airflow question

[KiwiBacon]

Originally Posted by Alastor187

The only similarity between a car and airfoil, as suggested in post 8, is that both have longer 'path' lengths along the upper surface.

My point was that this is not a criterion characteristic for developing lift, despite the fact the most common explanation of airfoils suggests the opposite.

A flat plate for example can create a significant amount of lift even though the top and bottoms surface path lengths are equal.

To digress even more off-topic, a car really isn’t shaped like a wing it is shaped like a car. Not to say the shape won’t create lift, but in my opinion it is often a misnomer to call it a wing just because it creates lift and has the airfoil similarity already mentioned.

The similarities between a car and an aerofoil include a curved top surface and a large flat area underneath.
This is consistent with both the traditional explanation of lift (faster air = lower pressure) and the alternative lift mechanism described in your links (reaction of downward accelerating airstream).

A flat plate can creat lift, but in doing so it creates a large amount of turbulence. This leads to a large amount of drag and makes it a particularly inefficient device for creating lift (or downforce).

Design features used in the automotive world to reduce lift (and create downforce) include air dams to restrict airflow under the car, external aerofoils (upside down wings) and rear diffusers (which are again an upside down wing).

[Alastor187]

Originally Posted by KiwiBacon

This is consistent with both the traditional explanation of lift (faster air = lower pressure) and the alternative lift mechanism described in your links (reaction of downward accelerating airstream).

Just for clarification since it sounds like you took the time to read the links.

The alternative explanation(s) involves the downward acceleration of air, and thus respects Newton’s Third Law. It also still respects Bernoulli’s principle with one subtle but key difference. The change in air velocity doesn’t change the static pressure; the change in static pressure changes the air velocity.

Originally Posted by KiwiBacon

A flat plate can creat lift, but in doing so it creates a large amount of turbulence. This leads to a large amount of drag and makes it a particularly inefficient device for creating lift (or downforce).

I agree, and the same is true for most ground vehicles. This is why I think it often a misnomer to say a car is wing shaped. Because people are thinking since it has a curved upper surface and flat lower surface it behaves similarly to a airfoil. However, an airfoil is a highly specialized device that maximizes lift and minimizes drag.

[KiwiBacon]

Originally Posted by Alastor187

Just for clarification since it sounds like you took the time to read the links.
The alternative explanation(s) involves the downward acceleration of air, and thus respects Newton’s Third Law. It also still respects Bernoulli’s principle with one subtle but key difference. The change in air velocity doesn’t change the static pressure; the change in static pressure changes the air velocity.

I'm having trouble agreeing with that theory.

Applying it to an accelerating flow can make sense, as you can visualise the higher pressure upstream causing the acceleration. But applying it across a diffuser doesn't seem logical.

[GreyGoose006]

not sure if this is dead or not yet, but the only way a flat plane will create lift is if it is put at an angle to the direction of the air rushing past it.
its the same effect as when you stick your hand out the window of a moving car.
the lift created is because there is a massive low pressure area right about where your knuckles are (on your hand that is) and a high pressure area underneath your knuckles.
this design works well at low speed, but due to the ammount of turbulence created, an airfoil is required at any higher speed than a paper airplane would travel.

if you look at an airfoil, the bottom is identical to the flat plane. the top, however, is specifically designed to minmixe turbulence, which creates drag.


i think that even if there were wheels that were designed as an impeller to suck air from beneath the car, the brake disks get in the way of any serious airflow, and the sheer ammount of air coming in from other places negates any effect the wheel would have anyway.

the only way it could have much of an effect is on oa car with low ground clearance, tight side skirts, a massive front spoiler, and inboard brakes.
basically, a GTR racer.

the Mercedes benz CLK DTM AMG is a good example of this on a road car.

[AMGalltheway]

well this is turning into an argument but thanks every body for helping

[GreyGoose006]

haha, sorry