## 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/projects/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/projects/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/projects/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/projects/new?accuracy=regular">
 Run Your Own Simulation
</ExternalLink>

Formula Air Grand Prix - Racing in the Sky

## Introduction

During this interview, we had the pleaseure of talking to Dominic Harlow, Motorsport Engineer with a wide backround in F1 sport. His passion towards motorsport and enthusiasm towards engineering have alowed him to be involved in many interesting projects throughout his career.

<ImageWithCaption
 src="/assets/images/profile-picture-dominic-harlow.jpg"
 alt="Dominic Charles Harlow"
 width="318"
 height="422"
/>

## And It's Lights Out & Away We Go

**Tell us about yourself and your career path?**
I’ve been involved in motorsport a long time, it’s where I have always wanted to take my career. When I arrived in F1, I started to work in data engineering at the track, performance engineering and vehicle science. A little bit of design work as well. In F1, at that stage with the great proliferation in use of simulation tools, lap simulation particularly, data acquisition and analysis tools, teams had quickly realised the importance of aerodynamics as the primary performance driver for the cars they could influence. So, as has always been the case, many years before I ever got involved, the aerodynamics were fundamental for the performance and were what really differentiated in the largest part between the teams. Thus, it is easy to understand that it is something which interested me a great deal, involving myself with the team in this respect. F1 is unique in the amount of aerodynamic development effort that a team expends, much more than what you find in any other formula. It is even multiple times the effort OEMs put into launching a new model. If you just look at CFD and wind tunnel hours F1 is doing far more work than an OEM does, in a single team and on a short period of time.

<ImageWithCaption
 src="/assets/images/formula-one-cars-on-track.jpg"
 alt="Australian Grand Prix - Melbourne 2014"
 width="3267"
 height="2174"
/>

## Thrive, Don't Just Survive

**How is aerodynamic testing embedded within the design cycle of a car? Do you start with a clean sheet or do you iterate upon previous designs?**
It is a constant interplay between both. There is always a debate in F1 (and motorsport in general), when developing a car on whether to think of new concepts or to optimize the existing one. Dreaming up the latest and greatest designs for a car will allow you to unleash new areas of performance. Afterwards, you can evaluate how much should you continue pushing your existing avenues of development and iterate towards better solutions. Usually the iterative approach wins out against the complete reinvention of a new concept. But one cannot underestimate the importance of starting with the right concept, fundamentals and layout for car, so that you don’t force the iteration into areas that are not fruitful or where the ultimate performance is limited. The third aspect that comes into play are the regulations: just like the cars, the regulations become increasingly complex, so they place additional constraints on the development process and the car concept, and they change from time to time. Thus, they force you to rethink, to abandon certain areas and come up with new ones.

**When you start the design cycle of a car, is aerodynamics positioned as the top priority?**
Aerodynamics do dominate conversations in F1, as does the power unit. In terms of chassis design, it is more of an integration task. It goes without saying that the power unit supplier is the one in charge of delivering maximum efficiency and good energy recovery. So, for the chassis designer, aero comes first. Tyres (and tyre management) and all the other aspects around that are next, along with good power-unit integration.

Additional research is performed to optimize structures and reduce weight. Satisfying the safety criteria (which thankfully continue to evolve) also requires quite a lot of effort. And the teams are always looking for improvements in stiffness and structural integrity. All the teams improve year on year, so not paying attention to a certain aspect will have you lose competitiveness.

<ImageWithCaption
 src="/assets/images/formula-one-chassis-model.jpg"
 alt="Formula One Chassis Model"
 width="870"
 height="732"
/>

## Simulations & Testing

**With regards to the simulations, how are aero mappings tested, are these done altogether with other suspension tuning or chassis adjustments?**
Almost all simulations involve a full model of the car (masses, suspension data, tire data, ...) and the aero map is one of the crucial elements in such a model. The higher the fidelity of the aero map, the more reliable the results of the complete simulation will be (like lap time simulations for example). It all depends on what aspects of the performance you are looking to focus on. Once you have the model, you can play with the inputs and evaluate the changes in the output.

<ImageWithCaption
 src="/assets/images/formula-one-cfd-total-pressure-coefficient.jpg"
 alt="The total pressure coefficient obtained through CFD simulation"
 width="1795"
 height="919"
/>

**Could you give an idea of the volume of CFD work done behind these cars?**
It is difficult to quantify the exact number of simulations done; it depends on how you define a simulation. There are so many recipes and methodologies applied to F1 CFD from the smallest sub-models of parts of the car to fully unsteady simulations at complex attitudes. And things get even more challenging when simulating multiple cars in order to better understand the wake and its effect during close following. How many of those you do depends on the size of the simulations, but you might see around 30,000 a year per team. By regulation the teams can only use a certain amount of resources to apply to elements of testing, thus it is constrained. It is still an intensive level of research and the balance between wind tunnel and CFD is now clearly leaning towards CFD as it becomes more and more available and efficient.

**You have been working as a race engineer. From that position, have you seen a change in attitude towards aerodynamics from driver’s side? How big is such awareness of the importance of communication with engineers?**
The drivers certainly learn and develop in the same way teams do - as the team’s understanding grows, that becomes embedded in the drivers. The drivers do understand from early stages of their careers, that they have to speak the same language as the engineers. That way, they can help the engineers understand where certain aspects of the behaviour of the car are coming from and how those might be aerodynamically driven. A good driver that is aware of this will be able to speak to the team and help them develop a better understanding of the aerodynamics of the car. Also, they are heavily involved in the simulations back at the factory (like driver-in-the-loop-simulations), discussions with the engineers on concepts for the new car, ... giving feedback on setup & pointing out areas for improvement on the car.

# F1 Future - Straight Line or Not?

**Let's talk about the new regulations, which constrain the aerodynamic development of the car. How do you see the future for F1?**
For F1 as a sport, I certainly see a strong future - it has all the elements of a great sport and spectacle. It is unique in that it combines the individual brilliance of the driver along with teams and engineers. A spectacle in all its essence with huge events at each Grand Prix, touring all around the world.

From a technical and regulatory point of point of view, it is also about efficiency and a real-world challenge. There is nothing in life that is not constrained by what’s available. I think the sport is relevant, in terms of the mobility strategy, and certainly there is still an element of internal combustion engine innovation and trickle down of technology to the public. As long as things like sustainability & entertainment have been kept in mind, I think everything that has been decided upon is for the good of the sport.

<ImageWithCaption
 src="/assets/images/formula-one-fernando-alonso-malaysian-grand-prix.jpg"
 alt="Fernando Alonso - Malaysia GP"
 width="1024"
 height="670"
/>

**As for the upcoming change in rules, what is the next big aerodynamic point of innovation in F1?**
The biggest changes will come in 2022, with the introduction of new regulations (based on development work that has already been done). Certainly, it will be interesting to see how this 'reset' plays out after all the progress that had been made on the current cars & the success of that philosophy. Engineering is a continuous process, new things are built and continue to evolve - so we may have to wait a few races to gather enough 'sampling points' before drawing conclusions on the success of the new regulations. Coupled with that is the change of tyres which is a huge thing aerodynamically.

**Any other thoughts?**
I am certainly very interested to see the development of CFD and HPC as it applies to motorsport over the course of the coming years, to look how it is delivered and made available; on-premise, cloud, as open source or vendor code, exploring different workflows and applications.

Interesting links:

<ExternalLink href="https://dominicharlow.com/">
 Dominic Harlow Consulting
</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/race-car-aerodynamics-3-aero-mapping/u-GyTRblNmc">
 Aero mapping for race cars
</ExternalLink>
 

<ExternalLink href="https://app.airshaper.com/projects/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>

Formula One Aerodynamics - An Interview with Dominic Harlow

## Introduction

On this occasion, we've had the chance of speaking to one of the engineers in charge of designing sailboats for two of the toughest and most prestigious sailing competitions of all times; the Volvo Ocean Race and the America's Cup. Britton Ward, Vice President of Farr Yacht Design has given us some thought-provoking and fascinating insight into the aerodynamics of sailing.

<ImageWithCaption
 src="/assets/images/britton-ward.jpg"
 alt="Britton Ward"
 width="2000"
 height="1214"
/>

## Setting sail towards a Childhood Dream

**To put things into context, talk me through your career path and how you got into this industry?**
My name is Britton Ward, I'm Vice President and Senior Naval Architect at Farr Yacht Design in Annapolis Maryland, USA. My fascination with sailing yachts happened at a young age. Growing up in Western Australia I was completely enthralled by Australia II's America's Cup victory in 1983. The 1987 Cup defence was in my home Fremantle waters and from that point on I knew I wanted to be involved in designing racing yachts. I attended the Webb institute of Naval Architecture in New York and followed that with a master's degree from MIT. From MIT I joined Farr Yacht Design and have been lucky enough to work on a wide range of projects including 4 America's Cups, Volvo Ocean Races, grand-prix racing projects, cruising boats and a number of high-performance powerboats.

## Aerodynamics in Yacht Sailing

**Throughout these years have you seen a significant change on the aerodynamics side of competition?**
Yes, what makes sailing design so unique is that we have to operate across such a wide range of operating conditions; from no speed to 30,40, sometimes 50 knots, upright and at heel and at different angles of sideslip or leeway. The designs must work across a really broad range of conditions which makes simulating every aspect very demanding. The second part is that we are in perhaps the ultimate efficiency game, trying to maximize aerodynamic drive forces while remaining always on a quest for minimum hydrodynamic drag. So, we are constantly trying to improve both the hydrodynamic and aerodynamic sides of the performance equation. Given water density is 800 times that of air, we work really hard at hydrodynamic optimization trying to reduce drag but the sails are our engine and so improving aerodynamic drive and minimizing aerodynamic parasitic drag is critical to achieve maximum efficiency. We work with sail designers in analysing sail shapes and we put a lot of effort into reducing windage by shaping hull and deck surfaces. At the highest end, in America's Cup programmes we have looked at the effect of having a rope in front of the mast for the windage gain or shaping of bowsprit sections to achieve aerodynamic driving force. With the recent push into hydrofoiling yachts that achieve speeds of 40 to 50 knots, the importance of reducing windage drag has become ever more critical and is getting a lot of focus.

**In terms of all these features and challenges you have tried to improve, tell me about the design cycle of these sailboats.**
The challenge is whether the team can support enough R&D to do multiple design refinement cycles using high fidelity tools; whether that be tow tanks or wind tunnels or CFD. For a lot of our regular designs the design budgets and timelines can't support unlimited research, so we work to leverage our existing databases, use empirical methods and perhaps validate with some limited simulations.
Whether it is empirical models or experimental data or simulation results, we use different techniques to build Response Surface models that characterize the hydrodynamic and aerodynamic forces acting on the boat, appendages and sails across the range of operating conditions. These models are then used to predict the performance of the boat using a Velocity Prediction programme that can be either 'steady-state' or for very high end projects a full time domain simulator that allows the boat to be sailed virtually. We can then couple that information with expected race conditions or race simulations and begin to optimize the design for the targeted conditions.
We have invested heavily in an automated design analysis system called IDEOS that brings together a lot of these elements and automated shape morphing and generation to allow us to look at 1000's of design options before committing to final design.
Even with the most complex simulations and computing we are a long way from a black box design process. Anything the computer spits out needs experienced eyes that understand both what's 'under the hood' in the codes but also appreciates real life sailing complexities that aren't able to be fully captured in models.

<ImageWithCaption
 src="/assets/images/Vo65Hydro.jpg"
 alt="VO 65 (Volvo Ocean) Pressure Mapping"
 width="1043"
 height="930"
/>

**With regards to quantifying and modelling the interaction of different components, what impact does the pressure difference from the main sail have on the entire aerodynamics of the boat?**
Like in most industries, one starts with computationally simple things, just analysing a set of sail geometries in the air without the presence of the mast, rigging, hull etc.. For sailing at low apparent wind angles with minimal separation we can use Vortex Lattice or Panel methods but at wide angles with spinnakers we have a much more complicated flow regime requiring RANS and in some cases DES simulation to properly capture the flow. Modelling only the sails misses the interactions with mast, rigging, hull and deck which can have a really big impact on the forces and the flow field physics.
Much as with hull hydrodynamics we always want better and better accuracy but also need to run a lot of operating conditions to properly model how forces change in different conditions. Every design team needs to find the right balancing act here that can capture as much physics as possible but provide enough data to answer the design questions.

<ImageWithCaption
 src="/assets/images/WindTunnel1.jpg"
 alt="Wind Tunnel Testing on a sailing boat."
 width="479"
 height="639"
/>

**To what extent is it worth developing these foiling sailboats if cavitation effect comes into play at high speeds?**
The shift to foiling sailboats has dramatically changed the performance zone for these types of boats. Hydrofoiling is not new but the advent of advanced materials has allowed us to achieve exceptionally light weight and strong boats that can be lifted clear of the water by hydrofoils even in quite light conditions.
At a basic level hydrofoil design is the same as airfoil development but we are operating in a much more dense fluid. With the foils supporting the boat the total drag is reduced dramatically as the hull is now in the air and so aerodynamic efficiency becomes even more critical.
At the higher speeds the low pressure on the foil can drop below the vapor pressure of water cause the water to 'boil' or cavitate and this phenomena tends to govern the upper end of the speed range. Its fundamentally related to the pressure at the foil and the minimum pressure coefficient, if that exceeds the vapour pressure, the water boils. The question is, how do we reduce that? Generally, a bigger foil will have a lower loading on it, which will delay cavitation, but it also has more drag. You are kind of flirting on that cavitation edge or looking for solutions that are somewhat benign to cavitation.

<ImageWithCaption
 src="/assets/images/streamlines.jpg"
 alt="Bottom view of the hull with hydrofoils showing surface pressure & 3D streamlines."
 width="3443"
 height="1217"
/>

# Essence of Competition

**Are there any limitations dictated by competition or regulations that limit aerodynamic design freedom?**
Yes, in America's Cup, for the current AC75 specifically there is a rule that governs the parameters of the boat in a similar way to Formula1. These rules control dimensions, materials and construction processes and the number of components of different types that can be built. It also prescribes limits on control system etc. In the current rule it precludes the use of towing tanks and wind tunnels, requiring design optimization to be completed using only simulation-based analysis.

**I see that there is a strong similarity to F1 sport. Recently F1 has been forced to prove itself useful for the general industry, have you felt that there is the same sort of pressure on America's Cup?**
Everyone involved feels that there must be some trickle down of technology to the average sailor, and there is always a big debate about how much technology will trickle down from the current America's Cup boats. There are certainly a lot of design processes and tools that can be immediately applied to all manner of boats. Refinements in deck hardware and mechanical systems always feed into a range of boats.

**How many engineers are dedicated to aerodynamics within the teams?**
Every company organises itself in different ways so the way we are structured is probably a bit different to other companies or teams. Depending on the scale of the project we would typically have dedicated one or two guys to the aerodynamics in general, and one of those may be heavily involved in the sail design area. Fundamentally the hydrofoil is an airfoil wing, even if it is operating in water so all of the aerodynamics expertise is directly relevant and we use a lot of the same tools and methodologies. In our team we have often had naval architects working with aerospace engineers and I always find it is important to cross-pollinate from different disciplines.

# Iconic Designs

**Tell us what is so special about the VO65?**
VO65 was designed for the Volvo Ocean race, which is a fully crewed race around the world race. The VO65 is a one-design boat in which each of the boats are as identical as possible. This was a big change from prior races where they utilized a design rule and each team employed designers and sought to find a design edge. In the 2011-2012 Volvo Ocean race the boats were designed to the VO70 rule and there was a lot of design freedom but also a tendency to push the limits which resulted in a lot of breakages.
Thus given the economic situation and the issues in 2014 the race organizers felt that best option to insure the future for the race was to have a fleet of absolutely identical boats and we were commissioned to design the VO65. The main directives for us were to make the boats robust and reliable, as identical as possible. We sought to get as much performance as we could but without sacrificing those core factors. There was limited amount of budget for research and simulations which we utilized to explore some appendage options and develop refined performance predictions. We utilized our internal methods to refine the boats windage characteristics but were not able to complete a lot of detailed aerodynamics refinements. We worked closely with the sail and mast design teams in the sizing of the rig and selection of sail sizes, trying to develop the sail wardrobe to be as solid as possible.

<ImageWithCaption
 src="/assets/images/volvo-ocean-race-yacht.jpg"
 alt="Volvo Ocean Race Yacht."
 width="1400"
 height="350"
/>

**This was back in 2012, but what are the main areas of improvements currently in 2020?**
The next ocean race will start in 2022, having two classes, the VO 65 and the IMOCA60. Much like the older VO70 rules, the IMOCA60 is a development class, having a core set of rules but allow a lot of design freedom. The boats are now employing hydrofoils as well which has resulted in large performance improvements. In this case, they are not fully airborne as in America's Cup boats, but the foils lift most of the hull clear of the water so are perhaps better seen as 'foil-assisted' boats.

# Technical Insights

**What is the actual difference between foil assisted and fully flying?**
Primarily, the IMOCA60 is not allowed to have a tail elevator, so there is no T-rudder, and it uses passive hydrodynamics to maintain 'stable' flight. A big push in that design space is both on sizing and placement of the foils, and in developing a pitch-stable boat across the speed range that while still meeting all the stability and safety rules for an ocean going yacht. The IMOCA60 is an exciting design arena right now as there are a lot of areas to explore and optimize; how much stability you need from the hull design, from the appendix, keel or bulb, the size of the foils; There is plenty of room for a big leap forwards, since there is so much latitude to explore, but typically these budgets are much smaller than America's Cup ones so you have to have bright people and a good understanding of the constraints to make an improvement.

**You previously mentioned pitch-wise stability, are there any similarities to the oscillatory modes present in aviation?**
Yes indeed there are, in aeroplanes it is the phugoid mode, in powerboats we call it porpoising and it is a dynamic instability. A lot of work has been done in the power boats along the years to understand what characteristics of a hull shape make it more or less susceptible to porpoising. Much like an aeroplane, the position of the centre of gravity relative to the hydrodynamic centres is an important part of it. When we come to foil assisted sailboats, this gets even more complicated as we have the extra influence of the hydrofoils changing the boats attitude and varying dynamically with speed. Even in some of the initial simulations I have been doing in the last 6 months with some of my team, we have seen some configurations which appear to be pitch unstable and requiring a bit of trial and error, to understand the right combinations of running trim, foil sizing and placement and centre of gravity position. Now we are coming up with a design methodology using lower fidelity simulation methods to give us immediate guidance on whether a particular design configuration is going to be stable or not.

<ImageWithCaption
 src="/assets/images/AC75.jpg"
 alt="AC 75 - Richard Gladwell, Sail-World.com/nz."
 width="2407"
 height="1354"
/>

**Does the actual position of the crew significantly impact the aerodynamic efficiency and separation points?**
In any of our designs we focus on crew placement, for their center of mass impact, their ability to ergonomically complete their tasks and for their impact on windage and aerodynamics. Depending on the size of the boat, the weight of the crew has a big impact on the stability of the boat. A smaller boat, the crew weight is a much larger proportion of what the entire boat is, then thus greater impact on resisting the sails and tipping the boat over, therefore you automatically have a trade-off between aerodynamics and crew righting moment.

When you get to a boat like the AC75, the speeds have gone up so much, the aerodynamic impact of the crew is even more significant while the impact of the crew weight on stability of the boat is much smaller. As a result, we see the crew essentially 'buried' in tunnels with their heads down to be as streamlined as possible.

# On Course for a Bright Future

**What are the projects you have in mind in the near future?**
We are marching down this path of hydrofoils, not just for racing, but also for cruising boats. We recently launched 142-foot cruising boat with a 9-meter Dynamic Stability Systems hydrofoil. The addition of the foil improves performance and reduces heel angles by up to 15+ degrees while improving pitch motions which dramatically improves crew comfort. I think we are seeing other avenues where these technologies can be applied. Placing a foil in a 142-foot superyacht was a big challenge and one of the hardest projects we have done recently. This was a sliding foil, one foil works on both sides, so it has to be actuated and pulled in to the boat and put out the other side, when the boat tacks. Because this boat will sail the globe we needed to do a lot of assessment of damage possibilities to ensure the boat would be safe in the event the foil collided with something.
On a simulation front I am always trying to utilize more simulation tools in all of our designs. Recently we have done a lot of work with OpenFOAM, also Numeca's Fine/Marine primarily for hydrodynamic simulations. We also make a healthy use of panel methods and vortex lattices, X-Foil and XFLR5, depending on the types of problems we are looking at. Since we need so much data in order to make an informative design choice we are always trying to balance fidelity versus run-time. Just running one point of one geometry teaches us very little, so we are constantly looking at ways to use advanced statistical fitting techniques to make the most value out of the data we get from simulations and apply it to broader answers. Beyond that, we have been putting a lot of focus into the automation of design cycles; all the way from geometry morphing though to meshing to running simulations and post processing.

<ImageWithCaption
 src="/assets/images/DSS_Baltic142_Canova.jpg"
 alt="ABaltic 142 Canova"
 width="1246"
 height="815"
/>

Interesting links:

<ExternalLink href="http://www.farrdesign.com/">Farr Yacht Design</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/airbus-talks-part-3-of-4-americas-cup-aerodynamics/ZcD9iA9DPrI">
 America's Cup Aerodynamics - Interview with AIRBUS - Part 1
</ExternalLink>
 

<ExternalLink href="https://airshaper.com/videos/airbus-talks-part-4-of-4-americas-cup-aerodynamics-part-2/AdGuENBuZ-Y">
 America's Cup Aerodynamics - Interview with AIRBUS - Part 1
</ExternalLink>
 

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

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