Increasing underbody downforce

[Jared_80]

Here is a rather technical question regarding underbody downforce. could you raise the despoiler angle significantly without breaking up your air flow if you inducted the radiator air through vents in the despoiler? I know that it is illigal in F1 racing to do this, is there something dangerous about it, or did they just ban it to reduce downforce dependency like when they baned the venturi tunels? How many additional degrees could you use assuming a normal radiator flow?

[454Casull]

What's a dispoiler?

[Jared_80]

A despoiler essentaly is a device that draws air out from under a car, creating a lower pressure under the car, thus creating downforce. A dispoiler is located on the back underside of a car (not many cars have them) it curves upward at a slight angle (most aftermarket body kits have what looks like a functional despoiler but they curve upward too sharply and break up the airflow making them cosmetic only). It works kind of like turning the underside of your car into the underside of a wing, and yes they can produce massive downforce when designed properly, plus they do not have nearly the aerodynamic drag of a GT wing. In fact some cars have improved their aerodynamics by using despoilers.

[454Casull]

You mean a diffuser?

[454Casull]

AFAIK, they are still used in Formula 1 racecars.

A cool thing to note is that diffusers are one of the few ways to increase downforce without increasing drag.

[Jared_80]

Originally Posted by 454Casull

AFAIK, they are still used in Formula 1 racecars.

A cool thing to note is that diffusers are one of the few ways to increase downforce without increasing drag.

A difuser extends out of the rear of the car, a despoiler is underneath the car or at leased that is how I understand it. (but the both do the same thing) Anyway I said that using artifical vacume to prevent stalling of the despoiler in illigal, not the despoiler itself. You seem to be the only other person that knows what I am talking about so do you actualy have any information on this topic?

[454Casull]

Maybe I would if I knew what the heck a despoiler was (you spelled it dispoiler earlier?)...

[Jared_80]

Originally Posted by 454Casull

Maybe I would if I knew what the heck a despoiler was (you spelled it dispoiler earlier?)...

I am not sure wich way it is spelled, but you basicly know what I am talking about.

[Hu_Dat?]

Im pretty sure a rear air diffuser isn't used for underbody down force. I think its used to straighten out and stabalize the air comming out of the underbody wether there is a despoiler or not (Usually there is). This makes the car able to handle better under high speeds. it prevents the air from diffusing improperly by making several channels of air comming out the back side. the new pro drive 550 ferrari has massive ones that you can check out, and the new 2003 wrc ford focus kinda has the same idea comming out of the rear wing.

correct me if I'm wrong

I have definetly seen the under channel thing you call a "despoiler" before. I may be thinking when you say despoiler angle and its vents. tell me, where is the despoiler angle and vents located? does it kinda look like the front bumper of the Green mitsubishi eclipse in the first fast and furious(I know its prob cosmetic)? send me a pic of where the vents are and I could prob tell you if it could happen or not

[Neutrino]

Originally Posted by Hu_Dat?

Im pretty sure a rear air diffuser isn't used for underbody down force. I think its used to straighten out and stabalize the air comming out of the underbody wether there is a despoiler or not (Usually there is). This makes the car able to handle better under high speeds. it prevents the air from diffusing improperly by making several channels of air comming out the back side. the new pro drive 550 ferrari has massive ones that you can check out, and the new 2003 wrc ford focus kinda has the same idea comming out of the rear wing.

well you are correct about the diffusers being used to straighten out the air from under a car but in doing this it helps extract and accelerate the air from underneath the car and as we all know faster air is less dense and it will create a desirable vacuum effect and therefore downforce....


so the question that needs to be asked is: Will the modification underneath the car accelerate the air down-under or slow it down?

now i have no ideea what a despoiler does under the car? could you post some pictures?

[Jared_80]

Unfortunetly I don't know how to post pictures here but what it does underneath the car is increase the volume of the air flow at the rear of the car. Think of it this way if the top of the difuser/dispoiler is 8 inches off of the ground, that means that it is pulling air from 8 inches above the groung in the front, (the airflow is always assumed to return to its normal level) if the underside of the car is only 4 inches tall then you have doubled the amount of air moving underneath the car, thus moved it faster, thus created downforce. I know that this is as basic as explaining fire as "hot stuff" but it is a rather hard concept to grasp at first. As far as what it looks like just imagin the rear (past the rear suspention) underside of the car as the bottom of an inverted wing.

[Jared_80]

correct me if I'm wrong

I have definetly seen the under channel thing you call a "despoiler" before. I may be thinking when you say despoiler angle and its vents. tell me, where is the despoiler angle and vents located? does it kinda look like the front bumper of the Green mitsubishi eclipse in the first fast and furious(I know its prob cosmetic)? send me a pic of where the vents are and I could prob tell you if it could happen or not[/quote]



The angle is just the vertical slant of the "inverted wing" and the vents are not present on most dispoilers so I doubt that you have ever seen them. But the purpost that they serve is to create vacume and prevent the "inverted wing" from stalling (breaking up the smooth airflow) Thus allowing you to use a more affective dispoiler. There are vents on some cars located in the front, these usualy serve as an adition to an airdam, they are mostly cosmetic but when used properly (low ride hight) they have been known to create some downforce. Vents behind the front wheels serve as exit vents for air that has passed through and cooled the brake rotors. They also reduce the drag coeffecency slightly.

[jhillyer]

What we want at the rear is as smooth a return flow, after the craft has displaced the air from the roadway. Rearward turbulence sucks the car rearward as drag.

I read another's example here about car height of 8" and 4". Getting lower to the roadway helps peel air over and to the sides of the craft, reducing the high pressure stackup under the car, which we know among more subtle losses can dangerously lift the nose at speed, and a little lift can pitch the nose enough to gulp a catastrophic plunge of air pressure and flip the vehicle nose over tail.

We want the air to flow to the sides of the craft, and we'll avoid lift forces over the top and rear of the craft. What we allow to flow over the craft can be trapped near the rear trailing area, costing turbulence, but creating another stack of high pressure for localized downforce. But once at high speed with great ground effects and little flow over the craft, we don't need the high wing or air dam at the trailing edge. Winglets at the leading edge of the craft help trap flow toward the sides, further helping vacuum the craft without later vacuum at the upper trailing edge where we can further lose downforce. -- just babble.

-edit-
Rear diffusers are generally decorative, beyond helping shape the rear flow to reduce turbulence. However, it would be possible to increase vaccum under the craft if ducting were facing aft and high enough or sideward enough into a slipstream, thereby drafting air from under the vehicle, but if done high, again, costing more turbulence. This should work.