What a drag

[randywebb]

[ragnarhairybreeks]

hey this is supposed to be fun.

no need to get all super serious about it. I say why not make the shape that you like, stick it on the luggage rack, attach wool tufts in a grid pattern, then drive the van and have a friend drive alongside and video.

look for the tufts to be mostly lying flat and (and most likely fluttering), not sticking up or curved forward and fluttering.

"fill in" the curves that show deviation from the smooth flow and try again.

simplistic yes, but its not stupid.

I don't want to fuel an argument here, just want say have fun and experiment.

Talented amateurs are capable of great design, take old Georgi Georgiev as an example: http://www.varnahandcycles.com/hpv.htm


alistair
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'86 7 passenger syncro, converted to westy pop top, project still in progress
'82 westy, diesel converted to gas in '94, now gone...
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Old address still works...
http://shufti.wordpress.com

[jackbombay]

Randy, if you would look at the question in the context of reality (risk vs reward) your input might actually be of some benefit here, but as you're only interested in proving your intellectual superiority your input has provided no benefit.

Ragnarhairybreeks, my thoughts exactly
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[Vanagonner]

[msinabottle]

Flashback!



I can remember seeing those things on the street. They moved very, very slowly.

Best!
_________________
'Winston,' '84 1.9 WBX Westy
Vanagon Poet Laureate: "I have suffered in
many ways, but never, never, never in silence."

[jackbombay]

[ragnarhairybreeks]

[iiigoiii]

[Classicvibe]

Hmm, I am thinking back through some early aerodynamic schooling I had. There are multiple questions on the table here, but perhaps the most important is a status quo metric. It is difficult to set up a tunnel, and only provides a visual unless you have some other cool measuring going on.

Since you are really just talking about changing air flow over the top, and perhaps the bottom, then measuring air flow behind the van would seem to be all you need. This is interesting, because the dynamics change with speed, but, alas, this is still difficult to measure, even in this manner. Maybe someone with an EV can help us out here, measuring the force to move forward with a certain set up, and again with some modifications?

I just saw a big diesel with a rear drag smoother like the one mentioned here earlier. It is called a trailer tail. You can view a summary of some other drag reducing technologies being tested on those big rigs here:
http://news.cnet.com/geek-gestalt/?categoryId=2047

To simply remove the technology hurdle, you could use tape and ribbon, and film the vehicle at different speeds. In short, anything you can do to reduce and shorten the chaotic air behind the vehicle is a win, but like a few have mentioned, that crappy drag on that vehicle is not really important until you really get moving, but at what speed? My guess would be, somewhere around 50+? Along with some long plastic tape, you could measure sound as well. Other than road noise which would not change, the engine should run softer, air should have less impact (better flow). FOr someone that has insulated against pavement/wheel well noise, this device could compliment the tape testing. I have seen some cool measuring devices around that are not expensive. I am planning to buy one to test my sound insulation efforts this summer.

I think I like the goofy looking rear trailer tail thing more then messing with the front. I think I would work from the tail forward, as that seems to be the biggest bang for the buck. Smoothing out the back can solve a lot of issues in the front, whereas smoothing out the front may not have as much effect on the tail drag, perhaps simply changing it rather than smoothing it out.

Simple stuff for most of you...I was just kind of thinking out loud, wondering if I could make this a little more simple to play out. My 16 MPG is making my conservation rants outrageously hypocritical...
_________________
On a mission, the destination is just an excuse.

Syncro Solstice 2022...see you there!

1986.5 Wolfsburg Syncro Westfalia Poptop Weekender Transporter

[Vanagonner]

I can see that a mock-up with ribbons flying is in my future, before I make the effort of building a mold. This is going to take some time, I have a life to attend to also .
Just a note here on my approach. I am not trying to prove anything to anyone. I will not generate perfectly accurate data regarding what this does or doesn't do. The value of it seems like a no-brainer from what is known and what has been tried. Since I don't have mathematical or computer modeling skills, I won't even pretend to work that way. All I have is (nearly) 50 years of paying attention to my environment, and I'll go with that.

ragnarhairybreeks, wouldn't that H 16 be great! until it came time to adjust the valves...

Classicvibe, You are right about the back being possibly more important (and I'll work on that at some point), but the CD numbers that come up on the above listed comparison (and all the wind noise we get from the cap) point to it being a horror show of turbulence, so I'm starting there.
I'm also trying to keep in mind crosswinds, and trying designs to reduce the pulling force of crosswinds by having a couple of sharp lateral edges to help the air come off of the side without pulling too much.
_________________
Sage
'82 Westy 1.6 D
the mighty n/a

[silverbulletuk]

[tencentlife]

To measure results, you could compare the throttle position needed to maintain a set, GPS-verified roadspeed on a consistent course, always run in both directions to cancel out wind direction, attending closely to all other variables (weight, tire pressure, etc.). Install a 0-5V TPS and record exact voltage. Throttle position to maintain a set speed will vary with the real attrition loads. Drivetrain and rolling resistance will remain pretty consistent at consistent temperatures, that leaves air resistance, which dwarfs all other loads at cruising speeds so it should register as a change in needed throttle opening.

It would at least be a lot better than trying to do controlled measurements of mpg. To do that at all accurately would require weighing the fuel used, not measuring its volume.
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Experience is kryptonite to doctrine.

[Jake de Villiers]

Interesting thread. I've admired Bob Parsons' work for a few years now but never actually got off my ass and did anything about it until last Thursday.

It was nice out and I was tired of working on violins and banjos so I went outside and cut a piece of 1/2" plywood to fit the top of the luggage rack, put a couple of pool noodles under it and a couple of bungees over to hold it down.

The wind noise reduction on the highway drive to work in Vancouver on the following day was amazing! 75 mph sounded like 65 mph had only the day before! We'll see what happens gas mileage wise but its worth the trouble for the quietness alone.

I've already installed peel & stick in the front doors and the slider and put damping material in the air intake pillars at the back along with smearing the underside with roofing tar. My Continental tires are pretty quiet and the Subaru engine is very quiet too, so the wind noise really stands out.

I'm going to have to track some some white polystyrene to make a proper lid!
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'86 Westy Weekender Poptop/2.5 Subaru/5 Speed Posi/Audi Front Brakes/16 x 7 Mercedes Wheels - answers to 'Dixie'
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[Jake de Villiers]

[randywebb]

somebody should custom-make a short luggage bag to just fill that space -- it's seems like a good way to cut down on the noise
_________________
1986 2.1L Westy 2wd Auto Trans.

[Classicvibe]

[silverbulletuk]

Apologies for reviving a year-old thread almost to the day, but it looks like it's still worthy of some attention...
My interest in the subject comes from my dormant "tin-pop" concept, that centres on a salvaged roof skin panel that's hanging from the garage rafters. I was/am going to make a full-length, fully elevating roof with slide-out sides (think original Viking Spacemaker meets roof tent) to sleep 3 upstairs. For when the kids get taller but won't leave home...
When I get the decks clear I'll get back to it!
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1986 syncro twin-slider rhd, 3.2S Oettinger wbx6
1990 SA Microbus - Supercharged wbx going in with UN-1 trans.
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[randywebb]

[IdahoDoug]

Someone mentioned adding a Dehler top reduces Vanagon drag by 10% "if that's how you read CD" (which is an auto industry term Coefficient of Drag). Coefficient of Drag is a ratio of the vehicle's frontal area, to its total drag if I recall correctly. So you can put a taller top on and reduce the CD. But you have much higher total fuel-sucking drag despite a CD "improvement". So don't use that as a measure of aerodynamic improvement that will reduce drag. I cannot accept that putting a heavy object atop a vehicle that makes the vehicle taller can cause the vehicle to move through the air more easily. No way. It is total drag, plus or minus any mass you've changed that will determine which way you move the fuel consumption needle when making body changes.

DougM
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[silverbulletuk]