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19 hours ago, JDChristianson said:

What’s the best way to adjust aero for balance, or different conditions ( ie dry v wet).  Wing angle?height?  Splitter?   I think it’d be cool to have a splitter that’s adjustable in and out. Is that a waste or time? 

Our splitter is (was) adjustable in both height and length and we would start with wing AoA for adjustments and once we felt we were adding too much wing, we would pull splitter length back or if we were damn near laying the wing flat, we would start to pull the splitter out.  All referenced against lap times

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Disclaimer: I have no formal aerodynamics training and most of this info I am going to share I have just picked up on the side for fun. Feel free to critique anything I am about to say.   I

one more before i hit the road.  not quite.  The air being directed over the top of the car does add downforce. It's not the temp to blame, it's the speed. So to make downforce, the general

Put a hole in the top of the fender above your control arm/spindle/whatever. Attach a rod to the top of your control arm that is long enough to protrude above the fender at full droop. Mark the rod at

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1 hour ago, ablesnead said:

Mender , I am  pretty sure you are full of baloney....that  is why I am hoping an expert will chime in'....

 

What Mender said is correct. You're removing air that would otherwise be flowing underneath the car, and instead turning it upwards. There's a reaction force component and a reduction of pressure underneath the front of the car.

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1 hour ago, ablesnead said:

Mender , I am  pretty sure you are full of baloney....that  is why I am hoping an expert will chime in'....

 

He's not new to this and he's no dummy either.

 

Listen to him he speaks the truth.  Look at all of the manufacturer built.cars in JGTC, Super GT, ALMS, and WEC.  Many of them sport ducting to vent heat exchanger air up out the hood.

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1 hour ago, ablesnead said:

Mender , I am  pretty sure you are full of baloney....that  is why I am hoping an expert will chime in'....

You forgot the green font ... ;)

 

If not, let's hear why you think otherwise. :)

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1 hour ago, SonsOfIrony said:

 

He's not new to this and he's no dummy either.

 

Listen to him he speaks the truth.  Look at all of the manufacturer built.cars in JGTC, Super GT, ALMS, and WEC.  Many of them sport ducting to vent heat exchanger air up out the hood.

I run a hood vent on the TT its in a low pressure zone right behind the radiator its there to help pull  heat out only to help cool the car!! I list it as ducking for the radiator.

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I didn't forget the green font , But glad you knew it was intended  , if  I knew how  how to do the green font thing I would have .....At any given speed , and the resultant pressure  beneath the car there is a fixed volume of air more without a dam and splitter , less with one ....it that volume of air is warm  it has less mass  , to resist the downforce , that any devices added to produce that  ,apply....Now with warm air flowing over the car there is  lift ...that means it would contradict  the down force devices to an extent...how would that help.....I have a big hole in my hood to provide a low pressure spot behind the radiator to promote flow and the resulting cooling.....this Quandary I have isn't about hood vents as a useful tool...it just doesn't  gel with cool air higher pressure , warm air lower pressure....To muddy it up more for me  , I have seen warm air ducted under downforce devices to make them more effective , but other than the hood vent , never over them.....where in the hell is that expert guy !

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1 hour ago, ablesnead said:

I didn't forget the green font but glad you knew it was intended. If I knew how how to do the green font thing I would have .....

 

At any given speed, and the resultant pressure beneath the car there is a fixed volume of air more without a dam and splitter, less with one. If that volume of air is warm, it has less mass to resist the downforce that any devices added to produce that apply. Now with warm air flowing over the car there is  lift. That means it would contradict  the down force devices to an extent; how would that help?

 

I have a big hole in my hood to provide a low pressure spot behind the radiator to promote flow and the resulting cooling. This quandary I have isn't about hood vents as a useful tool: it just doesn't gel with cool air higher pressure, warm air lower pressure. To muddy it up more for me, I have seen warm air ducted under downforce devices to make them more effective, but other than the hood vent  never over them.

 

Where in the hell is that expert guy?!

At the top of the reply box you'll see a bold capital A with a line under it. That's where the colour options are. Highlight the text you want to change and select the appropriate colour (green for sarcasm, red for irony, I usually use blue for "edits") and click - done! And my wife is a teacher so I get to help mark papers. I apologize for editing your post for punctuation and such but I can't help it! ;)

 

I suspected that's what you were getting at, and it sounds like you're referring to an exhaust blown diffuser with your warm air and downforce example. I'll let the expert sort this one out for you. :)

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On 2/19/2019 at 8:08 PM, wvumtnbkr said:

Is a splitter necessary for this type of racing or can an airdam be effective by itself?

an Air dam does help. mostly with drag in most cases. although a splitter would help a great deal, if you could incorporate a belly pan you'll notice a performance increase in front downforce with minimal drag increase. 

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On 2/19/2019 at 8:36 PM, SonsOfIrony said:

Aerodynamically where do we go next?

 

Home made diffuser?  Side skirts?  Both?

 

Have a bottom mount single element wing that will be replacing the Lexan rear lip.

 

We are power limited, and maximizing cornering speed has so far proven the only way to be fast.  The car is relatively stable now, but I know we're leaving grip on the table.  Will skirts and a diffuser held reduce drag and increase total downforce enough to be worth the time investment?

 

Thanks.

FB_IMG_1550626321229.jpg

 a wing will help you most. ours is only 9lbs of drag, that spoiler might be a hundred lbs.  the small spoilers can add good downforce. problem is we have seen 5" spoilers add up to 50% of a vehicles drag.  with limited power you want to fight drag at all costs.  things you should do before a diffuser. 

- cover those headlight holes with levan. that's a biggie. 

- add something to the Pass side window. lexan if the rules allow it, otherwise a window net pulled very tightly. 

-your radio is located in the area with high-speed air, try moving it to behind the greenhouse. 

Drag is death by a thousand papercuts try to limit it especially at the front of the car. . 

 

 

 

 

 

On 2/19/2019 at 8:54 PM, JDChristianson said:

What’s the best way to adjust aero for balance, or different conditions ( ie dry v wet).  Wing angle?height?  Splitter?   I think it’d be cool to have a splitter that’s adjustable in and out. Is that a waste or time? 

 

the best way is with a wing's aoa. normally the front splitter and front aero are static (doesn't move). we then can adjust the wings angle to match the fronts downforce. ideally, you want a balanced aero set up.  

 

 

On 2/19/2019 at 9:59 PM, mindspin311 said:

Adding downforce while limiting drag. We all want huge wings and giant splitters, but those come at a cost, drag. As budget racers, how can we get an idea of how much drag we're adding? Most reputable wings will come with that data, but what about a homemade plywood splitter?

 

splitters are low drag. not no drag, but low. a wings drag all comes down to the shape and how the air flows around it. i've tested huge wings that all the made was drag,  with our wing, drag is very low in fact many people take other wings off and gain top speed with ours. You're looking for a lift to drad ratio. there is no free lunch with downforce and drag, but you're looking to get the most cheeseburger for your dollar.  

 

a link to our cfd numbers https://9livesracing.com/cfd-testing

 

On 2/19/2019 at 10:33 PM, MMiskoe said:

Similarly to what others have asked.

 

Most of these cars are speeds less than 100mph for most turns, 130mph top straight line speed.  200WHP or less.  Based on this, what provides more gain?  Making the the car more slippery in air with air dams and flat bottoms or adding splitters, wings & diffusers?

 

Pretty generous of you to offer this advice.  We're all basing our efforts on guesses and "well, it looks faster".

 

 

 

the Goal for most cars is lap times. with a secondary goal of MPG.  Lap times and average speed being joined at the hip, we need to raise average speed to make a faster lap. The easiest way to raise an average is to raise it's the lowest number. sorry if I'm getting mathie'. added downforce can suddenly raise road atlanta's turn 3's apex speed from 70 to 72, you've just increased your average speed and will get a faster lap. fastest lap, and no mistakes, mean you'll win. now aero comes with a drag penalty, and drag means less mpg. I've found that generally speaking a wing like ours with only 9lbs of drag, that is substantially less drag than a brake duct, or an oversized radiator opening. On most cars that the builder hasn't considered drag, you can go faster with aero and have less drag by fixing issues.

 

Clif noses make it streamline... the whole body, add aero,  you could gain mpg and drop lap times.  

 

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On 2/20/2019 at 12:03 AM, mender said:

I can answer that one: venting the air through the hood (I assume that you mean from the rad from the hot air reference) adds downforce by changing the position and speed of the air coming into the radiator. Changing the location and speed requires force, and the car provides that force.

 

For every action there is an equal and opposite reaction, so the car gets forced down as the air gets forced up.

 

 

On 2/19/2019 at 11:13 PM, ablesnead said:

In have a general question ....Hot air moves faster and is less dense ....so why do people think venting air over the hood helps down force...isn't the opposite true ?

 

one more before i hit the road. 

not quite. 

The air being directed over the top of the car does add downforce. It's not the temp to blame, it's the speed. So to make downforce, the general rule of thumb, is Fast under-Slow over. that creates the pressure difference and forces an object down. To make lift it's slow under-fast over. that's why airplanes mount engines and large objects on the bottom of the wing and the top is smooth. to help airspeed.  

To take the applied Fast under-slow over the concept and we apply it to a car. the air that passes through a radiator is moving very slowly,  with your hood closed and no vents, the only path for it to take us under the car. this mixes slow air from the rad and fast-moving air. That mix creates turbulence, and turbulence is slow, not good in an area we are trying to speed up.  we want to keep the air under the car as fast as we can. to fix this issue We take that slow-moving air and we force it (with ducting)  to go up. this speeds up the air under the car, increasing downforce and it slows the air going over the top of the car...also... increasing downforce. so that's why you see hoods vented up.  

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20 hours ago, @NineLivesJohnny said:

 a wing will help you most. ours is only 9lbs of drag, that spoiler might be a hundred lbs.  the small spoilers can add good downforce. problem is we have seen 5" spoilers add up to 50% of a vehicles drag.  with limited power you want to fight drag at all costs.  things you should do before a diffuser. 

- cover those headlight holes with levan. that's a biggie. 

- add something to the Pass side window. lexan if the rules allow it, otherwise a window net pulled very tightly. 

-your radio is located in the area with high-speed air, try moving it to behind the greenhouse. 

Drag is death by a thousand papercuts try to limit it especially at the front of the car. . 

 

 

Excellent info, Thank you.  Most of the headlights are covered.  Just one side is open for the air filer, and it's boxed in to create high pressure there.  Is that causing more harm than good?

 

Moving the Antenna is easy.

 

Not sure if nets are allowed on the passenger side, Lexan is not.  Is there a way to make a deflector that will kick air around the opening without causing too much turbulence/drag?

 

 

FB_IMG_1550840890848.jpg

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On 2/21/2019 at 8:47 PM, ablesnead said:

thanks  that helps , although the speed of warmer air kinda messes with the over under ratio ...

 

The effects of velocity, pressure, and temp are not all the same magnitude. While true that warmer air is less dense in this case temp has so much less effect that the net gains you get with velocity and pressure gains far outweigh any loss you get with the warmer air.

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Thanks mhr650 , I really to want to understand this , and am asking not arguing..So  if the stalled air   thru the radiator , with its reduced velocity, goes over the top of the car , where you really want the slower air , relative to the underside , how is that a down force multiplier......I am trying to reconcile the greater velocity outweighing the heat  density part of your response , because hot air is faster air...and faster air is better underneath the car...The above is not very clear , but maybe you can grasp my quandary....

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2 hours ago, ablesnead said:

Thanks mhr650 , I really to want to understand this , and am asking not arguing..So  if the stalled air   thru the radiator , with its reduced velocity, goes over the top of the car , where you really want the slower air , relative to the underside , how is that a down force multiplier......I am trying to reconcile the greater velocity outweighing the heat  density part of your response , because hot air is faster air...and faster air is better underneath the car...The above is not very clear , but maybe you can grasp my quandary....

 

First a question, and then a comment.

 

Why do you think hot air inherently moves faster?

 

 

You're correct in saying that increasing the speed of the flow under the car is good. However, the best way to do this is by decreasing the amount of air flowing under the car. Less air having to fill the same volume means pressure goes down and velocity goes up. This is why sideskirts are important on a car trying to take advantage of ground effect. An airdam and splitter keep most of the air in front of the car from flowing underneath it, and the sideskirts resist air flowing in from beside the car. Fixed-volume theories only work if you have a mostly fixed volume.

 

Put simply, think of it like stop-and-go traffic on a highway. What's the better way to make the traffic flow faster: adding more cars to the road that are moving quickly, or removing half the cars from the road?

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Forget heat.  The delta of the hot air to the cold air is not very great in the entire scheme of things.  It's not like it is super heated.  You can hold you hand 1 inch off the air coming out of a radiator.

 

Turning air creates a force.  Venting the hood helps it vent over the car and creates some downforce.

 

Not allowing the air under the car also creates downforce by the above post description. 

 

There really is no aero downside.  (I would think the drag is no more than a slight adder compared to the air being forced through the radiator.)

 

There can be a downside if your radiator overheats or your exhaust melts stuff from too much under hood heat.

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