aerodynamics

[kevtherev]

Neither do I.....I've always loved the look of your van...

Those round taillights, though...

went years ago...

[keith]

Neither do I.....I've always loved the look of your van...

Those round taillights, though...

But heavy oil burners DO sound like tractors

No they don't.....unless you know of some seriously refined John Deres....

Your average modern tractor is as mechanically refined as your average modern diesel car. Common rail injection, DMFs, variable vane turbos, the lot. All a bit more sophisticated than the JX and friends... Let's be honest, the Mk2 Golf diesel was never particularly refined, even by contemporary standards 25 years ago.

I swopped out my jx for one of those nice refined smooth powerful torqy diesels....and it's still a vw one.

[silverbullet]

What happened there? Can we get back to the airflow chat, it was getting interesting....

I do wonder if mounting the spare on the front Bay-style has any benefit for aerodynamics, since it would give a bit of "lead-in" and maybe a slightly convex cover would help too? Now before you all go off screaming about overheating, this spare wheel matter was discussed in syncro circles a while back and one of the chaps in Australia has no probs with his Subaru-powered bus even in 100F+ summer days.

As for the boat-tail nonsense, ducting air into the Low Pressure zone behind the bus has to be a good thing towards reducing drag. Quite how to do it though...vents where fancy blenders would usually live, maybe?

PS anyone know about the benefits of those front corner air scoops they fit to commercial truck cabs? I guess they are to pull air around the sides of the cab and fill the LP areas at the cab doors? While on the subject, the increasing popularity of parabolic roof profiles on curtain-side trailers might be worth considering.
I may well do something similar for our roof tent...

[col.decker]

Anybody know if these are any good?

Clicky Linky

Made to order for £80, might treat my van next pay day.

[trucker]

Also the on top of the curved roofed trailers there is always a ridge on the roof set at about 20° towards the rear of the roof I've always wondered what this bit does. The side scoops on unit corners are as I understand it to try and lessen the area of low pressure between the cab and the trailer which after the flat front is the area of most drag on an artic, continentals tend to close couple their tractor/trailers to try to alleviate it but you have to have a matched combination to do this.
Apparently teardrop trailers have a fuel saving of roughly 10% = big bucks.

[silverbullet]

I've noticed that angled spine on the roof too, I wondered if it's a some sort of turbulence breaker or even just to stop rainwater cascading off the back like a waterfall, by simply deflecting it to one corner. The latter seems most likely.

[karmannkarmann]

Does anybody have any info on the under trays as mentioned earlier? If it could save on MPG then that's a good thing.

[Mocki]

Now when I was talking to a old truckman some years ago, he told me those corner air deflectors were there to stop or at least reduce the amount of dirt /water ect that gets on the side windows ..... Then not long after they all had them.... The "v" on the back of trailer has always been there , long before the Eco roofs, only you couldn't see it, and it was mostly just a single "/" accross the roof , to stop the rain pouring in the back doors when on loading bays ect.

One thing I do know is my bike rack stops my back window getting as dirty and wet on the motorway in the British summer ! Not sure if that's lower pressure or if its higher pressure tho

[trucker]

That's one less thing to wonder about! The thing on the roof I mean.
I can't see how those deflectors would keep muck off the windows though as they're too low down and if that is what they're for they don't work.

[silverbullet]

I still think that the front corner jobbies are to help "fill" the LP volumes that would be generated from HP air being pushed out sideways from the front panel and airflow seperating from the cab doors.

I wonder if one of our number is in the fluid dynamics game and could do a basic modelling of airflow, that could be played with in the absence of a free wind-tunnel

To Karmann, for undertray pics you might want to check out Busboy's old Carat project on the Brickyard, it was built a few years ago though so you'll have to go digging. Let us know what you find!

PS Mods, could we get this moved to Tech/bodywork or Modified as that's the best home for this topic?
Might get a few more contributors...

[boxer]

A few more I can't believe I started a thread that has run this long!

Re the Northern Classic Campers link. If I'd seen that first I would have bought it instead of the big 'clunky' bumper/splitter combo I have just picked up.

[boatbuilder]

Couldn't resist translating that with google... a bit rough but more understandable than german!

Campers in the wind tunnel
Wind faces

Top speed, fuel economy and driving performance depend more or less directly on the air resistance of the body.
How much impact a special roof or even a residential building on end face and drag coefficient, the following examples show:

Standard Van Wind Resistance 1.40m2
Considering its box shape, the serial bus is relatively streamlined.
The drag coefficient of 0.44 multiplied by the front surface of 3.06 m2 is the air resistance of 1.35 m2
With an extremely flat lifting roof the values ​​deteriorate as good as not at all. The measurement gives a drag coefficient of 0.45. The slightly larger frontal area of 3.11 m2 provides cw x A of 1.40 m2

Pop-top Van Wind Resistance 1.62m2
The front luggage well in the pop-up creates energy-consuming air turbulence, which is reflected in the drag coefficient value of 0.51. The relatively small frontal area of ​​3.17m2 can hardly improve the overall value:
Cd x A = 1.62 m2

High Roof van Wind Resistance 1.44m2
Clean airflow around the Dehler professional high roof Result: A drag coefficient of 0.40. Despite of the front face of this roof being 3.61m2, air resistance (1.44 m2) is lower than the pop-up with luggage tray.

Separate body Wind Resistance 2.38m2
A separate living body can not by design have a wonderful drag coefficient. Nevertheless,with 0.46 it is better than the pop up roof for comparison. The front surface of 5.17 m2 deteriorated balance
Cd x A = 2.38 m2

[DavidPallister]

That's one less thing to wonder about! The thing on the roof I mean.
I can't see how those deflectors would keep muck off the windows though as they're too low down and if that is what they're for they don't work.

Aerodynamics is a bit of a black art, just because the deflectors appear too low down doesn't mean that they do not have an affect.

I can remember a story from the 2nd gulf war, all of the challenger tanks were having issues with the air filters clogging up with the very fine sand from the desert. It was caused by the vortecies generated by the spinning caterpillar tracks beneath the tank, even though the air filters were way up on top. The solution was to fit a series of canvas skirts along the sides of the tracks to reduce the vortecies.

[AdrianC]

Pop-top Van Wind Resistance 1.62m2
The front luggage well in the pop-up creates energy-consuming air turbulence, which is reflected in the drag coefficient value of 0.51.

I wonder how the Atlantic/California "fang" would fare, compared to the Joker-style tray?

[silverbullet]

There was a bit of chat on the samba a while back about Westy fang vs. luggage tray. IIRC the consensus was to fashion a canvas cover for it and making sure that there was always something filling the tray. Much quieter in the cab thanks to reduced turbulence, apparently.

I'm now looking for suitable vent grilles for the rear panel. I have it on good authority that the T3 engine bay is positive pressure thanks to it's Aircooled origins (drive around with the hatch unlatched and the pressure differential will make it lift!) so balancing that high pressure into the van's wake has to be a good thing afaics.