Things you always wanted to know the answer to [Vol. 2]
Discussion
RenesisEvo said:
TheEnd said:
juan king said:
What are the vents for? Seen on the front corners of most tractor units
It looks like this grabs that air, and directs it along the side to get rid of that pocket.
I can obviously appreciate the aerodynamic limitations of these blunt-faced trucks. My question is, are the American-style trucks with the long nose / bonnet arrangement any better aerodynamically?
And if you could design a truck with more optimal aerodynamics, what are the legislative and working practices that you speak of which prevent such a thing? Shirley in this age of 'green fuel reduction' it is in everyone's interest to improve this?
As I know that the fuel costs are the major make-or-break costs for haulage firms?
Ray Luxury-Yacht said:
And if you could design a truck with more optimal aerodynamics, what are the legislative and working practices that you speak of which prevent such a thing? Shirley in this age of 'green fuel reduction' it is in everyone's interest to improve this?
Length, it's the reason that you don't see many bull nosed tractor units over here. I think it's 55ft, obviously America etc allow longer vehicles which is why they have the engine thrown out the front and a living space much bigger that most caravan 
Blib said:
I was thinking that the tea bag would retain heat in the mass of the tea leaves. Like a radiator does.
I think the major difference will be the fact that your starting point will be lower for a tea-bag filled cup.Since the same volume of water is used in both cases - one is just heating the cup and then cooling whereas the other is also heating up the bag too. As a result the temp will be lower just after pouring for the one with the bag.
Perhaps the convection currents will be affected though too as nimby says.
If the bag floated to the top and effectively formed a seal on the surface (damn you round teabags) it would insulate the tea from convection - this happens with cappuccinos where the foam forms a nice insulating layer and when you eventually make it down to the coffee it is still hotter than Satan's armpit.
leafspring said:
CraigyMc said:
mug81 said:
Do banks really charge small retailers 50p for a debit card transaction? It really irks me (much more than it should)
It's more like 10p. Credit cards are usually a percentage.It's when the shop keeper charges US 50p that annoys me... I don't know if it's because they have to rent/buy the card readers from the bank or just to make a profit because the bank charges him when we pay wit the card (boo hoo, sob story about how running a business isn't easy with Tesco on every corner yadda yadda yadda
)Credit cards vary - corporate cards are charged higher than all others (>2.95% !!) and online transactions are higher % than in person.
In other words, card handling is big money. Potentially big risk too. On top of that you rent the terminal and pay a monthly facility fee, plus even the automated data calls...so it all costs. But if the retailer is well organised they should absorb the cost (tiny percentage of overall costs usually and really not worth upsetting potential customers with - all imho).
The Don of Croy said:
But if the retailer is well organised they should absorb the cost (tiny percentage of overall costs usually and really not worth upsetting potential customers with - all imho).
That depends on the size of the average transaction.Running a coffee stand with an average basket size of £2.00 is gonna be pissed to pay 37p each time!
Sure, if you are selling an MRI scanner at $10m a pop, you can probably cover it. (Yes, I know, hospitals don't usually buy their capital equipment with a credit card... they use organs.)
Ray Luxury-Yacht said:
Ok, got another question for you then, seeing as you've done some CFD studies on trucks.
I can obviously appreciate the aerodynamic limitations of these blunt-faced trucks. My question is, are the American-style trucks with the long nose / bonnet arrangement any better aerodynamically?
And if you could design a truck with more optimal aerodynamics, what are the legislative and working practices that you speak of which prevent such a thing? Shirley in this age of 'green fuel reduction' it is in everyone's interest to improve this?
As I know that the fuel costs are the major make-or-break costs for haulage firms?
I didn't do any work on the long-nose style trucks, but there is definitely more potential to make it aerodynamic. This is what I meant about legislation. AIUI, EU rules limit the combined length of truck and trailer (and on the continent, the height too). Loads are limited either by volume (e.g. groceries), or by mass (e.g. construction), rarely both. So for volume, a shorter cab means a longer trailer, means more goods moved per truck, less cost. This means in the UK, and the rest of Europe, where big trailers are wanted you are forced into the cab-over design. You occasionally see the conventional (bonnet) design even in the UK on construction trucks and other times where the total length isn't the issue, but the weight of the load. In the US, the trailer length is the limiting factor, so the cab can be whatever length (to a point), so you can stick the engine out front rather than underneath. The advantages of something longer and wedge-shaped than box-shaped are obvious.I can obviously appreciate the aerodynamic limitations of these blunt-faced trucks. My question is, are the American-style trucks with the long nose / bonnet arrangement any better aerodynamically?
And if you could design a truck with more optimal aerodynamics, what are the legislative and working practices that you speak of which prevent such a thing? Shirley in this age of 'green fuel reduction' it is in everyone's interest to improve this?
As I know that the fuel costs are the major make-or-break costs for haulage firms?
I can't discuss some things I looked at for various legal reasons, but consider for example enclosed wheels on the tractor and/or trailer. That will help reduce drag, therefore save fuel. There's a whole lot of issues with that - being unable to access or even check the wheel nut torque (those green plastic flags on the nuts), servicing/repairs etc. Changing a truck tyre is hard enough without a load of bodywork in place. There's also the weight of any additional bodywork - subtracts from total payload, as well as cost - there has to be enough drag reduction to justify spending the money for a solid ROI well within in the truck's service lifetime. Even human inertia gets in the way of making improvements - like how many drivers do you think will spend the necessary time before each drive adjusting the height of the top spoiler to match whatever trailer they're pulling (unless you have the same trailer every time of course), getting it right is important. They're far more concerned with getting on the road and worrying about the super stringent driving hours. Also the legislation on what you can fit to a truck makes finding something effective aerodynamically very challenging.
The last thing I'll mention is current testing limitations. Trucks are big. Really big. Wind tunnel testing therefore is challenging; very few tunnels are big enough to fit a full-size one in, sometimes just a cab. Half-scale models need twice the windspeed for a representative test (look up Reynolds number if you're curious), so a 50% model needs 112mph wind to be representative - that requires lots of fan power, which is expensive. A 25% scale EU truck and trailer is still 3.4metres long, and would need 224 mph windspeed to represent motorway conditions. The size problem also means testing is generally done straight into the wind; most trucks run in the real world with winds gusting, i.e. some element of side wind. This requires yawing the model, which due to its length blocks the tunnel at even small yaw angles. Those curvy-roofed trailers (below) that appeared have lower drag when tested purely straight-ahead can be worse than a conventional box with a side-wind - these factors need to be considered. CFD is going a long way to solve these issues, but has its own limitations.
I hope that helps answer your questions. I'm very glad I don't work with trucks at the moment, it's a minefield.
There was the Scania T cab which is the long nose you might see every now and again.
Because of the limitations above, it wasn't all that popular, apart from looks.
Sometimes a haulage company might buy one as a flagship, but it often tended to be low loaders and flatbeds that would use them, I guess they would be the ones where they'd be working on weight limits rather than length.
Because of the limitations above, it wasn't all that popular, apart from looks.
Sometimes a haulage company might buy one as a flagship, but it often tended to be low loaders and flatbeds that would use them, I guess they would be the ones where they'd be working on weight limits rather than length.
Why do some aerosols go cold when you shake them? I'm aware of Boyle's law (yay high school physics!) but the pressure inside the can should be constant as the volume is constant (unless you spray it of course) and although I'm no chemist I'm pretty sure that there are very few, if any chemical reactions that are endothermic (lose heat) than exothermic?
MissChief said:
Why do some aerosols go cold when you shake them? I'm aware of Boyle's law (yay high school physics!) but the pressure inside the can should be constant as the volume is constant (unless you spray it of course) and although I'm no chemist I'm pretty sure that there are very few, if any chemical reactions that are endothermic (lose heat) than exothermic?
Aluminium is a good heat conductor - so it will rise from room temp to your hand temp very quickly.Liquids tend to be much worse and take far longer to rise in temp.
As they hit the can where it is hot (where your hand is) it will rapidly cool the metal as the energy is transferred into heating the liquid.
Thus it will feel cold when the liquid hits the inside of the can where you are holding it.
When President Obama travels to a foreign country then uses the Marine One helicopter or his presidential car how does this hardware get to the country he is visiting?
How many people travel with him? How much equipment, personnel, security, etc is needed and how many days/weeks before the President do they arrive?
It looks like it is a huge undertaking.
How many people travel with him? How much equipment, personnel, security, etc is needed and how many days/weeks before the President do they arrive?
It looks like it is a huge undertaking.
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