Car speed from engine sound

[WhiteBlue]

I would challenge the 5 kN vertical force. Which F1 car would have a downforce less than the legal minimum weight? Drag coefficient also looks a bit low. AFAIK the F1 cars all come in above 1.0.

[Ciro Pabón]

I would challenge the 5 kN vertical force. Which F1 car would have a downforce less than the legal minimum weight? Drag coefficient also looks a bit low. AFAIK the F1 cars all come in above 1.0.

Well, this force works only in the rear end. The downforce in the front end is of no significance for traction, as you can easily imagine. Also, the rear end weight, even taking weight transfer in account is NOT equal to the weight of the car (duh).

What drag coefficient would you suggest?

I am not sure if it is KN or Kgf, btw. Sorry, I haven't checked again what I calculate years ago, I just reposted... Finally, I am pretty sure that the speeds you get by this method are OK: when I used the engine sound in karts, downforce was inexistent, of course.

[WhiteBlue]

I would challenge the 5 kN vertical force. Which F1 car would have a downforce less than the legal minimum weight? Drag coefficient also looks a bit low. AFAIK the F1 cars all come in above 1.0.

Well, this force works only in the rear end. The downforce in the front end is of no significance for traction, as you can easily imagine. Also, the rear end weight, even taking weight transfer in account is NOT equal to the weight of the car (duh).

What drag coefficient would you suggest?

I am not sure if it is KN or Kgf, btw. Sorry, I haven't checked again what I calculate years ago, I just reposted... Finally, I am pretty sure that the speeds you get by this method are OK: when I used the engine sound in karts, downforce was inexistent, of course.

I would think that the total vertical force would have been at least 15 kN at 250 kpm if not more. If we assume a 40/60 distribution we should still have at least 9 kN at the rear wheels.

I seem to remember that F1 cars historically had coefficients between 0.95 and 1.4 so that we probably have to look closer to 1.4 for a 2007 car.

[747heavy]

The total vertical force is more or less 5 kilonewtons at 250 kph (cell B13).

Maybe I see this totally wrong, but what you (try to) calculate in cell B13, has nothing to do with downforce - IMHO.

If anything, you calculate the "weight" shift (loadtransfer) towards the rear axle, due to longitunal acceleration. (calculation is 600kg*8m/s^2 (0.8g))
but for the complete analysis of weigth(load) transfer due to longitunal accel. you would need to include CoG height and wheelbase in your calculation, and add the result to your static rear axle load (in the case of accel.).
This calc., is normaly used to define the traction limit of your (rear)tires.

note example is shown for braking (0.8g) but the calc is the same for accel.



But all of this has nothing really to do with the matter at hand.
I think (perhaps wrongly) that the "Doppler effect" is an "issue" when you measure with a trackside (external) microphone, if you use a on board recorded soundfile, where the distance and orientation between the sound source and the mic don´t change, it should be not much of a problem.
But you would have to account/filter for reflections/echos, due to surounding obstacles.
Monaco in the tunnel would be the extreme worse case scenario for this - IMO
Anyway, good job Ciro

[Tim.Wright]

For me, the number in B13 is just the resultant longitudinal force on the car.
F = Mass_car x Accel_car

Nothing to do with downforce at all.

To investigate aero information, you will need to compare the acceleration profile of the vehicle in 1st gear to the same in top gear but adjusted for the gear ratio. This will help you find the drag but I think its impossible to calculate downforce.

Tim

[JulianW]

Thanks Ciro - just what I thought you had used FFT for.

[piast9]

Wheel spin stops at top speed (acceleration equals zero)

Ok, there's no wheel spin but I am afraid that there is still significant tyre slip. You have 700hp at the wheel forcing against the drag which causes that the tyre rotates faster than it would result from the angular speed and the radius of the wheel. As far as I know, in motorbikes the speed measured at the driven wheel is nowhere near the actual speed.

[Tim.Wright]

Its reasonably safe to assume no slip at top speed. Due to the gearing, the torque at the wheels in top gear is much lower than it is in 1st gear.

In any case, the wheel slip (and therefore your speed error) is only likely to be a few percent.

The main innacuracies in using wheel speed to calculate speed is the vertical deflections you get in the tyre under braking and acceleration will alter the rolling radius and affect the speed calculations.

Tim

[Ciro Pabón]

Well, Tim, glad to meet you.

I just wanted to say to you (and, to my surprise, to 747heavy) that the traction force is equal to the vertical force on the rear wheels multiplied by the friction coefficient, by definition.

As the weight of the car, in a car with wings, is equal to the 'real weight' (that is, the mass) plus the downforce, voilá.

[alex1015]

Apologies for bumping this old topic but I've been trying it on my own and running into a bit of trouble. Could someone perhaps the topic creator elaborate on the mathematics of it? I've imported my wav file into MATLAB and understand I need to preform a Fourier transformation, and that the resultant frequency must be multiplied by 60 and then divided by half the number of cylinders to produce RPM but I can't come up with anything close to an RPM graph.

Can someone help or advise?

[HampusA]

Doesn´t really add anything to the thread but swedish commentators are 99% of the time quiet when watching the pole lap after Qualifying ends.

[alex1015]

Anyone? A little MATLAB help?