In this article, we are going to discuss designing the plane, and after which, in the next article (RC Airplane Series – 4), we will discuss how exactly we should select a motor for our RC Airplane. There is a proper procedure for motor selection, which is one of the important steps in RC airplane designing. 

Designing the plane

This RC Airplane Series is going to be for ‘Beginners’ or for those who are not very experienced in this field, but just want to know the basics of RC Airplane. For this reason, we avoid getting into the details of the analysis. The actual Analysis includes a lot more, like: Airfoil selection through XFLR software, ‘Ansys Fluent’ software for model analysis, etc. 

But for now, we keep it very simple.

For beginners, my suggestion would be to use online available plans in order to develop your aircraft. By ready-made plans, I mean plans that include detailed measurements and figures for the fuselage, rudder, elevator, horizontal stabilizer, vertical stabilizer, and other components.

Some Tips from My Side to Choose a Good Plan:

When I used to browse online, I could see hundreds of designs, from sleek fighter jets to bulky cargo planes. But don’t get overwhelmed by all of that. Because, if you do, you will lose that fire inside you to build your first RC airplane. So, as a beginner, you should specifically look for a High-Wing Trainer. In these designs, the main wing is mounted on top of the fuselage. Let’s build this one first, because we can always upgrade later.

You should also look for a plane with some Dihedral (an upward V-shape angle to the wings). Keep it simple: look for a 3-channel (throttle, rudder, elevator) or basic 4-channel design.

How to Apply the Theory?

Let’s take an example for now: 

I have considered the plan below as an example. You will get a lot of similar plans online on various YouTube channels and websites. 

The one that I am using below is from this video: Video Link. I have modified the plan a bit for simplicity! Do check out his website mentioned in the given video description.

• As shown in the above flowchart, after selecting a plan, we need to choose the material which we are going to use.

Choose Your Material Wisely!

Before cutting, you need to understand the material you are working with. You can proceed with any one of them.

• Foam Board (e.g., FliteTest style): Very cheap, easy to find at craft stores, and easy to cut. It has paper on both sides of a foam core. It is slightly heavier, but excellent for beginners.
• Depron / XPS (Extruded Polystyrene): Lightweight and rigid. It’s a great material, but the drawback is that in case your plane crashes while piloting, the parts might break, which doesn’t make it a great choice for continuous prototyping. It doesn’t have the paper backing, making it lighter than foam board but slightly more brittle.
• Styrofoam (EPS): The classic white beaded foam. It is very light but can be messy to cut without a hot-wire cutter.
• Balsa Wood: Balsa is incredibly strong for its weight, but requires more tools, glue, and patience. I would recommend sticking it to foam wherever some extra strength is required.

In this case, I decided to go with Styrofoam, and after which I searched for the density of Styrofoam on the internet, or you can also get it in the ‘specifications’ section from the website page, using which you are going to buy it. It is usually mentioned over there.

The density came out to be 60 g/L.

• Then, We calculate the mass of the seperate component using the density formula.
• For this, first calculate the Area first. Area can be calculated by breaking the figure into simple geometric figures (rectangles, triangles, trapezium, etc.). Then, calculate volume, and then calculate mass using the density formula.

Volume = Area \times thickness\ of \ the \ sheet

$\rho = \frac{m}{V}$

Please Don’t Ignore This!

You must have often heard people in RC Airplane competitions talking about ‘CG’. While calculating your model’s weight is important, where that weight sits is even more critical. This is known as the Center of Gravity (CG).

If a plane is too tail-heavy (a lot of weight is towards the tail portion of the airplane), it will be completely unflyable. If it is too nose-heavy, it will act sluggish and dive toward the ground. CG is usually located about 25% to 30% back from the front edge (leading edge) of the main wing. When we discuss adding electronics and motors in the next article, we will strategically place our battery (which will constitute the major portion of the total weight of our airplane) to ensure the plane balances perfectly on this mark!

Conclusion

The whole idea is to keep everything simple. After all, that’s the main goal of this website.

Enjoy Learning!

RC Airplane Series

• Part-1: How to Build Your First RC Airplane | Part 1: Understanding Terminologies
• Part-2: How to Build Your First RC Airplane | Part 2: Control Surfaces – Working Explained
• Part-3 (You are here): How to Build Your First RC Airplane | Part 3: Deciding Dimensions
• Part-4: How to Build Your First RC Airplane | Part 4: Selecting Correct Motor & Propeller
• Part-5: How to Build Your First RC Airplane | Part 5: Choosing Correct LiPo Battery
• Part-6: How to Build Your First RC Airplane | Part 6: Choosing Correct ESC (Electronic Speed Controller)

About the Author

I am a Mechanical Engineering student at IIITDM Kancheepuram, interested in teaching, as simple as that! I love to simplify the so-called complicated topics and present them to you in very lucid language. I’m also the author of ‘ Life Lessons from Physics ‘, a book aimed at showing what Physics would have to tell if it were made to give a lecture on Life.