Returning to C3 Aerodynamics
05-02-2009, 08:24 PM
#41
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Are you talking about the ones on the insight or the ones on the EVO? The ones on the evo were actually engineered to help with the wing.
05-02-2009, 11:16 PM
#42
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Vortex generators can definitely help keep a flow attached. Could help a '79-82 but I'm not sure where it would be useful on an earlier C3. If a diffuser was added it could find use there.
I find it funny that the headline picture in that article they have VG's right before the 90º edge at the rear of that car! Somehow I don't think they're helping there! (Not to mention screwing up the flow on its way into that car's little wing.)
I find it funny that the headline picture in that article they have VG's right before the 90º edge at the rear of that car! Somehow I don't think they're helping there! (Not to mention screwing up the flow on its way into that car's little wing.)
VG's are used in the aviation world to prevent boundry layer airflow seperation at high angles of attack - they are normally placed in front of control surfaces such as ailerons. VG's are very common on early Learjets - I do not see much need for them in an automotive application unless they are placed forward of some type of negative lift device such as a downforce wing.
Seems to me the best way to prevent lift is to get the front of the car low and to prevent as much airflow as possible from getting under the car.
05-03-2009, 12:14 AM
#43
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Road vehicle wind tunnels measure forces through the tire contact patches. There is an SAE recommended practice that gives the details. The six axes of forces are resolved into drag force, side-force force, lift force, rolling moment, pitching moment and finally yawing moment. All forces and moments are resolved about the center of the wheel base and track at ground level. This is a departure from the aircraft convention that resolves F&M's about the CG. Strain gauges and weigh beam balances are the most commonly used methods to measure the forces. Wind tunnel balances are very complicated mechanical devices..
Open holes at the headlamps would certainly increase lift and drag on any C3.
Gene, I don't recall all of the details of the article just now, but these numbers are most likely direct readings from corner weights taken at the tire patches during the various test conditions. Whether or not pressure differentials and/or "simple" leverage is responsible (I'm curious and would like to know more about this), the bottom line is that having the headlights up does effectively change weight distribution at speed.
I'd think having open holes where the headlight buckets reside would primarily increase drag, but would hesitate a guess as to how that would affect the lift/downforce picture.
As I've stated elsewhere, it's too bad they didn't test variations of the C3, given that it evolved somewhat over the course of the generation's run. By '82, aerodynamically the C3 was a considerably different animal than it was in '68.
Maybe Blue71vette will chime in with his take on this...
I'd think having open holes where the headlight buckets reside would primarily increase drag, but would hesitate a guess as to how that would affect the lift/downforce picture.
As I've stated elsewhere, it's too bad they didn't test variations of the C3, given that it evolved somewhat over the course of the generation's run. By '82, aerodynamically the C3 was a considerably different animal than it was in '68.
Maybe Blue71vette will chime in with his take on this...
Open holes at the headlamps would certainly increase lift and drag on any C3.
