Which of the two makes less wake behind the car? I would assume tunnels, but wasn't sure.

Ground effect tunnels create much less turbulence aka "dirty air." Ideally, the next IndyCar will get most of its aero grip from ground effect tunnels instead of large wings.

The undertray and diffuser created downforce with less drag.

The DP01 made great PR about the "ground effects" and 60% of the downforce at 200mmph coming form underneath the car. But understand that on road couses that level of efficiency happened maybe twice a lap. And on oval's where that number makes more sense there were other issues to contend with. In the 90's, CART was reducing the size of the diffusers (continued evolution that started with the first full ground effects Indycar in 1980). On ovals, turbulence from cars ahead would disrupt airflow underneath the cars and make it difficult for cars to run nose to tail (the following car would become loose).

Anyway, those who ignore history are destined to repeat it. Point is mechanical grip and aero grip from wings and diffusers are all tools to refine a racing car's performance. But each have their positive and negatives.

tunnels generate downforce much more efficiently. however, there are two things to consider.

first is that it is really hard to 'adjust' tunnels. while for a given underbody you can play with rake, spring rate, and ride height, you do not have the ability to adjust them on the fly in a pit stop, for example.

second is that generally, by the shape of the tunnel forced by the realities of oil/water cooler placement, etc., tunnels tend to be mid- and high- speed devices. primarily on street courses (but slower road courses as well), you still need wings to provide a lot of downforce in slow and mid speed corners.

but on the superspeedways, if you recall the cart days, the front wings were essentially vestigal and used just for minor trim adjustments. the cars probably could have qualified without them.

VNAF Ace - 11 June 2009 06:43 PM

Ground effect tunnels create much less turbulence aka "dirty air." Ideally, the next IndyCar will get most of its aero grip from ground effect tunnels instead of large wings.

I beg to differ... The tunnels create MUCH more wake turbulence than the wings. The wings can only compress air and then expand it within the laminar flow area of the surface of the wings. At best, this take place in an area where there are three sides to control and channel this air. The tunnels have a small area where air can evacuate (i.e., between the bottom of the chassis and the roadway itself) but ad hoc, they produce a four-sided captive tunnel that is much more effecient in moving air, compressing air, expanding air, changing air pressure than that of an open wing. More efficiency means more 'action' taking place. More 'action' means more of a by-product produced by the elements working on the car -- by-products meaning turbulence.

Now, if one was talking about what has more effect... ...the wings might win out because their turbulent airflow will pass through to directly engage a car exactly behind the lead car whereas the tunnels stay relatively close the surface of the track and have less of an area to engage another car and have a negative effect on the trailing car.

I would imaginer the tunnels would work about equally well in still or turbulent air because they are dramatically compressing and accelerating the air anyway.

Wings need laminar flow and without it, simply do not function.

Tyhe real issue isn't, which creates less turbulence, but which works better with turbulence.

If the car is designed to run with tunnels, I think a good portion of the front of the car is designed to direct and smooth out the airflow to get it to the entrance of the tunnels as clean as it can. Hence the weird front wing shapes in F1.

With a tunnel car, the best balance is a multi-part front wing, so the top section can be adjusted in the pit stop and the rest still works effectively to route the air under the car. At least by MY understanding of F1 tech stuff.

Even then, I think there are issues with the air leaving the rear of the car, which is why the whole "double diffuser" issue came up this year in F1. The original idea was to have a clean exit, but they didn't close a loophole and Brawn and a few others added stuff to the rear to gain more grip. You also have turbulence from the rear wheels themselves and the rear wing. I don't think you can do much about the wheels, and still be "open wheel" racing. The rear wing can be addressed with changes in size, height, and angle. F1 attempts didn't show a lot of improvement, as far as I could tell. However, they are still a flat bottomed car, by the rules, so the bulk of the aero work can be seen.

I agree, the turbulence off the rear tires cannot be avoided. However, with aggressive ground-effect tunnels, hopefully, the rear wing can be a lot smaller.

Still the issue isn't what kind of wake the two cars leave, byt how the two types work in a wake.

I am not sure, but if the ground-effect car works as well in turbulence as in clean air (because it is just going to compress the air anyway)then tunnel cars should be betetr able to follow one another closely, and maintain downforce when following as well as when pulling out to pass.

But I don't know.

Where are the engineers?

Maelochs - 24 November 2009 02:19 AM

I am not sure, but if the ground-effect car works as well in turbulence as in clean air (because it is just going to compress the air anyway)then tunnel cars should be betetr able to follow one another closely, and maintain downforce when following as well as when pulling out to pass.

But I don't know.

Where are the engineers?

The following car almost always loses more front end grip and pushes/understeers due to the loss of front wing downforce as opposed to a more balanced overall loss of grip when following too closely.

This is possibly due more to their position ahead of tunnels and rear wings, allowing for turbulent wake air from the followed car to become more laminar by the time it reaches tunnels and rear wings as opposed to a difference in efficiency in turbulent air between the two types of aero devices, but I doubt it.

The more smoothed the air can be made, before it leaves the front car, the less the next car would be affected. Of course, it will NEVER be as clean as no car in front.

I suspect, in general, that a "tunnel car" could have less need for a large front wing, and therefore would be less affected by turbulence. But, on the other hand, a tunnel car would be more affected by bumps in the road, as the ride height changes, the distance from the tunnels to the road changes. Wings don't care if the car is on the road or not.

I hope the goal is to find the right mix of tunnels and wings. I wonder of the bulk of the work should be at the rear, to make the air flow as smooth as they can. That way, tunnels or wings work as best as they can.

Many of the early F1 ground effects cars actually actually had sliding vertical skirts that ran on constant light contact with the ground in order to seal the airflow.

Famously, there are pictures of the Lotus 80 sitting on its skirts with no wheels on the car, the springs in the skirts were so strong.

the thing was, if you tore one loose going over a kerb you lost a ton of downforce. they were banned after the 1979 or 1980 season, I think.

Steve