NASCAR technical question

[Racefreak24]

OK...this question is racing related but only heard discussed in NASCAR, mabe you can help me understand. On cooler days typically at superspeedways you hear of the crews taping off the grill. Obviously you can only do this in cool enough conditions or for small quantities of time such as qual. They say it creates more front downforce and reduces drag..........OK here we go. How do you INCREASE downforce and REDUCE drag. Seems unusual but mabe I'm missing a formula somewhere.

Thanks

[Conover]

I'm no wind tunnel guru, but from what I gather, you tape off the grill, an opening, that air pushes into and piles up in front of. When you get rid of the opening, and substitute tape for mesh, your providing a slicker surface area that moves the air up along the body instead of piling up in the grill opening. so the air moves more freely which reduces drag, and you give the air something to push down on, the tape provides a surface area for the air to push on, where as before hand it could have even been causing lift, who knows.

Help any? big parachute, small parachute

[Racefreak24]

That's the theory I'v been using all along so hopefully we are just naturally born for this kind of thing. There's just been this question in me that prompted me to ask to see if there was anything i was missing but I think we may be onto something....Interesting though

[BobsAuto]

Exactly. On cooler days, the air has more moisture, therefore, it is heavier. Have you ever watched the air come off the back wing of an FA or F1 on a cool and cloudy day? You can actually see the moisture (heavy air) fall off the back. The heavier the air, the slower the cars go.

[chuck baader]

One other consideration....any air that goes over the car rather than under or through an opening is considerably more aerodynamic...so, you get more downforce with less drag...sorta, kinda, maybe... Chuck

[lateapex911]

Definately. Think of a wing...Lots of lift, little drag. Now, punch a few holes in the leading edge. More drag, less lift.

Or, conversly, fill the damaged front edge, more lift, less drag.

Taping the grill is merely optimizing an imperfect shape. If it wasn't for the darn engine, they could go grilless, LOL.

In summary, the two results are NOT mutually exclusive.

BTW, Nextel Cup cars produce a LOT of downforce.

[Knestis]

Exactly. On cooler days, the air has more moisture, therefore, it is heavier. Have you ever watched the air come off the back wing of an FA or F1 on a cool and cloudy day? You can actually see the moisture (heavy air) fall off the back. The heavier the air, the slower the cars go.
[/b]

Sorry - science misconception alert!

Humid air is LESS dense than dry air, because gaseous water molecules have less mass than gaseous nitrogen and oxygen molecules. Aero functions (lift or drag) are greater in nice, dry air. Liquid water is more dense than air, of course.

Those vortices (vortexes, more than one vortex, whatever) you see off the wingtips of F1 cars or jets are water condensing (going from gas to droplets of liquid) because of the relatively sudden local air pressure changes.



K

[BobsAuto]

OK, then why, when it is humid, yet cool, is the air so "heavy" as the meterologists around here say? It is cooler, currently, than over the weekend and more humid. It feels like you have the weight of the world on you. Isn't that heavy air? That's what I was taught, but then again, nuns taught me who had no scientific experience and just used the teachers manual to teach science.
Hmmmm....this may be a huge learning experience.

BTW, the Hood blimp is flying overhead and over the track...the passengers are enjoying the Porsche club event....now where are they for the SCCA events?

PS>>>>LOVED the picture of the F15???? or F10????

[Knestis]

Cooler air = More dense
Warmer air = Less dense

Higher air pressure = More dense
Lower air pressure = Less dense

Lower elevation = More dense (higher air pressure)
Higher elevation = Less dense (lower air pressure)

The problem is that separating cool/warm from humid/dry from low pressure/high pressure might not be very easy out in the real world.

K

[Z3_GoCar]

OK, then why, when it is humid, yet cool, is the air so "heavy" as the meterologists around here say? It is cooler, currently, than over the weekend and more humid. It feels like you have the weight of the world on you. Isn't that heavy air? That's what I was taught, but then again, nuns taught me who had no scientific experience and just used the teachers manual to teach science.
Hmmmm....this may be a huge learning experience.

BTW, the Hood blimp is flying overhead and over the track...the passengers are enjoying the Porsche club event....now where are they for the SCCA events?

PS>>>>LOVED the picture of the F15???? or F10????
[/b]

F/A-18 B, the Blue Angles would fly nothing less. I see them all the time around here. There are two effects going on, temperature and humidity. With a lower temperature, the ability of the air to hold onto the humidity (water vapor) decreeses. Cold dry air is the best, hot humid air is the worst. The main point is that the water vapor displaces the O2 molecules as possible.

James

[Racefreak24]

I guess I opened up a topic and a half here cause now you all got me thinkin. Im gonna commit sin yet again here and speak of Drag racing....in drag "racing" they prefer lower elevations....why if higher elevation was less dense air? I hear that lower elevation created more HP......any input here?

And another, if cool air is more dense yet slower.......why are lap times on cool days sometimes FASTER?

Is there a civilian speaking scientist in the house?

BTW

Blue angels F/A 18 Navy/Marines
Thunderbirds F16 Air Force

[Eagle7]

Well, you started discussing aero, now we're moving to lap times. Lower elevation will have denser air. Denser air will give more downforce (good) and more drag (bad). With the right car you can tune for the balance you want.

But the big issue with faster times at lower elevations and cooler days is HP. Denser air can mix with more fuel to give a more powerful mixture - more HP. Yet another reason why qualifying times (morning) are commonly faster than race times (afternoon).

[BobsAuto]

That is also why NASCAR qualifies in the afternoon. They have a more realistic idea of what the car will do at breakneck speed in the race as well. (Going back to that OTHER racing organization.) Also, have you noticed that the big guns in drag racing often race at night? Cooler=more HP.

BTW, topics like this sure make the mind think and work and actually are good learning experiences. Thanks for starting the thread.

[Racefreak24]

Don't thank me....thank you and to everyone who posted to get to the bottom of this....

[Conover]

I saw an article about a month ago, Grassroots maybe, Racecar engineering, I'm not sure where, but they actually improved the aero with racer's tape on a Honda Integra, must've been RE, anyway pretty good article for a club racer, they put the Integra in the wind tunnel and took drag numbers and what not, then they taped up all the seams in the body, including around the hood, along the fenders and so on. Kinda cool, but I don't know who wants to go around with tape all over their car.

[lateapex911]

Not to mention it's not legal.

There have certainly been protests upheld at the Runoffs for exactly that.

[Knestis]

That is also why NASCAR qualifies in the afternoon. ...[/b]

I'll bet that the real reason has more to do with scheduling and attendance. There are a number of Cup venues where they qualify and race at very different times, and most of their races are long enough that conditions just change a lot, as a matter of course...

... Also, have you noticed that the big guns in drag racing often race at night? Cooler=more HP. ...
[/b]

And darker=better show.

Seriously - these games are so much more popular and professional than ours (road racing, broadly) because their first commitment is to the fan. We continue to collectively make decisions for the drivers. Or worse, decisions are may BY the drivers - or team owners.

K

[Wreckerboy]

I guess I opened up a topic and a half here cause now you all got me thinkin. Im gonna commit sin yet again here and speak of Drag racing....in drag "racing" they prefer lower elevations....why if higher elevation was less dense air? I hear that lower elevation created more HP......any input here?

And another, if cool air is more dense yet slower.......why are lap times on cool days sometimes FASTER?

Is there a civilian speaking scientist in the house?

BTW

Blue angels F/A 18 Navy/Marines
Thunderbirds F16 Air Force
[/b]

The "squirt racers" prefer lower elevations like the late great LACR which was nearly at sea level for example becasue lower elevations = denser air = more air per a given volume (say a cubic foot) for cramming into the combustion chamber.

[Greg Amy]

How do you INCREASE downforce and REDUCE drag.[/b]

It's not as difficult as you think. First, some basics:

- Lift causes drag. Pilots and aeronerds know that you cannot increase lift with a wing (or any surface, really) without also increasing induced drag (the drag produced not by the resistance to airflow - parasitic drag - but that created by the force of lift itself).

- "Downforce" is a bastardized simpleton NASCAR term; for the most part, very few cars produce "downforce" without wings or special underbody tricks. In fact, NASCAR has done a whole lotta stuff to these things to KEEP them from "producing downforce". In the real world, of which NASCAR is a part, the best you can do for a wingless, undertray-less automobile is MINIMIZE LIFT.

- Airflow beneath a car - without special undertrays - is turbulent, thus creates drag. (That's why you see The Boys faring in exhaust system and crossmembers and such. How many of you are paying attention to such details when building your exhaust...?)

- Airflow beneath a car - absent special undertrays - creates lift due to Bernoulli's Equation.

- Airflow through a cooling system is EXTREMELY draggy, not only because it is extracting copious energy from the cooling system but its passage is horribly turbulent. You'd be amazed at the total drag on most cars simply from the cooling system. ('Tis why manufacturers love small grills.)

Ergo, what is actually happening by taping up the "radiator" for a short while is that airflow through the cooling system is being reduced and airflow beneath the car is being reduced. This is not CREATING DOWNFORCE (thus creating drag) it is actually REDUCING LIFT (reducing drag). Reduced lift = reduced drag; reduced turbulent airflow = reduced drag. Reduced drag = Old Ford Falcons with pretty bodywork and decals go faster.

Quite simple, really...

...in drag "racing" they prefer lower elevations....why if higher elevation was less dense air?[/b]

Lower elevation = more dense air; more dense air = more oxygen molecules per cubic inch of air. More of that means bigger "go boom".

The power increase from the increased oxygen in denser air far exceeds the increased drag from it; to a point. For example, if I am williing to let the engine in my light airplane rev to whatever it wants, I can exceed the redline at sea level and make some serious speed from the inreased power. However, if I limit my flying to redline my best speed at attained at around 8,000 feet with full throttle (less intake restriction) due to the reduced drag. Any lower and I have to pull back on the throttle to stay within redline; any higher and I cannot make enough power to reach redline.

A turbocharged or turbine airplane, on the other hand, can fly much higher and will make better speed up high because it will hav ethe decrease drag from less denser air PLUS increased power from turbocharged manifold pressure. That's why commercial aircraft, almost all powered by turbine engines, fly as high as possible.

...why are lap times on cool days sometimes FASTER?[/b]

More oxygen = more power. More power = faster lap times.

[lateapex911]

Ergo, what is actually happening by taping up the "radiator" for a short while is that airflow through the cooling system is being reduced and airflow beneath the car is being reduced. This is not CREATING DOWNFORCE (thus creating drag) it is actually REDUCING LIFT (reducing drag). Reduced lift = reduced drag; reduced turbulent airflow = reduced drag. Reduced drag = Old Ford Falcons with pretty bodywork and decals go faster.

[/b]

Greg, isn't the "downforce" a result of all factors? Not just the removal of internal and underbody drag/lift?

My thoughts would be that the resultant increasse in downforce was due to the removal of the lift quotient under the car AND the increase in surface area of the carefully angled grill...which now acts like a diveplane.

Also, and i wish I could find the souce, I read some figures about downforce and I was amazed at the positive numbers these cars produce. (As long as they aren't going backwards)

(It makes what the guys like Lorenzen and Petty did back in the 60s more impressive)