Don't understand
Dear Daughter (OTR Semi Driver) called to ask me what part of "CLOSED to High Profile, light-weight vehicles" do RVers not understand?? So far today she has seen four RVs rolled off the road (I-80 in...
Forum Discussion
"All RVs are basically boxes of air. Nothing to them. They have a huge amount of windage. Traveling in still air at 60mph is no problem however if a 60mph gust of wind hits them broadside then there is a huge problem."
Crosswinds are an equal opportunity destroyer. They don't care what vehicle is being driven. The physics are generally the same.
The general formula to determine the wind load on a flat surface is
L = 0.00256 x A x W^2
L = the overturning wind load in lbs.
A = the loaded surface area of the vehicle in square feet (usually the side of the MH)
W = the crosswind wind speed in miles per hour
This is a greatly simplified equation for static conditions. Rollover forces are always dynamic, change rapidly, and are much more complex.
So what does this mean?
Suppose you have a 30 foot class A MH. The side area is approx.
9' high x 30' long or A = 270 square feet.
If you have a 40 mph crosswind the force on the side of the MH is
L = 0.00256 x 270 x (40)^2 = 1106 lbs.
Now what happens if you hit a sudden crosswind gust of say 70 mph? Since the wind speed is squared, the force is now
L = .00256 x 270 x (70)^2 = 3387 lbs. (more than triple)
It may seem inconsequential, but when combined with driver inputs, road conditions, suspension dynamics, and a few other things, it can be enough to put you on your side, or, in a ditch, very quickly. It's usually the crosswind GUSTS that get you. Not the constant steady crosswinds.
Chum lee
Crosswinds are an equal opportunity destroyer. They don't care what vehicle is being driven. The physics are generally the same.
The general formula to determine the wind load on a flat surface is
L = 0.00256 x A x W^2
L = the overturning wind load in lbs.
A = the loaded surface area of the vehicle in square feet (usually the side of the MH)
W = the crosswind wind speed in miles per hour
This is a greatly simplified equation for static conditions. Rollover forces are always dynamic, change rapidly, and are much more complex.
So what does this mean?
Suppose you have a 30 foot class A MH. The side area is approx.
9' high x 30' long or A = 270 square feet.
If you have a 40 mph crosswind the force on the side of the MH is
L = 0.00256 x 270 x (40)^2 = 1106 lbs.
Now what happens if you hit a sudden crosswind gust of say 70 mph? Since the wind speed is squared, the force is now
L = .00256 x 270 x (70)^2 = 3387 lbs. (more than triple)
It may seem inconsequential, but when combined with driver inputs, road conditions, suspension dynamics, and a few other things, it can be enough to put you on your side, or, in a ditch, very quickly. It's usually the crosswind GUSTS that get you. Not the constant steady crosswinds.
Chum lee
