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Will mass affect the drag/lift force ?

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srjhere View Drop Down
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    Posted: Dec/18/2012 at 5:34am
Will the mass of the object ( as in a car ) affect the drag or lift force. WIll the car have the same drag/lift forces when the shape or size of the car is kept constant and the mass alone is varied.

Explain why the drag/lift forces will not change !
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/18/2012 at 9:23am
Have you seen the equation for lift or drag? Take a look at the variables. That should be explanation enough.

Lift and drag are aerodynamic effects, they only depend on the shape of the object that the air is striking, not the mass of the object. Mass affects other things like CoG location, handling characteristics, jump characteristics, etc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/18/2012 at 12:57pm
Originally posted by srjhere srjhere wrote:

Will the mass of the object ( as in a car ) affect the drag or lift force. WIll the car have the same drag/lift forces when the shape or size of the car is kept constant and the mass alone is varied.

Explain why the drag/lift forces will not change !

Mass will increase the static downforce of your vehicle. It will also increase your "drag" since the 10 horse briggs will struggle to keep you going fast in a heavier vehicle.

Obviously I am being sarcastic and true aerodynamic forces are not effected by mass, but you will see similar effects to an increase in "downforce" and "drag." The increased "downforce" is good for traction, but the increased "drag" is bad for acceleration and top speed. In general, a lighter car is better for Baja, but having proper traction also matters as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Dec/18/2012 at 7:57pm
Alright, here's a case where mass matters: Ballistic Coefficient. This has applications for Baja cars when jumping (but is it important? maybe?), and I think the concept can be applied to the car coasting/overdrive down hills. Basically, you want a high BC when you want the momentum of the object to be greater than aerodynamic drag.

A high ballistic coefficient is better for less deceleration, but the overwhelming trend is for sub 400 lb cars to be competitive. You would never make a car heavier so it could jump better. That leaves you with trying to minimize the drag coefficient and frontal area, which should be no-brainers for all the Baja designers already. So, ballistic coefficient is really just a redundant property.

Long story short, if you're talking about mass and aerodynamics, you're only interested in dynamic cases like jumping. It probably isn't an immediate concern to anybody.

http://en.wikipedia.org/wiki/Ballistic_coefficient
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: Dec/18/2012 at 8:39pm
Drag = (RSV^2Cd)/2
No effects of mass whatsoever.
However, a heavier car with a front biased COG will pitch your car lower in a jump condition.

It's good to have a lighter car, with heavy traction at the driven wheels.

I love aerodynamics.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Purduebaja Quote  Post ReplyReply Direct Link To This Post Posted: Dec/19/2012 at 7:08am
F=ma

If the driving force (or torque in this case) you put to the wheels is held constant, a lighter car will accelerate and achieve top speed faster. Theoretically under steady state conditions additional mass should not affect your aerodynamic drag. In the real world however, additional mass will reduce top speed through additional rolling losses incurred in the wheel bearings and tires. In baja a good amount of the total losses is in rolling resistance of the tires. W=FD. If you have a heavier car you might increase tire pressure such that tire deflection is the same, however the force is greater and in off road the deflection on the track surface will be greater leading to more non aerodynamic "drag".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: Dec/19/2012 at 9:36am
Consider a plastic ball and in iron ball, thrown at the same initial velocity.
The plastic ball retards much faster than the iron ball, which some people might interpret as heavier ball experiencing lesser drag.
But that is not the case.
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