Drones are everywhere these days. As with many technologies, the advancements made in energy storage with lithium-ion batteries has been a game changer. The drone industry is estimated to be worth $43 billion in 2025. They are no longer toys for hobbyists, but serious pieces of hardware used throughout the world and have even flown on <ExternalLink href="https://mars.nasa.gov/news/8923/nasas-ingenuity-mars-helicopter-succeeds-in-historic-first-flight/">Mars!</ExternalLink>

<ImageWithCaption
 src="/assets/images/quadcopter-drone.jpeg"
 alt="Quadcopter drones are used for everything from filming movies to supporting search and rescue operations. CREDIT: www.london-fire.gov.uk"
 caption={
 
 Quadcopter drones are used for everything from filming movies to
 supporting search and rescue operations. CREDIT:{' '}
 <ExternalLink href="http://www.london-fire.gov.uk">
 www.london-fire.gov.uk
 </ExternalLink>
 
 }
 width="700"
 height="341"
 positionCenter={true}
/>

---

## Quadcopters

The first type of drone that comes to mind are quadcopters, which use multiple rotors to provide lift and propulsion. These are small and easy to use and therefore perfect to replace helicopters in a range of tasks where hovering is a key element.

<ImageWithCaption
 src="/assets/images/drone-thermal-camera.jpg"
 alt="Emergency services use drones equipped with infra-red cameras to capture thermal images. CREDIT: www.dronedj.com"
 width="700"
 height="350"
 positionCenter={true}
/>

However, as the applications for drones has increased in areas such as agriculture, mining, defence, mapping and surveying, the range and flight time of quadcopters makes them less ideal for these types of tasks. For example, if you want to map a vast area of agricultural land using advances in drone automation, battery life becomes a major issue. A quick look at a typical manufacturer’s website shows that flying time and range are among the first things that need to be considered.

<ImageWithCaption
 src="/assets/images/drone-field-survey.jpeg"
 alt="Field surveys for agriculture can be automated with drone technology. CREDIT: www.pix4d.com"
 width="700"
 height="394"
 positionCenter={true}
/>

---

## Fixed wing VTOL drones

This has given rise to fixed wing VTOL drones. These are hybrid aircraft with lift producing bodies and wings that also have the ability to hover using rotors. Once airborne, the wings are able to support the drone and the only power requirement is for horizontal motion. This is especially important for drones with heavy camera payloads which are very energy hungry. They also give operational benefits where there isn’t space to land a standard winged drone.

<ImageWithCaption
 src="/assets/images/vtol-drone-example.jpeg"
 alt="VTOL drones combine wings and vertical rotors for short and vertical take-offs. CREDIT: www.deltaquad.com"
 width="700"
 height="266"
 positionCenter={true}
/>

---

## Optimizing fixed wing VTOL drones

The combination of aerodynamics and rotor dynamics makes a fixed wing VTOL drone a more complicated vehicle to design than a quadcopter. From a purely aerodynamic perspective, the basic design of the body can be taken as a standard 3D modelling and CFD problem. AirShaper has a number of tools to make this design process as simple as possible.

We have created a video which explains some of the <Link href="/videos/airfoil-design-for-a-drone/kAXN3MlQxxc">design considerations for drone airfoils</Link> and another video which shows a <Link href="/videos/drone-design-2-3d-flow-analysis/FZHYcqRcDJM">3D flow analysis of blended bodies</Link> using AirShaper. The capability of our software was fully tested during our project with <ExternalLink href="https://www.neuralconcept.com/post/sensefly-airshaper-and-neural-concept-designing-the-ultimate-drone">Sensefly and Neural Concept</ExternalLink>. Using our cloud simulation capabilities as their CFD engine, they optimised the design of a blended wing drone.

- <Link href="/research/deep-learning-automated-drone-design">
 Check out our technical paper on using Neural Networks to optimize a
 fixed-wing drone
 </Link>

<ImageWithCaption
 src="/assets/images/blended-body-drone-optimization_2.png"
 alt="The blended body of the original design (left) was optimized (right) using AirShaper and neural networks to increase overall lift"
 width="800"
 height="298"
 positionCenter={true}
/>

---

## Propulsion is important to all aircraft

Once there is an optimized basic vehicle that meets the various design requirements, the next stage is to integrate the power source. That requires aerodynamic design input in two areas: the propeller itself and the way it interacts with the rest of the design.

In isolation, propeller designs are a complicated field of aerodynamic study in their own right. Studies of propeller thrust and efficiency have been carried out from the original Wright Flyer to the current day. Drones share many similarities with full size aircraft and so their propulsion systems have been researched for a surprisingly long time.

---

## Integrating propellers into aircraft design

Putting the intricacies of rotor design aside, adding one or more to an aircraft design can be seen as a problem. The complex flows can dramatically affect an otherwise well-designed shape. This doesn’t have to be the case with careful design and modern CFD.

In the world of full-size aircraft, <Link href="/videos/electric-aviation-nasa-interview-on-maxwell-x57-part-2-propeller-design/UDZBqDQGU8o">NASA’s X-57 Maxwell aircraft</Link> studies have shown how electric propulsion can be used to revolutionise wing design. We covered this in a series of videos where we interviewed NASA engineers and discussed that there is minimal difference between a drone and a full-size aircraft.

“They are all going to have to deal with some of these trade-offs,' highlights Nick Borer, Performance and sizing lead at Armstrong and Langley. "How does the flow interact with the wing, are you using it for efficient thrust production or are you using it to efficiently generate lift in edgewise flight?”. These are just some of the challenges that face drone designers when integrating propellers.

- <ExternalLink href="https://ntrs.nasa.gov/api/citations/20170005883/downloads/20170005883.pdf">
 Find out more about the NASA X-57 high lift wing propeller system{' '}
 </ExternalLink>

---

## Adding rotating elements to an AirShaper CFD project

To understand all the airflow interactions caused by the propellers, modelling the effect of the propellers and rotating elements in CFD is essential. We have recently introduced this to the AirShaper platform and explain how it works in this <Link href="/videos/how-to-model-rotating-elements-in-cfd-computational-fluid-dynamics-using-mrf-ami-and-more/zFSXtRGk_H8">rotating elements video</Link>.

<ImageWithCaption
 src="/assets/images/airshaper-propeller-cfd.png"
 alt="Drone rotor simulation in AirShaper allows the use of multiple propellers"
 width="700"
 height="343"
 positionCenter={true}
/>

Simulations can now be run with and without a rotor implementation to establish the effects on the design. For a VTOL drone design, it may also be important to look at the effect of rotating and non-rotating propellers to ensure flight characteristics remain unchanged if they are not in use. Drones have come a long way in the last 10 years and we look forward to continuing developing the capabilities of AirShaper to help simulate these fascinating types of aircraft!

---

##### Interesting links:

 

<ExternalLink href="https://airshaper.com/cases/sense-fly-increasing-drone-flight-time">
 Increasing flight time of drones
</ExternalLink>

 

<ExternalLink href="https://airshaper.com/videos/how-to-model-rotating-elements-in-cfd-computational-fluid-dynamics-using-mrf-ami-and-more/zFSXtRGk_H8">
 Learn more about modelling rotating elements in CFD using MRF, AMI and more
</ExternalLink>

---

How CFD can optimize VTOL drone design

The Audi TT concept was first unveiled at the 1995 Frankfurt Motor Show. This two door coupe featured four wheel drive and was powered by a 1.8 litre inline four cylinder turbocharged engine. The clean lines of the <ExternalLink href="https://www.tate.org.uk/art/art-terms/b/bauhaus">Bauhaus-inspired styling</ExternalLink> wowed the Frankfurt audience and the wider media and was deemed a revelation for the previously conservative Audi brand.

The production car sold well initially, but some high-profile incidents in Germany made it clear that the car had some problems with high-speed stability. Audi had to solve these issues fast and developed a new version which incorporated a small rear spoiler and revised suspension settings.

<ImageWithCaption
 src="/assets/images/audi-tt-spoiler-side.jpeg"
 alt="Audi TT rear spoiler side view"
 caption={
 
 The comparatively small rear spoiler was rejected by stylists initially
 but made a huge difference to the high-speed handling of the revised car.
 CREDIT:{' '}
 <ExternalLink href="https://www.caranddriver.com/reviews/a15140613/we-take-audis-tamed-tt-for-a-spin-first-drive-review/">
 Car And Driver
 </ExternalLink>
 
 }
 width="700"
 height="283"
 positionCenter={true}
/>

---

## Modelling the Audi TT in CFD

The changes Audi made to the TT were a success and the car has now become something of a classic. But how much difference did that rear spoiler actually make to the aerodynamics and overall performance of the Audi TT? To find out, we decided to use AirShaper software to conduct an aerodynamic study which compared the original version of the Audi TT without the spoiler against a revised version with the spoiler.

This was fairly easy to do: we purchased a public 3D model of the Audi TT with a spoiler, and then created a copy without spoiler. Further detail could be added by automatically incorporating a rotating wheel simulation. This identifies the wheels from the base geometry and is a valuable tool when investigating automotive aerodynamics.

- <Link href="/videos/how-to-model-rotating-elements-in-cfd-computational-fluid-dynamics-using-mrf-ami-and-more/zFSXtRGk_H8">
 Learn more about modelling rotating elements in CFD using MRF, AMI and more
 </Link>

---

## CFD results

AirShaper allows simulations to run in the cloud and produces a number of different ways to visualise the results, all of which are detailed in an automatically generated PDF report. However, one of the simplest methods to compare results is to look at key numbers. The drag and lift coefficients for both the front and rear are shown in the table below.

| | Without spoiler | With spoiler |
| --------------------------------------- | --------------- | ------------ |
| Drag Coefficient, Cd | 0.305 | 0.265 |
| Total Lift Coefficient, Cl | 0.098 | -0.018 |
| Front Lift Coefficient, Cl,f | -0.063 | -0.072 |
| Rear Lift Coefficient, Cl,r | 0.161 | 0.053 |

As this is a public 3D model, don't focus on the absolute numbers, but rather on the relative differences. The most important change for the Audi TT is the reduction in rear lift coefficient from 0.161 to 0.053. This clearly indicates how a small feature like a spoiler can have a strong impact on the rear lift of the car.

---

## Correlating results with reality

Fortunately for us, after the Audi TT had been revised, the changes were covered in various automotive magazines. <ExternalLink href="https://www.caranddriver.com/reviews/a15140613/we-take-audis-tamed-tt-for-a-spin-first-drive-review/">Car And Driver</ExternalLink> in the US conducted a correlation study between the original Audi TT, the revised version with the spoiler and several competitors at 125mph. The rear lift values of this study are detailed in the table below.

| | Original TT | Revised TT | BMW Z3 | Mercedes SLK | Porsche Boxster |
| --------------- | ----------- | ---------- | ------ | ------------ | --------------- |
| Rear Lift (Ibf) | 148 | 53 | 64 | 104 | 68 |

Although absolute values cannot be compared (due to the lack of detail on the 3D model), both simulation and test feature a comparable 65% drop in lift.

---

## Visualising the results

The power of CFD is that it gives detailed visualisations of the results. For example, surface pressure and surface friction can be displayed as coloured maps, while velocity streamlines show how the air behaves as it flows over a vehicle. These visualisations help us to really understand the interactions between airflows and the differences between the two configurations with and without a spoiler.

---

## Streamlines

<ImageWithCaption
 src="/assets/images/audi-tt-spoiler-comparison-top-view.png"
 alt="CFD streamlines of the wake with and without the spoiler on the Audi TT"
 caption={
 
 Streamlines show the wake with the spoiler (top) vs the wake without the
 spoiler (bottom) in{' '}
 <ExternalLink href="https://airshaper.com/">AirShaper</ExternalLink>
 
 }
 width="800"
 height="596"
 positionCenter={true}
/>

In its original form, the Audi TT acted similar to an aircraft wing. The flow over the top surface has to speed up to meet the under-car flow at the rear of the car. As Bernoulli’s equation sets out, this higher velocity means the static pressure is lower above the car than below, otherwise known as lift. The air follows the body shape all the way to the rear bumper, creating a strong downwash to the wake.

The spoiler works by disrupting this flow and slowing it down. A pocket of recirculating air is created ahead of the spoiler. This slow-moving air means a higher static pressure, eliminating the lift. The flow also separates from the rear window much earlier, creating a recirculation behind the car and a much larger wake that no longer downwashes.

<ImageWithCaption
 src="/assets/images/audi-tt-spoiler-comparison-side-view.png"
 alt="Streamlines showing that with the spoiler the flow seperates earlier creating a large wake. Without the spoiler, the flow remains attached and creates a strong downwash"
 caption={
 
 The results from{' '}
 <ExternalLink href="https://airshaper.com/">AirShaper</ExternalLink> show
 that with the spoiler (top) the flow seperates much earlier creating a
 large wake. Without the spoiler (bottom) the flow follows the shape of the
 rear bumper and creates a strong downwash
 
 }
 width="800"
 height="374"
 positionCenter={true}
/>

---

## Pressure maps

The effect of this is illustrated in the pressure maps shown below. The increased pressure on the spoiler affects the surrounding areas of the car as well. Hot colours show where pressure rises on the rear window, the top of the boot and even on the areas downstream of the spoiler. Lift is decreased by the higher pressures on horizontal surfaces and drag reduced by the increases on rearward-facing areas of the car.

<ImageWithCaption
 src="/assets/images/audi-tt-spoiler-comparison-pressure-3d-view-2.png"
 alt="Two pressure maps showing that the spoiler increases the surface pressure on the rear window and boot compared to without the spoiler"
 caption={
 
 Comparing the two pressure maps in{' '}
 <ExternalLink href="https://airshaper.com/">AirShaper</ExternalLink>, we
 can see that the spoiler (right) increases the surface pressure on the
 rear window and boot compared to the original version without the spoiler
 (left)
 
 }
 width="600"
 height="341"
 positionCenter={true}
/>

---

## A simple solution to a big problem

The Audi TT demonstrates how a big problem can be solved with a relatively small solution. The spoiler added here is not a rear wing element generating downforce in its own right. It is simply a trip to interrupt the airflow, which changes the aerodynamic behaviour of the whole car. Audi made changes to the rear suspension too, but it is likely that the spoiler had the most significant effect on improving high-speed handling.

It is interesting to see how a problem like this caught out a large automotive company like Audi in 1998. Now, modern computing power and tools like AirShaper allow us to carry out analysis like this from a home PC.

---

##### Interesting links:

 

- <ExternalLink href="https://www.tate.org.uk/art/art-terms/b/bauhaus">
 Learn about some design history whilst studying aerodynamics
 </ExternalLink>

 

- <ExternalLink href="https://www.caranddriver.com/reviews/a15140613/we-take-audis-tamed-tt-for-a-spin-first-drive-review/">
 Read the Car And Driver road test review of the revised Audi TT
 </ExternalLink>

---

A CFD analysis of the Audi TT spoiler

Few road cars are capable of achieving top speeds above 250mph (402kph) - the realm of the hypercar. Cars like the multi-million-dollar Bugatti Chiron Super Sport 300+ or the McLaren Speedtail are a couple of examples. But what if you had a supercar and wanted to achieve this hypercar level of performance?

This was the goal of <ExternalLink href="https://7x.design/gallery-1">7X Design</ExternalLink>, who converted a Lamborghini Huracan from a 600bhp, 200mph (320kph) production supercar into a 2000bhp, 300mph (480kph) coach-built Lamborghini Rayo hypercar.

---

## 21st century coachbuilding

Coachbuilding is the engineering art of taking a base vehicle chassis and making it into something unique. In the 1920s, companies like HJ Mulliner created one-off Rolls Royce bodies for their customers. More recently, Pininfarina developed the Ferrari Enzo-based P4/5, also known as the 'Glickenhaus', which generated more downforce and less drag than the original Enzo. This year, 7X Design took a Lamborghini Huracan and created the Lamborghini Rayo, which featured a bespoke carbon fibre body as well as extreme engine tuning.

---

## The Lamborghini Rayo brief

The project was instigated by David Gomez, founder of 7X Design and the owner of a tuned Huracan. He approached <ExternalLink href="https://www.adrianoraeli.com/7x-rayo">Adriano Raeli Design</ExternalLink> to see what was possible. 'The brief was pretty straightforward,' reveals Adriano Raeli, Design Specialist at Adriano Raeli Design. 'We had to re-engineer the aerodynamics of a car with around triple its original horsepower to create a matching aero body that would allow it to achieve its best top speed.'

'There were some practical limitations as we wanted to maintain the original road-going capabilities of the car,' continues Raeli. 'For example, the McLaren Speedtail is a special vehicle with an elegant shape, but it is compromised on the road in terms of ramp angles and overall length. We wanted to avoid this. We also couldn't change the roof and wide windshield because they were part of the structure. The A-pillar in particular generated problematic drag-inducing vortices.'

<ImageWithCaption
 src="/assets/images/7x-design-lamborghini-rayo-rear.jpeg"
 alt="The starting point: a 1,900bhp twin-turbo modified Lamborghini Huracan. CREDIT: www.undergroundracing.com"
 width="700"
 height="390"
 positionCenter={true}
/>

---

## Inspiration to reality

Automotive styling is a unique mixture of engineering and design. The most elegant of lines often create unworkable aerodynamics. Despite the different aerodynamic requirements and <Link href="/videos/the-relation-between-turbulence-reynolds-and-wind-tunnel-testing/sV8l8xd4MEQ">Reynolds numbers</Link>, the project was specifically inspired by figher aircraft.

<ImageWithCaption
 src="/assets/images/f35-fighter-jet.jpg"
 alt="Fighter aircraft provide some of the inspiration for Adriano Raeli's high performance automoitve projects. CREDIT: www.lockheedmartin.com"
 width="800"
 height="294"
 positionCenter={true}
/>

'They are one of the fastest and highly technological vehicles on the planet, short of spacecraft,' observes Raeli. 'When David saw the initial sketch he said, 'this is it!' That was the starting point of the design process. We then went from those quick couple of lines to a 3D model and then evolved the aerodynamic design of that model in simulation.'

<ImageWithCaption
 src="/assets/images/7x-design-lamborghini-rayo-initial-sketch.png"
 alt="The elegant original napkin sketch required engineering input to turn into a workable package. CREDIT: www.adrianoraeli.com"
 width="800"
 height="209"
 positionCenter={true}
/>

---

## CFD simulation with AirShaper

There were three aerodynamic aims for the CFD programme:

1. Reduce the drag to allow the car to achieve the 300mph (480kph) target

2. Create balanced downforce to ensure the car remains stable at speed

3. Limit the total amount of downforce so the car doesn't get squashed at high speeds

To help achieve this, Raeli experimented with the design of the rear wing and in the end replaced it with two winglets. 'For some projects, a rear wing is a must, there's no other way to achieve that kind of downforce without a wing,' explains Raeli. 'To reduce drag, we opted for winglets instead, which are located in cleaner air. So I designed a general aerofoil profile and tested it in CFD. There was no specific math behind it initially, just general design and aerodynamic principles. AirShaper’s morphing tool was instrumental to evolving the design and it's helped us achieve better speeds and downforce without a rear wing.'

<ImageWithCaption
 src="/assets/images/7x-design-lamborghini-rayo-rear-winglets.png"
 alt="Rear winglets replace the full width spoiler and are key aerodynamic elements of the design. CREDIT: www.adrianoraeli.com"
 width="800"
 height="302"
 positionCenter={true}
/>

AirShaper's aerodynamic shape optimization tool also helped with the design of the underbody and the rear diffuser, which are essential as they generate significant downforce with minimal drag. The software showed that instead of a fairly square cross section, a more rounded and larger central tunnel with smaller side tunnels performed better.

A lot of effort went into the front splitter, to optimize the way the air is accelerated underneath the car. Additionally, large air curtains were added to shield the front wheels and reduce their drag. Other areas of improvement included the height and length of the tail, the rear window cover, side air intakes, front wheel well ventilation and more.

---

## The benefits of CFD

AirShaper is not just designed for aerodynamicists, but also designers as well. The intuitive and easy to use software allows designers to make CFD a key element in their design process. 'You are able to test your design changes and see how they affect the aerodynamic performance of the car,' highlights Raeli. 'If we test a specific detail or a volume change in the nose for example, within a few simulations we can understand how it is affected, positively or negatively. We can then adjust the design for the next round of optimizations whilst keeping in mind the proportions we wanted to maintain.'

---

## The results

Through the rounds of development, the drag coefficient was reduced by 28.5% to a Cd of just 0.279 whilst doubling the downforce (thanks to the optimized underfloor aerodynamics and top winglets).

<ImageWithCaption
 src="/assets/images/7x-design-lamborghini-rayo-pressure-clouds.png"
 alt="The pressure clouds of the final design show a signifcant drag reduction which is vital for the top speed attempt"
 width="800"
 height="315"
 positionCenter={true}
/>

The car was taken to the <ExternalLink href="https://www.applusidiada.com/global/en/what-we-do/services/spain-proving-ground">IDIADA test track</ExternalLink> in Spain for initial testing of the new body, rendered in carbon fibre. The results were better than the team had hoped for, despite the limitations on the available straights. The car achieved 278mph (447kph) with more to come from further powertrain and aerodynamic development. Later this year, the car will be taken to a more suitable location to try to reach the 300mph (480kph) target.

<ImageWithCaption
 src="/assets/images/7x-design-lamborghini-rayo-testing-2.png"
 alt="The finished car was tested at the banked turns and long straights of IDIADA's proving ground. CREDIT: img1.wsimg.com"
 width="800"
 height="448"
 positionCenter={true}
/>

'What we have here is a great achievement because, if you think about it, how many companies attempt something like this?' questions Raeli. 'They usually have to invest millions of dollars in R&D and a lot of time. Whereas our small team, together with AirShaper's expertise and the knowledge of the people who built the car, allowed us to upgrade the Lamborghini Huracan to achieve those ambitious speeds. I think that's a pretty big accomplishment.'

---

##### Interesting links:

 

<ExternalLink href="https://www.instagram.com/7xdesign/">
 Check out 7x Design's Instagram
</ExternalLink>

 

<ExternalLink href="https://www.applusidiada.com/global/en/what-we-do/services/spain-proving-ground">
 The IDIADA proving ground
</ExternalLink>

From supercar to hypercar - the Lamborghini Rayo

The world is very lucky to have NASA, a publicly funded body with a requirement to openly share all of its research. As we discovered in our <Link href="/blog/best-aerodynamic-resources">guide to the best aerodynamic resources</Link>, the NASA report database is a goldmine of freely available data for aerodynamicists and engineers. It also contains a huge archive of photographs and publications chronicling their history.

That’s where we came across <ExternalLink href="https://ntrs.nasa.gov/citations/20205009237">'The World’s Largest Wind Tunnels'</ExternalLink> book by Kenneth W. Mort. This publication covers the history of the 40 x 80ft closed loop and 80 x 120ft open loop tunnels at NASA Ames in California, known as the National Full Scale Aerodynamics Complex (NFAC). It provides the perfect starting point to delve into the world of full size wind tunnel testing.

<YouTubeEmbed
 videoId="m4rysu8LlLM"
 title="Electric Aviation - NASA interview on Maxwell X57"
/>

---

## Why full size?

A lot of wind tunnel testing is done at model scale for obvious reasons. The test facility can be much smaller, fans less powerful and it is much easier to produce models and test parts. If you want to take an Airbus A380 and put it into a wind tunnel, its 80m wingspan is only the start of the problems that need to be solved.

If that is the case, why do engineers and aerodynamicists still want to try to test in very large wind tunnels? NASA’s 80 x 120ft tunnel (roughly 24m by 36m) will take an actual example of full size fighter aircraft. The key word here is actual.

<ImageWithCaption
 src="/assets/images/fighter-jet-wind-tunnel-testing.jpeg"
 alt="An F/A-18 Hornet fighter jet undergoing high angle of attack testing in a wind tunnel. CREDIT: www.nasa.gov"
 width="600"
 height="579"
 positionCenter={true}
/>

The main reason for wanting to investigate a production aircraft is to establish its real-world performance. A typical problem when using wind tunnel models is that they can be too good a representation of the vehicle. For example, on a real aircraft, rivet heads, panel gaps, antenna and actuators all create drag and prevent aerodynamic surfaces working in the same way that they would do on a scale model. This is particularly vital for low-speed scenarios like take-off and landing where lift is at a premium.

The same applies for ground vehicles. A scale model Formula 1 car is very clean and stiff, so wind tunnel measurements are very accurate. A real Formula 1 car though, has gaps in the bodywork and lightweight carbon structures that deflect, giving quite different results on some occasions. Investigating these details led Williams, Toyota and Sauber to build their own full size wind tunnels in the early 2000s, which are unfortunately now banned by the regulations.

- <ExternalLink href="http://www.icas.org/ICAS_ARCHIVE/ICAS2002/PAPERS/3103.PDF">
 Check out this paper which summarises a wind tunnel test of the Dash 8 Q400
 airliner in the NASA tunnel
 </ExternalLink>

---

## Tunnel interactions

As we saw in our <Link href="/videos/scale-model-wind-tunnel-testing/qqYiz1eo-F4">scale model wind tunnel testing video</Link>, a large wind tunnel section also helps achieve more accurate results with scale model testing. Keeping the section large with a small model allows you to minimise blockage effects and interactions with the floors and walls. A lot of work carried out in the NASA tunnels centres around low speed/high angles of attack scenarios and rotorcraft where there are high downwashing effects which are very sensitive to these things.

A large air volume and working section is particularly useful for quite bluff bodies that displace a lot of air. This was demonstrated in the NASA wind tunnel during a <ExternalLink href="https://www.llnl.gov/news/lawrence-livermore-national-lab-navistar-work-increase-semi-truck-fuel-efficiency-full-scale">fuel efficiency test of a road going truck and trailer rig</ExternalLink>. The NASA 120 x 80ft tunnel is actually very well suited for this type of testing because it can only achieve 100mph in its large configuration.

<ImageWithCaption
 src="/assets/images/truck-fuel-efficiency-test.jpeg"
 alt="A full semi-trailer under test in the 80 x 120ft section of the NASA wind tunnel. CREDIT www.llnl.gov"
 width="700"
 height="483"
 positionCenter={true}
/>

These tests are desirable to help bridge the gap between CFD and the real world. CFD can model a vehicle without the constraints of a working section, but correlating the results is often difficult. Testing a truck on the road is too uncontrolled and instrumentation limited to do this effectively.

- <Link href="/videos/cutting-truck-bus-emissions-the-vecto-airdrag-tool/s2QyP6n4Zxs">
 Find out how to apply the Vecto Air Drag tool to truck and bus aerodynamics
 </Link>

---

## Large scale engineering and lots of power

NASA’s 80 x 120ft tunnel is the largest in the world and is an engineering marvel in its own right. The basis for the building complex was a closed loop 40 x 80ft tunnel conceived in the 1940s. It was converted to add the 80 x 120ft open loop section in the 1980s, powered by the same fans.

<ImageWithCaption
 src="/assets/images/external-view-of-nfac.jpg"
 alt="An aerial view of the complete NFAC. CREDIT: www.nasa.gov"
 width="700"
 height="516"
 positionCenter={true}
/>

The six fans are 40ft in diameter and each is rated at 22,500hp which generate 115mph flow in the 80 x 120ft tunnel and 345mph in the 40 x 80ft closed loop.

<ImageWithCaption
 src="/assets/images/main-nfac-fans.jpeg"
 alt="The bank of fans powering the NFAC. CREDIT: www.nasa.gov"
 width="700"
 height="560"
 positionCenter={true}
/>

Whilst the headline working section numbers for the NASA tunnels are large, the nature of a wind tunnel means that other aspects of the air circuit are much larger. Upstream of the 40 x 80ft section, before the contraction, the tunnel is 132 x 173ft (40 x 52m).

<ImageWithCaption
 src="/assets/images/1947-nasa-wind-tunnel-working-section.jpeg"
 alt="View of the 40 x 80ft working section from 1947. CREDIT: www.nasa.gov"
 width="700"
 height="467"
 positionCenter={true}
/>

The engineering challenges don’t stop once the wind tunnel itself has been built. Such large test items each come with their own logistical problems during installation and removal. The tunnel working section has a hinged roof to allow access.

All-in-all, the facility is as much a wonder of engineering as the different vehicles that have been tested in it over the last eighty years.

<YouTubeEmbed
 videoId="4PabZAx-4Yw"
 title="Testing a Boeing aircraft tail in the world's largest wind tunnel"
/>

---

##### Interesting links:

 

<ExternalLink href="https://airshaper.com/videos/wind-tunnel-test-section/L1AYo9Mk1EI">
 The wind tunnel test section explained
</ExternalLink>

The largest full size wind tunnel in the world - NASA

## Introduction

We are designing a versatile all-electric amphibious aircraft to transport people and goods. The amphibious aircraft concept we are developing is a flying boat type and it uses a hull-based fuselage to meet the hydrodynamic requirements for the aircraft to take-off and land on the water bodies. Operation from land airports is achieved through the retractable landing gear system onboard the aircraft.

<YouTubeEmbed
 videoId="ZPjjg4_UDlA"
 imgSize="hqdefault"
 title="1/5th scale model testing"
/>

We want people to travel emission-free from city centre to city centre at a fraction of the time. Small and flexible sea terminals will facilitate the onboarding and offboarding of our passengers, which is especially useful in mountainous areas along the coast.

## Efficiency is key for electric aviation

For electric aviation to be technically & economically viable, improving efficiency is key, especially when it comes ot aerodynamics. A low drag coefficient and a higher lift-to-drag ratio have a direct impact on the aircraft performance and eventually on the range and endurance of the plane. Some of the ways we have tried to achieve this include:

- the use of natural laminar flow airfoils
- optimised high lift devices
- a streamlined hull design without compromising on the hydrodynamic requirements
- the use of a push-pull electric propulsion setup to further reduce drag.

Overall, we are currently involved in multidisciplinary optimisations and expect to freeze the design in a year from now.

## Hydrodynamics

Hydrodynamic design is crucial for amphibious operations. For the past 12 months, we have been conducting intense hydrodynamic testing of various hull designs for the plane. In order to evaluate the hull designs for the plane in terms of stability and hydrodynamic resistance, we have performed multiple open water tests and also testing in a towing tank in collaboration with SINTEF Norway.

<YouTubeEmbed
 videoId="Et8UBTX7xDo"
 imgSize="hqdefault"
 title="Byfly Towing Tank test at Sintef Norway (video credit: El-Fly)"
/>

How simulations have helped, which parameters are important (lift and drag, roll pitch yaw) Which insights you had, which improvements you'll make based on the results.

## Analysis & optimization through simulations

With the online CFD simulation platform AirShaper, we were able to verify the feasibility of particular flight conditions. Getting the angle of attack of the wing right is crucial towards for economical cruise conditions. Using the lift & drag values from the simulations, for different angles of attack, allows us to optimize further for efficiency. Furthermore, by analysing surface pressure & surface friction, 3D streamlines, flow structures in the wake and other simulation results, we’re able to spot areas for further improvements to the aerodynamics of the plane.

<YouTubeEmbed videoId="62QS4M6M_9Q" title="Full scale model CFD in AirShaper" />

## Experimental testing

We are currently in the R&D phase involving experimental testing. Our goal is to first launch the commercial service in Norway by 2030, where it is highly suitable for the challenging terrain. We will operate from city centre to city centre, and then expand operations to other parts of the world.

Interesting links:

<ExternalLink href="https://el-fly.no/">El-Fly</ExternalLink>

Electrict Aviation - The Byfly Seaplane

Tim Barber runs a prep shop and race team, <ExternalLink href="http://www.tfbperformance.com/go-racing/">TFB Performance</ExternalLink>, out of Sonoma Raceway in California. TFB Performance provides vehicle preparation, track support and driver coaching to its customers who race in Trans-Am, endurance prototypes, Spec Miata, SRO World Challenge and many more.

Customers who run racecars with aerodynamic packages typically rely on Tim’s team to optimise aero performance. The convenience and affordability of <ExternalLink href="https://www.rapidscan3d.com/software/polyworks/modeler">RapidScan</ExternalLink> and <Link href="/videos/how-to-run-an-aerodynamic-simulation/O_DNDxCtI_I">AirShaper</Link> allowed Tim to not only access aero data, but analyse the effect of set-up changes quickly and accurately, without investing in wind tunnels or complicated CFD software. Making aerodynamics accessible to a much broader range of racer than ever before.

---

## Establishing an aeromap

The amount of downforce of a racecar varies significantly with ride height and rake. So it is vital to fully understand this relationship if you want to have any chance of establishing an effective set-up over the weekend.

The best way to achieve this is to create an <Link href="/videos/how-aero-maps-can-improve-race-car-performance/u-GyTRblNmc">aeromap</Link>. This maps aerodynamic properties such as downforce and drag as a function of car set-up such as ride height and rake. These plots help to understand the sensitivities between aero coefficients and car set-up, which is an important tool to utilise to adjust the car.

- <Link href="/videos/how-aero-maps-can-improve-race-car-performance/u-GyTRblNmc">
 How aero maps can improve racecar performance
 </Link>

<ImageWithCaption
 src="/assets/images/trans-am-ta2-mustang-surface-pressure.png"
 alt="Surface pressure plot of a Trans-Am TA2 Mustang"
 width="800"
 height="469"
 positionCenter={true}
/>

OEM’s obtain these sensitivities through wind tunnel testing, but this is far too expensive for most small teams and typically requires aerodynamic specialists. Furthermore, the rules in most race categories prevent the use of wind tunnels.

Track testing is the next best option. However, varying weather and track conditions along with other cars on track, make it difficult to run representative comparison tests. Track testing also requires a lot of time from the drivers and as most of our clients have full-time jobs, this is simply not possible.

Consequently, our small team cannot afford the luxury of aerodynamic data, but our customers still rely on our expertise to optimise the aero performance of their cars. Typically, this means spending a lot of time analysing onboard data and combining it with driver feedback. However, the short race weekend formats and lack of testing makes it incredibly difficult to gain an accurate picture of how set-up changes affect the aerodynamics.

To help solve this problem, we decided to partner with RapidScan and AirShaper for our Trans-Am TA2 program. This is a road race stock car that has simple aero adjustments available. However, getting the set-up right is essential as qualifying and the 100-mile race are run on the same set of tires. So an unbalanced car will unnecessarily wear the tires that already degrade heavily throughout the race.

<ImageWithCaption
 src="/assets/images/trans-am-ta2-mustang.jpg"
 alt="Trans-Am TA2 Mustang"
 width="700"
 height="444"
 positionCenter={true}
/>

---

## 3D scanning

The first stage was to create a 3D model that could be imported into AirShaper, which involved 3D scanning one of our TA2 cars. This required no preparation from our side, and within a day Richard Feijoo, 3D solutions specialist from RapidScan, scanned the entire car from top to bottom. This scan was then converted into a 3D surface model, ready for simulating in AirShaper.

<ImageWithCaption
 src="/assets/images/raw-3d-scan-ta2-mustang.png"
 alt="The raw 3D scan of the Trans-Am TA2 Mustang"
 width="700"
 height="383"
 positionCenter={true}
/>

---

## Simulating in AirShaper

Within minutes, I had imported the 3D model into AirShaper and adjusted the set-up parameters of the simulation. I modelled a range of different car configurations with two main objectives. One was to understand how much ride height affected straight line drag, and the other was to quantify how much rake affected downforce.

Being able to quantify the aerodynamic performance from a given ride height or wing change is invaluable. This was the first time that we were able to achieve this with reliable data rather than using educated guesses. The results from AirShaper also benefitted our drivers, as we could explain what to expect instead of them having to rely on feeling the changes themselves.

<ImageWithCaption
 src="/assets/images/trans-am-ta2-increased-rake.png"
 alt="Velocity slice illustrating the aerodynamic effect of increased rake on the Trans-Am TA2 racecar"
 width="700"
 height="543"
 positionCenter={true}
/>

To understand the results in more detail, I was able to connect with AirShaper online where a specialist walked me through the data and the various models they created for our car. The PDF report provided, was also really useful. It presented the results in an understandable way and included a wide variety of colour maps illustrating surface pressure, surface friction, velocity streamlines, pressure clouds and even noise analysis. Within a few simulations we had quantitive values of the aero effect of set-up changes, without the need for wind tunnel or track tests.

---

## Beyond lap time

Drivers and teams typically prioritize speed and lap time first, but the AirShaper data can also be used to improve cooling and reliability. For example, in Trans-Am TA2, there are a number of different options for radiator and brake duct openings. By using the simulation results, we were able to adjust these openings to the optimum position that allowed enough air flow for cooling, whilst maintaining maximum downforce and minimising drag.

Furthermore, the regulations specify that the overall surface of our TA2 car has to meet body templates, but we are allowed to design and manufacture our own airbox and ducting. Again, using the data from RapidScan and AirShaper we simplified our build process and can now quantitatively say that we have the best aerodynamic option available. I'm looking forward to running some more cars through this process so that we can optimise the aerodynamic performance of those too!

<ImageWithCaption
 src="/assets/images/trans-am-ta2-isosurfaces-2.png"
 alt="3D pressure surfaces on the Trans-Am TA2 reference model"
 width="700"
 height="213"
 positionCenter={true}
/>

---

##### Interesting links:

 

<ExternalLink href="https://www.racecar-engineering.com/tech-explained/what-is-an-aero-map/">
 What is an aeromap?
</ExternalLink>

 

<ExternalLink href="https://www.rapidscan3d.com">RapidScan</ExternalLink>

Helping teams understand the aero of a Trans-Am TA2 Mustang

In competitive cycling, aerodynamic wheels have become a standard. Every pro rider, along with many amateurs now ride them on a daily basis. However, cyclists are often concerned about the effects of these wheels on the riding experience and the theoretical aerodynamic benefits never seem to quite match reality.

To help address this issue, <ExternalLink href="https://www.sorcycles.com/pages/about-us">Sōr cycles</ExternalLink> have developed an innovative new wheel that allows anyone to ride in any condition. To find out more about this ground-breaking technology, we interviewed the co-founders of Sōr cycles; Nicole Van Beurden (ex-triathlete) and Phil White (co-founder of Cervelo).

---

## The importance of aerodynamics in cycling

Aerodynamics has a huge effect on cycling performance and is therefore an important consideration in the design of a bike as well as the positioning and clothing of the rider. Check out our previous blog posts and videos, where we have covered <Link href="/videos/aerodynamic-clothing/A0Gx-lBzSFA">aerodynamic clothing</Link> for cyclists, the features of an <Link href="/videos/designing-an-aero-bike/DqlDpUFcScc">aero bike</Link> and discussed how teams in the <Link href="/blog/cycling-aerodynamics-team-dsm">UCI World Tour deal with cycling aerodynamics</Link>.

<ImageWithCaption
 src="/assets/images/trek_madone_bike_frame.png"
 alt="The TREK Madone SLR is a good example of an aerodynamic bike frame. CREDIT: www.magliarosso.co.uk"
 width="600"
 height="450"
 positionCenter={true}
/>

In general, one of the largest factors of resistance that a cyclist feels is <Link href="/videos/what-is-aerodynamic-drag/DbIIw-WryHY">aerodynamic drag</Link>. On flat surfaces, up to 90% of the total resistance a cyclist feels is due to aerodynamic drag. If you can minimise this, the cyclist can go faster with the same power output; gaining time over their competitors.

Over the years, there have been many innovations to improve the aerodynamics of cycling and these have mostly focused on reducing the frontal cross-sectional area. This is often achieved by making the frame thinner but using taller tubes to maintain stiffness. To further improve aerodynamics, manufacturers have also introduced fairings to cover the wheels, commonly known as “disc wheels” to reduce the wake produced by the wheel.

<ImageWithCaption
 src="/assets/images/aero_bike_wheel_covers.jpg"
 alt="An extreme example of an aerodynamic wheel cover. CREDIT: www.triathlonvibe.com"
 width="600"
 height="451"
 positionCenter={true}
/>

While these aerodynamic advancements have helped reduce cross-sectional area, it has influenced bikes to become more unstable in crosswinds. The nature of thin bicycle wheels means a small tyre contact path which results in less rolling resistance and aerodynamic drag, but also instability. Innovations such as disc wheels can further increase this instability.

The majority of the work carried out by the cycling industry to reduce drag has concentrated on relatively low yaw angles (i.e. not much sidewind). The yaw angle is the angle of the wind relative to the direction of travel. "We felt that the real-world side winds were higher than the theoretical models and that typical rider speeds were lower than the speeds used in testing," explains Nicole Van Beurden, ex-pro long-distance triathlete and co-founder of Sōr cycles.

To prove this, Sōr cycles conducted some real world testing, with the results in the video below. It was found that the yaw angle is a lot higher in real life than in the theoretical scenarios bike manufacturers have been designing their aero for.

<YouTubeEmbed
 videoId="--uvHp_UaqE"
 title="Measuring yaw angle in real world conditions"
/>

"At these high yaw angles, cyclists often feel instability and are vulnerable to high crosswind gusts," says Van Beurden. "They can also experience further instability from flow separating from the disc wheel causing buffeting. This phenomenon is like a wing stalling, the result is instability, turbulence and drag. These instabilities make it especially difficult for smaller and lighter cyclists, most often women, to take advantage of these disc wheels."

---

## The Sōr wheel

To solve this problem, Phil and Nicole developed a unique new wheel, the Sōr wheel, and Sōr cycles was born. "We have designed a wheel to work at the yaw angle that the rider is feeling," highlights Van Beurden. "The Sōr wheel design immediately adapts to the conditions the rider feels at that second."

In other words, the Sōr wheel is a full wheel for race bicycles that is capable of deforming. When subjected to a headwind it remains a simple narrow wheel, but under side winds the wheel deforms with the leeward side bulging out to form an aerodynamic shape. This encourages the airflow to remain attached for longer, helping to reduce drag and eliminate buffeting.

Should the conditions change a second later, the shape of the wheel automatically adapts to a new optimal shape. This avoids the instability and buffeting problems that is common with aero wheels because the wheel is constantly changing to suit the conditions.

<ImageWithCaption
 src="/assets/images/sor-wheel-morphing.jpg"
 alt="The Sōr wheel changes shape according to the conditions to achieve optimal cycling performance. CREDIT: www.sorcycles.com"
 width="700"
 height="428"
 positionCenter={true}
/>

What is truly innovative about this design is that the wheel’s aerodynamic morphing is completely passive. "We took inspiration from the way the wing of a bird or bat can instantaneously and passively optimize itself to wind conditions," explains White. "There are no control systems, no actively moving parts, no linkages, no sensors, no power, just a thin balloon like material that stretches freely but snaps back into shape."

"This intelligent material can dynamically adjust to even the changes in airflow caused by the riders legs," continues White. "It is also so smooth that the rider will not feel any vibrations from the material deforming. Furthermore, the design has a central hidden structure which carries most of the load without effecting the aerodynamics and keeps the wheel extremely lightweight. By separating out these duties, each component is optimized for its role and the overall wheel weight can be much lower while also being more aerodynamic."

<VideoEmbed
 videos={[
 {
 src: 'https://airshaper.storage.googleapis.com/website/video/slo_mo_lswt.webm',
 type: 'video/webm;codecs="vp8, opus"',
 },
 {
 src: 'https://airshaper.storage.googleapis.com/website/video/slo_mo_lswt.mp4',
 type: 'video/mp4',
 },
 ]}
/>

---

## The aerodynamics behind the Sōr wheel

The principle behind the Sōr wheel is relatively simple. At 0 degrees angle of attack, the wheel is in its default position and is thin to keep the frontal surface area low. At angles of attack higher than 0 degrees (combined sidewind and forward velocity), the leeward side of the wheel features low pressure and will “bulge out” creating a convex shape. The windward side feels a higher pressure and becomes concave.

The flexibility of the material allows the wheel to absorb gusts of wind. While the Sōr disc can keep the airflow attached up to around 28 degrees of apparent wind, compared to approximately 15 degrees for the leading competitor with a rigid disc.

<ImageWithCaption
 src="/assets/images/drag-graph-of-aero-wheels-2.png"
 alt="The Sōr wheel keeps airflow attached up to approximately 28 degrees and delivers around 90 Watts of thrust. CREDIT: www.sorcycles.com"
 width="600"
 height="427"
 positionCenter={true}
/>

The material of the Sōr wheel not only changes shape leeward versus windward side, but it also changes shape across a single rotation. So, the shape at the same side of the wheel can be different in front and behind the hub. This allows the Sōr wheel to turn into an airfoil and even result in thrust at certain angles. Similar to a sail on a boat, the difference in pressure created by the concave windward side and the convex leeward side generates thrust.

<ImageWithCaption
 src="/assets/images/sail-physics.png"
 alt="A diagram illustrating the physics behind a sail on a boat. CREDIT: www.2.bp.blogspot.com"
 width="400"
 height="600"
 positionCenter={true}
/>

---

## The other benefits of the Sōr wheel

The benefits of this wheel are not just purely aerodynamic, the confidence this technology provides to the rider can also contribute to optimising performance. "By having more stability, people peddle more efficiently," reveals Van Beurden. "If a normal disc wheel is destabilising you, you use your core to compensate for this. This represents a loss in terms of power going to the pedals."

Overall, the Sōr wheel provides a paradigm shift on how aerodynamic devices on a bike wheel can work. Not only does it reduce the buffeting and instability, but also provides measurable advantages over traditional disc wheels in crosswinds. This will help cyclists of all abilities ride faster for longer in a wide range of conditions.

---

Interesting links:

 

<ExternalLink href="https://www.sorcycles.com/">Sōr cycles</ExternalLink>

 

<Link href="/videos/aerodynamic-clothing/A0Gx-lBzSFA">
 Aerodynamic clothing for cyclists
</Link>

 

<Link href="/videos/designing-an-aero-bike/DqlDpUFcScc">
 Designing and Aero Bike to win the Ironman
</Link>

 

<Link href="/blog/cycling-aerodynamics-team-dsm">
 Cylcing aerodynamics - Interview with Team DSM
</Link>

The technology behind the Sōr wheel

The impressive processing power now available to home computers is quickly changing the way people apply complicated engineering principles. The types of CFD simulation and analysis that companies such as Airshaper now provide used to be the domain of high-end software, only available to large engineering concerns. Now, cloud computing means that the only thing you need to conduct CFD simulations is access to a web portal.

At the same time, there is a vast amount of aerodynamic information and research on the internet. Knowing where to start and what sources to trust can be overwhelming. So, to help you on your aerodynamic journey, we have put together this guide which lists our favourite aerodynamic resources, research and tools that we think you will find the most useful.

---

##### [1) Fluid Mechanics 101](#fluidmechanics101)

##### [2) Advanced Fluid Mechanics course from MIT](#advancedfluidmechanicscourse)

##### [3) OpenFOAM tutorials](#openfoamtutorials)

##### [4) NASA Technical Reports Server (NTRS)](#nasatechnicalreports)

##### [5) Technical paper websites](#technicalpapers)

##### [6) OpenFOAM](#openfoam)

##### [7) XFOIL and XFLR5](#xfoilandxflr5)

##### [8) Airfoiltools](#airfoiltools)

##### [9) AirShaper](#airshaper)

##### [10) KYLE.ENGINEERS](#kyleengineers)

##### [11) Official Formula 1 website](#formula1website)

##### [12) Aerodynamic books](#books)

---

## Education

It is essential to thoroughly understand the fundamental principles behind aerodynamics before diving into your own CFD studies. Massive online open courses (MOOCs) are widely available and, whilst some are quite basic, others are very comprehensive. YouTube also has a huge variety of technical content created by some engaging and knowledgeable engineers.

### 1) Fluid Mechanics 101 <a name="fluidmechanics101"></a>

<ImageWithCaption
 src="/assets/images/fluid-mechanics-101-home-3.png"
 alt="Fluid Mechanics 101 YouTube channel"
 width="700"
 height="492"
 positionCenter={true}
/>

##### What is it?

- A very popular YouTube channel that focuses on explaining the principles of fluid mechanics as well as computational and numerical methods

##### Why do we like it?

- An accessible set of videos that cover all the theory you need to understand when running CFD simulations
- All content is scientifically validated and referenced correctly
- Provides formulae, methods and data which saves you having to dig through textbooks and research papers

##### Where can you find it?

- You can watch the videos on the <ExternalLink href="https://www.youtube.com/channel/UCcqQi9LT0ETkRoUu8eYaEkg">Fluid Mechanics 101 Youtube channel</ExternalLink>
- For more detailed lectures and courses check out the <ExternalLink href="https://www.fluidmechanics101.com/index.html">Fluid Mechanics 101 website</ExternalLink>

---

### 2) Advanced Fluid Mechanics course from MIT <a name="advancedfluidmechanicscourse"></a>

<ImageWithCaption
 src="/assets/images/advanced-fluid-mechanics-mit-course-2.png"
 alt="Advanced Fluid Mechanics course from MIT"
 width="700"
 height="462"
 positionCenter={true}
/>

##### What is it?

- A four-part course that is free to use as long as you are happy not to receive any certification and have time limited access
- It covers the continuum viewpoint, fluid statics, inviscid flow, Bernoulli, control volume theorems and applications

##### Why do we like it?

- This set of courses is aimed at a relatively high level and requires a healthy time commitment, but does cover a lot of ground
- If you choose to be a verified learner, you can complete the course at your own pace
- Good mixture of teaching videos and interactive concept questions to help you practice what you have learnt

##### Where can you find it?

- You can register and access the <ExternalLink href="https://learning.edx.org/course/course-v1:MITx+2.25.1x+1T2022/home">Advanced Fluid Mechanics course here</ExternalLink>

---

### 3) OpenFOAM Tutorials <a name="openfoamtutorials"></a>

<ImageWithCaption
 src="/assets/images/openfoam-tutorial-collections-2.png"
 alt="OpenFOAM tutorials"
 width="700"
 height="479"
 positionCenter={true}
/>

##### What is it?

- A collaborative database of teaching materials that make up the official OpenFOAM user tutorials

##### Why do we like it?

- Every resource has been compiled by aerodynamic experts from all over the world
- Tutorials are categorised into specific collections to suit different levels
- A wide variety of resources including videos, presentations and articles

##### Where can you find it?

- All the tutorials can be found on the <ExternalLink href="https://wiki.openfoam.com/index.php?title=Tutorials">OpenFOAM Tutorials homepage</ExternalLink>
- You can also find AirShaper's contribution on the <ExternalLink href="https://wiki.openfoam.com/Adaptive_Mesh_Refinement_by_Air_Shaper">Adaptive Mesh Refinement page</ExternalLink>
- Before founding AirShaper, I also created a variety of <Link href="/courses">OpenFOAM training courses</Link> to teach companies how to utilise OpenFOAM in their design process. These are somewhat outdated, but may still be useful

---

## Research

Once you have completed your learning, it’s time to take on some projects! As with any new undertaking, it's always worth exploring previous studies. This not only gives you a head start, but can also help you avoid making mistakes.

### 4) NASA Technical Reports Server (NTRS) <a name="nasatechnicalreports"></a>

<ImageWithCaption
 src="/assets/images/nasa-technical-reports-2.png"
 alt="NASA technical reports"
 width="700"
 height="377"
 positionCenter={true}
/>

##### What is it?

- A searchable database of a vast library of research papers and technical reports
- It dates back to the beginnings of the NACA, forerunner of NASA, in the early 20th century

##### Why do we like it?

- These papers cover everything from airfoil and duct design to hypersonic research
- Even the Apollo mission reports are available

##### Where can you find it?

- You can search through the database via the <ExternalLink href="https://ntrs.nasa.gov/search">NTRS - NASA Technical Reports Server homepage</ExternalLink>

---

### 5) Technical paper websites <a name="technicalpapers"></a>

<ImageWithCaption
 src="/assets/images/technical-paper-libraries.png"
 alt="Technical paper libraries"
 width="700"
 height="546"
 positionCenter={true}
/>

##### What is it?

- Online databases containing abstracts for technical papers

##### Why do we like it?

- There are thousands of papers on a whole range of engineering subjects available
- Similar to the NASA reports, they summarise fascinating and useful research
- They tend to be for members only, but can be bought individually or are often free in academia

##### Where can you find it?

- Many industries have their own society websites which include a library of technical papers, such as the <ExternalLink href="https://www.sae.org/publications/technical-papers">Society of Automotive Engineers</ExternalLink> and the <ExternalLink href="https://www.aerosociety.com/news-expertise/national-aerospace-library/e-library/">Royal Aeronautical Society</ExternalLink>

---

## Tools

There are many commercially available software products out there, but the licence costs mean that only large companeis can afford them. Fortunately, there are many free tools that can do a similar job.

### 6) OpenFOAM <a name="openfoam"></a>

<ImageWithCaption
 src="/assets/images/openfoam-paraview.png"
 alt="OpenFOAM ParaView. CREDIT: commons.wikimedia.org"
 width="700"
 height="424"
 positionCenter={true}
/>

##### What is it?

- OpenFOAM is an open-source library for running CFD simulations

##### Why do we like it?

- It is extremely powerful and forms the basis of many commercial CFD products and consultancies
- It’s widely used as the maths engine behind bespoke front-ends in industry, so learning about it is a useful skill for your CV. Discover other ways to boost your CV by reading our blog on <Link href="/blog/building-your-career-in-aerodynamics">building a career in aerodynamics</Link>

##### Where can you find it?

- You can download and install it from the <ExternalLink href="https://www.openfoam.com/">OpenFOAM homepage</ExternalLink>
- Check out our tutorial video on <Link href="/videos/cfd-results-how-to-analyse-openfoam-data-with-paraview-25-minute-tutorial/kczZPc4M-ms">how to analyse OpenFOAM data with ParaView</Link>

---

### 7) XFOIL and XFLR5 <a name="xfoilandxflr5"></a>

<ImageWithCaption
 src="/assets/images/xflr5-example.png"
 alt="An example of XFLR5. CREDIT: www.sourceforge.net"
 width="700"
 height="548"
 positionCenter={true}
/>

##### What is it?

- These tools are quite similar and allow you to perform a preliminary aerodynamic analysis on basic shapes like airfoils and sails

##### Why do we like it?

- A complicated CFD simulation of a full design is usually the end goal of a project but it can be very time consuming and difficult to set-up. These tools are free and easy to use and are effective ways of getting into the right ballpark

##### Where can you find it?

- You can download and install these tools from the <ExternalLink href="https://web.mit.edu/drela/Public/web/xfoil/">XFOIL homepage</ExternalLink> and the <ExternalLink href="http://www.xflr5.tech/xflr5.htm">XFLR5 homepage</ExternalLink>

---

### 8) Airfoiltools <a name="airfoiltools"></a>

<ImageWithCaption
 src="/assets/images/airfoiltools-4.png"
 alt="Airfoil plotter on Airfoiltools"
 width="700"
 height="470"
 positionCenter={true}
/>

##### What is it?

- A comprehensive database containing lift, drag and moment performance characteristics for different airfoils
- A lot of the data comes from the NACA reports previously discussed

##### Why do we like it?

- It makes a lot of sense to start from a known <Link href="/videos/airfoil-design-for-a-drone/kAXN3MlQxxc">airfoil design</Link> when trying to create a wing or blade, so a database like this eliminates a vast range of unsuitable designs, saving you a lot of time

##### Where can you find it?

- You can browse through different airfoils on the <ExternalLink href="http://airfoiltools.com/">Airfoiltools website</ExternalLink>

---

### 9) AirShaper <a name="airshaper"></a>

<ImageWithCaption
 src="/assets/images/airshaper-simulation.png"
 alt="AirShaper"
 width="700"
 height="391"
 positionCenter={true}
/>

##### What is it?

- AirShaper is a cloud-based virtual wind tunnel software that runs CFD simulations on 3D models

##### Why do we like it?

- It's very accessible as no license is required, you just need internet access
- You can upload your own 3D models easily and these don't even have to be watertight
- Simulations run quickly and afterwards, you receieve a PDF report containing all the results and graphs

##### Where can you find it?

- Log in to run your own CFD simulations on the <ExternalLink href="https://airshaper.com/">AirShaper homepage</ExternalLink>
- Find out how to use AirShaper to <ExternalLink href="https://airshaper.com/videos/how-to-run-an-aerodynamic-simulation/O_DNDxCtI_I">run aerodynamic simulations</ExternalLink>
- For further information on aerodynamic theory, concepts and applications, check out <ExternalLink href="https://airshaper.com/videos/page/1">AirShaper's video database</ExternalLink>

---

## General interest

There are also plenty of online resources that explain interesting aerodynamic concepts from industry that you can then apply to your own projects. There’s nothing better than gaining a new insight into a topic without it feeling like you are actually learning!

### 10) KYLE.ENGINEERS <a name="kyleengineers"></a>

<ImageWithCaption
 src="/assets/images/kyleengineers.png"
 alt="KYLE.ENGINEERS YouTube channel"
 width="700"
 height="418"
 positionCenter={true}
/>

##### What is it?

- A YouTube channel which focuses on all things related to motorsport engineering

##### Why do we like it?

- This channel has been created by a former Formula 1 aerodynamicist, so there is a lot of aerodynamic content
- Good use of annotations which makes it easier to understand the complex aerodynamic concepts used in motorsport

##### Where can you find it?

- You can watch the videos on the <ExternalLink href="https://www.youtube.com/c/KYLEDRIVES">Kyle.Engineers Youtube channel</ExternalLink>

---

### 11) Official Formula 1 website <a name="formula1website"></a>

<ImageWithCaption
 src="/assets/images/f1-technical-website.png"
 alt="Technical page on F1.com"
 width="700"
 height="634"
 positionCenter={true}
/>

##### What is it?

- The Technical section of the official Formula 1 website

##### Why do we like it?

- As it's the official F1 website it has good access to photography, information and contributors
- Useful illustrations explain complex and often hidden aerodynamic tricks that race teams use to maximise performance

##### Where can you find it?

- You can find it on the <ExternalLink href="https://www.formula1.com/en/latest/tags.technical.4lP4Pth1kICO2iCQqGAIIU.html">Technical page of the official Formula 1 website</ExternalLink>

---

### 12) Aerodynamic books <a name="books"></a>

There are thousands of technical books that cover aerodynamics and although these require purchasing, this doesn't mean that they should be ignored. Below is a selection of our favourites and remember that many are available as eBooks and can be bought second hand from the likes of eBay and Adebooks.

#### 12.1) <ExternalLink href="https://link.springer.com/book/10.1007/978-3-642-56026-2">Computational Methods for Fluid Dynamics</ExternalLink>

<ImageWithCaption
 src="/assets/images/computational-methods-for-fluid-dynamics.jpg"
 alt="Computational Methods for Fluid Dynamics book"
 width="400"
 height="400"
 positionCenter={true}
/>

#### 12.2) <ExternalLink href="https://www.wiley.com/en-gb/Low+Speed+Wind+Tunnel+Testing%2C+3rd+Edition-p-9780471557746">Low-Speed Wind Tunnel Testing</ExternalLink>

<ImageWithCaption
 src="/assets/images/low-speed-wind-tunnel-testing.png"
 alt="Low-Speed Wind Tunnel Testing book"
 width="262"
 height="371"
 positionCenter={true}
/>

#### 12.3) <ExternalLink href="https://www.cambridge.org/core/books/lowspeed-aerodynamics/077FAF851C4582F1B7593809752C44AE">Low-Speed Aerodynamics</ExternalLink>

<ImageWithCaption
 src="/assets/images/low-speed-aerodynamics.jpeg"
 alt="Low-Speed Aerodynamics book"
 width="262"
 height="376"
 positionCenter={true}
/>

#### 12.4) <ExternalLink href="https://www.amazon.co.uk/Race-Car-Aerodynamics-Designing-Technical/dp/0837601428">Race Car Aerodynamics</ExternalLink>

<ImageWithCaption
 src="/assets/images/race-car-aerodynamics.jpeg"
 alt="Race Car Aerodynamics book"
 width="262"
 height="347"
 positionCenter={true}
/>

---

Our guide to the best Aerodynamic resources

## Back to the Future

The case for streamlined cars isn't new - for decades, mankind has searched for higher top speeds, especially in racing. And because aerodynamics are by far the most dominant force to overcome at high speeds (even at highway speeds, over half the energy goes to pushing air away...), reducing the aerodynamic drag coefficient has been key.

With 1.000+ HP Bugatti Veyron's and Chiron's, it's easy to think speeds above 400 km/h are a very recent achievement. But already in 1938, Mercedes reached 432.7 km/h with their W125 - on a public road!

<ImageWithCaption
 src="/assets/images/mercedes_w125.jpg"
 alt="The record breaking Mercedes W125 - Drag coefficient Cd of 0.235 (Image credit: mercedes-benz.com)"
 width="810"
 height="540"
 positionCenter={true}
/>

So how did the Mercedes W125 beat the Veyron decades ago? You guessed it - aerodynamics. The aerodynamic power required to push the air away scales with the cube of velocity, whereas mechanical losses (like drivetrain and rolling resistance) only scale linearly with velocity. So at these speeds, aerodynamics easily account for over 90% of all energy needs.

The Bugatti Chiron has a drag coefficient of around 0.36. That's not very impressive, but then again, sports cars are usually aiming for good downforce & style. An F1 car, for example, has a terrible drag coefficient of around 1.00, as it has enough power to overcome the drag penalty in favor of more downforce.

But when top speed is your goal, the case is different. The W125 had 'just' 616 HP (still a massive amount by 1938 standards) and still was able to reach over 400 km/h/. How? Via a super streamlined bodywork which featured a drag coefficient of just 0.235 - that's over a third more streamlined than the Chiron!

## Fuel economy

Of course, road cars need to carry people around, preferably in a practical, safe and affordable way, so the constraints are quite different. Still, as mentioned above, even at regular highway speeds, aerodynamics are by far the most important source of energy loss.

So it's no surprise OEMs have been trying to cut those losses, even long before the breakthrough of electric cars. After all, aerodynamic efficiency has a direct impact on fuel consumption. Ford, for example, experimented with different shapes for their "Probe" concept car series. The Probe V had a drag coefficient of just 0.137!

<ImageWithCaption
 src="/assets/images/ford_probe_y.jpg"
 alt="The Ford Probe Y - Drag coefficient Cd of 0.137 (Image credit: hotcars.com)"
 width="810"
 height="540"
 positionCenter={true}
/>

## It's all about the looks

So why don't all vehicles look like this? Well, apart from practicality, I would argue the looks are the biggest problem. You could convince me to like such a shape, as I love aerodynamics, but a car for the masses simply needs to look stunning.

Recent attempts have been made to make cars as aerodynamic as possible while still maintaining good looks, like the Lightyear One (featuring a Cd value "below 0.20") and the Mercedes EQXX (featuring a Cd value of 0.17!).

<ImageWithCaption
 src="/assets/images/mercedes_eqxx.jpg"
 alt="The Mercedes VISION EQXX concept - Drag coefficient Cd of 0.17 (Image credit: mercedes-benz.com)"
 width="810"
 height="455"
 positionCenter={true}
/>

Still, although it looks nice, I think this design is "compromised". The long, low tail, for example, is very specific. Too specific to appeal to the masses, at least in the beginning.

That's why I'm so impressed with cars like the Tesla Model S Plaid and the Lucid Air, which both claim a Cd value of around 0.20. Yes, that's higher than the VISION EQXX, but only slightly. And in my opinion, the Tesla and Lucid both still look like normal cars - no compromise in terms of design and therefore much more appealing towards the masses.

## The EV push

With the breakthrough of electric cars, a lot of focus is now on the range of these vehicles. Every kWh/km of energy consumption that can be saved, makes the car cheaper (fewer battery cells), lighter (less battery weight) and more efficient (less weight means lower rolling resistance). With range anxiety holding back a lot of potential buyers, aerodynamics again play a key role. The more streamlined the car, the bigger the range for the same battery.

It's not a coincidence that Tesla has a massive focus on aerodynamic efficiency - not only for their cars, but also for the Tesla Semi truck. And they are not alone: newcomers like Lucid and Rivian also work hard to make surfaces as clean and streamlined as possible.

## The Future

So what could we achieve in the future in terms of no-compromise design? Well, a lot depends on what you define as "no-compromise design". Some designs just take time to get used to.

#### GAC ENO. 146

If we stick to open wheels, then the GAC ENO. 146 concept, presented in 2019, presents a nice example of what is possible. A drag coefficient of just 0.146 is extremely low, even compared to the EQXX, and the car still looks fairly normal in terms of proportions / tail length.

<ImageWithCaption
 src="/assets/images/gac_eno.jpg"
 alt="The GAC ENO. 146 concept - Drag coefficient Cd of 0.146 (Image credit: evspecifications.com)"
 width="810"
 height="377"
 positionCenter={true}
/>

#### Pimp my Tesla Model S Plaid

Another option is to further refine existing designs and perhaps add just a little bit of compromise. Vincent Keromnes, domain leader dynamic benchmarking at our partner <ExternalLink href="https://portal.a2mac1.com/">A2MAC1</ExternalLink>, took a Tesla Model S Plaid (yup, they 3D scanned the whole car down to the last detail) and then covered the rear wheels (like on the Lightyear One).

<ImageWithCaption
 src="/assets/images/tesla_model_s_plaid_with_wheel_covers.jpg"
 alt="The Tesla Model S Plaid with wheel covers - 3D models by A2MAC1"
 width="810"
 height="411"
 positionCenter={true}
/>

Vincent then ran both cars on our platform and the results couldn't be more clear: the wake & energy loss normally caused by the rear wheels "chopping up" the air has been reduced dramatically. The impact on Cd? A 3.5% drop in drag coefficient, which is very significant in terms of aerodynamic efficiency!

#### Aptera

You can actually go even further and question the entire layout of modern cars - start over from scratch, aiming for the highest possible efficiency. That is exactly what Aptera did - they basically took a drop shape and added wheels to it. 3 that is, not 4.

<YouTubeEmbed
 videoId="VwQXGKmDGgU"
 title="Aptera - Drag coefficient Cd of 0.13"
/>

## A note on Cd values

The Cd values in the article are the official values as stated by the manufacturers. Very often, we see differences when taking these cars to the wind tunnel.
Different tyres, rims, ride height settings etc can make it harder to compare these cars.
Nevertheless, the relative differences in this article do tell a very interesting story of substantial progress.

## Conclusion

The aerodynamic efficiency of vehicles has come down dramatically, especially with the focus on range for electric vehicles. Somehow, it feels like we have not reached the limits yet and we may be seeing even more streamlined designs in the future!

Some may look like normal cars with cleverly concealed aero tricks. Others may look downright futuristic and appeal to a more specific audience. But one thing is certain: aerodynamics will play a key role in the design of our future (electric) cars!

##### Interesting links:

 

<Link href="/videos/how-to-run-an-aerodynamic-simulation/O_DNDxCtI_I">
 How to run your own simulation
</Link>

 

<ExternalLink href="https://portal.a2mac1.com/">A2MAC1</ExternalLink>

 

<ExternalLink href="https://aptera.us/">Aptera</ExternalLink>

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