tuft testing

[Varn]

I got out my tuft testing wand for yesterdays commute. My wife drove the mini van. My wand is basically a 5' fiberglass rod with 4-5 yarn tufts taped on the end.

Air flow was straight back on all areas of the hood. There was slight turbulence behind the wipers but 3-4" above them the air was moving well on the windshield. Along the nose at the sides it was once again good all the way to the wheel well opening. Tufts seemed fine above the wheel well even back a ways above it. Like wise the area behind the mirror was very turbulent. Of course the window was down so that I could use the wand. You cant test without introducing change.

I plan on doing some more tuft testing but have already obtained some data. Just goes to show that viewing data and copying from someone else's car is useful.

[Cd]

Tuft wand ?
If it is just the two of you, you could also stand by the side of the road with a video camera and video as she drives by at 45-50
Much safer ( unless she is a bad driver : ) )

[Varn]

Yes. Taped on tufts is the next plan but hard to stand along the side of the road while commuting. .

[Otto]

Any chance you could do some pics of tufts under the car nose, esp. to see airflow to and around the front wheels?

I'm especially curious about the angle of incidence of flow to and around the wheels.

[Varn]

Hi Otto,
I did notice that the wand when held down near the front wheel gave me a lot of swirling. I couldn't observe the any lower than about the top half.

There is a short smooth belly pan from the grill at the bottom to the radiator.

A couple of weeks ago I had removed the rear mud deflectors and screwed them in front of the front wheel. I thought that they might work out perfectly but they were tilted as the front of the body curls around underneath more than the shape does further back. Also they were only half as wide as the tire.

I am in the process of fabricating a custom wheel deflector. I used 9 gauge wire and bent and welded it into shape. I am hand sewing some dacron fabric onto it. I will then shrink the fabric a bit with heat then lay on some composite cloth and wet it out with epoxy. The wire and fabric can be removed after it cures.

I have taken some photos of the frame and will try and document it. I realize that these are not the photos that you are asking about. I might suggest that pictures of air flow around my front tires may not be relevant to your car.

It truly has not been tuft tested but the shape makes some sense. I may create a rubber dam under the front.
EDIT
wire only:


Here is the form that I am going to carbon.

Originally Posted by Otto

Any chance you could do some pics of tufts under the car nose, esp. to see airflow to and around the front wheels?

I'm especially curious about the angle of incidence of flow to and around the wheels.

[Weather Spotter]

looks good!

[Otto]

Originally Posted by Varn

Hi Otto,
I did notice that the wand when held down near the front wheel gave me a lot of swirling. I couldn't observe the any lower than about the top half.

There is a short smooth belly pan from the grill at the bottom to the radiator.

A couple of weeks ago I had removed the rear mud deflectors and screwed them in front of the front wheel. I thought that they might work out perfectly but they were tilted as the front of the body curls around underneath more than the shape does further back. Also they were only half as wide as the tire.

I am in the process of fabricating a custom wheel deflector. I used 9 gauge wire and bent and welded it into shape. I am hand sewing some dacron fabric onto it. I will then shrink the fabric a bit with heat then lay on some composite cloth and wet it out with epoxy. The wire and fabric can be removed after it cures.

I have taken some photos of the frame and will try and document it. I realize that these are not the photos that you are asking about. I might suggest that pictures of air flow around my front tires may not be relevant to your car.

It truly has not been tuft tested but the shape makes some sense. I may create a rubber dam under the front.
EDIT
wire only:


Here is the form that I am going to carbon.

Thanks, Varn, I look forward to seeing how this works out.

Reason I asked in the first place is concern after seeing pics in Hucho of smoke trails on an Opel Calibra and in his airflow sketches, which show undercar flow at the nose to splay outboard at about 60 degrees off centerline axis. That's right, about 60 degrees, such that apparently the bow wave splatters off the pavement and flow hits the inner side of the wheels at about a 60 degree angle. So, wheel fairings should evidently be canted inboard (pigeon-toed) to fair the wheels from the relative wind as it occurs in that region.

Hucho also says wheel drag doubles at only a 15 degree angle of incidence, yet the actual flow to the wheels is about 60 degrees, nearly as bad as hanging the wheels broadside into the breeze. This is a big deal, and so proper fairing orientation could potentially yield big benefits.

So, please keep us posted, esp. regarding actual tuft results under the nose.

Maybe tape some tufts to the bottom of the nose or on inverted golf tees, and photograph or videotape as the car drives past?

[Varn]

I was reading about the Nissan Leaf headlights acting as splitters and small turbulators in other threads. A week or two ago I saw a blade from a large wind generator being hauled on the back of a truck It had turbulators about the same shape every foot or so about a 1/3rd of the way along the top edge of the wing surface. I did some more tuft testing on my wand. I noticed that on the top of the fender I was getting pretty laminar flow over the top of the fender pointing toward the rear view mirror.

I made three 1" high fins (cut from some 3/16" balsa wood that I had laying around) to act as turbulators and taped them on (about 15 degrees from the air flow) where I thought that the flow would intersect the mirror. I noticed that there was less air noise with the window open and that the air behind them had reduced velocity.

I need to finish my front of the wheel air deflectors and make another 20 wedges. I am going to put some in front of the wipers and at the top of the windshield.

[Varn]

I got enough time to make my right side front wheel skirt and trial fit it to the car.

I previously had mounted the rear skirts on the front wheels, here is the left side.

You can see that the coverage is poor.

My right side unit looks like this.

The fairing covers the entire front aspect of the wheel.

And a 3/4 view.


Right now the wheel fairing is a single layer of carbon covered with some pink micro type filler.

[Varn]

Today I did a 29 mile round trip with 2 stops in the middle. On the way down I was averaging 30 mpg. On the way back my instant mileage was not as well as I left town. About a mile out the Ultragauge gave me a warning that I was over 4000 rpm. I looked down and I had inadvertently had the auto transmission in second, oops. No wonder the instant mileage wouldn't go over 18mpg. I ended up with 28+ mpg round trip.

I think my single front wheel cover made some difference. I made the left side steel frame and laid the composite. It is curing.

Maybe averaging 30mpg is a reality in my minivan.