Streamlined Trucks

Interesting answer to the huge drag from big square mirrors (I read somewhere that at 100kph two standard "West Coast" mirrors absorb 14hp). The MAN has aerodynamic wings and the Volvo thin aerodynamic arms obviously with reversing camera style display in the cockpit.

Lang

Hi,

I would think that back in the early days HP was low and production skills were high and relatively cheap so you could afford to spend the time and money to craft something to reduce drag and look good too.

As HP went up aerodynamics would be less of an issue and construction costs and payload area would have been the high priorities so we got boxes and now they are reaching their peaks the focus is going back to aerodynamics and economy as way to balance the economics of transporting.

Terry

Drag increases in proportion to the square of the speed. Double the speed, drag goes up four times. So drag that was acceptable at 30 mph suddenly becomes enormous at 60 mph. Need more & more horsepower - no problem till fuel gets expensive (it didn't follow the 'square' rule - it was worse than that.) Hence the focus back to aerodynamics.

It appears that some of these designs would have less drag in reverse.

They all look pretty good to me with variations on the perfect teardrop shape hampered by practical considerations. The Walmart one looks to be the product of some serious wind tunnel testing but the designers must have been pissed off by the art department's big propeller (or is it a Mercedes badge?) stuck on the windscreen and the builders rough solution of sticking high drag mirrors and brackets all over the streamlined body.

You can see in this chart the drag from different shapes compared with the perfect "Streamlined Body". Interestingly a round pole - mirror brackets, bull bars etc - have 10 times as much drag as the same size streamlined pole. A square fronted truck has 25 times as much drag as a fully streamlined shape.


In this chart you can see the power required (basically the total drag curve) as speed changes. Where the lines cross is the finish of your speed as you are full throttle. The only way to get more final speed or a greater speed with less throttle is to reduce the drag and push the point where the power available/power required lines cross further along. You can see here how it takes more power at 120mph than 60mph, much more than double!

This chart is for a nicely streamlined aircraft with low coefficient of drag but, as we see from the top chart, a square high-drag truck with the same power might run out of steam at 50 or 60mph. We all know an old square truck in the 100-150hp range will finish on the flat well below 60mph while the same hp slippery sports car will do 3 times that. Weight only affects acceleration and hill climbing, once you have the mass rolling along both truck and sports car are subject to the same airflow problems.

IMHO stockcrates would have to be the worst things for drag we’ve got an open mesh crate and I always think it knocks you down a gear empty
If you meet a cattle truck on a motorbike you have to hang on whereas a pan or tarped load you don’t notice unless there’s a cross wind
Cheers Bluey

Will a tail wind put fuel back into tank
:lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:
cya

Theres a interesting (to me anyway) facebook page going over in the States about the Mack Anthem

The gearing and driving style can produce some pretty spectacular results
Some blokes are averaging over 11MPG

Im sure we can all pick it apart, trucks arent as heavy, trucks arent as high and so on

www.facebook.com/groups/2198506597074278/

Paul

I remember years ago, an article in Truck and Bus, where Monash (I think) Uni did some testing on trucks and loads. One thing that struck me was the fact that a truck carrying a load of long pipes on a trailer had less drag and used less fuel if the front end of the pipes was tarped.

Apparently, it gave less drag than the air passing through the length of the pipes.

Bluey

As Wee-Allis says cleaning up the front will change things tremendously. I reckon a tarp just big enough to cover the front of the stock crate would get you back most of your power available.

There are two types of drag - Form Drag and Induced Drag

Form drag is the resistance caused by the frontal area eg stick your hand out the window. Same hand going through the air but lay it flat and it floats in the breeze, turn it vertical and it will fly back just about breaking your arm. This just gets worse and worse the faster you go.

Induced drag is the resistance caused by turbulent air flow and vortices when it breaks away from the moving object after passing over it eg sharp corners, wire racks, the cut-off ends of pipes as it exits. This relatively decreases with speed but if you are starting with a vehicle causing all sorts of disrupted air flow you are on a hiding to nothing.

To overcome both these:

Build a streamlined shape that allows the air to pass smoothly over the surface with no gaps, sharp corners or protrusions to cause break-away vortices. The huge drag on trucks from the back of even a very smooth trailer with closed prime mover/trailer gaps, is cause by the square end creating a giant vacuum and huge swirling, energy sapping wind vortices. A trailer should have a pointy tail to allow the air to pass smoothly the full length without breaking away. Unfortunately not practical so the best they can do is round corners to keep the air flowing along the surface as long as possible before creating whirlwinds that steal power.

This Navistar video explains it clearly.