effects of changing ride height

[sporty.dave]

Does changing ride height affect the Drag or just the downforce? I guess that decreasing rideheight would increase drag (as downforce is usually a function of drag), however my degree project supervisor thinks the opposite as he guesses that the vortices produced under the car increase with increased ride height lowering the downforce (in addition to the loss of ground effect) and increasing the drag
Who is correct? The Dr or the Student?

[THR]

well lowering the car gives effectivly free downforce... as no more drag is created by the groundeffect, which is y its so good!

if you decrease the ride height there is less air under the car.
less air less drag
less air less turbenlent air.. less drag.

Dr is right!

[sporty.dave]

Thank you for the help. It's really annoying that he is correct. Has anybody any idea of an equation that could model this effect?:confused:

[THR]

lower=better

hehe

depends on the rake of the car too... not just the height..
ie.. FRenault run about 11m rake.
the rake creates the downforce.

[enzo]

Sorry to rain on the parade, but that ain't necessarily so.

Quite often, when trimming a flat-bottomed car for top end speed, the rake must be decreased - usually by raisng the front.

You can also go too far in lowering the car. If too low, you will choke off the airflow under the car, which will dramaticly decrease downforce, and raise the drag.

Sorry, but it's not a pat answer!

[THR]

ohh i was assuming that you cant run the car right on the ground due to bumps, kerbs and downforce.
so you are right i agreee.. this is y they play about in the wind tunnel so much trying to see wot happens with the ride height.

[sporty.dave]

All of the above leads to the effect used in sports car racing where the teams run nose down (when car is seen at rest, giving more downforce in low speed areas of the track) and with much softer rear suspensions than front. This leads to the rear of the car sinking more on the straights leveling the bottom of the car and decreasing the drag. (Does anybody remember that mercedes flipping at le mans this was apparantly caused in part by this effect)
However for my project (which was the reason that i first posted the question) none of this is very important due to the F1 rules which say (and I don't have my copy here at the moment) somthing along the lines that the bottom of the car must be parallel to the track surface at rest. The loss of smooth airflow point is a good one ( I assume that the drag increases significantly if the two boundry layers join)

More research still needed

[THR]

F1 cars aint run parralell to the ground... they have rake too..
so it is all applicable to it.

i guess you could work out if the boundary layers actually touch each other... say the car is 3m long with a 12 front height and 23 at the back.

[sporty.dave]

As the car is the moving body (rather than the air as in most text book examples) I reckon that I should take the air as only moving over the car and not over the ground. This leaves the drag increasing suddenly when the boundry layer reaches the ride height (which if the car is running nose down changes with the distance along the underside of the car) and oh my.... this looks like some horrible differential equation may result.. I'll let you know how I get on. It may take a very long day working on this one (and then once I have a result I will have to incorporate it into my simulink model) oh well. That's the first week of the Uni holidays gone then..

[sporty.dave]

Oh and about the rule I thought made you run the car parallel to the ground. It doesn't say that at all but it is a little verbose and I just misunderstood it when I read the entire rules in one sitting (quite early in the morning)

PS: I suggest that nobody should read the F1 rules, unless they really have to, because they are reallllly dull