Hi Speed Lift
- Thread starter Bill D
- Start date
Well Bill, unfortunately, no manufacturer appears to have
addressed this fully. Some have modified the nostrils to
create a little more frontal downforce, but none have designed
splitters or any other aero/diffusers underneath.
However, Mark La Vea ( http://www.xtremeclassics.com ) has
designed a splitter for ERAs and GTDs/CAVs, and is working
on some other stuff as well.
Ian
addressed this fully. Some have modified the nostrils to
create a little more frontal downforce, but none have designed
splitters or any other aero/diffusers underneath.
However, Mark La Vea ( http://www.xtremeclassics.com ) has
designed a splitter for ERAs and GTDs/CAVs, and is working
on some other stuff as well.
Ian
Bill,
Just remember that you can’t change downforce at only one end of a car without messing up the high-speed balance of the car. The original GT40 with the single nostril as used in 68-69 was well balanced front to rear and handled well as a result.
If you increase the downforce at the front only, you create a situation where the front sticks better as the speed goes up and the car transitions more and more into oversteer at higher speeds. This is exactly the opposite of what you want. For a car to handle well, it should have proportionately more downforce and grip at the rear as speed increases.
Unfortunately, the chassis and engine compartment of the GT40 are not well suited to the addition of diffuser tunnels without a complete redesign. This somewhat limits what you can do at the rear if you don’t want to add wings or significantly larger spoilers.
Kevin
Just remember that you can’t change downforce at only one end of a car without messing up the high-speed balance of the car. The original GT40 with the single nostril as used in 68-69 was well balanced front to rear and handled well as a result.
If you increase the downforce at the front only, you create a situation where the front sticks better as the speed goes up and the car transitions more and more into oversteer at higher speeds. This is exactly the opposite of what you want. For a car to handle well, it should have proportionately more downforce and grip at the rear as speed increases.
Unfortunately, the chassis and engine compartment of the GT40 are not well suited to the addition of diffuser tunnels without a complete redesign. This somewhat limits what you can do at the rear if you don’t want to add wings or significantly larger spoilers.
Kevin
Kevin-
My reason for asking this question is that the original GT40 had some aerodymaic problems which were addressed by a whole team of engineers. The same with the current Ford GT. These problems were fixed to a great degree. However, in the pursuit to make replicas, how is this problem addressed? I would hate to drive one at 180+ MPH and have the front end suddenly become airborne.
Bill
My reason for asking this question is that the original GT40 had some aerodymaic problems which were addressed by a whole team of engineers. The same with the current Ford GT. These problems were fixed to a great degree. However, in the pursuit to make replicas, how is this problem addressed? I would hate to drive one at 180+ MPH and have the front end suddenly become airborne.
Bill
Bill,
You have to remember that most of the lift problems were in the first 2 years of the GT40’s life. The 1963 and 64 cars went through a number of different nose designs, which looked nothing like what we think of as a GT40. Look at some pictures of early cars and you will see what I mean. By the time Ford came out with the Mk II they had pretty much solved the lift problem on both the MK 1 and MK II cars by using very similar nose designs. The other problem was that FIA rules required the cars to carry a spare wheel while racing and change it at each pit stop. The Mk 1 cars carried the wheel laying flat in the nose of the car and thus ended up with the double nostril nose, which was not as good aerodynamically, but was required to clear the spare.
By the time you get to the Gulf cars in 68 – 69, they had gone to the single nostril from the Mk II and the cars were stable at well over 200 MPH. A well-designed replica with proper ride heights front and rear should be fine aerodynamically up to 200 MPH. We have no tracks like LeMans in the US so there is nowhere that you are going to find a straight long enough to reach that kind of speed anyway (even LeMans has chicanes now to limit speeds).
Kevin
You have to remember that most of the lift problems were in the first 2 years of the GT40’s life. The 1963 and 64 cars went through a number of different nose designs, which looked nothing like what we think of as a GT40. Look at some pictures of early cars and you will see what I mean. By the time Ford came out with the Mk II they had pretty much solved the lift problem on both the MK 1 and MK II cars by using very similar nose designs. The other problem was that FIA rules required the cars to carry a spare wheel while racing and change it at each pit stop. The Mk 1 cars carried the wheel laying flat in the nose of the car and thus ended up with the double nostril nose, which was not as good aerodynamically, but was required to clear the spare.
By the time you get to the Gulf cars in 68 – 69, they had gone to the single nostril from the Mk II and the cars were stable at well over 200 MPH. A well-designed replica with proper ride heights front and rear should be fine aerodynamically up to 200 MPH. We have no tracks like LeMans in the US so there is nowhere that you are going to find a straight long enough to reach that kind of speed anyway (even LeMans has chicanes now to limit speeds).
Kevin
Kevin
Minor point. You didn't have to change the spare or use the spare. You had to remove it and touch it to the ground. You could then put it back. I believe in 67 you no longer had to do this but you still had to carry it.
Jim
Minor point. You didn't have to change the spare or use the spare. You had to remove it and touch it to the ground. You could then put it back. I believe in 67 you no longer had to do this but you still had to carry it.
Jim
Was the lift problem worked out of the later original GTs? I'm not sure if I have this straight, but I thought that in wind tunnel testing for development of the new GT they also tested the original road car they had. I thought they observed the ca. 200 pounds of lift at 200 mph and remarked to having a new found respect for the original drivers.
This topic has been covered as far as the aerodynamics part of it in this thread.
Aerodynamics
This thread covers the nostril problem, probably the most significant one by the kit manufactures.
Nostril
and this thread shows some more ideas that a builder can complete after the kit is delivered, including canards, and an adjustable rear spoiler.
ADD-ON's
Aerodynamics
This thread covers the nostril problem, probably the most significant one by the kit manufactures.
Nostril
and this thread shows some more ideas that a builder can complete after the kit is delivered, including canards, and an adjustable rear spoiler.
ADD-ON's
Mark,
In the article you mention, they didn't say which version of the original car they tested. Most of the figures I have seen in various places have put the total lift front and rear at 150 to 200 lbs @ 200 MPH. Given that the cars weigh 2,400 to 2,500 lbs with driver and fuel, that is not enough to be a problem if it is evenly distributed front to rear. It is probably most useful to note that the drivers didn't complain about lift or stability problems once they developed the later version of the nose. (The one we think of as the normal GT40 nose).
Kevin
In the article you mention, they didn't say which version of the original car they tested. Most of the figures I have seen in various places have put the total lift front and rear at 150 to 200 lbs @ 200 MPH. Given that the cars weigh 2,400 to 2,500 lbs with driver and fuel, that is not enough to be a problem if it is evenly distributed front to rear. It is probably most useful to note that the drivers didn't complain about lift or stability problems once they developed the later version of the nose. (The one we think of as the normal GT40 nose).
Kevin
Kevin is on the right track. With 400+ lbs on each front corner, 200 lbs of lift is not going to flip a car under normal racing conditions. What happens is the car gets light in the front and the steering goes away on high speed straights. It's really not that bad as long as you don't have to turn at that speed.Kind of feels like steering a boat.
Guys,
Maybe having been "raised on Lotus" has altered my brain patterns but I have to ask "Why put up with lift?" My Lotus gets more stable with increasing speed. Call me spoiled but I expect the same characteristics from a higher performance car.
Don't forget when you have that light front end your car is sitting higher, more air is funneling under the car and your roll center is higher. All these things have an accumulative affect and add to instability.
I read the aero article and was under the impression they tested a MkII. Also the aero data on my site was, um, borrowed from the Mulsanne Corner site and it showed lift for the MkII and the MkIV. This is the only data I could find on the subject and I'm hoping it's correct. If anyone has any other data on lift I'd like to see it.
1967 Ford GT40 MkIV
Lift:
148 lbs. @ 150 mph, with 365 lbs. of drag
213 lbs. @ 180 mph, with 554 lbs. of drag
263 lbs. @ 200 mph, with 648 lbs. of drag
318 lbs. @ 220 mph, with 828 lbs. of drag
1966 Ford GT40 MkII
Lift:
100 lbs. @ 150 mph, with 525 lbs. of drag
144 lbs. @ 180 mph, with 756 lbs. of drag
177 lbs. @ 200 mph, with 933 lbs. of drag
I have developed a front splitter to "chop off" air flow under the car, some rocker panel sill extensions to help keep air from slipping in under the car along the sides and an adjustable rear under car wing to balance the set up front to rear. I am presently making inquiries into wind tunnel time to fine tune the system.
Some cars do not have enough room for my rear wing but may still benefit from my splitter and sill extentions if they develop their own diffuser panel and adjustable rear spoiler.
Mark
Maybe having been "raised on Lotus" has altered my brain patterns but I have to ask "Why put up with lift?" My Lotus gets more stable with increasing speed. Call me spoiled but I expect the same characteristics from a higher performance car.
Don't forget when you have that light front end your car is sitting higher, more air is funneling under the car and your roll center is higher. All these things have an accumulative affect and add to instability.
I read the aero article and was under the impression they tested a MkII. Also the aero data on my site was, um, borrowed from the Mulsanne Corner site and it showed lift for the MkII and the MkIV. This is the only data I could find on the subject and I'm hoping it's correct. If anyone has any other data on lift I'd like to see it.
1967 Ford GT40 MkIV
Lift:
148 lbs. @ 150 mph, with 365 lbs. of drag
213 lbs. @ 180 mph, with 554 lbs. of drag
263 lbs. @ 200 mph, with 648 lbs. of drag
318 lbs. @ 220 mph, with 828 lbs. of drag
1966 Ford GT40 MkII
Lift:
100 lbs. @ 150 mph, with 525 lbs. of drag
144 lbs. @ 180 mph, with 756 lbs. of drag
177 lbs. @ 200 mph, with 933 lbs. of drag
I have developed a front splitter to "chop off" air flow under the car, some rocker panel sill extensions to help keep air from slipping in under the car along the sides and an adjustable rear under car wing to balance the set up front to rear. I am presently making inquiries into wind tunnel time to fine tune the system.
Some cars do not have enough room for my rear wing but may still benefit from my splitter and sill extentions if they develop their own diffuser panel and adjustable rear spoiler.
Mark
With diffuser tunnels, you don’t run splitters. You want air to move under the car, as that is what feeds the diffusers. A splitter and sill extensions would greatly reduce the effectiveness of the tunnels. With diffusers what you need to do is streamline the underbody so that you have minimal obstructions to the airflow and then encourage the air to flow to the tunnels. Air Dams (Splitters) are used to keep air from going under cars that have “Dirty” underbodies with a lot of exposed pieces.
One problem is that you would have to drastically change the appearance of the rear of the car. You would need to cut away a large portion of the lower rear panel to allow the diffusers to exit.
The GT40 is what it is. If you want maximum aerodynamic efficiency for track use, an Ultima is a far better car. I suspect most people who are interested in the GT40 wouldn’t want to do anything that would seriously change the looks of the car. It worked well enough to win LeMans twice in the later MK 1 Gulf form and had no reported problems on the Mulsane straight. In fact, I remember reading that the drivers talked about “Hands Off” stability at 170 MPH+.
Kevin
One problem is that you would have to drastically change the appearance of the rear of the car. You would need to cut away a large portion of the lower rear panel to allow the diffusers to exit.
The GT40 is what it is. If you want maximum aerodynamic efficiency for track use, an Ultima is a far better car. I suspect most people who are interested in the GT40 wouldn’t want to do anything that would seriously change the looks of the car. It worked well enough to win LeMans twice in the later MK 1 Gulf form and had no reported problems on the Mulsane straight. In fact, I remember reading that the drivers talked about “Hands Off” stability at 170 MPH+.
Kevin
You know, I think this may have drifted a little from where it began. Looking over this thread I think Mark may be feeling that I am trying to discourage people from using his products. That is not the case. There are situations in which a front splitter could be a useful addition to the aerodynamics of a GT40. The object of all of this was to point out that where aerodynamics and downforce are concerned, you cannot make changes to only one end of the car. (You can, but you are not likely to be happy with the result)
For anyone who is actually going to operate their car at speeds over 150 MPH it would probably be a good idea to have a basic understanding of aerodynamics as it applies to cars. I was thinking it would also be interesting to get comments from some of the more experienced racers (I think we have a lot among the British contingent) as to how they have found the cars to handle at speed and what sort of top speeds they are actually able to reach on the track.
Kevin
For anyone who is actually going to operate their car at speeds over 150 MPH it would probably be a good idea to have a basic understanding of aerodynamics as it applies to cars. I was thinking it would also be interesting to get comments from some of the more experienced racers (I think we have a lot among the British contingent) as to how they have found the cars to handle at speed and what sort of top speeds they are actually able to reach on the track.
Kevin
Kevin,
When I think of GT40s and diffusers this is what comes to mind:
No full length venturi tunnels feeding a diffuser, just the diffuser. Granted this is less than optimal but since there is no room for tunnels it's the compromise we are stuck with.
To be honest all I've done is plagerize Ford's work on the 2004 GT and adapt it to the Mk1. I figured I could learn from the $750K that Ford spent to review the MkII and tune the 2004. There is 35 years of accumulated aero knowledge that created that simple splitter.
I have seen the "hands off" 170mph video but 170 is not the critical speed for GT40s. Also I doubt if our friends across the pond have seen 200+ mph on a road course thus "V rotate" is not achieved. We have heard testimony that the car gets light at speeds over 200. It's my goal to eliminate that.
If we can all have a little patience I promise to publish data from my wind tunnel time. Then we can have hard data to mull over.
Mark
When I think of GT40s and diffusers this is what comes to mind:
No full length venturi tunnels feeding a diffuser, just the diffuser. Granted this is less than optimal but since there is no room for tunnels it's the compromise we are stuck with.
To be honest all I've done is plagerize Ford's work on the 2004 GT and adapt it to the Mk1. I figured I could learn from the $750K that Ford spent to review the MkII and tune the 2004. There is 35 years of accumulated aero knowledge that created that simple splitter.
I have seen the "hands off" 170mph video but 170 is not the critical speed for GT40s. Also I doubt if our friends across the pond have seen 200+ mph on a road course thus "V rotate" is not achieved. We have heard testimony that the car gets light at speeds over 200. It's my goal to eliminate that.
If we can all have a little patience I promise to publish data from my wind tunnel time. Then we can have hard data to mull over.
Mark
Friends
I never intended this thread to upset anyone. My only concern was with how have the replica manufacturers addressed the high speed lift problem encountered by the originals and the new Ford GT. As companies emerged making replicas of the GT40, I doubt they looked at this issue. Since they aren’t making cars, there is not a liability issue. With Ford, it’s another story.
Mark has done a great job trying to mitigate this problem with some very good ideas. I applaud that. But I would hate to see someone become airborne because he wanted to see if he could hit 200 MPH on some back road. I know of two very respectable people who have gone very fast in a GT40 replica on the freeways here in the states. Thankfully, the cars performed flawlessly.
I do not intend to attempt this feat myself. I will be happy playing around at Willow Springs, or an occasional auto-x event. But trying to go 200 MPH in a fiberglass car without a full roll cage just doesn’t appeal to me.
Bill D
I never intended this thread to upset anyone. My only concern was with how have the replica manufacturers addressed the high speed lift problem encountered by the originals and the new Ford GT. As companies emerged making replicas of the GT40, I doubt they looked at this issue. Since they aren’t making cars, there is not a liability issue. With Ford, it’s another story.
Mark has done a great job trying to mitigate this problem with some very good ideas. I applaud that. But I would hate to see someone become airborne because he wanted to see if he could hit 200 MPH on some back road. I know of two very respectable people who have gone very fast in a GT40 replica on the freeways here in the states. Thankfully, the cars performed flawlessly.
I do not intend to attempt this feat myself. I will be happy playing around at Willow Springs, or an occasional auto-x event. But trying to go 200 MPH in a fiberglass car without a full roll cage just doesn’t appeal to me.
Bill D
Well, I know Rick Merz has gone ~190 mph in his GTD - no aero
devices AFAIK.
Also, Gordon Levy had an RF on the track, and I think he hit
similar speeds - Robert or Hersh - any comment?
I'd like to see what Mark comes up with in tunnel testing.
If it works out, I think a splitter, deep nostril, taller
spoiler (like the metal ones used on the Gulf cars), MkII
style snorkels, and enlarged rear vent (again, like the Gulf
cars) might all improve downforce somewhat. These are all ideas
I have entertained, and someday, hope to test out.
Ian
devices AFAIK.
Also, Gordon Levy had an RF on the track, and I think he hit
similar speeds - Robert or Hersh - any comment?
I'd like to see what Mark comes up with in tunnel testing.
If it works out, I think a splitter, deep nostril, taller
spoiler (like the metal ones used on the Gulf cars), MkII
style snorkels, and enlarged rear vent (again, like the Gulf
cars) might all improve downforce somewhat. These are all ideas
I have entertained, and someday, hope to test out.
Ian
