GT Mk1 aerodynamics

mlevea · 08-24-03, 07:00 PM

Does anyone have any hard engineering data (or failing that some word-of-mouth) on aerodynamic lift or downforce that the Mk1 sees at speed? Basically is there downforce at the front and rear or is there lift at either end?

Thanks in advance,

Mark

Trevor Jones · 08-24-03, 10:29 PM

Mark,

According to an old (1967) SAE article, when a 3/8 model was tested in the Maryland wind tunnel. the results extrapolated to full scale at 200mph suggested that lift at front axle was 236 lbs and 272 lbs lift at rear axle. This was from the version with spoilers added. What's not clear from the article is whether this is for the definitive Mk 1 shape or an interim shape.

The article implies there were later full scale wind tunnel tests but results are not reported

mlevea · 09-02-03, 07:34 PM

Interesting. Got this off the mulsannescorner database.

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

It's interesting also to note that todays cars that have 1000 lbs of drag also generate 3000 lbs of downforce.

Sebring GT · 09-29-03, 09:10 AM

A very interesting subject. Close visual comparison of the pictures of the new Ford GT vs. the original GT40 reveals what appears to be a diference in the leading edge (over the radiator opening). The shape of the original GT40 in this area is bull-nosed while the new Ford GT appears to be pointy (with the sharp edge possibly continuing along the edge of the front clip and meeting with the upper line of the side scoop in the door panel). My question is whether this is the change that was required in order to go from the front end lift of the original GT40 to the downforce of the new Ford GT? After reading the following the answer would appear to be "yes" (unless there is some more info which is not being revealed):

From the July 2003 Automobile Magazine article by Mark Gillies on the new Ford GT, at page 45:
"Close attention has been paid to the aerodynamics. After all, the GT's shape mimics closely the original GT40, and automobile aero has moved on since the 1960s. Tom Reichenbach, vehicle engineering manageer, says that 'lots of time was spent in the wind tunnel. The original car went there, too, and we found that it was good for flow but had bad front-end lift. As the designers wanted to keep the shape faithful, we knew there would be lift problems. What we found was that the guys in the 1960s simply needed to add a proper front-end splitter with clean separation.
"We actually ended up with more front end downforce than we initially wanted,' he continues. 'We balanced that with extra rear downforce.' which is provided by a racing-style venturi tunnel that starts ahead of the rear axle line. There is also a rear wicker spoiler.'"

Does anyone on the Forum have any more info or insight into the question of how the design was modified to change lift to downforce? Would it be a good idea to modify the front end of a replica vehicle by making leading edge pointy like the new Ford GT in order to create downforce rather than lift, etc? Thanks. Best regards, Orin Meyer

Gary Gibbs · 09-29-03, 11:31 PM

Try Katz's book on race car aerodynamics. It addresses the basic concepts of front splitters and rear underbody tunnels.

Katz: Race Car Aerodynamics

Julian West · 09-30-03, 09:59 AM

Anyone got any idea about aerodynamics around the rear deck? ie getting air in & more importantly out?

I have a crazy idea there may be a weird airflow that stops air exiting the engine bay around the back of the car... It's been proven that there is a build up of pressure under the rear deck.

Robert Logan · 10-08-03, 06:55 AM

Julian,

We have a RF car that has put two small fans either size of the exhaust. They are activated by a temperature sensitive switch which monitors the under hatch (engine bay) temperature. The fans are small oil cooler style units and the results are great. The area that the hot air is expelled into (rear of car) is a low pressure area and the fans work very well.

Hope this helps,

Best wishes,

Robert

Bill Musarra · 10-08-03, 08:41 AM

Robert,
Rear bay temps are a concern to me. As a previous Lotus Esprit owner I am all to familiar with rear bay temps (Oil cooled turbo in an enclosed bay area). Their setup was to have the fan above the engine, which blew the air up and out the louvers of the rear hatch cover. Worked well but was rough on the fiberglass.This was a low pressure area as well. Do you have any pics of the fan setup you mentioned.
Bill

Space Monkey · 10-08-03, 09:12 AM

There is an article in last week's autocar about the Ford GT. It says that the designers have new found respect for the drivers of the GT40 because when they put a MK1 GT40 in the wind tunnel they found it suffered from serious nose lift, so serious that they calculated it would have become completely airborne if it reached 230 mph!

Julian West · 10-09-03, 04:49 AM

[ QUOTE ]
Julian,

We have a RF car that has put two small fans either size of the exhaust. They are activated by a temperature sensitive switch which monitors the under hatch (engine bay) temperature. The fans are small oil cooler style units and the results are great. The area that the hot air is expelled into (rear of car) is a low pressure area and the fans work very well.

Hope this helps,

Best wishes,

Robert

[/ QUOTE ]

Hi Robert,

Thanks for the idea, I may well use it!

All the best,

Knighton · 10-10-03, 02:11 PM

What effects did the canards have at high speed?

91740Gt · 10-10-03, 03:45 PM

Stopping the driver saying .... V1 , V2 , Rotate!!!!!!!

Bigend · 10-10-03, 07:53 PM

Didn't work for Mercedes.......

David Morton · 10-10-03, 07:55 PM

V1, rotate, v2 (surely) [img]/ubbthreads/images/graemlins/wink.gif[/img] [img]/ubbthreads/images/graemlins/wink.gif[/img]
Jasper, did you know that they were fitted on the grid just prior to the race and had never been tested on that car. Apparently Adrian Newey was telephoned in Canada and suggested they be fitted. Your right, they didn't work - at the incidence they reached they only contributed to further lift. I was in the Schnitzer garage at the time it happened in the race and everybody thought the worst. He was very very lucky and even more so that it happened out in the country and not along the main straight.

Dave.

Bigend · 10-11-03, 10:49 AM

David, I saw the video of both of the "flying" incidents, the scariest things I have ever seen. To have been there must have been just horrific.

Mike

mlevea · 10-11-03, 01:24 PM

I was just thumbing through the latest Car & Driver and found an article on the latest developments of the GT as its design converges on the real production car.

They ran a mkII through Swift Engineering's rolling road wind tunnel. As we have seen there was substantial lift front and rear for all GTs. Their fixes were simple.

1. Add chin spoiler (splitter) ala Lotus Europa.
2. rocker panel extensions
3. ducktail spoiler
4. rear under-car diffusers

The result is modest downforce.

The chin spoiler is almost invisible. I wouldn't mind adding one of those. I don't think it would really hurt the overall appearance but it could aggrivate the purists. I also think the rear diffuser looks mean.

I think I need those two pieces.

Mark

Bill Musarra · 10-11-03, 03:16 PM

Anyone got any pictures of these?
Bill

mlevea · 10-11-03, 08:00 PM

**patbarry** · 10-11-03, 08:34 PM

You can just see it in this picture I took at Indy twoo weeks ago. This one cruised downtown Indy later that Saturday afternoon and then Jackie Stewart drove it Sunday morning.

Howard Jones · 10-13-03, 12:20 AM

Since you asked for a seatofthepants point of view... I have been driving my GTD quite a lot sorting out the systems and have the following advice. The front ride height must be no less than 1/2" lower than the rear. The first time I had it up to around 100 I had it set to 5" front and 5" rear. I didn't like that much at all. The front end felt light although not unsafe. I concluded that given the speed these cars can reach something should be done. During the next few weeks I reset the front alinement and also lowered the front rideheight to 4 3/8". About a week after that I had ocasion to put my foot into it again, corvette this time, and the car felt MUCH better at about 120 than it did at 100. I have also installed a rear adjustable duckbill plate like the MK2's had with about 3/4" of plate above the top of the duckbill. I have also not installed any of the rear loovers in an effort to expel as much air from the engine bay as possible. I think that a chin spilter, for track use, like above would also help to keep the airflow out from under the front of the car, the main problem with its design. Street use requires, at least for me, that the front of my car can be no lower but if a spliter were done right you might be able to raise the front ride height without ill effect . Also it is very important to vent ALL the airflow into the radiator inlet, along with the brake ducts if you don't use them for the brakes, out thru to top of the cars nostrils with whatever ducting you might add in the nose. Thats my 2cents worth.