Aerodynamic Streamlining Template: Part-C - Page 5 - Fuel Economy, Hypermiling, EcoModding News and Forum

Bicycle Bob · 08-14-2009, 10:47 AM

I think a bit of wiggle is OK, as long as the tell tales stay flat, but keep checking. A kamm back is generally close to vertical. The roof and sides can usually taper in at 15 degrees on the way to Kamm's truncation, the bottom at 4, but other details will affect the optimum angle.

orange4boy · 08-14-2009, 04:41 PM

I had disappointing results with the mpg and seat of pants from the new back. I had thought the angles were wrong. Top was 15-17 and sides were 15-20. I changed to 12 top and 12 sides but the van still seems to be sluggish on coastdown. It was much better with just the short extensions. It's possible the cooler weather is affecting the results. Just how much difference is there in air density between 85F to 70F? Or could the half shell create some massive vortex, increasing drag?

Of course it could be a dragging brake or some other increased friction like a toast bearing. I guess I should take the sucker off and try it that way.

aerohead · 08-15-2009, 05:11 PM

Quote:

Originally Posted by orange4boy

I had disappointing results with the mpg and seat of pants from the new back. I had thought the angles were wrong. Top was 15-17 and sides were 15-20. I changed to 12 top and 12 sides but the van still seems to be sluggish on coastdown. It was much better with just the short extensions. It's possible the cooler weather is affecting the results. Just how much difference is there in air density between 85F to 70F? Or could the half shell create some massive vortex, increasing drag?

Of course it could be a dragging brake or some other increased friction like a toast bearing. I guess I should take the sucker off and try it that way.

With just the 1/2 shell, it's predictabilty lies in the realm of the netherworld.My intuition suggested benefit,but no science to support it.----------- No books with me here so I cannot address the air density question,sorry.Falling temps will also affect all your lube viscosities and wheel bearing grease and tire RR.Lots of variables which is really bad for testing.------- If I lived next door,I'd help you fabricate sides and bottom for a re-test,back -to-back,same day,with and without,to minimize those variables.

Rokeby · 09-13-2009, 12:01 AM

aerohead,

Finally, I found a true overhead shot of the iMIev Sport Air all-electric concept car... 80 mph, 73 mile range:

http://photo.netcarshow.com/Mitsubis...9_photo_12.jpg

From this site, which has more Sport Air info than most folks will ever want to
know:

Mitsubishi i MiEV Sport Air Concept (2009) with pictures and wallpapers

Hmmm... no windshield wipers in any of the views. Clearly,

still in the
concept car stage.

aerohead · 09-15-2009, 05:18 PM

Quote:

Originally Posted by Rokeby

aerohead,

Finally, I found a true overhead shot of the iMIev Sport Air all-electric concept car... 80 mph, 73 mile range:

http://photo.netcarshow.com/Mitsubis...9_photo_12.jpg

From this site, which has more Sport Air info than most folks will ever want to
know:

Mitsubishi i MiEV Sport Air Concept (2009) with pictures and wallpapers

Hmmm... no windshield wipers in any of the views. Clearly,

still in the
concept car stage.

Rokeby,thanks for the pic.There is definitely some camber to the sides of the body and gradual taper to the aftbody.Windshield also has generous radii around the sides.They could have done a lot worse.

orange4boy · 09-15-2009, 06:35 PM

Quote:

I had disappointing results with the mpg and seat of pants from the new back. I had thought the angles were wrong. Top was 15-17 and sides were 15-20. I changed to 12 top and 12 sides but the van still seems to be sluggish on coastdown.

Turns out my brakes were dragging. Time to rebuild the right front caliper. The rear drums were also dragging because of the automatic adjusters. Now disabled!

Posted my best ever highway 36mpg. Go kamm.

aerohead · 09-15-2009, 06:50 PM

Quote:

Originally Posted by orange4boy

Turns out my brakes were dragging. Time to rebuild the right front caliper. The rear drums were also dragging because of the automatic adjusters. Now disabled!

Posted my best ever highway 36mpg. Go kamm.

Glad to hear that the beautiful stainless steel will be making a comeback! Thanks for the info and update.

Bajascoob · 03-01-2010, 01:14 AM

So where should I put this curve, and is the numbers 10,20 the percent of length?

Bajascoob · 03-01-2010, 01:19 AM

doubled the first set..

RobertSmalls · 03-01-2010, 09:32 AM

Bajascoob, the template doesn't work when it's not lined up properly.

You've got the ground planes aligned correctly, that's good. Then you have to make the template as tall as the truck, then move it forwards or backwards until the highest point on the template (where the arrow is) lines up with where you start your teardrop shape. Assuming you won't be using a sawzall, that's the end of the cab.

Then look up a top view of the truck, make the template + its reflection just as wide as the truck, and align the arrow with the back of the cab.

And yep, the 20, 30, etc is % of its length. If you get to 70%, you're going to have a drag coefficient that would be respectable for a car. Yep, trucks have terrible aerodynamics.