a glue gun, but if the wattage on your gun is to high (above 20W), the hot glue can melt the depron. Besides, glue from a glue gun puts a lot of weight on your plane.

Be very patient about the gluing process! Have paper towels ready at all times. Don't glue if you don't have a place to put the plane down afterwards and keep it steady. Make guiding marks in the depron before gluing, and make sure to get the angles right before leaving it to dry or applying CA kicker. There's no second chance when using CA on depron.

Step 5 - Installing rudders and electronics
You'll need hinges for all rudders. Instead of buying these small expensive parts, you can make them yourself. I got this tip off the internet, and I'm very satisfied with the results. Get one of those old floppy disks you have lying in your drawer and haven't used for years. Rip it open and cut rectangular pieces from the magnetic material. It's incredible flexible and durable. Install it by creating small slots in the depron with a scalpel. One drop of CA will make the hinge stay there till Armageddon comes.

When it comes to connecting the servos to the rudders there are two options. I recommend using thin carbon rods with a bit of wire glued to each end. A more difficult, but lighter alternative, is using wires like I've done on my MiniMaster.

The motor mount is a tricky part. I used a small aluminum plate and fastened it to a piece of pine using a small screw and plenty of CA. Make sure you fasten your motor angling it little bit downwards (to compensate from the planes lift). It must also be angled to the right to compensate for the motor's rotation, which will try to roll your plane over to its left side.

On a 2D profile body you should fasten the electronic speed controller (ESC) and radio receiver on one side, and the battery on the other to compensate. Making a hole for the battery and embedding it through the body is an alternative, but fastening it with velcro on the side produces far less damage to the plane during a crash. Remember the battery is the single heaviest component on your plane, and it will keep going even if the plane comes to a sudden hold. You should also use the battery to get the center of gravity right. There are complex algorithms to get this exactly right, but a rule of thumb is to have it 1/4 of the wing's width from its leading edge.

The results
MiniMaster version 1 was a parkflyer, minimal motor power and minimal weight. I tried to combine higher motor power with the light weight. But the wings caved in during flight. A sad sight. My MiniMaster version 2 is a so called 3D plane. That means it can do any kind of acrobatic trick. It weighs 186 grams, but has the brushless motor to carry it well. I'm sticking with this design. Until I decide to build a bigger and better version that is.


October 12, 2008 Blogger yashu said...

u'r tips r excellent

October 12, 2008 Blogger Ramon Arellano said...

Well, thank you, Yashu!

November 05, 2008 Anonymous Anonymous said...

boss!u r genius!!!!!

March 26, 2009 Blogger kapil said...

hello sir, , i am kapil from Mumbai, India, You have made nice and simple plane, i am making my first plane from scrach..but small brushless motors, small servo's also are not available in india.what advice /suggestions u will give me?

April 08, 2009 Blogger Fayad said...

Very cool Ramon...

I was wondering if I could scavenge some parts from RC toy cars (good ones) to get things like transmitters, receivers, turn motors etc.. please advise. It's extremely difficult to get the right parts in India.

April 08, 2009 Blogger Ramon Arellano said...

You might be able to use a transmitter from an RC car, but the receiver and servoes required are made especially for light weight airplanes. Check out parts and prices from !

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