Hug the road

[Losiboy784]

I just wanted to know how people are going to keep there cars on the road? I just think when you get to 100 mph it is going to be hard for people to keep the cars form flying off the road. Could you put a wing on the front and the back, would that help? Please Inlighten me.

[Chris LaPanse]

Probably a clipped down wedge (like 1/8 on road bodies)

[Combatcm]

At those speed there will be at least 10 lbs of downforce

[cretin]

indy cars get enough downforce to run inverted at 120 (theoretically, i don't know of anyone willing to try it), so i don't think it'd be hard for professional rc builders to figure it out.

[DualBL]

the Saleen S7 creates enough downforce at 160mph and up, that it would be able to drive it upside down, and it'd stick to the road.
-Nick

[Chris LaPanse]

So do most high performance cars. How do you think an indy car can pull 4G corners? The only ones I know of that don't produce a lot of downforceare Daytona cars, and even they produce enough to stick to the road. I honestly don't think there will be any problem, unless there is a bump in the track.

[SteveK]

I think for this contest, ground effects and underbody aerodynamics will definitely have to be taken into account. Bodies will have to be reinforced against the downforce, but something will have to be done to prevent air from collecting under a body that is essentially a hard parachute in the event of the aerodynamic seal being broken.

While the wedge body isn't a bad idea, it's not the best idea. NASCAR teams tried this in the 70s, and when they began putting their cars in wind tunnels in the 80s, they found they would have almost been better off running the cars tail-first. It's not so much how the cars split the air up front, but how smoothly they allow the air molecules to collect behind them that makes the biggest difference. The more turbulance you have behind the car, the greater the vacuum.

Cutting out the back of the body, such as in a wedge, will help produce downforce but it can also slow the car. On a racetrack this doesn't matter much since you want traction not low drag. Of course, leaving the rear of the body in place without some sort of ground effects will also create drag, but without the added bonus of downforce holding the car to the road.

[cretin]

another concern is frontal area. warren johnson was very upset to go from his square oldsmobiles to the pointy firebirds. why, when the olds was so obviously non-aerodynamic? because the firebird, for all its swoopiness, has a lot more frontal area. back when the late 80's trans ams came along, they were the best factory-built cars possible for land speed racing. another good, although odd choice is the vega. the legendary lamborghini countach is about as aero as a vw microbus. as important as the front end design is, the rear of the body is also a big deal. the air has to close around the back of the car, so a smooth transition there is also a good idea. just look at bonneville rides and see what is good. i bet an old bolink superbird would be great, if it could be molded to be more like the real car. those cars had ludicrous downforce

[Spoon37]

ahs anyone thought of sculpted suspension arms and louvred wheel arches(if u use wheel arches that is)

look at formula1 and DTM cars, they do lots to help the air flow around the wheels and increase down force.

dont go too nuts over downforce tho, as such you dont want much downforce at all, just enough to keep it planted at 100+ but you also want the air to flow smoothly to allow you to reach high speed

;)

[MegaMe]

thing is most normal sedan shaped bodies actually produce lift rather than downforce if they dont have wings on it - so you have to be careful... anything that produces a tiny amount of lift at normal speeds will cause liftoff at 100mph...

also with what you other guys said i agree after making sure the car dosent produce lift then frontal area should the next biggest aerodynamic concern... ideally we want a body that can only just clear the battereis and motor and wheels + whatever the rules say about a cockpit or something.

about the wedge shape thing - from my fluid mechanics courses the biggest factor in drag is the "wake" area behind the car - the low pressure area behind the car that literally sucks the car back. big wake = big drag. obviously having more frontal area means more drag.
below you can see why a wedge is bad... also think about those fancy shaped helmets that they wear in the tour de france and stuff:
i havent shown it but if you think of the top image as being like a sedan body then you can see that there is a little of the wake above the back of the car.. because the wake has low pressure you can see why most cars have rear end lift... it makes you realise why some cars like the audi tt i think had to have rear wings put on the back to make them stable at speed...

http://www.yoxio.com/img/44241.jpg
http://www.yoxio.com/img/44242.jpg

[cianhanrahan]

Yes I reckon teardrop, or rather half teardrop shape, enclosing the wheels would be the way to go. I suppose under the car would be some sort of simple ground effect system, up swept at the back, as smooths as possible, no cutouts for batteries etc... I know there a more technical explanation for these ground effects, but I can't think of them right now. (too much coffee on a monday..)

[DualBL]

I have a question for steve...
the car is limited to a size. but does that include body? \
thnx
-Nick

[sosidge]

I'm not Steve...

But I know the answer...

Yes, it does include the body!

[MegaMe]

Yes I reckon teardrop, or rather half teardrop shape, enclosing the wheels would be the way to go. I suppose under the car would be some sort of simple ground effect system, up swept at the back, as smooths as possible, no cutouts for batteries etc... I know there a more technical explanation for these ground effects, but I can't think of them right now. (too much coffee on a monday..)


the thing is theres no point having any more frontal area than you need. ie if we are talking electric how you fit the batteries in. being that a half teardrop is kinda tall compared to flatter designs - if you fill up a half teardrop full of batteries the center of gravity will be relative high - and when you are going around corners and over bumps at 100mph i would want the cg to be as low as possible.. when you see videos of big block t-maxx's and things like that you can see even at 40 or 50mph how having a high cg makes a difference...

of course with a nitro a half teardrop shape could be something like what you would want - but that would kinda suggest you have the motor at the front - which could also be good having weight over the front to stop it flipping - but i dont know how you would get drive to the rear wheels...

personally id have a car with full of either 1 or 2 layers of batteries (or not so many if you use lipo's i guess) and have the body just flat but raised on the outside to fit over the wheels. of course i dont know where you would put the motor - especially if has a big diamater. the teardrop shape suggests having the motor near the front, but i would think that drivetrain losses you would have from getting drive to te rear wheels would more than cancel out the difference in drag.

[cianhanrahan]

OK, not exactly half teardrop, just trying to explain the shape, a teardrop shape will create the least turbulence as it moves through the air. You could also try it backwards, if the tallest part of your vehicle (I presume engine) is going to be back there?

[Soupisgoodfood]

Perhaps something like the Oldsmobile Aerotech?

http://www.marchives.com/85O_Comtec_Aerotech_M_Lawrence_with_Oldsmobile.JPG
http://images.google.com/images?svnum=50&hl=en&lr=&ie=UTF-8&safe=off&c2coff=1&q=oldsmobile+aerotech&btnG=Search

Certinally a nice looking car to model anyway.

[cretin]

there's an idea. the 200 mph turbo 4 cylinder.

[DCLXVI]

Notice in the first pic, the body has a big "lip" at the bottom, I'd say that is an important design to make the body create more downforce...

[Soupisgoodfood]

http://www.aircraftresourcecenter.com/Gal2/1701-1800/Gal1785_Oldsmobile_Williams/gal1785.htm

If you have a look at the images in there, you can see 2 channels underneath at the front, and how they come out the back.

[cianhanrahan]

Yup, that's what I was talking about, though I've never seen that car before. :D
The channels under the car for ground effects, absence of big wings (though the tunnels by the cockpit work similarily...) it's all about avoiding drag and lift...

[kart38]

Those channels are called venturis. They start out narrow and shallow (chassis to ground) and end up wide and deep. As the air passes through them is slows, thus creating a low pressure area under the car and thereby creating downforce. The stuff next to the cockpit is actually inlets and exhausts for the radiators. On a R/C car they would do nothing but create drag (they would delaminate the air flowing over the body).

The basic shape of the Aerotech is probably pretty close to perfect. Or at least close enough for the purposes of this speed challenge. IMHO, creating an enclosed body (sealed along the bottom using lexan) is the only way to sensibly brake the record.

Jason

[NotWalkinBlind]

Dunno which of the bodies would be available, but don't forget all the work Porsche has done in the windtunnel over the years...
http://website.lineone.net/~ted.martin/images/Porsche%20908F(1).jpg
http://website.lineone.net/~ted.martin/images/Porsche%20917LH(1).jpg
http://website.lineone.net/~ted.martin/images/Porsche%20917-30(1).jpg
http://website.lineone.net/~ted.martin/images/Porsche%20917K%20(4).jpg

[REVOman]

of course with a nitro a half teardrop shape could be something like what you would want - but that would kinda suggest you have the motor at the front - which could also be good having weight over the front to stop it flipping - but i dont know how you would get drive to the rear wheels...

LOL, the same way you get drive to the front wheels in a 4 wheel drive RC, RUN A SHAFT :p

[Spoon37]

LOL, the same way you get drive to the front wheels in a 4 wheel drive RC, RUN A SHAFT :p

Rofl!! ;)