Textured Paint Question
 

Hi All,

So...

My paint is looking pretty rough and I am playing with the idea of using a bed liner product instead of paint. I have used it before on a truck to protect the lower portion of the doors and it looks great and works great.

I would think that it decrease the aerodynamics. My other thought is that I have seen textures that actually have better aerodynamics than flat surfaces. ie: sharkskin...

Has anyone had any real world trials with this?

Thanks,
Mr. Previa

Mr. Previa -

I like the thought of this for lower car protection and even aesthetics, but I also wonder if it helps. It will add weight and I am not sure if there is hard proof that the rough surface that the specific coating you describe will produce an aero benefit that is greater than the added weight.

I just don't know,

CarloSW2

Hmm, it wouldn't add that much weight. Maybe 10 pounds? Not sure, I would have check the can. I use Rustoeum Roll On. You are right on the surface texture. I wish we had more proof. The sharkskin is a proven one though. That is why skiers and swimmers have suits with the same texture.

swimmers wiggle through the water, and water is pretty "thick", and most of the drag from a swimmer is surface drag.

cars the vast majority of drag is form drag. Washing and waxing your car will probably show more improvement, and I would bet the coatings you are talking about would have more drag then paint.

For sure rhino linings slow down boats. Been tried many many times.....

Mr. Previa -

Ok, my mistake. I was thinking of the spray-in truck bedliners. They are thick, so I have heard they can weigh quite a bit.

CarloSW2

Well I had a multi paragraph detailed explanation all typed up for why you'd be wasting your time with the texturized surface, but Ecomodder had a glitch and ate what took me an hour to prepare. I guess I've gotten lazy and am not essentially writing my posts in Word and then copying them back into here. Shame on me I suppose.

So I'm a little upset right now and don't really feel like typing it all in again.:mad:

Research what you want to do and you'll see it does not work for cars.

The reason is your car is not a shark in the water. It is a brick trying to push its way through air. Laminar flow disruption helps the shark because laminar flow drag or skin drag is a large component of the total drag on a object in water.

Skin drag is a very minor and essentially insignificant drag component on a car moving through air compared with pressure drag. If you want to improve your cars aerodynamic performance you need to change the way the air flows around it by changing the shape of the car and optimizing the pressure differentials.

Here is a picture of shark skin which I think is amazing in its complexity. It is one of my favorite images of all time, the shapes are just spectacular. It is the result of billions of years of evolution. Trying to reverse engineer this would be a lifetimes work in getting to understand all the details involved in it. The image was created by Eye Of Science.

http://i53.tinypic.com/icpcli.jpg

texture
 

A turbulent boundary layer enables airflow to remain better attached in regions of unfavorable pressure gradients as on a downward-sloping roof or inward sloping sides.
A polished automotive paint finish has enough surface roughness to trigger the transition from laminar to turbulent boundary layer at around 20 mph.So your Previa already has the automotive equivalent of golf ball dimples!
If you were going to attempt to get attached flow over a very steep slope,you'd want to look at turbulators/vortex-generators.
And you'd want to calculate the thickness of your boundary layer in the suspect location to properly size them.
It would have to be pure coincidence that the textured paint just happened to have the proper dimension surface roughness.:p

I just read about aerodynamic paint in National Geographic magazine (either Jan or Feb 2012 I can't remember). It was basically saying the same things about drag, but that in aircraft around 40% of the total drag in from skin friction alone. Most sources, that I've seen, say 30-50% and over 50% on supersonic planes. With the lower speeds we are working with, form drag becomes a bigger component. I would say surface drag still makes up a good portion, specifically at highway speeds 55+ MPH. I can't find the article, but this link talks about the Fraunhofer Institute in Germany and their aerodynamic paint based on a sharks skin. They estimate the paint can reduce skin friction drag by 4-7%. NOTE: The talk about laminar flow and turbulence is confusing, just know they are talking about making the whole flow laminar by making the boundary layer turbulent...

equations
 

If you'll take the hit and invest in one if Hucho's books,you'll find all the equations you'd need to calculate hard numbers,as surface friction drag.The science should convince you that there's nothing you can do about it.
If you're under water,then it's a different story.

Why does everyone always assume everyone else is an idiot...? I actually have a B.S. In Aerospace Propulsion, Commercial Pilot's License, and Flight Instructor certificates. It's not like I just make this stuff up.