Aerocivic - how to drop your Cd from 0.31 to 0.17

[Smokingwheels]

Originally Posted by Joenavy85

a thin fiberglass layer could be laid down, heck you could use a golf ball to make the dimples, how appropriate would that be?

I think they scaled the dimples up to about 2.5-3 inches across

[fidalgoman]

Originally Posted by Smokingwheels

I think they scaled the dimples up to about 2.5-3 inches across

That was the problem. Golf ball dimples don't scale up. It has everything to do with Reynolds numbers. That means how thick the air appears to the object. For example the air seems much thicker (low reynolds number) to a bee than an airliner (high Reynolds numbers). Scale of the part to the comparable air viscosity is what matters. If you want the dimples to work like they do on a golf ball you need to make them golf ball size to solve golf ball size flow problems. There is a ton of information on this subject for all to see.

Similarly it's like floating a needle on the surface of the water due to the surface tension. You can only go so far before the scaling no longer works. Water surface tension is a relatively fixed value. There is just no way that it will scale to even floating a crow bar. It just doesn't scale past a certain point. It also becomes more extreme in effect the smaller an object gets. So like surface tension, the atmospheric viscosity is a relationship with the part, scale, and speed.

At the scale of our automobiles, Aerodynamics is entirely different than it is to a golf ball. Kind of like the drag on the wheels from a gravel road is different to a skateboard than a Honda.

[basjoos]

I had my brakes worked on 565,000 miles. The front brake pads had lasted 165,000 miles, the rear pads 235,000 miles, replaced the front pads/rotor, and the rear pads. I didn't have time to reinstall my wheel well skirts before driving off to work, so I have been driving this week without them and seeing the effect of their absence on my miileage. Going skirtless has dropped my mileage by 3mpg and without the drawing action of the rotating wheels in the inclosed front wheel wells, the radiator fan is having to come on about a third more often. I'll get the skirts back on this weekend.

[orange4boy]

Hey, Mike,

That just reminded me to give you a durability report on the closed bottom side skirts on my Prius. Durable. They hit speed bumps all the time and are still holding up. The weak points are all due to my lax attachment methods. I'll be making new ones soon in pure white with some tweaks. Mainly tabs to aid in attachment.

Keep on rockin' in the free world.

[wyatt]

Originally Posted by basjoos

Going skirtless has dropped my mileage by 3mpg and without the drawing action of the rotating wheels in the inclosed front wheel wells, the radiator fan is having to come on about a third more often.

It is probably a combination of that and the higher drag that you are seeing without the skirts.

[basjoos]

Originally Posted by wyatt

It is probably a combination of that and the higher drag that you are seeing without the skirts.

I thought about that, but I didn't think that the additional engine loading from a 3 mpg drop in mileage while running in the mid 70's mpg would create enough additional heat to cause the fan to run 1/3 more often. I can notice the effects of the additional drag while coasting and while climbing hills that are at my limit of maintaining speed while remaining in lean burn.

[Arragonis]

Basjoos - how flat is your daily, or usual route - what is the elevation changes you get and over what distances - gradients if you like ?

EDIT (pressed post too quick ) - and what is your preferred technique for hills especially ones either steeper or too long to coast ?

[basjoos]

My commute to work initially climbs very steeply in 3 km from 400m elevation to 640m and then the remaining 80 km is fairly flat except for two 100m high hills. On my other main route (115 km long), the elevation goes from 400m to 150m over gently rolling terrain.

When climbing hills that are too steep to maintain speed at full throttle in 5th gear, I drop to 4th and maintain a speed of 65 to 70 km/h, even steeper and it drops to 3rd gear and 55 km/h.

Going downhill on those 100m high hills, I take the gravity ride in FAS at speeds up to 120 km/h (road, speed limits, and traffic permitting). On longer downhills (or on shorter downhills once I reach the maximum speed I'm willing to go) I'm using engine braking in 5th with full fan and A/C and occasionally open windows for additional drag, with the occasional application of friction brakes as needed.

[JasonG]

You've got to love a car that to slow down, you roll down a window and turn on the AC !

Awesome.

[Midniteoyl]

Think you guys could actually try and make these mods look good? That civic that started this thread, while prolly a real gas saver, is prolly the ugliest thing I've seen... C'mon, at least try...