Let's say I wanted to build a challenge car with lots of aero. (So effective at autox speeds). But I don't want to change the car's appearance too much. What can/should I do?
Let's say I'm ok with a splitter sticking out a bit in front of the bumper, but not ok with a giant plywood 3 element wing on the nose.
Flat bottom? Splitter? Diffuser? Ground effect tunnels? Tunnels with wings inside?
I'm no expert, but I think for aero to be effective at low speeds, it has to project a LOT of surface area into the air stream, because at low speeds the air itself just doesn't offer that much pressure per square inch.
As a theoretical exercise I suppose you could build massive tunnels through the body with internal wing elements that couldn't be seen from the outside. That would only be effective when traveling in a straight line, though. It also assumes that you don't need any internal room for, you know, engines, drivetrains, or operators.
big splitter in front, big spoiler out back made of clear lexan.
Sucker fan
I mean this is going to depend pretty heavily on the chassis and drivetrain setup. There's a lot of ways to skin the cat... but you're going to be constrained by the area available via the car's volume... and the autocross portions speed.
I'm not certain going 'suckervette 2.0' is the right approach, though. Reading Pete/Stampie's accounts of the Gainesville sight, it sounds like there's a pretty good hump in the lot... which would break a skirt's seal while transitioning.
Tunnels with wings inside are an idea I've played with conceptually. Especially if you can reconfigure them for 'bypass' for the drags (although this will have a relatively minor effect on et, so make sure the weight penalty is minimal). It's certainly a way to make maximize your 'S' term within L=-0.5*rho*(V^2)*S*Cl
But, otherwise, you're going to have to find ways to maximize Cl... which will be difficult because of the speed regime. Although, not impossible, keep in mind that Reynold's number is a function of speed and length. So, as you go slower, you need 'longer'/larger' elements to have the same flow dynamics. Additionally, there's plenty of ways to use 'forced air velocity' to compensate for low vehicle /base-air-volume speed... that don't require the same sealing demands the sucker car does. These could be passive, like VG's... or the could be active, like fans or turbo out-flows.
In reply to sleepyhead the buffalo :
That hump was always there, including when the Sucker Vette won.
SVreX said:In reply to sleepyhead the buffalo :
That hump was always there, including when the Sucker Vette won.
Guess that shows the limit of my experience with $challenge. Thanks for the clarification.
bolt a snowmobile engine in the trunk
They do some really ool stuff with Lexan in the RC car world. Same principle idea.
Or a REALY big Lexan wing like they do on the mita's on every single leading edge.
In reply to sleepyhead the buffalo :
Any ideas on how to make a long and skinny high downforce airfoil? (Large chord low wingspan)
It's my impression that in general camber makes downforce, and unfortunately if you want to make camber on a wing with large chord then you need a lot of vertical space as well as horizontal space.
But yes, making the wings removable so the tunnels become a simple frontal area reduction for the drags is cool too.
SVreX said:
Some cool ideas there, thanks!
Robbie said:In reply to sleepyhead the buffalo :
Any ideas on how to make a long and skinny high downforce airfoil? (Large chord low wingspan)
It's my impression that in general camber makes downforce, and unfortunately if you want to make camber on a wing with large chord then you need a lot of vertical space as well as horizontal space.
But yes, making the wings removable so the tunnels become a simple frontal area reduction for the drags is cool too.
Robbie, what you are describing is typically called a "cascade". Think of it as something like a turbo impeller or jet engine intake fan section that is laid out flat rather than being wrapped around a central axis. Basically you can use the same shape repeated to get your length. The efficiency is limited by the width. Wider is better, but can be helped a fair bit with endplates or walls (which you could use to support the element of the cascade). The cambered plate you focused on for the challenge car lends itself to cascades quite well, but could be made of lighter/stiffer materials to reduce the unintended consequences. Also, try to get the leading edges more generously radiused and the trailing edges sharper. The shape of the cascades does not have to be exactly the same for all elements, but it would make production easier if they were.
These types of devices are used in the corners of wind tunnels (turning vanes is the common name) to help keep the airflow more or less even across the section, even when the air is turned 90 degrees. They can be quite efficient, but they do take up a fair bit of space. If you could come up with a catamaran style body, you could use a cascade along the entire center section.
Slot gaps become the biggest tuning tool behind the camber of each segment/element. Adjusting the pitch of the elements can be ganged together if they are all the same shape, which could be activated differently for forward acceleration Vs cornering acceleration (drags Vs autocross) or even infinitely between the two if you built a control system (mechanical or electronic).
Robbie said:In reply to sleepyhead the buffalo :
Any ideas on how to make a long and skinny high downforce airfoil? (Large chord low wingspan)
It's my impression that in general camber makes downforce, and unfortunately if you want to make camber on a wing with large chord then you need a lot of vertical space as well as horizontal space.
But yes, making the wings removable so the tunnels become a simple frontal area reduction for the drags is cool too.
You can do a remarkable amount of turning in a tunnel without having turning vanes in it. You can turn more in a tunnel if you add velocity to the stream within. And you can do that by either reducing the area before the turn (but not so much that you choke the flow), or by electro-mechanical means (fans, compressors, etc).
I think the big challenge, and it's always the big challenge, is going to be making enough front-end downforce. Especially if there's and engine/motor up there to contend with. I've been thinking on/off about rally cars and their widened fenders, and the louvered exits... and that weird sonata front grafted onto a civic hatch body that got hot linked a couple times (and how trackwidth is usually a detriment to autoX times).
One of the other hurdles to ducting inside the unibody is the offset driver volume, and the firewall area. There's some interesting possibilities with taking a windshield & (some, all?) windows out for the autocross and putting them back in for the drags... then you've got a a roof acting like a first element. But, you'll have to work pretty hard to direct the flow around the driver and where you want it. Or, how if you want to draw air in from underneath, how you'd want to run larger diameter tires, to give you more volume underneath, but how raised ride height is usually a detraction for AutoX.
I realize you're holding things close to your chest... and there's a wide range of platforms and powertrains on the table. But, just like the DeltaWing and GTR LM Nismo... you can accomplish similar goals with radically different approaches/platforms. So, it's complicated to map the terrain and give suggestions when there's so much available terrain via you initial 'brief'.
Hidden aero for auto-x speeds might be difficult. But see-through aero, as spacecadet and wearymicrobe mentioned, is totally doable. And potentially even cooler looking.
Imagine bolting a huge pikes-peak splitter and wing onto a regular car, but having all of the sticky-outy-bits made up of a clear polycarbonate. Kind of like this, but with all of the black add-on pieces being made out of clear plastic:
From a distance the car would look like it was just a regular unassuming budget hatchback. You'd have to give it a second glance before you realize that some insane person has had his way with the car. And then a third to recognize and appreciate the hard work that went into making it possible.
Fabrication would be relatively straightforward because most of the elements are just made up of large, flat plates. The large fences on the sides of the splitter give you extra reinforcement on the sides so you can run a longer splitter without needing visible front support rods.
You'd just need some clear track tape to protect the leading edges, and several cases of this stuff to keep it clean:
This car and aero concept has always been interesting to me:
http://www.speedhunters.com/2012/06/for-my-ally-is-the-force/
Not sure that it would be super effective at autocross speeds but since I have seen it I have wanted to cut the floor out of the low buck endurance racer I have to see the effects of it.
I forgot you had the Datsun... now F-Dat. Is that the platform?
If so, then re-reading loosecanon's thread is a start. I forget what the mgb's predicted total downforce numbers are. but, that'd be the beginning of a ballpark.
alpinecoupe said:This car and aero concept has always been interesting to me:
http://www.speedhunters.com/2012/06/for-my-ally-is-the-force/
Not sure that it would be super effective at autocross speeds but since I have seen it I have wanted to cut the floor out of the low buck endurance racer I have to see the effects of it.
Now that's cool! Thanks for the link
In reply to sleepyhead the buffalo :
Yep, this is for the F-Dat
Robbie said:In reply to sleepyhead the buffalo :
Yep, this is for the F-Dat
so, yeah... the F500 chassis makes me think about this...
I honestly don't know if the tunnel needs to be exposed to the ground, or if you can blank off the bottom with a 'splitter' between the wheels. I'll defer to stafford1500 on that. One of the challenges with draping the datsun body over it, will be feeding those tunnels... and extracting as much downforce as you can will be important because it's kind of "balance neutral"... which is somewhat rare in modern motorsports. Although... it's kind of complicated by where you exit the flow out of? I'll dig around, but do you have a shot of the rear of the Datsun handy? It'd also be handy to have 'planform dimensions' (i.e. x & y from above) of the hood, and the 'sidepods' on the f500 chassis.
off hand, though, from you original question:
1) Yes, you'll want a front splitter... but probably nothing extending outside the width of the wheels, and probably doesn't need to go forward too much
2) Yes, you'll probably want a diffuser... but that'll mainly be partially cosmetic, partially to lower drags for the drags, and partially to aid extraction of the 'sidepods'
as ever... this is only worth $0.04 (my .02 and the .02 for my degree 
), it's only a suggestion, caveat emptor & lector, ymmv, etc
In reply to sleepyhead the buffalo :
I can get you those dimensions shortly
Robbie said:Let's say I wanted to build a challenge car with lots of aero. (So effective at autox speeds). But I don't want to change the car's appearance too much. What can/should I do?
Let's say I'm ok with a splitter sticking out a bit in front of the bumper, but not ok with a giant plywood 3 element wing on the nose.
Flat bottom? Splitter? Diffuser? Ground effect tunnels? Tunnels with wings inside?
I forgot you had the Datsun... now F-Dat. Is that the best [invisible canoeing platform?]
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