Physics Question; High Sided Vehicles & Sidewinds

[Joey Shabadoo]

https://knottlab.com/wp-content/upl...Tractor-Trailers-in-Winter-Conditions-SAE.pdf

 

[marinyork]

A- level books often have examples of 'slide or topple'.

 

[Spinney]

[QUOTE 5108574, member: 9609"]but would the wind still be from the side ? if you put a wind vane on the top (in the original example) it would be pointing 45 degrees to the side not 90 degrees.


and yes I totally agree there are many other factors involved hence trying to keep it simple with a flat surface and steady wind and no buildings or other vehicles, or steering with your kness whilst rolling up a smoke.[/QUOTE]
To answer this simply, if you also measured the speed of the air hitting the lorry at 45 degress, it would be greater than the original side wind, being a combination of the side wind and the air movement from the lorry's speed.
So you are right about the angle, but that apparently faster air hitting at 45 degress has the same sideways effect on the lorry as the original crosswind.

 

[Spinney]

[QUOTE 5108733, member: 9609"]so at 50 mph speed with a 50 mph side wind, the apparent wind would be at 45 degrees and at 70.7mph ? makes a lot of sense[/QUOTE]
Yup, spot on.

 

[Randomnerd]

Yup

I’m seeing “Bimbleur” in your blurb.... If you used this nomenclature before January 2nd, carry on. Otherwise, please contact your local Club des Bimbleurs and speak to one of the Officiers du Grand Ordres des Bimbleurs et Tootleurs, and explain you’d like to be considered for membership. I hope you’ll be able to meet the criteria, but do worry that your rather in-depth knowledge and appreciation of complex physics may well count against you in this round of competitive acceptance into l’ordre.
As you were.

 

[Spinney]

I’m seeing “Bimbleur” in your blurb.... If you used this nomenclature before January 2nd, carry on. Otherwise, please contact your local Club des Bimbleurs and speak to one of the Officiers du Grand Ordres des Bimbleurs et Tootleurs, and explain you’d like to be considered for membership. I hope you’ll be able to meet the criteria, but do worry that your rather in-depth knowledge and appreciation of complex physics may well count against you in this round of competitive acceptance into l’ordre.
As you were.

Sorry - have you got contact details for them, please?



Is there a separate club for pootleurs?

 

[nickyboy]

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?

A lorry is just as likely to tip over when subjected to a lateral force when it is travelling at 56mph or when it is stationary. Park a lorry on a very exposed hilltop in a crosswind and it will blow over just as readily as those driving past

 

[Joey Shabadoo]

A lorry is just as likely to tip over when subjected to a lateral force when it is travelling at 56mph or when it is stationary. Park a lorry on a very exposed hilltop in a crosswind and it will blow over just as readily as those driving past

From the link I posted earlier:

There are also some references [1 which refer to the effects of tractor trailer traveling speed and the reduction of available traction, relating to rollover of the tractor trailer. As the traveling speed increases, the aerodynamic lift increases and causes the tractor trailer to become "lighter" and potentially easier to roll onto its side.

additionally, there are figures there relating to sliding where you can see the load at the axles decreases with speed by 15% between 25 and 45mph.

 

[marinyork]

additionally, there are figures there relating to sliding where you can see the load at the axles decreases with speed by 15% between 25 and 45mph.

Interesting.

Quite contrary to what one other poster put, because I think what they said is unhelpful, if people are interested they want to google Ahmed body. That's the technical term. Although I think you did quite well there to find something so comprehensive without that.

 

[ClichéGuevara]

A lorry is just as likely to tip over when subjected to a lateral force when it is travelling at 56mph or when it is stationary. Park a lorry on a very exposed hilltop in a crosswind and it will blow over just as readily as those driving past

If that was true, the advice should be to drive really fast to get through the area of high wind more quickly, rather than the usual 'drive with extreme caution'.

 

[Globalti]

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.

1 - Wrong. Bridges have speed limits because there's no shelter and it's easier for vehicles to be blown over.

2 - Not quite relevant to the discussion. Standing still, I can anticipate and brace myself against your push but moving fast I won't have time to react and you could divert my course enough to cause me to crash into something.

 

[nickyboy]

If that was true, the advice should be to drive really fast to get through the area of high wind more quickly, rather than the usual 'drive with extreme caution'.

Not really. The reason to drive "with extreme caution" is so that, if a gust of wind pushes you across the road, you're more able to control and correct it at slower speeds

 

[Joey Shabadoo]

n more moderate conditions it’s safer to continue driving. However, be mentally prepared to prevent accidents. When driving in high winds:

• Drive slowly. High speed can create low-pressure areas around your truck, which can put you at greater risk of toppling when faced by high-pressure crosswinds.

https://gtgtechnologygroup.com/strong-winds-serious-hazards-truck-drivers/

 

[Andy_R]

I think....if the wind is coming at you from the side, as you move forward the wind does not veer, as it is not delivered at a point. Instead the wind is delivered across a broad front (depending on weather conditions and funneling caused by geographical features). Imagine walking or running along a straight beach, with the tide coming in. the tide will come towards you from the same direction, no matter how far along the beach you are. That's just my take on it though.

 

[Spinney]

I think the discussion about the 'wind direction' was changing should have said 'the direction from which air appears to be moving towards the lorry', which does change from sideways on when the truck is stopped (in our scenario) to 45 deg when the forward speed of the lorry is the same as the wind speed.