|
I've been asked: what are the three misconceptions this passage addresses that have occurred in discussion in this group in the last few weeks?
1) Lift is defined in terms of frontal area, not plan area. Aerohead recently calculated the lift coefficient for a car using plan area.
Lift coefficient is defined in a similar way to drag coefficient: Lift = Dynamic pressure × Frontal area × C. Note that for convenience, the reference area is still the projected frontal area...
2) Lift decreases when flow separates. Aerohead argues that lift increases when flow separates. Barnard is talking about aerofoils but you can see from the context of the para he is also (correctly) applying that to car shapes.
...once the flow starts to separate, the lift begins to fall off....
3) The stalling (separation) angle is not easily able to be predicted for car shapes. Aerohead argues that his template shows this precisely.
... for a car shape, the complex geometry and high degree of three-dimensionality mean that the stalling angle is not readily predictable...
4) Lower lift is beneficial in normal cars. Aerohead (and others here) argue that it is of no consequence. Note the use of the word 'good'.
...recent good designs CL is nearly zero...
So there are four (not three) misconceptions briefly addressed in just the one passage!
Incidentally, if you can't understand lift/downforce, it's very unlikely that you will understand thrust/drag, and vice versa. They're all part of the one picture.
|