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Questions regarding the affects of air drag on a vehicle

Posted: Fri Nov 04, 2016 12:11 am
by bpbusse
Hello all I have some questions regarding the affects of drag forces on vehicles and I am hoping to hear some peoples input on this subject who are a little more knowledgeable on the topic then I am. Any responses to these questions would be greatly appreciated.

1. Which drag force has more of a negative impact on a sports car that is traveling at a high speed, the frontal pressure on the vehicle or the rear vacuum created by flow detachment? And is it significantly greater?

2. How can a vehicle be designed to minimize flow detachment?

3. In what ways does lift negatively impact a cars performance?

4. Can you explain how friction on a cars surface slows down the car?

Re: Questions regarding the affects of air drag on a vehicle

Posted: Fri Nov 04, 2016 4:00 am
by admin
Hi,

These are some good questions and I'll do my best to answer them for you:

1. Which drag force has more of a negative impact on a sports car that is traveling at a high speed, the frontal pressure on the vehicle or the rear vacuum created by flow detachment? And is it significantly greater?


The rear vacuum portion would generally be far greater as rear bodywork on a vehicle rarely converges in an ideal way and the compressive force at the front is smaller than the vacuum created by truncated bodywork at the rear. If you look at those solar race cars, they choose a converged teardrop shape to minimize drag as do land speed record cars. However, practicalities of street/track cars limit how long a "tail" the car can have, so they leave a hole in the air that they travel through. Drag increases as the square of speed, so if you are trying to go very fast, reducing the cross section where flow detachment occurs will reduce drag.

2. How can a vehicle be designed to minimize flow detachment?


Converge bodywork to a minimum cross-section. You can also potentially direct air flow from high pressure areas to parts of rear bodywork where the flow detaches, delaying flow detachment and reducing drag. A lot of effort for the gain.

3. In what ways does lift negatively impact a cars performance?


Reduced weight (vertical force) on tire contact patch means reduced traction.

4. Can you explain how friction on a cars surface slows down the car?


You are referring to the boundary layer that forms as air travels over the car body. I believe the simple answer would be that the initial friction of the body against air molecules causes the air molecules to slow down. As the slower air progresses over the body, faster moving particles further away from the body collide with and are slowed down by these slower moving particles and this further deepens the boundary layer, creating more friction drag as it progresses toward the rear of the vehicle.

I hope that helps!

Re: Questions regarding the affects of air drag on a vehicle

Posted: Sat Nov 05, 2016 7:29 pm
by bpbusse
Thanks a lot! this helps a ton.