FWD-GT TOP SPEED CAR

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Re: FWD-GT TOP SPEED CAR

Post by SFC K »

romulus22 wrote:
Sixtysixdeuce wrote:
What you need to find if a very aerodynamic body that is long and narrow, leaving the wheels and arms exposed. Basically like an airplane fuselage.
Like this?

Image

That would do the trick. :wink: Nic Case uses bodies that are long and narrow for his land rockets. I believe he still holds the record for the fastest RC car.
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Re: FWD-GT TOP SPEED CAR

Post by Seabass »

You know reading the article, it mentions Kent Clausen who just happens to be a member here. I bet he would be willing to give some advice on keeping your car planted on all fours during you run.

Cool car.

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Re: FWD-GT TOP SPEED CAR

Post by romulus22 »

I've seen Kent post from time to time on here. I think the main key is lots of downforce. That's about the only thing that could really help in this case. I was really just hoping the shape of the body would give enough downforce but that apparently doesn't work. I'm working on mounting a Protoform high speed thunderbird body now. It's a thicker lexan which should retain its shape better. And I'm also going to add a rear wing with some large side fins for stability. If this fails there is another body that should certainly give enough downforce in the works too. Sadly I'm out of town till Thurs so no testing till Friday or Saturday. I want to get a few numbers with the body off first since I know its stable like that. Once I get a few good numbers ill work on making the car stable with a body.

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Re: FWD-GT TOP SPEED CAR

Post by RC10th »

Try making a diffuser panel and run your undertray, it would suck the car to the ground. Also leaving the wheel cut outs intact but leaving them clear would make any body more streamline reducing drag.
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Re: FWD-GT TOP SPEED CAR

Post by CAT3K »

I think it would always be best to keep the cars wheels inside the bodyline to reduce drag.

Have a look at this Schumacher speed run car : http://technabob.com/blog/2011/06/10/schumacher-mi3-worlds-fastest-remote-controlled-car/

Image

It looks to have very little downforce, just low drag and stability. What surprises me the most with that car is that they've left it 4wd.

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Re: FWD-GT TOP SPEED CAR

Post by romulus22 »

I think if I had more rear down force on this it might have actually worked. The under tray/diffuser alone wasn't enough to keep traction once the car stopped pulling forward. I may go back to this similar setup once I figure the amount of wing needed to keep the rear in line when I go off throttle.

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Re: FWD-GT TOP SPEED CAR

Post by kink »

A typical car will always cause lift. This is because the air travels a shorter route under a flat chassis, compared to the air travelling the longer route over the top of a body. This means the air at the top of a body will travel faster and so causes negative pressure / lift. A cross section of a typical car from the side will look rather like an aeroplanes wing. Same principles at work.

You can combat this in a couple of ways. Adding downforce will help, but that adds a lot of drag, which is not helpful where you are searching a high vmax.

Another way is to keep a streamlined body with no wings, but to ensure the under tray has exactly the same shape / length as the top body surface. This means the air will travel at the same speed under and over the top of the car, hence causing no negative pressure / lift. If you look at the orange Schumacher car above, that is clearly the approach they took. For a really high speed car I think the undertray and body shape need to be designed from the outset as a single shape. Maybe construct it in a similar way to how you may build an rc aeroplane fuselage. Or Just have the wheels hanging out of a strong cardboard tube with a nose cone (like a rocket) for a basic approach. Not that it will look much like a car anymore. Look at the worlds fastest 1:1 land speed cars for ideas in shape.
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Re: FWD-GT TOP SPEED CAR

Post by Sixtysixdeuce »

I think it would always be best to keep the cars wheels inside the bodyline to reduce drag.
See what kink said.

With your typical chassis, it becomes a question of trade-off in downforce versus drag. Increasing downforce increases wind resistance. Leaving wheels open also creates drag, but the smaller body profile generating less lift reduces the need for drag-inducing downforce implements. Now it becomes a question of weight: If the drag coefficient of a full body with more required downforce ends up being the same as the lesser body and open wheels, the latter will be lighter weight, hence faster.
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Re: FWD-GT TOP SPEED CAR

Post by SFC K »

This is a picture of some of Nic Case's cars. If you could make a body like this (The front one), you could break the 100 mph mark.
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Re: FWD-GT TOP SPEED CAR

Post by LoboNYC »

now those are some cool aero dynamic bodies!!!

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Re: FWD-GT TOP SPEED CAR

Post by SteveK »

romulus22 wrote:I think if I had more rear down force on this it might have actually worked. The under tray/diffuser alone wasn't enough to keep traction once the car stopped pulling forward. I may go back to this similar setup once I figure the amount of wing needed to keep the rear in line when I go off throttle.

Image
Can air get in between the body and the front splitter?

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Re: FWD-GT TOP SPEED CAR

Post by romulus22 »

The body was almost perfectly flat on top of the splitter. I would imagine some air was getting through but it was a pretty tight fit. I've got a couple different bodies in the works now. One I plan on doing some serious vertical stabilizers. Another is just a super downforce body. I'm also working out a couple other small details right now too. I've got a little while till the weather gets back to normal so I'm taking my time now. Ill keep updating as I make changes.

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Re: FWD-GT TOP SPEED CAR

Post by romulus22 »

Pretty bored this morning so I thought I'd start on what I had in my head.

Here's the picture show of what I'm doing next for this car.

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Re: FWD-GT TOP SPEED CAR

Post by Brandon G »

Very nice project!

I have a friend at work whose passion is for the speed runs in the full size cars. His current project is to make the worlds fastest '29 Ford. He has run many times in the past with a different car, based off of a '32. He got really close to his 200mph goal in that car but was having trouble with traction when getting above 150. His car was relatively light. Meaning he didn't really use any additional weight besides what the car and himself weighed.

He asked around to many other drivers at the salt flats to get some hints. Their advice for an aerodynamically challenged body was weight. Lots of it. Were talking like 2000lbs extra of lead all placed low in the chassis.

I got to reading these posts, and the car seems to be pretty light. With 6S power, I wouldn't think that adding additional weight to the car would be a bad thing. More traction also. After all, its not about how quickly it can get up to speed (that would be drag racing), its about top speed. Something to try maybe?

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Re: FWD-GT TOP SPEED CAR

Post by romulus22 »

Thanks for the tips and advise Brandon. And honestly when I had this project in my head I thought I was going to have major traction issues. I had the whole plan of using a lot of space to get up to speed. To my surprise even on 6s power I'm not having that much traction issues. I would guess within the first hundred feet I'm full throttle with little/no wheelspin. This leads me to believe the nose of the car is plenty heavy. I just need to add rear downforce to keep the rear in check. And now the more I think of it maybe the extra downforce from the nose of the car is the reason the rear gets so light and comes around off throttle. In my one video you can hear the nose scraping pretty bad and its really not that low. I'm also getting ready to change the gearing completely.

I just need a bunch more tuning and testing. But the winter has put a hold on this car.

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