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If you collect data, specifically the acceleration G channel you can calculate the acceleration in m/sec and then graph it against speed to draw a graph.
this is from consecutive sessions in November
This is from an August session and the November session. As you can see the acceleration has improved. Now acceleration can be effected by power, weight or drag. Since the cars power and weight have not changed but there have been some small changes to reduce drag.it could be safe to infer that drag has reduced. The data could be made more accurate by filtering out data that has too much linear g forces.
That's obvious, but the second you change anything else, or in the case of my car - everything else (and ignore the fact that the weather can change this too), this becomes impossible to quantify.
This means collecting data is down to spending some thousands of dollars on CFD and that's a no-go.
Originally Posted by Madjak
Most low drag cars actually have the nose up higher with a focus on diverting air to either side rather than over the top of the car.
I was merely bringing the question back because I don't know that this ^ is the case at all, I'd love to see an example of this.
The examples I can come up with for this taking any kind of form are either rule driven necessity or an extreme example that does not apply to the world of racing where you're after both reduced drag AND downforce, enter solar powered hypermilers here.
I made a quick fastback from the plastic alloy composite material. Took about 1.5hrs to come up with the design, cut it out and bend it. I was goin to pull some cloth over the back of the car and saturate it in resin to ake it stiff, but this was easier and quicker. It is just a test piece to see how the aero is working. I will do some runs with wool tufts.
I have a spare hood and will put some vents in to see how that changes things too. So once i have done a couple of sessions i will take off the fastback and put some more wool tufts on to see the difference. Then take off more aero to get some comparisons.
What material was used for this fastback, brand/name/specs.? tks.
I was merely bringing the question back because I don't know that this ^ is the case at all, I'd love to see an example of this.
The examples I can come up with for this taking any kind of form are either rule driven necessity or an extreme example that does not apply to the world of racing where you're after both reduced drag AND downforce, enter solar powered hypermilers here.
I am curious to understand the logic behind the lowered front end AND the statement made about forcing air around the car instead of over it as well. If you look at creampuff from the front, the frontal area of displaced air does not appear to have changed, but the profile from the side is drastically different. Intuitively it would seem to me that the low front end would be a drag reduction effort due to a shorter air dam with a compromise to having less downforce if all else was equal, but I'm just spit-balling what makes sense to me. The downforce that I'm speculating was lost is definitely gained back, plus some, with the addition of the "carbon splitter from the gods" so as a whole it would seem you improved your lift/drag ratio by doing the combination of both the splitter and front end work?
It's awesome to see experimentation at this level being done. I'm just trying to learn as much as I can for my own car in the meantime as I've just begun to dabble in the aero fun.
The around the front nose instead of over/under is counter-intuitive to me. I would think the less distance the air has to move would give it the least resistance. Since the car is wider than taller it would mean to me that around the sides would be more work (and thus more drag) than going over / under. I'm sure there's a point where moving 90% of the air over and only 10% under is less productive than 50 to the left and 50 to the right. I don't know where that inflection point is though.
The around the front nose instead of over/under is counter-intuitive to me. I would think the less distance the air has to move would give it the least resistance. Since the car is wider than taller it would mean to me that around the sides would be more work (and thus more drag) than going over / under. I'm sure there's a point where moving 90% of the air over and only 10% under is less productive than 50 to the left and 50 to the right. I don't know where that inflection point is though.
Only reason to seek to shunt air down the sides is if you have aero devices doing work there. Otherwise, you are better off directing air over the top to hit the wing. It's also easier for the air mass to flow into the void behind the car from the top after it passes.
In classes or situations where a front air dam is not required to be vertical, the simple fix is to slant the nose at 20-30°. This allows the pressure bubble building up on the nose to exert some downward pressure and also requires less pressure differential to escape over the hood. Small downside is you need to extend the splitter further forward to provide a horizontal surface for that pressure bubble to work on. Slanting the nose has almost the same benefit as reducing the height of the nose. Frontal area is dictated by windshield height anyway.
Our next time attack build for Unlimited will have a slanted nose. Not nearly as radical as Crushers experimental slant nose pictured here from early 2012. This nose was a low drag config I designed specifically for enduro. It worked very well but was about 1" too low and was damaged a bit underneath. Sent back to autokonexion to be modified and he lost it, never returned my calls. Who knows where it ended up.
That's obvious, but the second you change anything else, or in the case of my car - everything else (and ignore the fact that the weather can change this too), this becomes impossible to quantify. This means collecting data is down to spending some thousands of dollars on CFD and that's a no-go.
Agreed weather can affect the results. What I was trying to point out was that there are quick ways of determining/evaluating changes and the effects without having to resort to spending large sums. At a minimum G forces and speed are all that is required in my example. If a car was road registered then it would be possible to do coast down testing which takes even less technology. The next step up would be linear sensors on suspension but this is not very cheap!
What I try and do is look for % change in the data. I was also very careful to not use the word "correlate" rather used "infer".
Only reason to seek to shunt air down the sides is if you have aero devices doing work there. Otherwise, you are better off directing air over the top to hit the wing. It's also easier for the air mass to flow into the void behind the car from the top after it passes.
In classes or situations where a front air dam is not required to be vertical, the simple fix is to slant the nose at 20-30°. This allows the pressure bubble building up on the nose to exert some downward pressure and also requires less pressure differential to escape over the hood. Small downside is you need to extend the splitter further forward to provide a horizontal surface for that pressure bubble to work on. Slanting the nose has almost the same benefit as reducing the height of the nose. Frontal area is dictated by windshield height anyway.
Our next time attack build for Unlimited will have a slanted nose. Not nearly as radical as Crushers experimental slant nose pictured here from early 2012. This nose was a low drag config I designed specifically for enduro. It worked very well but was about 1" too low and was damaged a bit underneath. Sent back to autokonexion to be modified and he lost it, never returned my calls. Who knows where it ended up.
I like that a lot. They'll probably have it on their site soon enough. It's time for me to start looking at the front end on my car. I've been scouring this thread. But I like this one better than the rest.
I'm actually not sure which is better... lower tapered nose or original. I think it all depends on the other aero on the car.
So most open wheelers will work better with a raised nose, but these aren't pushing air that far sideways. Other cars with a raised nose are tear drop shaped cars designed for super low drag.
I think the optimal shape for sedan is half a tear drop cut in half by the ground. The closest you can get to this the better it is for drag.
For a normal miata, lowering the nose pushes a larger percentage of the air up over the roof effectively increasing the height. Whilst a normal nose pushes more air underneath and to the sides. Which is better I don't know but there will be an effect on the downforce generated at the splitter and also more air / turbulence? at the rear wing.
I need to get into cfd and have a play.
My planned WTAC build will have the body dropped on the chassis 50mm and widened for extra track. I have to run a windscreen so I don't think a dropped nose helps or not.
This is exactly the reason I was asking to see what you had in mind as an example, open wheel and solar student challenge cars aside, there's really not much, and Emilio pointed out, unless something works for you on the sides it's better to have the air running on top.
The half tear drop shape you're describing isn't as low on drag on drag as you might think and to add an insult to injury it's also huge on lift since you're essentially creating an airfoil, hence why older 911's (which are the shape you describe) are lower on both drag and lift once the wing was added in.
For a hatchback a Kamm back takes you most of the way there, but not applicable for a Miata, a fastback is most likely the happy middle ground if you're allowed to run it.
How are you planning on dropping the body? cut the frame rails and lift the driveline from the subframes up?
Wider track does allow you to vent out the front fenders more effectively which is a good thing, on Creampuff I had to do a bunch of scary cutting to vent out the front more effectively, it's kinda hard to see in pics but the new front fenders are tapering inwards many inches more than the previous version.
How are you planning on dropping the body? cut the frame rails and lift the driveline from the subframes up?
Wider track does allow you to vent out the front fenders more effectively which is a good thing, on Creampuff I had to do a bunch of scary cutting to vent out the front more effectively, it's kinda hard to see in pics but the new front fenders are tapering inwards many inches more than the previous version.
I have detached the outer body skin from the rest of the chassis. There are 3 vertical plates in the sills that are the heaviest part of the body so its the best way to remove them. Once the floor, firewall and shock towers are trimmed to bare minimum I'll reweld it back together but with a 50mm drop. I need to get 200kg out of the car so the chassis needs to be light.
The area around the drivers seat might meed to be dropped and the transmission tunnel will get modified to fit over the drivetrain.
I'll start a dedicated build once I get a bit further into it.
I take it that you're working on an NA chassis which makes a lot more sense for WTAC than the NB.
Your plan sounds a lot like what I've looking at doing with Morpheus in terms of the weight drop at the rockers, also works well for narrowing them down.
Looking forward to see it
I take it that you're working on an NA chassis which makes a lot more sense for WTAC than the NB.
Your plan sounds a lot like what I've looking at doing with Morpheus in terms of the weight drop at the rockers, also works well for narrowing them down.
Looking forward to see it
Does the aero on the swan neck work out better with the mounts on the top side of the wing? It looks like it could help with packaging setting the wing further back too.
Yes, the air under the wing typically does more work than the air over the top. Also imo well designed swan neck mounts also act to straighten out the airflow when it's not perpendicular to the wing.
We built some quick and dirty end plates for the GT1000 on Bullet yesterday at Buttonwillow. 16" wide, 20" tall, with about 15" of that below the foil. Someone driving behind me on track told me the end plates were being sucked inward several degrees below the foil. Dat low pressure.
Material is some cheap wet carbon plate off of Amazon. Not nearly as rigid as proper dry carbon so we'll chuck them and do it over with more rigid stuff.
That is what I'm going to, the video was done to confirm what the simulation was saying...
Will post a video comparing the two when my wing is done. Will also make it a bit more stable!
Also did some video on vortex generators (on/off). The ones on the car are made by Airtab | Aerodynamic Fuel Savers | About Airtab and they do appear to give some benefit, however not around the edges on the window. Plan is to get some different types of vortex generators and test them out. Will try and install them down the side of the hardtop to see if this will clean the air up.
We built some quick and dirty end plates for the GT1000 on Bullet yesterday at Buttonwillow. 16" wide, 20" tall, with about 15" of that below the foil. Someone driving behind me on track told me the end plates were being sucked inward several degrees below the foil. Dat low pressure.
Material is some cheap wet carbon plate off of Amazon. Not nearly as rigid as proper dry carbon so we'll chuck them and do it over with more rigid stuff.
That's why you see a lot of endplates with the trailing edge flared out 30-45 degrees, makes the end plate a bunch stiffer with minimal aerodynamic downside and no added weight.
11-22-2017, 03:48 AM
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