Why aren't lorries more aerodynamic?
Discussion
doogz said:
I believe part of the reason is that to make them more aerodynamic, you'd need to add to the length. And there is a maximum train length on our roads that they're not allowed to exceed.
So they could make them more aerodynamic, but they couldn't carry as much. There's a trade off somewhere in there though.
Correct. It's about maximising the payload.So they could make them more aerodynamic, but they couldn't carry as much. There's a trade off somewhere in there though.
And besides, I seem to remember that the front of the vehicle is less important than the rear, when it comes to aerodynamic efficiency and it would be quite hard to do anything much with the back of a lorry without making it unstable or much longer. 
I'm sure that space efficiency is indeed the major reason, but I am quite sure that a lot more could still be done, even if the basic box shape of a truck has to be maintained.
Trying to push a heavy, solid square block through the air cannot be very efficient. I've seen a few trucks with spoilers on the roof to deflect windflow over the top of the trailer. There are also some trailers around which have a higher front and taper back toward the end.
I suspect the truck industry is quite conservative and slow to change however.
Trying to push a heavy, solid square block through the air cannot be very efficient. I've seen a few trucks with spoilers on the roof to deflect windflow over the top of the trailer. There are also some trailers around which have a higher front and taper back toward the end.
I suspect the truck industry is quite conservative and slow to change however.
toppstuff said:
I suspect the truck industry is quite conservative and slow to change however.
The truck in the picture above is a good example of the 'teardrop' trailers that many hauliers are using. The side panels between the wheels you can see are also becoming more common place as they aid air-flow aswell - trailers too are having panels in front of the wheels to aid airflow too.
Scania do have a 'bullnose' tractor unit - the T-cab but this is no longer made and was only really popular with the tipper industry as they have shorter trailers so the extra length on the tractor unit is not such an issue.
Slightly off topic but the maximum legal length of a trailer looks like changing soon - 13.6m to 15.65m.
mig25_foxbat2003 said:
There has been an effort made, as a number of trailers (M&S logo ones spring to mind) have roofs designed to increase lift and therefore improve fuel economy of the tractor unit. Not seen any figures on their effectiveness, though.
ETA Bugger, toppstuff beat me to it!
I'm not sure they are trying to increase lift. Lift causes drag and would have no advantage. They have the aerofoil shaped top is to keep the flow attached rather than create lift although I suspect lift would be a side effect. ETA Bugger, toppstuff beat me to it!
The standard design will have a huge patch of turbulent detached air above and behind the cab. That detached bubble effectively increases the wake of the truck above the truck. You can decrease the drag significantly by just keeping the flow attached and trying to have a Kammback type back.
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