Truck Aerodynamics

[hilifta]

This is a subject that has had me very curious for quite a while. It was while looking at 2 photos this morning that I took yesterday, that has finally made me put pen to paper.
Firstly look at Blair's International with it's air deflector covering the whole of the front of the curtainside, then look at the air deflector on the Semco Mack. It looks a real half arsed effort and only covers about half of the front of the curtainside and surely it can't be anywhere near as effective as the one on the Inter.

Now, I am not an expert by any means on this subject, but here are a couple more observations.

Out here it is very common for trucks to have mud flaps not only behind the wheels but all the way across the rear of the vehicle. Now surely this hinders the flow of air escaping from under the vehicle and causes drag, which in turn must increase fuel consumption.
I also notice when in a straddle, high up, that many of the bulk grain trucks do not put their covers back on when empty. Again with all the air swirling around the trays, this again must increase drag.

Now to container trucks, I know there is not a lot you can do to eliminate the gap between the cab and a 20ft box, but surely in this state it is better to have no deflector at all, especially the big high ones as fitted to some trucks.
Having a big high deflector must increase the dirty air swirling around between the deflector and container.

One more thing, does having skirts down the side of truck improve the aerodymanics. If it does, why do so few trucks have them fitted.

And finally, why oh why do you have all those lights up on the roof, as I see on UK trucks. They must play hell with air flow.

I get the feeling that very little intelligent thought is going into this area, which is very surprising due the large cost component that fuel represents.

What are your thoughts, or is it me that's way off beam here.

Mike

[G-CPTN]

I think that all your points are pertinent, however, operators will only equip their vehicles with aerodynamic devices according to what they see other operators doing.

The extra lamps are a fad (presumably dictated by the drivers).

An unladen truck will consume less power than a laden truck, therefore less fuel.
Operators are predominantly interested in the laden fuel consumption and will therefore ignore unladen figures (or factors that will affect it). Air deflectors could be made adjustable, but it's doubtful if the drivers would bother (after all they don't bother to cover the empty bed - which would reduce drag). Maybe the owner hasn't requested their drivers to do that.

Skirts would reduce drag, but cost money and restrict access for maintenance (and are liable to damage).

It's possible that a 'half-arsed' deflector might be almost as efficient as a full-height one (the angle encourages 'deflection' whereas the frontal are of a full-height one has to be pushed through the air (frontal area is a big factor in drag).

What you are seeing is the application of generalised solutions instead of tailored ones specific to each truck. Better than nothing in many cases, but customising the actual devices to the shape and size of whatever is being carried would be better, but time-consuming (and maybe expensive).

Try telling the drivers to sheet over their empty beds and see what response you get . . .

[G-CPTN]

http://www.uni-leipzig.de/~mielke/ma...sich/truck.jpg

http://smsread.com/blog//home/smsrea...ent/107849.jpg

http://www.bangertinternational.de/c...ni_truck_2.jpg

http://psipunk.com/wp-content/upload...kalinin-01.jpg

http://lh3.ggpht.com/_hVOW2U7K4-M/Sh...4b924dc3_o.jpg

http://www.roadtransport.com/blogs/b...ation_02_h.jpg

Notice how they are are all 'conventionals' rather than cabovers!

[G-CPTN]

http://www.sciencedaily.com/releases...0106113455.htm

http://www.sciencedaily.com/releases...0417105446.htm

http://www.sciencedaily.com/releases...1105121037.htm

http://gtresearchnews.gatech.edu/new.../FLYTRUCK.html

[hilifta]

Thanks for all that info GC, some of those truck were weird, to say the least.
The articles are very thought provoking. But I'm not sure on the "boat tail" Overall lengths would be a major hindrance here.

As for tarping an MT truck. I was only refering to the bulkies where they have a manual rollers system and only takes a minute at most to cover or uncover the tray.
So there should not be an issue.
Apparently those high sided tippers generate a lot of disturbed airflow if not covered.

[Fazer9553]

Originally Posted by hilifta

Apparently those high sided tippers generate a lot of disturbed airflow if not covered.

Haha try following one at speed on a bike - then overtaking!

[hilifta]

Overtaking, on a bike, .... boy you must be peddling fast.!!!!!

[robertdavey6]

I have seen some tippers driving round with the tailgate unfastened to allow it swing in the wind. All our trailers are tall enough for me to leave my air deflector in the fully raised position. If I pull a very tall trailer (most recent was 15' 5".) the fuel consumption drops drastically. Even with a light load and an empty return.
I could save a bit more fuel by pulling the trailer closer to the rear of the unit but, unfortunately, then some trailers would foul on the rear of the chassis. When YK54 BVJ was new, the fifth wheel was further forwards but rear lights kept getting hit by the trailer legs. The fifth wheel was moved back, one hole (it's a fixed one. Not a sliding one.), and that problem was cured. It's possible that, by now, the cost of rear light fittings would be similar to the cost of the extra diesel I might now be using.

[reinaldo]

Thanks for sharing. I also notice that mud flaps are quite common in trucks but I don't know it's use. Maybe there are lot of truck parts that I need to study.

[robertdavey6]

Originally Posted by reinaldo

Thanks for sharing. I also notice that mud flaps are quite common in trucks but I don't know it's use. Maybe there are lot of truck parts that I need to study.

Full width mud-flaps help to keep the rear of the trailer clean. Dirty air, quite often literaly, swirls around the back doors and deposits the dirt there. Ideal for those that like writing in it but not so good for the company's image.