NoTrespassing
Elite Member
Wind direction makes a big difference on the mileage I get on my work commute. Tuesday I managed 50.5 mpg, Wednesday I only got 43 mpg. Tailwind vs headwind and full tank compared to almost empty tank were the variables.
Battery based vehicles of today and tomorrow pt 2
- Thread starter Jchonline
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WinterDeere
Elite Member
.
Another good example of why speed influences mileage. Every sailor on this forum is thinking "apparent wind", right about now.
RSR
Platinum Member
To throw a little more technical knowledge into the discussion,
Power = (Force)(Velocity)
Drag Force due to air resistance is
F_D = 1/2(rho)(V^2)(C_D)(A)
where
rho is the fluid density,
V is the velocity,
C_D is the drag coefficient,
A is the projected frontal area
So, Power = 1/2(rho)(V^3)(C_D)(A)
Or, the power needed to overcome wind resistance is proportional to the velocity cubed.
If you double your speed, the power needed to overcome wind resistance will increase 2^3 = 8 times.
To triple your velocity, you need 8 times the power.
Note, this assumes C_D is constant with velocity, which is not a horrible assumption at normal road speeds, but it's not exactly true.
Power = (Force)(Velocity)
Drag Force due to air resistance is
F_D = 1/2(rho)(V^2)(C_D)(A)
where
rho is the fluid density,
V is the velocity,
C_D is the drag coefficient,
A is the projected frontal area
So, Power = 1/2(rho)(V^3)(C_D)(A)
Or, the power needed to overcome wind resistance is proportional to the velocity cubed.
If you double your speed, the power needed to overcome wind resistance will increase 2^3 = 8 times.
To triple your velocity, you need 8 times the power.
Note, this assumes C_D is constant with velocity, which is not a horrible assumption at normal road speeds, but it's not exactly true.
txdon
Super Star Member
Does rain increase the drag?
RSR
Platinum Member
Yes, rain will increase wind resistance. Will it increase it appreciably to where you would notice? No.
However, it can increase rolling resistance as well, but that's a different topic.
Gale Hawkins
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/pine
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Elon Musk hoping for a couple more OJ juries in the upcoming liability trials....!
RSR
Platinum Member
Are you referring to the coefficient of friction of the raindrops, or the rolling wheel?
If you are referring to the raindrops, the answer is, I'm not.
Aerodynamic drag is comprised of two components. Pressure drag (see previous equation) and skin friction drag (due to shear forces on the surface of a body). At relatively high velocities and for large bodies (e.g., cars) drag due to friction is negligible. Pressure drag dominates.
Skin friction drag arises due to the velocity profile near the surface (the velocity gradient to be precise). This force acts near the surface of the car.
Rain drops will have two effects. (1) They will disrupt the flow over the car, much like dimples on a golf ball. This can actually reduce drag (more space would be needed to explain why), but at highway speeds isn't going to make much difference. (2) The airflow will push the raindrops, causing them to move, thereby increasing drag.
The physics that will cause the raindrops to move is very similar to the same physics that produces skin friction on the car. It is a result of the tangential shear force, either acting on the solid surface or on the protruding droplet, right next to the surface. So, just as skin friction (i.e., the shear force) is negligible, the increase in drag due to a protruding and moving raindrop is going to be very small as well. It will have an influence, but enough that you will notice a change in gas mileage? Not likely.
Gale Hawkins
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Park and do not drive recalls do not work for the one car family working to make payments on the recalled vehicle. One would think after 120 years Ford would know how to make vehicles. This is both an ICE and EV concern.
www.motorbiscuit.com
The Car Companies With the Most Recalls so Far This Year
Recalls are a normal part of the life in the auto industry. However, some companies have had a concerning amount this year.
www.motorbiscuit.com