## Introduction 📢

Train aerodynamics is a fascinating, yet sometimes forgotten world, particularly with the increasing number of high-speed trains that are currently in use worldwide. We had the pleasure to interview two experts working at <ExternalLink href="https://www.caf.net" >CAF</ExternalLink>, a rail systems company born in the Basque Country (Spain) which designs, manufactures and maintains rail systems around the globe. Joseba Murua, head of the dynamics and rolling area within the R&D department, leads a team focused on analysing suspension forces and vehicle–track interaction. On the other hand, Mikel Iraeta works in the fluids mechanics department, predicting the external aerodynamic phenomena related to high-speed trains.

<ImageWithCaption
 src="/assets/images/CAF-oaris.jpg"
 alt="The CAF Oaris train - Image credit: CAF"
 width="800"
 height="542"
/>

## The role of train aerodynamics

**What are the main focus points when working on the aerodynamics of trains?**

(Mikel) Acknowledging that trains are a means of transport used daily by millions of people, passenger safety is a top priority. My team ensures that European guidelines are followed, such as the Council Directives on interoperability of the trans-European high-speed and conventional rail systems and the Technical Specifications for Interoperability (TSIs). Safety is determined by the stability of the train as well as its functioning in case of failure or accident.
Although train aerodynamics varies greatly among the different types of vehicle to be analysed and is highly dependent on operating conditions such as speed range, exposure to crosswinds, altitude and tunnel operation, there is a common focus point: efficiency. There is an increasing demand from the European Union towards designing long-term sustainable vehicles which maximise energetical performance. This implies an improved vehicle design based on experience, collected data and simulations (predicting drag, head pressure waves and crosswind stability, among others) that shall lead to a better train performance and tends to avoid the overestimations of components.
(Joseba) The increased efficiency requirements have a crucial impact on the vehicle system dynamics, which we analyse by evaluating stability behaviour, curve negotiation, rolling physics and train-infrastructure interaction, among others. In particular, the response to cross winds has to be considered.

<ImageWithCaption
 src="/assets/images/train-aerodynamics-cfd-mesh.jpg"
 alt="Computational mesh for the CAF Civity train - Image credit: CAF"
 width="1980"
 height="1080"
/>

## Crosswind Effect

**What is the importance of crosswind and how does it affect train dynamics and safety?**

(Mikel) The stability against crosswind is a technical compatibility problem that can be described by three aspects:

- The wind speed a vehicle is able to withstand in some reference conditions
- The wind exposure of the line
- The characteristics of the infrastructure

This means that equivalent wind conditions (in terms of wind speed and angle of attack) will not necessarily have the same effect on all trains. For example, the resulting wind force acting on a vehicle running over a 6 m high embankment will be different from the resulting force acting on a vehicle running on a flat ground for the same wind conditions.
The role of the train manufacturers is to determine the wind speed the most sensitive car of the unit is able to withstand for some given conditions. At European level this is carried out according to the EN14067-6:2018 which is the normative reference for this purpose and is applicable for vehicles running above 140 km/h. The methodology described in the standard implies:

- An aerodynamic characterisation of the studied vehicle. This is normally carried out by wind tunnel tests where the aerodynamic coefficients are obtained.
- A characterisation of the vehicle performance against crosswinds. For this purpose multibody simulations are usually performed by using a validated vehicle model that uses some input data such as the previously obtained aerodynamic coefficients

As a consequence of this process a number of CWCs (Characteristic Wind Curves) are obtained, which show the wind speed the vehicle is able to withstand for certain simulated conditions.
However, establishing a safe operation strategy is the responsibility of the infrastructure manager, who is given inputs on train assessment, infrastructure characteristics and path environmental characteristics.
The higher the train speed, the more sensitive it is to perturbations and the more likely (although worst case scenario) overturn is.

(Joseba) We must therefore estimate the dynamic response of trains after a velocity perturbation or lateral force, as in aircraft aerodynamics.

## Head pressure pulse & slipstream

**The effect of a train passing through a station is also an important aspect. Can you detail how this affects safety of passengers and railway workers?**

(Mikel) In order to answer this question, we must first picture a train as a large mass in movement that disturbs the pressure and velocity field around it. The acceptable amount of perturbation is determined, once again, by the TSI and the European Standards (EN) that determine the limit of acceptable pressure variation and wind speeds.
The safety distance (measured relatively from the person to the closest surface of the vehicle) is determined by the magnitude of the velocity and pressure induced, which is directly proportional to the size and geometry of the train.
Although a more appropriate approach to this question is "what is the velocity at which the train should be approaching", rather than "what is the safe distance at which passengers should be from the train". It is for this reason that the train velocity is always reduced when approaching a station.

<ImageWithCaption
 src="/assets/images/train-aerodynamics-pressure-slice.jpg"
 alt="Static pressure at the front of the CAF Oaris train - Image credit: CAF"
 width="1920"
 height="956"
/>

## Tunnel train performance

**What are the main challenges associated with tunnel entrance and exit?**

(Mikel) As mentioned, when a train is in movement, it displaces a large air volume around it. When the vehicle is in open air, this perturbation is not constrained, unlike in tunnels, where air displacement is limited by the tunnel’s cross section.
At the entrance of the tunnel, part of the air perturbed is displaced forwards as a wave front while part of the air is moved rearwards out of the tunnel..
Every time a train enters or leaves a tunnel it creates a pressure change that will be higher or lower than the given atmospheric pressure. This pressure variation is propagated into the tunnel as a wave front at the speed of sound. When the pressure wave reaches the end of the tunnel, it is partly dissipated into the atmosphere while the rest is reflected back at the portal. In case the incident wave front was above the atmospheric pressure (which is the case when the train head enters the tunnel) the reflected wave at the opposite portal will be under the atmospheric pressure and vice versa.
When the tail of the train enters the tunnel, a similar process occurs: the wave front below the atmospheric pressure travels upstream and will be reflected at the opposite portal as a wave front above the atmospheric pressure.

All of these waves cause two phenomena to occur simultaneously. On the one hand, in the vicinity of the train surface, a quasi static flow field can be assumed (even if it is not strictly quasi static, the observed variations may be considered negligible to the overall values). On the other hand, the train will be moving through a complex superposition of waves due to the interaction with the wave fronts. Additonally, the air between the tunnel walls and the train surface will be constrained, as the combination of wall and surface boundary layer growth reduces the effective area in between. The smaller the ratio of tunnel to train cross section, the more significant this effect will be which can have a big impact on the wave fronts and the drag in tunnel.

**Does the interaction between these compressible waves cause vibrations in the train?**

(Mikel) A vibration may be induced and noticed by passengers at the entrance and exit of the tunnel, but not along the journey inside the tunnel. A small impulse is induced, but is not constant nor periodic, as the impulse is quickly normalised.

**How can the “tunnel boom” occur even if trains rarely travel above Mach 1?**

(Mikel) When the front wave reaches the end of the tunnel, the energy transmitted to the outside is propagated in a way that can produce a sonic boom. After all, we are talking about a large variation in pressure within a very short timescale and this can be manifested in an audible manner known as tunnel boom.
This potential boom would not be perceived by the passengers, as the pressure waves are propagating much faster than train speed. It would only be heard by someone standing outside the tunnel, which is why special consideration must be given to this effect if people live in the vicinity of a high-speed train tunnel. Moreover, it’s a complex phenomenon, difficult to predict as it doesn’t occur in all trains nor tunnels, only within specific characteristics and speed ranges.

**Is the induced pressure on the windows significant enough to be considered?**

(Mikel) The pressure inside the tunnel is limited by regulations to ensure that windows do not burst under pressure.
(Joseba) Both the pressure and velocity inside tunnels are estimated using our own application, which was developed between CAF and the Universidad Politécnica de Madrid. A full CFD analysis is not required in this case and therefore a computationally less costly application can be used.
(Mikel) The pressure experienced by the surfaces is determined so that manufacturers can design the windows and doors accordingly.
Although window burst due to pressure is not very worrying, special attention must be taken when considering the scenario of debris impact that has a higher probability of bursting a window. This would induce a great pressure variation that could be harmful to passengers, causing ear damage. Once again, the maximum pressure variation acceptable is set by safety standards.

## The pantograph

**What is the effect of the pantograph on the aerodynamics of the train?**

(Mikel) Pantograph effect is only considerable at high speeds, where it can cause not only aero acoustic issues, but also propagate waves in the catenary. Moreover, it is important to understand that the pantograph is a contact between a metallic thread and a rubbing band. It is this contact that provides the energy supply to the train and therefore, it should not be interrupted. The contact must be constant and stable, which is difficulted in the presence of oscillatory forces that may indeed be aerodynamic forces but can also be induced by mechanical movements. To ensure stability, dynamic tests are performed to estimate the forces experienced and the number of actuators and dampers required. It is very difficult to simulate, which is why it is mostly based on experimental data.

(Joseba) The aerodynamic effect of the pantograph is quite peculiar, because although it is very local (as it only acts within a small percentage of the train’s surface), it is highly affected by the globality of the train. The boundary layer developed upstream of the pantograph is critical and complex to predict, and the velocity profile seen by the pantograph is very intricate and three-dimensional, particularly acknowledging the disturbances that roof-mounted systems cause on the flow field.

## Frontal Shape Efficiency

**How is the train’s head designed to ensure maximum efficiency?**

(Mikel) There isn’t a direct answer, as we need to consider for which parameter is the head optimised for, depending on the vehicle to be designed. It is evident that in trams and subways, the frontal shape is not very important, but as operating velocity increases, the head will have different functions and will affect factors like the wave front and pressure waves strength, stability, drag and crosswind effects, as the geometry can condition the way flow is propagated downstream and its interaction with other train systems.
Therefore, an “optimal” design cannot be found such that it minimises all detrimental effects, but a good enough design can be found such that it satisfies all requirements.
Usually, past vehicle data is used as reference on which innovative designs are based, which are later validated in railway trials or wind tunnel tests.

<ImageWithCaption
 src="/assets/images/train-aerodynamics-pressure-contours.jpg"
 alt="Static pressure countours around the CAF Civity - Image credit: CAF"
 width="3840"
 height="2160"
/>

I am particularly fascinated by Japanese trains heads, whose lengths can range up to 15 m, far larger than the maximum 6 m commonly designed in Europe.
One would be surprised with such design, particularly because the nose cannot host passengers and it is therefore “unused” space which could theoretically minimise the financial benefits of such train. But it is because of the bullet trains operating speeds of over 300 km/h that these noses are needed to avoid tunnel booms. They ensure that the transition of free area to tunnel restriction is more gradual, such that the pressure waves act within a longer timescale, progressive, alleviating this phenomenon and attenuating the sonic boom effect.

## An aeronautics point of view

(Joseba) Having an aeronautics background, it is interesting to present an analogy and a difference between aircraft aerodynamics and train aerodynamics.
Starting from the analogy, in both cases their design is highly limited and determined by safety considerations. At the end of the day, it is human lives that are at risk on both vehicles. It is for this reason that all developments and changes undergo a great quantity of checks and standard compliance before they can be introduced in the market. All aerodynamic analysis and predictions must have solid foundation that can back up the safety of their implementation.
With regards to the main difference, an airplane is a lifting body while a train is not, which is why much of the aerodynamic knowledge that was obtained a century ago is not always applicable to the analysis of trains.
I particularly believe that the aerodynamical theoretical foundation of trains has not been as widely studied and developed as airplane aerodynamics, which is why we must, more often than not, rely on simulations and empirical data to obtain the knowledge that we require of our vehicle.

Interesting links:

<ExternalLink href="https://www.caf.net/">CAF</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/simulations/new?accuracy=regular">
 Run Your Own Simulation
</ExternalLink>

High-speed Train Aerodynamics

## Introduction 📢

For this blog post, Nicolas Berberoff interviewed James Warren, head of communnication at <ExternalLink href="https://www.airspeeder.com">Airspeeder</ExternalLink>. Airspeeder is an upcoming racing series with a bespoke Octocopter set to reach speeds of up to 200 km/h!

## Racing to solve congestion?

<ImageWithCaption
 src="/assets/images/speeder1.jpeg"
 alt="The high-performance AirSpeeder Octocopter"
 width="1080"
 height="720"
/>

**Talk us through the actual nature of this competition, the origins of the company. Why translate motorsports to the aerospace sector?**
One must start by apprising the scale and potential of electric takeoff and landing (eVTOL) vehicles, the next great mobility revolution. In its commercialised form it promises to liberate our cities from congestion, massively cut journey time in urban areas and revolutionise aerial logistics. This industry is estimate to be worth more than 1.2 trillion dollars by 2040, backed by the likes of Uber, Daimler, Toyota, Porsche and many other manufacturers.
What we have envisioned is that despite the shift to autonomous transport, there will always be a desire amongst people to drive or pilot vehicles. Our founder Matt Pearson, after finding success in a technology start-up in south Australia, found himself in a position where he had time and resources on his hands and was frustrated he couldn’t buy a flying electric car, something we have been promised for years in science fiction.
He decided to investigate the automotive history and aviation to see what elements accelerate the development of such technologies, assessing how mobility revolutions have come across and societal acceptance has been built up. Competition is within human nature; thus, racing will always remain relevant. Historically competition has propelled the acceptance and incorporation of such technologies into our lives, so we at Airspeeder are playing that same role with the revolution of flying cars.

**Establishing a bond with society is important, technology must be relevant. How does Airspeeder intend to impact society?**

We impact society in the sense that we are working towards a technology that will liberate congestion, by utilising a clean-air technology, let’s not forget the environmental impact too. We are proud of the role we are already playing in hastening that technology; bringing to maturity quicker, answering safety questions quicker, being more robust in testing or even addressing noise pollution quicker than the design process of a passenger craft will.
Hence the technological advances that we are making, are going to make the development of passenger taxies possible, underpinning the technology that will eventually be there. Racing but with purpose, much in the line of what Formula 1 has brought us; ABS, energy recovery systems etc.

## A Blank Sheet of Paper

<ImageWithCaption
 src="/assets/images/speeder2.jpg"
 alt="The Airspeeder - Literally taking the race from the tarmac to the sky"
 width="1920"
 height="1080"
/>

**Will this be considered motorsports? How are other racing institutions reacting to this?**

We are widely regarded, certainly in racing communities, as the Formula 1 of the skies. There are several implications to this. Number one, when you are defining a new sport, new technology and craft to go with it, you start with a completely blank sheet of paper. We are not having to fight against the traditions or legacies that other sports might face. Thus, we can design the sport from a conceptual stage, defining its essence, deciding the way that we enable teams to approach racing.
For example, we as Alauda Aeronautics Pty Ltd. will supply the craft to different teams so that the technological plane field will be completely even. Hence allowing teams to have separate strategies and recruit their own pilots, resulting in an ‘ideal’ equitable competition that we, all motorsports fans, want to see. Without doubt, it will certainly be something people will globally respond to. In terms of how we interact with our fans, we are yet exploring; not bound to existing broadcast agreements or restricted in any other way, we have complete freedom. The way we are approaching the spectator interaction is as a very two-way competition; fans will be able to live-stream the races, interact with the pilots and engage with the sport itself.

**Currently there are openings for pilots. What backgrounds or requirements should those pilots have?**

Again, starting form this blank sheet of paper, we made an open call to elite pilots. Back in June, Matt Pearson spoke in an event hosted by an organisation called Mobility Prime; basically, the US AirForces’ accelerator eVTOL technology. People have come to us from a range of backgrounds; test pilots from civil and military backgrounds, very strong acrobatic and competition pilots. To our minds, we don’t want to limit it, we are making an encouraging call to strong UAV or even drone pilots. Same thing goes with people from esports.

**With there be different locations across the season?**
Number one focus at the moment is in 2021. We have already spoken about Coober Pedy desert in South Australia, or the Mojave Desert. During this first season (season alfa), there will likely be one-on-one time trial races or duels. In the future it will be opened up for a much larger grid. Note that our MK4 craft, reaches 130kph, flying around an electronically governed circuit around the locations in time trial. Eventually everything will build up to more traditional close-racing events. Technology is ready; by combining lidar sensors and virtual force fields we will liberate our pilots to race each other hard.

## High Tech Racing Nostalgia

<ImageWithCaption
 src="/assets/images/speeder3.jpeg"
 alt="The Airspeeder blends nostalgic design cues with high-tech performance"
 width="1080"
 height="719"
/>

**Design seems to be inspired by Formula One cars from the fifties with the air intake at the front, I suppose this also satisfies cooling requirements for batteries and systems? How much performance are you getting from batteries, range-wise, maximum thrust and so on?**

Our Head of Design, Felix Pierron really worked to create a profile that instantly evokes the sense of a racing craft. This is so important to building enthusiasm and acceptance for Vertical craft like ours. In many ways, design of a flying racing car is dictating by the need for performance in the same way the F1 cars of the fifties and beyond were. Air intakes are therefore not superfluous they are there to cool the high performance electric powertrain. While our contemporaries in the eVTOL passenger sector are focused primarily on range, efficiency and the ability to carry large loads we can be very focussed in developing the vehicle for pure performance and manoeuvrability. We will race at speeds of up to in 20 minute bursts with rapid pitstops that will really add to the drama and tension on race-days. We aim to race at speeds up to 200km/h.

<YouTubeEmbed
 videoId="Fl0hl2_E9Mg"
 title="How eVTOL Flying Cars Are Made | Airspeeder Factory Tour at Goodwood SpeedWeek"
/>

## Blending Design, Safety and Aerodynamics

<ImageWithCaption
 src="/assets/images/speeder4.jpeg"
 alt="The Airspeeder will even feature pitstops!"
 width="1000"
 height="1000"
/>

**How did you work on aerodynamics in general: lots of simulations? Did you involve industry experts? Did you / do you plan on doing wind tunnel tests?**

We’ve gathered a team of engineers and designers drawn from both the aviation and performance automotive worlds. With that, we are able to blend knowledge and processes from multiple disciplines including computer modelling and simulation. They will work with wind tunnel testing to hone aerodynamics that are then validated through extensive flight testing.

**Why this layout (4 double props on each corner)? Very good for manoeuvrability, less energy-efficient?**
The real benefit of the a performance eVTOL craft in this configuration is the rapid manoeuvrability that physics dictates is not possible with more traditionally specified aircraft. In essence, our pilots will have the same rapid hairpin turning ability at their disposal as an F1 driver but with the addition of a third dimension because we’re in the air. We refer to our layout as an octocopter ‘H configuration’ - this adds an important layer of safety as it adds redundancy. In event of a motor failure the craft will not become unstable as per a traditional quadcopter setup.

**The "rotor arms" have been given an aerodynamic profile, is that correct? How do they contribute to the performance of the aircraft?**
Like any craft participating in an elite sport, every surface or function must be honed to do perform optimally. Our philosophy here is that form must absolute service function, therefore the shape of the rotor arms does much to make the craft move through the air efficiently which provides enormous benefits in terms of overall performance and manoeuvrability. To go into more detail, they have an airfoil profile to improve performance by generating lift and reducing drag.

<YouTubeEmbed
 videoId="JaAVelVsaU4"
 title="Powering Up Our eVTOL Flying Car | Airspeeder"
/>

## Conclusions

The Airspeeder series promises to pave the way for new urban air mobility technology as well as to entertain the masses. Will the virtual force field hold under the pressure of racing? Will the pitstops cause drama during the races? And most importantly, does air mobility really hold the key to sustainable transportation, truly reducing CO2/km without shifting the congestion problem to the skies? Let's find out when the Airspeeder series kicks off in 2021!

Interesting links:

<ExternalLink href="https://www.airspeeder.com">Airspeeder</ExternalLink>
 

<ExternalLink href="/videos/nascar-in-the-sky-interview-with-air-race-e/kcx23YY1Kms">
 Air Race E
</ExternalLink>
 

<ExternalLink href="/blog/formula-air-grand-prix">
 Formula Air Grand Prix
</ExternalLink>

Airspeeder - The Electric Flying Car Racing Series

## About the Author 📢

Sheetalkumar Patil is founder and director of <ExternalLink href="/partners/engineering/speed-engineering-solutions">Speed Engineering</ExternalLink> where they focus on engineering for a wide variety of segments like aerospace, automotive, electronics and so on. In this article though, the speed is much reduced as he takes us through the process of optimizing the aerodynamics of the famous Rickshaw at just 15 m/s.

## Introduction

When people think of aerodynamics, they automatically think of airplanes flying at 800 km/h, rockets blasting into space or race cars lapping the Nürbürgring at insane speeds. But aerodynamics play a role as any object starts to move through the air, no matter how low the speed. And they start to play a significant role, i.e. an impact on fuel consumption & range well above 10%, at much lower speeds than people would expect. In this article, we dive into the details of the Rickshaw, one of the most popular vehicles in India & Sout-East Asia. And we come to the conclusion that much can be gained from improving its aerodynamics!

## Bluff body aerodynamics

In fluid mechanics terms, vehicles are bluff bodies travelling very close the ground. A complex three-dimensional flow occurs around the vehicles with flow separation being very common. Such flow is typically analysed and optimized through external aerodynamics studies.

Sports cars, passenger cars and commercial vehicles - all of which move at relatively high speeds - experience significant aerodynamic drag forces which impact performance and increase fuel consumption. For ground vehicles, this is mainly pressure drag; so avoiding or reducing the separation is one of the main objectives of vehicle aerodynamics.

External aerodynamics is also becoming increasingly important in the shift from fossil fuel vehicles to electric vehicles. In the context of electrification of vehicles, the drag force is an important factor to be considered as it impacts the operating costs of the vehicles, sizing of the drive train and the range of the vehicle before recharge. Reducing drag force is important even for relatively slower speed electric vehicles and if not optimized, it can have significant impact on cost and performance. Therefore, design improvements through external aerodynamics simulations of drag resistance using CFD is a necessity for all electric vehicles.

External aerodynamics simulations using CFD though have some constraints, such as:

- Huge time required to create watertight geometry. This task is very tedious.
- High-end hardware requirement to reduce the analysis turnaround time (high RAM and number of CPU cores etc.).
- Huge computational costs. Major drawback of high-end computation is cost (hardware + software license).
 During the conceptual and preliminary design phases, these constraints may prove detrimental to the project's timeline and budget.

Here we are presenting a case study to depict how CFD analysis can be used to improve aerodynamics of a relatively slower speed commercial vehicle while overcoming the above constraints.

## The Baseline Rickshaw Design

This case study has been performed on the legacy design of auto rickshaw (3-wheeler). It is mainly used as short distance taxi in India and South Asia. The body design was done in the last century and aerodynamic considerations were not the primary factors back then. If we want to convert such vehicle to an electric one, we need to consider aerodynamics and check how much electric power can be saved and also, if the range can be increased through design improvements to the body shape.

The shape of the 3-wheeler considered for this study is as shown below.

<ImageWithCaption
 src="/assets/images/3wheeler_baseline_design.jpg"
 alt="The baseline Rickshaw 3-wheeler design"
 width="1182"
 height="776"
/>

- This design is primarily used with a gasoline engine.
- Engine power rating is around 7.5 kW@4500 RPM with a peak torque of 19 Nm@3200 RPM
- Carries a maximum of 4 people - 1 driver + 3 passengers.
- The range of the vehicle is around 350km with full tank.

## Revised Design

Based on the AirShaper results of the external aerodynamics study on the baseline design, the body shape was revised within the following constraints:

- Change in overall envelope should be minimal. No change in the ground clearance.
- No change in the drive-train interfaces (track, wheelbase etc.)
- Driver and passenger comfort should not be affected. No interiors should be affected.
- No major changes in ergonomics etc.

The following changes were made to the baseline design:

- The underfloor was made flat. All the steps are removed.
- The roof was given a downward slope towards the rear to delay separation.
- The frontal area was made more round.
- A feature just above the rear wheels was added to bleed air in the wake region.

The revised design is depicted below.

<ImageWithCaption
 src="/assets/images/3wheeler_revised_design.jpg"
 alt="The revised Rickshaw 3-wheeler design"
 width="1327"
 height="829"
/>

## Simulation Results

Both designs were analysed for aerodynamic performance at a vehicle speed of 15 m/s. The drag coefficient of the Rickshaw has dropped form 0.45 to 0.39. This reduces the power required to overcome aerodynamic forces by 17.4 %. This will result in an increase in the range of the vehicle as well.

<ImageWithCaption
 src="/assets/images/3wheeler_drag_curve.jpg"
 alt="The drag coefficient of the baseline and revised Rickshaw design"
 width="1287"
 height="367"
/>

<ImageWithCaption
 src="/assets/images/3wheeler_drag_table.jpg"
 alt="The drag force & power of the baseline and revised Rickshaw design"
 width="663"
 height="302"
/>

The aerodynamic plots below, comparing the baseline & revised design, show how various aerodynamic considerations were implemented:

- The wake should be as small as possible (see "red clouds" behind the vehicle). This was achieved by an improved roof line, the removal of steps in the underfloor and the bleeding of air into the wake via slots on the sides of the vehicle.
- The pressure build-up at the front was reduced by increasing the radius of the front of the vehicle.
- The number & size of separation locations was reduced by eliminating steps at the underfloor, sharp edges at the front, and so on.
 The modifications done on the baseline geometry based on the recommendations by CFD analysis show significant improvement in the drag performance of the vehicle.

<ImageWithCaption
 src="/assets/images/3wheeler_pressure_clouds.jpg"
 alt="The aerodynamic wake locations of the baseline and revised Rickshaw design"
 width="1289"
 height="511"
/>

<ImageWithCaption
 src="/assets/images/3wheeler_surface_pressure.jpg"
 alt="The aerodynamic surface pressure locations of the baseline and revised Rickshaw design"
 width="1315"
 height="602"
/>

<ImageWithCaption
 src="/assets/images/3wheeler_streamlines_side.jpg"
 alt="The 3D streamlines around the baseline and revised Rickshaw design - side view"
 width="847"
 height="733"
/>

<ImageWithCaption
 src="/assets/images/3wheeler_streamlines_top.jpg"
 alt="The 3D streamlines around the baseline and revised Rickshaw design - top view"
 width="933"
 height="719"
/>

## Efficiency

The total project was done in just 50 hours, of which 40% was CFD run time. The rest of the time was spent on geometry modifications, post-processing the data and drawing conclusions & reporting. So, computationally this is not a very expensive analysis.

## Conclusions

- Estimating the performance parameters related to external aerodynamics by CFD during vehicle development can yield significant benefits even for relatively slow vehicles.
- Design improvements to the body shape based on external aerodynamics can help reduce drag, reduce power consumption and improve range. This is especially important for electric vehicles.
- The CFD analysis method presented here, gives an opportunity to perform external aerodynamics CFD analysis at very low cost and which is adequately accurate. In this arrangement, multiple CFD analysis iterations of external shapes are possible within a short timeframe.

Interesting links:

<ExternalLink href="/partners/engineering/speed-engineering-solutions">
 Speed Engineering
</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com">
 Running your own CFD Simulation
</ExternalLink>
 

<ExternalLink href="/videos/cfd-results-how-to-interpret-an-aerodynamic-analysis/XntO27S5Urc">
 How to interpret a CFD Simulation
</ExternalLink>

Rickshaw Aerodynamics - Drag at 15 m/s

## About the Author 📢

Yann Le Fraillec works at <ExternalLink href="https://www.decathlon.com">Decathlon</ExternalLink> as Project Manager, engineering bikes, helmets and more. In this article, he explains how they benchmarked the aerodynamic of their own helmets versus that of the competition. To that end, they used 3D scanned models made by <ExternalLink href="/partners/engineering/jf3d">JF3D</ExternalLink> and ran those through AirShaper for a digital comparison.

## A New Identity

Up until 2019, all Decathlon bikes & helmets were part of the BTWIN label. But as of January 2019, Decathlon decided to use the BTWIN brand mainly for kids bikes and create 2 additional brands for the road bikes, each with a different identity:

- Triban: aimed at enjoying cycling in a comfortable way
- Van/Rysel: aimed at performance, with less compromise towards comfort. Named after the Flemish name of Lille, the city where Decathlon HQ & BTWIN Village are located. And perhaps more importantly, Rijsel (Lille) is the capital of the (French) Flanders region - the cycling-walhalla with classics like Paris-Roubaix!

## Van/Rysel - On a mission

There are numerous challenges to developing a performance brand: each product needs to improve on the performance & experience of the rider. When we dediced to create an aerodynamic helmet, we needed a starting point. We applied digital simulations to our own helmet to understand the airflow. In a first iteration, we compared our new design to our existing Endurance helmet, the Van/Rysel 900.

<ImageWithCaption
 src="/assets/images/aerodynamic_comparison_decathlon_old_new_helmet.jpg"
 alt="Aerodynamic comparison between the existing Van/Rysel helmet and the new design"
 width="1916"
 height="452"
/>

The simulations provided us with good insights, but the real challenge came when comparing to the competition - that was an entirely new game.

## Benchmarking the competition

We had 3D scanned models of Ekoi and Giro helmets and mounted those on a "generic" head to have an objective reference.

<ImageWithCaption
 src="/assets/images/3d_scans_of_helmets.jpg"
 alt="3D scans of the Van/Rysel Giro & Ekoi helmets position on a generic dummy head"
 width="2000"
 height="751"
/>

Of course much depends on the "angle" of this head (tilting a bit more forward or backward can really change the ranking), but we had to start somewhere. When the results of our first design came in, they were bad and simply not acceptable for a performance brand claiming to deliver performance.

<ImageWithCaption
 src="/assets/images/aerodynamic_drag_cycling_helmets.jpg"
 alt="Aerodynamic comparison between the Van/Rysel, Giro and Ekoi helmet"
 width="1999"
 height="539"
/>

## Aiming for the win

So we kicked off an aerodynamic development track together with AirShaper to improve the performance of our design. Digital simulations provide an easy and flexible way to virtually test the aerodynamics and learn as you go at a reasonable cost. And scanning competitor helmets to benchmark our own design is a really powerful and efficient way of making progress. Using the results, our design & engineering team is working hard to deliver drastic aerodynamic improvements. Our goal is to provide one of the most aerodynamic helmets out there and we won't stop until we achieve that.

Interesting links:

<ExternalLink href="https://www.decathlon.com">Decathlon</ExternalLink>
 

<ExternalLink href="/partners/engineering/jf3d">JF3D</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/sports-aerodynamics-1-winning-the-ironman-triathlon/DqlDpUFcScc">
 From 3D scan to Aerodynamic Analysis
</ExternalLink>

Decathlon explains - Using 3D scanning & simulations to design aerodynamic helmets

## About the Author 📢

Vincent Keromnes works at <ExternalLink href="/partners/engineering/a2mac1">A2MAC1</ExternalLink>, a company specialized in benchmarking the performance of cars. Lots of cars. Vincent is in charge of what they call "Dynamic Benchmarking", covering Kinematic & Compliance testing, Energy Management Strategy, Battery Thermal management and so on. With his hands on full 3D models on nearly every major car out there, he couldn't resist tweaking one of those cars on AirShaper to improve the aerodynamics :)

## Introduction

The launch of a new generation of the VW Golf is always seen as a major automotive event. A few months ago, we had already ran an AirShaper simulation on the Golf V (one with doors closed and <ExternalLink href="https://www.linkedin.com/pulse/my-first-aero-encounter-pushing-door-open-180-kmh-golf-remmerie-">one with Wouter's foot pushing the driver door open</ExternalLink> 😉) and on the Alltrack version of the Golf VII. So with the arrival of the Golf VIII at A2MAC1, we were curious to see the evolution in aerodynamics over the years. Also, we couldn't stop wondering if there might be ways to further improve fuel consumption with minor tweaks to the car.

## From Golf V to Golf VIII

### Roofline

As you can see on the profile picture with the "pressure clouds" (isosurface for Cp equal to zero), the aerodynamicists have had lots of influence on the shape of the car, in particular with the end of the roof that is now really going down with a bigger spoiler thus reducing efficiently the height of the wake. You can also notice the A pillar improvement including the side view mirror area.

<ImageWithCaption
 src="/assets/images/golf_8_total_pressure_cloud_comparison_side.jpg"
 alt="Drag analysis of Golf V versus Golf 8 - Side view"
 width="1765"
 height="1109"
/>

### Wheels

The wheels of the VIII are far bigger and larger than on the V. This results in a larger wake close to the ground. But as you can see on the front picture this is balanced by an improved frontal coverage of the tire by the front bumper. As a consequence, the global efficiency of the wheel arch area is improved.

_Note: a reader has pointed out that there was no change to the available choice of tyre widths and sizes from Golf 5 to Golf 8_

<ImageWithCaption
 src="/assets/images/golf_8_total_pressure_cloud_comparison_front.jpg"
 alt="Drag analysis of Golf V versus Golf 8 - Front view"
 width="1379"
 height="1205"
/>

### Underbody

It's interesting to see that the famous golf ball structure was applied to the aero shield of the V version but abandoned on the VIII (it was already gone on the VII). At the same time, Audi has been making a lot of marketing around the use of this pattern on the underbody of the etron …

<ImageWithCaption
 src="/assets/images/golf_5_golf_ball_dimple.jpg"
 alt="Golf ball dimple pattern on the underfloor of the Golf V"
 width="2046"
 height="963"
/>

Apart from that side fact, it's quite remarkable that on the Golf VIII, as you can see on the picture, it looks like the underbody coverage extends backward only up until underneath the rear doors.

<ImageWithCaption
 src="/assets/images/golf_8_underfloor_dimension.jpg"
 alt="The underfloor cover of the Golf VIII doesn't extend all the way to the back"
 width="784"
 height="441"
/>

We could argue that it’s a challenging (and expensive) job to cover the areas with high levels of heat dissipation (exhaust line and associated products) but if we look at the underbody of the eGolfVII we can still see that the underfloor coverage stops before the battery pack.

<ImageWithCaption
 src="/assets/images/e_golf_8_underfloor_dimension.jpg"
 alt="The underfloor cover of the e-Golf extends further, but also not all the way to the back"
 width="784"
 height="441"
/>

### The numbers

The drag coefficient Cd has been improved by more than 12% from Golf V to Golf VIII. It’s important to notice that at the same time the frontal area has remained the same (about 2.23 sqm). That means that **from Golf V to VIII the overall drag has dropped by more than 12%**.

## Improving the Golf VIII Aerodynamics

### Design

Perhaps the underfloor wasn't extended all the way to the back because the gains in efficiency were too small? We kept wondering how much such efficiency gain would be, so we decided to design our very own "aero shield" by applying a few geometry modification. It is nicely cut (well, we did our best :) ) to respect the constraints of the hot parts from the exhaust line. As a consequence, it’s still not perfectly flat but it may be able to contribute to some improvement.

<ImageWithCaption
 src="/assets/images/golf_8_aero_shield_design.jpg"
 alt="The A2MAC1 aero shield design for the Golf VIII"
 width="784"
 height="472"
/>

### Aerodynamic Simulation

Proud of our design, we then launched simulations of the Golf VIII without and with aero shield to see how it would perform. Below you can see the effect it has on the flow underneath the car. The aero shield helps to maintain a cleaner flow all the way to the back of the car, as evidenced by the reduction in size of these "pressure clouds" (iso-surfaces for a total pressure coefficient equal to zero, in case you're asking :) ).

<ImageWithCaption
 src="/assets/images/golf_aero_shield_comparison.jpg"
 alt="Underfloor aerodynamics of the Golf VIII - without and with A2MAC1 aero shield"
 width="1495"
 height="1442"
/>

### The numbers

**The aerodynamic drag on the car was reduced by around 2%** - which is quite significant!
This reduction in drag can be extrapolated to **around 1g of CO2 savings per 100km**. Understandably, car manufacturers constantly need to strike a balance between profitability (the aero shield costs money and hinders maintenance) & emissions (clearly the aero shield helps to reduce emissions) and weight (we're guessing the aero shield would be fairly light). But still, it feels like this would be a fairly "affordable" win in terms of CO2 emissions.

## Conclusion

It's been very interesting to see how we can take a 3D scan of an existing vehicle to then modify it to see the effect on aerodynamics. The results suggest that there is definitely still room for improvement in terms of aerodynamic drag & fuel consumption! Sometimes small changes can have a big (positive) effect for the environment :)

Interesting links:

<ExternalLink href="/partners/engineering/a2mac1">A2MAC1</ExternalLink>
 

<ExternalLink href="/videos/cfd-results-how-to-interpret-an-aerodynamic-analysis/XntO27S5Urc">
 How to Interpret an Aerodynamic Simulation Report
</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/simulations/new?accuracy=regular">
 Run Your Own Simulation
</ExternalLink>

Volkswagen Golf Aerodynamics - How to cut emissions even further

## Introduction

Sometimes the limit to aerodynamic applications is only set by imagination. This time we had the pleasure of speaking to Jay White, Chief Technical Officer at Falcon Pursuit. We have focused on just one of the many fascinating and abstract projects they do in collaboration with the Red Bull athlete performance center.

<ImageWithCaption
 src="/assets/images/profile-picture-jay-white.jpg"
 alt="Jay White - CTO of Falcon Pursuit"
 width="248"
 height="248"
/>

## Extreme Sports and Science Combined

**How does this kind of project come together?**
Surfing came up because as part of the Red Bull performance group, we had just delivered our advanced avatar creation technology, the AVA kiosk to Santa Monica. In these buildings, things are going on that have less to do with delivering drinks, and more about athlete performance groups, e-sports and much more. We were scheduled to work with the triathlete Cameron Wurf and the surf team was also in the building, Ian Walsh being one of them. So, we put Ian into the Kiosk and scanned him in 3D, with and without his wet suit. Asked a few questions about what surfboard he was on currently, to get some basic data to model it.

We found some videos on Ian’s epic big wave ride achieved some months before. The challenge came when we had to model in 3D an ocean wave, which is incredibly dynamic, large and it interacts with the environment in subtle ways. That was the hard part of the story. Once finished, it was a matter of placing Ian’s avatar into the virtual model using 2D broadcast video, snapping his position into the surfboard, and modelling the wave + athlete + surfboard in dynamic 3D space.

<ImageWithCaption
 src="/assets/images/fullwave_Ian.jpg"
 alt="Aerodynamic simulation of Ian Walsh surfing a big wave - image by Falcon Pursuit"
 width="3184"
 height="1901"
/>

**Talk us through the transition from 2D footage to 3D model.**
The process of going from 2D to 3D uses an avatar. The avatar represents the way the athlete looks in space, same shape and even shirt colour. To do so, we “net” the athlete, taking off all the exterior baggy clothing to obtain a skin-tight surface. For a surfer that is no problem as it is basically how he performs naturally when surfing. Having done that, we ran it through our AI ARE (Avatar Rendering Engine), which takes that surface scan and clads it to an avatar adding joints, muscles, eye blink, moveable mouth etc.

Traditionally, this is a multi-day process. In movies for instance, they perform motion cpaturing using mounted sensor balls in 3D space, they hook it to a skeletal structure which in turn gets connected to an animated figure. It is a very long, tedious, high-end & precise engineering process that takes days to complete. Then there are literally hundreds of animators to converting 3D data from the actual actor moving around into a rigged character. All this cannot be done with the surfer since he is out on the wave, and such post-processing effort would be too expensive / slow.

Instead, what the AI ARE engine does is to track Ian in the 2D video footage and matches the 3D avatar to mimic his position. This allows us to model Ian in 3D space based on a single scene. Finer motion and details such as the position of head, fingers, foot and any accessories, is obtained from successive AI solves. Playing with the likelihood of certain positions, the AI does a secondary solve on that to locate such finer details on the avatar.

<ImageWithCaption
 src="/assets/images/avatar1.jpg"
 alt="The 3D Avatar of Ian Walsh on a surf board - image by Falcon Pursuit"
 width="3088"
 height="1901"
/>

The next step is to model the wave itself. For this, we used use Optical Flow. Here's how it works:
Say, for example, I take a picture of a baseball in flight with a normal camera, generally my frame rate is small enough that the baseball blurs only a bit. By taking an image at a high enough shutter speed, it will be super-sharp. By quantifying how much (parts of) images blur (one-thirtieth of a second, one sixtieth of a second image exposure time), you can tell the direction and velocity of that object. It allows us to accurately calculate the velocity for different parts of the wave front. Hence now having both the wave and Ian on a frame, we can calculate aerodynamic drag, hydrodynamic drag and more, based on parameters such as Ian’s velocity, wave velocity, salt content of the wave, air moving past him etc (note: this process has been patented under US patents 9,797,802 and 10,648,883).

## Analysis & Tangible Gains

**I imagine you can quantify lateral forces on the fins, drag coefficients… but how does this translate to actual improvements for the athlete?**
Skilled athletes understand how to look at and interpret their video footage, whether it’s a baseball swing or basketball shot. Taking the example of a gymnast, she goes running down the runway, hits the vault and does a flip. When we have 5 or so videos of successive vaults, we start evaluating and identify which ones were the best.

Adding the 2D to 3D analytics tells us that for the good vault, the hip rotation was 120 degs/s, shoulder rotation was 170 degs/s, centre of gravity and how far the foot hit from the vault when landing. Now having all these facts, we can interpret how shoulders over-rotated, hips under-rotated, and her CG was way far forward. Going back and forth through each simulation, the coach will understand what caused a successful event.

<ImageWithCaption
 src="/assets/images/aero_fins.jpg"
 alt="Hydrodynamic drag analysis on the fins of the surfboard - image by Falcon Pursuit"
 width="3092"
 height="1898"
/>

Now back to surfing, Ian coming across the wave front. His coach points out that in the successful manoeuvre where the wave did not crash upon him, his position was higher on the wave, water was moving a little faster and hence he was moving faster.

By positioning Ian 6 inches up in the wave, he will carry more speed. Evidence suggesting this might be an air current or how the air curves over the top. This software allows us to see where the air is moving in a favourable direction, pushing the surfer. Thus, we adjust the board angle to be in this position in order to have higher probability of a more successful event.

<ImageWithCaption
 src="/assets/images/ian_board.jpg"
 alt="Aerodynamic analysis of Ian Walsh on his surf board - image by Falcon Pursuit"
 width="3240"
 height="1896"
/>

## Simulation Details

**How do you go about the interaction between hydrodynamics and aerodynamics?**
With the more complex simulations, we model both simuataneously. Taking a “bottom turn” as example. When coming down, to go up again you could do a rail slide, a slip, or a flip manoeuvre. For this, the fins need to be in contact with the water, but with cavitation, the board will slip to the side instead of edging. Hence taking that snapshot and running a simulation, we may see that in the last one-sixtieth of a second, the fin went into the water to three-quarters of the way.

Cavitation happens when the fin reaches a certain angle relative to the water stall angle, that instead of slicing though it, bubbles generate in the trailing edge. Hence not contacting water anymore and loosing control.

<ImageWithCaption
 src="/assets/images/pressure_plot.jpg"
 alt="Velocity map of a longitudinal section through Ian Walsh - image by Falcon Pursuit"
 width="3234"
 height="1891"
/>

**From your simulations, what board settings can you change to increase performance?**
Solutions to this cavitation problem where your board is sliding instead of carving across the wave are relatively simple: change the shape of the fin, its length, position and so on. Cavitation is a relatively difficult phenomenon to show and explain to any athlete, but by using scenes and tangible data, you can show how the flow varies from fin A to fin B, highlighting the loss of adhesion with the water.

Hydrodynamics sound very esoteric, normally board shapers come with their magic wand and say: “This is a perfect board for Ian.” After Ian gives it a try, there seems to be a problem with the edge-rails when cutting into the wave. Red Bull Performance Group then comes and demonstrates with a simulation animation that the board is not well suited for him, arguing that it generates too much drag, requires greater flotation and so on. The tough part is that athletes are in love with their equipment; favourite board, position and so on. Asking to change something is monumental. Hence throwing a bit of science behind it will help the athlete trust the path to an increase in performance.

<ImageWithCaption
 src="/assets/images/ian_board2.jpg"
 alt="Flow lines of the air around Ian Walsh - image by Falcon Pursuit"
 width="3234"
 height="1901"
/>

Interesting links:

<ExternalLink href="https://www.dontbeadrag.com/">Don't be a drag</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/simulations/new?accuracy=regular">
 Run Your Own Simulation
</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/cfd-results-how-to-interpret-an-aerodynamic-analysis/XntO27S5Urc">
 How to Interpret CFD Results
</ExternalLink>

Big Wave Surfing - Simulating Ian Walsh's Ride

## Introduction

Mio Suzuki, Sr. R&D Engineer and Aerodynamics Lead at Specialized Bicycle Components gives us an extraordinary insight into how aerodynamic concepts in cycling are brought to live. Starting from the very beginning with fundamental research studies in CFD and wind tunnel testing all the way to optimizing the bike towards a design fit for production.

<ImageWithCaption
 src="/assets/images/profile-picture-mio-suzuki.jpg"
 alt="Mio Suzuki - Aerodynamics Lead at Specialized"
 width="450"
 height="450"
/>

## Historical steps into Aerodynamics

**Who pioneered bike aerodynamics?**
The race that comes into mind when thinking about the first stepts into cycling aerodynamics was the iconic victory of Greg LeMond at the 1989 Tour de France’s last time trial. Unusual for that time, he placed his arms at the center on the aerobar extension instead of the handlebars. His ambition to cut down seconds pushed the engineers to further develop the aerodynamics of the bike. The ”new tech” LeMond used was the triathlon style aerobar extension which enabled him to get into a more streamlined position for the time trial than using a grabbing handlebar. I have no doubt that aerodynamics played a decisive role in LeMond’s win. The bike having that characteristic slanted frame which helped LeMond get into that peculiar position which was indeed intended to reduce aerodynamic drag. I’m not sure if there was any bike frame tech that was intentionally embedded into his racing bike at that time, but what I recall heavily was his use of aerobars.

<ImageWithCaption
 src="/assets/images/greg-lemond-1989.jpg"
 alt="Greg Lemond in aerodynamic position - Tour de France 1989 - Image credit: capovelo.com"
 width="1024"
 height="671"
/>

## Aerodynamic Performance

**Is the bike itself, contributing perhaps 20% of total drag, really that relevant?**
Yes. Especially for the professionals who are competing at the highest level of the sport, a variation in drag within that 20% of the whole system is still big. I am personally in charge of conducting tunnel tests. My main objective always has been to create a meaningful test. Before stepping into the tunnel, I clarify the objectives of the test, so that we can capture the necessary engineering assets which are relevant for the development. Ultimately the question is: can a certain combination of bike, wheel, position… provide a relevant experimental number?

Testing is normally done in several ways. Sometimes bike-only tests (without the rider on top) are used to get a clean number. It is important to realise that the rider is a large bluff body, generating vortices causing vortex-shedding and significant experimental noise. Hence to objectively evaluate if our bike is faster than the competitor bike, it is essential to test the bike only.

More relevant to the rider however is the aerodynamic drag of the full bike-rider combination. To have the rider in the same consistent position, and to allow for proper comparison between tests, we work with Mannequins (dummy models). In the past we had two mannequin positions at Specialized; one for road bike and the other for time trial position. Recently, we added an extra one to reflect differences between male and female bodies.

Besides using mannequins, we perform a lot of athlete testing, at least before COVID-19, with internal as well as professional riders visiting our headquarters to work on their athletic goals.

**Tell me about the aerodynamic design cycle in bikes, the use of wind tunnels, CFD analysis and so on.**
Each manufacturer does it differently. It often starts from the product manager’s specifications for the next bike, which mainly reduces to three pillars; drag, stiffness and weight. I personally like to go hard on CFD from the start, getting numerical drag targets which give me a goal on what to redesign. Then I work with the design engineers, specialists in creating the 3D CAD model. In terms of the workflow, we start with competitor and current model analysis (through CFD and/or wind tunnel testing), where we typically perform at least one wind tunnel at the start of the project to correlate CFD and wind tunnel data.

Once aerodynamics traits and drag reduction requirements are established, we proceed to CFD-based design iterations. These days, using reasonably sized high-performance computing clusters, hundreds of design variations of the initial model can be analyzed in relatively short amount of time. We have partially automated this process by parametrizing CAD models, changing parameters and seeing the effect on drag. With the use of large-scale computing, I have remote access to a cluster set-up with a virtually unlimited number of cores. On these computers, I run about 15 simulations in parallel in a batch and repeat the process as often as I like.

Besides aerodynamics, the role of other physics parameters (weight & stiffness) is very important too. We simultaneously evaluate competing physics/physical objectives, and check if a certain combination of parameters results in the desired bike characteristic.
After this, one or two final prototypes are taken to the wind tunnel to select the winning design and until the design freeze. Once this is done, I am out of the game and the project focus shifts to the manufacturing, where industrial designers turn the prototype into a ready-for-production design. Project design engineers then work with vendors and teams that executes the manufacturing processes.

<ImageWithCaption
 src="/assets/images/specialized-road-bike-windtunnel1.jpg"
 alt="A rider in the Specialized wind tunnel"
 width="1500"
 height="722"
/>

## Future Path for Bike Aerodynamics

**What’s in store for the future? Are we already on the flat part of the improvement curve?**
Not at all! There is still room for improvement. Perhaps not the most drastic changes, but these will likely be driven by an increased understanding of the fundamentals of the aerodynamics. In the past, cycling/bicycle aerodynamic drag heavily focused on manipulating the frontal area (projected area, or the “A” in CdA). But simply reducing the frontal area by making frame tubes skinnier has its limit and will have the consequence on frame structure and weight, as well as influencing the ride quality.

So while paying attention to keeping the frontal area is important, understanding how the frame shape, and bike + rider influences a variation in Cd also becomes the key to create a performance bike that satisfies multiple physical attributes in play for the overall ride experience and rider performance. To do that, my hope is that the community treats aerodynamics as a science and not just only as trendy words. I am hopeful that this renewed industry focus could see a more serious and formal attitude towards the physics of aerodynamics.

<ImageWithCaption
 src="/assets/images/specialized-road-bike-windtunnel2.jpg"
 alt="Cyclists in drafting position in the Specialized wind tunnel"
 width="1367"
 height="934"
/>

**Do you see business moving towards customization of aerodynamics and bike elements based on body features?**
Each athlete’s body features, flexibility and mobility deserve a high degree of attention in time trial. These natural individual differences show up when athletes try to get into time trial position, particularly around the neck and shoulders and in the thoracic spine curvature.
Rather than offering a cookie-cutter approach, tailoring the goods and services to an individual athlete to take advantage of their natural body build makes sense.

Practice like that has been done for many years among the sponsored, professionally competing cyclists, but I think the idea of offering such services is becoming more common in the amateur cycling scene.

**What is the next domain where aerodynamics can be improved?**
I get that question asked very often, but I am selfishly going to keep the secrets to myself!
Computational tools available to the analysis engineers improved dramatically over the decade. Predictive engineering goes on so much beyond trying out simple 2D shapes. DOE, optimization and even statistical/data-driven methods such as machine learning/deep learning can be applied to define design spaces and frame shapes. Since computational hardware is no longer a barrier, adopting the right analysis methods that return large volumes of ride scenarios and relevant results in a timely manner may be the next frontier. There are various ways to approach CFD and experimental aerodynamics that simultaneously explore ride dynamics and frame structure/weight design spaces. I think it’ll be interesting to keep our eyes on how the future innovation practice evolves.

# Insight into Competition

**How are aerodynamics in teams limited by the regulations of competition?**
To be eligible to compete in UCI (Union Cycliste Internationale) races, such bickes must comply with UCI’s bicycle design guidelines. To give you an example, the airfoil aspect ratio cannot be more than 3/1. I personally don’t find the regulations very limiting, there are still rooms for creativity to blossom. On the other hand I feel that reguations on items like helmets can be bit more complex for a perfectly logical reson; they must also comply with safety certification standards. Also the considerations for ventilation comfort are relatively high too.

**How many aerodynamicists work on a single project at Specialized?**
Currently, on the product design, I’m the only one running CFD analysis at Specialized. When it comes to tunnel testing, I have my teammates who can lend hands for successfully completing the tests. It’s always nice to have multiple set of eyes paying attention to every detail during the test. My impression is that most other manufactures also have a similar set up as well.

# Standardising Testing - The Great Debate

<ImageWithCaption
 src="/assets/images/specialized-road-bike-windtunnel3.jpg"
 alt="Performance monitoring during wind tunnel testing at Specialized"
 width="1361"
 height="923"
/>

Towards the end, and interesting debate arose: how standardising testing across all manufacturers could be done. Mio asked us about our thoughts into this topic too.

**_Mio_** – I often hear from customers and journalists about them not able to trust the drag numbers and claims stated by the bike manufacturers because they all claim the title of “world’s most aerodynamic bike”. While I somewhat sympathize with this complaint, to someone like me and knowing that there are other engineers who exercise their best professional practice in conducting these tests and reporting the results, it also came as a bit of a surprise.

What can manufacturers do to earn the customers’ trust?

**_Our response_** - One of the first things to do would be to standardise the testing procedure, which would be similar to what you are doing internally at Specialized. Selecting two or three mannequins, specifying saddle and steering position, frame dimensions and so. Then run them through standardised wind tunnel tests, at a specified speed, yaw angle and so on in order to obtain comparable data. But there is no such standardised procedure yet. Competition teams may do this internally and confidentially by getting competitor bikes and testing them behind closed doors. Precisely behind those doors, every manufacturer has its own opinion on the ideal riding position and the most relevant yaw angle.

The truth is that “the most aerodynamic bike” is different for each race and each rider, so it is difficult to make a global claim like that. In any case, just as we can see in the automotive industry, which is a very mature business, there could be public rankings that fairly compare all designs according to industry standards (although even here we see that manufacturers pull all kinds of tricks to get the official values down). For the bike industry, a crucial question is who would be hosting such comparisons and tests? By all means it must be an independent institution, possibly the UCI, or maybe even an independent simulation service like AirShaper or an independent wind tunnel institute.

**_Mio_** - Ranking based on relative difference might be the best way to go. I have used different tunnels in the US, and I am aware that each tunnel is constructed differently, having different data acquisition instruments. Each tunnel is unique. Although these tunnels have good precisions within their measurements, trying to compare the results in absolute magnitude across different facilities presents challenges. This is because instrumentation as well as post-processing methods can differ among different facilities. Despite this, in general, ranking of the products and trends of drag vs. yaw tend to agree when testing the same object under the same protocol.

Interesting links:

<ExternalLink href="https://www.specialized.com/">Specialized</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/sports-aerodynamics-1-winning-the-ironman-triathlon/DqlDpUFcScc">
 From 3D scan to Aerodynamic Simulation of a cyclist
</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/simulations/new?accuracy=regular">
 Running your own simulation
</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/cfd-results-how-to-interpret-an-aerodynamic-analysis/XntO27S5Urc">
 How to Interpret CFD Results
</ExternalLink>

Specialized - How to Design Aerodynamic Road Bikes

## 🙋 About the Author

As a founder and CEO of multiple companies in the field of aviation, drones and other technologies, Lucas Marchesini co-founded <ExternalLink href="https://www.formulaairgp.com/">Formula Air Grand Prix</ExternalLink>, with Cristian Mendez Carmona (who is the CEO) and other ex-colleagues. Now he leads <ExternalLink href="https://www.mantaaircraft.com/">Manta Aircraft SA</ExternalLink> which is developing the ANN2, the hybrid-electric V/STOL race plane that will be used for the series!

## 📢 Formula Air Grand Prix

In the near future, new ways of transportation are likely to be added to the mix Urban Air Mobility (UAM). The key promises of this upcoming way of moving people and goods in the larger cities are fascinating: faster travel at reasonable fares; safe and enjoyable flight experiences; and smoother integration with the other transport modes. This can't be done with the existing helicopters and airplanes, therefore new aircraft types are being designed and developed.

<ImageWithCaption
 src="/assets/images/formula-air-grand-prix-illustration.jpg"
 alt="Aircraft racing in the Formula Air Grand Prix series - Illustration by Formula Air Grand Prix"
 width="1771"
 height="698"
/>

The Formula Air Grand Prix (FAGP) is a global air racing competition aimed at bringing
the stakeholders of this industry together, giving them a platform to showcase their
technologies to a larger and larger audience. As in many other disciplines, racing
competitions are an effective way to foster advancement in technology. FAGP's goal
is to accelerate the market entry of the best players in the industry.

Manta is developing the base aircraft for the series, the Manta ANN2. This, in turn, can be modified by the teams with the aim to improve its competitiveness. The development of the Manta ANN2 aircraft goal is to demonstrate the capabilities of a vehicle conceived as a HeV/STOL. That's H for Hybrid, e for electric and V/STOL for Vertical or Short Take-Off and Landing. In practice, it can take off and land vertically like a helicopter, and fly horizontally like an airplane.

One of the goals of the project is to make an aircraft with exceptional maneuvering capabilities resulting from this mix of airplane and VTOL characteristics: hover in midair; perform a backward flip; jaw and roll beyond what standard flight control surfaces – such as elevators, ailerons and rudders – would allow.

## 🌬 Propulsion layout

<ImageWithCaption
 src="/assets/images/manta-an2-2.jpg"
 alt="The propulsion layout of the Manta ANN2 Formula Air Grand Prix aircraft in VTOL mode - Illustration by Formula Air Grand Prix"
 width="1063"
 height="839"
/>

The propulsion layout is the result of a series of logical design choices:

- During take-off and landing, all the propulsion is needed to provide the vertical thrust that lifts the aircraft. By contrast, in horizontal flight, the propulsion needed is just a fraction of that thrust, as the remaining force comes from the aerodynamic lift produced by the wings. If you use the same thrusters in both modes, then they'll be working at around 15-20% of their maximum power for most of their life (remember that these aircraft are meant to spend 95% or more of their flight time as airplanes, and less than 5% as VTOLs).
- Using propellers, or any other form of "thruster" for vertical lift, means that they need to operate at high power for a short time. As this is the most demanding flight regime, you're obliged to optimize the propeller blades for vertical take-off and landing, leaving them less than optimal for other flight regimes such as mid- and high-speed horizontal flight. One option is to change the angle of the propeller blades depending on the flight regime (variable pitch props). This would require extra mechanical components that increase weight and also require more maintenance as well as spare parts in stock.
- The most reasonable solution is to choose a design point for the thrusters that falls somewhere in between the static and cruise conditions, with the effect of losing thrust in the demanding VTOL situation.
- To maintain the capability of vertical take-off and landing, additional thrusters are required. These can remain concealed in the fuselage during the winged flight to reduce drag in horizontal flight. And as they are of help only during take-off and landing, they can be fully optimized for such high-power static conditions, increasing efficiency in VTOL flight. The other thrusters, in contrast, are optimized for higher efficiency in horizontal flight mode.

<ImageWithCaption
 src="/assets/images/formula-air-grand-prix-1.jpg"
 alt="The Manta ANN2 Formula Air Grand Prix aircraft in VTOL mode - Illustration by Manta Aircraft SA"
 width="603"
 height="339"
/>

## ✈ Aerodynamic Layout

<ImageWithCaption
 src="/assets/images/formula-air-grand-prix-2.jpg"
 alt="The layout of the Manta ANN2 aircraft features a large canard setup - Illustration by Manta Aircraft SA"
 width="603"
 height="339"
/>

The aircraft features a canard layout, with the pitch-control plane set in front of the main wing (traditionally, these surfaces are in the tail). This provides the following advantages:

- All the surfaces generate lift, thus increasing efficiency in cruise
- The Centre of Gravity is located between the two lifting surfaces, which is necessary to have the position of the fuselage thrusters in the bow and stern of the airplane
- A concentration of the most important structural components such as the wing-fuselage intersection, engine bay and main landing gear, thus reducing the structural weight, in comparison with having them dispersed along the fuselage
- A large part of the fuselage is kept free from the aerodynamic disturbances of engine air inlets and outlets
- A wide lateral angle of downward view for the pilots, which is particularly useful in the surveillance and search missions (and also in racing competitions)
- In terms of maneuverability, canards of this substantial dimension offer quick response in pitch and, through differential rotation (a difference in angle of attack between the canard wings), a fair contribution to the roll control power.

The positioning of the ducted fans underneath the main wing, ahead of the flaps, also provides advantages:

- The lifting performance of the main wing is increased at low speed, especially during short take-off and landing. Exploiting the "vectoring" of the wing thrusters increases the maximum take-off weight, allowing the aircraft to launch on short semi-prepared airstrips.
- As in every canard configuration the effect of the forward surface ('front wing") on the rear main surface ("main wing") is not negligible, in the adopted configuration, the presence of the large wing fans in front of the wing helps decreasing this effect. This is optimal in cruise.

## 🔌 Power Management

The Manta ANN2 features a hybrid propulsion system: a gas turbine running an electric power generator, batteries and electric motors. This configuration reduces size, weight and cost. The turbine allows increasing cruise range, as it is used to recharge the batteries during cruise flight (or at idle on the ground, eliminating the need for a recharging infrastructure). For VTOL operations extra energy is sourced from the batteries, and that’s when the max turbine power output is required.

## 🖥 Design Tools

<ImageWithCaption
 src="/assets/images/formula-air-grand-prix-3.jpg"
 alt="CFD (Computational Fluid Dynamics) analysis of the Manta ANN2 Formula Air Grand Prix aircraft - Illustration by Manta Aircraft SA"
 width="603"
 height="307"
/>

Manta is following the fully simulated aircraft design approach, from the flight dynamics – through the use of Computational Fluid Dynamics (CFD) and wind tunnel data – to the different onboard systems (propulsion, electric, flight controls, etc.), being all integrated into a real time pilot-in-the-loop simulator. CFD have been extensively applied to analyze and optimize the pressure patterns on the aircraft, to obtain crucial inputs on lift and drag forces, and pitch, roll and yaw moments for the controller. And so on.

## 💡 Conclusion

Formula Air Grand Prix will be a fascinating playground and testbed for the upcoming technologies that will eventually make their appearance in the Urban / Regional Air Mobility scenery. Novel aerodynamic layouts, propulsion setups and drive train packaging will contribute to make it become a sensational sport!

Interesting links:

<ExternalLink href="https://www.formulaairgp.com/">
 Formula Air Grand Prix
</ExternalLink>
 

<ExternalLink href="https://www.mantaaircraft.com/">
 Manta Aircraft SA
</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/simulations/new?accuracy=regular">
 Run Your Own Simulation
</ExternalLink>

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