AirShaper

For part 1, check this link: https://youtu.be/kAXN3MlQxxc

In this video, we’ll be looking at what happens when we move to three-dimensional shapes.

For the full report of our Generic Drone Simulation, click here:
https://airshaper.com/assets/reports/AirShaper_sample_report_-_drone.pdf

To get started, let’s have a look at the aerodynamics of a fixed-wing drone. I have a simple 3D model that I’m uploading to AirShaper. I’ll just call it “GENERIC FIXED WING DRONE” and drag the STL file into the box. It’s a flying drone, so I’ll set it to “above the ground” and “moving” and give it a 15 m/s velocity. Now let’s rotate the nose forward and then pull it upwards, giving it an angle of attack of 15°. That’s not a very efficient flight regime, but it will allow us to see some more interesting flow results. The model was exported in meters and that’s it, now let’s order the simulation.

Ok, we’re back, 4 hours later and the simulation has finished. We’re interested in what happens at an angle of attack of 15°, which should cause a stall. But first, let’s relate to the drag & lift theory of the previous video. This drone has a lift of 21.61N versus a drag of 4.94N. That’s a lift-over-drag ratio of 4.37. Not very impressive, as we saw values of more than 100 in the previous video! Let’s have a look at some techniques to find out what is going on.
One way of finding sources of drag is to look at the total pressure coefficient. Plotting a 3D cloud of where this equals 0 is a good indication of where you have a wake or a draft zone, and thus a cause of drag. As we can see, the outer parts of the wings seem to cause quite a big wake.

To get more insight, surface streamlines & surface friction can help. Remember when we talked about flow separation and adverse pressure gradients? You can detect the edge of a separated zone by looking at low values of surface friction. Looking at the top of the drone, we can see that the outer parts of the wing feature such a separation zone. In that area, you can see the surface streamlines move in multiple directions, even opposite to the wind direction.

You can also see this reflected in the surface pressure map: for a wing to function properly, we need high pressure at the bottom surface and low pressure at the top surface. In this case, the air stays nicely attached to the centre part of the drone. High velocity, low pressure. But at the outer parts of the wing, the air separates right after the leading edge, rapidly increasing pressure and thus reducing lift.

Let’s build a few theories on why this happens. First of all, there is the airfoil that is used. At the centre, the airfoil has a high relative thickness. At the outer parts of the wing, the relative thickness is much lower. Airfoils with a high relative thickness tend to have a higher stall angle of attack. We can see this when comparing lift curves of the NACA006, NACA0012 and NACA0018, which are basically the same airfoil with a different thickness.

Another theory is the shape of this fixed-wing drone. It’s a blended wing body, with a triangular platform, the shape when viewed from above or below. The air first hits the bottom of the nose and is pushed sideways in the process. As it bends around the nose towards the top side, it is pushed back towards the centre by the surrounding air. As the left & right join at the top centre, they fill the wake that is there and prevent separation. This inward & upward pull of air towards the centre could increase the local angle of attack at the outer parts of the wings, triggering stall.

So then how do we prevent this? Well, the question could also be should we prevent this? We’ve deliberately triggered stall by setting the angle of attack to 15°, which is not a standard flight regime. We’ve also seen that stall only happened on parts of the drone, which can be a good thing: a gradual stall in function of the angle of attack will make the drone easier to fly at the limit for example, while it could still be very efficient at lower angles of attack.

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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Drone design #2: 3D Flow Analysis

The details of a drone design can signficantly affect it's aerodynamic performance. In this article, we use AirShaper software to analyseand improive the aerodynamics of a fixed wing drone

Drone design: 3D flow analysis

For part 2, check this link: https://youtu.be/FZHYcqRcDJM

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Drone Design #1 - Selecting an Airfoil

Selecting or creating the optimum airfoil design can be a signficant engineering challenge. AirShaper's guide below explains the theory behind airfoil design and the most important aspects you need to consider

Fundamentals of airfoil design and selection

DIY Aerodynamics #2: Vortex Generators

DIY Aerodynamics #1: See this link: https://youtu.be/CGmqdXKgBiQ


Volkswagen Beetle
You may remember one of our previous videos in which we analyzed the aerodynamics of a Volkswagen beetle, do it yourself style. We discovered that the airflow over the roof detached somewhere around the rear window. The theory was that the downward angle was too steep for the flow to stay attached.
Let’s dive into some theory on when this can happen.


Boundary layer
As air flows over a surface, it will stick to it, slowing down to zero. Away from the surface, air is moving at the free stream velocity.  In between the two, you’ll get a velocity profile. This transition zone is called the boundary layer.As the air in the boundary layer is moving slower, it contains less energy and less momentum than the faster air above.


Flow separation
If the curvature of the surface is too strong, the air in the boundary layer will not have enough momentum to follow it. The more energetic flow above will be dominant, wanting to continue on its horizontal course, pulling away from the surface causing the flow to detach or separate.
Locally, the velocity profile close to the surface can even feature a reverse flow, caused by an adverse pressure gradient, creating a rotating separation bubble. We saw this in our previous beetle test, where the tufts at the top of the window would move in the opposite direction, towards the roof of the car.


Drag reduction
This separated flow increases the wake behind the car, causing unwanted drag. So how can we reduce this effect? One way of doing so is by simply reducing the curvature of the roof and rear window. You can see this on modern, streamlined cars like the Mercedes CLA. Another way is to install vortex generators.


Vortex generators
Vortex generators are little devices that improve the energy and momentum transfer from the free stream air to the boundary layer, giving it more momentum to follow the curvature. A very simple example is small vertical planes, placed at a slight angle with respect to the airflow. As the air hits the front side of these planes, pressure increases. At the rear side, the pressure decreases.

As you may remember from our video on wingtip vortices, the air wants to skip from the high-pressure side to the low-pressure side, creating a vortex at the top of the planes. This will cause part of the flow above the vortex generators to dive downwards, carrying momentum into the boundary layer. It will become more turbulent, stimulating energy mixing between the free stream air and the boundary layer.


Field test on the beetle
So we installed some high-tech paper vortex generators on the beetle to see if it works. It turned out the distance between the vortex generators and the rear window was quite crucial, but after a while, we found a position that worked.


Results
By analyzing the movement range of each tuft, we were able to compare both setups.
Without vortex generators, the tufts near the top of the window featured a lot of movement and reverse flow caused by the adverse pressure gradient. With the vortex generators installed, the movement was much reduced and the reverse flow was eliminated. 


So that was it for this video! If you liked it, please click the like button and subscribe to stay tuned for more!

See ya soon!


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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

DIY Aerodynamics #2: Vortex Generators

Vortex generators re-energise the flow within the boundary layer to avoid separation. This article explains how they work and demonstrates how you could install these on your own vehicle to improve aerodynamic performance

How to improve aerodynamics with Vortex Generators

For part 2 on vortex generators, check this link: https://youtu.be/MC6woj6tsQY

In this video, we will be doing High Tech aerodynamic field testing do it yourself style. We took a 1970s beetle and equipped it with little tufts. 


Tufts
Tufts are small bits of light-weight wire that can move along with the wind. They allow you to see the local orientation of the air flow.
If they stay still and stick to the surface, this indicates nicely attached air flow.
If they wiggle around in different directions, this indicates turbulence, often occurring in zones of detached air flow.


Testing on a '70s Volkswagen beetle
We equipped the roof and rear window of a 1970 Volkswagen beetle with tufts, all around 10 cm apart.
We're curious to learn whether the air flow will nicely follow the curvature of roof and rear window, or detach and become turbulent at a certain point.


Observations
- Front section of the roof: at the very front of the roof, just after the jump from the front wind shield, we saw a slightly more nervous movement of the first tuft.
Admittedly, the effect was not very pronounced.
The other tufts further down stream were all stable.
- Rear section of the roof: all tufts on the roof stayed nicely flat and stable.
- Rear window: intense, nervous movement of the tufts


Interpretation
We saw that at the front of the car, we had a little bit of turbulence at the first tuft. This could indicate detachment of the airflow, possibly because the flow needs to rise up and jump on to the roof. 
The sharp angle between front wind shield and the top of the roof could cause local detachment of the air flow.
Right after that first part, the flow re-attaches again and all tufts are stable until it reaches the rear window: likely, the downward angle of the rear window is too steep for the flow to stay attached. The air detaches and follows a more horizontal trajectory, somewhere above the rear window, causing flow recirculation in the area below.


With special thanks to
- My dad, for being the best Go Pro Mount alternative in the market
- https://www.bensound.com/ for providing us with royalty free music that's easier to listen to than just wind.


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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

DIY Aerodynamics #1: a '70s VW Beetle

There are a variety of affordable and effective flow visualization techniques that you can use on your own car to analyse its aerodynamic performance

Flow visualization techniques for your car

In this video, we will be discussing race car aerodynamics.

Frontal area
If you want to reduce aerodynamic drag as much as you can, you want to keep the frontal area as low as you can. That is why race cars are quite small & low, very close to the ground.
Click here to learn more on aerodynamic drag:
https://www.youtube.com/watch?v=DbIIw-WryHY

Front splitter
At the front, the air hits the car. This generates a high-pressure zone pushing onto the car, but also onto the front splitter. The front splitter is a flat plate in front of the car that feels and captures this high-pressure air and pulls the car downwards generating down force.

Dive planes
Dive planes are the curved planes at the front wheel arches. They make sure that the wind jumps up, pushing the front of the car downwards as a result.

Wheel arch ventilation
The front wheels rotate at a high velocity creating a high-pressure air zone. If you ventilate that high pressure air at the top of the front wheel arches, this will push down the front wheel arches, especially as this air collides with the incoming air in front of the car.

Top air intake
We want to make sure that we provide high-pressure air to the engine, because that increases the power output. We can do so by positioning the air intakes high above the car in the free stream of the air to provide good capturing of air when it hits them.

Rear wing
This wing is comparable to the wing of an airplane, only it’s flipped upside down to not pull the car upward but to push it downward onto the asphalt. You want to make sure that the wing is positioned high enough so that it is in the free stream of the air and not in the dirty, turbulent air that is generated by the air intakes or other geometry of the car upstream.

Diffuser
The diffuser is the part that improves the transition from airflow underneath the car to the wake behind the car. If done right, this can strongly accelerate the air underneath the car creating a low-pressure zone pulling the car downward onto the ground. Click here to learn more on how a car diffuser works:
https://www.youtube.com/watch?v=9UgacwMJpuk&t=64s

Aerodynamic balance
This is the ratio between the down force at the front wheels and the down force at the rear wheels. You can play with this a lot in function of the track you want to race at. It is important as it influences the car’s handling, for example understeer and oversteer.

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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Race Car Aerodynamics

There are many devices that make up a Race car aerodynamic package, including the front splitter, dive planes, air intake, rear wing and rear diffuser. But what are the most important ones?

What are the most important Race car aerodynamic devices?

In this video, we will be discussing Reynolds number and Turbulence. Two closely related items. 

The Reynolds Number
The Reynolds number provides the ratio between the inertia forces and the viscous forces of a flow. It is calculated by dividing the product of the flow velocity, characteristic length and density by the viscosity. You can see it in this formula (00:00:18).

Laminar flow
At low Reynolds numbers, the damping effect of the viscosity is larger than the inertia forces that want to disturb the flow: fluid particles move on steady parallel trajectories. It looks very clean, very orderly. And that's why we call this laminar flow. 

Turbulent flow
At high Reynolds numbers, the inertia forces are big enough to overcome this damping effect and you will start to see nervous movements of particles superimposed onto the main flow. The trajectories are no longer parallel but they feature many local direction variations and swirls within the flow. We call this turbulent flow.

Transition point
As the Reynolds number increases, somewhere between laminar and turbulent flow there is a transition point or transition zone. As density, viscosity and object dimensions typically stay the same within a certain case, this often happens as the velocity increases beyond a certain point, a critical point. 

Example
A well-known example of this is the flow out of a faucet. If you turn it open only slightly, you will see a stable, clear stream of water. Turn it open completely and you will see a nervous flow full of bubbles.

Practical use
So how can you use this Reynolds number in your own application?
Unless you are running a case that is exactly identical to one that has been well tested, you cannot compare directly.

Because the Reynolds number is a subjective thing, there is no clear definition of the characteristic length. It's more of a subjective method to characterize a flow rather than a real physical property. But by calculating the Reynolds number for your application, you can roughly compare to other applications, to get the first idea on whether the flow will be laminar or turbulent in your case. Using the Reynolds number you can analyze the flow of a scaled model, that you have tested in the wind tunnel for example, and extrapolate to a full size one. That's pretty useful for wind tunnel testing.

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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

The relation between Turbulence, Reynolds, and Wind Tunnel Testing

The Reynolds number is a dimensionless quantity that is used to describe the flow characteristics of a moving body of fluid.

How to calculate Reynolds number

In this video, we will be discussing wingtip vortices. I will explain how wings on planes & drones generate vortices. What is causing them? How do they impact flight times? And how can you reduce them using winglets? 

Introduction
Have you ever seen those upward sharky fins at the tips of an airplane wing? 
They are called wingtips and they are there to increase the performance of the wing by reducing the vortices. And it doesn't apply just to airplanes, but also to fixed-wing drones, wind turbine propeller blades and others.

What is a vortex
Simply put, a vortex occurs when the air rotates around a line in the air, like a tornado for example. But how are they created?
To keep an airplane or a drone in the air, it needs to generate lift. This can only be done if the total pressure at the bottom of the airplane is bigger than the total pressure at the top of the airplane, generating a net force upwards. 

But as nature is always looking for balance, the air at the high-pressure side, at the bottom, wants to skip over to the low-pressure side at the top.
Luckily there is a wing in between which then captures this force and generates lift. But at the tips of the wing, the air can bend around the tip with a 180° turn to skip from the high-pressure side at the bottom to the low-pressure at the top. 

So as this airplane travels through the air, it generates a continues swirl or vortex in the air. These wingtip vortices create a loss in lifting properties of the wing as part of the crucial pressure difference between bottom and top, is lost. 

Preventing vortices
Eliminating wingtip vortices completely is quite difficult, but you can reduce them by adding a little wall at the end of the wing (a winglet).
This will prevent the air from crossing over from the bottom side to the top side. 

So how big is this effect? 
How much can you gain by adding them? We've done a project specifically on drone winglets. It was a fixed-wing drone and it already had wing tips. By analyzing and improving them, we improved the lift over drag ratio by up to 30%. 
Which is quite massive for a fixed-wing drone.

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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

What is a Wing Tip Vortex?

Winglets are miniature vertical aerofoils located at the wingtips of airplanes, drones and wind turbine blades. Winglets reduce the strength of wingtip vortices, reducing drag and improving aerodynamic efficiency.

How do winglets improve aerodynamics?

In this video, we will be discussing car diffusers. How do they work? Why do car designers install them? How can you make one for your design?  

Theory - the Bernoulli effect
The Bernoulli effect states that if you follow an air particle along its path within a flow the energy density remains constant. This means that if one term goes up, another must go down. This means that for example, if the velocity increases, the pressure has to go down.

Relation to the car underbody
The car underbody is the bottom side of a car. At the front of the car, you have high pressure because the air collides with the front of the car. At the back of the car, the pressure is lower because the wake wants to pull the car backward. This pressure difference between front and back of the car is the driving force of the airflow beneath the car which is called the car underbody or car underbody aerodynamics.

Down force
Because this section is quite narrow, the air has to speed up and this is where the Bernuit effect comes in:
higher velocity, lower pressure, creating a suction effect pulling the car downwards.
For a sports car that's fantastic, it means more grip. 

Diffuser
This effect of accelerating the air below the car can be much improved by shaping the rear of the car underbody, by giving it a slight upward angle.
This improves the transition to the normal velocity of the surrounding air and it helps to fill the wake behind the car.
The result is an even bigger acceleration underneath the car with more downforce as a result. 

Design
So if you want to design a diffuser, the question is, how large should the angle be?
Too low and the effect will be too limited. Too high and the air will separate and not follow the geometry of the diffuser.
So much depends on local dimensions and aspect ratios.
An angle between 7 and 10° is considered quite a good starting point for your design. 

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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com
Link to sample report: https://airshaper.com/assets/reports/aquilo.pdf

What is a Car Diffuser?

A rear diffuser utilises the Bernoulli effect to accelerate airflow underneath a car. Find out how a diffuser works and how to design one to maximise your car’s downforce and aerodynamic performance.

What is a rear diffuser?

In this video, we will be discussing Drag Coefficients.
What are they? How can you calculate them? And most of all, how you can use them in your design process!


Theory 
Drag coefficients are used to calculate the hydrodynamic (in water) or aerodynamic (in air) force on an object, given the density Rho (ρ), the speed (u) and the frontal area (A) of an object. So if you know the force on an object at a certain speed, for example after a wind tunnel test, you can calculate the drag coefficient yourself using this formula. (0:28)

Once you know the drag coefficient for a certain geometry, you can calculate the force for different object sizes or different velocities
That is very useful for example when you need to size engines, calculate required battery capacity, etc.
But keep in mind that the drag coefficient can vary in function of the Reynolds number. So be careful with large extrapolations to other speeds, sizes or densities.


Practical use
A drag coefficient allows you to analyze the aerodynamic efficiency of an object, irrespective of its size or velocity. That makes it possible to compare a cyclist for example to a building. They are quite different, but still, they have a normalized aerodynamic coefficient.
It is also quite useful within a design process: when you are looking at different concepts for example for your new project or new vehicle, you can rank them according to their drag coefficient. Or you could get inspired by aerodynamic shapes coming from a completely different sector (Mercedes once had a car design inspired by fish!).


Typical Values
A drop shape, which is quite efficient, can have a drag coefficient as low as 0,05, whereas a building typically has one above 1. Lower means more streamlined. 
So if you are working on a drone that needs to fly as far as possible on a single charge or a cyclist that wants a higher top speed, you will want to reduce the drag coefficient as much as possible. 



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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

What is a Drag Coefficient?

Drag Coefficients Cd are used to quantify the resistance of an object as it moves through a fluid. It is a dimensionless quantity which allows aerodynamicists to analyse the aerodynamic efficiency of an object.

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