To put this very simply, downforce is the exact opposite of lift, which is the very reason a 777 or a C5A fully loaded can fly. Can it fly the same way an F18 can given the same lift/propulsion properties?

Given an OPEN F1 rule book, we would currently have cars that humans couldn't survive without passing out. Racetracks could only have corners that lasted 1 or 2 seconds at most, much longer and nobody would make it out of the first corner.

mick viper - 18 August 2008 09:17 AM

Not sure how to ask the question: what are the physical differences and similarities between the two forces? How are F1 cars or any car affected by the two?

Weight is, with an exception to fuel and tire wear, a constant throughout the race. Down force is a variable of speed and settings. The setup of the car can determine the drag, lift/down force, and the ratio between the two all related to velocity.

speedsense - 22 August 2008 12:03 AM

To put this very simply, downforce is the exact opposite of lift

Naahhhh. It's exactly the same. A wing produces only lift..."downforce" is created only by inverting the wing and aiming the lift towards the ground. To produce downforce, as GW stated, one must deflect the air, as with a spoiler. (or create a low pressure area below the car ala the 2J as mentioned by GW, or ground effects as per the Lotus 78/79, but we won't go there... )
Most "wings" on racecars really are a combination of inverted airfoils and spoilers...

The jist of my original question was basically if drag and friction etc were not a factor, would down force ever act on a car to slow it down like weight does. Apparently no, which is interesting to me despite the fact I'm sure I understand why.

jimclark - 28 August 2008 01:46 PM

speedsense - 22 August 2008 12:03 AM

To put this very simply, downforce is the exact opposite of lift

Naahhhh. It's exactly the same. A wing produces only lift..."downforce" is created only by inverting the wing and aiming the lift towards the ground.

Correct, and hence the name, downforce the opposite of the lift. (one could term it as upforce, and you would still be correct.)

To produce downforce, as GW stated, one must deflect the air, as with a spoiler. (or create a low pressure area below the car ala the 2J as mentioned by GW,

Incorrect sir. Lift is produced by creating a high pressure area directly below a low pressure area (wing), downforce is the opposite.. Low pressure directly below a High pressure.
As far as the spoiler is concerned, it does not create any downforce what so ever. Nor does a front air dam w/ a spiltter. These devices are correctly termed anti-lift devices. The only "downward" force created is when the air drag or "diverson of the air" effect of the spoiler overcomes the lift (from turbulent air under the car}
Also,the front air dam/with or without a spiltter, is an air "blocker" (hence the name) to prevent air from getting under the car with 0 downforce properties. The only down ward force created is with the body shape overcoming the lessened turbulent lift under the car.

To further see these princples at work, think about the fence in your back yard, lean it over to the same angle as a spoiler and built over a slight hill (copying a trunk lid on a car), when a gust of 60 mph wind hits it, if it isn't stong enough, it will get slammed to the ground, this is downward force. If the ground was not there, the fence would just tumble off into space, as it has no lift, downforce/lift properties to make it fly or continue down ward, except gravity. It would just tumble.
The same applies to an air dam with a splitter. On top of your fence, built another fence at a 90 degree angle to it. It will do the same as the above paragraph. And in fact, splitters are called fences, by aero engineers, as they just seperate air.
The exact reason why you won't see air dams or spoilers on airplanes without wings, they won't fly, they don't have lift.

or ground effects as per the Lotus 78/79, but we won't go there... )
Most "wings" on racecars really are a combination of inverted airfoils and spoilers...

Ground effects are different properties than spoilers or wings. A ground effect is also an extremely effeicent anti-lift device and one that not only lessens high pressures under a car, but also creates low pressure areas almost to the point of vacuum. To a degree, one may correctly assume it is creating downforce, as by it's own device it can "create" low pressure where there is high pressure normally (much like a wing, but with any of the same properties (it doesn't intentionally, by design, create high press as well, which a wing does)

So the next time you hear a commentator or a CUP driver say they lost downforce on the front, they are incorrectly stating it and making every aero engineer cringe. The only thing on a cup car, producing downforce is the wing, the rest is all anti-lift at work.
I guess it's just easier to say downforce, even if they are incorrectly stating so.

mick viper - 29 August 2008 03:26 PM

The jist of my original question was basically if drag and friction etc were not a factor, would down force ever act on a car to slow it down like weight does. Apparently no, which is interesting to me despite the fact I'm sure I understand why.

You can't have downforce or lift without drag. The creation of high pressure, which is half of the job for making lift/downforce also creates drag. With downforce also comes fiction by way of the adding weight of the downforce. In racing practices, endplates are added to increase the downforce with smaller wings. Adding endplates increases downforce by around 22%, but increases drag by 50%. As almost all race car use endplates, it is worth it. The addition of a gurney, further increases downforce but again with a penalty of drag.

To answer your question, drag and friction are both present and increasing right along and in greater amounts, than with the amount of downforce increase. Both are present at all times.

When thinking about aero dynamics, think of how it would act under water that is flowing by, as the same principles apply and the physics are also the same.

"Lift is produced by creating a high pressure area directly below a low pressure area (wing), downforce is the opposite.. Low pressure directly below a High pressure."

I still, respectfully, disagree. A wing (more accurately, airfoil) knows not up or down....it creates lift. I never heard the turning of an aircraft being caused by "sideforce"...

and...

"As far as the spoiler is concerned, it does not create any downforce what so ever."
"lean it over to the same angle as a spoiler and built over a slight hill (copying a trunk lid on a car), when a gust of 60 mph wind hits it, if it isn't stong enough, it will get slammed to the ground, this is downward force."


Now I'm (you're?) confused...

'all good fun tho', ain't it???

A spoiler on a car DOES FORCE THE CAR DOWN when the car is moving. It does this by redirecting the flow of air that is hitting it. A car is moving parallel to the ground at 100MPH, it has drag caused by its shape penetrating the fluid that is air. By attaching a device at an increased angle to the flow of air, you are adding drag and you are causing the air you redirected to FORCE the part of the car to which the spoiler is attached DOWN. The proof of this is simple, the next time you're out driving, stick you arm out the window and hold your hand parallel to the ground. nothing much happens, move the front of your hand up and the wind created by forward motion will push your arm up. Since you arm isn't a wing, you are NOT creating lift, you're just causing the flat of your hand to hit the wind and IT IS causing your hand to force your arm up. Front spoilers are used to FORCE the front of the car down to try to prevent air from flowing AS FREELY UNDER IT. The redirection of any fluid is a FORCE. To label it otherwise is just wrong.

Attach a wing to the car and it will add both drag and lift (the lift will be either up or down depending on how the wing is situated, mount it upside down and the lift forces the wing down, mount it right-side up and the lift Will force the wing up). All of this depends on the airfoil of the wing and how it is positioned on the car. In either case the wing is causing lift because of Bernoulli's Principle. As stated above, the end-plates add drag as well if used.

A GROUND EFFECTS car is somewhat different. It seals air out (from under it creating a low pressure area under the car. Unfortunately it works exponentially better the higher the speed of the car. This means at low speed (or if for some reason air is allowed to get under the car) the force is likewise lessened. The fact is that this type of car DOES in fact require more HP to push it faster, because you have essentially created suction under the car and that force MUST ALSO BE OVERCOME TO PUSH THE CAR FASTER.

All of these devices no matter how small, ADD DRAG which must be overcome with HP. Since they don't add MASS, they don't add to the work the brakes have to do, but because they add down-force, they do ADD to the work the suspension and the tires have to do. AA JMHO

Bill

Excellent post.

speedsense - 31 August 2008 02:21 AM

So the next time you hear a commentator or a CUP driver say they lost downforce on the front, they are incorrectly stating it and making every aero engineer cringe. The only thing on a cup car, producing downforce is the wing, the rest is all anti-lift at work.
I guess it's just easier to say downforce, even if they are incorrectly stating so.[/color]

SS, while I know you are correct with the definitions of downforce and anti-lift, and I DO respect your knowledge and experience, I think most racers, and most posters here use the terms interchangeably because they ARE then same where it counts, on the contact patch, even if they are different in the wind tunnel and in concept. The fact is that when a Cup driver says he loses 'downforce' on the front, he is correct in the sense that his front tires have an aero force loading them, whatever it is properly called, and he felt them lose some of that. If there were no 'downforce' generated by the splitter and other front bodywork on a Cup car, for instance, only anti-lift, the splitters would not be lower at speed than at rest, right? After all, they have no front wing.............

While I understand this is a 'tech' board, it doesn't necessarily follow that the terminology has to be engineer speak proper. This a fan's forum, after all, and the most important aspect of it is understanding the subject matter, which, IMO, is best accomplished using the simplest available language and examples.