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Poor-sha asked: In the past you have answered questions about the center rubber deflector that is only present on C7 base and Z06 cars without the stage 2 or 3 aero. However, what is the aerodynamic effect of the smaller side deflectors that hang under the splitter in front of the front tires (seen below)? They have been described on the Camaro as there to increase front downforce but it appears as though on the C7 ZR1 these are only present on non-ZTK cars. Do the deflectors increase or decrease downforce and can they be used to tune front aero grip? Also, is there a likely aero benefit to using helicopter tape or an equivalent to cover over gaps in the front underwing like the recessed bolts and the radiator supports? As always, thanks!
Tadge answered: The ZR1 has, by far, the most downforce of any Corvette we have ever built. Getting that much downforce on a street car is very challenging and it is quite rare in the auto industry. Some auto makers talk about the downforce of their aerodynamics aids as independent features. They say things like “this spoiler generates XXX lbs of down force”. The entire vehicle may actually generate lift, but the impression is left that the car has true down force. When we talk about the ZR1 ZTK package generating 950 lbs of down force, we are talking about the whole car as a system. The most visible part, the big wing, is only part of the story. Sometimes that subtlety gets lost in some of the descriptions of the car.
When we start designing an aerodynamic package for Corvettes, we start with the front of the car. Down force on the nose is is the toughest to get. We developed a structural under wing similar to what the C7.R uses and tuned it to get maximum performance. Then we tuned the rear wing size, height and shape to precisely balance the car. We shoot for a pitch moment (think of the relative power of the front and rear aero aids) that keep the car stable and easy to drive all the way up to top speed. Too much down force on the rear relative to the front makes the car understeer and vice versa makes it oversteer at speed. This is obviously a gross simplification since we are simultaneously working driveline and brake cooling as the surfaces develop. We generally start with the max down force configuration (ZTK in this case) because it is easier to de-power aero aids than find more performance once they are designed. The image below on the left shows the underwing pressure distribution on the ZTK package. The blue color indicates low pressure or downforce. On the right you see a very different looking pressure distribution created by the tire deflectors, or air dams. Despite being relatively small, those features de-power the underwing by disturbing the flow pretty dramatically. High pressure in front of the dams causes the effect, but because they keep air from impinging on the front face of the tire, the net effect is actually a drag reduction. We can then pair the de-powered underwing with a smaller wing at the back of the car to yield a package that trades some downforce for drag reduction. This is why the standard ZR1 has the highest top speed.
As to the question on taping gaps…. You are right that creating smoother transitions will help drag and downforce performance. The effect is very small, but because it is more likely to improve front performance, it is in the less conservative direction for pitch moment – it will tend to make the car oversteer. We optimize the car for the real construction coming from the factory, so we don’t recommend additional sealing. Also, since we don’t test with those gaps completely sealed you may cause other problems. For example, hot soak issues where we count on convection drawing cool air from below the car after it stops moving or splash drainage when you drive on wet roads.
Whoa. If I read that right, the baffles in front of the wheels actually decrease downforce (but also decrease drag)? It's removed on the ZTK to balance (increase) the front downforce because of MOAR downforce in the rear?
I may have to (no I don't have a ZR1, just a lowly Grand Sport) remove the air dam/baffles for my next track event.
Whoa. If I read that right, the baffles in front of the wheels actually decrease downforce (but also decrease drag)? It's removed on the ZTK to balance (increase) the front downforce because of MOAR downforce in the rear?
I may have to (no I don't have a ZR1, just a lowly Grand Sport) remove the air dam/baffles for my next track event.
Note that Tadge said the air dam/baffles disrupted the airflow over the front under wing (in front of them) as I had suggested as a possible reason for their absense on the ZTK in an earlier thread(similar to raised flaps on an airliner at landing). Your Grand Sport has no front under wing to disrupt air from. You will likely only increase drag by removing them would be my guess, not increasing downforce like on the ZR1 with the front under wing.
12-17-2018, 05:17 PM
[ANSWERED] Effects of front tire deflector on downforce
