Aero

External options and variations: rear end mods, side vents, doors, cage mods, wings(!), etc.
Marcus
Posts: 9
Joined: 03 Jan 2011, 07:44
Anti-spam question: 4
Are you a spammer: No

Re: Aero

Postby Marcus » 18 Jan 2011, 18:39

Just a thought for my build, what your doing makes sense... I don't know how you would work out the looks without a radiator opening in front...

JackMcCornack
Posts: 10
Joined: 24 Dec 2008, 21:14

Re: Aero

Postby JackMcCornack » 19 Jan 2011, 21:29

Noted this from a post about a year ago:
Midlana1 wrote:... I'd been told that a Super Stalker, hitting 150 mph at the end of the longest straights, was lifting the front tires clean off the ground. I had a very hard time believing this and expected my buddy to agree it's impossible - but instead he said that it may very well have happened.
I ain't buyin' it. While a Stalker/Locost/Seven body surely generates lift at speed, it's not at the optimal angle of attack for maximum lift 'cause the nose is too low. So, if this happened, and the front wheels came off the ground from aerodynamic lift, why did they come back to the ground? If this were for real, lift would have increased as the nose got higher, which would have lifted the nose even higher, which would have increased lift even more, which...

If you have a car with sufficient lift to take its front wheels off the ground, there's nothing a driver can do to put them back--it's going over backwards at best, going airborne at worst. Your mileage may vary, but...nah, I don't think so.

spmF1000
Posts: 24
Joined: 08 Nov 2009, 10:16
Anti-spam question: 4
Are you a spammer: No
Contact:

Re: Aero

Postby spmF1000 » 19 Jan 2011, 21:50

Rolling tires in ground effect create lift on their own due to the high pressure field in front of them. If enough lift is generated to just get them off the ground, the tires would lose lift once they leave the pavement. If this loss in lift is enough to offset the gain in lift from the increased angle of attack, then they will return to the ground.
http://www.sm1design.posterous.com

Midlana1
Site Admin
Posts: 2537
Joined: 19 Dec 2008, 16:44
Anti-spam question: 4
Are you a spammer: No
Location: Southern California

Re: Aero

Postby Midlana1 » 20 Jan 2011, 06:40

I tend to agree with Jack. Lots of lift at the front, sure. But wheels completely off the ground down the entire straightaway? No - it's an unstable system. Since the back tires are pushing the car, it's like pushing a pencil across a table, or balancing a broomstick on your finger. The "push" is going in a straight line, but the nose of the car, being off the ground, has zero ability to prevent it from moving left or right, and wants to go any way except straight forward, so it'll rotate, spinning the car.

I think what really happens is that lift causes, oh, 70% of the weight on the front tires to go away, resulting in a very light steering wheel and an extreme case of understeer (the inability to alter the course of the car.) Between no steering feedback and not being able to steer,the driver would feel as if the front wheels are off the ground. (I also agree that if there's only lift and no downforce, the car would do a backflip once the bottom of the car increased above 0 degrees pitch.)

JackMcCornack
Posts: 10
Joined: 24 Dec 2008, 21:14

Re: Aero

Postby JackMcCornack » 05 Feb 2011, 12:02

spmF1000 wrote:Rolling tires in ground effect create lift on their own due to the high pressure field in front of them.
True, solid objects in transit through fluids will do that, and the common example is aquaplaning. A car (given enough speed and a tire design that doesn't bleed off the high pressure field through the tread) may ride on top of water that's on top of a road, but it won't ride on top of a lake. I'd say Midlana is a candidate for aquaplaning, as is the Stalker--they're light, they're fast, and they're going to get driven on relatively wide tires--so if it's raining on race day, you'll want to leave your slicks in the truck.

Air will have the same behavior, but since air is less dense than water, the "given enough speed" part of the equation goes up accordingly. Figuring a density difference of 900 (a good rule of thumb figure because it makes the math easy, though air density varies with altitude and temperature--when predicting water tunnel results on a cocktail napkin, specific gravity of air = 1/900) and presuming that dynamic pressure varies with the square of speed (which it does, for all practical purposes, at least at automotive speeds) the aquaplaning speed x 30 = the aeroplaning speed.

So a car that lifts the front wheels atop high pressure ground effect on water at 100mph, will do the same on air at about Mach 4, 3000 mph, whereas body effects could conceivably lift the front wheels (and keep lifting until the car flipped over backward) at 200 mph...which if true would make the tire ground effect less than 1/2% as influential as body effects. Which could surely be enough to win or lose a race, but it's not enough to hold a car stable in pitch. Unless you designed a car on purpose to hold its front wheels off the ground at speed (it could be done with a very large wing behind the rear axles), if the front wheels come off the ground and stay off the ground at top speed on a straightaway, the rest of the car will follow.

Sheesh, that was a lot of lecture for something that only I am obsessing about. Move along, there's nothing to see here.

spmF1000
Posts: 24
Joined: 08 Nov 2009, 10:16
Anti-spam question: 4
Are you a spammer: No
Contact:

Re: Aero

Postby spmF1000 » 05 Feb 2011, 22:07

That is true if you're assuming all of the forces needed to lift the front tires are generated exclusively by the wheels. I know the story is just here-say and is likely an exaggeration if the car was on flat ground. Going over a crest would be another story.

All that aside, the case I was making is that the lift of the front end may not necessarily be an unstable condition where the car flips ends. Hypothetically, if the loss in lift from the wheels no longer being in ground effect exceeded the lift gained due to increased angle of attack, then the front end would return to the ground. So, like I said, it's not likely to happen but if the conditions are correct it could happen.
http://www.sm1design.posterous.com

wakohn
Posts: 1
Joined: 06 Dec 2017, 09:46
Anti-spam question: 4
Are you a spammer: No

Re: Aero

Postby wakohn » 06 Dec 2017, 12:24

Midlana1 wrote:I talked to a buddy who knows all about this, or at least, knows of the people who know about this. I asked for his thoughts on how I'd been told that a Super Stalker, hitting 150 mph at the end of the longest straights, was lifting the front tires clean off the ground. I had a very hard time believing this and expected my buddy to agree it's impossible - but instead he said that it may very well have happened. He said that a traditional Seven shape has a nasty (aerodynamically-speaking) curved nose which generates a great deal of lift. I pointed out that a Super Stalker carries 800 lbs on its front tires, but he said that it could happen.[/img]


If the Stalker has its radiator in a laid back position similar to the Midland you will get lift just from that. The faster you go the more lift you will get. This was a problem with the original AC Cobras and one of the reasons for the Daytona Coupe to come into existence.


Return to “Body mods and options”

Who is online

Users browsing this forum: No registered users and 1 guest