Will mass affect the drag/lift force ? |
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srjhere
Bolt Sorter Joined: Dec/11/2012 Location: India Status: Offline Points: 18 |
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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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sandres913
Welding Master Joined: Aug/17/2011 Status: Offline Points: 216 |
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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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Shaun
Purdue University Calumet - PUC Motorsports 2010 - Washington #18 2011 - Peoria #30 2012 - Wisconsin #54 |
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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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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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Danny
Cornell (fall'07 - spring'12) Former Captain / MEng / that guy with all the carbon 10 races, 7 top ten's, 2 overall wins |
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p.lewis
Welding Master Joined: Oct/05/2009 Location: Greater Detroit Status: Offline Points: 296 |
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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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Priyank
Welding Master I don't search Joined: Jul/04/2011 Status: Offline Points: 241 |
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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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You never stop learning.
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Purduebaja
Welding Master Joined: Sep/19/2010 Status: Offline Points: 137 |
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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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Priyank
Welding Master I don't search Joined: Jul/04/2011 Status: Offline Points: 241 |
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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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