Drone Design #1 – Selecting an Airfoil

For more information, visit https://www.airshaper.com
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Drone types
Rotary wings, quadcopters, for example, use the vertical thrust of the propellers to keep the drone in the air. A fixed-wing drone, however, relies on conventional wings to generate the required lift, just like an aeroplane as it travels through the air. In most cases, this setup eliminates any hovering capabilities, but it greatly increases efficiency, giving you much longer flight times.
Fixed wing drones come in many shapes & designs. Some look just like minified aeroplanes, with a propeller at the front, a fuselage in the middle with a long slender wing at both sides and a tail with vertical and horizontal flaps. Blended wings, on the other hand, look very futuristic, with fuselage and wings morphed into a single piece, without any tail at all.

Airfoil basics
Whichever design you go for, you’ll need to choose some kind of wing section, called an airfoil, to generate lift. In more advanced designs, the size or even the shape of this airfoil can change along the width of the wing, but it’s always a good starting point to do some basic hand calculations first.
Let’s start with naming the basic parts of an airfoil. At the front, you have the leading edge, at the back you have the trailing edge. They are connected via the upper surface, also called the suction surface, and the lower surface also called the pressure surface.
The chord is the straight line connecting the leading & trailing edge. The camber line, on the other hand, runs nicely in between the upper and lower surface, showing the centre line of the wing.
The angle of attack is the angle between the chord and the relative wind direction. The relative wind is not only composed of the wind vector but also the velocity of the drone itself.

Lift and drag
Essential to airfoils is how much lift & drag they generate. Lift is the vertical force perpendicular to the relative wind direction. Drag is the horizontal force along the wind direction. These vary in function of the angle of attack. There is a great website called http://www.airfoiltools.com/ that provides you with tons of data on different airfoils. To understand drag & lift curves, let’s illustrate this using a symmetric airfoil, where upper and lower surface are identical. An example is the NACA0012.
At zero angle of attack, the lift is zero as well. There is only drag. As soon as the airfoil rotates its nose into the air, creating a positive angle of attack, it starts generating lift. The bigger the angle of attack, the larger the lift. Beyond a certain critical angle of attack though, the lift will start to decrease again. This operating region beyond the critical angle of attack is called aerodynamic stall and is caused by a separating flow at the suction surface of the airfoil. Trying to pull up too fast during take-off, for example, is a typical scenario in which planes can go into the stall, lose lift and risk crashing.

Another effect of increasing the angle of attack is the increase in aerodynamic drag, which could cancel out the positive effect of lift. To find the sweet spot, we can use the lift-over-drag curve, which plots the ratio of lift over drag in function of the angle of attack. The NACA0012, in this case, reaches its maximum efficiency at an angle of attack of around 8°. At this point, the lift generated by the wing is 80 times bigger than the aerodynamic drag!
This is not the best you can get through. In contrast to symmetric wings, asymmetric wings sacrifice performance at negative angles of attack to generate more lift and less drag at positive angles of attack or even at zero degrees. With airfoil tools, you can easily compare two different airfoils, like the symmetric NACA0012 versus the asymmetric NACA6412. You’ll see that the NACA6412 peaks at a lift over drag ratio of over 140!
As you may have noticed in these curves, lift and drag are expressed as coefficients Cl and Cd, rather than the real lift and drag force. This makes it easier to compare different airfoils, irrespective of their size. The coefficients are calculated by dividing the lift or drag per width of the airfoil by the product of stagnation pressure and the chord length.

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30 Comments

  1. Balaji Gunasekar on April 8, 2021 at 1:06 am

    Hi Wouter

    Am a Mechanical Engineering Student planning to do my Undergraduate thesis On Unmanned Aerial Vehicle could you suggest some books and website where i can start from scratch to build a UAV and all the basic concepts in aerodynamics to understand in a much detailed manner.

    waiting for your reply

  2. Stefan Raghavan on April 8, 2021 at 1:06 am

    1/2*rho*v^2 is not the stagnation pressure. It’s the dynamic pressure.

  3. Vicky Singh on April 8, 2021 at 1:09 am

    I study in 7th standard but I interested in mechanism of vehicles

  4. Hurtless status on April 8, 2021 at 1:09 am

    Hi sir
    I am an Aeronautical student doing my undergraduates .I am interested in designing drones but I don’t have any proper guidance of doing it done .Can you say me what to do exactly to learn to design and what are the things I need to mainly look after for getting it done .

    Waiting for your reply

  5. Saber Dokmak on April 8, 2021 at 1:10 am

    I just stumbled onto this video and I’m stunned how perfect it is. Good job 🙂

  6. Saber Dokmak on April 8, 2021 at 1:17 am

    Also I subscribed, you legend

  7. Mohamed Tarmizi on April 8, 2021 at 1:18 am

    Can airshaper provide CFD analysis for wing ground effect? Can it determine the center of pressure shift with respect to percentage of height to chord ratio. Thanks

  8. Ansh Nagpal on April 8, 2021 at 1:19 am

    Really good Explanation!

  9. Bilal Khan on April 8, 2021 at 1:20 am

    hi, im an engineering student and i m making a drone whose function is to carry an attachment that will throw a ball to a particular place at some height , i searched about drones , and i got to know that copters that lift more weight are difficult and too costlier to develop, so my q is can i opt for fixed wing to perform the same operation, whats your opinion?

  10. rai saro on April 8, 2021 at 1:21 am

    I have to search in english because there isnt anything in spanish.

  11. James Oluwadare on April 8, 2021 at 1:23 am

    this is a good video. though I’m currently having a hard time selecting an airfoil for my fixed-wing drone. can you help me?

  12. Chris Drake on April 8, 2021 at 1:25 am

    A new easy way is to grab the free Airfoil Tools add-in for Fusion360 – it asks you how big/fast/high/etc, and inserts the CFD-optimised shape you need directly. https://apps.autodesk.com/FUSION/en/Detail/Index?id=5447707798035545266&appLang=en&os=Win64

  13. Savio Christopher on April 8, 2021 at 1:25 am

    i didn’t understand the statement you said about the shape of the sections of rudders, flaps, elevators. symmetrical or an asymmetrical aerofoil which is favorable.

  14. Soufiane Boumkar on April 8, 2021 at 1:26 am

    Thank you sir

  15. AC Drone Video on April 8, 2021 at 1:27 am

    Hi Wouter, my name is Angelo Conte and I’m an aerospace engineer who has working on the designing of propeller for a multirotor. I would like to ask you a question: suppose that I want to design a propeller (10 inches of diameter and 4 for pitch). What approach do you can suggest me to analyze the blade of propeller near the hub in hovering condition, where the Reynolds number is very very low and the beta angle is about 30 degrees? I thought to use xfoil with viscous analysis but in that condition the convergence of solution is never reached. Thank you in advance and my compliments for your videos. Great job. Ciao

  16. Djsolstice on April 8, 2021 at 1:28 am

    No axis labels on your charts. I have no idea what your charts mean. Please explain them in future.

  17. Bello Aliyu on April 8, 2021 at 1:30 am

    This is amazing. Thanks for uploading this video.

  18. Reeshad Muntasir on April 8, 2021 at 1:32 am

    Why don’t Airlines’ use vortex generators to prevent drag, just like race cars & high performance cars use vortex generators to create downforce? Ok I just searched on google, that they do, after I actually typed the comment. I know i can delete it but I won’t.

  19. zhiwan omed on April 8, 2021 at 1:33 am

    Please i need help how can i contact with you

  20. amr magdy on April 8, 2021 at 1:33 am

    الله 👌

  21. Mike Ellertson on April 8, 2021 at 1:34 am

    Excellent information. I found it very easy to understand. I appreciate that you provided the math. It really helped to understand the underlying formula so I can tinker with different hypothetical designs before deciding on a few prototypes. Thanks very much!

  22. Madhu Kumar on April 8, 2021 at 1:37 am

    Sir I am an aeronautical engineer. Which designing software do you prefer for me for today aeronautical field. I really learned a lot of things by your videos.

  23. none None on April 8, 2021 at 1:39 am

    Do you know any hooks to teach designing airfoil? I need to learn to design airfoil wings but I have no knowledge. If you let me know what are the books I need to buy I thank you

  24. Mohit Joshi on April 8, 2021 at 1:42 am

    Sir make more vedios

  25. Imran Mani on April 8, 2021 at 1:42 am

    Hello Buddy, You explained it very well.
    I’m an undergrad student and I’m supposed to design a fixed wing vtol with 2 hours flight time and 2 kg payload carrying capacity, so which airfoil you would suggest to achieve these milestones?

  26. Ayush Raj Arya on April 8, 2021 at 1:46 am

    Which airfoil to use in 1045 propeller in typical quadcopters?

  27. سبايسي مان on April 8, 2021 at 1:50 am

    Iam frome sudan iwant learn about air but idont know english

  28. Omeroglu on April 8, 2021 at 1:51 am

    Can you share a resource about vertical takeoff fixed wing vehicles. Do you have a site or an article video?
    Thank you.

  29. sphericalsphere on April 8, 2021 at 1:51 am

    Really good video on the topic. Little tip: If you mention a website in the video, you should also link it somewhere!

  30. robert brander on April 8, 2021 at 1:58 am

    Great explanation , but use more Diagrams !

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