Any aerodynamic guru's on here? need your opinions..pics inside

[oilwell1415]

I would be hesitant to do anything that only adds downforce in the rear. If you do that it will just make you burn up your RF tire.

I doubt you will learn anything about downforce with smoke. That will tell you where you have attached and unattached airflow, but you can do that with drops of water or streamers and not have to mess with a smoke bomb. If you have a long flatbed trailer you could set the car up on the scales, drive down the road with it and read the scales. Just be careful how you strap it down or the scales won't read right.

 

[Ferris Bueller]

Makes alot of sense.. So in your opinion, increasing air speed to the spoiler would create more downforce than adding a windsheild? The only reason I am pondering a windsheild is for downforce, not wind noise or anything else. I am limited on spoiler size but it seems a windshield would be a large area wing creating downforce.

How about this idea I just had, no windsheild, but a partial rear window with about 6" open between deck and bottom of rear window to guide air to the spoiler, and it would actually create a funnel effect aiming straight toward the spoiler. Hopefully that made sense, if not I can draw a simple model at work tomorrow and post up on here.

A windshield may provide some downforce, but you would lose a large part of the downforce currently provided by the rear wing. You would also increase drag over your current setup. My guess is this would be a net loss. I'm not saying it's a sure thing, but this is my assumption based on some general principles of aircraft design. I'm sure there would be a way if you spent enough time researching into it, haha.

As for the rear windshield creating a tunneling effect, you are right in assuming that this would increase airspeed, but this has some drawbacks to consider. First, it takes energy to move the air into the smaller exit area, so you would be increasing drag. Second, the rear windshield will create a low pressure area behind it when moving forward, so the faster moving air you've created moving through the small opening will then expand into the low pressure area, slowing it down to a speed less than it entered the "tunnel". The effect you are describing works best in wind tunnels, where the cross sectional area changes in a controlled manor to promote efficient high speed flow though the test area.

There was previous mention of doing something to the roof. Adding a wing like you have on the rear to the trailing edge of the roof would probably give you a net gain in downforce. This would only marginally increase drag while putting the air that is currently doing nothing to good use. You would get some turbulent flow off of the back, but it might be high enough to not screw up the rear wings aerodynamics. Just a thought.

 

[TripleBlack]

Vteeeeeekkk!

:??: Gotta keep the average up huh? :lol: :beer:

 

[key]

Shot in the dark - but are you allowed to add ducts to the car? Specifically naca ducts?

I'm wondering if adding some to the roof could increase the amount of air reaching the spoiler?

Also I have been reading about the new Ferrari and it seems they do a lot to move air to low pressure areas of the body. For instance, they pipe air out the back so that the air doesn't swirl as much back there and cause drag. Might be worth adding some naca ducts to the side, behind the rear wheels to add some more air back there. My concern with that would be that it might take some down force off the spoiler, but I can't imagine it would with any significance.

 

[James Snover]

By adding a windshield and a rear window, wouldn't it be like a cross-section of an airfoil? Where what is lost in pushing the air over the windshield is largely offset by the increase in pressure on the rear window, assuming a nice long slope to the rear window?

Jim Snover

A windshield may provide some downforce, but you would lose a large part of the downforce currently provided by the rear wing. You would also increase drag over your current setup. My guess is this would be a net loss. I'm not saying it's a sure thing, but this is my assumption based on some general principles of aircraft design. I'm sure there would be a way if you spent enough time researching into it, haha.

As for the rear windshield creating a tunneling effect, you are right in assuming that this would increase airspeed, but this has some drawbacks to consider. First, it takes energy to move the air into the smaller exit area, so you would be increasing drag. Second, the rear windshield will create a low pressure area behind it when moving forward, so the faster moving air you've created moving through the small opening will then expand into the low pressure area, slowing it down to a speed less than it entered the "tunnel". The effect you are describing works best in wind tunnels, where the cross sectional area changes in a controlled manor to promote efficient high speed flow though the test area.

There was previous mention of doing something to the roof. Adding a wing like you have on the rear to the trailing edge of the roof would probably give you a net gain in downforce. This would only marginally increase drag while putting the air that is currently doing nothing to good use. You would get some turbulent flow off of the back, but it might be high enough to not screw up the rear wings aerodynamics. Just a thought.

 

[Scottyk]

Talking it over with my dad last night "he has a fairly large garage and its long" he thinks it would be a fun project to build a make shift wind tunnel in there and set the car on the scales to measure down force.. The only problem would be getting enough wind-speed to get decent measurements. Thinking of making wooden frame work to build a tunnel from front to back of garage "2 garage doors" and finding the biggest fans we can to put in the back door and suck air out. Need to find some type of cheap material to cover the wooden frame work with.

 

[oilwell1415]

There was previous mention of doing something to the roof. Adding a wing like you have on the rear to the trailing edge of the roof would probably give you a net gain in downforce. This would only marginally increase drag while putting the air that is currently doing nothing to good use. You would get some turbulent flow off of the back, but it might be high enough to not screw up the rear wings aerodynamics. Just a thought.

The rules don't allow that, but they do allow some measure of manipulating the entire roof panel.

By adding a windshield and a rear window, wouldn't it be like a cross-section of an airfoil? Where what is lost in pushing the air over the windshield is largely offset by the increase in pressure on the rear window, assuming a nice long slope to the rear window?

Jim Snover

Yes, it is like an airfoil, but it would be cambered in the direction that generates lift instead of downforce. Luckily it isn't very efficient at doing that.

Talking it over with my dad last night "he has a fairly large garage and its long" he thinks it would be a fun project to build a make shift wind tunnel in there and set the car on the scales to measure down force.. The only problem would be getting enough wind-speed to get decent measurements. Thinking of making wooden frame work to build a tunnel from front to back of garage "2 garage doors" and finding the biggest fans we can to put in the back door and suck air out. Need to find some type of cheap material to cover the wooden frame work with.

To get meaningful data from a wind tunnel it needs to have a cross sectional area about 10 times greater than the cross section of the workpiece. For a car that means about 250 sq ft., or a 16' by 16' square, 10'x25' rectangle, etc. That part isn't hard. The hard part will be generating enough airflow. For a 20 mph wind you will need over 400,000 cfm of airflow capacity. A single 48" fan may be able to generate 20,000 cfm, so you'd need 20 of them. More speed=more fans, but you can't make the tunnel larger or the velocity won't go up, so you have to build a tapered exit that will allow more fans. $$$$

Do you have any pics of the bottom of the car? I don't remember any rules about ground clearance or what you can do to the underside. A diffuser built in the floor pan could build a lot of downforce and nobody would be able to see it and copy it unless you flipped it over.

 

[Scottyk]

Ohhh, well that pretty much kills that idea then.. Daam I thought I was on to something there, oh well. The rules state "no inner panels" what does that mean? Im not totally sure, and I bet track officials dont know either but they will argue against anything they can.. These cars catch alot of air in them because of how open the front of them is, mainly in front of passenger door "which cannot be closed off" so Im kind of skeptical to build a floor pan and trap all that air in there. I need a dam wind tunnel of some sorts

 

[oilwell1415]

The air that comes in the front should go straight out the back, so it wouldn't be trapped.

 

[DKS2814V]

Didn't read all the posts....but, can you slide the spoiler back a few inches? If you have sufficient downforce on the front, a higher load further back of the CG will give you a bit more overall moment.

Just a thought....looks like there is room, and it may pull the spoiler out towards more air movement.

 

[DKS2814V]

If you're serious about the wind-tunnel, there are several low-speed wind-tunnels around the country that are pretty cheap. I used to work at one in College Station, Tx. It was like $150 an hour to run it....not bad considering it got up to speeds way faster than what you're hitting.