Aerodynamic Streamlining Template: Part-C

[aerohead]

Originally Posted by Bajascoob

doubled the first set..

Baja,sorry!,just now catching your post.
Robert is correct with respect to the template.Find the highest point of your roof and align with the point of max camber on the template.

[aerohead]

I've been working on a thread for 10-weeks now,am far from finishing but there is some activity with members doing rear spoilers so I wanted to share a few examples of cars which used spoilers to get to,or get closer to the template.
If you can GOOGLE-Images these, and find a side view photo,it will give you a peak at what some manufacturers have done to cheat the air.
1963 Alfa Romeo TZ
1964 Ford GT 40
1965 Ford Mk IV ( one of very few 'Kamm-back' cars actually made )
1967 Ferrari 330 P4
1968 Ford Mustang Fast-back
1988 Lotus Esprit Turbo
1991 Ferrari F40
1994 Saleen Mustang S-351
1994 Bugatti EB 110
1995 Ferrari F335 Berlinetta
1999 GM PNGV/Precept
2009 Toyota Prius
Note: three additional cars which follow the template,then morph into the von Mises profile/reflex-camber for down-force are :
1970 Porsche 917 LH ( long-tail )
1978 D-B/M-B C-111 III
1987 AeroVironment/GM Sunraycer

[SvdM]

Question:

I keep hearing people refer to 12° when talking about the 'departure angle' for the ideal boat tail. Is this 12° valid at a certain speed and what is this speed? My brain tells me it should be linked to the speed

[Bicycle Bob]

Tell your brain that the faster you push air aside, the more spring it has to come back. Or something like that. There are changes with speed, but nothing near linear. 12 deg is very conservative; 18 will maintain attached flow if you are careful.

[SvdM]

Okay, so I can assume 12° is the 'no fail' amount for DIY jobs that's still good for highway speeds, say 120km/h? I'm assuming the 18° works if your handiwork is tidy and you are a little morecareful with your right foot

So I can postulate:

1. That if you're going for the 'chopped off' boat tail design, best go for 18° rather than 12° in order to keep the low pressure area at the rear to a minimum.

and

2. Even if there is some detached flow on your 18° boat-tail, it's still better than no boat-tail at all (?)

[Bicycle Bob]

No, the right foot does not matter when planning angles.
Shape is as much an issue as workmanship, etc.
If your flow detaches, you are better off to have the kammback start there.
Please do more reading to firm up your understanding, but don't believe everything you see on this site. Outright conflicts are usually resolved, but there is still a lot of misleading or over-simplified stuff. Manufacturers still use wind tunnels to be sure of any results in this field.

[SvdM]

Thanks BicycleBob, will do more reading indeed. It's just sometimes hard to find stuff here and I don't have a lot of free time to just surf EM. But that's why I will try and create an Infographic to try and gather and share all the relevant info and so, have it in one place.

[3-Wheeler]

Originally Posted by Bicycle Bob

Tell your brain that the faster you push air aside, the more spring it has to come back. Or something like that.....

Hi Bob,

You're absolutely correct.

The faster one moves through the air, the more the air wants to return to the same spot it occupied before it was disturbed.

And the faster you go, the quicker the air is split also increases the local pressure, and this extra pressure moves the air towards it's original position with a higher degree of force.

This force/speed relationship is roughly "linear" for lower Mach numbers and speeds of less than 200 mph or so.

Jim.

[theycallmeebryan]

Here you go aerohead

1963 Alfa Romeo TZ



1964 Ford GT 40


1965 Ford Mk IV ( one of very few 'Kamm-back' cars actually made )


1967 Ferrari 330 P4


1968 Ford Mustang Fast-back


1988 Lotus Esprit Turbo


1991 Ferrari F40 (One of my favorite cars)


1994 Saleen Mustang S-351


1994 Bugatti EB 110



1995 Ferrari F335 Berlinetta


1999 GM PNGV/Precept


2009 Toyota Prius


Note: three additional cars which follow the template,then morph into the von Mises profile/reflex-camber for down-force are :

1970 Porsche 917 LH ( long-tail )


1978 D-B/M-B C-111 III


1987 AeroVironment/GM Sunraycer

[richtate]

So how does the 1978 D-B/M-B C-111 III above turn? Some pretty good lines in the gallery above.