Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Rounded corners vs. Straight edges on kammback

drmiller100 · 08-24-2012, 08:14 PM

so, in another thread aero, myself and the "clan" talked at length about angles you can run on a car without danger of separation.

the consensus seemed to be 20 degrees on the top and sides was "safe", and 10 degrees was "safe" on the bottom.

Further, the consensus, as I understood it, if you have 20 degrees on top/sides, and have MINOR disturbances, the air MAY reattach, but be very careful of the disturbances.

If you run greater than 25 degrees no matter what happens in front of the angles, you are pretty much guaranteed the air won't reattach for small disturbances, and there are studies which show 25 degrees you can't even guarantee the air stays attached without the disturbances.

It seems to me the SMALLER the back of the car, in general, the less drag. So, a reasonable goal to me is to have as small a "back" of the car as reasonably possible.

To have as "small" of a back fo the car, you should run the steepest angles you can safely get away with.

Those are some basic fundamentals for building a boat tail In MY OPINION.

So. when you go to DO something on a car, you need some guidelines or places to start. It is all fine and good to make fun of me. It is all fine and good to make fun of my name, or my education, or whatever, but that kind of stuff does not help anyone DO things.

My goal was to point out things to really focus on which are IMPORTANT. I don't think the angles the tops and sides meet are important, and I don't think a rolled edge vs a sharp edge is important, but that is my opinion, and there are no studies which indicate I am significantly wrong in that opinion.

There are PLENTY of studies which show greater than 25 degrees is horrible. There are plenty of studies which show IN GENERAL the smaller the back of the car, the shorter the trailing vortices, the less drag there is.

One of the goals in any scientific or logical discussion between people wishing to learn is to NOT attack the people making the opinions. Calling someone a big meany is a waste of everyone's time, but for sure strokes the ego.

is the goal to stroke the ego, or is the goal to BUILD something, or is the goal to LEARN something????

Neon has challenges, as he is DOING. When you DO things, you run into lots and lots of variables, most of which are adjustable. Which variables are important? Critical? Pretty, but functionally unimportant?????

I've built a LOT of cars, and theory is all great, but building something which WORKS is much harder.

Best wishes to Neon - keep it up, good job, and please report back your findings. What you are BUILDING is very hard - the vast majority of readers on this site, and even the vast majority of posters to this thread will never undertake any project as hard as you are doing.

Thank you.

08-24-2012, 08:14 PM	#41 (permalink)
drmiller100 Master EcoModder Join Date: Dec 2011 Location: Boise Idaho Posts: 842 Thanks: 39 Thanked 89 Times in 69 Posts	so, in another thread aero, myself and the "clan" talked at length about angles you can run on a car without danger of separation. the consensus seemed to be 20 degrees on the top and sides was "safe", and 10 degrees was "safe" on the bottom. Further, the consensus, as I understood it, if you have 20 degrees on top/sides, and have MINOR disturbances, the air MAY reattach, but be very careful of the disturbances. If you run greater than 25 degrees no matter what happens in front of the angles, you are pretty much guaranteed the air won't reattach for small disturbances, and there are studies which show 25 degrees you can't even guarantee the air stays attached without the disturbances. It seems to me the SMALLER the back of the car, in general, the less drag. So, a reasonable goal to me is to have as small a "back" of the car as reasonably possible. To have as "small" of a back fo the car, you should run the steepest angles you can safely get away with. Those are some basic fundamentals for building a boat tail In MY OPINION. So. when you go to DO something on a car, you need some guidelines or places to start. It is all fine and good to make fun of me. It is all fine and good to make fun of my name, or my education, or whatever, but that kind of stuff does not help anyone DO things. My goal was to point out things to really focus on which are IMPORTANT. I don't think the angles the tops and sides meet are important, and I don't think a rolled edge vs a sharp edge is important, but that is my opinion, and there are no studies which indicate I am significantly wrong in that opinion. There are PLENTY of studies which show greater than 25 degrees is horrible. There are plenty of studies which show IN GENERAL the smaller the back of the car, the shorter the trailing vortices, the less drag there is. One of the goals in any scientific or logical discussion between people wishing to learn is to NOT attack the people making the opinions. Calling someone a big meany is a waste of everyone's time, but for sure strokes the ego. is the goal to stroke the ego, or is the goal to BUILD something, or is the goal to LEARN something???? Neon has challenges, as he is DOING. When you DO things, you run into lots and lots of variables, most of which are adjustable. Which variables are important? Critical? Pretty, but functionally unimportant????? I've built a LOT of cars, and theory is all great, but building something which WORKS is much harder. Best wishes to Neon - keep it up, good job, and please report back your findings. What you are BUILDING is very hard - the vast majority of readers on this site, and even the vast majority of posters to this thread will never undertake any project as hard as you are doing. Thank you.