Here, I will show you how I made my twin motor RC airplane with a 75in (6.25ft) wingspan. These instructions will show you the basic ideas you need to think about and do when designing and building any RC Airplane.
Step 1: Find a Purpose for Your Aircraft
Why do you want to build a model airplane in the first place? It could be just to have fun with and fly around, or you may want to attach a camera and get some Aerial Photography and FPV.
For this plane, I just wanted to make a large twin motor plane to have fun with.
Step 2: Pick Your Electionics
You will need to choose what electronics to use for your aircraft. Pick a motor and battery that will give you a decent amount of thrust, and fair flight time. Once you do this, you can then pick an ESC (Electronic Speed Controller) that can handle the Amperage draw of the motor.
Motors ESC & Batteries
For this plane, I used 2 motors that would provide roughly 860g of thrust with a 10x4.7 propeller (1720g total) and draw about 12Amps each.(Info/ Recommended propeller found on motor manufacturers website). Using this equation, (Flight Time(min)=Battery Capacity(Ah)/Motor Amp Draw(Amperes)*48) Which takes into account the 80% rule of only discharging your batteries 80% of their capacity. I found that with a 2200mAh (2.2Ah) battery, I could get 8.8min of flight time per motor. So, in all, I will have two 2200mAh batteries on board. I then chose a 40amp ESC (which is quite overkill , I only needed a 25-30Amp ESC, but I wanted it to run cool) for each motor.
Determine what controls you want your model to have, and purchase an appropriate Receiver. For example, I wanted my twin to have Elevator, Ailerons, Rudder, Flaps, and throttle control. This is 5 channels, so I will need at least a 5 channel receiver. After equating the required spot on the receiver for the BEC (we'll get to that) I went with an 8 channel receiver so I would have plenty of free plugs.
Servos & BEC
I knew this plane would turn out quite large, so I chose to use larger servos, which draw more Amperes. The Servos I used each drew 400mA and I'm using 6 total, so they will draw 2400mA (2.4A) total, which could be more than the ESC's can handle with their internal BEC. So I had to use an external BEC. (The BEC basically takes power directly from the battery, and drops the voltage down to a desired level, and sends power only to the servos and Receiver.)
2x Electric Motors
2x Electronic Speed Controller (ESC)
1x Battery Eliminator Circuit (BEC)
1x 8 Channel Receiver
Step 3: Estimate the Total Weight of Your Aircraft
Now, with all of your electronics chosen, you can add up their weight and be sure to add in a large margin for the weight of the model itself. (The total weight could be 2 to 4 times the weight of all of your electronics). I estimated that my plane would weigh about 2000g total.
2 motors 80g each x2 =160
2 2200mAh Batteries 200g each x2 = 400g
2 ESC 35g each x2 = 70g
6 Servos 25g each x6 = 150g
1 BEC = 35g
1 Receiver = 15g
Total Electonics Weight = 830g
830g x2.5 (margin for aircraft weight) = 2075g Total
Step 4: Find Wing Cube Loading
Now that you have a total weight estimate, you can use the desired flight handling (affected by Wing Loading) to calculate the total amount of wing area you need for your plane to fly. The best way is to use an online calculator such as the one here:
Plug in your model weight, and experiment with different "Wing Areas" until you get a low wing cubed loading. The lower the better. I always try to start out with my models being in the "Glider Category" since after it is built it will most likely be heavier than you calculated, which would put it in the "Trainer Category", which in my opinion is the best for fun flying airplanes.
I found that 900 square inches would give the plane a Wing Cube Loading if 4.7, Which is in the "Glider Category."
Step 5: Decide on a Wingspan
Now that you have the total wing area needed, you can divide that number to find a wingspan and wing chord (width from front of wing to back).
For example, I divided my wing area (900 square inches) by 12 and got a wingspan of 75 inches.
Any combination of wing chord and wingspan that multiplies to get your total wing area will work, but different Aspect Ratios are also important. You can find the aspect ratio of the wing by taking the wing chord divided by the wing span.
So: 12in / 75in = 0.16
High aspect ratio wings (having a lower number - yes, its confusing) are generally used for gliders and trainer airplanes, while Lower aspect ratio wings will be used for more aerobatic models. A high aspect ratio basically means the wing will be long and skinny, while a low aspect ratio wing will be short and wide.
Step 6: Design Your Fuselage & Tail Section
Since your wing dimensions are already set, now you can design the tail and fuselage. For the tail, you will probably want the area of the Horizontal Stabilizer to be around 25% and 35% of the wing area.
Wing Area = 900 * .25 = 225in squared
Or, 900 * .35 = 315in squared
For my plane, I went with a Horizontal stabilizer area of 234 inches squared because it just looked right in my drawings. (Horizontal Stabilizer dimensions: 26in by 9 in)
For the Vertical stabilizer, just make its area about half of the horizontal stabilizer and you should be fine.
The fuselage can be any length you want (to a certain degree) as long as you get the center of gravity right. While drawing out your model, just make a fuselage that makes the plane look good.
I made my fuselage 52in long and 7in wide by 7in tall. I was designing my plane to be a cargo plane, so it was a bit large and boxy.
Step 7: Decide How to Transport Your Plane
If you are building a large plane, you may encounter a problem transporting it easily. I had to get this larger plane to fit in my car so I needed to think about how to disassemble it and reassemble it easily.
The best way to make your plane smaller for transport is to have the wing removable. I use rubber bands to hold on my wings which attach to 2 wooded dowels glued into the fuselage.
Since this plane was so large, I decided to use rubber bands to hold on the main wing, and the horizontal stabilizer, so they can both be removed for transportation.
Step 8: Begin Construction of Your Plane
Once you have a scale drawing of a design, and are happy with it, you can translate those plans over to the foamboard. I highly recommend using foamboard to construct your RC plane since it is very easy to work with and glue together. I use ADAMS REDI-BOARD from the Dollar Tree, but other similar foam boards should work fine.
Step 9: Construct the Fuselage
I began by dividing the fuselage plans into 3 sections since the entire fuselage would not fit on one sheet of foamboard. I first made the tail section, Which is made from 2 Triangles and 2 narrow Trapezoids glued together with hot glue.
Next, I made the center section which is just a box 7inx7inx30in. I added some bulkheads inside to help the foam keep its shape.
After that, I made the Nose section, and glued all 3 sections together.
Step 10: Attach Electronics and Vertical Stabilizer
Next, I went ahead and added all of the electronics that go in the fuselage.
I Attached the 2 ESC's and BEC on the outside of the fuselage so they will be cooled by the air flowing by the plane while in flight. I used a zip tie to hold these on.
I glued the receiver with hot glue inside the fuselage.
I glued in velcro strips onto a raised deck in the fuselage that will hold the batteries in place.
I also glued on the vertical stabilizer, and glued the rudder servo directly on the stabilizer and ran the wires down into the fuselage.
Step 11: Construct Horizontal Stabilizer
Next, you can cut out the horizontal stabilizer. I used an Exacto knife to cut halfway through the foam to make the hinge for the elevator. Then, I cut a diagonal 45 degrees on each side of the hinge so it can move freely. This is also used for the rudder, Ailerons, and flap hinges.
I then cut out a square for the servo, and glued it right onto the horizontal stabilizer. Some people like to keep their servos inside the fuselage, but I find it easier to just glue them as close to the control surface its moving, as possible.
Step 12: Make a Strong Motor Mount
You want to be sure that your motor mount is strong enough that it won't rip of when you turn the motor on. The way I construct my motor mounts is by:
1st: Gluing 2 pieces of insulation foam (the thick green or blue foam found at hardware stores) that are cut to fit inside the fuselage (touching the bottom and sides of the fuselage), together.
2nd: Glue this "block" of foam onto the sides and bottom of the fuselage. I recommend using a combination of Gorilla Glue and Hot Glue. The hot glue mainly holds the foam in place while the gorilla glue dries.
3rd: Glueing 2 sets of 2 popsicle sticks together. Then glue these 2 pieces to the foam with gorilla glue and hot glue. Be sure that their spacing is the same as the spacing on the motor between the screw holes.
Now, for my plane, I used this technique, but instead of glueing the foam blocks into the fuselage, I built 2 smaller "pods" that will attach to the wings via rubber bands (the same way the wing is held onto the fuselage).
4th: Once the glue is dry, you can screw in the motor onto the popsicle sticks, and you will have a very strong motor mount.
Step 13: Build Your Wing
This is probably the most difficult step. I build my wings based on the principles laid out by www.flitetest.com.
1st:Start by gluing together the foam boards so they are the correct length for your wing. For my plane, I used one full sheet (30" long) plus two 22.5 pieces on each side to equal 75in total.
For the width of the foam needed, take the wing chord and multiply it by 2. My plane will have a 12in chord, so the foam will need to be around 24 in wide. Understand that you will be folding this wing over, so that is why you want twice as much foam. Also know that the aileron and flap control surfaces (if your using both) will need to protrude past the wing bottom surface so they can move. So for my plane the top surface is actually 12in and the bottom surface is 9 inches.
You need your wing to be very strong to withstand the forces during flight, especially on a large model. I use 3 quarter inch wooden dowel rods glued in the wing and a foam spar built of four 1inch strips that go the entire length of the wing. I use gorilla glue and hot glue to glue these spars in. Place the foam spars about 1/3 the way back from the front of the wing so that when you fold it over, it creates an "airfoil" shape.
3rd:Next, Glue in the servos so that the wires are on the inside of the wing, and run the wire leads out a small hole in the center of the wing. (This is so you can connect them to your receiver).
4th: Now, comes the tricky part. You need to put plenty of glue on the foam spar, and then quickly fold the wing over and hold it down flat while the glue dries. Make sure the wing is not twisted as this could cause problems in flight. Once the glue is dry, you can glue the trailing edge of the bottom of the wing to the top of the wing. I just use hot glue for this part.
I found this video to be very helpful in explaining how to make the wing:
https://www.youtube.com/watch?v=karr67ZYho4 (Credit to "Experimental Airlines")
Step 14: Find Wing Placemant & Glue Dowel Rods That Hold the Wing to the Fuselage
Now you need to find the center of gravity of the fuselage so you know where to mount the wing. Place the batteries in a neutral spot, so you can move them a couple inches forward or backwards, and then place you fingers on the fuselage until you get it to balance level. Now mark this spot. This spot will need to line up with the 30% mark of your wing chord. So take the wing chord * .3 to find where this spot will be in relation to the wing chord. Now mark where the leading edge and trailing edge will be on the fuselage. This is where you will place the wooden dowel rods through the fuselage.
Use a pointed object, such as a screwdriver to poke the initial hole for the dowels. Then push the dowels through both walls of the fuselage. Make sure you have 0.5-1in sticking out on each side. This will be what your rubber bands hold onto.
Step 15: Attach Control Horns and Pushrods
Next, you need to transfer the movement of the servo to the movement of the control surface.
1st: Use half of a credit card and cut it as shown to make a control horn.
2nd: Draw a line straight from the servo arm to the control surface, and cut out a slit in the control surface so you can slide the control horn through it. You want the flat part of the horn to be on the bottom of the control surface, so it can't rip off. Use an Xacto blade to cut a small hole in the credit card for the pushrod to go through.
3rd: Glue in the control horn.
4th: Take s piece of push-rod and make a Z bend in one end. Put it through The servo arm, and line it up with the control horns hole. (Make sure the control surface is in a neutral position). Then take a pair of pliers and bend the pushrod at the point it would go through the hole of the control horn. Make another Z bend on this end.
5th: Cut of the extra push-rod wire, and unscrew the servo arm. Push the pushrod through the servo arm, and the control horn, and then screw the servo arm back onto the servo.
Step 16: Landing Gear?
Now you must decide if your model should have landing gear. If the answer is yes, I would strongly recommend using the taildragger style (Where 2 wheels are in the front and a small tail wheel or skid is in the rear) as this is easier to make strong than Tricycle Style Landing Gear.
I use 1/16in piano wire and bend it so that it forms a triangle like shape. I use a zip tie to secure the pointed end onto a popsicle stick (which was already glued onto the fuselage, with a hole on each side). Here is a video from Flite Test that I found helpful :
www.youtube.com/watch?v=po2P1X2OsGA (Credit to Flite Test)
I then glue in a full popsicle stick on the front of the fuselage, and use a rubber band to secure the front of the landing gear wire to the fuselage. The wheels are 3in that are held in place by a zip tie that is glued onto the end of the landing gear wire.
I recommend using bolt cutters to cut piano wire, but be careful as the end you cut can come out quite sharp.
To bend piano wire, I drill a small hole in my wooden workbench, and stick the wire in the hole, then bend it over. This gives the most leverage, as only using pliers will not allow you to bend it.
Step 17: Glide Test
Next, put a small mark on each wing approximately 25-35% back from the leading edge of the wing. With the battery in it's compartment, check that when you place your fingers on these marks, the plane balances with the nose down a bit. Its also helpful to plug in your design into an online Center of Gravity Calculator to find the correct balance point. Here is a good one:
Now, with everything set as it would be if you were ready to fly, make sure that all control surfaces are neutral, especially the elevator. Take your plane and run with it above your head, and let it go for just a second or two. In those seconds, see if the plane dips its nose down. If it does just a bit, it is balanced well. If it tries to nosedive, it is nose heavy. And if it wants to go up, and flip backwards, it is tail heavy.
Step 18: Test Control Direction and Motor Rotation
Your almost ready to fly! Power on your transmitter, and plug in the battery. Check the movement of each stick to be sure it moves the right control surface in the right direction. Your receiver should have a label on the website (if not on the receiver itself) telling what each plug controls.
UP - Elevator moves down
DOWN - Elevator movesup(These are confusing at first, but think of it as moving the stick back tilts the plane back, it doesn't make it go up)
LEFT - Right Aileron moves down& Left Aileron moves up
RIGHT - Right Aileron moves up & Left Aileron moves down
UP - Motor turns on
DOWN - Motor turns off
LEFT - Rudder moves Left
RIght - Rudder moves Right
A video that helped me remember this is one by Flite Test:
https://www.youtube.com/watch?v=Gf74geZyKYk (Credit to Flite Test on Youtube)
Step 19: Maiden Flight
Now its the moment you've been waiting for. Time to see if your calculations and designs were correct. Before you maiden your new plane, you should do a range test, to ensure you have a strong radio signal. (Range Check is a mode you put your transmitter in that reduces the power to simulate as if the plane were really far away.) Many transmitters are different, so check your manual to see how to do this. Once in "Range Check" mode, walk in a large circle around your plane while moving the controls. Make sure that you always have control over the plane.
After this, your ready to fly! Make sure you have a fully charged battery, check the CG one last time, and just go for it! Throttle up to full power, and pull back on the elevator. Expect the plane to be unstable and be ready for some aggressive controls.
Here is a video of my Cargo Plane's Maiden Flight:
Step 20: Trim Your Plane to Fly Perfectly
Once in the air, use your trim tabs to make the plane fly level. If you feel the plane wants to nosedive, then it may be nose heavy. Try moving the battery forwards and backwards to change the Center of Gravity.
Many of my planes want to climb aggressively when full power is applied. To combat this, Put some washers or plastic rings (such as the ones that come with your propellers) on the upper 2 screws of the motor mount, between the popsicle sticks, and the motor. This tilts the motor down a bit, dampening this effect.
After a while of changing the trims, CG, and motor angle, you will get your plane flying great!
Thanks a lot for reading this, and hopefully I made enough sense for you to understand some of this! If you have any questions, please ask. To see more of my planes, check out my youtube page: