Question about track altitude

[Renault-BAR]

Hey, I'm a newbie here. I just want to know how the track's altitude plays into it's challenge. I also would like to know the altitude of a few of the highest tracks.

Thanks

[marcush.]

i suppose you mean elevation changes.
Well ,a track like the A1 ring has several changes in elevation wich heavily influence the car setup.
there are several corners going uphill (end of pitstraight end and corner at the far end of the track but significantly the all important fast double lefthander as well as the doule apex corner leading to the pitstraight are both hanging to the outside as well as going downwards,so you have to compromise towards a setup with more understeer dialed in as usual wich is balanced out by the track going downwards.If you don´t do that you arive in thes corners with instant oversteer as soon as you look at the throttle.Same goes for the brakes you´d end up having more bias to the front as the weight is moving stronly forward as the track goes downwards giving you instability on applying the brakes if you leave the brakes as std.So it is an ideal site for the car with uncurable understeer trouble......of course altitude has lots of other implications...
aero,engine mapping,power,but it is as always ,you have to optimise what you have at hands...

[Renault-BAR]

Actually I meant the tracks overall altitude. Like whether it's located at a mountain or very low. I'm pretty sure at different elevations you've different winds and temperatures. Not to forget the dews. Btw, thanks for the insight on elevations.

[Steven]

important in the height relative to sea level is the air pressure. This means that a same volume pulled into a cylinder contains less oxygen to start the oxidation of the fuel (which is actually the burning) . So, higher altitudes require more air intake, and lower the engine's performance with up to 6% (from low to high current F1 circuits). I read this a couple of months ago in an interview with an engineer at Renault...

[marcush.]

ok,understood.
High altitude =thinner air=less aero drag +less downforce...

[Reca]

Obviously loss of power because of reduced density is the main effect of altitude, and indeed the first intent of turbo/supercharger was exactly to compensate the power loss airplanes with NA piston engines were suffering in altitude.
The subject became very important at the recent Mexico Rally, the WRC drivers were indeed impressed about the loss of power, many described the feeling as they were driving group N cars.
There are a few relationship hp vs altitude, mainly are based on statistical data and obviously you can use complex simulation to understand how the altitude influences the different parameters. While the loss of top power is basically a not so big issue (after all it happens to everyone more or less in the same percentage) the latter analysis is more important to understand how the power curve change.

As for downforce, again the reduction is in the same for everyone so it could be a problem only when the car is already at maximum downforce level and you need more, if your design is lacking in that aspect compared with others, same problem as in Monaco or Hungary.

IIRC the highest track was A1 ring, now which one is ? Interlagos ?

[Enzo]

I think that it's Interlagos. If we compare the Silverstone and Interlagos in terms of temparature and altituse then we will come uo with a 20% drop of air density which means a 20% drop of downforce. Power and drag will also drop by 20%, so max speed remains the same but acceleration (longitudinal and lateral) will drop. The maneuvre envelope of the car will become a lot narrower but with the same height. When you leave Silverstone and go to Interlagos is like you going back in time of about 10 or more years...!!!

[Reca]

I’ve found that Interlagos altitude is about 800 m and probably is also higher than A1 Ring.

If we compare the Silverstone and Interlagos in terms of temparature and altituse then we will come uo with a 20% drop of air density [...]Power and drag will also drop by 20%, so max speed remains the same

Are you sure 20% is right ? From the Interlagos altitude I’ve found, also assuming Silverstone is at sea level the pressure drop should be in the order of 8-9%, to have a 20% density drop you should have a difference of 10% in the absolute temp meaning for example 15°C in Silverstone and 41°C in Interlagos. Can you post the data you used for the calculation ?
Furthermore, the % of power drop isn’t the same as the % of density drop, the former is a bit higher so also assuming the same aero trim (hence a reduction of drag in the same % as density), the max speed will suffer a bit anyway.

[Guest]

Reca,

This was a simplistic estimation of Peter Wright in his book: "Formula 1 Technology". He stated that the altitude and temperature different will cause a 20% drop in air density with a 20% loss of downforce and a 20% drop of power.

I think that 20% drop of density means also 20% drop of power because d=m/V, d=density, m=mass, V=volume.
So let's say that in one engine operation cycle the engine can suck 100 ml of air, which means 23.2 gr (or 21 ml) of oxygen then with a drop of 20% of density then the mass of air would be 18.56 gr (or 16.8 ml) of oxygen. And as the oxygen is the main element of the combustion then the power drop will be 20%. Yes, i know that what i write is only in theory but i don't think that it's too far from reality.

[Reca]

First of all Happy Easter to all Forum members and readers.

Enzo (at least I think), if you read again my post you see that I’ve considered the variation of temp. The only doubt on my evaluation is about the standard air, I don’t know if it’s a good approximation for the pressure drop so I asked if you used real data for temp and pressure (as apparently you said you did) on the two tracks. 20% looks definitively too much according to my evaluation and also according to the figure Tomba posted. AFAIK the Wright’s book is relatively old (1995 or so), there’s the possibility he was referring to Mexico City (2000 m.) or he clearly states that the comparison is between Silverstone and Interlagos ?

About power, your analysis is correct but incomplete, I was just completing it. In fact, although the lack of O2 for the combustion is the main effect, the reduced density influences also a few other engine parameters, so the power lost is a bit higher in %, and as a consequence the top speed, also assuming the aero trim is the same (it really is in Interlagos and Silverstone ?), results a bit lower anyway. It was a further addition to explain why, as I said in my previous post, statistical data or simulations are used to calculate the power lost (otherwise it would be quite easy, don’t you think ?)

[Enzo]

Reca, Peter Wright is clearly writing about the difference between Silverstone and Interlagos. The altitude at Interlagos is 762m (2500ft). Let's use the next equation in order to find the density difference:

density = (C0/T)*10^(-z/C1)*C2, where

C0 = constant = 288.15 K
C1 = constant = 18000 m
C2 = constant = 1.2255 kg/m^3
T = absolute temperature
z = altitude

Let's say that we have a temperature in Silverstone of 15.16 'C, then the absolute temp. there will be 288.16 K and density = 1.2255 (all these data have been found from tables of Fluid Mechanics books assuming that Silverstone is on the sea level). And let's say that we have a temp. of 35 'C at Interlagos. Then you will see that density at Interlagos = 1.04 kg/m^3.

So the percentage diff. = (1.2255-1.04)/1.2255 = 0.15 or 15%

So Wright is quite correct (although simplistic) assuming that he wrote about a cold March test day and a hot afternoon at Interlagos two weeks later. Anyone from UK can tell us about temps during March?

[Enzo]

....the reduced density influences also a few other engine parameters, so the power lost is a bit higher in %, and as a consequence the top speed, also assuming the aero trim is the same (it really is in Interlagos and Silverstone ?), results a bit lower anyway. It was a further addition to explain why, as I said in my previous post, statistical data or simulations are used to calculate the power lost (otherwise it would be quite easy, don’t you think ?)

You are right that it would be very easy for people out to calcuoate the power loss due to density fall if density drop would mean exactly the same drop of power. That's why i wrote that all these are only in theory but theory is not so far from practise.

Air is coming into the combustion chamber and only so air density is affecting parameters relating to cyce operations i.e. induction, compression-combustion, expansion, exhaust. I will exclude the two last from the equation since the combustion has already teken place so there is not air in much quantities in order to affect these two operations.

During induction less denser air will lead to easier induction due to less air (O2, N2 etc.) molecules.

During compression again we will have gains as less molecules leads to less friction-> less compression power loss.

The other two parameters are air fuel mixing and combustion. Are these two parameters you are referring to?

[Reca]

About that calculation on density, you can see that I already obtained that result in my second post

the pressure drop should be in the order of 8-9%, to have a 20% density drop you should have a difference of 10% in the absolute temp meaning for example 15°C in Silverstone and 41°C in Interlagos

my point was exactly that to have 20% of difference in density you need a big difference in temp. I don’t wanted to say that 20% is impossible, only that it was unlikely considering the period the two GP are planned.
Here in Monza, during the period the track is constantly used for tests/races (hence between February and November), the temp can vary between 0°C (as last February) and more than 35°C (as last Summer) so the difference in temp can easily be in the order of 10%, and that on the same track. But if I have to talk about the effects of altitude and I have to compare Monza with Interlagos I assume the same temperature or the typical temperature I have at the race, in September for Monza and in March (this year in October) for Interlagos.

About engine power, the parameters I’m referring to are volumetric efficiency, combustion efficiency, mechanical efficiency etc etc etc, all concurring to define the power and all more or less affected by the ambient conditions. If you assume all parameters are fixed then you can say that power is directly dependant by density. A more precise analysis requires to consider each parameter and verify how ambient conditions affect it

[Enzo]

I don't think it's so much surprising to see a temperature difference of 20'C between UK and Basil during March. Or maybe Wright took the worst examples from the two countries in order to make his statement even more surprising. While i was searching through the online weather forecast sites i found that today the tepmarature range in Northampton was 8-13 'C and in Rio (sory i didn't find Sào Paulo) 22-27 although it is rainign today there. Here in Greece we had in March a temparature of 10-15 so i expect to see temps in UK during March well less than 10 'C. Anyway it's something between what weboth have estimated (between 8-9% and 20% drop in density)...

[Reca]

Here in Greece we had in March a temparature of 10-15 i expect to see temps in UK during March well less than 10 'C

You were “lucky” with weather then, and you don’t need to look at UK, here we had snow also in March. I remember that one of these cold days I’ve seen a few trucks carrying Supersport bikes to the track, I don’t think that test was really meaningful. Point remains that Silverstone GP is in July, not in March Just kidding... we are both “right” in our evaluations, simply we started with different hypothesis.