flow separation:Tiger Woods meets Cinderella,or 5-seconds to a perfect roofline

[SvdM]

I have often also wondered about this. It does appear from the smoke trails of very many cars that one can drop into the 22° quicker than the template suggests. However, these cars are ultra smooth already and I can see how sticking close to the template would be a safer bet for the DIYer.

Another thing to consider is the small amount of foreshortening in all of these photographs, which might of course appear more confidently to veer away from the template, but in fact does a little less so.

[aerohead]

Originally Posted by SvdM

I have often also wondered about this. It does appear from the smoke trails of very many cars that one can drop into the 22° quicker than the template suggests. However, these cars are ultra smooth already and I can see how sticking close to the template would be a safer bet for the DIYer.

Another thing to consider is the small amount of foreshortening in all of these photographs, which might of course appear more confidently to veer away from the template, but in fact does a little less so.

I think it was Bicycle Bob who first pointed out,how a manufacturer might position the camera in the wind tunnel to make for the most 'flattering' smoke filament images over the aft-body.
Without really long telephoto images,with outlines appearing closer to 'true-length',it's very difficult to actually 'see' the airflow sink.
Good eye!

[ChazInMT]

It was thanks to Aeroheads patient insistence here in this thread that I came to realize the Template may not be scaled as I was kind of insinuating with my posts. Notice I went silent? That's because Phil helped me see the light here. I suppose I should have posted such before now.

I still say, in a sense we were both right, yes, you can scale the template and flow will remain attached to it, but, the Cd will go into the crapper because you are creating gross pressure changes when you go sub-template that create drag. You can have attached flow over a shape, and its Cd will be mediocre. Attached flow is NOT the goal, it is a characteristic that must be present in order to optimize the Cd. The goal is to eliminate drastic pressure changes, allowing the air to build in behind a vehicle as gently as possible creating as little turbulence as possible.

Stick close to the template for Optimum low drag results, the further from it you get, the worse the drag will be.

Thanks again Phil!

[kach22i]

Originally Posted by ChazInMT

It was thanks to Aeroheads patient insistence here in this thread that I came to realize the Template may not be scaled as I was kind of insinuating with my posts. Notice I went silent? That's because Phil helped me see the light here. I suppose I should have posted such before now.

I still say, in a sense we were both right, yes, you can scale the template and flow will remain attached to it, but, the Cd will go into the crapper because you are creating gross pressure changes when you go sub-template that create drag. You can have attached flow over a shape, and its Cd will be mediocre. Attached flow is NOT the goal, it is a characteristic that must be present in order to optimize the Cd. The goal is to eliminate drastic pressure changes, allowing the air to build in behind a vehicle as gently as possible creating as little turbulence as possible.

Stick close to the template for Optimum low drag results, the further from it you get, the worse the drag will be.

Thanks again Phil!

I know that it's been a few years since this post and thread was active, but this is an excellent observation/realization by ChazInMT...............and one that eludes me from time to time.