Ford GT Aerodynamic Stability at 275+MPH


twobjshelbys

GT Owner
Jul 26, 2010
5,360
Las Vegas, NV
MoTeC could open up some vents at speeds to sessen the affect for these devices but it would require wind tunnel testing for sure.
I was looking at their system a couple of weeks ago. It's a very sophisticated system. Can they manage vents based on sensors (e.g., air speed (pitot tube like) or down pressure) vs just a speedometer reading?
 

Specracer

GT Owner
Mark IV Lifetime
Nov 28, 2005
6,516
MA
Well written Bill!!

And a big plus one, on the enjoyment of reading the SAE book. Wish I understood all of it, i guess Ill leave that up to the smart people.
 

Fast Freddy

GPS'D 225
Mark II Lifetime
Aug 5, 2005
2,556
Tucson, Arizona
Since the front end bottoms out the suspension would it be advisable to up the spring rates for the miles runs?
if i were to make runs in excess of 250 mph i would want stiffer spring rates both front and rear....
 

ChipBeck

GT Owner
Staff member
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 13, 2006
5,603
Scottsdale, Arizona
Bill,

IMO, that was one of the best posts that has ever been put up on this Forum, perhaps the best. I have read the book (of SAE papers) you referenced but I think I got more out of your brief distillation of that material than I did from the book itself. Thanks for the time & effort you put into that writeup. It was outstanding.

A side note as we approach GT Speed Day on April 21 with an extended run of 1.7 miles, an understanding and appreciation of the information in Bill's post is important. Especially the part about being your own test pilot. Just because our cars, especially the TT's, can effortlessly achieve velocities that were unfathomable in a street legal auto just a few years ago doesn't lessen the physics (read that-violent destructive forces) if something comes apart causing a loss of control. During my years on the airshow circuit over 40 of my friends died in their airplanes. The annual mortality rate in that profession is 2%. About 1/3 of those who died were killed by mechanical or structural failures. Time and again, one of my buddies would describe to me the "new innovation" that he had incorporated into his aerobatic plane and the cool things it was going to do for performance. But nature sides with the hidden flaw and every flight with that new improvement was indeed a "test flight". Way too often that improvement failed in a completely unexpected way, often causing the loss of the plane and the death of the pilot.

I could relate stories of 6 pilots who were killed when aerodynamic mods caused a structural failure and most of these occurred at lower speeds than our GT's are running at these mile events. Let that sink in.

At 200+ MPH you and your GT are a ballistic missile with a tremendous amount of energy. A structural failure, blown tire, or loss of control at these speeds would probably not be survivable in a car without a roll cage and serious safety equipment.

In aviation it is well known that there is no safety in theory, hypothesis, or conjecture, no matter how well thought out they are. There is only safety in history. Don't tell me what you "think" is going to happen based upon theory because unforeseen variables often come into play with unforeseen results. What "did happen" in actual testing is all that really matters. Actual test results (history) is where safety resides. Mark H and Ray have taken Hoosier R-6 tires to 255+ MPH. The stock aero has been taken to 269.9 MPH. I'd be a lot more nervous if I was the first guy going there.

Chip
 
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GT38

GT Owner
Mark IV Lifetime
Jan 19, 2008
720
Glendale, Arizona
Great post, Bill. :thumbsup For those who don't already know, Bill was associated with the SR-71 engine program and is no stranger to speed related engineering issues.

(Maybe someday you'll be discussing Mcr for the GT...!)
 

ChipBeck

GT Owner
Staff member
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 13, 2006
5,603
Scottsdale, Arizona
Frankly, I am more concerned with the GT tearing itself apart (literally) because of it's ability to shift headwind into downforce. If the front end bottoms out at 200mph, imagine the amount of force trying to rip the front splitter off the GT at 250mph or more.
I wonder what speed the back suspension begins to bottom out.
Mark,

Only a fraction of the front end downforce is generated by that splitter. I don't know what the % is though. Photos of my car at 220 show the outside edges of the splitter bent downward quite a bit. I have stiffer front springs (about 35%) and I still get a lot of front end dive above 200. At 260+ Ray's GT (also with higher rate springs) shows that the rear of the car does not level out by catching up with the front even at those speeds.

Here's what I do know from some members of the FGT build team. When the GT is level it has less drag and.... when a GT is lower it has less drag.

You brought up a good point Mark, if the front splitter came off at 200+, it might cause a loss of control.

Chip
 
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Mullet

FORD GT OWNER
Le Mans 2010 Supporter
Oct 21, 2008
2,464
Houston Texas
Mark,

Only a fraction of the front end downforce is generated by that splitter. I don't know what the % is though. Photos of my car at 220 show the outside edges of the splitter bent downward quite a bit. I have stiffer front springs (about 35%) and I still get a lot of front end dive above 200. At 260+ Ray's GT (also with higher rate springs) shows that the rear of the car does not level out by catching up with the front even at those speeds.

Here's what I do know from some members of the FGT build team. When the GT is level it has less drag and.... when a GT is lower it has less drag.

You brought up a good point Mark, if the front splitter came off at 200+, it might cause a loss of control.

Chip
I think Performance Power runs their GT without the splitter and says it is stable.
 

Indy GT

Yea, I got one...too
Mark IV Lifetime
Jan 14, 2006
2,435
Greenwood, IN
Thanks very much Specracer, Chip and Dick.

I try to put forth words (as best I can) to educate our owners, as many of these engineering related topics are complex, convoluted and interrelated. Chip you are absolutely correct, at 200+ mph things happen very quickly and tire/rim/suspension/aero package failures can be catastrophic. I am glad you reinforced the image of you being your own test pilot when you get beyond the test/prior experience range. Because you are....

And I really would not heap the accolades I do on the FGT team if I did not feel in my heart; these guys DID sweat the details! The GT product Ford delivered in the time allotted for the price they charged is IMO pretty spectacular. Having the privilege of talking to a number of the GT "team members" Dave has encouraged to attend our FGT rally’s has given me (as well as others) behind the scenes insight as to the blood-sweat-and tears these members went through to deliver our vehicle. I am proud to own one.

And although I certainly appreciate your nomination for the best Forum post ever, I must say your (Chip’s) dissertation on boutique blended gasoline has to be my favorite of all time. As we have had a number of new Forum members join us here, those who have not read this amazingly educational post should use the search function to find and read "My" all time favorite post.

Ok now Marky Mark, where are you???
 
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Mullet

FORD GT OWNER
Le Mans 2010 Supporter
Oct 21, 2008
2,464
Houston Texas
Indy

I'm debating something on another forum and think this is Right up your alley.

At a standing Mile I have said and FIRMLY believe every foot counts in relation to trap speed at the Mile. The main argument is my belief that if you do not hit it like a 1/4 pass all the way down you will not get as high of a speed if you were to rollout first gear at a medium pace.

Any wasted foot/feet means a lower trap speed.
 

fjpikul

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Jan 4, 2006
10,461
Belleville, IL
Mullet, you're going to "trap" him now since he doesn't like straight line racing.
 

Mullet

FORD GT OWNER
Le Mans 2010 Supporter
Oct 21, 2008
2,464
Houston Texas
Mullet, you're going to "trap" him now since he doesn't like straight line racing.
I'm banking on the strong Engineer side to prevail.
 

DBK

The Favor Factory™
Staff member
Le Mans 2010 Supporter
Jul 30, 2005
14,914
Metro Detroit
Indy

I'm debating something on another forum and think this is Right up your alley.

At a standing Mile I have said and FIRMLY believe every foot counts in relation to trap speed at the Mile. The main argument is my belief that if you do not hit it like a 1/4 pass all the way down you will not get as high of a speed if you were to rollout first gear at a medium pace.

Any wasted foot/feet means a lower trap speed.
Based on all the drag racing I used to do, I would think the effect of launching a car over the course of a mile would have a negligible effect. MPH is a function of horsepower, not 60 ft. If I ran my Z06 at the track and pulled a 1.68 60 ft, I'd run 11.3@~125. If I ran my Z06 at the track and pulled a 2.0 Z06 ft I'd run an 11.9@~125. Dead hooking or bogging both always hurt the mph. If I spun hard out of the hole, I'd often end up with the highest mph I'd see that day.

I remember that time the orange gallardo that flipped ran something like 248 or 249. He rolled out, bogged, and basically botched the first 150 feet of the run. I thought "no way will this be a good number." It ended up being the fastest the car had ever gone to that point. If there is science to hitting it hard out of the hole, I'd still argue it's not worth it in mile racing due to breakage.
 

ChipBeck

GT Owner
Staff member
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 13, 2006
5,603
Scottsdale, Arizona
The Weekly Standard, April 2, 2012

Chip’s dissertation on boutique blended gasoline has to be my favorite of all time. As we have had a number of new Forum members join us here, those who have not read this amazingly educational post should use the search function to find and read "My" all time favorite post.
Bill,

It appears that my "Boutique Gasoline" post is still circulating around. It was cut and pasted on many websites and a copy made it's way to both Chevron and Exxon-Mobil top management who distributed it to their executives coast to coast. I have read segments of it almost word for word (most often without credit) in several petroleum related articles. Rush Limbaugh quoted a section of it on his show some time back. But the topper came just this week. I opened my April 2, 2012 copy of "The Weekly Standard" (which I subscribe to) and on page 10 was a feature article by Steven F. Hayward titled "Bureaucratic Gas, To lower prices at the pump, abolish the boutique fuel regime". Mr. Hayward followed the structure of my writeup very closely and in sections nearly quoted me word for word. To illustrate:
__________________________________________________________

My words:

Ahhh, I'm sure there's a big environmental payoff for all of the economic pain that these blend requirements have imposed upon us right?? We now have the answer to that question. President Bush understood that problem because after hurricane Katrina he immediately issued an executive order suspending all fuel blend requirements nationwide. He knew that without taking this decisive action there is no way that America's remaining undamaged fuel refineries could keep up with demand. For about two months after Katrina all gasoline sold in the United States was essentially the same blend. There was no detectable difference in air quality during this time.

From Steven Hayward's article:

But hey, it's all worth it if our children can breath cleaner air right?...Indeed, the boutique gasoline requirements were waived in the aftermath of hurricanes Katrina and Rita in 2005, when half of the gulf coast refineries were knocked out of commission for several weeks. During the waiver...there was no noticeable uptick in ozone levels in EPA data.
__________________________________________________

Steven Hayward is a fellow at the American Enterprise Institute and has published several books. I'm glad he liked my GT Forum post!

Chip
 
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2112

Blue/white 06'
Mark II Lifetime
You are referring to this post I believe (for those who have not read it yet);


http://www.fordgtforum.com/forums/s...such-a-rip-off&p=280646&viewfull=1#post280646
 

PeakCompletions

Boost is an addiction...
Le Mans 2010 Supporter
Jan 6, 2007
1,414
West Texas
Some great posts and information in here for sure!

When we analyzed many different options and configurations for the GT and what we could do to get "cheap" or "free" HP by reducing drag and trying to increase MPH this was something we spent a lot of time on. In fact we even had MATECH design and send a lower downforce front end for the yellow car.

At the end of the day, all of the efforts and reviews that we put in pale in comparison to the engineering that was put into the car in the first place and we decided to leave the AERO alone for now. This was evident from the testing we did in Miami with the car before the Exotics Rally race and how stable the car felt at speed with a BONE STOCK OEM AERO configuration. (minus mirrors and wipers actually)

AMAZING JOB FORD IN DESIGNING WHAT I THINK IS THE BEST AERO PACKAGE OF ANY STREET CAR BAR NONE!!

We will be experimenting with some of the things we have in place for the next level and still need to get my schedule sorted to take the yellow car back out again to show what we have done in the last year and a half even with stock aero :biggrin

we are still debating the use of the custom aero we had designed but again, at 270+ things happen fast so once we have pushed the stock aero and our current design platform as far as we can then we will start easing into the testing of the new aero... a true test pilot scenario which has been detailed in the previous posts and not always with the best results LOL

One of my biggest worries is the tires and as such have 2 full sets of rims and heat cycled brand new hoosiers. No one can tell us what they are good for. We know at these speeds they are fine for at least 6 runs (8 miles per set?? HAHA)... we just switch them out for new ones to eliminate any risk of breakdown in the tires or risk of blowout...

Good news is there is a lot more MPH available in the stock aero so we don't really have to worry about that just yet :cheers
 

Matech GT1

GT Owner
Apr 2, 2009
337
London
Our ex-race engineer at Matech is a highly experienced aero chap, and I'm sure would be able to contribute to this debate on improving front end downforce and controlling unwanted rake above 200 mph, potentially at the reduction of comfort below those speeds.

There were lots of trials, adjustments and tweaks made both during the development and during the season of the GT1 car to improve aero performance for both handling and speeds - though clearly in the same speed bands that you are discussing here.

Steve.
 

STORMCAT

GT
Mark IV Lifetime
Le Mans 2010 Supporter
May 25, 2006
7,441
Ft. Lauderdale
Some great posts and information in here for sure!

When we analyzed many different options and configurations for the GT and what we could do to get "cheap" or "free" HP by reducing drag and trying to increase MPH this was something we spent a lot of time on. In fact we even had MATECH design and send a lower downforce front end for the yellow car.

At the end of the day, all of the efforts and reviews that we put in pale in comparison to the engineering that was put into the car in the first place and we decided to leave the AERO alone for now. This was evident from the testing we did in Miami with the car before the Exotics Rally race and how stable the car felt at speed with a BONE STOCK OEM AERO configuration. (minus mirrors and wipers actually)

AMAZING JOB FORD IN DESIGNING WHAT I THINK IS THE BEST AERO PACKAGE OF ANY STREET CAR BAR NONE!!

We will be experimenting with some of the things we have in place for the next level and still need to get my schedule sorted to take the yellow car back out again to show what we have done in the last year and a half even with stock aero :biggrin

we are still debating the use of the custom aero we had designed but again, at 270+ things happen fast so once we have pushed the stock aero and our current design platform as far as we can then we will start easing into the testing of the new aero... a true test pilot scenario which has been detailed in the previous posts and not always with the best results LOL

One of my biggest worries is the tires and as such have 2 full sets of rims and heat cycled brand new hoosiers. No one can tell us what they are good for. We know at these speeds they are fine for at least 6 runs (8 miles per set?? HAHA)... we just switch them out for new ones to eliminate any risk of breakdown in the tires or risk of blowout...

Good news is there is a lot more MPH available in the stock aero so we don't really have to worry about that just yet :cheers
Hey Ray,

Ford really needed the front Splitter for the Ford mandated stock ride height. Once you rake the car that requirement goes away. The wind tunnel reading we got with a raked car and stock splitter was 4 to 1 front to back. You know our old Friend JB with the white car has run over 250mph with no front splitter at all just a raked set up.. That front splitter is probally costing you some serious top speed.. I am sure there is some concern in your mind but it's been done. Take it off and do a run to 240 and I am sure she will feel fine.. removing the front splitter would reduce the front down force and give you some more rear down force and improve traction..
 

Waxer

Well-known member
Le Mans 2010 Supporter
Jul 22, 2007
927
This has to be one of the best threads ever.

Awesome.
 
H

HHGT

Guest
First off congrats to all those that have bigger cajones than I do achieving astonishing speeds with an unbelievable piece of American history. Having said that, much has been discussed about the incredible down-force the GT was designed for. However, I can not find any technical reference to the Aerodynamic Stability and speed limits specific to the GTs front end. Is 275 MPH the limit for these cars' front end design? Did Ford ever publish this data? What was the maximum speed testing done in the simulator(s)?
 

Mullet

FORD GT OWNER
Le Mans 2010 Supporter
Oct 21, 2008
2,464
Houston Texas
First off congrats to all those that have bigger cajones than I do achieving astonishing speeds with an unbelievable piece of American history. Having said that, much has been discussed about the incredible down-force the GT was designed for. However, I can not find any technical reference to the Aerodynamic Stability and speed limits specific to the GTs front end. Is 275 MPH the limit for these cars' front end design? Did Ford ever publish this data? What was the maximum speed testing done in the simulator(s)?
if a 12 year old Camaro can do 253 in the Mile a GT should be able to handle 300 or more. :)