Greg Locock wrote:I am fully aware that real aerodynamcists often use F/(1/2 rho v^2) when comparing things, nonetheless on cars even an aerodynamicist like Katz uses frontal area basis when comparing them. Sure for individual wings use S. It doesn't matter what you use so long as you know what you are using. But pedantic statements like yours are just silly.
There was nothing pedantic about that statement: this is a forum based on F1-specific
facts, and the statement, or implication, that F1 uses C_L or C_D to compare between vehicles is incorrect, not to mention misleading if you know aerodynamics. Sure, Katz can use frontal areas, and yes, of course I believe Katz knows what he is on about, but no, that is not how F1 quotes its values. If I were to try and analyse RBR's current car you can be 100% confident that I wouldn't figure out the frontal area, I would try to correlate its sector times to a generic C_x and C_z. The frontal area is irrelevant information to the performance, unless you are specifically looking at does my element X work the air more efficiently than element Y on the RBR, which is exactly what C_L and C_D are useful for but not the question asked by the forum poster.
Per wrote:Now you are being REALLY confusing. First you say L/D changes because they have changed the wings and the diffuser (with which I agree), then you say L/D doesn't change from year to year. And how on earth does the power curve influence L/D? It changes the optimum setup for a certain track, so they can opt to run more downforce (and as a result, more drag) but L/D will not change nearly as much as L and D individually.
What you're saying about coefficients is just another way of saying that they don't look at Cd only, but at S*Cd.
Yes, that's exactly what I'm saying about the coefficients, but almost coming from it the other way, you never really consider the C_D of the individual elements, or the planform (or frontal) area, you just observe the forces they produce. This is for two reasons: 1) when you use a wind tunnel to test, you can't isolate the forces produced by each element, so you can't state use planform areas; you could use frontal area, but it's less useful when you come to 2) at the end of the day, you're looking to improve the performance of the car, so you don't really care about anything other than that headline value of C_X and C_Z.
As far as L/D is concerned, yes it has fallen since the end of the double-diffuser era, because drag has gone up, but your target wouldn't change if the power unit (/some other big performance component) didn't change. Imagine a circuit full of long straights: your performance is probably limited by your top speed, so there is a premium on dropping drag, even if it costs you quite a bit of downforce. Now of course, if you could add downforce without increasing drag, and in doing so you increase your L/D, you'd do it, but generally the two are related, and you try to find the sweet-spot between losing drag and losing even more downforce, where you do it until losing downforce becomes more detrimental than the benefits of losing drag.
Now, change to a circuit full of corners (which the driver can't take flat), where you aren't limited by engine power, you're limited by the cornering speed you can sustain with your tyres: here adding on downforce could well improve lap times, even if it brought a hefty drag penalty, all the way until you were taking corners flat. Basically, circuit downforce/drag targets are sensitive to the circuit profile, so you might elect for a lower than optimal L/D ratio for more ideal absolute L or D values.
The reason the engine can change these ratios is that if you had unlimited power (and therefore torque), you would never been top speed limited, and traction would be extremely important, do you would obviously slap on downforce, even if it cost you a tonne of drag. Changes to aero regulations also change these ratios as the L-D relationship of any car is not going to be linear.
