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Does anyone have a lap time simulator?


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#1 pizzalover

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Posted 05 June 2013 - 18:27


Just wondering if anyone can model these figures?

"McLaren's stated aim in producing the P1, was to make it the fastest production car around a race track. My question is, would it be faster without the battery power?

The P1 weighs 1400kgs dry. Of this, the battery, motor and ancillaries weight around 140kgs dry. The electric motor puts out 176 bhp, V8 turbo 727 bhp. Down force 600kgs.

Nurburgring less than 7mins."

I'd be interested to see the comparative lap times, with and without the batteries.

Any help would be much appreciated.

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#2 MatsNorway

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Posted 05 June 2013 - 18:37

To clearify we must assume one singular lap. Time attack style.

#3 pizzalover

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Posted 05 June 2013 - 19:09

To clearify we must assume one singular lap. Time attack style.



Yes, the full beans.

#4 Greg Locock

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Posted 05 June 2013 - 22:32

Question

Does increasing the power to weight ratio of a vehicle suually improve its lap times for a single lap?

If not, I suggest you remove some spark plugs from your car when qualifying.

#5 gruntguru

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Posted 05 June 2013 - 23:33

:rotfl:

Seriously though, there is more to the story than power to weight. More important than P/W is latacc and that will usually improve with weight reduction (higher mu) and definitely improve if the car has significant aero DF. I don't know how fast the P1 has to be going to generate 600 kg. but at that speed the lat acc will improve by at least 1400/2000 x (2000-140)/(1400-140) = 1.033 (or 3.3%). Same for braking and traction-limited-acceleration.

Of course if McLaren were totally single minded about the stated goal, they would have deleted the hybrid bits and put 140kg of extra IC engine in the thing. Probably pick up an extra few hundred hp.

#6 pizzalover

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Posted 06 June 2013 - 00:42

Question

Does increasing the power to weight ratio of a vehicle suually improve its lap times for a single lap?

If not, I suggest you remove some spark plugs from your car when qualifying.


Errrr.......

There's a bit of difference between a "lap" and a drag strip. Once you throw in a few corners, power to weight just becomes another factor, which is why you'd need some fancy software for a definitive answer.

Edited by pizzalover, 06 June 2013 - 00:46.


#7 pizzalover

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Posted 06 June 2013 - 00:46

:rotfl:

Seriously though, there is more to the story than power to weight. More important than P/W is latacc and that will usually improve with weight reduction (higher mu) and definitely improve if the car has significant aero DF. I don't know how fast the P1 has to be going to generate 600 kg. but at that speed the lat acc will improve by at least 1400/2000 x (2000-140)/(1400-140) = 1.033 (or 3.3%). Same for braking and traction-limited-acceleration.

Of course if McLaren were totally single minded about the stated goal, they would have deleted the hybrid bits and put 140kg of extra IC engine in the thing. Probably pick up an extra few hundred hp.



Over 2g cornering. 600kg is at 160mph, after which active aero bleeds it off.

#8 Greg Locock

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Posted 06 June 2013 - 02:45

Seriously though, there is more to the story than power to weight. More important than P/W is latacc and that will usually improve with weight reduction (higher mu) and definitely improve if the car has significant aero DF. I don't know how fast the P1 has to be going to generate 600 kg. but at that speed the lat acc will improve by at least 1400/2000 x (2000-140)/(1400-140) = 1.033 (or 3.3%). Same for braking and traction-limited-acceleration.

Of course if McLaren were totally single minded about the stated goal, they would have deleted the hybrid bits and put 140kg of extra IC engine in the thing. Probably pick up an extra few hundred hp.

True dat - mu sensitivity of tires is typically (gotta love the units) -0.01 to -0.02 mu per kN of load -it is of course far more complicated than that. So, 1400N of extra load will knock maybe 2% off the max latacc ignoring aero, rather less if aero is really significant.So if we were driving round a skid pan no aero then the lap time would increase by about 1%



#9 Greg Locock

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Posted 07 June 2013 - 01:09

I used Lapsim 2008.3, Donnington, Porsche Cup set to 1400 kg, 903 hp, 1'39.8, virtually no aero

power down to 727 hp 1'40.6

weight down to 1260kg and power at 727 hp 1'39.6

That's pretty funny.

To do this properly you should set the gearing up for the circuit etc etc, and add the aero in.






#10 gruntguru

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Posted 07 June 2013 - 05:43

That's pretty funny.

Yeah, but think of the fuel/CO2 savings McLaren achieved by hybridising the P1.

#11 Greg Locock

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Posted 07 June 2013 - 06:49


I've just added aero which even things up, they are within 0.1 seconds all the way round. But the tires in my sim are grip limited out of every corner, they are smoking for roughly 20% of each lap .

Turning up mu to prevent that, to 2 which is silly, gives the hybrid car a 1 second advantage over the lighter gas car.

So, the differences are small, but the setup has not been optimised for each case, the lighter car should carry less aero than the hybrid for a start.

#12 gruntguru

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Posted 07 June 2013 - 06:54

Surprising. I thought aero would increase the margin in favour of the lighter car (additional 3% in high speed corners in my post above). Is the aero in your sim very draggy?

#13 pizzalover

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Posted 07 June 2013 - 17:33

I used Lapsim 2008.3, Donnington, Porsche Cup set to 1400 kg, 903 hp, 1'39.8, virtually no aero

power down to 727 hp 1'40.6

weight down to 1260kg and power at 727 hp 1'39.6

That's pretty funny.

To do this properly you should set the gearing up for the circuit etc etc, and add the aero in.


Thanks for that. A really interesting result. If you could refine it with the aero and the extra torque that would be superb.

If you really want to make yourself popular, you should post your results a McLarenLife.

They love to see them ;)

#14 JimboJones

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Posted 07 June 2013 - 20:30

So, the differences are small, but the setup has not been optimised for each case, the lighter car should carry less aero than the hybrid for a start.


Why would a lighter car generate less downforce?

Surprising. I thought aero would increase the margin in favour of the lighter car (additional 3% in high speed corners in my post above). Is the aero in your sim very draggy?


Extra downforce, even at constant efficiency (so extra drag too) will always increase power sensitivity, and so favour the heavier, but more powerful car. The more of the lap you make power limited, the bigger the gains of having more power. The extra drag also increases the sensitivity to power, as you spend longer on the straights. Imagine you have so much downforce that every corner is flat out, the laptime becomes purely dependent on power - even the mass becomes irrelevant.

Edited by JimboJones, 07 June 2013 - 20:30.


#15 Greg Locock

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Posted 08 June 2013 - 02:58

Why would a lighter car generate less downforce?


The less powerful, in this case lighter, car, would normally need less drag (and hence downforce) for its optimum lap time than its more powerful competitor. I made no attempt to optimise either setup.

One reason I didn't do that is the tradeoff between Cd and Cl is unknown to me. L/D could be as high as 10 or as low as 3. I currently have Cd as 0.34 and Cl at 1.057.

One approach would be to assume that all the Cd excess over a competent car at Cd=0.30 is due to the downforce, giving an L/D of 26, which seems too high to me.

Well OK, that is a good test case. Bear in mind this is on mu=2 tires around Donnington
Run Mass Power Cd	 CL	 time
1	1260 727   0.34 1.057 1'33.52
2	1260 727   0.30 0.010 1'37.76
3	1400 903   0.34 1.057 1'24'55
4	1400 903   0.30 0.010 1'28.89
5	1400 903   0.38 2.114 1'21.47

So the more powerful car gains more from downforce than the less powerful car, but there isn't much in it. The tires are still saturating occasionally by the way on the 4th run in particular. Run 5 shows that at this (I think unlikely) L/D the car benefits from even more downforce on this track.



Edited by Greg Locock, 08 June 2013 - 05:14.


#16 JimboJones

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Posted 08 June 2013 - 12:45

The less powerful, in this case lighter, car, would normally need less drag (and hence downforce) for its optimum lap time than its more powerful competitor. I made no attempt to optimise either setup.


ahh, I misunderstood you, you are quite right. However, we are talking about a McLaren P1, which wouldn't have the ability to adjust downforce level.

One reason I didn't do that is the tradeoff between Cd and Cl is unknown to me. L/D could be as high as 10 or as low as 3. I currently have Cd as 0.34 and Cl at 1.057.


An F1 car is around 3, I'm not sure what would ever generate L/D of 10, but I'm guessing it would have to be massive ground effects.
As for the P1, if it generates its 600kg of downforce at 160mph, and we assume it's top speed (218mph?) occurs at 727bhp (DRS active), then we can back calculate it's effective L/D.
rho = 1.2

F = 1/2 * rho * v^2 Cl.A
600 x 9.807 = 1/2 * 1.2 * (160*8/5/3.6)^2 Cl.A
Cl.A = 1.94

P/v = 1/2 * rho * v^2 Cd.A
(727*746) / (218*8/5/3.6) = 1/2 * 1.2 * (218*8/5/3.6)^2 Cd.A
Cd.A = 0.994

Assuming the reference area is the same, L/D comes out at about 2.
All you need now is a circuit file for Nurburgring, and you can probably answer the OP's question...

#17 MatsNorway

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Posted 08 June 2013 - 14:18

For lap time comparison i prefer Tsukuba, a small track that the japanese consider the benchmark for time attack cars.

Simulating it is probably a lot easier than a huge track like burgering. And more trustworthy due to less bumps?

Problem then is that european cars do not use it.

Edited by MatsNorway, 08 June 2013 - 14:27.


#18 Greg Locock

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Posted 09 June 2013 - 01:39


The free version of lapsim does not include a track editor and has a very limited choice of track, 3 Rivers, donington, hockenheim klein, miami, moport zandvoort zeltweg and zolder It is possible to build a circuit model in matlab and import it but frankly it takes forever and I'm not inclined to do it.

#19 pizzalover

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Posted 11 June 2013 - 17:06

The free version of lapsim does not include a track editor and has a very limited choice of track, 3 Rivers, donington, hockenheim klein, miami, moport zandvoort zeltweg and zolder It is possible to build a circuit model in matlab and import it but frankly it takes forever and I'm not inclined to do it.



Sorry to be a pest, but do you think you could complete the simulation with the added down force and 900nm of torque? Many thanks for any help you can give.

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#20 Greg Locock

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Posted 11 June 2013 - 23:59

Sorry to be a pest, but do you think you could complete the simulation with the added down force and 900nm of torque? Many thanks for any help you can give.

I think I've covered that, if not you need to specify exactly what you mean. Runs 3 4 and 5 are at the high power, high mass configuration

Jimbo - yes the tunnel downforce in an F1 car had an effective L/D of about 10 in 2000. I'll run 3 and 5 with an L/D of 2, when I get round to it.

#21 pizzalover

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Posted 13 June 2013 - 03:06

I think I've covered that, if not you need to specify exactly what you mean. Runs 3 4 and 5 are at the high power, high mass configuration

Jimbo - yes the tunnel downforce in an F1 car had an effective L/D of about 10 in 2000. I'll run 3 and 5 with an L/D of 2, when I get round to it.


Ok, I get that now.

I tell you what might be an interesting comparison, say instead of going down the battery route, McLaren had just opted for a bigger engine? For example, two of their V8 units strapped together. Each unit weighs 200kgs and puts out 727bhp.

So for arguments sake lets say the "new" P1 weights 1460kgs but puts out 1450 bhp. What would that do to the lap times?



#22 Greg Locock

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Posted 13 June 2013 - 03:36

You're into the silly money now, because your optimum tune is just to throw downforce at the thing to get traction, and drag is irrelevant. I'll use jimbo's L/D of 2, because it seems pessimistic to me so will be less sensitive to tuning.




#23 Greg Locock

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Posted 13 June 2013 - 08:27

[codebox] Run Mass Power Cd CL time L/D
no electric A1 1260 727 0.34 1.06 1m33.52 na
no electric no DF A2 1260 727 0.30 0.01 1m37.76 26
baseline as designed A3 1400 903 0.34 1.06 1m24.55 na
A4 1400 903 0.30 0.01 1m28.89 26
A5 1400 903 0.38 2.11 1m21.47 26
No electric,no DF, LD 2 1260 727 -0.18 0.01 2 waste of time
no electric B1 1260 727 0.34 1.06 1m33.52 na check
baseline as designed B2 1400 903 0.34 1.06 1m24.55 na check
Baseline+2*DF at LD=2 B3 1400 903 0.87 2.11 1m23.62 2
Baseline+1.5*DF at LD=2 B4 1400 903 0.60 1.59 1m23.96 2
Baseline+3*DF at LD=2 B5 1400 903 1.40 3.17 1m23.05 2
Baseline+4*DF at LD=2 B6 1400 903 1.93 4.23 1m23.22 2
Pizzalover 1*DF B7 1460 1806 0.34 1.06 1m20.84 na
Pizzalover 3*DF at LD=2 B8 1460 1806 1.40 3.17 1m15.70 2 [/codebox]

Hope that makes sense. So if the incremental L/D is 2 then the optimum CL around Donnington is around 3, with all the previous assumptions, and fitting two engines is worth 4s with normal aero, and 8 seconds with lots of aero.

Late edit - I note that I have used the wrong power for B7 and B8

Edited by Greg Locock, 14 June 2013 - 01:47.