- Nov 24, 2005
- 228
This piece of overdone plastic has to go. Does anyone have a picture of a car with this removed ?
Diffuser Removal
- Thread starter Dr Robert Harms
- Start date
- Nov 24, 2005
- 228
Can I get the citation you use to state "at risk of stability " and "integral" and definition of "at speed" ?
Thanks
Thanks
FGT4me
GT Owner
- Oct 19, 2005
- 95
I can't speak to the GT in particular but I'm sure you are aware that diffusers, in general, allow a more rapid exit of the air which is flowing under the car.
This decreases lift and improves stability as speed increases.
I do not know the shape of the curve (car velocity vs. air pressure under the car or, inversely, "relative" downforce) but you can bet it's not linear. I'm sure the aerodynamacists at Ford know the specifics.
This is also why they have all those panels under the car, to make flow less turbulent (more laminar).
I realize you know all this and you are probably only wondering it's effect on the kind of driving you do with the car (street only?).
This decreases lift and improves stability as speed increases.
I do not know the shape of the curve (car velocity vs. air pressure under the car or, inversely, "relative" downforce) but you can bet it's not linear. I'm sure the aerodynamacists at Ford know the specifics.
This is also why they have all those panels under the car, to make flow less turbulent (more laminar).
I realize you know all this and you are probably only wondering it's effect on the kind of driving you do with the car (street only?).
Although I can't prove it, rear diffusers I suspect are functional in the purpose of maintaining a negative pressure to the undercarriage and therefore serve a purpose aerodynamically. The undercarriage construct of modern sports cars is an essential part of its aerodynamics. You may loose some indirect down force. Would be interested to hear how more knowledgeable people than myself ring in on this topic. Before doing it be sure.
californiacuda
GT Owner
- Oct 21, 2005
- 919
The profile of a car is similar to a section view of a wing. Bernouli tells us that the air that is on the top of the wing travels a farther distance than the air underneath it and in doing so it accelerates and creates lift. The diffuser is intended to accelerate the air traveling under the car to try to offset the lift from the accelerated air on the upper side of the car.
Below 60mph the rolling resistance is greater the air friction pushing against the car. So, as long as the driver of a diffuserless GT doesn't go too fast, it should be ok.
Below 60mph the rolling resistance is greater the air friction pushing against the car. So, as long as the driver of a diffuserless GT doesn't go too fast, it should be ok.
analogdesigner
GT Owner
Swift Engineering tour
This is where to get the answer regarding performance:
http://www.fordgtforum.com/forums/showthread.php?t=1306
Dr Robert Harms said:
This is where to get the answer regarding performance:
http://www.fordgtforum.com/forums/showthread.php?t=1306
satx
Well-known member
Dr Robert Harms said:
I haven't seen it removed.....however I doubt you're car will suddenly flip over if you decided to remove it :wink
Might want to keep it under 180 MPH or so as a precaution :thumbsup
fjpikul
GT Owner
If you check the reviews in the car magazines (MotorTrend, Car & Driver. Road & Track, Edmunds.com, etc) they all discuss the utility of the diffusers. That doesn't mean you can't take it off, but I wouldn't ride with you over the legal speed limit. You may as well take off the front one as well and then you'll never scrape bottom.
Neilda
GT Owner
I would always act on the assumption that a team of Ford's top designers probably put it there for a pupose.
It aids the venturi effect - as air enters and is forced through the narrow center, its speed increases, creating a low pressure area between the bottom of the car and the track. This creates a suction effect, which holds the car to the track. Increased speed results in a reduction in pressure. The underbody venturi is shaped to create this low pressure area between the road and chassis which creates downforce.
I guess if you're just going to take it down to the shops then you could take it off - but then why buy a GT if that's all you're going to to? :biggrin
It aids the venturi effect - as air enters and is forced through the narrow center, its speed increases, creating a low pressure area between the bottom of the car and the track. This creates a suction effect, which holds the car to the track. Increased speed results in a reduction in pressure. The underbody venturi is shaped to create this low pressure area between the road and chassis which creates downforce.
I guess if you're just going to take it down to the shops then you could take it off - but then why buy a GT if that's all you're going to to? :biggrin
valart
GT Owner
When I watched the Ford GT Discovery Channel documentary (http://shopping.discovery.com/product-56022.html) I remember it points out the difficulties the design team had when trying to make the GT look as close as possible to the old GT40.
During speed testing, the retro-shape of the GT wasn't good enough to keep the car safely on the road. They had a hard time trying to find a way to avoid a rear spoiler/wing while preventing the car from "flying" under certain conditions. The diffusers where the solution. They keep the car down on the road and respect the original GT40's look.
If you drive fast, don't event think about removing the diffusers... :frown
Another design problem was making full working door windows. The Discovery Channel video address that too.
During speed testing, the retro-shape of the GT wasn't good enough to keep the car safely on the road. They had a hard time trying to find a way to avoid a rear spoiler/wing while preventing the car from "flying" under certain conditions. The diffusers where the solution. They keep the car down on the road and respect the original GT40's look.
If you drive fast, don't event think about removing the diffusers... :frown
Another design problem was making full working door windows. The Discovery Channel video address that too.
AtomicGT
GT Owner
Bernoulli was a cool dude but I think Venturi would also claim some effect here too!
Bernoulli Effect
For horizontal fluid flow, an increase in the velocity of flow will result in a decrease in the static pressure. The equation describing this effect is known as Bernoulli's law. The most practical example of this is in the action of an airfoil. The shape of an airplane wing is such that air flowing over the top of the wing must travel faster than the air flowing under the wing, and so there is less pressure on the top than on the bottom, resulting in lift.
Venturi effect
The Venturi effect is a special case of Bernoulli's principle, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after the Italian physicist Giovanni Battista Venturi.
The reduction in pressure in the constriction is a result of conservation of energy: the fluid (or gas) gains kinetic energy as it enters the constriction, and that energy is supplied by a pressure gradient force from behind. The pressure gradient reduces the pressure in the constriction, in reaction to the acceleration. Likewise, as the fluid or in the case of the GT, air under the car being forced into the constriction, leaves the constriction, it is slowed by a pressure gradient force that raises the pressure back to the ambient level
Net effect is about 250 lbs of downward force on the rear end at high speeds. So if you take off the Venturi constrictors, let me know, I have a few psychatric friends that owe me favors and I can get you a consult for free, even by email ! :willy
So what we are experiencing here is the Venturi application of the Bernoulli Principle.
If you are bottoming out entering or leaving your driveway, have some aluminum perforated trailer ramps made that you can lay down and drive the car over and avoid the scratching sound putting the GT in the garage. I have the problem with an angled drive way, I can provide an image of the trailer ramps if so desired.
Bernoulli Effect
For horizontal fluid flow, an increase in the velocity of flow will result in a decrease in the static pressure. The equation describing this effect is known as Bernoulli's law. The most practical example of this is in the action of an airfoil. The shape of an airplane wing is such that air flowing over the top of the wing must travel faster than the air flowing under the wing, and so there is less pressure on the top than on the bottom, resulting in lift.
Venturi effect
The Venturi effect is a special case of Bernoulli's principle, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after the Italian physicist Giovanni Battista Venturi.
The reduction in pressure in the constriction is a result of conservation of energy: the fluid (or gas) gains kinetic energy as it enters the constriction, and that energy is supplied by a pressure gradient force from behind. The pressure gradient reduces the pressure in the constriction, in reaction to the acceleration. Likewise, as the fluid or in the case of the GT, air under the car being forced into the constriction, leaves the constriction, it is slowed by a pressure gradient force that raises the pressure back to the ambient level
Net effect is about 250 lbs of downward force on the rear end at high speeds. So if you take off the Venturi constrictors, let me know, I have a few psychatric friends that owe me favors and I can get you a consult for free, even by email ! :willy
So what we are experiencing here is the Venturi application of the Bernoulli Principle.
If you are bottoming out entering or leaving your driveway, have some aluminum perforated trailer ramps made that you can lay down and drive the car over and avoid the scratching sound putting the GT in the garage. I have the problem with an angled drive way, I can provide an image of the trailer ramps if so desired.
Last edited:
ByeEnzo
GT
I think the diffusers look cool and aggressive on the back of the car. As stated in scientific terms by the forum members, they are integral to the road holding of the car. All you have to do is look at what happened to the Mercedes effort a few years ago at LeMans. Poorly designed aero kit on their cars. Driven at WOT, the rear of the car squats, you hit a rise in the road, and the next thing you're doing is a "ground loop".
AMER SPD
GT Owner
Design
Dr Harms,
It was a bit of a task for Ford’s Aerodynamics and Vehicle Dynamics Team to keep the classic body look while also giving today’s drivers the modern stability they’ve become accustom to.
I believe if the Team was to design a 200+ MPH vehicle without the restriction of the GT40 body style, the vehicle would look very different including possibly eliminating such prominent splitters and diffuser.
I hope the attachment helps explain the need for the air splitters and diffuser.
Sorry the file was too large to post here. I had to post the 5 pages in members photos. key word "vehicle aerodynamics" under Amer Spd. Unfortunately the pages didn’t display in order but the pages are numbered at the bottom.
http://www.fordgtforum.com/gallery/showphoto.php?photo=403&cat=500&ppuser=98
Cheers,
Dr Robert Harms said:
Dr Harms,
It was a bit of a task for Ford’s Aerodynamics and Vehicle Dynamics Team to keep the classic body look while also giving today’s drivers the modern stability they’ve become accustom to.
I believe if the Team was to design a 200+ MPH vehicle without the restriction of the GT40 body style, the vehicle would look very different including possibly eliminating such prominent splitters and diffuser.
I hope the attachment helps explain the need for the air splitters and diffuser.
Sorry the file was too large to post here. I had to post the 5 pages in members photos. key word "vehicle aerodynamics" under Amer Spd. Unfortunately the pages didn’t display in order but the pages are numbered at the bottom.
http://www.fordgtforum.com/gallery/showphoto.php?photo=403&cat=500&ppuser=98
Cheers,