Light up front, Heavy in the pants

[Kevin81]

Alrighty smartass. Since I'm so "without knowledge" and you're allegedly an aerospace engineer, maybe you can baby spoon feed me my error through these steps:

A) If creating vertical force increases drag, does that also mean creating lift increases drag?

B) If A, does reducing lift reduce drag?

C) Is the total net downforce (or lift) on a vehicle a sum of the total downward and upward forces being applied?

D) If A, B and C, does reducing aerodynamic lift increase the net downforce AND reduce drag?

Also is a drag coefficent of 1 a good thing or a bad thing?

I anxiously await your own personal wisdom on the subject.

If you generate lift without leaving the ground, yes, it creates drag. All vacuums must be filled. Drag is the force hold an object back while the vacuum of its passing is filled by air. If the object is on the ground, air can't travel through the ground to fill the void, ergo, longer period of time to fill, or greater force required to pull the air through faster. If the object is not on the ground, the vacuum can be filled from above and below, thus, less drag. But there will still be drag.

 

[Kevin81]

Another way to think of it...air is a fluid. Like all Newtonian fluids, if you put it under pressure, it begins to behave more like a solid. When you travel through a fluid fast enough, you place the fluid in front of you under pressure. Its why water stops bullets.

Down force as a design is to redirect that pressure onto specifics spots on the car. Unless you can redirect that pressure to being behind you pushing forward (physically impossible), this creates drag.

Imagine I sit on the hood of your car. I weight 240 lbs. But imagine I get heavier the faster you go. 80 mph, I weight 320 lbs. 100 mph, I weight 400 lbs. 150 mph, I now weight 600 lbs. The force increases in magnitude as speed increases.

Eventually, I weight so much, your engine is no longer capable of pushing.

That's down force.

 

[High on Ethanol]

Another way to think of it...air is a fluid. Like all Newtonian fluids, if you put it under pressure, it begins to behave more like a solid. When you travel through a fluid fast enough, you place the fluid in front of you under pressure. Its why water stops bullets.

Down force as a design is to redirect that pressure onto specifics spots on the car. Unless you can redirect that pressure to being behind you pushing forward (physically impossible), this creates drag.

Imagine I sit on the hood of your car. I weight 240 lbs. But imagine I get heavier the faster you go. 80 mph, I weight 320 lbs. 100 mph, I weight 400 lbs. 150 mph, I now weight 600 lbs. The force increases in magnitude as speed increases.

Eventually, I weight so much, your engine is no longer capable of pushing.

That's down force.

This is what I was referring to as far as less drag in essence is like more power when it comes to speed.

But realistically aerodynamics don't really matter for most street cars except for fuel economy. Almost all aftermarket spoilers, wings, canard, splitters, scoops, grilles, etc....slow the car down. Same is true with a lot of aftermarket bolt on mods....but that's another day.

 

[stripSHO]

If you generate lift without leaving the ground, yes, it creates drag. All vacuums must be filled. Drag is the force hold an object back while the vacuum of its passing is filled by air. If the object is on the ground, air can't travel through the ground to fill the void, ergo, longer period of time to fill, or greater force required to pull the air through faster. If the object is not on the ground, the vacuum can be filled from above and below, thus, less drag. But there will still be drag.

Thanks Kevin I understand that. My main point is that there’s two ways to increase downforce - create it from scratch, or eliminate sources of lift (such as a custom hood that perhaps created a larger low pressure area on the top of the car). One increases drag, one reduces drag. I figured rocket man with his extensive wind tunnel experience should’ve easily been able to point out how this is wrong

 

[SM105K]

Gentlemen,

We can settle this relatively easy......

Shall I call the Quantum Mechanic?

 

[Jordan_R]

@Ryan Selcer we need your expertise

 

[DouglasB_SHO]

Thanks Kevin I understand that. My main point is that there’s two ways to increase downforce - create it from scratch, or eliminate sources of lift (such as a custom hood that perhaps created a larger low pressure area on the top of the car). One increases drag, one reduces drag. I figured rocket man with his extensive wind tunnel experience should’ve easily been able to point out how this is wrong

Lower pressure on top of the car results in lift, not down force. Basic physics: lift = lower pressure above, higher pressure below.

 

[High on Ethanol]

https://www.wired.co.uk/article/bugatti-chiron-300mph-speed-record

 

[Kevin81]

Thanks Kevin I understand that. My main point is that there’s two ways to increase downforce - create it from scratch, or eliminate sources of lift (such as a custom hood that perhaps created a larger low pressure area on the top of the car). One increases drag, one reduces drag. I figured rocket man with his extensive wind tunnel experience should’ve easily been able to point out how this is wrong

Eliminating a source of lift =/= down force.

Consider the theory of the formula 1 open wheel racers. They generate enough down force to drive upside down, since, at 140mph, the down down force exceeds the weight of the car. This is not achievable by eliminating lift.

Its why those cars handle relatively poorly at slow speeds.

 

[stripSHO]

Lower pressure on top of the car results in lift, not down force. Basic physics: lift = lower pressure above, higher pressure below.

We’re saying the same thing in different forms. If you eliminate a low pressure area above the car you gain downforce and lose drag in the process. Sorry if I’m not making that clear enough

 

[stripSHO]

Gentlemen,

We can settle this relatively easy......

Shall I call the Quantum Mechanic?

It’s really simple. Just detour through a parallel dimension to go AROUND the air. You’ll gain 40 mph in the 1/4 mile and run 8’s with a stock SHO. But only if you pull the ABS fuse!

 

[High on Ethanol]

I don't think the problem is so much downforce as it is the way the aerodynamics are flowing....


For example

https://media.ford.com/content/ford...ns-on-f-150-help-reduce-aerodynamic-drag.html

 

[Eric Morris]

We’re saying the same thing in different forms. If you eliminate a low pressure area above the car you gain downforce and lose drag in the process. Sorry if I’m not making that clear enough

Technically- still no.

Downforce is an actual force that can be measured acting in the downwards direction.

By reducing forces in the upwards direction- you do not create forces in the downward direction, you simply have decreased the vector length of the upwards force. If you add the upward and downward force vectors, the net force in the downwards direction does increase, which is what you are trying to say, but the downward force vector itself does not change. In that scenario, there is no downforce gained, only uplift lost. Which is what Kevin is saying.

 

[Bluezone]

Technically- still no.

Downforce is an actual force that can be measured acting in the downwards direction.

By reducing forces in the upwards direction- you do not create forces in the downward direction, you simply have decreased the vector length of the upwards force. If you add the upward and downward force vectors, the net force in the downwards direction does increase, which is what you are trying to say, but the downward force vector itself does not change. In that scenario, there is no downforce gained, only uplift lost. Which is what Kevin is saying.

Gentleman

I like what you're saying, but everyone is simply describing the same phenomena with more and more complex descriptions.
In essence we are describing pressure differential. In simplest terms high pressure moves to low pressure. An open-ended plane placed between pressure regions, will have force applied to it in direct proportion to the pressure differential and the size of the area involved.
Almost everything we're describing is a modification of the Venturi effect.
The question is how to create higher air velocity (Venturi effect), without creating more drag.

 

[SM105K]

Gentleman

I like what you're saying, but everyone is simply describing the same phenomena with more and more complex descriptions.
In essence we are describing pressure differential. In simplest terms high pressure moves to low pressure. An open-ended plane placed between pressure regions, will have force applied to it in direct proportion to the pressure differential and the size of the area involved.
Almost everything we're describing is a modification of the Venturi effect.
The question is how to create higher air velocity (Venturi effect), without creating more drag.

SO what you are saying is block all major holes in the front and add a skid plate that runs the length of the car?

I would love to see what an SHO looks like in a wind tunnel.....

 

[Eric Morris]

Gentleman

I like what you're saying, but everyone is simply describing the same phenomena with more and more complex descriptions.
In essence we are describing pressure differential. In simplest terms high pressure moves to low pressure. An open-ended plane placed between pressure regions, will have force applied to it in direct proportion to the pressure differential and the size of the area involved.
Almost everything we're describing is a modification of the Venturi effect.
The question is how to create higher air velocity (Venturi effect), without creating more drag.

I was not talking about differentials, or venturis, or anything complicated.

I'm simply talking about the most basic things in physics, a force.

You posted that reducing a low pressure area on top of the car increases the downforce, but as Kevin81 first pointed out, but that is not that case. It reduces the upward force only.

I know what you are getting it and it's somewhat just semantics, but also, it's 100% not just semantics. One is technically correct, the other is technically wrong. Physics has laws.

 

[Bluezone]

I was not talking about differentials, or venturis, or anything complicated.

I'm simply talking about the most basic things in physics, a force.

You posted that reducing a low pressure area on top of the car increases the downforce, but as Kevin81 first pointed out, but that is not that case. It reduces the upward force only.

I know what you are getting it and it's somewhat just semantics, but also, it's 100% not just semantics. One is technically correct, the other is technically wrong. Physics has laws.

In an indirect way maybe that could be assumed. But a very astute observation nonetheless. (Additive total "+"s and "-"s in pressure differential)

What I was talking about though was increasing AirSpeed underneath the car in order to decrease pressure. There is already a Venturi like structure beneath the nose of the car behind the air dam.

I was not tackling the top surfaces at all. Though if I were to address those I would suggest a hood Edge splitter running along the hood side edges. There is already a high pressure area that forms in forward movement at the base of the windshield. Unfortunately the roof of the car acts like the top part of a wing, providing its own Venturi effect.
This is why NASCAR installs blow out panels on the roofs of cars, in case they spin and are traveling backwards. This is to disrupt airflow and reduce lift (low pressure), so that cars don't flip while traveling backwards.
But again I'm referring to undercar modifications. Mind you I myself would not employ such a strategy as I personally don't want my driver to look like an extra from The fast and the furious . LOL

 

[stripSHO]

Technically- still no.

Downforce is an actual force that can be measured acting in the downwards direction.

By reducing forces in the upwards direction- you do not create forces in the downward direction, you simply have decreased the vector length of the upwards force. If you add the upward and downward force vectors, the net force in the downwards direction does increase, which is what you are trying to say, but the downward force vector itself does not change. In that scenario, there is no downforce gained, only uplift lost. Which is what Kevin is saying.

Gravity is also an actual force that can be measured acting in the downwards direction. Force is force no matter the semantics. A chassis doesn’t differentiate a 1000 lb of downward force due to air pressure on earth from 1000 lbs worth the Kevins stacked above the car on Saturn.

I appreciate the middle school science talk down about physics and what was and wasn’t created though. You might notice I’m not the one using the word, because I already know that you’d not actually be creating it in such cases. When you reduce body lift you sure as **** can’t say you created more gravity.... and downforce is apparently not a term for down force, so you guys just let me know exactly what terms you want me to use that will get us all back to something substantive.

The actual point is that downforce, downward force, down facing dog, acceleration towards the center of the earth, or whatever I have to call it— a practical increase of suspension load and traction— was professed to carry with it an absolute and unavoidable penalty of more aerodynamic drag and it’s just not true.

 

[High on Ethanol]

My only point is, for a rental car, it ain't bad.

 

[Kevin81]

Gentleman

I like what you're saying, but everyone is simply describing the same phenomena with more and more complex descriptions.
In essence we are describing pressure differential. In simplest terms high pressure moves to low pressure. An open-ended plane placed between pressure regions, will have force applied to it in direct proportion to the pressure differential and the size of the area involved.
Almost everything we're describing is a modification of the Venturi effect.
The question is how to create higher air velocity (Venturi effect), without creating more drag.

Vacuum.