HOME OF -VIRTUAL STOPWATCH- THE VEHICLE ACCELERATION AND LAP TIME CALCULATOR

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28 April 2016 Khamsin Virtual Racecar Challenge 2016
   

The KVRC pits cars designed by budding vehicle designers and aerodynamicists against each other. Each car is CFD analysed using OCCFD software and then the Virtual Stopwatch program is used to generate a lap time at one of several iconic motorsport venues; the fastest car wins!

Not only will Competition-Car-Engineering continue to provide lap time prediction software to the KVRC in 2016 but we shall also be entering a car into the challenge with the aim of creating some aerodynamic in-sight articles.

In the meantime a number of resources are made available to all competitors and those interested in following the challenge:-

For new entrants we have produced an introductory guide to racecar aerodynamics:

A basic Competition-Car-Engineering Bodykit is available which makes it easier to enter a car into the challenge: just add your own wings and diffuser:

The KVRC version of Virtual Stopwatch is available to test your designs:

Visit the official website to register a team and find the latest results:-

www.khamsinvirtualracecarchallenge.com

 

 

 

13 May 2015ray Nissan GTR-LM vs Traditional Racecar layouts
   

The Nissan GTR-LM breaks from the prevalent racecar mould with the aim of winning Le Mans.  The car features a front engine, primarily driving the front wheels, but with a Hybrid system that can power all four wheels.  Aerodynamically the car looks very clean with air from the front diffuser area being led right back through the car to the back, where it is released underneath the rear wing.

Before getting into the details of the GTR-LM, we should answer the question of why evolution has led to the "normal" racecar layout of mid-engine, rear wheel drive:

When a car accelerates there is a load shift rearwards giving additional traction to the rear wheels; hence a benefit to rear wheel drive. Added to that a racecar works well if it is "balanced".  That means the distribution of mass, downforce, tyres and motive forces are in synergy with each other front to rear.  That's why racecars have tended to be rear-wheel drive with a rearward mass bias afforded by a mid-engined layout, have a rearward downforce distribution and bigger tyres on the rear.

A 4WD configuration (as featured on the Nissan GTR-LM) frees up the option of utilising a different distribution of mass, downforce and tyres, whilst still being "balanced" overall, as the motive forces can be redistributed front and rear. This allows a front engined configuration to be used which on its own doesn't represent an advantage, it just means its not at a disadvantage.

So is there an advantage of a front bias to the balance?  There is of course the obvious marketing potential of having a race car configured similarly to your road cars... and don't underestimate that fact!  However, the Nissan philosophy is also clearly one of low drag; indeed the car was originally run in testing without a rear wing at all. By moving all the big mechancial components to the front this allows a really clean rear end with the intention of reducing the wake of the car to an absolute minimum.  Of course cluttering up the front end doesn't help with front-end aerodynamics, particularly downforce production, but that doesn't matter so much if the car is designed for a low drag configuration.

The question then is whether an ultra low-drag configuration is best?  If that philosophy is going to work anywhere, Le Mans (with its long straights) is the place where it might work, but being fast on the straights is one thing; what really counts is being fast around the track overall; only time will tell if they have struck the right compromise. It is worth noting that since the dissection of the Mulsanne straight some years ago, no other manufacturer has seen benefit to an ultra-low downforce configuration, although all manufacturers run lower downforce packages there than they do elsewhere.

One final point to note is that the overall tyre footprint area of this car is lower than the other cars due to the decision to run narrow rear tyres (again to reduce aerodynamic drag). Couple that with the fact that the mass distribution is reportedly 65% to the front and the majority of braking forces and accelerative forces need to go through the front tyres and that could manifest itself as a propensity to use up its tyres quicker than the other cars...

PRE LE MANS TEST DAY NOTE: Due to problems with the hybrid system there is a rumour that the GTR-LM may run in pure front wheel drive configuration at Le Mans, in 2015 at least.  This would appear to put the car at a serious disadvantage coming out of the slower corners where naturally 4WD has an advantage, but so too does RWD where the rearward load shift under acceleration helps traction. A pure FWD arrangement would also further exacerbate the tyre endurance problem; with even more accelerative forces going through the front tyres.

POST LE MANS NOTE: Unsurprisingly the car failed to live up to the hype, partly this was down to the failure of the car's Energy Recovery Systems, but also the car faced tyre longevity problems (unsurprisingly, as predicted pre-event), and also a lack of downforce: a twin-element rear wing was hastily added (despite the car designer insisting before the event that only a single element rear wing would be used).  The car may have looked different, but its performance was poor, and the Nissan Motor company withdrew the team from all remaining races.

 

21 April 2015rch Low Drag FR-DRS Single-Seater Bodykit
   

Depending on the wing configuration, the open wheels of a single seater racing car can contribute around 25% or more of the total drag of the vehicle, and also produce significant lift.

Clearly the reduction or even elimination of this drag and lift would lead to significant performance gains, therefore Competition-Car-Engineering set about investigating what could be done to solve this problem if competition rules allowed, such as is the case in the various UK sprint and hillclimb championships.

Wheel fairing design for low drag is a fairly intuitive affair, however, it is also possible to inadvertently create more lift from a faired wheel if the designer is not careful.  The final design selected by Competition-Car-Engineering was obtained using an iterative CFD process in which many different initial designs were tested and later refined to achieve an optimum result.

Although the wheel fairings alone achieve an appreciable performance gain, the space within these fairings provided scope for further performance gains in the form of Front and Rear Drag Reduction Systems or FR-DRS.  At the press of a switch the upper element of each wing assembly adopts a low-drag orientation, returning again to its high downforce position when the button is released. The actuator systems are fully enclosed within the wheel fairings ensuring that they do not add to the aerodynamic drag as is the case in some F1 designs.

The aim with the Competition-Car-Engineering FR-DRS bodykit was that it could be adapted and retro-fitted to any single-seater design, working symbiotically with the car's existing aerodynamic schemes and requiring very little modification so that it could be removed at a later date if the owner so wished.  Depending on the specification of the base car, lap time reductions in the region of 6% and upwards are possible with the Competiton-Car-Engineering FR-DRS bodykit.

The FR-DRS bodykit is shown below on an ex-F3000 Lola B02/50 singleseater with optional bubble canopy for the ultimate low-drag/high downforce configuration.

For further details of the Competition-Car-Engineering FR-DRS singleseater bodykit please email mail@competiton-car-engineering.com

 

10 March 2015rch Khamsin Virtual Racecar Challenge
   

Competition Car Engineering will again be providing a special version of Virtual Stopwatch for the purposes of determining lap times to the Khamsin Virtual Racecar Challenge for 2015.

A version of Virtual Stopwatch has been made available to the KVRC competitors for the first time, to help them dial their car in to each track that the championship visits.

This can be accessed by anyone by clicking on the image below:-

 

11 October 2012 Gear Selection Optimisation using Virtual Stopwatch
   

Virtual Stopwatch can be used to help optimise the gearing on your track car for improved performance.

The gearing on a car essentially does one thing; it matches the power output curve of your engine to the road speed at which the car is travelling.  There is only one problem with this; an engine generally only achieves peak power over a very small RPM band and your car is expected to travel at many different road speeds.  If you only had one gear that would mean you could only use peak power at one road speed, and therefore at other road speeds you would have much less power to accelerate your car.

Optimising for Acceleration

The multispeed gearbox combats the issue of internal combustion engines only making peak power over a small RPM band by matching the peak power output curve of your engine to 4, 5, 6 or 7 different road speeds (depending on how many gears your gearbox has), and increasing the average power output that the car has available to use over the full range of road speeds from 0 to its top speed.

The graph below graphically displays the advantage the multispeed gearbox gives (for an explanation on how this graph is derived click here).

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Take for example the case of the car above travelling at 50mph.  The driver has the option of using 2nd gear (with approx 105bhp available at the wheels), 3rd gear (70bhp available at the wheels), or 4th gear (40bhp available).  The road speed is too high for 1st gear.  Clearly using 2nd gear in this instance is going to result in more force at the driven wheels (since Force = Power / Velocity), and hence higher acceleration (since Acceleration = Force / Mass -where the "mass" term must also account for the inertia of any rotating parts on the car).  You can see that if you remove any of the gears from the diagram above you will be left with a power "hole" where the power available in that "hole" is much less than when the gear is available, so in general more gears means more acceleration.

There are however, four exceptions;

1, Adding a further low ratio gear (one below "1st", or reducing the overall gear ratio using tyre diameter or diff ratio) will rarely result in better low speed acceleration since most high performance cars are traction limited at low speeds anyway (the blue dotted line indicates the limit of motive force that the tyres can transfer) -if your car can already spin its wheels you are traction limited and not power limited.

2, Once you have optimised top gear (* see description later), adding a further gear ratio at the top of the gearbox will not increase acceleration at higher speeds since the power absorbed by resistances (green line above) will be greater than the power generated by the engine.

3, Too many gears can result in slower acceleration since you have to perform more gear changes which always introduce some delay in acceleration (although modern F1 seamless shift technologies make this delay barely perceptible).

4, If your engine has a flat power output right across its rev range, then anything more than 1 gear ratio optimised for the car's top speed will not give you any further increases in acceleration at any speed, since by definition your engine can already generate its peak power right across its rev range.

 Optimising for Top Speed

Your car will keep accelerating when its power output is higher than the power absorbed by resistances (air drag, rolling resistance, and gradient "resistance").  Your car will stop accelerating (i.e. reach its top speed) when its power output equals the power absorbed.  In the example above the car will be able to reach a speed of approx 112mph -where the power curve in 4th gear crosses the resistance curve.

This intersection occurs at about 94bhp, but we can see that the engine has the capability of producing about 105bhp at the wheels.  In order to increase the top speed what we need to do is change the gear ratio (or the diff ratio /driven wheel diameter) so that the power curve shifts to the right on the graph above until the peak power output crosses the resistances curve.

The graph below shows the effect of "lengthening" top gear; the car can now reach a top speed of approx 118 mph, however, we have also decreased the amount of power available at road speeds between 85 and 105mph. Here's where an additional gear (to fill in the power "hole" between these road speeds would be beneficial).

It is worth noting the effect of lengthening top gear past the optimum point, which is shown on the graph below. The point at which the power curve crosses the resistance curve has now fallen back to 112mph.  Not only that but the power "hole" between 85 and 110mph is now even bigger -resulting in even less acceleration between these speeds!

Use the Virtual Stopwatch demo to observe the effect on acceleration and lap times of varying the gearbox type or the final drive ratio, here.

 

 

9th Sept 2012 How does Virtual Stopwatch Work?
   

After a fair amount of questions being asked on the subject, I thought I would provide the basic steps that Virtual Stopwatch takes to determine the performances of the vehicles.

See the Intro page for more information.

 

28th August 2012 Khamsin Virtual Racecar Challenge
   

I have been given the opportunity to get involved in an on-line Formula1 car design competition, being run under the name of "The Khamsin Virtual Racecar Challenge". There is already a big community of people building CAD models of F1 cars, but, to my knowledge, no championship doing CFD testing to see which design is actually the best.

So, where does Competition-Car-Engineering come in?  Well obtaining the aerodynamic coefficients for the various designs does not actually tell you which car would be quickest, as aerodynamic optimisation of a racecar is normally one of balancing the downforce against the increase in drag, and furthermore the optimum balance between the two will change according to the racetracks the car is run over.  To determine the best design a special version of Virtual Stopwatch was created for use by the Khamsin championship organisers.

The special version of Virtual Stopwatch allows the Aerodynamic drag and downforce coefficients plus the aerodynamic centre of pressure to be inputted into the calculator for three test conditions;

  • Medium speed, straight ahead
  • High speed, straight ahead
  • Medium speed at 3 degrees of yaw

These override the normal aerodynamic data of the F1 car model in the calculator with a simple aeromap of each of the championship's participants, whilst keeping all other car variables the same (spring and damper settings are optimised automatically in accordance with the downforce generated).  The program then calculates the optimum lap time from the data.

The base car in the calculator has a wheelbase of 3.4metres, and a weight split of 46:54 Front:Rear.  Therefore to gain the optimum lap time the championship participants must aim to replicate this split in the aerodynamic downforce their model generates.  If, for example, the model generates too much rear end downforce compared to the front it will be no faster in the corners (since cornering performance will be limited by the front end of the car) but it will be slower around the lap due to the extra drag the rear wing generates.

To maintain parity between models the championship organisers will mandate minimum areas for items such as radiator and engine intakes/outlets.

For further information on the championship, and to get involved, go straight to the The Khamsin Virtual Racecar Challenge website.

To try out the normal version of Virtual Stopwatch and find out how various aerodynamic kits affect F1 car lap times, click here.

 

27 May 2012 Putting Virtual Stopwatch to the test
   

Given some very basic information about a car, how closely can Virtual Stopwatch predict its performance? The challenge was to predict the performance of Andy Laurence's sports prototype sprint racer (an ADR2 prototype). For my prediction I used chassis data for the newer ADR3 that I had available, and knowing that Andy runs a 1000cc motorbike engine I selected a Yamaha R1 engine and gearbox (I later found out Andy has a Suzuki GSXR1000), I guessed slick tyre sizes and compound and I estimated a final drive ratio based on what I thought its top speed would be given an engine output of approximately 180bhp.

So, how did it go? First I declared my predictions online and then only afterwards did Andy provide the 3 "real" data points obtained from his datalogger to compare them to. As you can see, the predictions are just a few mph out for a given time, and the overall shape of the acceleration curve is very similar showing the high level of accuracy of the physics engine in Virtual Stopwatch;  with a little bit more knowledge of the spec of Andy's actual car we would have got very close indeed.
                          

                      


Many thanks to Andy for supplying the data. You can follow Andy's sprint blog here. You can try the ADR3 sports prototype on
Virtual Stopwatch, here .

 

7 May 2012

Deltawing -The future of Motorsport?

   

The performance benefits of downforce on a racecar are well understood, and in recent years Formula 1 cars have been designed in favour of better aerodynamics over mechanical grip. But what if we take that to its extreme? The Deltawing concept eschews the mechanical advantage of 4 widely spaced wheels in the search for better aerodynamic efficiency, taking on an almost trike-like layout that is not too dissimilar to a land speed record car.

In a break from the current rules the Deltawing car running at Le Mans this year has been allowed to run with fully developed venturi tunnels (the traditional "ractangular" cars being forced to run a restrictive flat-floor arrangement) -something not seen at Le Mans since the Group C sportscar days some 2 decades ago.

The Deltawing is also running without the minimum weight restriction of the rectangular cars but to counter that its light-weight engine develops only 300bhp (half the power of the LMP1 category).

These differences make it impossible to directly compare the Deltawing wheel layout with the traditional layout from the actual on-track performances, so to try and answer the question of which wheel layout is better I have simulated the performance of the Deltawing car based on the published data and compared it to a hypothetical small light-weight rectangular car having aerodynamic characteristics based on the 25 year old XJR-9 (ground effects) sportscar. Both cars will use the same engine, transmission and tyre compounds, although tyre sizes will be in accordance with the respective designs.

The rear-ward weight distribution of the Deltawing confers a natural low speed traction advantage (like a dragster), giving it better low speed acceleration. The low drag shape and higher downforce provides better high speed acceleration and improved high speed cornering ability.

The wheel layout and mass distribution of the Deltawing means that it will see a greater percentage force imbalance during lower speed cornering and braking, making its low speed cornering performance (despite its slightly lower mass) worse than the rectangular car, and hence a slower lap time at a track like Brands Hatch Indy circuit.

So, which wheel layout is better? Well the answer depends on the characteristics of the track around which the cars are racing; around a typical race track the traditional rectangular car is quicker.   Around a track dominated by long straights the straight-line advantage of the Deltawing's low drag shape allows it to equal the performance of the regular car.

It is also worth remembering that the XJR-9 body shape is an old design, and it does beg the question; what aerodynamic performance could be achieved from a modern rectangular car not restricted to the current flat floor configuration mandated by the rules?

RETROSPECTIVE NOTE:  The Deltawing failed to live up to its performance claims at Le Mans: being slower than the traditional cars of the LMP2 category, despite having a higher power:weight ratio and no aerodynamic restrictions.  The car continues to run in the US, but despite being given significant performance breaks in terms of power:weight ratio compared to its rivals it has yet to post comparable lap times nor score a significant race result.  Many of the car's supporters claimed the original tyres were not suitable for the car, but it has since run on various compounds from three tyre manufacturers without appreciable change in performance.

 

17 Feb 2012  

I have added a new free App to help you set the optimum cornerweights on your competition vehicle, click here.

 

30 June 2011  

I've decided to tackle the debate of Power vs. Torque... hopefully in a much more illustrative way than has been done before.. click here to read.

 

23 June 2011  

Whilst performing some Formula 1 simulations I came up with an idea which would reduce the fuel consumed by an F1 car, maintain current lap times, still promote over-taking, and not require any physical changes to the current cars!  Its all about the DRS... Click here to read.

 

25-April 2011 Website launched!

Whilst sorting through my hard drive recently it struck me how much information I had gathered, created and developed on the subject of  performance vehicle tuning, dynamics and simulation, and what a waste it would be to let it all sit idle. The idea behind this website was to get the information out to the wider world where it will hopefully prove a useful resource.

   

COPYRIGHT 2011 Richard Machin. All Rights Reserved