Aerodynamics

[Ross Nicol]

I agree with Paul's comments about high speed stability.At the end of the straight at Phillip Island
the car is doing 150 to 160 mph.Just before braking the car feels twitchy in the rear but not unsafe.The front of the car is not lifting at that speed.On the back straight at Sandown The steering goes light and crosswinds can be a problem as I go over the top of the crest, however the speed is not as high as at Phillip Island.I have no aerodynamic extras on the car at the moment.I would never do those speeds anywhere else but the track in fact I stick to the speed limits on the road due to the fact I detest fines.
Ross

[Gary Gibbs]

An interesting post. I wonder which car has seen more high speed track testing. All of the GT40's driven leading up to, during, and subsequent to the great Le Mans effort or the "new" Ford GT? The old cars were certainly capable of being driven by expert drivers at 200+ MPH for many hours. What was the top speed of the Mk I, II and IV at Le Mans?

[Ross Nicol]

Well they say anyone can go fast in a straight line and you would have to say that there are not a lot of corners at Le Mans, however you have to hand it to the drivers in the 60's because from what I experience in my car at speeds 40mph at least lower than the 200mph they were doing on the straights,I bet they had some moments, especially when passing slower cars.My bet is top speed not much in excess of 200mph Gary, but I don't know for sure and you can bet there has been a lot of false information on top speed, as it's one parameter that would have been difficult to confirm in those days,unless they took elapsed time over a known distance.
Ross

[Richard O'Clery]

About canards/dive planes, I remember McBeath (Competition Car Downforce) saying something along the lines that they may create some downforce of themselves, but it seemed the cars produced far more downforce than could be accounted for merely by the angle of attack of the canard. He thought that they may create a vortex along the bottom edge of the car, aerodynamically sealing the undertray. He cautions that the amateur is unlikely to get this right.

I think that at worst a canard would create some downforce and maybe a lot of drag. At best there might be some containment of the airflow under the car it has a smooth undertray and a very low ride height. A diffuser (and a wind tunnel) would be important to maximise the effect.

As I think about it, Katz (Race Car Aerodynamics) may have some more info and drawings. Unfortunately, my tech books (except Carroll Smith and a few others) are still boxed away after the last house move. That was only 4 years ago ... that's very slack!

The picture Bill posted of 1076 is one of my favourite GT40 pics. I know it's very subjective, but I just love how the big Al spoiler adds to the visual balance and aggressiveness of the car.

[Gary Gibbs]

We may get some data on a CAV this fall. I am teaching a course "Racecar Performance" at Old Dominion University and partial payment includes wind tunnel time at the Langley Full Scale Tunnel

It might be interesting to include some xtreme classics options like the front spliter and a rear diffuser. We have not finalized time nor details at this point. Could be interesting though.

[jmvelez]

http://xtremeclassics.com/aero_devices.html

The Problem.

The original Ford GT has aerodynamic lift over the front and rear axles. Figures are:

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

The Solution.

Ford did some extensive development at Swift Engineering's rolling road wind tunnel on the new GT. Test results showed 4 fairly minor alterations canceled the aerodynamic lift and yielded modest downforce.

1. Add front chin splitter.
2. rocker panel extensions
3. ducktail spoiler
4. rear under-car diffusers