Leading-Edge Motorsport Technology Since 1990
YOUR FREE COPY WITH THE COMPLIMENTS OF
Formula Student
2018
CONTENTS
Many Formula Student teams utilise CFD software such as SimScale to develop aerodynamically efficient cars. But it’s important to use simulation to analyse trends rather than absolute values. Other important tips for success can be found on pages 6-8, 14-16, 24-26 and 34-36.
CONTENTS 5 6 10
Tread Pattern How Formula Student has all the bases covered in today’s turbulent motorsport world OptimumG Pt1 Former FSAE judge Claude Rouelle provides the first 25 golden rules of how to win the competition FS UK All the tech talk behind the scenes of the 2018 UK competition
14 18 24
OptimumG Pt2 The masterclass continues with further insight into the judging world Team structure We talk to leading engineers in top level motorsport about how they cut their teeth in racing OptimumG Pt3 Cash, toe and CFD correlation are all covered in the third instalment of this comprehensive blueprint
28 34
Spaceframe or monocoque? With Formula Student regulations so open, we look into the positives and negatives of both structures OptimumG Pt4 The final part of the 101-point plan to be victorious at Formula Student competitions worldwide
Editor: Gemma Hatton Designer: Barbara Stanley
TREAD PATTERN
Formula Future What will power racecars in the coming years and how is Formula Student going to help you to prepare?
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here is no doubt that Formula Student remains the perfect learning platform for students to equip themselves with the skills and knowledge required to survive and succeed in motorsport. However, the world of racing is entering a new era, with radical changes planned in many categories. Formula E’s electric racing continues to grow, taking drivers, engineers and manufacturers along with it. Autonomous racecars are popping up everywhere, WEC and F1 will be revolutionised in 2020 and 2021 respectively, and Le Mans is targeting a hydrogen future in 2024. How can Formula Student prepare the next generation of engineers for that?
Daydream believers
Formula Student seems to have the answers as it continues to keep a step ahead of the wider motorsport industry. Both Formula Student Germany (FSG) and Formula Student UK (FSUK) introduced an all-electric category back in 2010 – four years before the first season of Formula E. By 2012, both competitions merged this electric class together with the original combustion category and although this was initially met with scepticism, today both electric and combustion cars race side by side. Not only does this add another layer of entertainment as some teams cheer on the growl of their 2-cylinder racers while others champion the whine of their electric cars, but electric competition provides a platform for electrical engineering students to develop their skills, which is becoming an ever-increasing requirement to secure a job. Add to this the fact that many well-funded universities bring two teams to competition; one combustion and one electric and it’s fair to say that Formula Student has successfully integrated electric racing. Next is the concept of autonomous racecars. As automotive manufacturers pursue this ideal, they once again turn to motorsport to provide a platform to test, develop and improve their technologies. Roborace has developed the world’s first driverless electric racing car. Although technically impressive, two years into the programme we are yet to see any form of racing. Why? Arguably, there is a lack of trust between man and machine that is an even bigger barrier than electric racing had to overcome. If I can’t trust my computer to save a document then how can I trust an autonomous car to stop when a traffic light turns red?
The only way to conquer these feelings of anxiety is proof of concept, and once again Formula Student has stepped up. FSG were the first to introduce a driverless category into their competition in 2017 and FSUK followed suit by running their first driverless demo this year, with plans to run a full driverless category in 2019. Interestingly, the organisations have gone for completely different approaches. FSG decided that to get the competition off the ground and avoid teams building brand new cars, the best strategy was to allow teams to adapt their two year old cars to include AI technology. However, this resulted in skewing the competition towards those teams who had the best mechanically performing cars, rather than the best performing AI cars. Teams that had fast cars two years ago will retain that mechanical advantage, regardless of how effective their AI algorithms are. However, this approach does cater for all engineering disciplines, rather than just programmers.
Stepping stones
Of course, new categories don’t come without their teething issues and in FSG’s case this came in the form of several cars failing scrutineering due to their emergency brake and steering systems. To avoid this scenario, FSUK went a different way, and have developed a standardised vehicle platform, the ADS-DV. This comes equipped with all the required safety features and the challenge for the students is to simply design an ‘AI-driver’ and download their software algorithms onto the ADS-DV.
Formula Student is a learning platform to develop the engineers of tomorrow, whether that be mechanical, electrical, aerodynamic or control system engineers, as well as computer programmers. Adding an autonomous dimension to a Formula Student competition caters for a new discipline of engineering, and if this then encourages those programmers to pursue a career in the motorsport industry then it works. Formula Student’s ability to quickly integrate new forms of racing to help young engineers learn new skills is an invaluable asset to the motorsport industry. FSUK even accommodated a hydrogen fuel cell car from Delft University of Technology in 2012!
Good times
A recurring phrase in motorsport is ‘if you stand still, you go backwards’. However, the pace of these new technologies seems to be increasing, creating an industry so competitive that it is no longer good enough to be excellent at what you do; you have to be outstanding. This is forcing students to think outside the box when they are hunting for ways to demonstrate their capabilities to future employers. However, as motorsport continues to evolve between electric, autonomous and even hydrogen racing, Formula Student continues to react accordingly. Formula Student is the best place to start pursuing your motorsport career, whatever kind of engineer you want to be. GEMMA HATTON Deputy Editor, Racecar Engineering
Integrating AI technology into Formula Student could be an even bigger hurdle to overcome than electric racing FORMULA STUDENT 2018 www.racecar-engineering.com 5
TECHNOLOGY – SLIP ANGLE
Formula Student 101 Slip Angle provides a summary of OptimumG’s seminars
Building a Formula Student car? Then you need to read OptimumG engineer Claude Rouelle’s 101 top tips for teams chasing FS glory. In Part 1 of this mini-series he runs through his first 25 points
p, balance, control and stability simulations are e of the main focuses at OptimumG.
It’s a mistake to study successful Formula Student cars before you start your design process; it could cramp your creativity
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esides his leading role at vehicle dynamics consultancy OptimumG, Claude Rouelle often offers his services as a design judge in many Formula Student competitions. Rouelle started his 40-year racecar engineering career by designing and building a racecar and a wind tunnel. It was his engineering degree master thesis. The challenges he faced then were quite similar to those faced today by students building a first racecar. In this new mini-series Rouelle offers some advice on engineering and team building for Formula Student teams; though many of these tips are also applicable to professional race teams.
1. To finish first you must first finish. Think reliability before you think performance.
2. Accuracy, relevance, usefulness, meaningfulness,
5. There are three main goals you need to always
repeatability are five words that should be part of your everyday engineering vocabulary.
keep in mind during your Formula Student concept phase: minimum weight, lowest centre of gravity, minimum yaw inertia.
3. There are two rules with software use. Rule 1: You cannot make the software work unless you read the user manual/help file (and, ideally, some good case studies) from start to finish. Rule 2: Nobody reads the user manual. The same goes for the little sensor spec sheet.
4. The best way to predict the future is to look at the past. Often the best simulation and performance predictions are provided by the exploitation of previous data collected during previous races and on-track or in-labs tests.
6. A low inertia goes against stability but helps with control. The low limit of stability is mainly dependent on driver skills and speed. The reality is that inertia is always too big on a Formula Student car. Want proof? Look at the low mass and shorter wheelbase in karts. Besides, the best way to make a light car is to make a short car. I do not see any reason why you would not build a Formula Student car at the minimum legal wheelbase. Ergonomic and short cars are possible. I have seen many Formula Student cars with the minimum wheelbase
A low inertia goes against stability but it does help with control 6 www.racecar-engineering.com FORMULA STUDENT 2018
where a 1.8m 90-kilo driver can easily sit and comfortably drive the car.
7. Ergonomics is fundamental. It plays a huge role in the driver’s ability to feel and control the car. Head, shoulder, ribs, hips, side, legs, heels, support is too often neglected. If, when you turn the steering wheel 180 degrees, the driver’s hands rub his legs, or his elbows hit the chassis, he won’t be able to get the most out of the racecar. You wear a cockpit like you wear a suit. A wood mock-up cockpit tested by your drivers will teach you more than any CAD software with dummy drivers.
8. If your steering torque is more than 5Nm, you will need to hire Arnold Schwarzenegger to drive your racecar. As a reference, most passenger car steering torques are in the 3Nm region. It is a pity that the majority of Formula Student teams do not simulate or measure the steering torque.
9. When you go to a job interview, you need to dress for the job you want, not the job you have. Same for design. Flip flops and dirty T-shirts are not the best clothes to impress design judges.
10. The gods of mechanical engineering are never with you. Mistakes keep being added to each other, and they do not cancel each other out. You must remove phrases such as ‘this compensates for that’ from your brain.
The three main goals you need to keep in mind during your Formula Student project’s concept phase are keeping the car weight to a minimum, with the lowest possible centre of gravity and minimal yaw inertia
11. There are some numbers you should naturally know by heart, not because you memorised them but simply because you played with them so often: weight distribution, anti-roll stiffness distribution, wheelbases, tracks, motion ratio, damping ratio range, etc. If you must look for this kind of basic information in your binder during a conversation with a design judge, it sends a signal that you are not in control of your work.
12. In terms of project management, you must think about your racecar concept, simulation, drawing, machining, and assembly as an aeroplane that must land. If you keep flying your plane and run out of fuel, you crash. Similarly, a fantastic car design that is not finished on time won’t help you. There must either be a dictator or a common agreement to have each car part finished on time. Winning starts at the workshop with on-time and on-target design achievements.
13. It is possible to create a car that is both stiff and light. The best way to achieve this is to keep in mind the lessons of Darwin: Form follows function. First, function and second, form, not the other way around. 14. Start any new Formula Student project with two separate brainstorming sessions that answer these simple questions; what makes a great team and what makes a great car. Make the wildest dream list of what defines an ideal team and a perfect car. Then, and only then, be reasonable and choose the goals that are within your team’s means.
Cockpit ergonomics are a crucial part of the Formula Student design process. Your driver must be able to feel and control the racecar properly and it is important that no part of the chassis restricts movement
I do not see any reason why you would not build a Formula Student car at the minimum legal wheelbase FORMULA STUDENT 2018 www.racecar-engineering.com 7
TECHNOLOGY – SLIP ANGLE
If you don’t know why you win, you won’t know why you lose 15. The worst thing that you could do when you start to design a Formula Student car is to look at other existing car pictures or videos on the Internet. Do not let pictures of other racecars influence you. Looking at other cars restricts your creativity and your ability to think function then form. Once your car has been designed, then, and only then, look at other racecar pictures, and if necessary, modify your own drawings.
16. You need to think SMART goals, an acronym that stands for Specific, Measurable, Attainable, Relevant, and Time-bound.
17. If you don’t know your strengths, you don’t know your weaknesses. You get your car out of the truck and you are the quickest all weekend. Good. Then two weeks later, conditions are different: it rains, or the circuit is bumpier. You get lost. If you do
not know why your car was that good two weeks ago, you won’t know how to fix it when it under performs. To put it another way; if you don’t know why you win, you won’t know why you lose.
18. A design judge will be expecting you to demonstrate how you chose your suspension rod ends and tube sizes, hub and upright shape and material, etc. with load case studies from tyre to chassis starting with simplified tyre load in longitudinal acceleration (braking and acceleration), lateral acceleration (cornering), vertical load and acceleration (mass, weight transfer, aerodynamic forces and moment, and bumps), and then a combination or all of any of these, and finally with track replay. Without this, you take the risk that any designed part will be either over engineered (too heavy) or under engineered (too weak).
19. Formula Student teams cannot use the same safety factors as in the passenger car industry. Do not compare cars that are run 2000km a year (for the most organised team running several competitions) and cars that are supposed to be reliable without any major issue for 100,000km.
20. There is only one definition of a ‘too light’ part: that’s when it breaks. Do the best you can with intelligent design and FEA. Go lighter until it breaks, then go one step backwards.
21. You need to look at your racecar assembly as well as each car part and wonder ‘if something breaks, what will it be?’ If you know the answer and you don’t do anything about it, that is just insanity, because there is a great chance that once you are on the race track that part will break. Analysis. Awareness. Communication. Action. 22. If something broke on your car and you do not do anything about it because you do not know why it broke, there is a big chance that part will break again. Worse, if you know why that part broke and you don’t do anything about it, that is laziness.
23. Not having a Plan B, and ideally a Plan C,
A common error with Formula Student teams is not simulating or measuring steering torque, making the car hard to drive on the handling tests. This needs to be no more than 5Nm; road cars are around 3Nm
for any car part failure during its development phase demonstrates a lack of either imagination, objectivity, or preparation. Example: you test your new racecar and after a few laps, your front wheel hub breaks. You will now do a failure analysis, redesign, reordering the material if you do not have it in stock, re-machining … You could lose several weeks during which your engine and your aero are not developed. Now, imagine having a Plan B: you can mount last year’s uprights on the new car. During that time, you can at least continue the other car parts’ reliability tests.
24. Einstein said that ‘Intelligence is the ability to find a solution to a problem you never encountered before. Insanity is doing the same thing over and over again and expecting different results.’ I am also convinced that the biggest thing that slows down our ability to develop our intelligence is our inability to control our emotions. Control, not suppress.
25. ‘We cannot solve our problems with the same thinking we used when we created them’ (again Einstein). No more comment needed. See page 14 for points 26 to 50
CONTACT Claude Rouelle Phone: + 1 303 752 1562 Enquiries: engineering@optimumg.com Website: www.optimumg.com All parts need to be lightweight and the only part that is too light is the one that breaks. You need to figure this out with intelligent design and FEA. Go lighter until it breaks and then go one step back 8 www.racecar-engineering.com FORMULA STUDENT 2018
Simulation software reinvented for the web Welcome to the future of design validation. SimScale is a revolutionary cloud-based CAE platform that gives instant access to professional grade finite element analysis (FEA) and computational fluid dynamics (CFD) simulation technology in the web browser. Engineers can now easily test, compare and optimize designs, by investigating car aerodynamics or stress in components as well as work on projects involving thermal management of engine parts or brake cooling.
Try SimScale for free and start simulating in minutes at simscale.com
FORMULA STUDENT – TECH ANALYSIS
Technical studies
During FSUK Racecar patrolled the paddock to uncover the very best of the many technical innovations on show at Silverstone By GEMMA HATTON
The designs at this year’s FSUK event were as inventive as ever. Bespoke engines, dampers and uprights, and even a combustion four-wheel drive car, gave the judges plenty to consider
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hen you give a group of enthusiastic engineers the chance to design and manufacture a solution to win a competition, you are always going to end up with some fascinating designs, and at this year’s Formula Student UK that was certainly the case. One of the most memorable cars competing was the Sapienza Corse car from the University 10 www.racecar-engineering.com FORMULA STUDENT 2018
of Rome, scoring an impressive 142 points (out of 150) in Design. ‘We are the only internal combustion Formula Student car that has an allwheel drive transmission,’ says Nicholas Longo, team leader and drivetrain manager at Sapienza Corse. ‘The drivetrain was a completely unique design because we had to fit this system to a formula car. We devised a system with a central differential which is split left and right unlike the
usual one which splits front to rear, and we have two propshafts; one on the left and one on the right side of the monocoque. This allowed us to use bevel gears at each end of the propshafts, so we achieved a three-to-one reduction ratio which lightens the stresses on the components, so we could use smaller and lighter parts.’ The nature of Formula Student tracks requires the cars to have good agility and fast
The nature of Formula Student tracks requires the cars to have good agility and fast acceleration
IMECHE FORMULA STUDENT
acceleration. The latter is optimised with 4wd, but to improve the car’s agility Rome also incorporated torque vectoring. ‘This is achieved through two slipping clutches, an electric actuator which actuates the disc so one clutch is connected to the right side, while the other clutch is connected to the left side,’ Longo says. Of course, with such a complex system, comes an increase in the number of
The Munich car featured plenty of advanced technology including topology optimisation to reduce the weight of its upright. It also made use of GKN metal additive manufacturing techniques to minimise the motor housing to fit within the wheel hub FORMULA STUDENT 2018 www.racecar-engineering.com 11
FORMULA STUDENT – TECH ANALYSIS
Suspension design and set-up was yet another area which resulted in a vast array of solutions from the teams
The Munich car features a very advanced aerodynamic package including DRS on the rear wing, a Formula 1-style shark fin, a monkey seat and a complex front wing and undertray
components and therefore weight. In addition to positioning the three differentials next to the driver to minimise the effect on balance, the Rome team also used carbon fibre extensively throughout the design to try and account for this mass increase. The wheel assembly, for example, is entirely made of carbon fibre, including the uprights, hubs and rims. Carbon fibre was also used for the suspension arms which are actually flexible. The engine is longitudinally mounted while the team arrived in Silverstone this year with its first ever full aerodynamic package. Unfortunately, a retirement during Endurance meant that Sapienza Corse finished the competition down in 20th place. However, it’s car design was the talk of the paddock and even more impressive was the fact that the majority of the components were manufactured in house and by the students.
Gram prix
In addition to hydraulic interconnected suspension Edith Cowan’s car features a beam axle and a heave spring at the rear
Another team that always arrives with a fascinating car is Munich, and this year was no different. You might describe Formula Student as ‘Formula 1 cars, but made by students’ and Munich’s car is exactly that. This year’s iteration features an impressive F1-style aero package including DRS, a monkey seat and a shark fin. The chassis is a full carbon fibre monocoque with an inventive powertrain solution and an award-winning upright design. ‘We’ve really focused on light-weighting, our car weighs 156kg which I think is the lightest four-wheel drive electric Formula Student car,’ says Julian Ratschiller, head of suspension at TU Fast from Munich. ‘For example, we have built our very own silicon carbide inverter which has been a really big step for us. Our inverter weighs around 2.6kg, compared to 7kg if you were to buy one, so ours is much lighter. We also have carbon fibre rims that weigh only 800g, which is one of the lightest designs in Formula Student, and we have also changed to lightweight dampers for this year.’
Perfect package Edith Cowan produced many of its car’s parts in-house including its own dampers, which are based on a design from Ohlins 12 www.racecar-engineering.com FORMULA STUDENT 2018
Packaging has also been a key consideration; effective packaging of the accumulator has led to a very slim rear chassis and it’s the same story for the suspension, uprights and powertrain.
A diagram illustrating how the innovative hydraulic interconnected suspension on the Edith Cowan car works for each of the modes
‘At 90km/h, in theory our car will actually generate enough downforce to run upside down’
The all wheel drive wheel hub consists of an electric motor with a laser sintered aluminium body which was designed and developed by the students at Munich themselves. By using the GKN metal additive manufacturing technique, the motor housing could not only be optimised to fit within the wheel hub, but could also incorporate cooling channels to maximise efficiency. So, in effect, the electric motor is actually part of the chassis. ‘In terms of overall downforce, we have a CLA of 6.8 which equals approximately 1100N of downforce at 60km/h, so at 90km/h, in theory our car will generate enough downforce to run upside down,’ highlights Simon Biechele, aerodynamic team leader at Munich. ‘The monkey seat we have is quite unique, it is actually part of the cooling system, so it guides the airflow coming out of the radiators and helps to create a low pressure zone on top of the radiator to help suck the air out.’ Munich, unsurprisingly, came first in the Design part of the competition, whilst winning the Sprint, Acceleration and Skidpad events. It was also awarded a prize for the most efficient car. Sadly, its Endurance event did not go quite as well and overall it finished fourth.
Interconnected
Suspension design and set-up was yet another area which resulted in a vast array of solutions. One of which was the hydraulic interconnected suspension system on Edith Cowan’s car. ‘The main purpose of this is to increase roll stiffness whilst reducing warp stiffness.
Warp stiffness accounts for a higher mechanical grip than you might otherwise have without decoupling the suspension,’ explains Bryson Murphy, head of suspension and manufacturing at the Australian based team. ‘It also allows for a stable aero platform to maximise downforce,’ Murphy adds. ‘For example, the roll motion is governed by the pressure in the accumulators and this pressure acts as a gas spring, which enables us to tune the roll stiffness. The set-up of the lines in the system and how they are routed is what allows the accumulators to have minimal effect in warp and heave, but a significant effect in roll. Therefore, during cornering, the whole chassis doesn’t roll, maximising the downforce of the aero platform in the corners.’
Custom made
The entire suspension system is made by the team in-house, including producing its very own dampers which were based on a variant from Ohlins. The only part that was carried over were the valves. This development philosophy applies to the engine too, which is a completely custom engine based on the Ducati 695. ‘We carry over the heads and engine rotating assembly and the block is designed and cast by the students,’ explains Murphy. ‘The block is a single-speed powertrain with the ability to interchange an external gear to vary the gear ratios for each track. We decided to go for this custom v-twin because it decreased complexity and weight whilst also maintaining torque at low rpm.’
Herts and minds
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Hertfordshire turned up with an interesting rear wing design featuring DRS and an additional element forwards of the main arrangement. Simulation showed the aero package was worth a ‘couple of seconds’ around the Silverstone course
ne of the most interesting rear wings at this year’s FSUK was to be found on Hertfordshire’s car. This featured three elements, DRS and an additional aerofoil situated in front of the main arrangement of elements. ‘We had a target to increase the downforce by about 20 per cent on the rear end to give us a nice 50-50 balance, but we knew that increasing this would increase the drag so that’s why we have implemented the DRS system,’ explains Elliott Cook, team leader and drivetrain manager at UH Racing. ‘The top element serves two purposes,’ Cook adds. ‘Firstly, it gives the rear wing more rigidity and it does actually produce a lot of downforce on its own. There’s no point putting something on the car if you don’t know how it works so we have tested with the aero kit on and off to see if there is any lap time advantage. Around this track [Silverstone] we gain a couple of seconds with aero. When we went out testing on a much shorter track we gained 0.8s per lap. These wings weigh about 3kg at the front and about 4kg at the rear so to be faster with that weight disadvantage clearly shows just how much downforce is produced.’
FORMULA STUDENT 2018 www.racecar-engineering.com 13
TECHNOLOGY – SLIP ANGLE
Formula Student 101 Slip Angle provides a summary of OptimumG’s seminars
OptimumG engineer Claude Rouelle’s 101 top tips for Formula Student teams continues with some thoughts on dampers, chassis rigidity, and even finding sponsorship for your FS project
p, balance, control and stability simulations are e of the main focuses at OptimumG. Formula Student is really a project management and engineering design competition based on a racecar, rather than a true motorsport discipline
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esides his leading role at renowned vehicle dynamics consultancy OptimumG, Claude Rouelle also offers his services as a design judge in Formula Student competitions. Which means he’s well-placed to advise those looking to take part in Formula Student events.
26. Let’s start off where we finished last column, with a quote from Albert Einstein: ‘We cannot solve our problems with the same thinking we used when we created them’. No more comment needed here.
27. There are two kinds of people: People who win and people who make excuses. Choose what kind of person you want to be.
28. What makes a car perform is tyre grip. The first thing that influences a race tyre’s grip is its temperature. The first thing that influences tyre temperature is damping. Sometimes an overdamped car makes the car half a second slower because it is more difficult to drive, yet one second faster because you can generate more lateral and longitudinal accelerations.
29. The ideal damping in heave is not the ideal damping in roll and pitch. In heave, the dampers control the chassis movement and the tyre deflection against the forces acting on suspended and non-suspended masses. In roll, the springs and the anti-roll bars control the chassis and tyre movements against the forces and moment acting against these masses and their inertias. It is difficult to get the most from heave and roll control unless you decouple heave and roll stiffness and damping.
30. Formula Student competition is not motorsport. It is good training if you want to work in motorsport, but it is not motorsport. It is a project management and engineering design competition based on a racecar. The best proof is that a so-so car can get a pretty good result with a very good driver. Formula student is about preparing future engineers for their career. Focusing on car performance only is
There are two kinds of people: the people who win and the people who make excuses. Choose what kind of person you want to be 14 www.racecar-engineering.com FORMULA STUDENT 2018
The good race engineers know what the ideal tyre temperature is – it is simply the one they had when they were winning races good but not enough. You need to explain, with an engineering approach, why your car is good and what could make it better.
31. Put your steering wheel straight. Is your rack centred? Do you have a tool to lock your steering rack in its centred position? Now measure your left and right wheelbase. Are they the same? If you have more than 1.5mm of difference (that is about one per cent of the wheelbase), you have real issues with your jigs or your manufacturing process, or both.
32. No two dampers are the same. Put the same bump and rebound damper setting on two different dampers and test them on a dyno. You will most probably see big differences. To have two dampers giving the same force vs velocity curve, you could need different bump and rebound settings. That is the very reason you need to use a damper dyno.
33. Many water coolers are way too big and, consequently, too heavy. They also create unnecessary aerodynamic drag. With good inlet and outlet ducts inside your sidepods, you can significantly increase your cooler efficiency.
34. Here’s a recipe for tubular chassis design: Minimum of tube, minimum of nodes (ideally three tubes per node), and maximum of triangulation. That is how you can get both high chassis stiffness and low mass.
The first thing that influences a race tyre’s grip is its temperature and the first thing that affects this is damping. It’s also worth remembering that no two dampers are quite the same, so damper dynos are vital
35. Most students do not understand, or they simply underestimate, the importance, of chassis and suspension compliance. Nothing is rigid; 0.2mm of deflection here and 0.3mm of deflection there, and suddenly your front camber or you rear toe is far, far away from what you thought it was. From the driver input (steering wheel, brake pedal, throttle) to the tyres’ contact patch, there are dozens of non-linear springs, dampers, and hysteresis that compromise the racecar’s response to that driver input. Compliance is the biggest enemy of your driver’s control and confidence.
36. Chassis torsion stiffness FEA analysis does not mean a thing unless it has been compared with workshop measurement. If the two numbers are not the same, that’s okay, providing you can explain why that’s the case.
37. If you simulate or measure the chassis torsion stiffness, you need to apply realistic loads at suspension pickup points instead of irrelevantly at the front and rear bulkhead.
38. A soft spring in series with a stiff spring is still a pretty soft spring. There is no point in having a very stiff chassis and compliant suspension wishbones.
To achieve both high chassis stiffness and low mass with a tube frame there is a simple recipe to bear in mind: minimum of tube, minimum of nodes (ideally three tubes per node) and maximum of triangulation FORMULA STUDENT 2018 www.racecar-engineering.com 15
TECHNOLOGY – SLIP ANGLE
You can’t solve engineering problems without engineering inputs 39. Camber compliance from rims can easily be 0.7-degree per g. If your car takes 3g in lateral, your dynamic camber calculation is already wrong by two degrees compared to a simplified kinematics software simulation. That is from the rim only.
motion ratio different than the one calculated without FEA is the deflection in the region of attachment of the rocker axis on the chassis.
then that is not what Formula Student is really about) I don’t know how you can design suspension without a relevant tyre model.
43. The last thing you should be drawing is the
46. A tyre is a complex system that includes many
40. Designing a suspension with rod ends in
chassis. The chassis is nothing more than a big bracket that holds everything.
different sciences, it is part engineering and part black magic. Track and ambient conditions that could change lap after lap, car set-up, driver’s style, etc. That is why a tyre model only gives you an indication, not a perfect prediction of what the tyre forces and moments will be on the track.
bending is simply criminal.
44. Good race engineers know what the ideal tyre 41. The same goes for suspension linkages axis that do not pass through a chassis node.
temperature is – it is the one they had when they were winning races. Pretty much the same can also be said for the tyre pressure.
47. You should be spending as much time testing
42. Single shear is a bad idea. Toe link rod end attachment on an upright is an example of this. Another example is a rocker axis on the chassis. One of the biggest sources of compliance that makes the real, measured wheel versus the spring
45. You can’t solve engineering problems without engineering inputs. That is why, for example, you need tyre force and moments models. Unless you use extensive and expensive trial and error (but
and developing your racecar as designing and manufacturing it, especially if you are a new team. The two most common Formula Student weak points that I see are the driver’s lack of skill and a lack of car reliability. How do you train your drivers and improve your car reliability if you do not test it? Professional teams with zillions of dollars and hundreds of people still manage to break things during races. How can the members of a little, inexperienced Formula Student team believe their car will be reliable without testing? Three to five months and 500 to 1000Km of efficient testing before the competition is an absolute minimum. You will reduce your lap time much more by testing your car one month earlier than by spending one more month designing it.
48. Some students can’t give design judges a
A single tyre is in itself a complex system that’s subjected to a multitude of variables, from driving styles to track conditions, which is why a tyre model only gives you an indication and not a perfect prediction
precise number on testing time and distance. You need to carry a notebook all the time which contains your test run sheets that show all the test data: the start and end set-up, start and end time of each run, numbers of laps ran, lap time, tyre temperature and pressure , atmospheric conditions, track temperature, weather conditions, driver comments, set-up changes, and so on.
49. Unless your design decisions are backed up by in-lab tests and on-track validation, you won’t impress anybody. Remember, this is a design competition, not a simulation competition.
50. You just can’t ask for money from a sponsor so that you ‘can put his company stickers on your car and have fun building and running your mini Formula 1’. Ask yourself what is the win-win situation for both you and your sponsor. See page 24 for points 51 to 75
CONTACT Claude Rouelle Phone: + 1 303 752 1562 Enquiries: engineering@optimumg.com Website: www.optimumg.com There are plenty of stickers on this car but gaining a proper sponsorship deal for Formula Student is tough and a team needs to persuade a company it will be getting more than just decals in return for its support 16 www.racecar-engineering.com FORMULA STUDENT 2018
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INSIGHT – WORKING IN MOTORSPORT
Pole positions If you want to know what it’s really like to work in professional racing and, more importantly, how to clinch your own dream job in motorsport, then you need to talk to those on the front-line. Racecar did just that By GEMMA HATTON
18 www.racecar-engineering.com FORMULA STUDENT 2018
I
n professional motorsport every racecar requires a team of full-time engineers who dedicate their lives to maximising its performance. But how many engineers make up a team? What does each of them do? How does this improve the performance? Not many know the answer to all these questions and, unfortunately, this lack of insight into the inner workings of race teams, particularly in the trackside environment, is the reason why motorsport is facing a huge shortage of quality engineering talent. It’s by no means a new problem, either. ‘I had no exposure to motorsport growing up,’ says Bernadette Collins, who is senior strategist at Racing Point Force India. ‘The TV coverage at the time was very focused on the drivers and the cars and not so much on the engineers working on the pit wall, or the mechanics working in the garage, so I was unaware that those jobs
‘When you are instructing your race drivers or mechanics there has to be absolutely no doubt in your voice’ Trackside, the engineering ladder usually starts with a data or performance engineer who ensures that all sensors are recording reliable data, which is then analysed to advise the race engineers on potential areas of improvement.
Race engineers
Race engineers sit on the next rung of the ladder and are the link between the team in the garage and the driver out on track. Not only are they responsible for managing and working with the drivers to get the best out of them, but they also work with the mechanics, tyre and strategy engineers as well as the suppliers, absorbing as much information, data and feedback as possible to converge on the optimum set-up changes for their racecar. ‘There is a general misconception of what a race engineer’s position is,’ says Leena Gade, three-time Le Mans-winning race engineer.
‘Really, you’re just another engineer on the team who just happens to have a lot more responsibility because you are in charge of the whole car as opposed to one component.’ And that responsibility means making decisions. ‘In endurance racing, what you decide to do at the pit stops dictates how much time you’ve lost in the pits and you therefore have to try and balance that off later in the race,’ Gade says. ‘When you make that decision, sometimes you are basing that on only having 80 per cent of the information, but when you are instructing your drivers or mechanics there has to be absolutely no doubt in your voice. Even if you think your decision is wrong, a decision that is wrong is better than no decision at all. Everyone is a good quarterback on the Monday after the race, but in the heat of the moment if you are not confident about your decision, watch what happens at the pit stop – it will be utter chaos.
Getting this many people to achieve a 2.5s pit stop requires teamwork of the highest order. The ability to work in a team is a fundamental attribute if you are after a job in motorsport
even existed. I just never considered that it takes a team of engineers to run a racecar and no one explained to me that those engineers had probably done a mechanical engineering degree. I didn’t study mechanical engineering to get a job in Formula 1, I studied it because I really enjoyed maths, physics and technology, as well as the more practical aspects.’
Quick work
There are approximately 80,000 components in a modern Formula 1 car and each one of these components requires engineers to design, simulate, test, manufacture and optimise it to achieve the highest performance. Then you have the trackside engineers who are responsible for exploiting this performance at the circuit through analysing data and tuning the characteristics of these parts to the desired set-up for that particular track, car and driver.
Race engineers are responsible for optimising the performance of both the car and the driver and the only way to become one is to gain experience in the lower formulae. Leena Gade (left) started her successful career helping out in Formula Vee FORMULA STUDENT 2018 www.racecar-engineering.com 19
INSIGHT – WORKING IN MOTORSPORT
‘Motorsport is a culture, a lifestyle, it is an environment in its own right and you have to be in it to really know if you like it or not’ You have to be quite tough skinned and there is always going to be times where you get it wrong. But afterwards, if you can be pragmatic about it and analyse the areas of improvement, then you can fix it ready for the next race.’
The bosses
Then there are the chief race engineers, the technical directors and/or the team principals who oversee the engineering of both cars as well as the entire trackside operation and are the only ones who can overrule the race engineer’s decisions. Depending on the size of the team there will also be engineers responsible for strategy, tyres, control systems, aero, reliability and electronics, who not only feedback to the race engineers at the track, but also their corresponding departments back at the factory. ‘Before the event we have two days at the factory where we do as much prep work as we can, so we try and determine which tyre compounds we are going to use and in which session,’ says Collins. ‘We try to pre-empt what the degradation, pace and therefore race strategy is going to be like based on historical data to give our drivers an idea so that they can then drive accordingly. Throughout the weekend we then try to manage the sessions and take as much information as we can from our car but also from across the field. ‘Going into the race we try to plan a strategy for every eventuality, whether that be weather conditions, crashes or safety cars,’ Collins adds. ‘While during the race it’s about being in a position where we’ve done all the background work so we are ready to react to the ever-
Trackside jobs do not stop with the race teams and another route into high-end motorsport is working for the suppliers – tyres, brakes, oils, lubricants and many others – that are an essential part of the racing scene
changing situations and hopefully stop on the right lap and change to the right tyres. I then spend the entire week after the race analysing our performance and comparing that to other teams to determine if and how we could have done better and what we need to learn so that hopefully feeds forward to the next race.’ Then the whole process begins again. A group of trackside engineers who are less well known are those of the suppliers and partners. Whether they manufacture brakes,
tyres, transmissions, electronics, oils, engines or radios, each supplier will send representatives trackside to help teams utilise their products. ‘Being on the engine side you get to work with both the mechanics and engineers of both cars and I enjoy that diversity,’ says Margarita Torres Diez, F1 power unit engineer for Mercedes-AMG HPP, who is currently responsible for the running of Valterri Bottas’ power unit. ‘Friday is the first time the engines are run properly during the race weekend, apart from a few fire ups on Thursday. My job is to ensure that we can extract the maximum performance out of the engine and sort out any issues. We spend many hours analysing the data and sending reports back to the factory and then set up the calibrations for the weekend. ‘During the sessions I am mainly checking all the temperatures, the energy deployment, ensuring we are within our pre-determined limits as well as making sure that the driver is in the right engine setting,’ Torres Diez continues. ‘The current V6 engines are a lot more complicated than the previous V8s, but that means they are also a lot more interesting too, so it is always a new challenge.’
Home work
Working in motorsport will give you a lifestyle that’s unlike most other occupations. To survive the long hours at the track and being many miles from home you have to be passionate about it. You also need to understand that you are a part of a team 20 www.racecar-engineering.com FORMULA STUDENT 2018
Of course, it’s not just the trackside environment that can offer you a thrilling and fulfilling engineering career. The factories of race teams, suppliers and manufacturers are all hives of activity, filled with engineers who spend their days delving into the finite detail of designing,
making and optimising complex parts. ‘My main responsibility is the aerodynamic development of the LMP1 car from the very first concept right through to the finished racecar,’ says Silvia Santarelli, senior CFD engineer at Toyota Motorsport. ‘Of course, my main goal is to maximise the performance of the car through improving the aero efficiency. I mainly use CFD to design the shape of the parts, run simulations and then analyse the results and then work closely with the wind tunnel engineers to try and obtain the best performance. I have the opportunity to work on many different areas of the car, whether that be the low or high downforce bodykit. ‘We have a lot of freedom to be creative because you always need to do something new to try and improve to beat the competition,’ Santarelli adds. ‘I get a huge sense of satisfaction and pride when I see a part on the real car which I have designed, it is extremely rewarding.’
The lifestyle
But what is it really like working in motorsport? ‘Motorsport is a culture, a lifestyle, it’s an environment in its own right and you have to be in it to really know if you like it or not,’ says Gade. ‘It’s great thinking it’s glamorous, or that race
engineers are gods with a sixth sense for setting up racecars, but that doesn’t exist. It’s about hard work in an environment that is alien to a lot of other industries, educations and people. I think people assume it’s really easy but it isn’t. You have to learn that in racing it’s all about everything working together. Yes, you may need one or two people to pull it all together but you need everyone to be on the same wavelength and thinking in the same way. ‘It’s easy to agree things as a group, but it’s a whole other thing to take a command or give a responsibility to someone without questioning them,’ Gade adds. ‘Success or failure is never down to one person and I get hugely frustrated when people say “you won Le Mans”. No I didn’t, my team won Le Mans and I happened to be part of that group. Your team always comes first, otherwise you will be unemployed, then it’s your car crew and then your ego if it even gets a look in. There were weekends where we were better than most, but I can guarantee that there was always something we needed to fix, but that’s what I like about motorsport; there is always that challenge to win, or win again. ‘Then there will be other weekends that are just horrendous from start to finish and it becomes a downward spiral which you have
to try and stay on top of otherwise it becomes uncontrollable. Those weekends are actually where you learn the most, not just about the car or yourself, but also about people’s personalities and how that affects your team.’ Arguably the most pressurised motorsport jobs are those on the pit wall, where decisions are made live, during the race, and need to be right. ‘Equally those are the jobs with the most instantaneous reward and that does become almost addictive,’ says Collins. ‘The adrenaline, the extreme peaks of pressure and focus really gets your heart going, which is something you don’t often get back at the factory. Everything is sort of amplified at the track. Of course that makes it tougher, you lose more weekends and work longer hours, but that rewarding feeling of achieving a good result is worth it.’
Getting started
Of course, the chills and thrills of working on the pit wall of a race team can often seem in another galaxy compared to you sitting on the sofa watching the race on TV. But in truth, it is much closer than you think. You just have to be proactive, ready for a challenge, and first of all become a weekend warrior. ‘I started out making cups of tea for a Formula Vee team,’ says
Arguably the most pressurised of all trackside jobs are those on the pit wall, because decisions need to be made live during the race – but the adrenaline rush can become addictive
‘Your team always comes first, otherwise you will be unemployed’ FORMULA STUDENT 2018 www.racecar-engineering.com 21
INSIGHT – WORKING IN MOTORSPORT Gade. ‘We would clean and fix the cars, replace gearboxes and lift the engines out and I didn’t care because I was getting my hands dirty, I was involved in motorsport and I was learning. That set me up for a Formula BMW team who needed someone to download the data from the car, and of course then I ended up analysing this data and becoming their data engineer. I wasn’t being paid for anything, it was voluntary on my weekends, but those were the weekends I learnt the most. I had zero intention of becoming a race engineer when I went to Audi, I went in as an engineering assistant and then one thing led to another and, all of a sudden, I was race engineering Audi’s only surviving car, 10 hours into Le Mans in 2011!’
Helping out
Getting yourself to race tracks, introducing yourself to race teams and offering to work for free – even if it means cleaning wheels to start with – is the only way to make it in motorsport. Not only does this improve your knowledge, but it gets you moving within the circles of racing; making those all important contacts. Engineering degrees from highly regarded universities have become an expected and expensive formality to get you through the doors of HR. But no longer is achieving a firstclass degree good enough to make you stand out from the crowd. Not even taking part in
‘The adrenaline, the extreme peaks of pressure and focus, really gets your heart going’ Formula Student warrants a cheer anymore, because it is already the norm. You need to have real motorsport experience. ‘I completed my degree and got a place on McLaren’s graduate scheme. But alongside that I gave up my weekends to do data and then race engineering for one of the GTE teams,’ says Collins. ‘I also got involved with race support in mission control during the F1 races, just helping with reports to try and integrate myself within the team. I then got the opportunity to stand in for one of the performance engineers in 2013 and became a full-time performance engineer in 2014 before I moved to Force India to take up my current role as a strategy engineer.’
The right stuff
Getting involved at your local circuit doesn’t necessarily have to be as part of a race team. There are many other roles that can gain you invaluable experience to help you get your foot in the door. ‘When I was 18 I got my license to be a marshal for my local race track and so marshalled the pit exit position for one year,’ says Torres Diez. ‘I then did my license to be
a scrutineer, and then I became technical scrutineer for four years, and then I was a technical delegate of the Spanish Rally Gravel Championship for the Spanish Federation.’ Degrees, experience, contacts are not the only ingredients you need to succeed. You also need to believe. Motorsport is an industry that thrives on competition, and there will be times where you fail that interview, or lose that lap of data, and you will probably get rejected by almost every team you apply to. But it only takes one ‘yes’ to begin your motorsport career. ‘My 10-year old self would never have imagined that I could have this position in Formula 1 and I maybe should have had a little more confidence in my ability,’ says Collins. ‘I just felt that my background was so far away from motorsport that I didn’t realise it was really an option for me and I should have had more self belief to just go for it’. The message is: no matter what your background is, how old you are, or whether you are male or female, never give up – because if you want to work in motorsport enough, then you will find a way to get there.
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TECHNOLOGY – SLIP ANGLE
Formula Student 101 Slip Angle provides a summary of OptimumG’s seminars
OptimumG engineer Claude Rouelle’s 101 top tips for Formula Student teams continues with some thoughts on budgets, aerodynamics and racecar set-up
C
laude Rouelle plays a lead role at renowned p, balance, control and stability simulations are vehicle dynamics consultancy OptimumG. e of the main focuses at OptimumG. On occasion he also offers his services as
with you many observations about your racecar ergonomics and its on-track behaviour, but they might also attract the TV reporters.
a design judge in Formula Student competitions, which means he’s in an ideal position to offer advice to those looking to take part in these events.
53. Be realistic: you will not make a competitive
51. Let’s begin where we left off with point 50,
54. The best sponsors are not necessarily the ones
discussing sponsorship. Sponsors do not buy your project; they buy into what you believe in. So it’s all about selling your emotions.
giving you money. You will get more benefit from technical partners who give you material or parts free of charge; you might also be able to engage in fruitful engineering conversation with them, too.
Formula Student car with a budget of $10,000.
52. There are only two kinds of sponsorship: with and without television. If you can have your racecar shown on local or even national TV, it will also be easier to get sponsors. Invite a professional racing driver to drive your car. Not only will he or she share
55. Never say to a judge that you ‘did not have the money’. The money is there. If you do not get it, it is because you do not know how to find it. Similarly, never say to a judge ‘we did not have the time’. If
you do, you are presenting yourself as a victim. Instead, say ‘we did not take the time’. You are the one overseeing your project, deciding your goals and priorities within your means.
56. It’s worth including in your upright and chassis design some adjustability in suspension pick up points. A difference of just a few millimetres of suspension pick up points coordinates can sometimes give you major performance increase. Of course, you won’t have the possibility to test different suspension kinematics if your racecar is finished just a few weeks, let alone a few days, before the competition starts.
57. On any circuit, even street courses with a lot of braking and acceleration, a five per cent increase in
A five per cent lateral grip increase will give you three to five times the lap time gain of a five per cent increase in longitudinal grip
While sponsorship of any type is always welcome it’s often the companies that supply parts and advice rather than cash that prove the most useful of backers 24 www.racecar-engineering.com FORMULA STUDENT 2018
Of all the car set-up parameters the rear toe adjustment has by far the biggest influence on the racecar’s control and stability lateral grip will always give you three to five times the lap time gain given by a five per cent increase in longitudinal grip. That is why camber control in roll is more important than camber control in heave.
58. I have seen slow motion videos of in-lab tests of Formula Student cars (four- or seven-post rigs) where, at some frequencies, the wheel moves versus the chassis but the damper-spring unit doesn’t! Indeed, in one case, I saw the edge of the rocker axis moving on a circle of about 12mm of diameter. Sometimes your compliance is the suspension. It’s worth performing some FEA with frequency, as all good aircraft engineers will do.
59. I would expect a good team to show design judges each wheel toe and camber compliance (in deg/KN or deg/KNm) graph versus separate or combined inputs of tyre Fx, Fy, Mx, My and Mz in simulation and from workshop measurements. That implies building a simplified K&C test rig. Of course, such workshop measurements are not worth anything unless you explain how they helped you to validate (or not) your FEA simulation, to design this year’s car (or will help you to design a better next year car), and how you included these numbers in your vehicle dynamics simulation.
60. Good drivers can feel the difference of a
It’s worth including some adjustability in suspension pick up points in both your upright and your chassis design. A difference of just a few millimetres can sometimes reward you with a major performance gain
0.1-degree of rear toe adjustment. That gives you an idea of the importance of the accuracy and the repeatability of the rear toe adjustment. In fact, within all the car set-up parameters, the rear toe adjustment (and compliance) has by far the biggest influence on the car’s control and stability.
61. If a design judge with his hands on the front and rear part of your wheel simulates a selfalignment Mz torque and he can see or feel a toe angle variation your suspension has unacceptable toe compliance. Back to the drawing board. The Mz that even a strong human being will be able to produce is smaller than the Mz created by your tyre.
62. The two best ways to avoid toe compliance is to make sure you design your upright with a large distance between the toe link pick up points and the wheel centre while also having the toe link (or the steering arm) as perpendicular as possible to the chassis longitudinal axis.
63. The fishing string is simply not an accurate enough tool for measuring toe.
64. If you want to play aero, play aero. A good aero design judge will want to see your downforce, drag, side force, aero-balance, aerodynamic roll, pitch, and yaw moments numbers in 5D; front and rear ride height, yaw angle (with as much as
Extreme aerodynamic packages are part and parcel of Formula Student competition. But you will need to ensure you have all the relevant figures at your fingertips if you want to impress a good aero design judge FORMULA STUDENT 2018 www.racecar-engineering.com 25
TECHNOLOGY – SLIP ANGLE
CFD numbers are usually 20 per cent too good compared to reality 180-degree yaw angle when your racecar spins and goes backwards), steering angle, and roll angle. Of course, they will also want to see how you use an aeromap in your vehicle dynamics simulations.
65. Bear in mind that CFD numbers are usually 20 per cent too good compared to reality.
66. Do not even consider playing with CFD unless you simulate a moving floor and rotating wheels.
67. A few years ago, we were asked by a journalist to predict the lap time of a Formula 1 car on the Austin circuit before the first visit of F1 to the COTA (Circuit of the Americas) race track. We were wrong by six tenths of a second, which in Formula 1 is a pretty big gap. But the reality was that two weeks before that first grand
prix took place we did not know what the tarmac temperature was going to be and in which direction the wind would be blowing, and that’s to name just two of the parameters that influence the lap time. There are too many parameters (the racecar, the driver, track, environmental conditions, etc.) to be spot on in your predictions. What is important is to evaluate the lap time variation (much more than the absolute value) versus the amount of fuel, or the front wing angle or the static rear ride height. We really need to work in delta, trends and sensitivities more than in absolute value.
68. If two numbers (for example, performance prediction from simulation and recorded test data) are not the same, at least one of them is wrong. It could be your simulation input or algorithm is wrong, or it could be your sensor is not properly
calibrated, or it might be both. However, if two simulations give you the same results it doesn’t necessarily mean they are correct. In any case, all simulations are wrong, but some are useful.
69. There is no useful measurement without another kind of number: the degree of uncertainty.
70. You cannot get realistic and useful anti-dive, anti-lift and anti-squat numbers unless you have a relevant tyre model, a good knowledge of your brake balance distribution and, in the case of combined lateral and longitudinal accelerations, a relevant differential model.
71. Any bodywork part (sidepods, engine cover, nose, panel to access the pedal box, etc.) should be able to be removed and then attached back on to the car in less than 30 seconds. If not, you need to go back to the drawing board. Similarly, any toe or camber or ride height adjustment should not take more than two minutes. If it takes longer, again, back to the drawing board.
72. Do not start to manufacture any car part or jig unless all drawings are complete. If you do so, you should be able to manufacture and assemble your car in six weeks with no surprises, and you will know the complete list of materials and parts to purchase.
73. Brake fluid is hygroscopic. The boiling temperature point goes down significantly with the humidity percentage. Flush and replace the brake fluid after a test or a race in the rain.
74. Brake fluid is incompressible, right? Then why
Competing in the wet is about more than simply considering the reduced grip – for instance, brake fluid is hygroscopic and so this needs to be flushed out and replaced after the racecar is taken out in the rain
is there a brake pedal stroke? Put a dial gauge right where the brake master cylinders are mounted on the chassis, or on the brake caliper. Push on your brake pedal and look at your dial gauge. You will get a good example of what compliance is here.
75. Performance is like a volume. That is, Volume = Surface x Height. But the surface here is your starting conditions: the size and experience of your Formula Student team, the strengths of your teacher, the software you have access to, etc. You cannot blame yourself for the things you have no influence on, such as the team state at the time you joined it. However, you can influence the height of the volume – and that is your input. See page 34 for points 76 to 101.
CONTACT Claude Rouelle Phone: + 1 303 752 1562 Enquiries: engineering@optimumg.com Website: www.optimumg.com Bodywork pieces such as sidepods and engine covers need to be removed and then replaced within 30 seconds. Similarly, any toe, camber or ride height adjustment should not take more than two minutes 26 www.racecar-engineering.com FORMULA STUDENT 2018
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FORMULA STUDENT – CHASSIS DESIGN
‘As a general rule of thumb the torsional stiffness of the chassis should be at least 10 times the stiffness of the suspension’ 28 www.racecar-engineering.com FORMULA STUDENT 2018
The chassis of Formula Student cars range from steel spaceframes to fully moulded carbon fibre monocoques, plus some interesting alternatives
Skeleton key With chassis choice relatively free in Formula Student the debate over whether spaceframe or monocoque is best – or even some other solution – rages on. Racecar weighs up the pros and cons of each approach By GEMMA HATTON
H
umans have skeletons, and racecars have chassis. Although, unlike a skeleton, a racecar chassis can come in many different configurations and materials using a variety of manufacturing processes – this is particularly the case in Formula Student. The regulations in Formula Student are relatively free, permitting teams to experiment with both metal
tube spaceframes and composite monocoques. The only restrictions are that of the main hoop and its bracing which must be made of steel. This has led to some very interesting designs over the years, with some teams even arriving at the track with bamboo bodywork. As long as a team can prove that its material satisfies the required safety tests, and all the data is submitted to the scrutineers, it can race.
Chassis options
Essentially there are three main types of chassis in Formula Student: a tubular spaceframe, a full monocoque and a hybrid of the two with a monocoque at the front and a spaceframe at the rear. The most common is a tubular spaceframe, with around 75 per cent of this year’s teams at the UK competition arriving
with one. This is typically made of mild steel tubes that have been welded together. The bodywork can be non-structural or structural with the latter consisting of composite panels such as carbon fibre reinforced plastic or aluminium skins with aluminium or Nomex honeycomb cores. These panels are permanently bonded to the steel tubes whereas the non-structural bodywork is a simplistic shell which can be removed with fasteners. ‘Although we don’t have the resources or the money to design a monocoque, we did spend a lot of time using our simulation tools to determine what we thought was the best chassis, and that was a steel spaceframe,’ says Elliott Cook, team leader and drivetrain manager at Hertfordshire. ‘We have also put in carbon panelling and bonded those in place to increase the stiffness of the chassis, without having to invest in expensive tooling. The raw steel cost us in total around £300. Add to that the cost of the carbon panels for the side impact structure and manufacturing a spaceframe is a really cheap thing to do.’ Cost is obviously the key advantage of racing with a spaceframe, particularly in
FORMULA STUDENT 2018 www.racecar-engineering.com 29
FORMULA STUDENT – CHASSIS DESIGN
Steel spaceframes, such as this design from Warwick Racing in GRM Genesis software (left), are an effective solution for Formula Student. Full moulded monocoques, such as this Formula 1 example (right), are lightweight and have increased torsional stiffness. It is often the expense of the latter approach that drives Formula Student teams to opt for the former
a student competition where the resources at some universities can be extremely limited. A spaceframe is also relatively simple to design and manufacture and any modifications required during testing and competition can be easily achieved through a few simple welds. A monocoque, on the other hand, requires re-manufacture if damaged.
Stiff test
Yet despite the teams’ efforts of bonding composite panels to a spaceframe to increase chassis stiffness, this is by no means the optimum solution. Martin Ogilvie, former Formula 1 car designer with Lotus and the mastermind behind cars such as the Lotus 92, explained why when he visited Warwick Racing earlier this year. ‘As a general rule of thumb, the torsional stiffness of the chassis should be at least 10 times the stiffness of the suspension. For a spaceframe, ideally you want 2000ft.lbs per degree and that is very difficult to achieve on a Formula Student car due to features such as the high rear roll hoop. Whereas with an aluminium or carbon honeycomb chassis you are much better off. For example, you can build the chassis up to the roll hoop, which is by far the strongest part of the car.’ Trying to increase the stiffness of a spaceframe is a challenge as it usually results in increasing the weight, which is a major disadvantage, particularly when spaceframes are relatively heavy structures to start with. Alternatively, teams can fall into the trap of focusing on a lightweight spaceframe, which can actually be designed to achieve a similar weight to a monocoque, but of course it will have compromised stiffness.
Hot tubs
Top: A fully moulded monocoque, shown here on the Bath car, can achieve a much smoother curved profile which can be more aerodynamically efficient. Bottom: A car that makes use of a folded monocoque can have a more boxy appearance 30 www.racecar-engineering.com FORMULA STUDENT 2018
This is why the teams that can afford it choose a full moulded carbon fibre monocoque, because this allows them to create a lightweight yet stiff chassis. Furthermore, teams can adjust the angle of each ply during layup, as well as the number of plies to tune the strength of their monocoque to their specific requirements. ‘We have improved the layup of our carbon fibre monocoque and now we think
Cost is obviously the key advantage of competing with a spaceframe chassis, particularly in Formula Student we have one of the stiffest chassis,’ says Julian Ratschiller, head of suspension at Munich. ‘With a monocoque you are also more free in terms of packaging, particularly for an electric powertrain such as ours. In our opinion, if you want to manufacture a good aerodynamic car, then you have to go for a monocoque rather than a steel spaceframe.’
Cut and fold
Manufacturing methods can often play an important role in improving performance, especially when it comes to the development of the chassis. For those teams who wish to design and make a monocoque, but don’t have the necessary resources to make moulds and undertake a full composite layup, there is an alternative; the cut and fold technique, which several of this year’s teams have opted for.
This process starts with a large sheet of aluminium honeycomb with either aluminium or carbon fibre skins bonded on either side. A CNC machine mills out grooves corresponding to the flat template of the chassis. The width and number of these grooves dictates the bend radius and bend angle required. This machining process does not penetrate all the way through the material. This therefore allows the honeycomb to bend along these grooves, creating each side of the chassis – similar to how cardboard boxes are folded together. The assembly is then secured through a series of jigs all held together with ratchet straps. The joints are then glued and left to set. Once cured, the inside of these joints can then be reinforced with additional material such as wet carbon layup or folded aluminium sheet, depending on the skin material, for increased strength.
Cut and fold is a cheaper alternative to making moulds and doing a full composite layup. This is Edith Cowan’s pattern for its monocoque. Note where the carbon fibre skins and the honeycomb have been CNC routed to allow the material to bend
‘The trick comes in the actual folding,’ Ogilvie says. ‘Obviously you need a gap at the joint which then closes up to zero when it is folded. Therefore, each gap has to be tailored to a different width which is another challenge. The really difficult debate is how deep the groove is. If you groove it right down to the bottom and take all the honeycomb out, then it tends to kink once it has been folded, but if you leave some of the honeycomb in, then it won’t fold. It is a very difficult compromise, that is even more difficult with carbon fibre skins because the carbon tends to be too stiff.’
Skin in the game
Despite this, carbon fibre skins seem to be the preferred choice for those teams exploiting the cut and fold technique. ‘Our monocoque is made up of two carbon fibre reinforced skins with a Corex aluminium honeycomb in the middle and we essentially have three panels; the floor and the two sides,’ explains Joseph Jones, business development manager at Oxford Brookes. ‘Bending carbon fibre is not always easy because as everyone knows, it is very brittle. However, we can manufacture our whole monocoque in house, by ourselves, although it is a labour intensive and timeconsuming process. We developed this technique back in 2014, where our monocoque had a carbon skin on the inside, and an aluminium skin on the outside. In 2016 we moved to carbon skins for both and have been refining the manufacturing process ever since.’ The main benefit of the cut and fold technique is that it requires minimal tooling and machining, as the jigs can be made out of MDF or metal, and there are no complicated tooling blocks. These cost savings allow teams to then pump more resources into other design areas of the car to improve performance.
Accurate jigs
Once bent into shape the material needs to be accurately jigged and held together with ratchet straps while the glue cures, otherwise the chassis can move during the curing process which could result in inaccurate suspension mounting points
On the other hand, there can be issues with the accuracy of the folds, joints and the suspension mounting points. If the chassis is not jigged effectively during the bonding process, then the joints and therefore the chassis can move around as the glue cools back down to room temperature, which is where the inaccuracies can begin to creep in. For example, this can result in misalignment of the wheelbase, track width and wheel alignment, all affecting the overall suspension geometry. ‘Our jigs are made of CNC routed wood and laser cut metal, so the jigs are quite accurate,’ says Ross Marais, head of manufacture at Oxford Brookes. ‘Throughout the jigging process we took a lot of measurements, consistently
FORMULA STUDENT 2018 www.racecar-engineering.com 31
FORMULA STUDENT – CHASSIS DESIGN
‘If you want to manufacture a good aerodynamic car, then we believe you have to go for a monocoque rather than a steel spaceframe’ re-checked them and also compared it to our CAD data so that we could try and transfer the accuracy of the jig over to the folded monocoque. The variances in our kinematic points between CAD and the real monocoque were very small. I think our biggest difference was one point which was approximately 5mm different, but we were able to deal with that because we had good communication with the suspension team so that they could adjust the wishbone geometry accordingly.’
Mounting rescue
Another benefit to a monocoque is the freedom to mount the suspension in the optimum position. A fully moulded monocoque allows complete freedom with this, whereas a cut and fold monocoque requires the suspension to be mounted away from any folds. A spaceframe, on the other hand, is extremely limiting in terms of suspension design because there are set points, called nodes, to which the wishbones, springs and dampers have to be mounted for structural integrity. These nodes are typically the triangulation points where several bars are joined together. This therefore restricts the region on the chassis in which the suspension elements can be attached whilst maintaining an efficient design. In terms of the actual fixtures, again this is yet another area where there are both pros and cons. Physically attaching the suspension mounting points to the middle of a honeycomb panel can be a challenge, especially if the honeycomb sheet is already bonded to the skin. This typically requires complex inserts which act as local reinforcement to avoid crushing the composite panel. These inserts again need to be accurately jigged while the glue cures in order to maintain the desired suspension geometry. A spaceframe, on the other hand, does not require any additional reinforcement, therefore the suspension brackets can be welded on at any time.
Space race
Despite the challenges of folding carbon fibre this seems to be the preferred solution for some teams, including Oxford Brookes which uses carbon fibre skins and aluminium honeycomb as shown here: top image is front and bottom is rear 32 www.racecar-engineering.com FORMULA STUDENT 2018
Overall the optimum chassis solution will always depend on the available resources of each team. Like anything in engineering, there is no point in doing something if you can’t do it well. Monocoques, whether moulded or folded, require an extensive amount of research to ensure the manufacture is carried out accurately to capitalise on its lightweight and torsional stiffness benefits. On the other hand, a spaceframe will continue to be a reliable, effective and cheap way of constructing a chassis, and therefore these will continue to dominate Formula Student grids.
TECHNOLOGY – SLIP ANGLE
Formula Student 101 Slip Angle provides a summary of OptimumG’s seminars
OptimumG’s 101 top tips for Formula Student success concludes with Claude Rouelle’s final 26 pearls of wisdom – including advice on bump-steer, stability and communicating with drivers
B
p, balance, control and stability simulations are esides his leading role at OptimumG, Claude e of the main focuses at OptimumG. Rouelle also often offers his services as a design judge in many Formula Student competitions. He started his 40-year racecar engineering career by designing and building a racecar and a wind tunnel; it was his engineering degree master thesis. The challenges he faced then were similar to those faced today by students building a first car for Formula Student competition. He is then, ideally placed to offer his advice. Below are his final 26 short engineering and team building tips, the rest can be found on pages 6-8, 14-16 and 24-26. If you’re not a student? Well many of these gems are also applicable to professional race teams.
thickness between the set-up pad and the bottom of the chassis) versus the ride height variation will give you a bump-steer law that most kinematics software with no compliance will give you too. With compliance it is worth adding load (sandbags for example) to simulate the aero load and/or the longitudinal weight transfer. You do that with real springs and real tyres at hot pressure and measure the toe variation and the ride height variation. The ratio between these two measurements will give a more realistic motion ratio number. The other alternative could be, lucky you if so, putting your car on a K&C rig. But the usefulness of these K&C tests depends very much on the test preparation.
80. It is worth putting your car on the set-up pad
76. When you design your Formula Student car,
78. You can’t perform serious tests without an
81. In the same spirit, it is useful to load your
think about the installation on the chassis of the tools that you will be using to measure each wheel’s toe: fishing string or, much better, laser beam on a flag. The fixture of these tools on to your chassis should be part of your racecar design.
accurate set-up procedure. You need a set-up pad with four scales that are perfectly horizontal. It is well worth making sure your measurement reference plane is, and stays, horizontal.
Formula Student car step by step with sandbags and measure your dampers’ length, your tyres’ loaded radius, chassis ride heights, cambers and toes. It will give you very useful information that is worth comparing with your simulations. In any case, always believe more what you measure (if you measure accurately) than what you simulate. Simulation is for trends and sensitivities (the slope of the curve) not for absolute values.
79. Car balance is very sensitive to the tyre static 77. A bump-steer target should be part of your set-up sheet. You need to define how to measure the toe variation versus the ride height variation. Without compliance, the toe measured with step by step dummy damper length reduction on a set-up pad (or blocks of wood of different
load variation. On an FS car 0.5kg of cross weight difference (LF + RR compared to RF + LR) statically with an asymmetric set-up, or dynamically, with for example an anti-roll bar adjustment, could change yaw moment (and hence car balance) by as much as 20 per cent: a huge difference in the car’s behaviour.
and turning your steering wheel from full left to full right and return, and let’s say every 30 degrees of steering wheel movement, measure your LF, RF, LR and RR ride heights, your corner weights, your cambers, your damper lengths, and your LF and RF steering wheel angle. It will give you camber, corner weight, ride height, motion ratio and Ackermann curves that will be worth comparing with your simulation curves. Moreover, if these curves are different from turning the steering wheel from full left to full right and full right to full left, you know there is an asymmetry in your car and it is worth investigating what the causes of this are.
82. There are four ratios that are, ideally, linked and which will determine your racecar grip and balance. These are the weight distribution, the tyre cornering stiffness distribution, the aero-balance and the anti-roll stiffness distribution.
83. In a rough estimation, the front and rear tyre cornering stiffness ratio is within a few per cent of the front and rear tyre width ratio. But that really is a rough estimation. Ideally, you will have to look at your front and rear tyre cornering stiffness from your non-linear tyre model. Beware: a tyre cornering stiffness (N/deg) is not the tyre lateral stiffness (N/mm). They are related though; a larger tyre will give you a bigger lateral stiffness and a bigger cornering stiffness but the ratio between the two stiffnesses is not necessarily linear.
84. On a rear-wheel drive car that has the same
Drivers are much more sensitive to the racecar’s balance than they are to the amount of grip available 34 www.racecar-engineering.com FORMULA STUDENT 2018
front and rear tyres your simulation will show that your best lap times are reached when your weight distribution is about 46 to 49 per cent. That is often the best compromise found between pure cornering (skid pad for example), pure braking or
Formula Student corners are so tight and so low-speed that stability is less of a concern than on more normal race tracks acceleration (in a straight line) or a combination of both braking and cornering (in the corner entry) or acceleration and cornering (at the corner exit). If you are outside that percentage, you are probably compensating undesirable chassis and/or suspension wishbone and upright compliance with your springs and anti-roll bars.
85. I have no problem with a Formula Student racecar with a weight distribution of 40 per cent front and 60 per cent rear, but that car should necessarily have larger rear than front tyres.
86. Usually, on a good car with limited compliance, the weight distribution (front weight / front + rear weight) and the cornering stiffness distribution are within one or two per cent of each other.
87. The wheel rate is the spring rate divided by the square of the motion ratio. Motion ratios are rarely constant by design (and/or by compliance); for an aero car you want a decreasing motion ratio (increasing wheel rate) versus ride height as the downforce is square-of-the-speed sensitive.
With suspension you should always put far more faith in what you measure than in what you simulate
88. Usually the front to total anti-roll stiffness (spring and anti-roll bars in parallel, themselves in series with the tyre wheel rate) distribution percentage (front Nm/deg / [front + rear Nm/ deg]) is not far away from your weight distribution. If there is more than five per cent difference that means you compensate severe chassis or suspension compliances with your spring and anti-roll bar stiffness. Patches on patches: you could get a good balance (yaw moment) but not the best possible grip: less lateral acceleration than your tyres should give you.
89. The need for stability increases with the speed. On most racecars the aero-balance percentage is one or two per cent smaller than your weight distribution. In other words, the centre of pressure (CoP) is always behind the centre of gravity (CoG). That number could go up one or two per cent at very high speed. But a Formula Student car is a different animal; the corners are so tight and so low-speed that stability is less of a concern than on more usual race tracks. It is very possible to have a five per cent, or even more, bigger aero-balance number than the weight distribution.
90. There’s no such thing as understeer or oversteer. There is under yaw moment (or under yaw acceleration) or over yaw moment (or over yaw acceleration). The goal is to get the biggest possible lateral acceleration and the yaw moment you want when you want it. There are 12 causes of yaw moment: four tyres Fy, four tyres Fz and four tyres Mz. Good vehicle dynamics knowledge will help
It is good practice to have a driver report car balance, grip etc on a sliding scale rising from zero to 10
you to decide how to change your set-up and from there your tyres’ forces and moments, and from there your balance (yaw moment). You will know the yaw moment you need at every part of the circuit if you have a good car, tyre aero model, and you know the shape of the trajectory.
not feel a 0.5s lap time difference, although the best ones will conclude they have a better car because at the corner exit they change gear earlier. But give them a touch of understeer or oversteer and they will complain, believe me!
92. Lap time simulation is good, but not good 91. All drivers are much more sensitive to balance than grip. I defy even good drivers to feel a difference between 2.1 and 2.2g lateral. If you remove the lap time from the dashboard they will
enough. Many students will use it, often randomly changing the set-up, and see improvement, but do not often understand, qualify and quantify the why and the how of the set-up change on performance.
FORMULA STUDENT 2018 www.racecar-engineering.com 35
TECHNOLOGY – SLIP ANGLE
Race engineers should ‘translate’ their simulation results or data analysis into a language that the car’s driver can understand 93. It is a bigger priority to first understand how your racecar design and set-up parameters influence these six essential targets: grip, balance (yaw moment), control (yaw moment created by a given steering angle variation, in Nm/deg), and stability (yaw moment created by a given yaw angle variation, in Nm/deg) on corner entry and in the corner, and stability at the apex.
car is dirty. This leads us to the next advice on the order in which you should perform the different tasks; you clean, you inspect and maintain and only then you set the car up. Cleaning the car helps you to inspect it in every detail. What is the point in adjusting the ride height with a 0.5mm accuracy if you have not seen a crack in an upright?
96. The goal of the racecar engineer is to correlate 94. Let’s go testing. Testing what? How? When? In which order? You can’t go to a race circuit to test your racecar without a test plan.
95. A good mechanic is a clean mechanic. You should be able to work on your car all day long wearing a clean white shirt. If not, that means your
subjective feedback from the drivers as well as objective simulation/data results. Most engineers are not good drivers and good racing drivers are rarely good engineers. Race engineers should ‘translate’ their simulation results or data analysis in driver language. The driver involvement in the racecar design and set-up is valuable but has its
limitations. His or her focus should be to get the best out of the racecar out on the track, whatever the car’s strengths and weaknesses are, and get back to the engineers with the most accurate and detailed racecar behaviour description.
97. A good way to help each other as an engineer and driver is to create a correlation between subjective and objective measurements. Here is an example of how this can be done. The driver is asked to quantify the racecar stability from zero to 10. Based on previous debriefs, the race engineer knows that when the driver’s happy (a 10) the stability number at corner entry is, for example, 4000Nm/deg. But today the driver is not happy and gives a four on the stability subjective quantification. The engineer sees the stability number is 2500Nm/deg. With good vehicle knowledge and a good simulation software and a bit of experience, the engineer will know what to change to go from 2500NM/deg to 4000Nm/deg.
98. A design judge will want to see your internal engineering reports, not only the eight-page design report that teams will submit a few weeks ahead of the competition. They will want to see the big binders with calculation methods, test reports, lessons learnt from success and failure, the ‘if-money-and time-were-not-an-issue’ dream to do list. It shows how well the knowledge is transmitted inside the team from one year to another.
99. There are two questions a design judge will ask
The driver’s role in the build is valuable but has limitations, and they should concentrate on the driving
themselves when they look at your racecar: ‘If I had the opportunity would I like to drive that car?’ and ‘If I had to buy a Formula Student car, would I buy this one?’ Some Formula Student cars could be fun to drive but not to buy because their maintenance cost and reliability are questionable.
100. If you have 100 teams at a competition you will only get one winner. Does that mean you have losers? No. There’s always something to get from these events. What every student learns at a competition is teamwork and delivering on-time, on target performance, as well as leadership – and God knows this world needs leaders. 101. There is no need to panic in design judging. And remember, this is not about life and death. It’s much more important than that!
CONTACT Claude Rouelle Phone: + 1 303 752 1562 Enquiries: engineering@optimumg.com Website: www.optimumg.com
Every part of the car should be spotless. By cleaning it carefully before setting up you might spot issues 36 www.racecar-engineering.com FORMULA STUDENT 2018
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