Reducing drag on old-shape sedans (notchbacks)

[JulianEdgar]

1) M_a_t_t, this one is for you!

2) For people following the Aerohead / template debate, as far as I can tell, this video covers how Aerohead thinks the aero of all sedans behave. (Primarily, because back in 1987 - the year of the textbook Aeroheads most often cites - this is indeed how aero on sedans was.) But things have changed...a lot. So don't use this video to modify modern-shape sedans that have attached flow.

https://www.youtube.com/watch?v=ea8FFmbYams

[deluxx]

following the Aerohead / template debate

Where/what is that??

this video covers how Aerohead thinks the aero of all sedans behave.

wait.. are you aerohead?

1987 - the year of the textbook Aeroheads most often cites

now im really confused..

[JulianEdgar]

following the Aerohead / template debate

Where/what is that??

Have a look around.

this video covers how Aerohead thinks the aero of all sedans behave.

wait.. are you aerohead?

Nope. Perhaps I should have said: as far as I can work out from what he posts here, Aerohead appears to believe that the aero of all sedans behaves as in this video on old shaped cars.

1987 - the year of the textbook Aeroheads most often cites

now im really confused..

Aerodynamics of Road Vehicles, 1987. Aerohead has repeatedly said he has not read any more recent aero textbooks.

[M_a_t_t]

When I got the notification on my phone I did think "finally, something that I could more directly apply"

I was thinking I could just use that adhesive spoiler and run it along the edge of the back window/c-pillar.

I hadn't though of raising the spoiler either. Do you think the angle of the spoiler matters? The stock one on my car points a little toward the front of the car, but if I'm making risers I could probably just account for that.

[JulianEdgar]

Originally Posted by M_a_t_t

When I got the notification on my phone I did think "finally, something that I could more directly apply"

Yes, when I ran across the drag % details for each modification to VERA I figured that I'd better do a video! I used VERA as a role model for my first aero car modifications back in about 1989.

I was thinking I could just use that adhesive spoiler and run it along the edge of the back window/c-pillar.

For separation edges? You could do that - easy and it would look fine - but I'd test with cardboard first.

I hadn't though of raising the spoiler either. Do you think the angle of the spoiler matters? The stock one on my car points a little toward the front of the car, but if I'm making risers I could probably just account for that.

It might look odd but perhaps have the spoiler top surface tilting the other way (ie downwards towards the rear) - like a hatch rear extension to reduce wake area?

[freebeard]

Originally Posted by deluxx

Where/what is that??
[mostly in Aerodynamics, it's best to hide out in The Lounge]
wait.. are you aerohead?
[see Scott Adams on mind reading]
now im really confused..
[everything changed in 1989. ]

.

[JulianEdgar]

Originally Posted by freebeard

[everything changed in 1989.]

Not that date specifically, but in the late 1980s yes, a huge amount changed in airflow patterns on sedans. Basically, we went from separation occurring at the end of the roof (sometimes with reattachment on the trailing edge of the boot/trunk, but often not), to largely attached flow down the rear window and onto the boot/trunk lid.

In turn this dramatically changed:

1) the main cause of rear lift

2) drag coefficient

3) how rear spoilers work


Old shape sedan (1986):



New shape sedan (1988):



Even newer shape sedan (2013):



Notice the change in rear window angle and C-pillar curvature.

So yes, basing your understanding of airflow patterns on sedans on a 1987 textbook is highly problematic.

[freebeard]

So yes, basing [one's] understanding of airflow patterns on sedans on a 1987 textbook is highly problematic.

Can we cast that in the third person?

The was for the over-specificity.

For me it starts with the first four generations of the VW Jetta with it's raised rear decklid. ....in 1979.

[M_a_t_t]

Originally Posted by JulianEdgar

It might look odd but perhaps have the spoiler top surface tilting the other way (ie downwards towards the rear) - like a hatch rear extension to reduce wake area?

I might be able to just flip it around. If the angle isn't quite right I could probably just adjust the riser for a different angle. Or I could just remove the spoiler and play around with the pitot tube. How do you adjust the angle on your pitot mount?

I think the "old" sedan looks the sharpest. I think my Fiat is one of my favorites in the looks department.

[JulianEdgar]

Originally Posted by M_a_t_t

I might be able to just flip it around. If the angle isn't quite right I could probably just adjust the riser for a different angle. Or I could just remove the spoiler and play around with the pitot tube. How do you adjust the angle on your pitot mount?

I think the "old" sedan looks the sharpest. I think my Fiat is one of my favorites in the looks department.

I don't think I have ever driven an old Fiat, but I remember watching them at race tracks do very well indeed. An X19 is on my list when someone gives me a lot of money and says, "Buy cars!". (My second car was an Alfasud Ti, so I kinda understand the era.)

I adjust the angle of pitot tube by either adjusting the angle bracket at the pitot tube itself or at the suction mount. But I'd be assessing different drag values of a modified spoiler with the throttle stop technique, not the pitot. Pity you don't live around the corner, because it'd be a really interesting test to do, I think.