RCE- Formula Student 2013 Event Review by The Chelsea Magazine Company

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DIGITAL SPECIAL

Formula Student

Evaluating FSAE aerodynamics 2013 event report Alternatives for a spaceframe chassis

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CONTENTS – FORMULA STUDENT EDITION

Sustainable racing History was made at the 2013 Formula Student UK competition at Silverstone as an electric car took overall victory for the first time. This result can be read one of two ways; either electric is the future for Formula Student, and needs to be embraced by all teams that have ideas about winning, or that the categories need to change. In other competitions, electric cars are classed separately, but that brings its own problems - why would a team invest so much money in this new technology if it is only for a class win? There needs to be a compromise. In this special edition, we also discuss the increasing presence of carbon chassis into the competition. Motor racing is expensive, and will never be cheap, and some may argue that it is better to explore these new technologies at the Formula Student level of competition

than wait until graduates are exposed in professional motorsport to this technology. Yet there is a sustainability issue here - top teams have turned towards major motor manufacturers to help them prepare for the competition, both with composites and with hybrid technology. That sort of backing is not widely available, and raises the spectre of the haves and the have nots. Should the marketing departments be put to use to put together sales pitches to these companies? After all, for the competition to replicate the reality of motor sport, being able to lay hands on money is key to success. It boils down to the point of Formula Student, a valuable competition in an ever more competitive and expensive world. Is it to train engineers to find innovative solutions, or is it to train them to work in motor racing?

Carbon Hybrid chassis

The alternative to a steel tube spaceframe chassis - we look at whether or not it works

Aerobytes

For me, it should be the former. That does not mean that students shouldn’t explore electric systems and carbon chassis, but there should be other solutions. Motor racing is about to go through a change; it is no longer only about raw power, it is about fuel economy, weight and reliability. Also, increasingly, motor racing teams are finding lucrative funding sources from outside motorsport (look at Williams Hybrid, Zytek and McLaren). Hybrid systems are undoubtedly one part of the solution, but they do not solve our crisis. Look at Gordon Murray’s city car, or read Professor Andrew Graves’ book ‘Build to order - the road to the 5 day car’. In the business presentation of the competition, sustainability is a critical feature of the scoring and for good reason. Motor racing will not continue forever, or even for long, if it is not relevant.

EV Motor technology

The latest alloys used in motors

Getting a job with Mercedes

We put a Formula Student car in the wind tunnel, and let the students run the programme

Mercedes High Performance Powertrains uses Formula Student to recruit the best new thinkers, and puts them to work on its latest F1 engine

Electric shock

Save Formula Student

Electric cars dominate the Formula Student UK competition for the first time

One of our readers takes exception to the way in which the competition is developing

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Formula Student supplement • www.racecar-engineering.com

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TECHNOLOGY – TUBULAR FRAMES

Perfecting the spaceframe chassis It's been written that the spaceframe chassis has been optimised. It hasn’t, says one former Coventry University student

The hybrid spaceframe has a torsional rigidity of 4,450Nm, which is over four times greater than the steel spaceframe that it was designed to replace. There were negligible weight savings due to constraints on material dimensions, although the specific strength of a hybrid spaceframe is significantly higher

he tubular steel chassis is not fashionable any more. These days almost every young engineer wants to use advanced composite materials like carbon fibre to design their new car. They even turn their noses up at the use of a tubular chassis. They argue that steel chassis are heavy, lack rigidity and are not as safe as composite monocoques. Those in favour of the tubular steel chassis argue that the ‘spaceframe’ is cheap, easy to manufacture, easy to repair and highly versatile. But one student at Coventry University in England wondered if it would be possible to get the best of both worlds. Replicating the thoughts of many low-cost formula car designers over the years, such as those

behind the British-built Rossalini FV391 Formula Vee, could he replace at least some of the steel with readily available composite tubing? Giorgio Demetriou took his university’s 2012 Formula Student car design (a steel tube frame) and investigated converting the design into what he calls a hybrid spaceframe. The results are relevant to anyone designing or building cars in an open rules environment, such as Formula Ford, Vee or a number of SCCA classes. ‘I aimed to develop a chassis which is competitive with composite monocoques used in Formula Student, but which could be manufactured for substantially less cost in a shorter timeframe,’ explains Demetriou. ‘I realised quickly

that there were two key points to address: the use of tubular carbon fibre in spaceframe construction and the application of direct metal laser sintering as a manufacturing process to create connection nodes.’ One of the key points of the project was that Demetriou and the other Coventry students did not want to modify the existing design in any way, leaving the hard points and geometries as they were. ‘Spaceframes have been used

for many decades, and as a result much research and testing has gone into the optimised design. An ideal framework would consist of only struts and ties, pin jointed and loaded at the joints,’ adds Demetriou. ‘It could be argued that tubular chassis design has been completely optimised, and literature has been written to this effect. The design of a spaceframe chassis is unique to each vehicle and each will pose a new set of packaging constraints. A good spaceframe will receive

Table 1: carbon tube selection Tube

Material

Wall Thickness

Baseline 1

Steel

25.4mm

1.6mm

Baseline 2

Steel

25.4mm

1.25mm

Replacement 1

CFRP

28mm

1.84mm

Replacement 2

CFRP

26mm

1.56mm

Formula Student supplement • www.racecar-engineering.com

TECHNOLOGY – TUBULAR FRAMES EQUATIONS

!"#$%"&' !"#$%&' !"#$ (!!! ) = 32! ! !"#$%ℎ(!!)

!"#$%&'( !"#$%&' !"#$ !!! = 36.8! ! !"#$%ℎ (!!)

∴ !"#$% !"#$ !!! = !"#$%"&' !"#$%&' !"#$ + !"#$%&'( !"#$%&' !"#$

!"ℎ!"#$! !"#$% !ℎ!"# !"#$% = !"#$% !"#$ ! !"ℎ!"#$! !ℎ!"# !"#$%&"ℎ

! !!!

The required Joint Shear Force was to be equal to the force required to take a baseline steel tube beyond its elastic limit. This force was calculated, using the below formula, as 18.8KN. !"#$$ !"#$%&'() !"#$ (!!! ) = !!! ! − !!! ! = 62!!! ! !"#$% !"#$% ! = !"#$% !"#$!"#ℎ ! !"#$$ !"#$%&'() !"#$ (!!! ) !!! = 18.8!"

Figure 1: FSAE chassic comparison

loads directly into nodes and distribute these throughout the chassis, causing minimal distortion to any of the members.’ The ethos of the Coventry University 2012 FS Vehicle was ‘lightweightness’, which restricted the quantity of tubing that could be used to construct the chassis. There was a balance to be found between torsional rigidity and mass. Collected data for various Formula Student vehicles can be seen in Figure 1 above, which

shows mass vs rigidity. Demetriou wondered if the same stiffness could be achieved for less mass by using off the shelf carbon fibre tubes, which are relatively low cost and readily available. He realised that he would have to overcome the metal-tocomposite bonding challenge, and went on to investigate how the concept would impact the 2012 Coventry car. The Carbon Fibre tubes were sponsored by Exel Composites

UK and were to be from their Exelite range of high strength tubes. A spreadsheet was created which utilised macros to derive wall thickness. This allowed the outside diameter of a tube to be specified, due to compact packaging constraints, while the wall thickness was varied. The spreadsheet also had the ability to display the mass of each tube and thus derive the percentage weight saving between the two tubes. Savings for equivalent

tubes were 68 and 75 per cent respectively. These savings, however, don’t include the mass of a metallic node. ‘Due to the sponsor only offering us a specific type of tube with 36.8mm OD and 32mm ID, we were a bit limited in the real world,’ says Demetriou. ‘This tube only provided a 46 and 45 per cent weight saving and was over-specified by a factor of 3-4 in terms of strength. The other major impact of the increased tube diameter was that the floor thickness would consequently change. That would have a big impact on the damper mounts on the Coventry car which are incorporated into the floor. With an increased diameter of the floor rails, it would not have been possible to use the same mounts or floor.’ STEEL OR COMPOSITE? Despite this, Demetriou managed to complete the modified hybrid design, which can be seen (see Table 1, p61) showing that while some steel members could be replaced by composite tubes, not all of them could be. However, in many cases, this was due to the lack of choice in carbon tube availability to Coventry, and in reality would not be a major concern. The bulkhead needed to remain in steel to accommodate the mandatory FSAE crashbox. The design of the Coventry crashbox was such that it required the anti-intrusion plate to be welded, around its perimeter, to the frame. With a carbon frame an alternative method of attaching the plate would be required. As previously explained, any increase in the diameter of the tubing would not accommodate the existing hardware for the damper mounts. There would also have been an issue regarding ground clearance – the bottom of the spaceframe would be 11mm lower, plus the depth of a node causing the vehicle to ground out when experiencing heave or single-wheel bump. The pull rod used for the

'A good spaceframe will receive loads directly into nodes and distribute them throughout the chassis with minimal distortion' www.racecar-engineering.com • Formula Student supplement

front suspension operated along an arc, which avoided a clash with the diagonal member (at point four) by 2mm as full bump/ rebound. Increasing the diameter of the tube to 36.8mm would create a bending moment at the point of clash, causing the pull rod to catastrophically fail. In a similar fashion, both the lower and upper rear wishbones would foul on the rear bracing supports if the diameter of the tube was increased to beyond 26mm. The wider tubes also meant that the FSAE mandated cockpit template would not fit, so the cockpit surround remained in steel. The next challenge was what to make the nodes out of and how to attach them to both the composites and the remaining steel chassis elements. Titanium has the greatest strength per unit of mass, although mechanical properties alone cannot be viewed in isolation when deciding node material. FSAE regulations state that: ‘alternative tubing geometry and/or materials may be used except that the Main Roll Hoop and Main Roll Hoop Bracing must be made from steel, ie the use of aluminium or titanium tubing or composites for these components is prohibited.’ This presented three possible methods of attaching a node to the Roll Hoops: Adhesives Mechanical Joint Welding An adhesive connection was designed, although it was deemed to be too high risk. It was thought that welding steel and stainless steel would be the most reliable method of joining the nodes to the roll hoops. However there is up to a 35 per cent reduction in yield strength when welding steel. The temperatures required to rework (Post Welding Re-annealing) under 300degC would damage the carbon and adhesive, so this process could not be used. So eventually Demetriou decided that a mechanical joint would be the simplest method of

attachment, although adhesives would replace any bolts. The addition of a bolt and the extra material used to create the node greatly increased the overall weight. A spaceframe chassis comprises of only ties and struts in tension or compression. The design of the node socket restrains a carbon tube in such a way that it cannot translate along its axis, thus removing any shear loading on the adhesive during compression. The tensile forces acting on a member are resisted by the adhesive; creating a shear stress. By using ALM (Additive Layer Manufacturing), it is possible to grow small arrowshaped pins on to the surface of the metal part, which embedded into a carbon fibre part can provide a tough and durable joint. The principle of incorporating mechanical ‘pins’ to reinforce a chemical joint in shear has been applied to the node ends. An alternative method of manufacturing a mechanical joint was creating cavities by allowing adhesive to flow through the substrate to form an adhesive pin, illustrated by the yellow region seen in the image above. The ideal dimensions of the node end would be 0.5mm larger/smaller than the carbon tube, with the ‘pip’ keeping the tube concentric and controlling the bond gap. The dimensions of the socket were dictated

One of the key elements of the chassis concept was the adhesive joint, which utilised small holes in the nodes to form an adhesive pin (seen above in yellow). These were the actual reason for the project not seeing fruition. Formula Student judges did not feel that an adhesive joint could be visually inspected. Giorgio Demitriou argued that you could indeed visually inspect such a joint, and offered empirical test data, but the decision went against him

by the internal and external diameters of the carbon tubes, and to compensate for any manufacturing errors in the tube, the size was made to accommodate a tube furthest from specification as per the manufacturers tolerances. The length of the sockets would dictate the surface area of the node socket, thus defining the bonding surface area and the resultant joint strength. A spreadsheet was created which computed the minimum socket

length required to produce the necessary bond area. The spreadsheet caters for different adhesives and baseline material dimensions and mechanical properties. This allowed retrospective changes to be made to calculations, should full-scale adhesive testing results vary from scale testing. But as anyone who has put up a modern dome tent knows, arranging a set of composite tubes and nodes is not always straightforward. Indeed, with

'The temperatures required to rework steel would damage the carbon and adhesive, so this method of joining the nodes was rejected' Formula Student supplement • www.racecar-engineering.com

Limited Slip Limited Slip

High Performance Differentials for High Performance Cars www.sperrdifferenzial.com

TECHNOLOGY – TUBULAR FRAMES the Coventry design it was impossible. Demetriou found that it would not be possible to slide multiple tubes into position as each tube/socket aligned along a different axis. The solution that the team created was to fabricate the chassis in segments, which could then be welded together. Meanwhile, the steel segment of the spaceframe would only be tack-welded during assembly to allow for the some flex in the members, permitting

the internal shapes of the nodes to locate on to the internal faces of the tubes. Even once the manufacture and design of the hybrid spaceframe had been worked out, the question remained: could the composite tubes take the load? A failure in any of the tubes when the chassis was at speed would likely be catastrophic in more ways than one. Extensive simulation work conducted by the Coventry students suggested all would

be fine, but it relied on a number of assumptions. ‘With minimal data it was crucial to complete physical testing to characterise the material to refine the limited FEA and verify theoretical values,’ admits Demetriou. ‘The only provided value for the tubes was to have a stiffness of 100MPa, although an orientation was not specified.’ Unfortunately, a proposed partnership to manufacture the nodes between the Coventry team and a German firm fell

LOAD TRANSFER AND ROLL STIFFNESS An investigation by The University of Leeds’ School of Mechanical Engineering was able to determine the chassis stiffness that ensures the vehicle’s handling is sufficiently sensitive to changes in the roll stiffness distribution. ‘If a vehicle has a 50:50 weight distribution, with a 50 per cent roll stiffness distribution, it is the case that no load transfer is required,’ they said. This is an idealised and unfeasible scenario, but serves as a useful example for the inverse. If an unbalanced vehicle has a large roll stiffness distribution, then the chassis is required to be capable of transferring large loads, achieved through high torsional rigidity. The total roll stiffness – defined as ‘the sum of front and rear roll stiffnesses’ – can be viewed as a multiplier when selecting a chassis

torsional rigidity. A vehicle is more sensitive to roll stiffness distribution and torsional rigidity as the total roll stiffness increases. The diagram below shows the results from a simulation by Deakin for a 50:50 weight distribution vehicle, with total roll stiffness of 15,000Nm using varying chassis stiffnesses. It can be seen that if a 40:60 roll stiffness distribution was required, then a disproportionally large percentage change of roll stiffness is required to achieve the target when using the softer chassis. For example, to achieve a 40:60 distribution with a 300Nm/degree chassis, an 8:92 roll stiffness distribution is needed. The weakest chassis (100Nm/deg) was not able to transfer the required load. The above figure shows that with significantly lower roll stiffness, the chassis which have a lower stiffness

are still responsive to changes in roll stiffness distribution. All but the weakest of chassis (100Nm/Deg) was able to provide the required load transfer with all above 600Nm/Deg having an almost linear relationship. The most crucial value used to decide the stiffness of a chassis is total roll stiffness as the non-linear relationship between roll stiffness distribution and load transfer worsens with higher roll stiffnesses. The nature of Formula Student creates lightweight vehicles which tend to have roll stiffnesses below 700Nm/Deg. Given that FSAE regulations insist on many safety tubes of given dimension, it is not physically possible to create a chassis which will be unresponsive to changes in roll stiffness distribution, for example below 300Nm/Deg.

through. This meant that the hybrid chassis was never completed, and the physical testing did not take place. But the design results showed great promise. A key criteria used to measure the success of the project was total chassis mass. The most basic of hybrid members had a total mass of 0.502kg, almost half of the equivalent steel tube (0.920kg). But the overall chassis weight saving was insignificant. The total mass of the original steel spaceframe was 26.2kg, not including the floor or bulkhead. The hybrid spaceframe had a calculated mass of 25.1kg, not including the adhesives. This is a total weight saving of 1.1kg, or 4 per cent. BULKY PACKAGING ‘The relatively insignificant weight savings are due to the over-sized carbon tubes,’ explains Demetriou. ‘Although the tubes still had 50 per cent less mass than the steel tubes, the packing of a 36.8mm tube created much larger and bulkier nodes, compared to one which was designed to accommodate a thinner tube. The most pertinent conclusion to make from my work is that tubular carbon fibre can be used to manufacture a spaceframe chassis, and that nodes are a simple and effective method of joining composite members. The scope for a carbon spaceframe, outside of FSAE, is vast and the ability to start from a blank sheet with design, as opposed to producing a replacement for an existing spaceframe, further extends the scope. The strength and weight advantages of carbon tubing, compared to steel, are considerable and without the mandated use of steel for roll hoops, further weight savings can be made. ‘Carbon tubes are available in an almost infinite array of sizes,’ concludes Demetriou. ‘There is no reason why the lessons learnt from this project cannot be extended to larger vehicles.’ Giorgio's thanks go to James Jarvis, Mark Ali Akbar, Stuart Jackson of EOS, and Mark Stewart of Dassault Systemes Ltd

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TECHNOLOGY – AEROBYTES

Students unleashed University of Hertfordshire Formula Student team won a wind tunnel session, courtesy of the IMechE and Racecar Engineering

Simon McBeath offers aerodynamic advisory services under his own brand of SM Aerotechniques – www. sm-aerotechniques.co.uk. In these pages he uses data from MIRA to discuss common aerodynamic issues faced by racecar engineers

Produced in association with MIRA Ltd

Tel: +44 (0) 24-7635 5000 Email: enquiries@mira.co.uk Website: www.mira.co.uk

ecent trends have seen the blossoming of wings and other downforce-inducing paraphernalia in Formula Student worldwide. How significant are these developments? To answer that question, Racecar Engineering provided a half day session in the MIRA full-scale wind tunnel to the team that the Institution of Mechanical Engineers and Racecar Engineering, judged to have the best publicity and on-event presence in the 2013 Formula Student competition. The winner was the University of Hertfordshire. This was the first year that the University of Hertfordshire, which has been involved in the competition since 1998, had entered a car with a full aerodynamics package, although aerodynamic designs had been worked on in previous years. Analysing the overall performance of its 2012 contender, UH15, the team, comprising 11 MEng students and 35 other members, decided that the only way to make up the three second lap time deficit in the sprint competition was with aerodynamics. An

aerodynamics group was formed under managers Sam Blood and Karl Mackle, who report to technical director Antonio Carrozza, and manufacturing manager and head of chassis development Matt Grant. The first aerodynamic package devised for the 2013 competitions comprised front and rear high downforce wings, with Blood tackling the rear wing design and development, and Karl Mackle the front wing. It was decided to utilise pre-existing aerofoil profiles with coordinates in the public domain, rather than spend time on bespoke profile design. A shortlist of candidates was whittled down with the help of Star CCM+ CFD software to the Selig1223 ‘high lift’ profile for the main elements and flaps, front and rear. The decision to run with dual-element wings front and rear for this first iteration was taken on the practical basis that this configuration required just one slot gap over the wide adjustment range to optimise the sprint, endurance and acceleration phases of the competition, even though a triple-element (or more)

the team decided that the only way to make up the three second deficit was with aerodynamics

Preparations for the session

configuration offered greater downforce potential. CFD was used to establish the optimal relative positions and angles of the main elements and flaps, and also end plate size and shape. Cost and time considerations were also involved in the choice of configuration and overall package design, as indeed were overall car design changes simultaneously underway. The planned quarter scale wind tunnel test of UH16, with wing package in the University of Hertfordshire’s own wind tunnel, unfortunately didn’t happen because of time constraints, apart from some runs on the wing sections only, which compared reasonably favourably with the CFD data. So, the MIRA test was the first opportunity to derive some hard data on the first integrated aero package. MIRA dAtA As ever we should restate that MIRA’s full-scale wind tunnel has a fixed floor and the test car’s wheels are stationary. The fixed floor tends to underestimate the downforce generated by ground-effect devices, including front wings. However, with the ‘boundary layer control fence’ installed and with no downforceinducing underbody on the car, overall under-estimates would be relatively minor, and rear downforce and drag would have been accurately determined. So, how did the car perform? Table 1 shows the data in the baseline configuration (maximum wing angles all round) at just 40mph and 60mph. As usual, and of especial interest in this application because of the very relevant speed range of the Formula Student competition’s dynamic phases, the car was run at two speeds to see if there were differences in the coefficients, and the data is shown in Table 2, together with the differences between the two speeds.

Formula Student supplement • www.racecar-engineering.com 51

TECHNOLOGY – AEROBYTES

The first iteration full aero package comprised front and rear dual-

Setting up the split front wing flaps to maximum

element wing set

The front wing’s upwash could be seen to encounter the rear wing’s flow field

The first observations to make are that although the drag coefficient was rather high, the overall negative lift coefficient was even higher, producing an efficiency figure, -L/D, of over 1.5. Out of interest, comparing this with other open wheel single seaters tested for this column, the Formula Student data is part way between the aerodynamic performance of an early 1980s ‘flat bottomed’ Formula 1 car and the more modern ones we have tested, a 1999 Benetton and a 2007 Honda. Of significance, though, are the differences between the coefficients at 40mph and 60mph. Aerodynamic forces normally increase with the square of speed so, all other things being equal, the calculated coefficients derived from the logged force data would be the same at the two different speeds. For the coefficients to vary with speed, all other things

Flows around the front wing end plate came in for close examination

Table 1 – baseline data at 40mph and 60mph, with the differences in ‘counts’ where 1 count = a coefficient change of 0.001 40mph 60mph Difference

CD 1.158 1.146 -12

-CL 1.758 1.797 +39

-CLfront 0.980 1.055 +75

-CLrear 0.778 0.742 -36

%front 55.7 58.7 +3.0

-L/D 1.518 1.568 +50

Table 2 – overall drag and lift forces in baseline configuration, with downforce as a percentage of static weight 40mph 60mph

Drag, N 244.7 515.6

were not equal. This is not an unusual situation, with the flows over (or more often, under) downforce-inducing surfaces not being fully developed at speeds as low as 40mph. In this instance, what we see in the results is that the front lift coefficient increased by 7.7% from 40mph to 60mph, leading to the conclusion that the flow was better developed (for which read ‘better

www.racecar-engineering.com • Formula Student supplement

-Lift, N 370.2 805.2

% of weight 12.9% 28.0%

attached’) at the higher speed. Remember, all the flaps were at their maximum angles in this baseline configuration, and this may have been too steep for the flow to be adequately attached to the front flaps at 40mph. Wool tufts on the flap undersides confirmed that these flows were not fully attached, and that the higher speed showed improved attachment.

It will also be noted that the rear lift coefficient decreased slightly at the higher speed. This could have been the result of any improvements in flow attachment at the rear being small enough to be masked by the increased mechanical leverage ahead of the front wheels arising from the improved front wing performance. This slightly offloads the rear wheels. Or it could have been the consequence of the upwash of the wake arising from improved front wing flap attachment encountering the rear wing more than previously, thereby slightly reducing its aerodynamic performance. The actual mechanisms are best left to CFD; the wind tunnel simply reports the results measured at the wheels. But the fact that the drag coefficient also decreased, something that is known to occur when a rear wing angle is reduced for example, suggests there may

Tip vortices created the usual fascination at front…

… and at the rear

Cooling flows were also examined

Wing flow attachment was visualised with smoke and wool tufts

have been an actual aerodynamic interaction here as well as a mechanical one. The net result of the front gains and rear losses was a 3% shift in balance to the front from 40mph to 60mph, something that might be felt by the driver if the track contained corners or braking areas taken at the two different speeds. Of more significance, though, is that for a car with a 50/50 static weight balance, the aerodynamic balance was forward biased even at 40mph, this aspect worsening at 60mph, which would make the rear more skittish as speeds increased, provoking some instability under braking, or oversteer in faster corners if the chassis was mechanically balanced at lower speeds. It’s all relatIve… The extent of the influence of aerodynamics on handling and grip does depend, though, on the

Table 3 – aerodynamic forces measured in MIRA at 60mph on the 2012 Dallara F3, and the 2007 Honda F1 with bargeboards removed Drag, N

-Lift, N

% of weight

F3, 2012

343.0

841.1

Approx. 14%

F1, 2007*

530.5

803.3

Approx. 13%

*Bargeboards removed

magnitude of the aerodynamic forces relative to the car’s weight. So, let’s look at the actual forces in that context. Table 2 shows the overall drag and lift forces compared to static weight. Thus, at 40mph, the downforce was 12.9% of the car’s weight, and at 60mph had risen to 28.0% of the car’s weight. At these speeds, these are fairly significant increases in the vertical forces acting through the tyres. (To go off on a tangent for a second - an irresistible calculation at this point is to work out the speed at which the car generates downforce equal to its own weight, at which speed

it could drive across the ceiling, and it comes to 113.4mph!). It is never a good idea to compare the data from cars in different categories except out of passing interest, but this also often proves irresistible…Table 3 speaks for itself. The levels of absolute downforce generated at 60mph was therefore quite similar to the Formula Student’s downforce, but it is the amount relative to car weight that is important, and in that respect the FStudent was well ahead! Clearly the F3 car was much more efficient though, with a lot less drag being created.

Two notes of caution; first, the Honda F1’s downforce was much greater with its bargeboards; second, both the F3 and F1 car generated a large proportion of their downforce with their floors, and as mentioned earlier, MIRA’s fixed floor would lead to a downforce under-estimation of this. Nevertheless the comparisons are interesting and show that the Formula Student car was able to generate a much larger proportion of its weight in downforce at these speeds than either the F3 or the F1 car in the guise mentioned. Next month we will look at the responses to adjustments made in the wind tunnel by the students. Racecar Engineering extends its thanks to the staff and students at the University of Hertfordshire Formula Student Racing Team

Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT

Electric shock The 2013 Formula Student competition made worldwide motorsport history – an electric car beat a combustion car. And the surprises didn’t stop there…

here is no doubt that hybrid and electric vehicles are taking centre-stage in the modern automotive and motorsport industries. In 1997, it all started when the Toyota Prius became the first mass-produced hybrid vehicle; next was the first mass produced all-electric vehicle which came in the form of the Nissan LEAF in 2010. 2012 saw the first hybrid win at Le Mans by the Audi R18 e-tron Quattro and in March this year alone, more than 6.3 million hybrid vehicles were sold worldwide. This trend will undoubtedly continue, as 2014 becomes more electric than ever with the world’s first electric race at the launch of Formula E, and the increased usage of hybrid powertrains in Formula 1.

by GEMMA HATTON And it’s exactly the same for Formula Student. The first electric Formula Student car to take part in a competition is thought to be what was called a ‘hybrid in progress’ (ie electric only), designed by the University of Florida for the 2007 Formula Hybrid competition. In the UK the bar was raised higher the same year with the introduction of a special alternative fuels category, dubbed class 1A. In 2012 it was decided to merge the classes

with both conventional and alternative powertrains running in the same class. At the Silverstone competition this year, electric cars made up 20 per cent of the Formula Student field, which at first seems a relatively small proportion. However, overall first and second place were both won by electric teams. The main issue is the extravagant investment required for an allelectric concept, something which most universities cannot afford. Many teams, when asked, would go electric if they had

Many teams said they would go electric if they had the funds, manpower and time required

ETH Zurich dominated the event with their all-electric car, the first win for an alternative fuelled vehicle in FSAE

www.racecar-engineering.com • Formula Student supplement

the extra funds, manpower and time required. The ‘electric percentage’ will undoubtedly increase over the coming years as more teams compete, the series becomes more global and students see the increased potential of electric powertrains. Another record-breaking fact for this year’s competition: not only was it the hottest event held in the UK, but also the driest. Sun shades, shorts and regular barbecues made the paddock almost glamorous compared to previous years of trekking around in Wellington boots, battling with the wind and rain. Of course, with unexpected highs of 28degC (82degF), teams and their cars now faced an unknown challenge of dealing with the heat – most teams had

completed minimal testing, and those that did tested for a day at most in mixed conditions. It was going to be an interesting weekend, not least for those teams using electric drive. Some were even seen taping bags of ice to the electric motors ahead of dynamic events in an attempt to keep them cool. The performance characteristics of the EVs were clear from the first dynamic events. Unsurprisingly, with torque instantly available, the electric cars dominated the acceleration event, claiming the top three positions, with the University of Stuttgart coming first, Delft University of Technology taking second and TU Dresden third, after the disqualification of the car from Karlsruhe (see p52). The most visually obvious trend for this year’s cars was the integration of advanced aerodynamic packages, and there

all being electric. TU Delft coming first this time with a fastest time of 51.365, the Stuttgart car was close behind at 51.795, and only a tenth of a second denied Zurich second place. They finished third. The toughest event is left until last and is the Formula Student equivalent of a grand prix. With 22km to complete, including a mandatory stop, driver change and hot restart the car’s reliability is pushed to its limits, and with 300 points up for grabs, completing the endurance discipline is what every team works towards. Every year cars fail, don’t restart or even catch fire which completely changes the standings. This year, however, with the added factor of the extreme heat, only 21 teams finished. That means 68 per cent of the cars failed – the highest dropout rate recorded. In the past, the notorious Silverstone weather has caused

The Warsaw team ran a striking design featuring two rear wings, a front wing and an underfloor were some highly interesting approaches, particularly for the acceleration event where reducing drag is essential. Most of the aero-dominant teams either adjusted parts of the rear wings, by altering the position of the slats to reduce frontal area, and therefore drag, or dropped the entire rear wing assembly down to increase top speed. This may seem an obvious tactic, but to actually implement adjustable aero into a Formula Student car can be extremely challenging and demonstrates a high level of forward thinking from the teams. It is fair to say that this year’s aero designs were the most extravagant, with the Karlsruhe Institution of Technology team running a full DRS system, which gained their combustion car sixth place in acceleration. However, the most striking aero design by far was the Warsaw team from Poland which ran two rear wings, a front wing and an underfloor. The same form was repeated in the sprint with the top three

havoc with sudden heavy rain, so for this year’s event, the top 10 cars from the sprint event took to the track at the same time in a ‘shoot-out’ to make it fairer, and – unsurprisingly – there was plenty of drama. The first teams on track were Zwickau, Karlstad and the University of Bath who were the fastest car, lapping at 65.1 seconds. After overtaking Zwickau, Bath then found themselves stuck behind TU Graz, who were a few laps in and ignored three blue flags. Last year’s winning Chalmers started their endurance, but only survived three laps before a rear left wishbone failure – a real shock for such a popular front-runner. Next to join was the Munich team, with their monster rear wing, but their car only lasted two laps due to a driveshaft problem. Zurich began their race, while the Bath car was next to fail at the driver changeover when the engine failed to restart. Karlstad followed suit by also retiring

AMG’s controversiAl enGine

t is fairly unusual for the legality of cars to be protested at Formula Student or indeed at any FSAE event, but that’s exactly what happened this year. During technical inspection the event officials suspected that the students of UAS Graz and Karlsruhe had not done all of the work on the engine themselves. Both teams use an AMG 595cc twin developed specifically for FSAE events. This led to the technical scrutineers requesting an official ruling as to the legality of the engines fitted to both cars, specifically in relation to section IC1.7 of the 2013 rules which states the following: ‘Turbochargers or superchargers are allowed if the competition team designs the application. Engines that have been designed for and originally come equipped with a turbocharger are not allowed to compete with the turbo installed.’ The concern was that from the start of the design process, the engine was designed with the turbocharger installed and this is the package fitted to both cars. It was not clear how much contribution was made by the students and how much by AMG. The protest committee met and produced the following conclusions: • The intent of the regulations is that if an engine is purchased with a turbocharger fitted then it

should not be eligible for the competition with that turbo installation, so the team must design the installation of the turbocharger. • The fact that the engine was originally designed with this turbocharger should not be considered as an issue if the original design was produced by the students. • The main question to answer was therefore: did the team design the installation of the turbocharger? • After discussion between the protest committee and the team members and with feedback from other sources, it was concluded that the turbocharger installation had been designed by the team with appropriate levels of advice and support from AMG etc. So the engines were deemed legal under the current regulations, but the information from the protest has been forwarded to the FSAE rules committee to consider future rules changes which could affect the legality of such engines and whether such engines conform to the spirit of the regulations. Many in the paddock have suggested that they feel future rules should only allow for commercially available massproduction blocks such as the Honda CBR or entirely student developed engines.

Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT COMPOSITE CONTRAVENTIONS

TU Delft’s electric car was a much fancied runner, but failed to deliver

from the race, as the all-famous Delft team came off the start line, but without their new aero package. The electric Karlsruhe car joined the track but due to previously breaking the rules, (see sidebar, p52), their car was running at a very slow 1 min 16 secs per lap. Zwickau were the first of the top 10 to finally complete the event.

as Hertfordshire completed 15 laps before an electronics failure struck, while Oxford Brookes also dropped out with a broken exhaust, which burnt the car’s chassis badly. That left the competition wide open for the overall best Brit position. Stuttgart’s combustion car was one of the few to finish, and

Out of the top 10 best Formula Student teams in the world, only two finished Meanwhile another previous winner, Delft, aborted their race after a disappointing four laps. The electric Stuttgart car joined the drama, but theirs was a shortlived race due to steering issues on the first lap. Another one bit the dust as TU Graz pulled to the side of the track with smoke and steam billowing out of their car, causing a major hold-up for the rest of the teams. The second car to cross the line was Zurich, which only left Karlsruhe running, but that car had damage to one of its motor-gear units. So, out of the top 10 of the best Formula Student teams in the world, only two finished, which although disappointing, made for a very interesting results table. Outside of the top 10 shoot-out, the endurance event continued to be just as dramatic. The battle of the Brits continued

came a close third behind Zurich, which won ahead of Zwickau. After an eventful five days in Silverstone, the overall winner was a fight between the two electric machines of Zurich and Zwickau. But with Zwickau just behind on five out of the eight judged events, Zurich won by 70 points, with the successful endurance result helping Stuttgart Combustion to take third. The top British team only finished 15th, but that was a fantastic achievement for the University of Huddersfield – which proves the effectiveness of having a reliable car that scores consistently. The other surprises were last year’s winners, Chalmers, finishing 17th and the event favourites, Munich and Karlsruhe electric coming 27th and 30th respectively.

www.racecar-engineering.com • Formula Student supplement

am frustrated by a few things from this year’s FSAE competitions, but one gripe has been with me for some years now and I’m fed up of it! It concerns carbon fibre chassis. For me these are all of very bad design indeed, not as engineering objects themselves – indeed some of them are very nice – but as objects designed to fulfil a specific purpose. In the rules there is a very clear statement, indeed it’s rule A1.2, almost the first rule in the book: ‘For the purpose of the Formula SAE competition, teams are to assume that they work for a design firm that is designing, fabricating, testing and demonstrating a prototype vehicle for the non-professional, weekend, competition market … additional design factors to be considered include: aesthetics, cost, ergonomics, maintainability, manufacturability, and reliability.’ I have been increasingly of the opinion that this rule is being largely ignored. I have been that amateur weekend racer mentioned in the rules, and I know many others. To a man they all say that they would not buy a car with a composite chassis. ‘Too expensive,’ they say, ‘if you crash it – which if you drive like we do you will, a lot – you can’t tell how bad the damage is without specialist equipment. And if you have a really good hit, you’ll probably write the chassis off as they are near impossible to repair.’ Further to this, amateur racers look for longevity from their chassis. Formula Ford 1600 chassis racing today are

often more than two decades old – indeed I used to race a 1960s Formula Vee chassis against 21st-century designs, and it could corner with the best of them. The life of a composite chassis is not fully understood, but the consensus in the sport seems to be that they are only good for three or four years before needing either replacement or major repair work. Something else that makes them really unrealistic for the non-professional, weekend, competition market. Students argue that carbon fibre chassis must be the best route because ‘that’s what they do in F1’. They contest that the composite tubs are lighter and stiffer. This is certainly true, but they have lost sight of the point of the competition. F1 teams do not build cars for the non-professional, weekend, competition market despite the performances of some pay drivers at the back of the grid. What frustrates me is that the design judges in all competitions seem to have forgotten this too, or simply don’t realise that composite cars don’t comply with rule A1.2, and we regularly see carbon chassis cars in the design finals. Yes the carbon cars with big budgets are very nice things with good aesthetics and ergonomics, but to my mind I cannot see how they can get good points in the design competition as they fall down on the cost, maintainability, manufacturability, and reliability criteria. But then I suppose I’m not a design judge. Sam Collins

The UAS Dortmund chassis, one of many composite-built models on show

OVERALL WINNER: ETH ZuRIcH This year’s ETH Zurich car featured four internal AMZ M3 Ac hub motors produced from scratch by the team. They produced the same power as their predecessor, but came in at 40 per cent lighter

nce the Karlsruhe electric car had been disqualified from two dynamic events, it is fair to say that the competition was essentially dominated by the team from Switzerland. Its neat electric car impressed many including the design judges, winning that event. The major development for the electric teams this year was the integration of four wheel drive, which Sven Rohner, ETH Zurich’s team leader explains. ‘This year we focused on our drivetrain concept. We changed it from last year’s rear wheel drive to a four wheel drive system, which is a major challenge because not only do we have more motors, but more electrical components and therefore more noise within the communication lines.’ Last year, Zurich ran two outer run AC hub motors, whereas this year’s car features four internal

AMZ M3 AC hub motors which were entirely made by the team. Weighing in at 5kg, the new designs produce the same power as the previous model (32kW) but are 40 per cent lighter. ‘The motors are something we are really proud of because we started with a white piece of paper and developed the

electrical and the mechanical aspects, which allowed us to alter the moment curves and generate efficient designs.’ Composite chassis remain controversial in FSAE, and many consider them to be outside of the spirit of the competition, but the Swiss team has been running carbon fibre

monocoques since 2008, and Rohner believes that is the right choice, ‘F1 use carbon fibre monocoques and it is possible to repair because if you know from the beginning then you make decisions when designing other parts to accommodate repair. Also, as it is naturally stiffer than a normal steel spaceframe, monocoques are the way to go for increased performance.’ Due to implementing the hub motors, the surface area of the chassis could be reduced, allowing the chassis weight to be reduced by 13.3kg. Another weight saving measure is the use of composites in the wheel rims. While far from unique in FSAE, the Swiss designs are very neat indeed. ‘They are single piece and weigh around 850g – one of the lightest in Formula Student. If compared to common aluminium shells, our rims are

"The composite wheel rims are single piece, weighing around 850g" Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT OVERALL WINNER: ETH ZuRIcH (continued) TEcH SPEc Length: 2930mm Width: 1410mm Height: 1550mm Wheelbase: 1240mm Track: 1200/1160mm Weight – no driver: -170kg Weight – distribution including driver: 107kg/131kg Suspension: Double unequal length A-arm. Pushrod actuated horizontally oriented air springs and oil dampers Tyres: 18.0x6.0-10 Hoosier LC0/R25B Wheels: 6.5-inch single-piece CFRP Brakes: Floated, hub mounted, 190mm dia., water-jet cut chassis construction: Single-piece CFRP monocoque Engine: 4xAMZ M3 electric motor

less than half the weight, yet double the stiffness and have increased yield strength.’ Of course, with the integrated gear and hub motor on a 10-inch wheel, space is somewhat restricted. ‘It is really on the edge and tight in there, which is another advantage of our self-developed rims,’ says Rohner, ‘because we can design it to be stiffer, to allow us to go a little tighter – something we wouldn’t have been able to do with aluminium shells.’ Like most of the top cars in the 2013 competition, the ETH Zurich car features large wings, and the trend towards downforce-generating devices has come as no surprise to the Swiss students – it was the first team to fit wings to an electric FSAE car. ‘Last year, aero was more of a “nice to have” feature,’ Rohner adds. ‘Although we completed simulations, wind tunnel and track testing, it wasn’t a fully integrated package – so we could run without it if there were any problems. After learning the performance gains from last year, we integrated

Fuel system: Lithium polymer accumulators Max power: 4x35kW @ 16.000rpm Max torque: 4x28Nm @ 0rpm Transmission: 1.5 stage planetary gearbox Differential: None Final Drive: 1:11.8

aerodynamics into every single part right from the beginning.’ A front and rear wing, shaped undertray and rear diffuser made up the aero package. Particular attention was paid to the font wing as this controls the entire aerodynamic characteristics of the car. According to the team, the overall aero package increased the downforce by 30 per cent while maintaining the same level of drag.

While the high temperature endurance caused many top teams issues, the Zurich car ran strongly and quickly. ‘One of the reasons why we finished endurance was because we really pushed the manufacturing of our car to be complete by May,’ Rohner says. ‘We had a lot of time to evaluate and deal with all the issues, but you also need luck, and we were lucky to be able to fix all the problems we had to finish the race.’

It is likely that some teams in the future will copy, or at least be heavily influenced by, the Zurich design, but Rohner believes it is inevitable anyway as he feels that the design concepts of top teams are converging. ‘In the last three to four years, we have seen major concept changes for electric cars. For instance, our team started with DC motors, no aero and 13-inch rims. Now with 10-inch rims, four wheel drive and an integrated aerodynamic package. This is the winning concept, which is proved by other top teams such as Delft and Karlsruhe.’ If that is the case then expect to see a range of similar cars in 2014.’

"This is the winning concept, which is proved by other top teams" www.racecar-engineering.com • Formula Student supplement

KArlsrUHe CAUGHT

ad it not been for its double disqualification from dynamic events, the electric car from the Karlsruhe Institute of Technology would have challenged for the overall win. It certainly was a neat piece of design, complete with a fully functional DRS wing. Its aerodynamic package was an area that even the team were not entirely convinced about, as team captain Benedict Jux explains. ‘This car is our second with an aerodynamic package, and it’s hard to define how effective it is,’ he says. ‘It has some positive aspects, especially for an electric car. It’s difficult to design because of the drag and the efficiency. It improves performance during skidpad and autocross and especially during the endurance, but if you have some problems or need some more energy it can be a burden. That’s why this year we designed DRS to decrease drag and improve the efficiency.’ Most of the evaluation work was done using CFD, and the team were keen to point out that they used Star CCM software to develop it, but they also had not ignored some well-proven techniques, and wool tufts were evident on the underside of the wing when the car arrived at Silverstone. Aerodynamics aside however, most of the work on the car was put into its four wheel drive powertrain. Unlike other cars driving all four corners, the Karlsruhe car does not use hub

A lot of development was put into the four wheel drive powertrain

motors – instead it is fitted with four inboard IPM motors. ‘The special thing is the drivetrain,’ says Jux. ‘It’s the first Formula Student car with this type of drivetrain, no one tried this concept before. The four-wheel drive concept that we built in the last few years was a centre motor in the back and the wheel hub motors in the front. This year two teams are having just wheel hub motors, which have much more unsprung mass. We decided that for the performance of the car, it is better to put the motors in the centre to reduce unsprung mass and lower the centre of gravity. The challenge is probably the dynamic control, if you want to use the advantages of the four wheel drive, but to get it to work it’s not that difficult. All four wheels turn forward.’ Reducing unsprung weight was a key aim for the Karlsruhe team, and for that reason it

moved to smaller 10-inch wheel rims. ‘I think you can see on our car that one main goal was to reduce the unsprung masses. We did some tests at the beginning and bonded some weights into the uprights which had a big influence – up to three-tenths difference per lap just because of the increase unsprung mass. So for the wheels we have gone smaller, it has lower masses and less rotational inertias. Most teams have changed and the results from the event show that better teams prefer 10 inches.’ But the smaller rims create their own issues especially when they are made from carbon fibre which has a direct influence on brake temperatures. ‘We don’t have any experience about 10-inch rims and our brakes,’ says Jux. ‘Our brake manager says that he’s not really sure this will work out for the whole of endurance so we

A number of teams were disqualified from the acceleration event at Silverstone, all of whom were running electric cars. Karlsruhe, University of Southern Denmark and Group T International University College were all found to have breached part EV2.2 of the 2013 Formula SAE technical regulations which states that: ‘The maximum power drawn from the battery must not exceed 85kW. This will be checked by evaluating the Energy Meter data. A violation is defined as using more than 85kW for more than 100ms continuously or using more than 85kW, after a moving average over 500ms is applied.’ The penalty for this is disqualification and all three were removed from the results. The biggest loser was Karlsruhe, which had won the event before its disqualification. It then repeated the violation in the sprint event and lost another strong finish, taking it out of overall contention. PENALTY: DISQUALIFICATION

have fitted brake ducts just for safety reasons. It’s not a problem we have had with 13, but we heard of some problems from other teams last year, especially with CFRP rims. The rims are really hard to develop. ‘We had a 13-inch rim which took about two years to develop, but now we have this which we will carry over on to future cars. They give weight reduction and maybe a little bit of stiffness, but if you know how stiff your rim is, you can manage it with other parts.’ Just how strong the Karlsruhe car really was will probably never become clear. It was certainly fast, but it was not legal, and when running in fully legal specification in the endurance it lacked pace. But the team were worried if it would go the distance on a single charge anyway.

Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT Wheely Small

t often seems that Formula Student is driven by the need for weight reduction. Over the last few years, teams have been downsizing their engines from four to two cylinders to reduce weight. More and more teams have been trading their steel spaceframe chassis for full carbon fibre monocoques to reduce weight. This year was no different, as teams switched from 13-inch to 10-inch wheels; to reduce weight. Indeed the overall top four cars had 10-inch wheels. The theory behind the smaller wheel is not only the weight saving, but the effectiveness of the weight saving in that area. As you may know, unsprung mass is defined as the total weight of components that are not supported by the suspension, which includes the wheels, tyres and uprights. The importance of reducing this mass is because it is effectively uncontrolled, so the lighter it is, the better the contact between the tyre and the road surface. After evaluating the dynamic equations, the translational and rotational inertia effects of a wheel can be expressed as an equivalent non-rotating mass, therefore it can be proved that the equivalent mass of a tyre is twice its static mass. In numbers this means that if 0.5kg is shaved off each wheel, it would feel 1kg lighter. Multiply this by four and you can quickly see the huge gains in weight reduction that can be made. The knock-on effect of reducing the rotating inertia is that it improves the performance drastically, as more power is available to accelerate the car, provided you are not traction limited, in which case the performance gains will still be made, just at higher speeds. Another benefit, although relatively small in comparison, is the effects under braking, as less rotating inertia reduces the brake load, and therefore heat. ‘The main advantage of the 10-inch is the weight saving and the improved acceleration characteristic due to the smaller

10-inch wheels offer a substantial weight saving, but there are disadvantages

circumference of the wheel, and therefore the lower final drive,’ says Oliver Hickman, consultant manager from Brunel Racing. ‘Whether or not we downsize for next year is a tough call because it would change how we run the engine – we’re currently setup to compensate for the 13-inch wheels, so we still get the good acceleration. The risk you get on the 10-inches, especially in damp conditions, is the increase in wheelspin due to the higher acceleration, as most teams don’t have intermediate tyres. With the 13-inch you have a higher top speed. Although it’s not a massive difference, it’s definitely something we need to test and verify.’ The smaller wheels require smaller components, so downsizing not only has the

multiple benefits of reducing inertia, but also the knock-on effects of even more weight reduction. However, the 10-inches do create major disadvantages – yet the constant push for lightweight concepts make these a small sacrifice, as the Stuttgart combustion team described: ‘Of course the packaging is very difficult with the brakes, because the system is very small and therefore gets hot easily and quickly. Also, as the front wing blocks air getting to the brakes, we’ve added brake ducts for cooling to utilise the flow from under the wing to travel into the duct. There are some disadvantages, but in the end you get more points with the 10-inch wheels than without.’ Marcus Linder, team leader for Chalmers, agrees. ‘It’s basically

due to the weight saving. Although the data does show the 10-inch wheels are worse in terms of peak lateral force and tyre temperatures, the gain we see in having less unsprung mass is worth the change.’ A further trend is the teams that run the 10-inches now make them wider. ‘We can get a better response and behaviour from the tyre when it is wider due to the increased contact patch,’ says Chalmers, ‘and the widening doesn’t affect the maximum lateral force too much.’ Not only has the actual size of the wheel changed for weight reduction, but the design of the wheel too, with some teams now developing carbon fibre rims. David Turton, driver for Team Bath and next year’s project manager describes their concept: ‘This year was the first time we’ve run carbon fibre rims with an aluminium centre and we have saved an approximate 600g per wheel. As well as this, there are stiffness gains to be made as the camber control is improved. Naturally, the design on CAD differs to real-life when the car is fully loaded, as it all deflects, which is why stiffness is so vital, because it directly relates to wheel control. We tried developing the rims in 2011, but it’s only this year that they were fully ready to implement on the car, which has just come from refining the design and practising the in-house lay-up technique. The lightest carbon wheels on the grid are on TU Graz and Zurich, which have a three spoke carbon design and weigh in at just under 900g per wheel.’ As impressive as this sounds, whether these lightweight wheels actually run in the race is another question. However, carbon rims look like the future, but once again the development costs and time required are powerful factors in determining just how many teams we will see with them next year.

"Downsizing for next year would change how we run the engine" www.racecar-engineering.com • Formula Student supplement

FORMULA STUDENT Adjusting Aero

he use of aerodynamic devices is quickly becoming a necessity in Formula Student. Last year, after the monster rear wing fitted to the Monash car, more wings, diffusers, undertrays and active aero concepts were seen at Silverstone than ever before. ‘It’s amazing the difference it makes, despite the fact that we race at very low speed,’ explains Dave Turton, current driver and next year’s project manager for Bath University. ‘The average

corner speed is 40-50km/h, so you would think that it’s not fast enough for aero benefits. We have done backto-back comparison with and without the wings and have found lap time. However, this is mainly due to driver confidence when braking.’ Bath have quite a small aero package when compared to other teams such as Munich and Monash, which is nearly three times the chord length, yet still weighs a small 10kg.

the Polish entry had the biggest wings, but perhaps not the most effective

Karlsruhe’s car was also bewinged. note the wool tufts on the underside

‘It then becomes a trade-off between downforce and mass,’ adds Turton. ‘If you have advanced manufacturing processes that make the wing lighter, you can run larger wings, yet still achieve the same centre of gravity and mass penalty. Our aero is approximately 11-12kg including the mounts.’ Monash are renowned as the ‘pioneers’ of aero in the Formula Student world and it has been their area of focus since the very beginning. Of course, access to their own full-scale wind tunnel has helped. Monash state that their size wings are the absolute minimum required to actually gain a benefit, in which case the circuits may need to become a little wider. AERO RESISTANCE One team that has resisted the challenges of aero until this year was Delft, which believes that bigger is not always better. ‘It’s been really difficult, but luckily we have a lot of aerospace engineers in our team,’ said a representative. ‘We also have great facilities at our university so we complete wind tunnel testing on scale and fullsize models, and so far the rear wing produces roughly the same amount of downforce as the CFD predicts. With the massive wings you see on other cars, you just add weight, which doesn’t make sense for our lightweight concept. This year with the simulations we concluded that an aero package would give us more points in the competition, but maybe next year the rules change and aero may not be so important.’ As mentioned in the race report, the adjustable aero systems were also making appearances this year with both the electric and combustion cars from the German Karlsruhe team running a very F1-style DRS. However, many of the teams, such as Chalmers, don’t see the benefit, as team leader Marcus Linder suggests. ‘We did the analysis into whether

it would be worth having DRS,’ he said. ‘But even though there is a potentially small gain, it introduces many problems from the control side as it adds complexity. However, we do adjust the wing depending on the type of event, but once it’s running the aero remains static.’ Other teams have similar approaches, such as Team Bath. ‘For the acceleration event we tried to neutralise the rear wing by adjusting the trailing edge. It costs nothing to implement other than a few extra holes in your sideplate, provided you’re not traction limited at high speed. In terms of DRS, it is a difficult one. In Formula Student you have no chance to learn the circuits, so to not only learn them and learn the use of DRS could be driver overload. It’s also extremely risky because if the DRS stays open you’ll lose a lot more time in that scenario, than the gain you would make with it fully working.’ A valid point, as Mercedes ably demonstrated with Michael Schumacher’s DRS a few seasons back. However, this is not stopping teams from developing active aero, as Turton commented: ‘A team in Oklahoma has an active front and rear wing, which is impressive, so all their multiple elements in the wing open and close when the car drives into corners. Another American team has an active rear wing that splits, so that they can activate half of the rear wing depending on the steering angle. Therefore, when they turn into a corner they use the angle of attack on one side of the wing to counteract body roll and increase the vertical force on the inside tyres. Of course, in theory it is interesting, but in practise if you’re counter steering, the system could be unstable unless you have an advanced control system. Nonetheless, the corners at Silverstone are relatively slow speed, so just how much benefit do you really get from aero?’

"It’s amazing the difference it makes, despite the low speeds” www.racecar-engineering.com • Formula Student supplement

FSAE – USA

Best in class – at last Stalwart competitors Stuttgart and Washington are celebrating their first FSAE wins FSAE MichigAn Universitat Stuttgart have competed in Formula SAE Michigan since 2010 and finished in third place every year. To some, a third place finish might be enough. However, to Stuttgart it meant there was always room for improvement. ‘We have finally been able to go the whole way to victory,’ said team captain Alexander Jorger. ‘All the hard work that was put in, in addition to the European competitions the year before, enabled us to finally win the sole event that Rennteam has participated in but never won so far. But we did it – meaning Rennteam Uni Stuttgart has achieved 13 overall championships. And that feels awesome.’ Formula SAE Michigan’s competition returned to Michigan International Speedway (MIS) for its sixth year at the venue. There were 120 teams registered for the competition, however, only 104 brought working vehicles. SAE International registered teams representing colleges and universities from Austria, Brazil, Canada, Estonia, Germany, Mexico, Singapore, South Korea, the US and Venezuela. Technical inspection saw more than 46 cars in scrutineering on Wednesday in early inspection due to an extended schedule; setting a new limit of cars having been reviewed on the first day. For those cars that passed all three steps of technical inspection on Thursday, teams took to the track on Friday morning, completing their acceleration and skid pad runs. With temperatures of 65 degrees and overcast (usual for Michigan), Cornell University took first place in the acceleration discipline with the fastest time of 3.830 seconds. Meanwhile in skidpad, Ecole De Technologie Superieure topped the board with the fastest time of 4.901 seconds.

The University of Washington finished first overall at Formula Sae lincoln

In the afternoon, teams completed their runs for the SAE autocross. Finishing in first place with a clean run and best time of 47.857 seconds was Oregon State University which was only 0.85 seconds faster than second place finisher Missouri University of Science and Technology. Clinching third place was Universitat Stuttgart with 48.827 seconds. Teams who completed the event and placed were assigned a position in the Ford Endurance run order. Eighty-four cars took the green flag; 41 cars finished the event with both drivers completing their 12 laps each. One team finished over the maximum time allowed and only received points for finishing all 24 laps. Placing first in this year’s endurance was University of Akron, which had a clean run and total time of 1363.225 seconds over 24 laps. Coming in second with an adjusted time of 1370.749 due to hitting two cones was Tallinn University of Technology. Third was Michigan State University with an adjusted run time of 1371.872, also due to hitting two cones.

Top 5 overall 1st 2nd 3rd 4th 5th

Universitat Stuttgart Tallinn University of Technology University of Akron Ecole De Technologie Superieure Universite Laval

FSAE LincoLn & FSAE ELEctric The University of Washington was awarded overall first place at the 2013 Formula SAE Lincoln competition in the internal combustion class. Always a contender in Formula SAE, this was their first championship victory. Universidade Estadual de Campinas captured the first victory in the inaugural 2013 FSAE electric class competition held in conjunction with the FSAE Lincoln event – this team previously competed in FSAE Brasil. The Formula SAE Lincoln competition continued its success for a second year at the Lincoln Airpark. Registrations for FSAE Lincoln had a limit of 80 cars for the internal combustion class while FSAE electric class allowed for 20 registrations. SAE International registered teams representing college and universities from Brazil, Canada, Japan, Mexico and the US. Taking first place in the cost event and receiving the SAE Cost Awards was the University of Illinois – Carbondale in the internal combustion class, and Universidade Estadual de Campinas in the electric class. Six teams participated in the design finals, with Car #4 University of Washington declared the winner. Although they did not make the design finals, Car #201 Universidade Estadual de Campinas impressed the judges and was awarded

first place in the FSAE electric class design award. The design judges also recognised the FSAE electric class second placed car of University of Kansas – Lawrence and the University of Washington in third place. San Jose State University completed a successful acceleration with the fastest time of 4.123 seconds. The skidpad event saw McGill University taking first with the fastest time of 5.340 seconds. Meanwhile, the electric car of Universidade Estadual de Campinas won both acceleration with a time of 4.452 seconds and skidpad in 5.444 seconds. In autocross, 54 cars started, topped by the time of 51.569 seconds set by Missouri University of Science and Technology. Finishing close behind in second was Auburn University having their best time of 52.100. Coming home third was University of Illinois – Urbana Champaign. Fifty-four cars took the green start of endurance. There were 28 finishers, headed by University of Washington, with a total adjusted time of 1403.120 seconds over 19 laps. Coming in second with an adjusted time of 1406.909 seconds with a completely clean run for both drivers was California State Polytechnic University – Pomona. And in third place was Missouri University of Science & Technology. First in the electric class was Universidade Estadual de Campinas with 1824.652.

Top 5 overall 1st 2nd 3rd 4th 5th

University of Washington Auburn University Missouri University of Science & Technology University of Kansas – Lawrence University of Texas – Arlington

Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT - VAC

AdVertisment feAture

Optimising performance Materials company VACUUMSCHMELZE GmbH & Co. KG (VAC) is playing an important role in the Formula Student Electric championship by supplying three teams with stator and rotor stacks made of cobalt-iron alloys VACOFLUX® and VACODUR® for their performance-optimised electric motors.

o maximise power density, electric motors and generators require soft magnetic materials with the highest saturation induction, and permanent magnetic systems comprising high energy rare-earth permanent magnets. These requirements are fulfilled by the materials produced by VACUUMSCHMELZE GmbH & Co. KG (VAC) in Hanau, Germany. The company also has the necessary technologies in place for processing these materials into components, before their installation into the finished motors and generators. The CoFe alloys VACOFLUX and VACODUR are examples of these advanced soft magnetic materials. With a saturation magnetisation of 2.3 T, significantly higher than conventional electrical steel, they can be used in electric motors and generators to maximise the energy density. Manufacture of the core stacks for electric powertrains requires special care to preserve the outstanding properties of the materials. A special production technology, known as VACSTACK® has been developed to produce core stacks with the very best properties. As an effective method of suppressing eddy current losses, ultra-thin tapes, no more than 50 or 100 µm thick, are used to achieve exceptionally high packing densities, typically 98%, with outstanding insulation between the individual tape layers. Using VACSTACK technology, VAC is sponsoring the Swiss AMZ racing team (ETH Zurich) with stacks made of VACOFLUX 48. The rotor stacks are assembled together with in-house produced

AMZ racing team: race car “julier“ Stator and rotor stacks made of VACOFLUX 48 and VACODYM 775 TP

AMZ motor for race car “julier”

rare-earth based permanent magnets VACODYM® 776 TP. The resulting components have been built into four motors for the 2013 all-wheel drive race car “julier”. Each motor – developed and built by AMZ racing team – produces a maximum power of 37 kW for a weight of only 4.6 kg.

An alternative way to produce such lamination stacks is by using interlocking technology. In partnership with AMK Kirchheim, VAC has supplied stator laminations stamped from the newly developed alloy VACODUR 49 for their AMK DT5-series. These motors have been used by

the DUT racing team (TU Delft, Netherlands) and Greenteam (University of Stuttgart, Germany) in their four-wheel drive systems. Comparable to the AMZ motor, extremely high power densities of greater than 7 kW/kg have also been achieved. This year, the three teams sponsored by VAC participated in the most important events at Silverstone (UK), Hockenheim (Germany), Spielberg (Austria) and Varano (Italy). At Silverstone and Spielberg, the electric cars started together with the combustion engine cars in one single competition. In both cases, the AMZ racing team achieved first place (overall winner). At Silverstone, it was the first time in the history of Formula Student that an electric powered car had beaten the best combustion car. At Hockenheim and Varano, there were separate classifications for the two drivetrain systems. The competition for the electric cars in Hockenheim was won by the DUT racing team while Greenteam Stuttgart achieved the first place in Italy. In addition to the results of the race competitions, two highlights are demonstrated by the outstanding performance of the race cars sponsored by VAC: While the AMZ racing team captured the first place in the world ranking, the Formula Student Electric Dutch team from Delft University improved the world record for acceleration of electric cars from 2.68 s to a fantastic 2.15 s for 0 – 100 km/h. VAC congratulates all of the sponsored teams for their amazing performance and looks forward to some close and exciting races in 2014. The future of electric racing cars has just begun!

Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT — MERCEDES

Recruitment drive for Mercedes AMG HPP For one manufacturer, Formula Student has proved to be a rich source of engineering talent. But the hunt for great young minds doesn't stop there… by ANDREW COTTON

ne of the big attractions in the Formula Student UK paddock was the Mercedes AMG Petronas Formula 1 showcar situated next to the Racecar Engineering stand. The draw for the students was not just that here was a real-life

F1 car in attendance, but also that the staff around the car were there to encourage applications for graduate placement schemes at its Mercedes AMG High Performance Powertrains company, based just 30 minutes away in Brixworth, Northamptonshire.

“Our sales pitch is: do you want to work in Formula 1?”

www.racecar-engineering.com • Formuls Student supplement

Mercedes AMG HPP is rapidly gaining a reputation among students for its schemes, particularly at the Cranfield University in the UK, and at Formula Student events. The schemes offer a wide range of opportunities, working on

various parts of the current and future Formula 1 power units. ‘You don’t know where the gems are, and essentially we are after the best students that we can find,’ says Paul Crofts, head of materials engineering at Mercedes AMG HPP. ‘While

students will be working on because we haven’t had a new engine on track yet,’ says Crofts. ‘At the moment it is like doing the 400m race at the Olympics, but everyone is in a different stadium. We have no idea how far ahead or behind we are, so we are not sure what the students will be working on. Clearly, though, anything around boosting systems, electrical hybrid systems, harvesting systems, deploying energy more efficiently – they are going to be the areas that we are continuing to work on,

as well as more traditional camshafts, exhaust pipes and so on. It is across the range. Formula 1 is about detail, and every detail, so we will be leaving no stone unturned.’ Recruitment starts in September 2013 and runs through to Christmas for a placement that starts in September 2014. In that time, Mercedes AMG HPP is looking to recruit the very best engineering students from all walks of the discipline. ‘We have a two-year formalised training programme

“Half of our graduate engineers have had an involvement with Formula Student at some point, so it is important to us”

WRI2

the quality of the students at Cranfield is very high, it would be naive to think that it’s the only place that they come from. It is a bit of a numbers game. The more people you talk to, the more people you will be exposed to and the more likely it is that you will find the gems of the engineers.’ Students who approach the stand are encouraged to apply for the scheme – with new Formula 1 technology on the way in 2014, fresh thinking is critical for success. Although the next placements start in September 2015, there will still be a significant amount of development focused on performance and efficiency ahead of the 2016 season and beyond. ‘I think at the moment, we are not that sure what the

Standout students may work on current and future Formula 1 power units

where each graduate rotates through our various engineering departments building up experience depending on what their base degree is,’ says Crofts. ‘We take on mechanical engineers, manufacturing engineers, electronic engineers, software engineers and we tailor it to that background, but we give them variety, so they get a bigger overview of our business. ‘Once we highlight that to them they start to get interested. Then we highlight the fact that we are in the UK. Mercedes AMG HPP may not have a high profile in the outside world, but we are not a stealth company any more. Still, we have to remind them that we are local, and that we’re only 30 minutes from Silverstone. The key thing is that candidates have to apply nearly a year in advance. Our application window is September to Christmas this year to start the job in September 2014.’ ‘We recruit about 10 graduate engineers each year, and take on about 25-30 placement students, who are just as likely to come from this event because it is not only final year students, it is years 1, 2 or 3. Generally speaking, 50 per cent of our graduate engineers have had involvement with Formula Student at some point, so it is important to us. Our graduate programme has only been going for five years, but our retention

With a new breed of Formula 1 engines on the way, there is huge demand for fresh thinking in engineering Formula Student supplement • www.racecar-engineering.com

FORMULA STUDENT — MERCEDES

“our ex-graduates are working on the 2014 F1 power unit at the moment” rate is over 85 per cent, and after the two-year course, they usually earn a permanent position in one of our departments. We do encourage our engineers once they have a permanent position to work in one place for two or three years, and then look to move to another place around the company anyway, so they can get that variety.’ That variety may not be in the diversity of projects – Mercedes HPP is 98 per cent concentrated on the Formula 1 programme – but there are occasionally opportunities to go slightly further afield within the Daimler Group. The company provided the battery pack for the Mercedes SLS Electric Drive, which was developed from the Formula 1 system and scaled up to meet requirements. Just within the scope of Formula 1, more than 400 people are employed at HPP, and over 100 of them are engineers with a hands-on role in developing the Formula 1 engines. ‘Our ex-graduates are working on our 2014 F1 power unit at the moment,’ says Crofts. ‘It’s less than six months before we have to be on track for the pre-season track test. We will have a much bigger ERS or hybrid

drive system, turbocharged technology, a downsized engine that has to be more fuel efficient – they are all areas that we have to work on, and everyone’s ideas

are valid. We are maximising our engineering team to work on that and get as much brainpower on it as possible. Whether you have worked in the

mercedes take on around 10 graduate engineers each year, in addition to an intake of placement students at various points in their studies

industry for 20 years, or a year, your ideas are probably just as valid at this point. ‘I think there will be significant evolution in 2015. Unlike the current V8 rules, we haven’t been able to change it for seven years. The way that the sporting regulations have been drafted, year by year from 2014 to 2020, you will be able to change less and less, but for 2015-2016 it is still very open, so I suspect there will be significant changes, not only because of reliability issues, but also to find more performance. ‘At the end of February 2014, the power unit will be homologated and effectively that is then fixed for the year. There is some calibration work to be done, and that work will continue. We had placement students working on the V8, so what they are working on is on track in two weeks time. In terms of the hardware, it will be fixed. However, those that are working on that will turn towards the 2015 power unit.’ The application process for the graduate training scheme starts in September. Students are encouraged to apply at www.mercedes-amg-hpp.com

Placement in action – Graham’s story

resent at Silverstone’s Formula Student event was one of the graduates on a two-year scheme at HPP who was approaching his first anniversary at the company. Already, Graham has worked in three areas of the company, worked on a thermal management programme on the current F1 engine, and graduates move to new roles in different departments every three months. ‘I first heard about [HPP] at a presentation that one of their ex-graduates did at the university, which got me interested,’ says Graham, whose surname cannot be printed for reasons of confidentiality. ‘I thought that it was quite exciting to do as a job. At the time I was involved in Formula

Student, which gave me a set of skills that are transferable into the job. It gave me a lot of experience of working under pressure, meeting short deadlines, that sort of thing. ‘For the first two years you do a mechanical engineering job, and then you specialise after that, and I chose automotive. I had done a placement for 12 months, which gave me some experience. It was about the company, it sold itself. I started on the graduate placement scheme in September, and since then I have been in three departments – the design office for mechanical engineering, performance for the existing engine, and manufacturing engineering. As part of the process, you visit all sorts of departments around the

www.racecar-engineering.com • Formula Student supplement

business, and the idea is that you are exposed to everything that is going on. By the time you have finished your two years, you have the mindset and are aware of the processes and you can be better at your job at the end of it. Of the ones I have experienced so far, the performance role was the one that I enjoyed the most, and I have subsequently applied for a job from that. ‘In performance you get a whole project that is yours, and I was given a project looking at heat rejection for the Formula 1 cars, and you could maximise our performance and see what cooling requirements we would need. That was my baby and it also used some simulation skills that I had used in university, so I really enjoyed that. I found it to be really rewarding.

‘It is quite normal for this company to be given that responsibility. The head count is lower, you have a big project to do, and everyone has their own significant part of that project, and in a large automotive company you might be working on something much smaller because there are more people around.’ Crofts adds: ‘We like to give our graduates responsibility. If you are going to give them a job, give them a real job to do. Make them feel that they are really contributing, because they are. There are over 400 employees, split between six engineering departments, and seven or eight departments on the operational part of the business. In engineering, we have over 100 engineers, and a lot of people who need to make that happen.'

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TECH DISCUSSION

Save Formula Student Teams are turning up with great tech, fine paint jobs and a well-drilled crew. But with one key rule routinely broken, is anybody actually learning anything?

participated in Formula Student competitions between 2006 and 2012, and was design leader for a student team that designed and built their own complete racing engine from scratch (and CNC machined everything that was possible by ourselves, see Race Engine Technology magazine #54). In my time I also TIG-welded entire spaceframes, wishbones, uprights and CNC programmed and machined our aluminium suspension uprights. My own experience was that five years of Formula Student were probably the best years of my life, and will probably never be equalled in terms of capacity for innovation, real teamwork, real camaraderie, and a pace of learning of such frantic magnitude that would put most of F1 to shame. However, the face of Formula Student has changed a great deal since 2006, and I saw the transition occurring with my own eyes. I would also state that this transition is not for the better. Formula Student has (for many teams, universities and apparently judges), increasingly become a showcase for turning up with the most technology, the best paint job, and the most professionally turned out and drilled team. All of which on the face of it seem very laudable qualities indeed. In fact, it is clear that unfortunately not one of these qualities necessarily contributes to the personal, intellectual, moral or technical development of the students themselves (of course there are exceptions to this in a small number of exceptional teams). It is a fact that the vast majority of FS cars at every event are in direct and clear contravention of Rule A6.1 (page 12, FSAE regulations 2013): A6.1 – Student Developed Vehicle ‘Vehicles entered into Formula SAE competitions must be conceived, designed, fabricated and maintained by the student team members without direct involvement from

professional engineers, automotive engineers, racers, machinists or related professionals.’ If this rule were enforced at the next competition, the number of eligible runners at an event like FSG might be counted on one hand. There is an argument that some teams cannot build their own cars because of safety fears at their establishment, or that they don’t have any equipment. But I think this is a copout, preventing teams really learning what running a racing business is all

intelligent group of students, building a vehicle to the letter of the rules in section A6.1, would be NO barrier to innovation nor to the technical level achievable. For example, UWA constructed their own moulds for their CFRP tub, and cured it by constructing a ‘hot box’, around the finished mould which was heated by hot air guns applied to well located vents. Not an autoclave in sight. Allowing teams to blatantly contravene rule A6.1 also allows universities to carry on denying

If rule A6.1 was enforced, students really would build it all themselves about, which is to need something, and then getting together to make a plan in order to achieve it. Not to complain that it’s ‘difficult’, and so allow a sympathy loophole though which anyone can now leap with anything up to an entire chassis being constructed almost 100 per cent by renowned motorsport firms, stickers being applied and this being declared a ‘Formula Student car’. When, in fact, it is nothing of the sort. For a really dedicated and

students access to manufacturing facilities, because ‘everyone else is doing it’ – as in everyone else is farming out machining, curing, testing, welding, moulding etc to external companies. If this rule were properly enforced, it would empower students to really have their own racing team, really build it all themselves and to really gain the sort of self-confidence that can only ever come from having done

it all yourself. It would also force universities to get behind learning, and to not merely listen to their litigation department’s risk reports. If there are teams who claim that they ‘cannot’ build their own cars, because it’s ‘difficult’, or because they’re not imaginative enough to beg/borrow/buy/rent appropriate facilities and equipment – I would question their eligibility to consider themselves worthy of competing to go home with their heads held high as young racing enthusiastic engineers of the future. The regulatory bodies responsible for running Formula Student are responsible for far more than just helping to setup and run the events, by their actions they shape the way students learn and function at their universities. Rule A6.1 should be either enforced to the letter, or it should be deleted with immediate effect from the rules and regulations. If it is to be deleted, all concerned must be comfortable with the fact that the competition would – in principle, practise and letter of law – cease to be a primarily learning exercise. Calum Douglas

Formula Student should be teaching people key design and engineering skills – but many schools are denying students this opportunity

Formula Student supplement • www.racecar-engineering.com

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