Physics Question; High Sided Vehicles & Sidewinds
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Jason
Senior Member
- Location
- Carnaby Street
"If we took a very simple scenario"
ColinJ
Puzzle game procrastinator!
- Location
- Todmorden - Yorks/Lancs border
The wind would still be from the side and the tipping over force is from the side. The drag (wind resistance) wouldn't make any difference.
That isn't to say that driving fast in strong winds is a good idea because even if the wind direction and speed are steady, changes in terrain, buildings and passing vehicles will interrupt the flow of the wind and create a gusting effect. Slewing across the road at 60 mph is not a great idea!
I have suffered from that effect on my bike several times. There is a fast descent from a local hill to the village of Oxenhope, near Haworth. I was dropping down that hill at high speed with a stiff wind coming from my left. Without realising I was doing it, I was leaning into the wind to keep going straight down the road. Halfway down there are some large buildings on the left. As I drew level with them they sheltered me from the side wind and without that force, my leaning took me towards the kerb on the left. I reacted quickly and corrected my trajectory only to emerge from the shelter of the buildings and then get blown over towards the right kerb instead!
That isn't to say that driving fast in strong winds is a good idea because even if the wind direction and speed are steady, changes in terrain, buildings and passing vehicles will interrupt the flow of the wind and create a gusting effect. Slewing across the road at 60 mph is not a great idea!
I have suffered from that effect on my bike several times. There is a fast descent from a local hill to the village of Oxenhope, near Haworth. I was dropping down that hill at high speed with a stiff wind coming from my left. Without realising I was doing it, I was leaning into the wind to keep going straight down the road. Halfway down there are some large buildings on the left. As I drew level with them they sheltered me from the side wind and without that force, my leaning took me towards the kerb on the left. I reacted quickly and corrected my trajectory only to emerge from the shelter of the buildings and then get blown over towards the right kerb instead!
Pale Rider
Legendary Member
I agree, in isolation whether the lorry is moving or not makes no difference.
Which is why in really adverse conditions you may see a lorry parked under a bridge parapet.
The driver knows that just stopping on the open road still leaves him at risk of his vehicle being blown over.
Slick
Guru
[QUOTE 5108562, member: 9609"]First of all I think the best advice is to slow down and get parked up, safer for everybody. however...
If we took a very simple scenario - Perfect flat road surface and a perfectly steady westerly wind of 60mph; would a high sided vehicle travelling exactly south be less likely to blow over if it was travelling at 60mph or if it was standing still ?
I'm thinking at 60mph the apparent wind would be from the SW (45 degrees head wind) so therefore less sideways force ? If the wagon could speed up to 120mph the apparent wind would only be at 30 degrees so even less sideways force ? So on that basis the faster it goes the less effect the sidewind will have?
The other bit I'm not a 100% about is
obviously cycling at 20mph with a 20mph wind behind you would experience no wind
and cycling at 20mph into a 20 mph wind you would experience a 40 mph head wind
But what about cycling at 20 mph with a 20mph cross wind, would the wind speed experienced be 20mph as a 45 degrees headwind? but then would that mean a side wind was helping a little ?[/QUOTE]
Wind doesn't act like that though, but ignoring all the many other factors, the faster the lighter so the wind would have more effect on a high sided vehicle.
Wind loads are a complicated business.
If we took a very simple scenario - Perfect flat road surface and a perfectly steady westerly wind of 60mph; would a high sided vehicle travelling exactly south be less likely to blow over if it was travelling at 60mph or if it was standing still ?
I'm thinking at 60mph the apparent wind would be from the SW (45 degrees head wind) so therefore less sideways force ? If the wagon could speed up to 120mph the apparent wind would only be at 30 degrees so even less sideways force ? So on that basis the faster it goes the less effect the sidewind will have?
The other bit I'm not a 100% about is
obviously cycling at 20mph with a 20mph wind behind you would experience no wind
and cycling at 20mph into a 20 mph wind you would experience a 40 mph head wind
But what about cycling at 20 mph with a 20mph cross wind, would the wind speed experienced be 20mph as a 45 degrees headwind? but then would that mean a side wind was helping a little ?[/QUOTE]
Wind doesn't act like that though, but ignoring all the many other factors, the faster the lighter so the wind would have more effect on a high sided vehicle.
Wind loads are a complicated business.
slowmotion
Quite dreadful
- Location
- lost somewhere
Shooting wildly from the hip, I think it might be something to do with a lack of downforce in a moving vehicle compared to a stationary one. Also, there are Bernoulli effects going on if the wind is at an angle. Yes, it's a very long time since I did Physics A level.
BTW, did you know that you could probably drive an F1 race car upside down across the ceiling at about 200mph, such is the downforce that they generate?
BTW, did you know that you could probably drive an F1 race car upside down across the ceiling at about 200mph, such is the downforce that they generate?
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U
User6179
Guest
One back wheel lifts off the ground and you lose power well before the wind is strong enough to blow you over.
nickyboy
Norven Mankey
- Location
- You want hills? We got hills
[QUOTE 5108579, member: 9609"]I was trying to avoid the down force or uplift element[/QUOTE]
You can't. Were there no upforce or downforce element, the fact the lorry is moving has no effect on the side force it experiences
However, in motion the lorry will experience an up or down force depending on specific aerodynamics. Downforce=less likely to tip over obviously
You can't. Were there no upforce or downforce element, the fact the lorry is moving has no effect on the side force it experiences
However, in motion the lorry will experience an up or down force depending on specific aerodynamics. Downforce=less likely to tip over obviously
Joey Shabadoo
My pronouns are "He", "Him" and "buggerlugs"
Yes, speed will make tipping easier which is why bridges have speed limits when it's windy.
If I push you whilst you are standing still, it is difficult for me to push you over but if I push you as you run past me at full pelt, it is very easy to send you flying.
If I push you whilst you are standing still, it is difficult for me to push you over but if I push you as you run past me at full pelt, it is very easy to send you flying.
nickyboy
Norven Mankey
- Location
- You want hills? We got hills
Nope
Bridges have speed limits as a vehicle in side winds is prone to be pushed across lanes of traffic and thus, if travelling more slowly, is easier to control
Your analogy re running past you is due to the inherent instability of a person when moving as opposed to standing still. When running, a person is permanently in a controlled state of falling over
Drago
Legendary Member
- Location
- Suburban Poshshire
On the one hand, the pressure per square inch on the side of the vehicle will be the same at 30 or 60.
On then other, that's a lot of pressure and the driver will be making constant adjustments to maintain course. At then lower speed those adjustments will be easier, and will be less abrupt as the driver will have more time when covering a given distance.
So my guess is that the effect is the same at either speed, but the driver will have more time to react at the lower speed, and won't need to react so abruptly, so would be more likely to remain shiny side up.
On then other, that's a lot of pressure and the driver will be making constant adjustments to maintain course. At then lower speed those adjustments will be easier, and will be less abrupt as the driver will have more time when covering a given distance.
So my guess is that the effect is the same at either speed, but the driver will have more time to react at the lower speed, and won't need to react so abruptly, so would be more likely to remain shiny side up.
swansonj
Guru
Not necessarily, because of Bernoulli, as someone mentioned upthread. Aerodynamics are complex and often counterintuitive.
Drago
Legendary Member
- Location
- Suburban Poshshire
Absolutely! That's why I made it very clear I was guessing! Something as simple as tyre pressures might make a vehicle less unstable at one speed than another.
gavroche
Getting old but not past it
- Location
- North Wales
It would be a hell of a long ceiling!!
Joey Shabadoo
My pronouns are "He", "Him" and "buggerlugs"
Is something more likely to tip when it's going forwards as designed or going sideways? Is a lorry more stable at 56mph or 0mph?
