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Old 08-16-2011, 12:33 AM   #1
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hi folks,
why does 1/12 scale pan car body has a large opening in the back of it?

i notice all of the twelve scale body has a wedge shape that contour all the way to the back of the car and then raised up real high, and leaving the rest of the rear end exposed where you can see all the axle wheels and motor.

is there a purpose to having this large opening this way?
how does it affect the dynamics and handling of the car with this large opening?

it could have curved down instead to have the rear end covered up and use a pair of stand off for a separate wing, but since it is design this way there must be a purpose for this large opening and i highly doubt its cost reason.

i'm looking to use one of those hpi body on a world gt chassis and i wanted to know if this large opening has a positive effect on body dynamic and handling charateristic, so i can plan ahead on how to cut the body.

thanks
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Old 08-16-2011, 07:23 PM   #2
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Basically on a 1/12 or 1/10 pan car the body is open in the back to allow air to exit at the rear. Pan cars, and most other on-road rc cars have very primitive aero in that they allow the air to enter inside the car between the body and chassis where it passes thorough the electronics, suspension, wheels, etc, before it finally exits at the rear. Very inefficient!

Full scale racing cars channel the air underneath the body to create a low pressure zone which creates downforce and reduces drag. They use an aero undertray that is keyed to the body along with a diffuser to accomplish this.

Unfortunately, there has been only limited experimentation in this area with regards to rc car design. Most manufacturers prefer to play it safe and go with the status quo in design rather than risk the expense involved with developing proper aero for the cars. To put it simply: It is not profitable for them, therefore it won't happen anytime soon.
That is why you will notice that most all of the pan car chassis and bodies are pretty much the same, with only very small detail differences. Pretty much the same deal with 4wd touring cars as well.
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Old 08-16-2011, 07:37 PM   #3
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There was some experimentation with ground effects for oval and on-road back in the early 90's

I believe the main drawback was not so much the lack of downforce.
It was more that the chassis & and tires were not up to the task of handling the extra load.

Most of the time simple is the best road to go.

More corner speed than we have in our simplistic pan cars now would be crazy
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Old 08-16-2011, 07:48 PM   #4
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A big problem with doing any kind of aero under a RC car is how much room of the chassis is the electronics placement. The electronics take up so much room in the car that there isn't enough room to move them to make room for tunnels and such aero. You could make tunnels and place the electronics on top of them but you would sacrifice a lot raising the CG of the car. I saw some guys who used to work for TRD made a killer oval chassis with a tunnel that had like 11lbs of downforce...it was really trick. That worked fine for oval because everything was off-set to one side...but not on a road car. Dahms used to make an aero under tray but to use it you had to raise the ride height of the car which again raises the CG. Technicraft had a very interesting diffuser idea but that was short lived as well.
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Old 08-16-2011, 08:01 PM   #5
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I remember those.

There was also a chassis from the guys at NPTi that worked fairly well for high speed oval racing.
It was an idea better suited for oval, where the speeds were more constant than road course.
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Old 08-16-2011, 10:07 PM   #6
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Quote:
Originally Posted by xxcysxx View Post
hi folks,
why does 1/12 scale pan car body has a large opening in the back of it?

i notice all of the twelve scale body has a wedge shape that contour all the way to the back of the car and then raised up real high, and leaving the rest of the rear end exposed where you can see all the axle wheels and motor.

is there a purpose to having this large opening this way?
how does it affect the dynamics and handling of the car with this large opening?

it could have curved down instead to have the rear end covered up and use a pair of stand off for a separate wing, but since it is design this way there must be a purpose for this large opening and i highly doubt its cost reason.

i'm looking to use one of those hpi body on a world gt chassis and i wanted to know if this large opening has a positive effect on body dynamic and handling charateristic, so i can plan ahead on how to cut the body.

thanks
There are other great answers,but the real question is will your body be legal if you race. Most places have rules about the rear of the car. If you can cut it out,its better. If the rules say you can not cut it out then you cant do it.
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Old 08-17-2011, 12:27 AM   #7
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With the exception of WGT pan car classes allow cutting the rear of the body out.
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