Posted by: drracing | April 12, 2016

Perrinn MyP1, LMP1-L and driving simulation

Hi everybody!

This post will be about a project i actually worked on last year, but never found the time to write about. And, finally, will be again a bit about something technical.
This will be a long (but hopefully not too boring) entry, so take some time, some drinks and seat comfortably!

As I already wrote in some of my previous posts, some time ago I decided to create a vehicle model of the Perrinn MyP1, the open source project created by Nicolas Perrin with the intention to share with the community much of what is connected to the design of an LMP1 car; Perrin’s dream was to find the funding to finally build the car and bring it to Le Mans, using a new and exciting approach where a whole community could potentially be involved. Unfortunately, this dream didn’t come true yet and, most probably, will sadly never do: the project is now already two years old and, beside the funding collected through the chance given to people to subscribe to it and to access all the data available, I am not aware of any big backers who materialized till now.

This is for sure sad, but takes nothing out from the goodness of the initiative from Mr. Perrin which, if nothing else, gave to many curious and passionate people a chance to access some very professional material, that would normally be kept and guarded very secretly.
This includes a lot of detailed CAD 3D models, aero data (coming from CFD simulations), suspensions data, something about the tires (although this was probably the least useful provided data) and still much more. Basically, what is still missing is only what should be provided by external supplier and cannot be shared for legal reasons; this unfortunately includes the engine, which is a pretty sensitive element to define any car performances.

The whole project has been developed planning to build a car to compete against the big manufacturers (Toyota, Audi and Porsche) thus the original idea was to include also a Hybrid system, targeting the 8MJ class.
Anyway, my idea have been from the very beginning to use it as a base to evaluate how quick an “non hybrid” LMP1 (like the privateers are, see Rebellion and ByKolles) could be: Perrin data and general design would serve as a realistic foundation for a LMP1-like design, about which would otherwise be impossible to find any detailed information.

Assuming that Perrin did a job at least as good as Oreca did for Rebellion and Adess engineering did for Kolles, my assumption is that MyP1 “platform” can be used to understand, at least on paper (or maybe we should say in a simulation) how quick such a car (LMP1-non hybrid) could approximately be.
As I will show later on, I reworked a bit some of the settings provided by Perrin with the goal to optimize vehicle’s performance/driveability, when something was looking not perfect to me (of course not “cheating”, like artificially increasing aerodynamics efficiency, but only working on setup parameters, like springs, antiroll bars, gear ratios, ride heights, etc) and I tried to approximate the best I could all the missing data: as I said, the complete powertrain system is a very important example (not only the engine was not shown in CAD, discussed or described, but also important parameters like gear ratios or differential setup were not available at the time I built my vehicle model).
The model and the final results are anyway probably still not really on the edge, in terms of performance, but could still form a good base to get a feeling about how such a car behaves.

But let’s start from the very beginning. How the car designed by Perrin looks like and which parameters are available about it?

As I initially said, a pretty big amount of CAD data has been shared with the “users”, including the complete bodywork, suspensions, cockpit items, wings and diffusers.
As soon as it has been presented, a couple of years ago, it was immediately noticeable how the design took a “different path” (compared to the other manufacturers) in some areas, like the engine cover and the front aero package: the first is very much “Bubbly”, with a shape that doesn’t resemble any of the Manufacturers design and looks, for somebody not too much into aero design like me, a bit strange and apparently too big; Perrin ensures anyway that this has no real bad effect in terms of performance.
The later shows a high nose, with a clean front wing design and with the nose itself being smaller than the one of other cars using a similar front end concept, see Audi and Porsche.
Interesting is also the position of the two air intakes immediately beside the nose, but a bit more rearward; it is a solution partially similar to the one proposed also by the unraced HPD LMP2 car at the beginning of 2015, although in that case the intakes were at the very front of the car, just beside the nose itself.

MyP1 Iso view

MyP1 Front viewMyP1 side aero

MyP1 side view

 

Perrin’s creature features a 2950 mm long wheelbase, with front and rear track widths being very similar to each other and in the region of 1545 mm (the four tires have the same dimensions, although the rims are different front to rear, as also seen in other LMP1 cars; the main difference is normally a different wheel offset).
According to the info provided by Perrin himself, in a non-hybrid configuration the car should be able to stick to the allowed minimum weight of 850 kg, of which about 48% should act on the front axle statically (also with the driver on board).
According to the designer, the CG height should be around 280 mm higher than the reference plane, which is not the lowest point of the car, as we will see shortly analyzing the front and rear suspensions.
Below the floor find in fact place a wood plank, as mandated by the rules; in its thickest point, it is 25 mm thick. This means that the CG should be more or less 305 mm higher than the lower point of the car body, assuming an idealized surface running through the two thickest points of the plank, one at the front and one at the rear.
MyP1 Iso low view

MyP1 Front aero

 

A very important point regarding dimensions and inertial properties is also linked to the moments of inertia of the complete vehicle that, as i mentioned in some older entries, play a very important role in defining how the care behaves dynamically. Since these data are normally not available, I use a simplified approach to estimate them, which consists in dividing the car in several blocks with simple shapes, calculate each block moments of inertia (basing on the mass assigned to it, which is calculated to finally achieve the “desired” static weight distribution, also basing on each block position) and then in “moving” each block’s effect to the CG using parallel axel theorem, to finally have the Moments of Inertia of the complete vehicle referred to the car’s CG (as required by rFactor).
Going “under the skin”, it is evident how the design was driven by the aerodynamics, including all what concerns the front suspension. Here, another important element is surely the maximum lateral width allowed by the rules, which forces to use relatively shorts control arms, making it harder to really optimize the geometry.
The front suspension employs a typical double wishbone scheme, with unequal length arms, pushrods and torsion bars. The antiroll bar is connected to the rocker through (more or less) vertical rods and it seats on the lower portion of the chassis, attaching to the front bulkhead. Although not shown, two linear dampers are meant to be used (this is one of the contents belonging to suppliers and that cannot be shown in CAD).

I analyzed it using a very well known Multibody software, focusing only on the pure control arms/Steering geometry (not on the motion ratios, for example, since the wheel rate contribution of each corner spring and of the antiroll bar was provided “separately” by Perrin’s data).
The results show a very high kinematic roll center (much higher than the rear), a pretty sensible track width variation with respect to heave motions, a relatively big scrub radius and a pretty small caster angle.
Also, bump steer is not really optimal, although not being out of sight. This underlines once again some of the compromises accepted in the design phase for the front axle for the sake of a higher overall benefit, probably.
Camber gain is also not too high, but this is not necessarily bad: for sure, together with the low caster angle, it doesn’t help to have an “optimal” tire vertical inclination for the outside tire in cornering situations, but it is also probably not a performance killer.

To be honest, if I had to wish something for “my ideal front suspension”, it would definitely not look like this. But this is only my opinion and I am sure there were reasons to justify the decisions taken, including (as we already mentioned) maybe freeing some space on air’s way through the front aerodynamics devices and to the sidepods. And anyway, this is only my personal opinion, which comes from a very different experience than the one of Mr. Perrin and surely not at such a high level.
In any case, some of the compromises connected to front suspension geometry are strictly linked to the short control arms in use, which are a direct consequence of the rules in place (maximum track width, chassis width in the driver’s leg zone) and also of the intention to design the front end leaving the chance to package a front electric engine to power the front wheels (not shown in the pictures).

MyP1 Front susp - Front w chassis

MyP1 Front susp - Front

MyP1 Front susp - Iso

 

MyP1 Front susp - Top
Beside the aero and package driven compromises we mentioned, it is easy to recognize a certain “F1 style” on the complete front suspension concept, see for example a very high attachment of the lower wishbone to the upright (relatively close to wheel center), to free air’s way in the region where it exits the front wing/diffuser (but surely not helping overall stiffness in cornering situations) and, also, the upward oriented front wishbones.

 

MyP1 Front susp - Front Upright - ISO

 

 

 

Here below a summary of front suspension’s most important features. Please note that the front ride height (plank) is referred to the lowest point of the car, namely the lowest point of the wood plank sitting below the floor and mandated by the rules (please see notes above about this part). It actually doesn’t extend up to the front axle, but, being its front edge pretty close to it, this approximation should not drive a big error.

 

Front Susp summary
I didn’t perform any calculation about the anti-effects, but it looks like there is something going on in this regard. A picture tells more than a thousand words!

 

MyP1 Front corner side view - Anti

 

Looking at the rear end of the car, Perrin provides the CAD models of the complete suspension (again with the exception of dampers and springs, probably third parties properties), the bell housing, the rear end of the gearbox and a solid block working as a placeholder of the main portion of the gearbox itself.
As for the front, the car employs a double wishbone scheme with pushrods, rockers and a general layout that could potentially allow both torsion bars acting directly on the rocker or coil springs mounted coaxially to the damper (I suspect the latter being actually the planned solution). The system allows the use of a third spring-damper unit, seating between the two rockers (not shown in the pictures) and activated by a traditional T antiroll bar, connected to the third element on the middle of the upper arm.

Again, it is evident how much of an influence the aerodynamics had on the general layout: this becomes clear, for example, looking at how low the rear top wishbone is attached to the upright, with its outer attachment z coordinate seating extremely close to the wheel center. This choice, which surely has a strong impact on suspension overall camber stiffness, had most probably a very beneficial effect in allowing the rear engine cover to be as low as possible. As far as I have seen, something very similar should also be used by the “big guys”, Porsche, Audi and Toyota.
Another interesting point is also the pushrod attachment to the upright being very low, probably (but surely not only) also to have a better kinematic alignment with the rocker plane.

 

MyP1 Rear corner side view - Anti

 

MyP1 Rear corner iso view - upright

Talking about suspension, also the rear one seem to be partially compromised for the sake of a bigger overall benefit, although the longer control arms undoubtedly helps to improve the situation.
I analyzed it again using the same Multibody software I used for the front one, again focusing on the pure control arms driven effects, since the wheel rates were anyway provided separately.
The results show a better bump steer, compared to the front axle, a much lower rear roll center (and also more in the region where I am used to see it, from my previous experience), a higher camber gain (which is, in my view, beneficial at the rear) and still a pretty high track width change, although not as high as on the front axle.

A summary of what I found is shown here below:

Rear Susp summary

 

For the ride height, what I said about the front is of course still valid also at the rear, with the plank value referring to the lowest point of the car, below the plank thickest area.

 

MyP1 Rear Iso view

 

MyP1 Rear Iso view 2

 

MyP1 Rear top view

 

In general, the design looks very neat, although any particularly new solutions have been deployed, compared to the standards visible of F1 cars or other LMP1 vehicles.
It is interesting to notice how all the rods (pushrods or tie rods) that need to have an adjustable length use a spacer system with plates in between, which is (or at least was) a standard in Formula 1. I am not totally sure of what the other LMP1 manufactures do, about this particular feature. For sure this is not a standard in LMP2.
It is also interesting to notice how the front upright is mounted to the upper control arms where the “clevis” on the arm side, while for all the other connections between control arms and upright (front and rear), the opposite solution is in place (clevis on the upright/chassis side).
Staying on the suspensions side, the vertical stiffness (wheel rates, spring contributions) suggested by Perrin in the provided datasheets was pretty high, with a stiffer setting at the front than at the rear (270 N/mm at the front, 230 at the rear).
According to the unsprung mass provided by Nicolas, this lead to a pretty high suspension natural frequency, both at the front and at the rear (in the region of 6Hz at the front, 5.4 at the rear).
As we will see later on, I had to work on the setup a bit, because the car was really hard to drive. More on this later, but I also tried to reduce the corners spring stiffness using third springs, with positive results.
A role about this issue was surely played by the tire model, which was basically carried over from my LMP2 project, but using four rear tires, since in LMP1 all the tires seem to be the of the same size (31/71-R18). For intellectual honesty, I have to say that, according to the information I have, LMP2 tires are vertically stiffer than many Michelin tires with the same dimensions (Michelin is used by all LMP1 work teams) and this could play a role, increasing the overall wheel rate; but, since in 2016 all the non-hybrid LMP1 teams should switch to the brand now producing LMP2 tires, this approach was (accidentally) useful to have a better picture of how the car should behave or could be set. Of course, we cannot know if the new LMP1 tires will be the same (or have similar features) as the LMP2 ones, but this was the only trustable data I had, so I had to stick to it.

Regarding the Antiroll bars stiffness, the material provided was pretty unclear, showing actually a negative stiffness for the rear, probably because of calculations done to achieve a certain roll gradient.
The reference value for front antiroll bar stiffness at ground (so its wheel rate contribution) was 380 N/mm. Even with no real antiroll bar, this would produce already a pretty high roll gradient, mainly because of the high roll axis and the relatively low CG. Anyway, rear roll stiffness was an important study parameter in my simulations, more on this later.

Moving away from the suspensions, a very important area, where no data was provided, as I said, is the powertrain.
I tried my best to replicate a Turbo engine with more or less the same features of the AER used by both Rebellion and byKolles, the two teams currently competing in LMP1-non hybrid class. Probably it is more correct to say that I tried to replicate the known features of this engine, since I found few or no data about it.
As far as I know, it should rev pretty low, with a shifting point around 7000 rpms, but I could not find any useful data about the overall power. I tried to enquire Mr. Perrin himself about a realistic power figure for an LMP1 engine and it came out he also had no trustable info to provide. I also had no direct contact to people working on the AER engines and all the people I could talk to were not really able to help or could only provide figures flying everywhere between 500 and 900 hp.
Sticking to the fuel flows (updated in September 2015) allowed by the FIA (106.5 kg/h, for the LMP1 non-hybrid class) and to what I think (hope) could be a realistic BSFC figure (219.5 g/kWh), at least for the peak power, I derived something in the region of 485 kW (640-650 horsepower, depending on the definition of hp/ps you want to use).
To draw a realistic power curve, I based on an engine produced by a tuner with more or less the same features (6 cylinders, low revs, high torque and about the same power) and came to something like this:

 

Engine

 

The gear ratios were not provided and I tried to build up something realistic, basing on engine power, drag and rolling resistance. For this first study, I only considered the sprint aerodynamic configuration, assuming a fixed rear wing angle and, thus, just one possible aero setup; it made it easy to define a single set of gear ratios that would more or less fit every track (not optimal, I know, and probably not completely realistic, but still enough to get a directional performance estimation, in my opinion).
The gear ratios I used at the beginning are listed here below and are based on the input from Nicolas, stating that the plan is to go with a 7 gears solution:

 

1st: 14/34
2nd: 16/31
3rd: 19/31
4th: 21/29
5th: 21/26
6th: 20/23
7th: 23/25

Bevel: 22/21
Crown and Pinion: 15/43

 

As we will better see later on, I had to work a bit on the ratios to allow a better use of engine power even at the exit of low speed corners, using lower gears, without relying too strongly on traction control.
As you have seen, the engine is pretty strong in terms of torque.

We will cover the setup work more in details a bit later, not only regarding the gear ratios.
Before we move to the next topic, though, I think we need to spend a couple of words about a pretty important missing input, which is again a part of the powertrain system: the differential. It has a very sensible influence on how the car handle and it is normally a tuning parameter whose effect than can be felt very clearly by experienced drivers.
Unfortunately, there were no info about it in MyP1 server, as the gearbox itself was not yet really defined in details.
To be honest, I don’t even know exactly what kind of differential setup do the other LMP1 cars use, being them hybrid or non-hybrid.
For my simulations, I have assumed a Salisbury Type limited slip differential, with ramps and clutches to set the desired locking effect and with a tunable internal preload.
Without going into details about how such a differential works (this could require an article in itself and is anyway very well explained in many other articles on the web), it can suffice to say that its tuning was initially based on the experience I had with other LMP cars and was finally brought to slightly different settings, with a pretty high locking percentage in braking (around 80%), an average one on power side (about 30%) and some 100 Nm of preload. All of this has made the car pretty stable, maybe even increasing a bit too much the understeering tendency on corner entry and “helping” in showing some other small issues, mainly connected to the front suspension. On the other hand, I guess no endurance drivers would probably love an understeering car.

Another very important performance area is, of course, aerodynamics.
All the available Perrinn MyP1 data was derived, as far as I know, performing CFD simulations, since no real car or wind tunnel model has been built so far.
According to the shared information, Perrin and his team worked mainly on the low drag configuration, meant for Le Mans, including testing the virtual model at different ride heights, to have at least a feeling about ride height sensitivity.
Regarding the Sprint configuration, only minor data was provided, giving baseline figures of drag and downforce/balance. The data sheet provided also included the effects of increasing or decreasing both front and rear wing inclination in terms of drag, downforce and balance shift.
To derive a complete aeromap (downforce, drag and balance depending on front and rear ride height), I used a combination of the data provided about the low drag setup (scaled up) and my previous experience with similar cars.
The reason behind this decision, instead of simply relying on Perrin data (appropriately scaled to match with the downforce and drag levels provided for the sprint configuration), is that, as far I could see for other projects, the low and high downforce setup of an LMP car behaves completely differently not only in terms of absolute drag and downforce, but also from a ride height sensitivity perspective. The reason behind this is that, if the rules allow it, the team will try to also optimize diffusers shapes; they are the parts creating probably the strongest ride height dependence.
One thing to keep in mind is that, anyway, we cannot say anything about the accuracy of the data provided, also considering the complete design was developed aerodynamically using “only” CFD simulations.
I personally have no direct experience in this field and I cannot say much about the accuracy that can be achieved and I heard very different opinions about it. What is for sure is that, if big LMP1 and F1 teams invest so heavily in wind tunnel testing, there must be a reason.
Data accuracy is anyway an extremely sensitive topic, for anybody doing simulations, no matter in which field. Every measurement is subject to an error and race cars are no exception: my experience taught me also how much of an influence the “human factor” could have, for example calibrating a sensor poorly or simply ignoring other issues in the measurement chain.
Beside this, every data derived through lab measurements, see for example a wind tunnel test, is something that refers to more or less ideal conditions, which are practically impossible to replicate on track.
With this, I don´t want to say that measurements are always wrong and that we should not rely on the data provided. I personally strongly believe that data are the key element distinguishing engineers by other professionals and, as long as I have access to reliable sources, I heavily rely on them for my models.
Simply, I know that sometimes it is not easy at all to identify and quantify error sources. That’s the reason why, for this study, which aimed mainly to produce directional results about Perrin’s car performance and behavior and, maybe, more in general, about an LMP1-L like vehicle, I felt I could took the freedom to “shape” the input data a bit, basing on my previous experience, more than simply relying on what was provided.
After this (probably boring) excursus about data in general, you can find here below the aeromap that could be derived from Perrin’s data for the Low Drag configuration:

Aeromap Low Drag

 

As we have seen talking about the suspensions, the ride heights refers to the wood plank below the car, so they are trying to represent the lowest point of car’s body.
As you may see, the efficiency is mainly between 4 and 4.5, showing the highest values when the downforce is higher, mainly because drag seems to be less sensitive than downforce to ride heights.
One very interesting point is the general effect of pitch/ride heights on Downforce and balance shift. We can get a better feeling about it looking to the only situation where we have two different rear ride heights value (25 mm and 31 mm) for the same front one (15 mm). Although 6 mm could seem a very small delta for the rear ride height, it is interesting to observe how downforce balance (portion acting on the front wheels) moves from 43.4% to 44.9%: a shift of 1.5% is in general something producing effects relatively big effects, easily detectable by an engineer when looking to telemetry data and normally clearly felt by the driver.
If you think that this shift was produce by “only” 6 mm difference in rear ride height (or pitch, in this case), you can immediately get a feeling of how important ride height (and pitch) control could be for such a car. This phenomenon goes hand in hand with an increase in overall downforce (CzA moves from 3.36 to 3.43, more than 2% difference).
The aerodynamic efficiency is, in general, pretty high, to underline once again, if needed, how effective could an LMP prototype be from this point of view. Anyway, keep in mind that, as far as I know, the efficiency obtained with Perrin’s design is not even close to what the “big guys” achieve with their cars.
Regarding the Sprint configuration, I took into account only a single point of the map, using it to determine a sort of scale factor, as I explained already.
In particular, for the base Sprint Setup, the data provides the following values:

 

aeromap sprint

 

As we may see, some interesting things are happening here: beside the expected increase in downforce and drag, we have a slight increase of the aerodynamic efficiency and very pronounced shift in terms of front downforce distribution, which saw a relative increase of more than 4%.

Before to dive into the simulations results, I think it could be worth to spend some words about the initial setup proposed by Perrin and the modifications I did in order to achieve a somewhat satisfying handling. We will mainly focus here on the mechanical settings, as we have seen how the aero was basically fixed. Please keep in mind, I will always refer to wheel rates from now on, when talking about stiffness.

According to the suspension setup proposed by the designer, the car should have a corner wheel rate of 270 N/mm at the front and 230 N/mm at the rear. The antiroll bar rate shown was of 380 N/mm at the front, with a negative value provided for the rear. Assuming, as a starting point, a contribution of 150 N/mm of the rear antiroll bar and bringing the front one to 400, we get a Total Lateral Load Transfer Distribution of about 60.8% on the front axle and an overall roll gradient (including tires) of about 0.22 deg/g, at the ride heights considered (15 mm front, 25 mm rear).
The TLLTD is, even with this base setup, pretty aggressively moved toward the front; if we consider that Perrin note seemed to suggest (see the strange negative roll stiffness contribution of the rear antiroll bar) the need to have an even bigger portion of the overall weight transfer acting at the front axle (with this being also partially driven by the suspension geometry features we saw at the beginning), you can already foresee some of the handling features of this car and some of the problems it may have or the designer was trying to anticipate.
After some testing, I came to a setup solution where some of the vertical stiffness was removed from the corners and partially transferred to the third elements, both at the front and at the rear. For this first evaluation stage, I didn’t use any bump stop, although it would probably make very much sense for a car like this, with pretty high downforce and high ride height sensitivity. It is something that could probably be further and investigated in a second step.
The final corner wheel rate I have used is of about 190 N/mm at the front and 160 N/mm at the rear, with both front and rear third elements using a 50 N/mm spring. Roll stiffness has been further decreased at the rear, coming to 100 N/mm and slightly increased at the front (420 N/mm) thus coming to a final Total Lateral Load Transfer Distribution (in static/setup conditions) of about 65% and to a roll gradient equal to about 0.24 deg/g.
As you may also see, the final corners vertical stiffness has been reduced, compared to the levels suggested by Perrin itself, making the car definitely much easier to drive also on kerbs and bumpy surfaces and, in general, more predictable.
We can generally say that the vehicle, because of its design and of the setup in use, showed a pretty marked understeering tendency in corner entry, probably making even more evident the compromises accepted on the suspension design side, above all in slow speed corners. The front end is not so easy to handle, producing sometimes pretty strange reactions and generally a worse feeling than the one you could get driving an LMP2, for example (where suspension design is much less compromised). On the other hand, this has probably help to give some confidence to the driver in the corner exit phase and in fast corners.

As we already mentioned, gear ratios were also slightly changed during the “development” phase, to make the engine output more usable in corner exit in slow corners. After testing a bit, I finally came to a solution with slightly longer 2nd, 3rd, 4th and 5th gears, ending up with the following solution:

 

1st: 14/34
2nd: 16/32
3rd: 18/31
4th: 17/26
5th: 21/29
6th: 19/23
7th: 23/25

Bevel: 22/21
Crown and Pinion: 15/43

 

The vehicle model, built and set up as described, was tested in Silverstone using a very detailed track model that should eliminate the fidelity/confidence issue on this side pretty completely. The results are shown here below with graphs relating to speed, RPM, lateral acceleration and longitudinal acceleration versus driven distance.
Now, before to comment on them, I want to share a word of advice, also to avoid anybody shooting at me because of sharing wrong results.
These results refer to a simulation which, as any simulation, was performed in ideal conditions (although using a real human driver), thus excluding a long list of disturbing factors that do exist in real life (see track conditions, traffic, etc) and other important factors as tire wear, all of which have a significant influence on lap times and, more in general, on the performance of the vehicle.
Also, the data I have used to generate this model are actually derived from a car (Perrinn MyP1 project) which doesn’t exist in real life and, unfortunately, probably never will; in some cases, as we have seen, I had to derive some missing inputs, sometimes related to performance critical subsystems, see for example the engine. For other critical areas, see for example aerodynamics, the designer has only performed simulations but never tested (in a lab or on the road) any part.
This means, on one side, that the input we have given could well be wrong or, at least, different from any other existing car; this depends, as we said, on many potential data errors and, on the other side, on having no means to check how good or close all of this data is compared to, say, a real existing LMP1-L vehicle, see for example the one used by Rebellion Oreca.
Nonetheless, I think it has been an interesting exercise, also to understand how close (or how much closer) an LMP1-L car could go to the manufacturers in terms of performance and, also, which issues (setup, handling, balance, etc) such a vehicle could present.

The final lap times obtained was about 1’42’’5. Let´s look at the speed trace first.

 

speed

 

First thing to notice is that the car reaches a top speed close to 300 km/h (about 297) on the Hanger Straight and is able to drive at very high speed through the fast sections of the track (Abbey, or first right corner, where we are travel at close to 265 km/h and nearly flat out; Stowe, with a minimum speed of about 215 km/h and finally through the Maggots-Beckett section, where the relative stability helps to carry high speeds through all of the corners).
We can take a look to the lateral acceleration trace, to further understand car’s overall grip potential:

 

lat g.jpg

 

Here we can see that the vehicle is able to carry about 3gs in the two quickest corner of the track, to underline how important the aero effects are. Interesting also to notice how also in lower speed corners the car can sustain accelerations over 2gs, see for example through the Maggots-Beckett complex.
The longitudinal acceleration trace seems to confirm more or less the same trends, also giving an idea about the trusting force that our engine could produce, additionally also showing the grip potential in braking.

 

long g

 

Finally, we can take a look to the RPMs trace, at least to have an idea about the engine usage and gear ratios and to try to stimulate somebody to come back and say if and how wrong my assumptions are. As I said several times, the engine is probably the biggest question mark of the whole article and, together with aerodynamics and tires, surely a very strong performance driver.

 

rpm

 

Taking into account all the error sources we already mentioned, I even dared to compare our data and results with what happened last year in Silverstone during the first WEC Race. Pole position was signed by Porsche with a stunning 1’39’’7 average (of two drivers), but with an overall best lap of 1’39’’5; the second best non-Porsche car was the Audi, with an overall best lap of 1’40’’2 circa.  It makes no sense to analyze the LMP1-L lap times, since Rebellion was absent for the first race and the ByKolles team was surely not yet in top form; also, the fuel regulations has been changed slightly at the end of the season, as we said, probably freeing some performance potential for the non-hybrid cars. Anyway, we could try to deduce a reasonable gap, looking to the typical lap times difference between LMP1-L and LMP1-H at the end of the year: LMP1-L were typically still about 6-7 seconds slower, if we look at qualifying results of USA, Japan, China and Bahrein races; this means the typical gap between LMP1-L and the manufacturers is normally bigger than what we have obtained with our study.
In general, we should surely allow an error window to my results, to take into account effects not easy to simulate (as the ones we already mentioned, see traffic, track conditions and conditions variation, etc). In any case, also assuming a +/- 1 second tolerance for the simulation results, we still have a pretty sensible difference to what shown in 2015 by the two LMP1-L teams, in terms of performance.
This opens some possible scenarios that we can analyze: the first one is that, simply, my model is not really representative of any existing LMP1-L car: the data I used are not coming from any of these cars and there are anyway some open questions about some critical areas, like the powertrain one.
Another explanation could be that only some of the subsystem are not really performing as we would think, basing on my simulation results: my first suspect lies, again, on the engine: to be honest, I still believe that, although being realistic when looking to the BSFC values we used, the power output I assumed was probably optimistic. This could also open another discussion about the pace difference between LMP2 and LMP1-L to be expected in 2017, when LMP2 should actually get an engine with a power output of about 600hp (much more than the 500hp c.a they have now).
But we also don’t have to forget that last year LMP1-L and LMP1-H teams were using the same tire brands (Michelin, which I doubt was providing the same tires to everyone), while all of my simulations refers to a tire model based on lmp2 tire data. Incidentally, the same brand will be used in 2016 by all of the LMP1-L cars, which moved away from Michelin. We could argue that any tire model used for simulation will never really give a precise picture about the final performances of its real counterpart, but I am pretty curious to see which pace the LMP1-L cars will have in 2016 in Silverstone. Assuming my simulations are anywhere close to being correct, LMP1-L teams should be able to free some performance potential, sooner or later.
For now, what we can say is that, looking to the only 2016 lap timing results available so far (namely the results of the Prologue, held in Paul Ricard at the end of March), we see already gap reduction, with the LMP1-L cars now being closer to the LMP1-H ones, with Porsche and Rebellion being some 4 seconds away from each other and this difference further reducing to about 3 seconds if we consider Toyota and Audi.

To better understand if and how our results are somehow trustable, we can look in more details at the performances registered by the LMP1 cars in Silverstone in 2015 comparing them with our simulations and to the results seen by LMP1-L teams at the end of the year.
The first “quick and dirty” comparison we can do regards the maximum top speed reached in our simulation (about 297 km/h), that is pretty close to the one achieved by Porsche (300-302 km/h) but pretty much quicker than the ones of Audi and Toyota (285 km/h c.a for the Japanese and something below 280 for the Germans). This should be no surprise if we assume that, even being probably more aerodynamically efficient, the LMP1-H has less power coming from the IC engine; this should mean that, after the boost of the hybrid out of the corners is over, the car is only pushed by a less powerful engine than the one we used. A comparison between our model and real LMP1-H performances could anyway be useful to understand which delta we could expect, in order to compare it with the top speed delta between LMP1-H and LMP1-L cars in other tracks.
So, without further ado, if we look at Fuji results, we can see that, while Porsche was topping at 309 km/h c.a, the best Rebellion was able to achieve a maximum speed of about 302 km/h. We would have here a 7 km/h difference, which compares relatively good to the 5 km/h difference we have seen in Silverstone with during our simulation.
If we then look to the USA results, we even see a Rebellion on top of the best speed charts, with a maximum speed of about 301 km/h, against the 300 km/h achieved by Audi.
This shows that, at least in terms of top speed, we should be not too far off from a realistic picture.

What about other sections of the track? The only source I found to gather some information are the onboard videos you can find in Youtube about and showing portion of the WEC races: sometimes, if you are lucky enough, some of them show some telemetry data which can help to identify (at least very generally) cars performance.
Before diving into details into this, again, please keep in mind that some aspects, like for example tire wear, were not simulated during this exercise and that they could play a role in defining small differences. Moreover, some other parameters like fuel load are unknown. Finally, our model represents a car that should be slightly lighter than a LMP1-H.
Watching this video, at the 1:21:00 mark c.a, we can seat for some time onboard of the #7 Audi beside the driver Marcel Fassler. At the very beginning of this video section, we see the minimum speed inside the last chicane (Vale), being about 90 km/h (in another section of the video, around the 1:55:00 mark, the minimum speed is around 94 km/h): this compares pretty good to the 92/93 km/h we see in our simulation; a few seconds after, the Audi goes through the first very fast right corner (Abbey), with a minimum speed of about 260 km/h, which is again very close to the 262-263 km/h shown in our speed trace at the same point. Again, Fassler drives through the first right hairpin (Arena track section) with a minimum speed of about 90 km/h, which is not too far off from the 95 km/h shown by our simulation. The following left hairpin allows a minimum speed of about 83 km/h to our model, against the 80 km/h c.a of the Audi.
Afterward, the displayed data seem to stop working, not allowing for a check on the following corners. This very rough sanity check tells, anyway, that our results should not be completely off compared to the real cars.

Closing, this exercise allowed us, on one side, to explore more into details the very interesting MyP1 project, from Nicolas Perrin, analyzing a bit how the car looks like and trying to identify some key aspects, at least in some areas. Afterward, basing also on my previous experience with other similar cars, we tried to build up a simulation model of the car, assuming it was running in an LMP1-L configuration. The results we obtained has shown that, assuming the data we have used are realistic, the LMP1-L car could actually have some potential, in terms of performance, that for some reason was not yet explored. The results we obtained were also (roughly) compared to available data about LMP1 vehicle performances to double check if anything was completely off.

Hope you enjoyed it and you did it to the end without falling asleep!

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Responses

  1. Anywhere I can get the CAD data now? Site seems down.

    • Hi,

      to be honest i don’t know.

      I have also seen that everything has been taken away, probably confirming the project will not go on.

      If the data are not available anymore on the internet, i would suggest to write an email to Nicolas Perrin himself. He is normally very kind and can surely give you more information about the current status.

  2. Professional article, appreciate.

  3. Thanks Andrea! Great post, as always.
    Regarding the tiny mismatch in laptimes with simulated lap being slightly quicker than expected real one, I would consider that as a kind of expected result, based on my experience in simwork with junior drivers (which is quite limited of course, but still better than nothing). It correlates pretty well with relative performance of real drivers: normally a driver in the sim is a couple of seconds faster than the same driver in his real car. This is the case for both rFactor (provided the car and track models are accurate) and iRacing.

    • Hi Dmitry,

      thanks a lot for your comment.

      You are right above the drivers being normally a bit quicker in a simulator compared to the real car (no fear, no possible damage to them or to the car, no changing track conditions, no traffic, etc), although in my experience this difference is typically smaller than what you mentioned (normally not more than half a second).

      I guess this is the difference between working with “off the shelf” car models, like the one produced by Iracing developers and building your own vehicle models, based on real and (hopefully) accurate data and going through a proper validation process to assess all what doesn’t seem to match.

      Regarding this article in particular, what i wanted to point out is that the whole LMP1-L class seems to be too slow compared to what should be their real performance potential, at least if all my assumptions were right. So, most probably, some of them were not exact and these cars have less performance potential than they should and than what we thought.

      The main suspect is, in my opinion, the engine: i have assumed they would have around 650hp, but this is probably not the case and rather only an optimistic assumption.

  4. Wow. That was quite an article. Thanks!


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